NOAA 'U chnical Report 142

,

Edited by

IzadOJ1 ar

o car osa- . .

Norman Bartoo

u. .Department ofCommerce

NOAA Technical Report NMFS 142

A Technical Report of the Fishery Bulletin

Biology and Fisheries of Swordfish,

Xiphias gladius

Papersfrom the International Symposium on

Pacific Swordfish, Ensenada, Mexico,

11-14 December 1994

Izadore Barrett

Oscar Sosa-Nishizaki

Norman Bartoo (editors)

Cover illustration by Katherine Zecca

December 1998

u.s. Department of Commerce

Seattle, Washington
Suggested reference

Barrett, Isadore, Oscar Sosa-Nishizaki, and Norman Bartoo (eds.). 1998.

Biology and fisheries of swordfish, Xiphias gladius. Papers from the

International Symposium on Pacific Swordfish, Ensenada, Mexico, 11-14

December 1994. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 142,

276 p.

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CONTENTS

INTRODUCTION

FISHERIES

M. A. BARBIERI

C. CA ALES

V. CORREA

M. DO OSO

A. GO ZALEZ CASANGA

B. LEIVA

A. MONTIEL

E. yANEZ

Development and present state of the swordfish,

Xiphias gladius, fishery in Chile

v

1

A. CATON

K. COLGAN

P. SAHLQVIST

P. WARD

C. RAMIREZ

M. SCOTT

A. L. CO JR.

M. VOJKOVICH

D. PRESCOTI'

G. T. or ARDO

W. KWOK

D. HOLTS

O. SOSA-NISHIZAKI

R. y. ITO

R. A. DOLLAR

K. E. KAWAMOTO

F. POISSON

E. TESSIER

D. ROOS

F. RENE

F. CONAND

R. A. SKILLMAN

K. UOSAKI

Y. UOZUMI

K. UOSAKI

Swordfish, Xiphias gladius, and the fisheries for tunas and 11

billfishes in the Australian fishing zone

The California harpoon fishery for swordfish, Xiphias gladius 37

Spatiotemporal dynamics of swordfish, Xiphias gladius, landings in 51

the Hawaii-based orth Pacific pelagic longline fishery

Swordfish, Xiphias gladius, fisheries of the eastern orth Pacific Ocean 65

The Hawaii-based longline fishery for swordfish, Xiphias gladius 77

Recent development of swordfish, Xiphias gladius, longline 89

fisheries near Reunion Island, southwestern Indian Ocean

Central Pacific swordfish, Xiphias gladius, fishery development, 101

biology, and research

Standardized CPUE of North Pacific swordfish, Xiphias gladius, 125

in the Japanese large-mesh driftnet fishery

Review of the Japanese swordfish, Xiphias gladius, fisheries in the 133

Pacific Ocean

iii
M. VOJKOVICH

K. BARSKY

P. G. WILLIAMS

METHODOLOGY

M. G. HINTO

R. B. DERISO

P. KLEIBER

. BARTOO

H.NAKANO

BIOLOGY

The California-based longline fishery for swordfish, Xiphias gladius, 147

beyond the U.S. Exclusive Economic Zone

Review ofswordfish, Xiphias gladius, catch in the western Pacific Ocean 153

Distribution and stock assessment ofswordfish, Xiphias gladius, in the 161

eastern Pacific Ocean from catch and effort data standardized on

biological and environmental parameters

Standardizing swordfish, Xiphias gladius, longline catch per unit of 181

effort using general additive models

Stock status of Pacific swordfish, Xiphias gladius, inferred from 195

CPUE of the Japanese longline fleet standardized using general linear

models

J. R. ALVARADO BREMER

G.M.LECLERC

B.ELY

D.W.AU

M. BARTHELOW

P. EKSTROM

S. MOBERLY

R. CASTRO-LONGORIA

O. SOSA-NISHIZAKI

S. CHOW

U. MARKAIDA

O. SOSA-NISHIZAKI

J. H. UCHIYAMA

R. A. SKILLMAN

J. D. SAMPAGA

E. E. DEMARTINI

SYMPOSIUM PARTICIPANTS

Mitochondrial and nuclear DNA analyses in the study ofswordfish,

Xiphias gladius, population structure

Protecting the reproductive value ofswordfish, Xiphias gladius,

and other billfishes

Report generation and data display from the NMT Archival Tag

Age determination of swordfish, Xiphias gladius L., from waters

off Baja California, Mexico, using anal fin rays and otoliths

Genetic comparison of Pacific and Mediterranean swordfish,

Xiphias gladius, by RFLP analysis of the mitochondrial D-loop region

Food and feeding habits of swordfish, Xiphias gladius L., off western

Baja California

A preliminary asssessment of the use of hard parts to age central

Pacific swordfish, Xiphias gladius

IV

211

219

227

231

239

245

261

275
INTRODUCTION _

The swordfish, Xiphias gladius, is a large migratory

oceanic species. It is widely distributed in tropical,

temperate, and sometimes cold waters of all oceans,

and is usually found in areas with sea-surface temperatures above 13°C. It can reach a maximum size of 540

kg, and is a favorite food fish in many countries. It is

excellent for steaks, canning, or teriyaki, the Japanese

dish of meat grilled with sugar, soy sauce, and rice

wine. Swordfish is harvested commercially throughout its distribution, in both coastal and high-seas fisheries. Sport fisheries for swordfish are very small compared to those for other billfishes, accounting for no

more than a few hundred fish per year.

In the Pacific, swordfish has been caught since one

can remember. The California harpoon fishery for

swordfish started in the early 1900's. Longline vessels

ofJapan, Taiwan, and Korea have fished in the North

Pacific since the early 1950's. A substantial increase in

fishing operations targeting swordfish has been observed since the 1980's. Today no less than ten nations, including Chile,Japan, Korea, the Philippines,

Taiwan, United States, and Mexico, are fishing across

the ocean. The Pacific-wide catch has reached an average of 30,000 metric tons per year in the last 5 years.

The objective of the symposium was to address recent developments in swordfish fisheries, markets, and

biological research in the Pacific Ocean. It provided a

forum for the interchange of information and ideas.

Twenty-five oral papers were presented, of which 22

v

were accepted as final manuscripts. Each manuscript

was sent to two anonymous reviewers, edited, revised,

edited again, and doublechecked by each author.

Because of the success of the first symposium, a

second symposium was proposed to continue the communication among the group formed in Ensenada; it

was held in Hawaii in March 1997, before the publication of this document. We hope to see a third symposium in the future.

We would like to thank MarthaJackson for her work

on the final drafts of all the papers; Martin Gutierrez,

Bob Skillman, Ricardo Suarez, and Yuji Uozumi for all

their ideas as steering committee of the symposium;

Gary Sakagawa and the personnel of the Southwest

Fisheries Science Center (LaJolla and Honolulu Laboratories) for their useful suggestions; Lupita Martines,

Ulisis Cruz, Nury Lopez, Margarita Margolles, Rogelio

Gonzalez, Cesar AJmeida, Leonardo Lizarraga, and

Silvia Ibarra from CICESE for their help in the organization of the meeting; and the Third World Academy

of Sciences, Northwest Marine Technology, Inc., and

the Swordfish Fishery Section of the National Fishing

Industry Chamber (CANAINPES) of Mexico for their

financial support of the symposium. And we especially

thank all the authors for their patience during the

long trip to publish this document.

Oscar Sosa-Nishizaki and orman Bartoo, Ensenada,

September 1998.

Development and Present State of the Swordfish,

Xiphias gladius, Fishery in Chile1

MARIA ANGELA BARBIERI

Escuela de Ciencias del Ma,.

Universidad Cat6lica de Valparaiso

Casilla 1020, Valparaiso, Chile

and

Instituto de Fomento Pesquem

Blanco 1067

Valparaiso, Chile

CRISTIAN CANALES*

Subsecretaria de Pesca

Bellavista 168

Valparaiso, Chile

VICTOR CORREA

Escuela de Ciencias del Mar

Universidad Cat6lica de Valparaiso

Casilla 1020, Valparaiso, Chile

MIGUEL DONOSO

1nsitituto de Fomento Pesquero

Blanco 1067

Valparaiso, Chile

ANTONIO GONZALEZ CASANGA,** BERNARDO LEIVA,*

ALEJANDRA MONTIEL, and ELEUTERIO yANEZ

Escuela de Ciencias del Mar

Universidad Cat6lica de Valparaiso

Casilla 1020, Valparaiso, Chile

ABSTRACT

The swordfish, Xiphias gladius, fishery in Chile was artisanal, for subsistence only, for

several decades. From 1938 through 1951, yearly landings ranged between 600 and 2,200

metric tons (t). During 1952-85, landings diminished, fluctuating between 13 and 570 t.

After this period, there were important changes in the fishery and landings increased from

764 t in 1986 to 5,959 t in 1991.

continued

* Present address: Instituto de Fomento Pesquero, Huito 374,

Valparaiso, Chile.

** Present address: Subsecretaria de Pesca, Bellavista 168, Valparaiso,

Chile.

I This research funded by grants made to SATAL II Project, lORCCanada; DGIP-UCV Projects 223-730/90, 223-736/91 and 223-756/

93; and IFOP-CORFO Diagnostics Projects from 1991 to 1994.
2 NOAA Technical Report NMFS 142 _

After 1985, a high demand for swordfish products and good prices, probably due to the

opening of the international market, made this fishery highly profitable. This led to the

replacement of harpoons by gillnets, considerably increasing yield; an increase in the

number, quality, and equipment of fishing boats, and the introduction of sea-surface

temperature satellite images for obtaining information on potential fishing grounds. Fishing by the industrial sector began in 1986 and contributed 39% of landings in 1991-94.

Recently yields have decreased noticeably, associated with the offshore displacement of

fishing grounds and reduction of mean fish size in the catch. These changes have produced

some management measures such as the prohibition on new fishing boats entering the fishery.

Introduction

7000 .,--------------------,

The swordfish, Xiphias gladius, fishery in Chile began at least

as early as 1938. Catches peaked at around 2,200 metric tons

(t) in 1946, then decreased and stayed at low levels for

over 35 years (Fig. 1). The recovery in the fishery after

1985 can be explained by the opening ofthe international

market, which generated great demand for this species

and good prices for the artisanal fishing sector.

Growth in the artisanal fleet, both in number and

capacity ofthe boats, was also encouraged by a new loan

policy. Drift gill nets were introduced and almost totally

replaced traditional harpoon fishing. The introduction

of sea-surface temperature satellite images to localize

potential fishing zones improved the surveying ability first

of the artisanal fleet, and later of the industrial fleet.

This paper analyzes the development of the Chilean

swordfish fishery between 1985 and 1994, includi ng

fishing practices, technology, effort and catch; swordfishing marketing; and relevant legislation.

Landings _

The pattern of annual swordfish landings (Fig. 1) suggests the fishery might be divided into four stages:

1. Early exploitation: from 1938 until 1951, landings

were normally over 600 t (2,146 tin 1946). Almost

100% ofthe catch was landed in the northern part of

the country, in the ports of Arica (18°20'S) and

lquique (200 10'S).

2. Low exploitation: from 1952 to 1985, catches were

very low (between 13 and 570 t); in the north, they

were almost non-existent. The fishery moved to the

central coast, landing in the ports ofValparafso (33°S)

and San Antonio (33°30'S). The manual harpoon

was still being used.

3. Expansion: from 1986 until 1991, there was a sustained increase in landings, mainly at the ports on

the central coast. Landings reached a peak of 5,959 t

6000

5000

:- 4000 m

c

'g 3000 o

-.J

2000

1000

oL~~~~:;,.,;::~~~~x..~,j

1934 1944 1954 1964 1974 1984 1994

Years

Figure 1

Total annual landings of swordfish in Chile, 1938-94.

(Sources: SAG, 1967-77; SER AP, 1978-94; A. Palma,

Yungay 1731, Valparaiso, Chile, personal commun.)

in 1991. During this stage the fishing effort obviously

increased and there were significant technological

developments associated with the introduction of

gillnets and the use of satellite images. During this

period the fishery developed between 27° and 400S;

the opening of export markets is believed to be the

main factor driving this development.

4. Decrease: after the record landings in 1991, landings

diminished steadily. Fishing effort still showed an

increasing trend, while artisanal yields continued to

go down.

Traditionally, the swordfish fishery was conducted by

the artisanal sector, mainly within the 200-nautical-mile

(n. mi.) exclusive economic zone (EEZ). However, since

1986 industrial sector landings have gradually increased

(Fig. 2), both within and beyond this zone. Artisanal

landings clearly diminished after 1989; figures for industrial landings, particularly after 1991, included

artisanal landings as well in a proportion that remains
_____________ Barbieri et al.: Development and Present State of the Swordfish Fishery in Chile 3

1990 1992 1994

Yeors

1988

600

500

-5 400 a

.!l

(; 300

.!l

"

E

:t 200

100

0

1986

1988 1990 1992 1994

Years

---a- Artisonol -+- Industrial -e- FAO

1986

-- Total

1984

1000

25000

4000

'6

3000

7000

8000,------------------------,

2000

6000

Figure 2

Total artisanal and industrial landings of swordfish in

Chile between 1984 and 1994 (SAG, 1967-77; SERNAP,

1978-94; A. Palma, Yungay 1731, ValparaISo, Chile, personal commun.).

Figure 3

Number of artisanal boats participating in the Chilean

swordfish fishery between 1986 and 1994.

to be determined. The swordfish is exploited by foreign

longliners in international waters off the Chilean coast.

Total national swordfish landings clearly showed a

seasonal component, with a peak between March and

August during 1985-94 (SERNAP, 1985-94). Between

1985 and 1989 catches were made fromJanuary through

September; in the 1990-94 period, both the artisanal

and industrial sectors registered catches in every month

of the year. Until 1984 fishing for swordfish was restricted to the mon ths of March through May, and was

conducted exclusively with harpoons.

Table I

Distribution by length range of artisanal boats participating

in the Chilean swordfish fishery in 1993.

Length (m) Quantity Percentage

8-9.9 8 2.1

10-11.9 9 2.4

12-13.9 34 9.0

14-15.9 193 51.4

16-17.9 II 30.6

18-19.9 17 4.5

Total 376 100.0

The Fleet _

Artisanal boats

The evolution in size of the artisanal fleet participating

in the swordfish fishery shows three stages between

1986 and 1994 (Fig. 3):

1. Until 1989, the number of boats increased, encouraged by loan accessibility and the opening of the

international market for Chilean swordfish.

2. From 1989 to 1991, the number of vessels remained

at around 500. Boats were equipped with improved

technology, and longliners began to operate in international waters.

3. Mter 1991 the number of boats decreased. The granting of new fishing permits was suspended, and the

resource was declared to be fully exploited. An offshore expansion of the fishing zones which were far

from the coast limited the operation of small boats,

which have less autonomy (Gonzalez, 1993).

Between 1989 and 1994, artisanal boats increased their

length, power, and gross register tonnage (GRT; Fig. 4).

In 1993, boats ranged from 8 to 20 m (Table 1). The boats

are built of wood (77%), steel (20%), fiberglass (2%), or

ferrocement (1 %). Wooden boats are represented in all

length strata, while steel boats are normally larger.

Industrial Boats

Since 1991 approximately 20 large boats have fished

swordfish in Chile, thus modifying the exclusive artisanal

character of this activity. These boats vary between 21

and 62 m long; some of them use drifting gillnets
4 NOAA Technical Report NMFS 142

The drift gillnet is the gear most used by the artisanal

fleet. It consists of a long wall of several mesh panels,

about 2,470 m long by 55 m high, made of polypropylene. Floats and buoys are attached approximately every 46 m. The mesh size is 22 inches.

The net is set at dusk and hauled at dawn of the

following day. While setting the net, disposable chemical lights are tied every 37 m to attract swordfish prey.

Setting depth is between 9 and 55 m, depending on the

amount of brightness at night.

The pelagic drift longline is composed of a twined

polyethylene or monofilament nylon main line; hook

branch lines are part polyethylene or monofilament

and part galvanized wire. Approximately 2,000 hooks

are set per haul. Horse mackerel, Scomber spp., and

squid, Illex spp., are commonly used for bait.

Longliners fish practically all day long. They mainly

use the ports ofCoquimbo (300 S) and Valparaiso (33°S)

year round. By law, these boats must operate farther

Pelagic Drift Longline

The harpoon is the most antique fishing gear of this

fishery; it used only by small artisanal boats. It is composed of a wooden or steel pole with a bronze point.

The point carries a segment of steel cable joined to a

line of approximately 20 m, to which a rope more than

500 m long is attached. Harpoon fishing is restricted to

the months of good ocean and weather conditions,

normally between January and May, when the fish dwell

at the surface. Boats fishing with harpoons are readily

identified by a steel structure at the bow.

Manual Harpoon

Drift Gillnets

gillnets work without major problems in rough weather

conditions, while harpoon fishing requires good weather

and visibility.

At the beginning of each season (January-May), the

small boats usually use both fishing methods in the

same trip, the harpoon in daytime and the nets at

night. During the rest of the season (June-October),

only the net continues to be effective. Although the

yield is less at the beginning and end of the fishing

season, the high price fetched by swordfish at these

times of year compensates for lesser yields.

The industrial fleet uses both gillnets and pelagic

drift longline; the latter is used more often because it is

more effective.

15'

I

L

C.

i

-' 14

A 13 1989 1990 1991 1992 1993 1994

165

160

il~~

..

"

t1.• 150

145

B 140 1989 1990 1991 1992 1993 1994

28

27

2 26

....

25

H

C 23 1989 1990 1991 1992 1993 1994

Years

Figure 4

Mean values of (A) length, (B) horsepower

(HP), and (C) gross register tonnage (CRT)

of artisanal swordfishing boats in Chile between 1989 and 1994.

(27%) and others pelagic longline (72%), and some

use both fishing methods (1 %).

16,------------------,

Fishing Methods and Gear _

The artisanal fleet normally begins fishing duringJanuary

in the area off Talcahuano-Valdivia (37°-400S), moving

toward the north and generally ending in SeptemberOctober off Caldera-Coquimbo (27°-300

S). Drifting
_____________ Barbieri et al.: Development and Present State of the Swordfish Fishery in Chile 5

than 120 n. mi. offshore. Thus, activity extends from

the limit of the EEZ up to 800 n. mi. offshore, between

Valparaiso and the northern limit of Chile.

The duration of trips depends mainly on a boat's

autonomy and on its catch maintenance system. The

industrial boats that use drift gillnets work no more

than 15 days, refrigerating the catch with ice in isolated

holds. Longliners can work for 2 months, since they

have freezing systems in their hold to preserve the

catch.

Use of Satellite Images

Since 1986, sea-surface temperature (SST) satellite images have been used in the Chilean pelagic fisheries for

finding probable fishing grounds.

Images are prepared with information gathered by

AVHRR sensors on NOAA satellites. These images were

first introduced in the albacore, Thunnus alalunga, and

swordfish artisanal fisheries (Barbieri et aI., 1989, 1991).

The industrial sector exploiting swordfish and small

pelagic fish such as the anchovy, Engraulis ringens, and

sardine, Sardinops sagax, also acquires this information,

which is then distributed to their fishermen (Yanez et

aI.,1994).

An SST image gives information in real time on SST

over a wide area. The course of a boat is determined on

the basis ofthe image, the distance, and the time needed

to travel to the fishing grounds. Satellite information

may be of great help, particularly after a period of bad

weather during which the boats stay in port, losing the

location of fishing zones. Nevertheless, satellite information has certain technical limitations. The most critical one is cloud cover, which prevents the satellite sensor from detecting SST. Fog also affects temperature

readings. Another aspect to be considered is the correct calibration of the sensor with in situ information,

which is not always available. A practical limitation is

information distribution, presently achieved by using a

modem and fax machine.

Although satellite information is available almost daily,

two images per week seems to be enough, depending

on meteorological conditions, since wind has an important effect on the distribution of SST.

CPUE and Fishing Effort _

Artisanal Fleet CPUE

Data on total landings of the artisanal fishing fleet was

taken from the logbooks of boats operating from the

ports ofValparaiso and San Antonio between 1987 and

1994, representing 68% of total landings of the fleet in

Table 2

onparametric statistical test (Kruskal-Wallis) for differences in CPUE between boat length classes.

Boat length

Years range (m) (K-W) 1 (X2 )2 n3 Conclusion4

1987 II-l7 11 15 7 accept Ho 1988 11-16 8 13 6 accept Ho 1989 11-16 17 13 6 reject Ho

1990 11-16 5 13 6 accept Ho 1991 12-17 10 13 6 accept Ho 1992 10-18 8 16 8 accept Ho 1993 12-18 9 15 7 accept Ho 1994 10-18 7 16 8 accept Ho

I Kruskal-Wallis test statistic.

2 Chi-square statistic (0,975, n-l).

3 Number of boat length strata.

4 Ho: no differences between boat categories.

HI: boat categories are different.

Ho is accepted if K-W < X2.

this period (Donoso and Montenegro, 1992; Correa,

1993; SERNAP, 1987-94). Fishing logbooks report on

each boat's activity: the departure and arrival dates,

base port, fishing area, and catch. Similar information

is not available for the industrial fle-et.

Catch per unit effort (CPUE) was used in our analysis

of the fishery. Mean monthly CPUEmwas estimated by

dividing monthly landings (kg) by monthly effort (days

at sea) of the artisanal fleet. Similarly, mean annual

CPUEj was calculated as the average of all CPUEm in a

year. For each year, fishing effort was estimated by

assuming that the boats in the artisanal fleet were homogeneous relative to their fishing power. Comparison

of annual mean CPUE's for boats of different length

classes using the Kruskal-Wallis statistical test showed

no significant differences between them, with the exception of 1989 (Table 2).

Estimated CPUEj shows a remarkable decreasing trend

between 1987 and 1994 (Fig. 5a), likewise the biomass

estimated by the virtual population analysis (VPA; Fig.

5b) of MacCall (1986), applied to the artisanal and

industrial landings of 1987-94 (Table 3). VPA was structured by number at age considering the sampling for

lengths and von Bertalanffy growth parameters, since

we lacked relevant length-age keys. Weight was estimated as the weighted mean between the weights estimated from the length-weight relation and from age

composition in the catch. These weights were later

used to estimate annual biomass. Natural mortality,

following the Pauly (1980) model, was estimated as

0.123 at a mean temperature of 16°C. Fishing effort for

1987-94 (Table 3) was used to calibrate the VPA.
6 NOAA Technical Report NMFS 142

Table 3

Total landings (artisanal and industrial), CPUE (artisanal), and total effort of the swordfish fishery in Chile,

1987-94.

1987 2,059 5,265 391

1988 4,455 17,200 259

1989 5,824 20,152 289

1990 4,955 19,057 260

1991 5,959 37,715 158

1992 5,481 34,043 161

1993 4,712 38,942 121

1994 3,801 41,315 92

Year

Landings Fishing effort CPUE

(t) (artisanal days at sea) (kg/artisanal day at sea)

500,---------------------,

A

"o 400

"0

>-

o

1J 300 a

c

o

III

:;:

5 200

'"

Ol

-=- 100 DU

O-'-__.___-___._-~--~-__.___-___._-___,--.,.__.J

1987 1988 1989 1990 1991 1992 1993 1994

Yeors

37000,-----------------,

It should be noted that Chilean catches represented

on average 80% of annual total landings in the southeastern Pacific (FAO Area 87) for 1987-94 (FAO, 1987-

94); and that the southeastern Pacific stock may be a

unique unit ofself-sustained stock.

The decrease in CPUE reflects the remarkable increase in total fishing effort, which was not followed by

the expected increase in landings (Table 3), probably

due to a significant decrease in resource abundance

and/or to changes in availability produced by interannual variation in environmental conditions. The increased distance of the fishing zones from the coast has

required the artisanal fleet to invest a greater number

of days at sea, mainly to reach those areas. In 1987 the

fishing zone of Valparaiso was located within 40 n. mi.

of the coast, while in 1990 it was >160 n. mi., and in

1993-95, 200 n. mi. offshore (Barbieri et aI., 1995).

This change in fishing areas is likely due to decrease in

abundance of the resource, probably caused by the

recent development ofthe Chilean fishing industry and

the internationallongline fishing industry. However, it

is also likely that environmental changes have affected

the resource distribution, and therefore its availability

(Gonzalez, 1993).

Total Effort

Annual total effort (f.) by the artisanal and industrial fleets

was estimated using the annual total landings of both

fleets (C) and the artisanal fleet's CPUEj

, as! = C/CPUEj •

Total fishing effort shows a clear increasing trend

during 1987-94 (Table 3). The 8-fold increase during

this period was associated with the increased number of

boats entering the fishery, the technological development of the fleet, knowledge of the fishing zones, and

an important decrease in abundance and/or availabilB

32000

227000

III

III

o

E

22000

17000

12000 -'-,.---.---,-------,------.-----,-------,--,-------'

1987 1988 1989 1990 1991 1992 1993 1994

Years

Figure 5

Swordfish abundance in Chilean waters, according to

(A) CPUE, 1987-94 and (B) biomass calculated by

VPA, ]987-94. Bars indicate standard deviation.

ity of the resource (Barbieri et aI., 1990; Ponce and

Bustos, 1991; Gonzalez, 1993).

Surplus Production Model

Based on the exponential relation between the landings (artisanal and industrial), the CPUE (artisanal) and

the total effort (artisanal and industrial) (Fig. 6), the

swordfish fishery in Chile would have reached adequate

levels of exploitation between 1988 and 1990. Hereafter,

increase in effort is related to diminishing abundance

and/or availability. There is no information about the

catches of the internationallongline fleet operating off

Chile. In any case, the swordfish fishery in Chile reflects

a delicate situation in the present status ofthe resource.
_____________ Barbieri et al.: Development and Present State of the Swordfish Fishery in Chile 7

The Catch

10000 20000 30000 40000 50000

O+----,-------,----.-----.,.--------j

o

500 -,---------------------,

w 100 ::>

0-

u

.......

o

"III 400

>-

o

u 300 o

c

o

.!!!

15 200

'"

0>

C,

Trunk Weight

The annual frequency distribution of trunk weights

(without the head, caudal fin, and guts) of swordfish

caught by the artisanal sector (Donoso and Montenegro,

1992; Gonzalez, 1993) showed a remarkable progressive displacement of the histogram peak toward lower

weights (Fig. 7). Since 1989 the mean trunk weight of

swordfish caught by this sector has been diminishing

(Fig. 8).

The distribution of trunk weights indicates that over

50% of the industrial catch was fish of <40 kg, while the

artisanal sector catch was almost entirely fish >40 kg

(Fig. 9).

Figure 6

Relation between total landings (artisanal and industrial), CPUE (artisanal) and total effort of the swordfish fishery in Chile (r2=0.96).

Growth

The relation between length (measured from the tip of

the snout to the lowerjaw, LJFL) and the trunk weight

of swordfish caught by the artisanal fleet in 1994 is

shown in Figure 10.

Leiva (1993), by means of a statistical analysis of

concordance and variability, established that the second spine of the anal fin is more suitable for the identification of growth rings than spines of the dorsal fin.

He calculated the linear relation between the radius of

the second spine ofthe anal fin and LJFL, which showed

significant differences between sexes.

On the basis of anal spines of a wide distribution of

lengths, Montiel (1996) estimates the following growth

functions:

7000

6000

5000

:- 4000 Ol

c

'g 3000 0

..J

2000 87

1000

a

0

94

10000 20000 30000 40000 50000

Tolol effort (ortisonol days al sea)

females: LJFLt = 282[I-exp(-0.2925X(t-0.l085))]

males: LJFL( =250[I-exp(-0.3216X(t +0.7545))].

Stomach Contents

Table 4

Proportions (%) of male and female swordfish in artisanal catches in the central zone ofChile, ]989 (n= 300).

Stomach contents from specimens caught in the central zone of the country during 1989 were analyzed.

Five prey fish were found, the most important being the

longtailed hake, Macruronus magellanicus, andjack mackerel, Trachurus murphyi (Fig. 11).

Month

Jan-Apr

May-Jul

Harpoon

Female Male

85 15

Gillnel

Female Male

100 a

51 49

TOlal

Female Male

92.5 7.5

51 49

Proportions of the Sexes

Leiva (1993) estimated the proportions of males and

females in artisanal catches of swordfish obtained with

harpoon and gillnet during the fishing season of 1989

in the central zone (Table 4). During the first 4 months

of the fishing season (January-April), females predominate the catch with both gears; during May-July, the

proportions ofthe sexes were even, although the sample

contained only specimens caught with nets.
8 NOAA Technical Report NMFS 142

Figure 7

Annual frequency distributions of trunk weight (kg) of swordfish caught by the

artisanal sector in Chile, 1987-93 (n = number of fish; x = mean weight in kg).
_____________ Barbieri et al.: Development and Present State of the Swordfish Fishery in Chile 9

150 ~----------------------, 400 -,------------------------,

300 350

"

"

1',1,"

,

150 200 250

LJFL (em)

100

TW =3.26 E-07 • (LJFLt3.6272

n = 332

o-J.--~-~e.----,--_,__--~-_____j

50

-'i

C

2

>-

100

1987 1989 1991

100

-'i

C

g 110

rn 130

2!.,

1:

.~ 120

140

Figure 8

Annual mean weight ofswordfish trunks caught by the

artisanal sector in Chile, 1987-93.

Figure 10

Relation between length (lowerjaw-fork length, LJFL)

and trunk weight (TW) of swordfish caught by the

artisanal fleet in 1994.

The State of Chile regulates the fishing methods and

areas for swordfish and associated fauna in waters of

national jurisdiction. Since January 1991, Decree 293

has been implemented to control this fishery.

Legislation _

The freight on board price (FOB) for fresh-frozen

Chilean swordfish has a clear seasonal behavior; best

prices are during the first quarter, then they decline

until June and thereafter recover until February.

n

industrial 2. 046 40

artisanal 2. 439 110

1994

o

oJt,.."::;'~~":;:;:::T'?'r-T'T'T.,..,..,~r=n-r.......,..,..,....,..,....,...........-~,....,J

50 100 150 200 250 300 350 400 450

Trunk weight (every 10 kg)

30

g

>- 20 u

c

..

..

..:: 10

- Industrial - arlisanal Decree 293

Figure 9

Frequency distributions of trunk weights (kg) ofswordfish caught by the artisanal and industrial fleets in 1994

(n = number of fishes; X= mean weight).

Article I-Subjects all boats participating in the swordfish fishery within the Territorial Sea (12 n. mi. off the

coast) and in the Exclusive Economic Zone (EEZ) (200

n. mi. off the coast) to this regulation.

The Market _

During the 1993 season, swordfish transactions totaled

US $25 million. In 1992, transactions were 12.7% less,

but prices were 4.9% higher. During recent years the

orientation is toward the North American market, where

the catch is destined for luxury restaurants and some

supermarket chains. In the U.S.A. the Chilean product

competes mainly with exports from Caribbean countries, and to a certain point with local catches.

Article 2-Establishes that the fishery is composed by

the target species Xiphias gladius and its associated fauna,

mainly tunas belonging to the genera Thunnus and

Gasterochisma, marlins of the genus Tetrapturus, and

billfishes of the genera Istiophorus and Makaira.

Article 3-Bans landing in Chilean ports of swordfish

caught by boats that have broken these rules.

Article 4-Establishes that a) boats of total length of

less than 28 m with current authorization may conductextractive fishing activities on the swordfish resource
10 NOAA Technical Report NMFS 142 _

70 n 55

60

50

'i{

':: 40 u

c:

Q)

~30

"-

20

10

0

III IV V

Type of food

Figure II

Stomach contents of swordfish captured in Chile during 1989. I = longtailed hake, Macruronus magellanicus;

11 =jack mackerel, Trachurus murphyi; III =shrimp,

Heterocarpus reedi; IV = other fish remains; V = squids, Loligo

gahi and Dosidicus tunicata.

and its associated fauna in the Territorial Sea and EEZ,

and b) boats with current authorization, of total length

equal to or over 28 m, may only operate in this fishery

within the EEZ west of 120 n. mi. off the coast.

Article 5-Establishes that the gillnets used in this fishery may not exceed a total length of 1,350 fathoms

(fm), measured on the floatline.

Article 6-Fixes the maximum surface of nets, for boats

with total length less than 28 m, at 25,000 fm2.

Article 7-Boats of total length of at least 28 m may use

gillnets with a maximum surface of 37,500 fm2.

Article 8-Fixes at 1,200 the maximum number of hooks

to be set on each haul for boats fishing with longline.

For boats with a total length of at least 28 m, a maximum of 2,000 hooks is allowed on each fishing haul.

Literature Cited

Barbieri, M. A., E. Yanez, L. Ariz, and A. Gonzalez.

1990. La pesqueria del pez espada: tendencias y perspectivas. In M. A. Barbieri (ed.), Perspectivas de la actividad

pesquera en Chile, p. 195-214. Escuela de Ciencias del

Mar, Univ. Cat6lica de Valparaiso, Chile.

Barbieri, M. A., E. Yanez, and M. Farias.

1991. La teledetection et la peche artisanale du germon et de

l'espadon au Chili: un cas de transfert de technologie. In

]. R. Durand,]. Lemoalle, and]. Weber (eds.), La recherche

face a la peche artisanale, vol. 2:817-824. ORSTOM,

Montpellier, France.

Barbieri, M. A., E. Yanez, M. Farias, and R. Aguilera.

1989. Determination of probable fishing areas for the albacore (Thunnus atalunga) in Chile's central zone. In Quantitative remote sensing: an economic tool for the nineties.

IGARSS '89, Vancouver, vol. 4:2,447-2,450.

Barbieri, M. A., E. Yanez, A. Gonzalez, M. Garcia, V. Correa, and

C. Bernal.

1995. Remote sensing in the artisanal fishery of the Valparaiso

region, Chile. Est. Doc. Univ. Cat6lica de Valparaiso, Chile,

173 p.

Correa, V.

1993. Analisis de la pesqueria artesanal de pez espada (Xiphias

gladius) desarrollada en Chile en tre 1987 y 1991. Thesis,

Univ. Cat6lica de Valparaiso, Chile, 83 p.

Donoso, M., and C. Montenegro.

1992. Monitoreo de la pesqueria de pez espada. Informe,

Instituto de Fomento Pesquero, Chile, 28 p.

Food and Agriculture Organization of the United Nations (FAO).

1984-94. Anuarios estadisticos de pesca. United Nations,

Rome.

Gonzalez, A.

1993. Distribuci6n espacio-temporal de la pesqueria artesanal

de pez espada (Xiphias gladius) desarrollada por la £lota

artesanal de Valparaiso y variaciones ambientales entre 1987

y 1991. Thesis, Univ. Cat6lica de Valparaiso, Chile, 94 p.

Leiva, B.

] 993. Analisis de estructuras para el calculo de la edad y del

crecimiento del pez espada (Xiphias gladius) y evaluaci6n

preliminar de los parametros de crecimiento. Thesis, Univ.

Cat6lica de Valparaiso, Chile, 83 p.

MacCall, A. D.

1986. Virtual population analysis (VPA) equations for

nonhomogeneous populations, and a family of approximations including improvements on Pope's cohort analysis.

Can.]. Fish. Aquat. Sci. 43:2,406-2,409.

Montiel, A.

1996. Determinaci6n de la edad y del crecimiento del pez

espada (Xiphias gtadius) explotado frent a las costas de

Chile. Thesis, Univ. Cat6lica de Valparaiso, Chile, 79 p.

Pauly, D.

1980. On the interrelationships between natural mortality,

growth parameters and mean environmental temperature

in 175 fish stocks. Rapp. P.-V. Reun. Cons. Int. Explor.

Mer 39(2):175-192.

Ponce, F. and R. Bustos.

1991. La pesqueria de pez espada en Chile. Pacifico Sur

19:25-34.

Sel"Vicio Agricola y Ganadero (SAG).

1967-77. Anuarios estadisticos de pesca. Divisi6n de Pesca

y Caza, SAG, Chile.

Sel"Vicio Nacional de Pesca (SER AP).

1978-94. Anuarios estadisticos de pesca. SERNAP, Chile.

Yanez, E., M. A. Barbieri, A. Gonzalez, O. Pizarro, M. Bravo,

C. Canales, and S. Salinas.

1994. Sea surface thermal structure associated to the pelagic

fish resources distribution in northern Chile. In Remote

sensing for marine and coastal environments, vol. 2, p. 149-

162. Environmental Research Institute of Michigan, Ann

Arbor.
Swordfish, Xiphias gladius, and the Fisheries for TWlas and Billfishes

in the Australian Fishing Zone

ALBERT CATON

Fisheries Resources Branch

Bureau ofRural Sciences

P.O. BoxEll

Kingston, ACT 2604, Australia

KATHYCOLGAN*

Australian Nature Conservation Agen0'

G.P. O. Box 636

Canberra, ACT 2601, Australia

PHIL SAHLQVIST** and PETER WARD

Fisheries Resources Branch

Bureau ofRural Sciences

P.O. BoxEll

Kingston, ACT 2604, Australia

CESAR RAMIREZ

2456 Esmeralda Street

Vita Cruz

Manila, Philippines

MARTIN SCOTT

Observer Programme

Australian Fisheries Management Authority

Box 7051, Canberra Mail Centre

Canberra, ACT 2610, Australia

ABSTRACT

Fishing operations that take swordfish, Xiphias gladius, in the 200-nautical-mile Australian fishing zone (AFZ) are summarised and data collections are reviewed. Swordfish are

incidental in commercial tuna longline catches in the AFZ; most are taken by licensed

Japanese longliners, but some come from a domestic longline fishery which includes a

rapidly-growing section targeted on swordfish. Although swordfish are taken in most of the

eastern, southern, and western AFZ, swordfish catches and catch rates are highest in the

central eastern area of the AFZ. Average annual logbook-reported catch for the last 5 yr was

continued

* Present address: Quarantine and Export Operations, Aust. Quarantine and Inspection Svc., Dep. Agriculture, Fisheries, and Forestry, G.P.O. Box 858, Canberra, ACT 2601, Australia. ** Formerly known as P. Stewart.

11
12 NOAA Technical Report NMFS 142

about 750 tons. Neither harpooning nor tangle netting for swordfish occurs in the AFZ.

Rare incidental catches of swordfish are taken in the troll/handline tuna fishery, but they

have not been reported from the bait-boat or purse-seine tuna fisheries. The number of

swordfish caught by recreational anglers is quite small.

Japanese logbook data have been collected and stored in the Australian Fishing Zone

Information System since 1979. Domestic longline logbooks have been collected since 1985,

but comprehensive coverage was not achieved until 1989. No catch data are routinely

collected from recreational anglers. Virtually no biological research has been undertaken

on swordfish in Australia, but a program of observer cruises aboard Japanese longliners has

operated since 1979, providing catch size composition data and limited biological observations.

Introduction

Swordfish, Xiphias gladius, has been prized in the Mediterranean and United States as prime table fish because

of its moist, rich, light-colored flesh, but it has never

been an important commercial species in Australia.

This reflects the absence of regular landings until the

establishment of a domestic longline fishery in the late

1980's. Even then, levels of mercury present in the flesh

of larger fish were higher than the Australian Food Standard acceptable limit at the time (National Food Authority, 1992 and updates), which restricted the extent to

which the catch could be marketed. The permissible mean

content was 0.5 ppm, with a 1.5 ppm maximum for an

individual fish. Recent adjustment ofthe Standard, whereby

the mean has been increased to 1.0 ppm, has increased

the marketable component of the catch.

To facilitate consideration ofthe swordfish resources

in waters adjacent to Australia, the present paper provides a summary of past and current fishing activities

that catch swordfish in the Australian 200-nautical-mile

fishing zone (AFZ) (Fig. 1). A review of the nature and

extent of Australia:l fisheries data on swordfish is also

presented. A summary review of distribution, life history,

stock structure, the commercial and recreational fisheries,

and resource status ofswordfish in the AFZ, concentrating

on the Australian situation but including broader comment where relevant, is provided in Kailola et al. (1993).

Cocos Is

Lord Howe Is

o

,

Sou I h

Pac; fie

Ocean

Nortolk Is

\:).,

Vanuatu""~•

~J4

New~ t>

Caledonia •

Tasman

Solomon~ \"

Islands 0&.•~~

Limito'

Australian

/ Fishing Zone

Cor a /

Sea

Southern Ocean

Christmas Is

In d ian

Ocean

30'

40'

20'

10'8

100"E '40' '60' 170·

Figure 1

The Australian 200-nautical-mile fishing zone (AFZ; dotted line) and localities mentioned in the text.
_______ Caton et al.: Swordfish and the Fisheries for Tunas and Billfishes in the Australian Fishing Zone 13

Figure 2

Ocean currents in the vicinity of Australia (after Cresswell, 1987).

Pac i fie

Ocean

Because these occurrences have been rare, they have

generated considerable interest in the popular angling

media. The distribution reported in 1985 was from

Sydney to Narooma (350 km south of Sydney) on the

New South Wales south coast, with fish in the 1-2 kg

range. The distribution was farther north in 1994, from

South West Rocks (400 km north ofSydney) to Ulladulla

(200 km south ofSydney), and fish were initially around

4 kg.

In the Northern Hemisphere, the northern extension of the land masses and associated temperature

regimes presumably prevent interchange of North Pacific and North Atlantic swordfish, In the Southern

Hemisphere, interchange between the South Atlantic

and South Pacific seems unlikely because of the southward extension of South America. On the other hand,

interchange between the South Atlantic and Indian

Oceans, and between the South Pacific and Indian

Oceans, would appear feasible given the sea-surface

temperatures at the southern boundaries of the intervening land masses. Regarding interchange between

the Indian and Pacific Oceans, it is not clear whether

swordfish represent a single stock in the AFZ or whether

sub-structuring occurs. Swordfish are reported to be

rare in waters shallower than 200 m (Williams et al.,

1994). The shallow waters across northern Australia

probably inhibit substantial east-west interchange in

the tropical region. Distribution is more or less continuous around the remainder

of the AFZ, but catches south

of the Australian mainland and

around southern and western

Tasmania (Fig. 5) are relatively

low despite substantial longlining effort in the latter region

in austral summer. Swordfish

are usually found in waters with

surface temperatures greater

than 13°C (Williams et al.,

1994). The southern range of

swordfish catches is reasonably

consistent with the August (austral winter) 13°C mean sea-surface isotherm for eastern Australia (Fig. 6), although in February (austral summer) the

l3°C isotherm is well south of

Tasmania. Even so, swordfish

are rare in the summer catches

of longliners southwest of Tasmania; there may not be much

interchange in the cool temperate region between the eastern

and southwestern AFZ. Reported preferred sea-surface

South

Equatorial

Current

Cor a I

Sea

South

~u~~~""'7'7 Equatorial

current~

Distribution of Swordfish _

I Goadby, P. 1994. 38 Stirling Ave., North Rocks, NSW 2151,

Australia. Personal commun.

2 Pepperell,]. 1994. Pepperell Research, P.O. Box 818, Caringbah,

NSW 2229, Australia. Personal commun.

Swordfish occur predominantly in oceanic waters of

the AFZ; they are distributed beyond the edge of the

continental shelf from the far northeast of the zone,

around the south edge of the continent, to the far northwest (Kailola et al., 1993). Concentrations are found in

the central eastern and the southwestern regions of the

zone. These aggregations are in areas influenced by the

East Australian Current (off the Pacific coast) and the

Leeuwin Current (off the Indian Ocean coast), warm

currents which move southwards through the eastern and

western sectors of the zone (Fig. 2, taken from Cresswell,

1987). The eastern concentrations are also located in the

vicinity of several seamounts (Fig. 3). Larvae have been

found in the oceanic regions of the northeast and northwest of the zone (Fig. 4, taken from Nishikawa et al.,

1985). In some years (perhaps three times in the last 20

years, including 1985 and 1994), smalljuveniles (1-15 kg)

have been reported from continental shelfwaters at around

60 fathoms (fm) off the New South Wales central and

southern coast such that there have been occasional incidental recreational catches (Goadbyl and Peppere1l2).
14 NOAA Technical Report NMFS 142

temperatures for swordfish in the North Pacific are

around 18-22°C (Williams et aI., 1994), and this is

consistent with the area of peak concentration ofswordfish catch off eastern Australia in austral winter (Fig. 5).

Fisheries _

The tuna and billfish fisheries 3 of the AFZ consist of

• Japanese and joint-venture Australia-Japan longline

fisheries;

• a domestic longline fishery;

• domestic surface fisheries;

• a recreational fishery;

• aJapanese handline (surface) fishery.

Occasional troll catches of tunas had always been

taken around the Australian coast, but a significant

commercial tuna fishery was not established until the

early 1950's, when bait-boat techniques for southern

bluefin tuna, Thunnus maccoyii, were successfully used

off New South Wales and South Australia (Caton, 1991).

Japanese longline fishing expansion into the Southern

Hemisphere during the 1950's saw the establishment of

operations throughout much of the area now encompassed by the AFZ, but it was not until 1985 that a viable

domestic longline fishery was established.

Swordfish are regularly taken as incidental catch by

the longline tuna fisheries. 4 The average annual (JulyJune) catch of swordfish reported in logbooks by the

Japanese longline fishery during the period 1988-89 to

1992-93 was 742 metric tons (t), with fish of an average

processed weight of 47 kg. This compares with about 30

t reported annually in domestic longline fishery logbooks in the last three years (East Coast Tuna and

Billfish Assessment Group5).

The Australian surface fisheries use bait-boat, purse

seine, or trolling gear. Rare incidental catches ofswordfish are taken by troll gear, but there are none from the

bait-boat and purse-seine fisheries. There are no harpoon fisheries because surface "basking" behavior of

swordfish is rarely reported in Australia.

3 The description here of the tuna and billfish fisheries of the AFZ is

largely reproduced from Caton and Ward (1991), Albacore tuna

and its fisheries in the Australian fishing zone. Bur. of Rural Res.

Working Pap. WP/3/91,43 p. Their report has been updated and

modified to emphasize aspects relevant to swordfish.

4 In addition, since this manuscript was accepted, there has been a

major expansion of domestic longlining targeted on swordfish,

with a 1997 catch of about 1,500 t.

5 East Coast Tuna and Billfish Assessment Group. 1994. Fisheries

assessment report, east coast tuna and billfish fishery 1994. Aust.

Fish. Manage. Auth., Box 7051, Canberra Mail Centre, Canberra,

ACT 2610, Australia.

Figure 3

Seabed topography adjacent to eastern Australia; the

200-m and 2,OOO-m isobaths are shown, and seamounts

are shaded. Heavy line indicates the boundary of the

Australian Fishing Zone (source: Kailola et a!., 1993).

The Japanese handline fishery is a seasonal (October-December) activity in the Coral Sea around 15°_

200

S which takes surface aggregations of yellowfin,

Thunnus albacares, and bigeye, T. obesus, tunas. There is

no incidental swordfish catch.

A pelagic gillnet fishery involving vessels from Taiwan operated around northern Australia (north of 15°S

between 1200E and 1400 E) from the mid 1970's until

the in troduction of gear restrictions in 1986. The restrictions limited the maximum length of net set to 2.5

km and made the fishery uneconomic. Spanish mackerels, Scomberomorus spp., and various sharks were the

targets of this fishery. Observers reported incidental

catches of black marlin, Makaira indica, and sailfish,
_______ Caton et al.: Swordfish and the Fisheries for Tunas and Billfishes in the Australian Fishing Zone 15

•

•

10·S

"'. I----t----+----+-----j--,.--'---,;--+-----+--------f----;;--'Tf-l

\J

Figure 4

Distribution of sampling effort, and swordfish larvae caught, in waters off Australia

(after Nishikawa et a!., 1985). Upper: volume of water strained; denser shading indicates greater sampling effort. Lower: presence oflarvae; shading indicates area sampled,

denser shading indicates presence of larvae.

Istiophorus platypterus, but no swordfish were reported.

Across the southern Australian continental shelf there

is a large-mesh bottom-set gill net fishery for small (1-2

m) sharks. No incidental swordfish catches are reported

from that fishery. A large-mesh shark netting program

protects swimming beaches off New South Wales and

Queensland. No incidental swordfish catches are reported there. Apart from the activities summarized

above, there are no fishing operations in the AFZ that

use gear likely to take swordfish.
16 NOAA Technical Report NMFS 142 _

0

·· e'" · .. . . ... . . · . .

I

100

CJCID> ·-. . . . . . · .. . .. . ..

· . .

· . .

I

100

CIJCID>

·. . . . .. . · . · .. . . , . . . . . . · .. . .. . . . . . .. ..

o. of Swordfish

• 2501 to 8000

• 2001 to 2500

• 1501 to 2000

• 1001 to 1500

501 to 1000

1 to 500

I

100

I

120

I

120

I

120

I

140

I

140

I

1 60

I

160

I

160

~~

", . - 20

- 40

- 20

CD··· ......

.. .... - .....

- 40

- 20

- 40

Figure 5

Distribution (by I-degree square) of swordfish catch (number of fish) by Japanese

bilateral-licensed and joint-venture longliners in the Australian Fishing Zone during

May-October (top) and ovember-April (center), and yearly (bottom), 1979-93 combined (from Australian Fishing Zone Information System logbook data).
_______ Caton et al.: Swordfish and the Fisheries for Tunas and Billfishes in the Australian Fishing Zone 17

10'S 1------+_-----+----" ------f"--.-+"---I-------+-~-----'._=E""'""---____i---'=~--+_---___1

28"

20" 28"

24"

22" 30"

20"

18"

16"

40"

14"

28"

10'S

28"

28"

24" ~k'i 26"

20" 22" 24" ,

20" 22"

18" 20"

JO" 18"

18"

14"

12"

40"

Figure 6

Austral summer (February; top) and winter (August; bottom) mean sea-surface temperature isotherms

adjacent to Australia from Edwards (1979) for eastern Australia and Hydrographic Department (1992)

for western and southern Australia.

Japanese andJointAustralia-Japan Longline FISheries

SubstantialJapanese longline activity occurs in eastern,

southeastern, and western areas of the AFZ, 6 and sword6 Since the time this manuscript was accepted,Japanese fishing activity

in the AFZ, as well as access to Australian ports, has been prohibited,

because the bilateral access agreement lapsed on 31 October 1997

and was not renewed, and may not be unless Australia and Japan

resolve their differences over management ofsouthern bluefin tuna.
18 NOAA Technical Report NMFS 142

fish are regularly taken as an incidental catch (Fig. 5).

Japanese longlining commenced in the region in the

1950's and was well established by 1960 (Ward, 1996).

The vessels freeze their catch and land it in Japan for

sale at sashimi markets.

The vessels operating in the AFZ may be separated

into several loose groups, partly reflecting port of origin, target species, and company links. The fleets tend

to adopt different campaign patterns, operating in different seasons and areas of the AFZ, as follows.

Large longliners (350 t or more) operate adjacent to

and south of Tasmania during May-August and October-January. Southern bluefin tuna are the target and

swordfish are a minor bycatch. At other times these

longliners fish for southern bluefin as far westward as

the southern Atlantic and, to a lesser extent since the

mid-1980's, eastward to the waters around New Zealand.

Vessels of this Southern Ocean fleet are generally the

largest and most seaworthy of the Japanese distantwater longline fleet, remaining away from Japan for up

to 18 mo, though calls at foreign ports are made every 2

or 3 mo.

Large longliners operate in the western AFZ during

September to January, some augmenting more southern and more extensive southern bluefin tuna operations. Bigeye tuna and southern bluefin tuna are the

main target of operations off the southwestern coast,

whereas bigeye tuna; marlins, Makaira and Tetrapturus

spp.; and yellowfin tuna are important in the northwest.

Swordfish are an incidental catch in these operations.

Smaller longliners (180-350 t), mostly from the northern islands ofJapan,fish a mixture of tunas and billfishes

in equatorial and tropical waters. The vessels concentrate on the eastern AFZ, some incorporating activities

in New Zealand, Hawaii, or both. They take yellowfin

tuna and bigeye tuna in the Coral Sea, and these species plus southern bluefin tuna in the Tasman Sea.

Billfishes (particularly swordfish and striped marlin,

Tetrapturus audax, and albacore tuna, Thunnus alalunga,

constitute a significant bycatch, but at times (especially

in July-September and around periods of full moon)

swordfish are the target of operations off southern

Queensland and south of Lord Howe Island.

Prior to commencement of operation of the AFZ in

1979, Japanese longline vessels were generally free to

operate within the area now encompassed by the zone,

apart from waters within 12 nautical miles (n. mi.) of

the coast (Caton and Ward, 1996a). With establishment

of the AFZ they became subject to progressively more

severe access restrictions (Caton and Ward, 1996b).

Initially these restrictions closed waters north of 35°S

across southern Australia and formalised voluntary seasonal closures off southern Australia which Japanese

longliners had adopted in 1971 (Fig. 7). Subsequent

restrictions had the most impact off the east coast, and

were associated with expansion of Australian commercial and recreational fisheries. In the south they also

addressed concern over the biological status of southern bluefin tuna, and off northeastern Australia they

reflected a desire by gamefish anglers to protect spawning fish and to maintain good strike rates oflarge black

marlin.

Currently, the far southeast of the zone (around

Tasmania) is the only area where a 12-n.-mi. limit still

applies. Elsewhere, the zone is either totally closed to

access or is closed within 50 n. mi. of the coast (Fig. 8).

Displacement ofJapanese longliners from areas where

southern bluefin tuna was the target species has increased activity levels in areas where yellowfin tuna and

bigeye tuna were the targets. As most swordfish are

taken in association with the latter species, there have

been effects on the distribution and extent ofswordfish

catches.

Access arrangements permitted the annual licensing

of 350Japanese longliners between 1979 and 1983, 290

longliners between 1984 and 1989, and 250 longliners

since then. However, these limits were well above the

actual fleet numbers in the AFZ and did not act as a

restraint on fishing effort; during the 1980's the number ofJapanese longliners actually undertaking licensed

fishing operations in the AFZ ranged between 109 and

184. Since late 1990, more restrictive limits on vessel

numbers have controlled the distribution of fishing

effort within the AFZ. In 1995, for example, 20 longliners

could be licensed for the Australian west coast and 55

longliners during each 4-mo period for the east coast

north of 34°S. Off Tasmania, a limit on the southern

bluefin tuna catch was a substitute for vessel limits.

From 1989 to 1995, up to 50 Japanese longliners

operated in the AFZ underjoint-venture arrangements

with Australian companies, mainly in the fishery for

southern bluefin tuna. Their style of operation was

essentially identical to that of Japanese longliners licensed under the Australia-Japan bilateral access arrangements. However, they had the advantage of access

to the AFZ across southern Australia. Thejoint-venture

arrangement was terminated in late 1995, with no plans

at that time for resumption.

Domestic Longline Fishery

Experimental, small-vessel longlining was carried out

irregularly off the Australian east coast in the 1950's,

1960's, and 1970's. A viable commercial fishery was not

established until the mid-1980's, after fishers operating

off the New South Wales central and southern coasts

successfully air-freighted high-quality, fresh-chilled yellowfin tuna to the Japanese sashimi market. By the late

1980's, more than 1,000 t of yellowfin were landed
_______ Caton et al.: Swordfish and the Fisheries for Tunas and Billfishes in the Australian Fishing Zone 19

o Permanent closure

o longline only

_ seasonal Closure

_ Longllne and handline

'@Ccc:oo" , 'Iv ",

(0\, ,

20"

In d ian

Ocean

30"

40"

~INDONESIA. A'

~~_.y

~~

12 nautical

mile contour

(not to scale;

indicative only

Southern Ocean Tasman

o

o

.

~"",oIk"',I',', '

,'w,...'" 50&lJ

'20" '30" '40" 'SO' '50"

Figure 7

Areal and seasonal access restraints applying to Japanese tuna longline vessels in the Australian Fishing Zone,

1979-80 (from Caton and Ward, 1996b).

20"

30"

40"

In d ian

Ocean

50 nautical

mile contour

(nol to scale;

indicative only

o Permanent closure

o Longline only

_ Handline only

DB Longline and handline

110"

Southern Ocean

'40" 1SO'

Tasman

'50'

o

.

Figure 8

Gear and operational area restraints applying to Japanese tuna longline vessels In the Australian Fishing Zone,

1993-1994 (from Caton and Ward, 1996b).
20 NOAA Technical Report NMFS 142

Figure 9

Management zones for domestic east coast tuna

longliners (from Australian Fisheries Management Authority).

annually, with over 130 full-time participants endorsed

for longlining and a further 120 longlining on a parttime basis. Many vessels have since left the fishery or are

not fishing because of variable yellowfin catch rates,

high freight charges, and unpredictable prices at sashimi

markets for the smaller fish. Catch has decreased to

around 550 t.

The domestic east coast longline fishery is managed

by zone (Fig. 9), and the number and size of vessels is

endorsed for each zone. Specific arrangements are quite

complex; essentially, separate zones are established inshore and offshore of 50 n. mi. from the coast. Within

50 n. mi. (12 n. mi. adjacent to eastern Tasmania),

vessel size is not to exceed 32.67 m overall length. Off

northeastern Australia, the inshore region is encompassed by the Great Barrier Reef Marine Park, and

longlining is virtually impractical there. To the north

and outside the Park there is an intermediate area

where sets are restricted to 500 hooks and all billfish

7 The limit was 0.5 ppm prior to 1995.

must be returned. Vessels have various rights of access

to zones, depending upon their history in the fishery,

vessel size, and target species.

Many local longliners fish part-time in trawl, trap,

and dropline fisheries. While 170 domestic longline

endorsements have been issued for the fishery, only

30-40 vessels longline regularly (East Coast Tuna and

Billfish Assessment Group4). Halfoftheir yellowfin catch

now supplies a growing local sashimi trade. A diversification to winter longlining for southern bluefin tuna

off southern New South Wales is renewing interest in

the fishery. The southern bluefin tuna catch is restrained

by a system of individual transferable quotas; operations

are subject to the purchase or lease of quota. There is no

catch limit for any of the other longline species.

Yellowfin, southern bluefin, and bigeye tunas are the

target species for the domestic fishery.4 Yellowfin comprise about 60% and southern bluefin tuna about 30% of

the reported retained catch of Australian longliners, but

very high prices for individual large southern bluefin and

bigeye tuna influence profitability. Swordfish constitutes

a minor component of the catch (Table 1). Its lower

value compared with the tunas makes air-freighting to

Japan unprofitable at times. Instead, small quantities are

sold fresh on the Sydney and Melbourne fish markets.

Despite a change during 1995 in national mercury

content standards, swordfish mercury content still imposes a significant obstacle to marketing. The current

Australian Food Standards Code Standard A12 (National Food Authority, 1992 and updates) for mercury

in fish covers, among other things, swordfish. If the fish

can be sampled in groups offive, whether whole fish or

fillets, then the mean mercury content for five samples

may not exceed 1.0 ppm. 7 Within that group of five, no

individual sample may exceed 1.5 ppm. If the fish are

unable to be sampled as a group, then the mercury

content of an individual fish may not exceed 1.0 ppm.

While this is the national recommended standard, its

adoption or application by states is variable.

Australian longliners fish mostly outside the 200-m

depth contour within 60 n. mi. of the New South Wales

coast, but activity has expanded recently off northern

Queensland in the vicinity of Cairns. The yellowfin

season commences offsouthern Queensland and northern New South Wales in August and spreads to the

south as the East Australian Current pushes warm (18°-

22°C) water southward. By April most of the yellowfin

catches come from the far south coast of New South

Wales. Southern bluefin tuna catches commence in

May to the south of New South Wales and continue to

September, when operations are centered off Sydney.

Domestic longline vessels are smaller (10-20 m) than

those operated by the Japanese in the AFZ. The domes150' 160'

146'E

140'

Northern

Territory

20'

40'S

---------------------------l

South Australia r------------------"--~' ..--_/

i Coff's Harbour i New South ! Wales

~-\-.

! '-',~''''"-~---,

! Victoria E~~~"

Queensland
_______ Caton et al.: Swordfish and the Fisheries for Tunas and Billfishes in the Australian Fishing Zone 21

Table 1

Annual Quly-June) swordfish catch (metric tons) by

the Australian domestic longline fishery, 1988-89 to

1992-93 (from Australian Fishing Zone Information

System logbook data).

Catch Catch

Year (t) Year (t)

1988-89 12.6 ]991-92 31.5

1989-90 10.9 1992-93 29.0

1990-91 34.1

tic vessels usually set between 400 and 800 hooks before

sunrise each day, store their catch in ice slurry, and

generally return to port after one or two days fishing.

Australian tuna catch rates are often higher than Japanese longliners because inshore productivity is higher,

fresh bait is used, and the shorter longlines target oceanic

frontal regions or topographic features where tuna appear to aggregate. Components of the fleet operate in the

region of Lord Howe Island, as far south as southeastern

Tasmania, and in the region adjacent to Cairns off northern Australia, but most activity is concentrated between

southern Queensland and southern New South Wales.

A logbook program, established in 1985 but not fully

supported by field liaison until 1988, now covers most

of the longline fleet. In the case of swordfish, logged

catches (Table 1) probably under-represent catch because mercury content restrictions prevent marketing

of larger fish. In such cases, the fish might not be

landed nor recorded in logbooks.

Recreational Fishery

Recreational fishers take a wide range of pelagic species

along the east coast at various locations from Cairns

(north Queensland) to Eaglehawk eck (80 km east of

Hobart, Tasmania) and near Lord Howe Island. The

main concentrations of activity in the east are off central and southern New South Wales, Brisbane (Queensland), and Cairns. Low levels of recreational fishing

activity for pelagic fishes are also reported from Western Australia and, to a lesser extent, South Australia

and Northern Territory.

Swordfish have provided an intriguing challenge for

anglers because, despite enthusiastic efforts, few are

caught. In his authoritative overview of Australian fisheries, Theo Roughley, who was Superintendent of New

South Wales Fisheries from 1939 to 1952 and President

of the Great Barrier Reef Game Fish Angling Club in

1937, stated, "No broadbill swordfish has yet been landed

by an angler in Australian waters, and fame awaits the

angler who first succeeds in catching this elusive fish. It

is known to occur here for it has been washed ashore in

several Australian states, including New South Wales,

Queensland, South Australia and Western Australia"

(Roughley, 1951, p. 265). Apart from years like 1994,

when small juveniles penetrate relatively close inshore

and are taken occasionally during trolling, it was not

until 1989 that a 56-kg swordfish was landed that qualified for record status under international game fishing

regulations (Kailola et a!., 1993). Since then, others

have been taken as a result of targeted fishing with

Cyalume "light sticks" at night. The largest taken to

date on rod and reel was 98 kg in April 1990 (PepperelI2). There is now an annual swordfish tournament

run from Merimbula (450 km south of Sydney) in southern New South Wales each Easter. Even so the number

taken remains very low, and the size of fish is less than

50 kg (GoadbyJ and PepperelI2).

Fishing Statistics in the Japanese Longline

Fishery _

The following is based on data gathered from Japanese

longline vessel logbooks since commencement of operation of the Australian Fishing Zone in 1979. A substantial

global time series of data aggregated by 5° x 5° squares by

month for the previous twenty years exists in Japanese

annual "yellow book" longline records (Fishery Agency of

Japan, 1962-1980), but those data are not addressed here.

Effort

Since commencement of operation of the AFZ and

maintenance of a national logbook program late in

1979, the annual level ofJapanese longline activity in

and adjacent to the zones has fluctuated between 16.5

million (1991) and 31.6 million (1989) hooks, with a

slight decline overall (Fig. 10). Longlines deploying

2,500-3,500 hooks are set and retrieved in a 24-hr period. Total days fished each year has declined (Fig. 11).

To some extent the decline has been counteracted by

an increase in the number of hooks set per day per

vessel (Table 2; Fig. 11).

Catches

Seasonal distributions ofJapanese longline (bilateral

and joint-venture) swordfish catches, aggregated for

8 The logbooks ofJapanese longliners working in the vicinity of the

AFZ boundary and moving back and forth into and out of the zone

include details of operations both within and outside the AFZ.
22 NOAA Technical Report NMFS 142

Table 2

Annual effort, operational days, and average hooks set per day byJapanese and Australia-Japanjoint-venture longliners in

and adjacent to the Australian Fishing Zone, 1980-93. (Source: Australian Fishing Zone Information System logbook data;

the logbooks ofJapanese longliners working in the vicinity of the AFZ boundary and moving back and forth into and out

of the zone include details of operations both within and outside the AFZ.)

Effort Vessel Hooks per Effon Vessel Hooks per

Year (106 hooks) days vessel day Year (106 hooks) days vessel day

1980 18.15 7,262 2,499 1987 23.36 8,245 2,833

1981 31.29 12,714 2,461 1988 25.76 8,982 2,868

1982 23.89 9,357 2,553 1989 31.56 10,822 2,916

1983 24.11 9,107 2,647 1990 27.15 9,399 2,889

1984 21.18 7,966 2,659 1991 16.46 5,616 2,931

1985 20.06 7,232 2,774 1992 20.05 6,679 3,002

1986 19.99 7,155 2,794 1993 23.93 7,901 3,029

2400

2600

i;' 2800 '0

Iii

o

o

:I:

3000

3200

1979-1993, are indicated in Figure 5. The central area

of the eastern AFZ has consistently been the main area

of swordfish catch. Current operations are subject to

the permanent closure of the area inshore of 50 n. mi.

from the coast. Japanese longliner access to eastern

seamounts has not changed, but the productive area

close to the east coast around 27°S is no longer accessible. Recent (1990-93) distributions of effort and catch

are shown in Figure 12. There is some annual variation

in location of activities (compare the 1993 effort distribution pattern with those for 1990-92), probably associated with changes in activity patterns oftarget species.

The lower swordfish catches in 1993 around 25°S coincide with lower effort levels there in that year.

Most changes in operational areas by Japanese longliners in recent years have been associated with operations directed atsouthern bluefin tuna.

The establishment of Australia-Japan

joint ventures re-opened access to a

wider area south of 34°S (compare

1990-91 with 1992-93), and effort increased offsouthern and southwestern

Australia. There has been a resumption

ofincidental swordfish catches there, but

the central southern region and southwestern Tasmanian regions still show

very low catch levels despite substantial

effort southwest of Tasmania.

Annual (calendar year) Japanese

longline (bilateral and joint-venture)

catches by species in and adjacent to

the AFZ since 1980 are provided in

Table 3 for the main species taken,

with breakdowns for the northeastern,

southeastern, and western regions. Annual effort level and catch in number

of swordfish and yellowfin, southern

III CD ... <Xl

'" a ;;; N

<Xl <Xl <Xl <Xl DO a> '" '" a>

a> '" '" '" Year

-- Hooks per Vessel Day i

+-------+-_+---+-_+---+-_+---+-_+---+-_+----+_-1----+--1- 2200

1--<>-- Days

15000

12500

10000

III

i;' 7500

0

5000

2500

0 0 ;;; N

'" ... <Xl <Xl <Xl <Xl

a> a>

Figure 11

Annual operational days and average hooks per set by Japanese tuna

10ngJiners in and adjacent to the Australian Fishing Zone, 1980-93.

Figure 10

Annual nominal effort (million hooks set) byJapanese

tuna longliners in and adjacent to the Australian Fishing Zone, 1980-93.

35

III 30

8 25

:I: 20

c: 15

10 :E 5

0 0 N

'" ... III CD ... <Xl a> 0 N

<Xl <Xl <Xl <Xl <Xl <Xl <Xl <Xl <Xl <Xl a> a> a> '"

a>

a> a> a> a> a> a> a> a> a> a> a> a> a> a>

Year
Figure 12

Annual distribution of total fishing effort (hooks set) and swordfish catch (number of fish) by Japanese and Australia-Japan joint-venture tuna longliners in the

Australian Fishing Zone, 1990-93 (from Australian Fishing Zone Information System logbook data).

...

o

:=

...

Q.

::l

'"=-

'"S'

;.

..

e:.

§'

:=1

'"=- S'

(Jq

N

o

:=

[I}

o

..

Q.

::l

'"=-

Q.

;.

:=1

'"=-

..

rD'

'"0'

..

=:=

- 40

b~

'" - 20

0-

"' ...

b~

,., .. - 20

- 40

CD

"

7\ '.: ':::'::'- ... . . . . .. .

"' ...

I

160

I

160

I

140

I

120

120

100

I

100

U

". . .... . O. ... ..

00

No. of Swordfish

• SOl to BOO

• 401 to 500

• 301 to 400

• 201 to 300

101 to 200

1 to 100

No. of Swordfish

• SOl to BOO

• 401 to 500

• 301 to 400

• 201 to 300

101 to 200

I to 100

b~

'" '. -20

- 40

- 40

Ci!

b~

", '. - 20

.,0-

"' ...

"' ...

I

160

I

160

I I

140

I

120

I

120

I

100

I

100

00

08. .. '

..: .. .

Hooks ('ODDs)

• SOl to 2400

• 401 to SOD

• 301 to 400

201 to 300

101 to 200

o to I DO

Hooks ('ODDs)

• SOl to 2400

• 401 to SOD

301 to 400

• 201 to 300

101 to 200

o to lOO

I>:>
Nl

z

o

O 0 VOO--~F IQ • i\' ~. ~,. -" - 0: 0 :-. -: - i ~. l~ '1 'J. n' o

,.,' - 20 '" '. _ 20 ;;

Q .::- i

H k ('000) UVH5'HI'- U"VI C ". N f 5 f' 5:. O·'. ::l- 00 5 5 .. :: .. _ o. 0 word Ish .,. z • 501 10 2400 • SOl 10 800 .. . .... s::: • 40 I to SOD • 401 10 SOD . :. . "!j

• 301 to 400 • 301 10 400 ... [IJ

201 to 300 201 10 300 ...

101 10 200 _ 40 101 10200 .

o to 1DO I 10 1DO \ - 40

I I I I I I I I I I I

10D 120 160 100 120 14U 1 60

O0 . "00--_~.F IQ • i\" '''L.

~. "',. -" - 0. 0 <>,. ,

~I~ '1 ,.,0, _20 ,.," _ 20

1993

H k ( 00 5 5 'oou) UVH5"H'- '-'''VI C g.. .. ... _ NO. 0 f 5 wardf'IS h Catch g.....

• SOl 102400 • 501 to 800 -

• 401 10 SOD • 401 10 500

• 301 10 400 ,.. • 301 10 400

201 10 300 • 201 10 300

101 10 200 _ 40 101 10200 ............ , ..( _ 40

o to I 00 1 to 100 \ .

I I I I I I I I I , I I I I

100 120 140 160 100 120 140 160

Figure 12 (continued)
_______ Caton et al.: Swordfish and the Fisheries for Tunas and Billfishes in the Australian Fishing Zone 25

bluefin, and bigeye tuna for these areas are shown in

Figure 13. It can be seen that the principal tuna species

in the northeast is yellowfin (albacore are abundant but

are not a primary target) and in the southeast, southern

bluefin tuna. In contrast, the western region supports a

mixed fishery in which bigeye has been an important

component of the catch, with yellowfin and southern

bluefin tuna also important at times. Swordfish is reasonably represented in the northeastern and, to a lesser extent, western regions but is insignificant in the southeast.

Changes in the management of southern bluefin

tuna in the AFZ and globally caused modification of

Table 3

Annual Japanese and Australia-Japan joint-venture longline effort (million hooks) and catches (number of fish) by

species, in and adjacent to the northeastern, southeastern, western, and entire Australian Fishing Zone, 1980-93. (Source:

Australian Fishing Zone Information System logbook data; the logbooks ofJapanese longliners working in the vicinity of

the AFZ boundary and moving back and forth into, and out of, the zone include details of operations both within and

outside the AFZ).

Hooks Southern Striped Blue Black

Region Year (x 106) Swordfish Yellowfin bJuefin Bigeye Albacore marlin Sharks marlin marlin Sailfish

Northeast 1980 3.82 6,532 21,706 8,190 7,672 10,744 4,237 2,351 587 1,085 621

(N of 35°S; 1981 Il.I9 12,991 78,678 10,221 11,021 60,174 13,201 11,988 2,192 1,811 1,075

E of 1400E) 1982 13.12 21,880 64,015 400 14,706 74,999 19,577 12,796 5,243 4,197 1,922

1983 8.33 10,984 65,807 555 18,869 97,750 5,522 6,939 2,089 2,032 1,279

1984 8.06 11,803 25,965 937 11,744 74,793 7,017 6,217 1,095 1,879 931

1985 9.31 15,281 80,712 136 19,038 113,603 6,434 5,652 1,467 1,148 1,047

1986 7.21 13,428 32,958 172 17,081 101,572 3,640 4,659 741 287 438

1987 8.83 15,097 73,995 257 15,809 103,891 4,32\ 6,985 1,630 1,995 2,323

1988 15.68 24,493 126,061 540 21,915 170,631 7,548 10,277 6,102 2,240 2,378

1989 15.68 16,556 87,576 1,439 21,330 170,025 12,354 9,150 4,956 1,044 2,403

1990 12.27 11,932 93,007 1,680 24,196 151,418 5,902 5,777 4,046 519 4,182

1991 6.24 11,120 32,875 1,088 9,783 86,717 3,202 6,399 344 259 692

1992 6.69 11,876 36,073 1,435 9,490 100,489 2,646 716 401 182 737

1993 7.89 6,939 64,776 12,322 7,439 162,178 3,812 774 653 361 2,228

Southeast 1980 10.22 684 93 45,897 307 8,341 75 8,616 2 2 0

(S of 35°S; 1981 12.31 1,949 733 61,128 663 30,362 567 9,412 8 6 2

E ofl400E) 1982 5.54 1,517 416 30,408 1,200 30,293 382 9,668 36 9 3

1983 9.32 1,261 301 38,157 1,222 42,932 823 7,119 23 24 I

1984 3.88 1,211 361 17,257 743 16,685 504 2,653 11 4 7

1985 3.45 1,467 581 6,337 881 13,707 383 1,374 13 20 5

1986 3.01 694 662 7,958 1,020 15,402 189 5,490 10 4 0

1987 6.71 975 831 15,651 852 16,430 129 4,952 11 2 9

1988 8.44 1,222 1,788 19,188 1,262 17,513 380 2,367 32 9 9

1989 14.2 5,287 5,620 54,615 3,831 134,542 978 8,881 39 16 14

1990 12.94 2,222 802 51,777 1,087 62,247 138 4,717 0 2 2

1991 9.47 1,756 2,187 55,575 1,465 33,452 221 38,688 7 I 4

1992 12.02 2,912 607 67,253 1,167 28,403 155 122 4 3 0

1993 12.68 2,884 751 83,457 811 32,138 355 576 16 17 I

Western 1980 4.1 1,153 3,796 20,575 11,110 5,372 684 430 215 295 7

(W of 1400E) 1981 7.79 1,834 17,138 38,414 17,849 21,374 1,296 2,823 630 550 115

1982 5.23 742 10,270 11,203 8,404 3,639 729 692 428 666 43

1983 6.45 1,179 12,591 11,368 23,460 10,639 1,545 2,628 388 704 92

1984 9.24 1,922 31,460 18,567 22,488 10,379 6,540 1,648 1,485 2,750 294

1985 7.31 2,460 23,652 8,028 18,445 13,317 3,672 2,085 1,298 2,515 166

1986 9.76 1,922 26,818 9,708 26,268 12,055 1,167 559 1,446 1,405 220

1987 7.82 2,166 16,480 4,884 33,355 11,851 1,108 1,029 458 878 231

1988 1.64 446 8,626 911 4,129 2,795 266 246 394 634 176

1989 1.68 433 7,165 1,222 3,109 1,560 118 391 297 441 192

1990 1.94 901 11,554 514 7,967 3,952 109 2,006 426 320 29

1991 0.74 731 449 1,305 2,151 255 0 224 3 4 3

1992 1.34 423 457 25,400 4,869 2,274 3 18 12 7 8

1993 3.36 2,593 1,738 11,118 12,364 4,275 40 36 11 24 36

continued
26 NOAA Technical Report NMFS 142

Table 3 (continued)

Hooks Southern Striped Blue Black

Region Year (x 106) Swordfish Yellowfin bluefin Bigeye Albacore marlin Sharks marlin marlin Sailfish

TotalAFZ 1980 18.15 8,369 25,595 74,662 19,089 24,457 4,996 11,397 804 1,382 628

1981 31.29 16,774 96,549 109,763 29,533 111,910 15,064 24,223 2,830 2,367 1,192

1982 23.89 24,139 74,701 42,011 24,310 108,931 20,688 23,156 5,707 4,872 1,968

1983 24.11 13,424 78,699 50,080 43,551 151,321 7,890 16,686 2,500 2,760 1,372

1984 21.18 14,936 57,786 36,761 34,975 101,857 14,061 10,518 2,591 4,633 1,232

1985 20.06 19,208 104,945 14,501 38,364 140,627 10,489 9,111 2,778 3,683 1,218

1986 19.99 16,044 60,438 17,838 44,369 129,029 4,996 10,708 2,197 1,696 658

1987 23.36 18,238 91,306 20,792 50,016 132,172 5,558 12,966 2,099 2,875 2,563

1988 25.76 26,161 136,475 20,639 27,306 190,939 8,194 12,890 6,528 2,883 2,563

1989 31.56 22,276 100,361 57,276 28,270 306,127 13,450 18,422 5,292 1,501 2,609

1990 27.15 15,055 105,363 53,971 33,250 217,617 6,149 12,500 4,472 841 4,213

1991 16.45 13,607 35,511 57,968 13,399 120,424 3,423 45,311 354 264 699

1992 20.05 15,211 37,137 94,088 15,526 131,166 2,804 856 417 192 745

1993 23.93 12,416 67,265 106,897 20,614 198,591 4,207 1,386 680 402 2,265

Japanese longline campaign strategies in the AFZ. Reduced access to southern bluefin tuna areas off New

South Wales and South Australia brought about a reduction of effort in the southeast until the mid-1980's.

Subsequent relocation of activities to the southeastern

Tasmanian area led to increased effort there. Levels of

effort off Tasmania remained high through the early

1990's as a result of the establishment ofjoint-venture

activities. The incidental swordfish catch has varied in

conjunction with these changes in the distribution and

extent of fishing effort directed at southern bluefin

tuna.

In the northeastern area, restrictions on marlin fishing and on inshore access forced operations farther

offshore. In addition, these offshore areas had to support some of the displaced southern bluefin tuna operations. As a result, effort levels in the region remained

moderately steady through the mid-1980's while southeastern effort decreased. Mter 1989, more restrictive

controls on effort in the northeastern area and the

improving southern bluefin tuna access resulted in reduced activity in the northeast.

The major drop in effort off western Australia between 1988 and 1992 was in part linked to extension of

the permanent closure area to include all waters within

50 n. mi. of the coast. However, it was also associated

with declining global catch rates for southern bluefin

tuna, effort restraints in the adjacent high seas area

resulting from the seasonal closures introduced by Japan to implement its major cut in quota for 1989-90,

and a concentration ofsouthern bluefin tuna effort off

eastern Tasmania (where viable catch rates persisted).

Increased western region effort in 1993 resulted from

the less-restrained operational conditions applying to

the joint-venture fleet. The incidental swordfish catch

changed in conjunction with those changes in distribution and level offishing effort.

Catch Rates

Annual November-April (austral summer) and MayOctober (austral winter) nominal fishing effort, swordfish catches in number, and number ofswordfish caught

per thousand hooks from 1980 to 1993, based on Japanese longline daily logbook data, are provided in Table

4. Plots ofsummer and winter effort, catches, and catch

rate for the northeastern (north of 20 0S), central eastern (200

-35°S), and southeastern (south of 35°S) AFZ

are shown in Figure 14. In the main swordfish region

and season (central eastern AFZ in austral winter),

catch rate was reasonably stable from 1980 to 1988, but

overall has declined slightly. The low 1993 catch rate

emphasizes this trend, but the pattern of effort distribution in that year (Fig. 12) was different from that in

1990-92, as mentioned previously. It is possible that

decreased swordfish catch rates reflect the changes in

access conditions and resultant patterns of targeting

rather than changes in local abundance. Further examination is warranted.

The graphs showing longline effort, catch, and catch

rate in the northeastern and southeastern areas and in

summer in the central eastern area (Fig. 14) depict

activity where swordfish is a relatively minor component of the catch. In the northeast, summer catch rates

declined during 1980-93, whereas winter rates were

variable. In the southeast, summer catches and catch

rates were negligible; winter catch rates are low and

have declined since effort increased in the mid-1980's.

This probably reflects increased southern bluefin tuna
Figure 13

AnnualJapanese and Australia-Japan joint-venture longline effort and catches of swordfish and southern bluefin, yellowfin, and bigeye tunas in and adjacent to

(clockwise from top right) the northeastern, southeastern, western, and entire Australian Fishing Zone, 1980-93. S'fish = swordfish; Y'fin = yellowfin tuna; S. B'fin

=southern bluefin tuna; B'eye =bigeye tuna; Hks =hooks. (Source: Australian Fishing Zone Information System logbook data; the logbooks ofJapanese longliners

working in the vicinity of the AFZ boundary and moving back and forth into and out of the zone, include details of operations both within and outside the AFZ.)

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28 NOAA Technical Report NMFS 142

Table 4

Annual Japanese and joint-venture Australia-Japan longline ~ovember-April (summer) and May-October (winter)

swordfish catches (number offish), longline effort (million hooks), and catch rate (number offish per 1,000 hooks) in

and adjacent to the northeastern, central eastern, and southeastern Australian Fishing Zone, 1980-93. Summers are taken

as commencing in the prior year, so that, for example, summer 1980 was November 1979-April 1980. Because these data

span 12 months from November to October, totals are not equivalent to those in Table 3 which is based on data for

calendar years. (Source: Australian Fishing Zone Information System logbook data; the logbooks ofJapanese longliners

working in the vicinity of the AFZ boundary and moving back and forth into, and out of, the zone include details of

operations both within and outside the AFZ.)

5ummer Winter

Region Year No. Million hooks No./I,OOO hks o. Million hooks No./l,OOO hks

Area A 1980 115 0.437 0.26 73 0.209 0.35

(N of 20°5) 1981 94 0.234 0.40 257 0.297 0.87

1982 632 1.844 0.34 575 0.763 0.75

1983 412 1.152 0.36 167 0.521 0.32

1984 141 0.568 0.25 1,048 0.701 1.49

1985 523 0.669 0.78 752 0.843 0.89

1986 100 0.538 0.19 12 0.033 0.37

1987 57 0.277 0.21 330 0.175 1.89

1988 678 1.883 0.36 582 0.741 0.79

1989 728 1.768 0.41 637 1.005 0.63

1990 287 2.310 0.12 573 0.607 0.94

1991 I 0.044 0.02 9 0.006 1.48

1992 10 0.034 0.30 7 0.030 0.23

1993 58 0.396 0.15 1,041 1.616 0.64

Area B 1980 1,219 1.143 1.07 4,258 2.209 1.93

(20°-35°5) 1981 3,944 2.141 1.84 8,053 7.431 1.08

1982 3,985 3.724 1.07 14,908 7.414 2.01

1983 5,313 2.365 2.25 9,189 5.152 1.78

1984 454 0.787 0.58 9,903 6.261 1.58

1985 315 0.681 0.46 13,936 7.090 1.97

1986 492 0.800 0.61 13,045 6.258 2.08

1987 200 0.345 0.58 13,882 7.380 1.88

1988 948 1.474 0.64 22,395 11.600 1.94

1989 1,595 1.577 1.01 14,079 11.800 1.19

1990 422 0.802 0.53 10,685 8.758 1.22

1991 254 0.414 0.61 lO,866 5.790 1.88

1992 721 0.554 1.30 11,163 6.124 1.82

1993 896 1.154 0.78 4,940 4.721 1.05

Area C 1980 12 5.314 0.00 674 1.070 0.63

(5 of 35°5) 1981 85 11.500 0.01 1,864 4.357 0.43

1982 31 5.018 0.01 1,486 3.501 0.42

1983 172 2.743 0.06 1,089 3.471 0.31

1984 38 5.602 0.01 1,173 3.227 0.36

1985 29 0.149 0.20 1,438 0.806 1.78

1986 7 2.687 0.00 687 2.784 0.25

1987 3 0.269 0.01 972 5.317 0.18

1988 35 1.698 0.02 1,187 4.709 0.25

1989 73 4.268 0.02 5,214 13.200 0.40

1990 336 3.766 0.09 1,886 9.178 0.21

1991 10 0.022 0.45 1,746 8.596 0.20

1992 9 0.932 0.01 2,903 8.271 0.35

1993 374 4.329 0.09 2,510 8.267 0.30

effort at the extreme of the swordfish range, rather

than a trend in swordfish abundance there.

It should be emphasized again that the catch rate

data outlined above are derived from nominal effort.

Observers aboard foreign longliners point out that various factors can influence swordfish catch rate, in particular moon phase, time of setting and hauling, and

bait. Some fishing masters target swordfish off the central east coast at periods offull moon. This will depend

on location of operations, anticipated catch rate, current price, and success of other components of the

vessel's campaign.
_______ Caton et al.: Swordfish and the Fisheries for Tunas and Billfishes in the Australian Fishing Zone 29

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300

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-------- Million hooks

--0-- No.ll000 hk.

Figure 14

Annual November-April (left) and May-October (right) Japanese and Australia-Japan jointventure longline effort (million hooks), swordfish catches (number of fish), and catch rate

(number of fish per 1,000 hooks) in and adjacent to the northeastern (top), central eastern

(middle), and southeastern (bottom) Australian Fishing Zone, ]980-93. (Source: Australian

Fishing Zone Information System logbook data; the logbooks ofJapanese longliners working in

the vicinity of the AFZ boundary and moving back and forth into and out of the zone include

details of operations both within and outside the AFZ.)

Size Composition

Average weights ofswordfish (processed weight of gross

catch/number of fish in gross catch) calculated from

Japanese longline logbook data for 1984-90 combined

show a trend of increasing size with increasing latitude

(Fig. 15). However, length frequency distribu tions compiled from data gathered by Australian observers on

the Japanese vessels (Fig. 16) do not show a clear trend

of increase in modal length with latitude. The observed

occurrence of swordfish >200 cm orbit-to-fork length9

9 Length from the eye to the caudal fork, using the posterior of the

boney surround of the eye as the forward reference point.
30 NOAA Technical Report NMFS 142

Figure 15

Latitudinal distribution of Japanese and AustraliaJapan joint-venture swordfish catches (% frequency by

10-degree band, 1980-90 combined) and of average

processed weight ofswordfish in the eastern Australian

Fishing Zone (from Australian Fishing Zone Information System logbooks).

!"';"""';';';';'d % 5wordfish by number - A_age Weight (kg)

70

60 at

50 E

'" 40 -;

• 30 f 20

80

40·505

10

-+---==----+ 0

10·205 20·305 30·405

50

o

r; 40

i

:>

30 ...

l.

-a 20

I/I) 10

(OFL), i.e. >320 cm bill-to-fork length,10 is consistent

with an increase in average weight with latitude. Fish

larger than 250 cm OFL (370 cm bill-to-fork length)

only occurred south of latitude 300S.

The observer data relate to many fewer fish than

those represented in logbook data, and they are from a

much-reduced time period. For each swordfish observed,

observers are requested to measure upperjaw (bill) -tofork length, lowerjaw-to-fork length (LJFL), orbit-tofork length, and, more recently, cleithrum-to-fork

length. Not all measurements were available for each

fish. One of the authors (M. Scott), who is an observer,

suggests that swordfish length measurements may have

been less frequently taken in northern waters (north of

200S) because the larger numbers of tunas and other

billfish requiring attention reduced the time available

to sample swordfish. This may have biased the data

toward larger fish if, as the logbook data suggest, small

fish are more abundant in lower latitudes.

The relationship between orbit-to-fork length and

lowerjaw-to-fork length, derived from 1,408 pairs of

observer measurements of swordfish between 70 cm

and 300 cm LJFL, was

OFL = 0.8971 x LJFL - 1.5944 (r2 = 0.9383).

Fishing Statistics in the Domestic Longline

Fishery _

Logbook data for the domestic fishery commenced in

the mid-1980's and is incomplete for early years. Current coverage is more comprehensive, but swordfish

catch is probably under-represented. Distribution of

total effort and swordfish catches are shown for 1990-

93 in Figure 17. The centers of activity are offsouthern

and central New South Wales, off southern Australia

west of Port Lincoln, southeast of Tasmania, and off

northeastern Queensland. Reported swordfish catches

are very low, mainly coming from the area of highest

effort and reflecting the incidental nature of the catch.

Comparison with areas of high Japanese catches suggests that expansion of domestic effort northwards off

eastern Australia in the region of 27°S could generate

improved swordfish catches.

species occurred in the region, but no specific surveys

or studies were directed at the species. Early Australian

research on tunas and billfishes was primarily concerned

with assessing their commercial potential. Most research

surveys were centered off the southeastern Australian

coast, where the Council for Scientific and Industrial

Research (later the Commonwealth Scientific and Industrial Research Organisation, CSIRO) carried out

experimental fishing around 1940 (e.g. Serventy, 1947).

Small catches of the now commercially exploited tunas

were taken with trolling gear. Subsequently, a commercial troll and later a bait-boat fishery for southern bluefin tuna were established, and there were attempts at

tuna longlining and purse seining. None of this activity

generated indications of potential for commercial swordfish operations.

Experimental Fishing

Research _

Surveys

An experimental fishing project which involved 25

longline sets using chemical light sticks was undertaken

off southeastern New South Wales between May 1989

and May 1991 (Williams 11). Each set consisted of 400 to

550 hooks (450 on average), with 6-10 (predominantly

For many years the strandings of isolated swordfish

around various parts of Australia indicated that the

10 The length from the anterior tip of the upperjaw (the "sword") to

the caudal fork.

II Williams, K. F. 1993. Target longlining for broadbill swordfish

using chemical light sticks. Report on FlRDC Project 88/

62. WW Fisheries Consultants, 167 Burraneer Bay Rd., Cronulla,

NSW 2230, Australia, 13 p.
_______ Caton et al.: Swordfish and the Fisheries for Tunas and Billfishes in the Australian Fishing Zone 31

Fishery Monitoring and Biological Sampling

6) hooks per basket and 11,110 hooks total in the 25

sets. For all sets, half of the hooks were set with a light

stick and the other half were set without, the gear

alternating every two baskets, so that the light-stick

sectors were separated by about 1 km of "dark" gear.

The total swordfish catch was 37 on light-stick hooks

and 1 on dark hooks. Over an extended period outside

the trials, involving sets totalling 49,620 hooks, the

vessel's catch rate was 0.68 swordfish/l ,000 hooks, while

during the trial period it was 3.42 swordfish/l,OOO hooks

overall and 6.66 swordfish/l,OOO light-stick hooks.

Swordfish catch rate off the east coast by Japanese

longliners, for sets when at least one swordfish was

caught, was 1.68 swordfish/l,OOO hooks. For comparison, using that cnterion, the project vessel returned

catch rates during the trials of 5.29 swordfish/l ,000

hooks overall and 10.32 swordfish/l,OOO light-stick

hooks.

Yellowfin tuna catch rates showed a statistically significant bias of 3:1 in numbers of fish caught on lightstick hooks versus dark hooks, but the overall yellowfin

catch rates during the trial sets were generally similar to

those during non-trial sets and to yellowfin catch rates

of other vessels. Williams!! suggests that this may perhaps indicate a degree of competition between lightstick and dark hooks.

Catches and catch rates of both species were better

during first-quarter, full, and last-quarter moon phases

than during the new moon.

000 0 0 0 0 0 0 0 0 0 0 c 0 N • G G 0 N • C G N N N N N

000 0 0 0 0 0 0 0 000

0 N • G G 0 N • G N N N N N

o 0

N

o 0

N

ao

80

20

5

50

200

150

25

20

i

E 40 ;:,

Z

i

E 100 ;:,

Z

i 15

E

:i 10

Figure 16

Length frequency distribution of swordfish in ID-degree

latitude bands (from top to bottom, 10-200S, 20-300 S,

30-400S, and 40-500S) in catches ofJapanese and Australia-Japan joint-venture longliners in the eastern Australian Fishing Zone, 1990-93. Circles indicate males, dots

indicate females, and bars indicate totals (including some

fish of unspecified sex). (Source: Observer Programme,

Australian Fisheries Management Authority.)

Eye-to-fork length (em)

o 0 000 0 0 000 0 0 0 0 0 N • G G 0 N _ _ •

_ G_ G_ N0 NN •N N N G G

12 Bureau of Rural Resources, Australia. 1989. A biological study

of east coast tunas and billfishes, with particular emphasis on

yellowfin tuna, Thunnus albaca1'es: review ofresults and recommendations for research. Bur. Rural Res. Working Pap. 11/89. Bur.

Rural Sci., P.O.B. Ell, Kingston, ACT 2604, Australia.

From 1986 to 1988 a study of the biology of tuna and

billfish resources of the eastern AFZ was carried out to

assemble information in support of their management

(Bureau ofRural Resources!2). The study concentrated

on yellowfin tuna. The main legacy of the project in

relation to swordfish has been the impetus it provided

for establishment of a domestic logbook collection.

Since establishment of the AFZ in 1979 there has

been a program involving placement of observers on

Australia-Japan joint-venture and licensed Japanese

longliners to monitor effort, catches by species, and

size composition of the catches. They also collect biological samples such as otoliths, gonads, tissue samples,

and stomachs on an opportunistic basis, and comment

on fishing equipment and techniques. Table 5 provides

details of the annual numbers of observers aboard foro 0 0 0 0 000 0 0 000 • eGO N • eGO N • G G N N N N N

o 0

N

10

40

50

i 30

E

:i 20
32 NOAA Technical Report NMFS 142

eign longlinersl3 between 1980 and 1994 and the monitoring and biological data gathered on swordfish. Tunas and marlins have generally received higher priority

than swordfish, and this is reflected by the absence of

collections of hard parts and gonads. While proces>ed

weight and one or more length measurements are usually obtained for each swordfish taken during observer

cruises, it is rarely convenient to weigh unprocessed

fish. Sex has been recorded for many of the swordfish,

but not gonad stage. Priority for observer collections of

hard parts has concentrated primarily on southern bluefin tuna, then on marlins, and then on other tunas.

There have been no Australian research programs focusing on age of swordfish, but it would be possible to

establish the routine collection of swordfish hard parts

during observer cruises.

During processing, small fish are usually trunkedl4

and large fish (>150 em) are filleted. Relationships

between OFL and processed weight, derived from observer data, are shown for fillets and trunks in Figure

18. The relationships are

Trunked weight (kg) = 2.0612 x 10-5 OFL2 8668 (em)

Filleted weight (kg) = 1.6151 x 1O-5 0FL2.

9301 (em).

Sex Ratio

14 Gilled and gutted, head removed anterior to cleithrum, and tail removed posterior to caudal keels.

- 40

- 40

- 20

- 20

0-

Observer data from foreign longline vessels (Table 5)

indicate an average female to male ratio in the swordfish catch of more than 3: 1. There are no data on

maturity stages. Observers have recorded very few male fish larger than

200 em OFL. Off eastern Australia,

observer data indicate little change

in sex ratio with size (Fig. 19). The

average was 2.7 females to 1 male.

Domination offemales in larger fish

is consistent with observations elsewhere, but it is unusual that they

dominate across all sizes. For example, Mejuto et al. (1994) analyzed

more than 65,000 swordfish sampled

from the Atlantic and Mediterranean. They indicated that for individuals measuring less than 115 em

LJFL, the sex ratio is around 50%,

whereas 90-100% of individuals

larger than 200 em are females. The

accuracy ofAustralian observers' classification of males and females has

not been checked. One of the authors (M. Scott), who is an observer,

suggested that sex ofsmall males may

commonly have been recorded as indeterminate or immature because of

uncertainty in identification.

Sex composition of catches by size

is shown by latitude for the eastern

AFZ (Fig. 16). Ratios calculated for

10-cm size groups show no indication of a trend in sex ratio with size

or with latitude south of 200S. The

ratio for the most northern band is

.0-

I

160

I

160

I

140

I

120

I

120

I

100

I

100

00

00

Hooks ('ODDs)

• 501 to 1600

• 401 to 500

• 301 to 400

201 to 300

101 to 200

1 to 100

No. of Swordfish

• 501 to 800

• 401 to 500

• 301 to 400

201 to 300

101 to 200

I to 1DO

Figure 17

Distribution of longline effort (top) and catch in number of swordfish

(bottom) for 1990-93 by Australian longliners in the AFZ (from Australian

Fishing Zone Information System logbooks).

13 Japanese and Australia-Japan joint-venture longliners were the

main foreign longliners operating in the AFZ. However, the observer program also monitored operations by 3 Australian-chartered Korean vessels in the early] 990's.
Caton et al.: Swordfish and the Fisheries for Tunas and Billfishes in the Australian Fishing Zone 33

highly variable because of the

small sample size. ... "0 I!.> '" I!.> The lack of data on maturity .D I!.> ...

'C "'" _ u

E o 0.. I!.> co r-- co stages prevents comment on size "" 0 E;:: ...... ..c:: ::l

'5 z '" 0 at maturity. '" u

-< c<") "" 0'> C'l 0 0 00 ... :? C'l 0'> 0 C'l 0

"" c c C:O 0'>

"" t!") C'l I!.> ..c:: I!.> ... E ... ..:.: 132 I!.> OIl", ... Parasites OIl c ... c - :E "" co o 00 t!") r-- c<") 0'>

'" I!.> '" ... ...... C'l r-- t!")0'> co t!") ... "0 C

"'" C ¢: ::l 0 00 co co C'l

'" 0 I!.> I!.>

There '" have been no systematic ... E ... u

'" I!.> I!.> E 8 ;:

studies of the parasitic fauna of I!.> .D ... 'C E '" ::l 0 ... ........, c<") ""- c<") c<") ...... t!") ...... I!.> ::l t.t: .:: ... ...... "" co 0'> 0

swordfish in Australian waters and ..c:: Z I!.> 0 I!.> 00 0'> co c<")

'" E 0.. ;:

only a few incidental records ex- l.i: 0

c -l

ist (SpearsI5 ). These taxa include .~

the giant trematode of the stom- -;; ... b ..c::

'" .2,1) ach, Hirudinella marina; cestodes, ::l I!.> co- ...... ...... c<") r-- 0'> -< ;: ...... "" o r-- t!")

Tentacularia coryphaenae, Callite- v ;: C I!.>

"" c<")

E I!.> "0 trarhynchus gracilis, and Bothrioceph- OIl":':

E JS ..c:: I!.>

alus manubriformis; a nematode, '" ;: ... "'" OIl c Maricostula incurva; a monoge- 0 0 I!.> "0 ... ... E Tristoma coccineum; and i=l-. I!.> c<") 0'>

"" "" nean, ... .D I!.> "" "" C'l 0'>

I!.> E ... 00 00 co copepods, Pennella iilosa and , ::l l.i: ::l '" I!.> Z Gloiopotes longicaudus. Worldwide, '" '" I!.>

.D E "0

numerous parasites have been re- O I!.>

..:.:

c r-- co co 00

corded from swordfish (>40) and I!.> ::l C'l c<") r-- 0 u

... ... C'l -

include taxa that have great po- ::l f-< 0

tential as biological tags for stock rJ) l.t') I!.>

11.>..;' -;; discrimination. :QO'> E t!") r-- 00 C'l

"" 0 00 t!")

'" ,I I!.> c<") c<") 0 co t!")

f-<~ x "" t!") c<")

I!.> 0'> rJ)

...... I!.>

Tagging ..c::' -;; c<") c<") c<") 00

"" t!") co

'" r-- C'l C'l c<")

t.=:

"0

... ..c:: Deguaral6 reports that the New 0 ... ;: I!.> t.=: '" South Wales Fisheries Research '" .D "'""0 t!") 0'> co co c<") ...... t!") - t!") 00 c E o ... ...... C'l C'l ...... C'l 0 C'l 0'> 0 0 c::.C'!.0'> c<")

Institute has managed the New "0 ::l ;: Z '" South Wales Game Fish Tagging u

I!.> ... '" "0 Program since 1973. The program v ..:.: v o t!") co c<")

"0 .D 0 , ""t!")t!") 0

encourages recreational fishers to u E 0 I!.> "". r-. c:. oq,

'" ::l ..c:: '" t!") C'l C'l co

tag and release fish. Competitions ... z",".D ~~~~

'" o 0 c<") co C'l C'l "0 • • C'i' •

have developed where points are "0

c ... ... awarded for tag and release of '" v v COC'lr---

'" .D e.- C'f~tC;~

... C'l 00 000'>

game fish, rather than their re- I!.> Eo..:.: r--' ",,' ",,' ",,' C ::l 0

tention. Australian releases of z .,g oooco""

bo C't~-co

tagged swordfish did c C'i C'i ~" ....: not com- '">.

mence until 1985. Since then c ... OIl I!.> "0'" (through June 1994) , reported 'v .D ... ... E "'" I!.> r-- t!") r- 2 ::l 0 , 0'> 00 r-- "" 0 C'l -.,roo "" c<") releases total 25. Most Australian c<") C'l ...... C'l 00 00 0'> ...... r- "" 00 '" "0 Z I!.> 00 r-- c::.t!") '" 0.'" tagged fish have been small juve- ... .D '" 0 E 0 . ;;l .D

'" ... '" ""..c

'" I!.>

>. i; .D. 1;;

15 Spears, P. '" E '0 .- C'l c<") "" C'J c<; .- - 00 0'> r-- c<") co c<") -: E 1994. Aust. Inst. Mar. Sci., "0 ::l 2 - co co 00 t!") '" 0 PMB No.3, Townsville Mail Centre, QLD ... Z u .D

,I!.> o '">- 4810, Australia. Personal commun. v- I!.> ... 0 C'l c<") - o .E "" t!") co r-- 00 0'> 0 C'l c<")

\6 Deguara, K. 1994. N.S.W. Fish. Res. '" "" '" 00 00 00 00 00 00 00 00 00 00 0'> 0'> 0'> 0'> 0'> .D .9 '"E 0 0'> 0'> 0'> 0'> 0'> 0'> 0'> 0'> 0'> 0'> 0'> 0'> 0'> 0'> 0'>

Inst., P.O. Box 21, Cronulla, NSW ...... ...... ...... ...... ......

2230, Australia. Personal commun.
34 NOAA Technical Report NMFS 142

Trunk Weight = 2.0612E-5 Eye-Fork Length" 2.8668

(383 fish, R"2 =0.81)

..

50

40

1:

CII

j 30

C 20 :s

..

I10

0

50 75 100 125 150 175

Trunk Weight

--- Fitted Curve

Eye-Fork Length

Fillet Weight = 1.6151 E-5 Eye-Fork Length" 2.9306

(1059 fish, R"2=0.85)

250

200

.r.

-

CII 150 j

- 100 .!!

ii: 50

0

75 100

.

... =-... ,

125

.-.

150 175 200 225 250 275

Fillet Weight

--- Fitted Curve

Eye-Fork Length

Figure 18

Relation of length (orbit-to-caudal-fork) to processed weight for trunked (top) and filleted (bottom) swordfish in the Australian Fishing Zone. Note different x and y scales. (Source: Observer

Programme, Australian Fisheries Management Authority.)

niles (4-15 kg). There has been one recovery reported,

of a fish released by an angler at Bermagui (375 km

south of Sydney) in southern New South Wales and

recovered by a domestic longliner 200 km to the north

atJervis Bay 3 months later at a size of 6 kg.

Potential for Expansion of Local

Operations _

Swordfish are regularly represented in longline catches

from the eastern AFZ. Domestic exploitation currently

remains incidental to a range of other fishing activities,

probably because of marketing restrIctions resulting

from mercury content limits. Recent review of the limits has eased restraints sufficiently to overcome some of

the wastage associated with unmarketable dead fish

and may provide scope to replace some of the Japanese

activity by increased domestic use of the species.

Experience in other regions suggest that swordfish are

a relatively slow growing, long-lived pelagic species with a

slower turnover rate and lower productivity than pelagics

such as skipjack and yellowfin tunas. In that regard they

are likely to be sensitive to exploitation, so that any

expanded domestic use should be monitored carefully,

as should exploitation in adjacent regions within the

range of distribution of locally-fished aggregations.
______ Caton et al.: Swordfish and the Fisheries for Tunas and Billfishes in the Australian Fishing Zone 35

Cresswell, G.

1987. The East Australia Current. CSIRO Mar. Lab. Inf.

Sheet 3, 4 p.

Edwards, R.].

1979. Tasman and Coral Sea ten year mean temperature and

salinity fields, 1967-1976. CSIRO Div. Fish. Oceanogr. Rep.

88,44 p.

Fishery Agency ofJapan .

1962-80. Annual report of effort and catch statistics by area

on Japanese tuna longline fishery. Far Seas Fish. Res. Lab.

[lnJapn. and Engl.]

Hydrographic Department of Great Britain.

1992. Australian Pilot, vol. 5.

Kailola, P.]., M.]. Williams, P. C. Stewart, R. E. Reichelt, A. McNee,

and C. Grieve.

1993. Australian fisheries resources. Bur. Res. Sci., Dep. Primary Indust. and Energy, and Fish. Res. Dev. Corp., Canberra, 422 p.

Mejuto,].,J. M. de la Serna, B. Garcia, M. Quintana, and E. Alot.

1994. Sex ratio at size of the swordfish (Xiphias gladius L.) in

the Atlantic and Mediterranean Sea: similarity between different spatial-temporal strata. Int. Comm. Conserv. Atl.

Tunas, ColI. Vol. Sci. Pap. 42(1) :322-327.

National Food Authority.

1992 and updates. Australian Food Standards Code. Australian

Gov. PubI. Sve., Canberra.

Nishikawa, Y., Honma, M., Ueyanagi, S., and Kikawa, S.

1985. Average distribution of larvae of oceanic species of

scombrid fishes, 1956-1981. Contrib. Far Seas Fish. Res.

Lab. 236: 1-99.

Roughley, T. C.

1951. Fish and fisheries of Australia. Angus and Robertson,

Sydney, 343 p.

Serventy, D. L.

1947. A report on commercial trolling tests in southeastern

Australia. J. Coune. Sci. Ind. Res. Ausl. 20:1-16.

Ward, P.]. (ed.).

1996. Japanese longlining in eastern Australian waters (1962-

1990). Bur. Res. Sci., Canberra.

Williams, D. McB., M. Cappo, and P. Speare.

1994. Coral Sea region billfish atlas. Seasonal distribution

and abundance around the Coral Sea rim: Solomon Islands,

Papua New Guinea, Vanuatu. AusLlnsL Mar. Sci., Townsville.

o 000 0

'" 0 ,.. C"f M .... ('If N N N

Figure 19

Ratio of female to male swordfish by length group in

the eastern Australian Fishing Zone; the average ratio

was 2.7: 1 (n = 1,366). There was no significant trend in

the ratio by length. (Source: Observer Programme,

Australian Fisheries Management Authority.)

o+--<--<--+--+---+---+---+----t----t---+---+---+---+---+---+---+----'

Literature Cited

5

$a

1l 3

E.! 2

'0

.21

iQ

a:

Eye-to-fork length (em)

til

Q)

4

Caton, A. E. (ed.).

1991. Review of aspects of southern bluefin tuna biology,

population and fisheries. In R. B. Deriso and W. H. Bayliff

(eds.), World meeting on stock assessment of bluefin tunas:

strengths and weaknesses. Inter-Am. Trop. Tuna Comm.

Spec. Rep. 7: 181-357.

Caton, A. E., and P.]. Ward.

1996a. Access arrangements for Japanese longliners in eastern Australian waters. In P. ]. Ward (ed.), Japanese

longlining in eastern Australian waters 1962-1990, p. 7-

30. Bur. Res. Sci., Canberra.

1996b. Arrangements on fisheries between the governments

of Australia and Japan on tuna longlining. Annex to P.].

Ward (ed.), Japanese longlining in eastern Australian waters 1962-1990. Bur. Res. Sci., Canberra.

The California Harpoon Fishery for Swordfish, Xiphias gladius

ATILIO L. COANJR.

Southwest Fisheries Science Center

National Marine Fisheries Service, NOAA

8604 LaJolla Shores Drive

LaJolla, California 92038

MARIJA VOJKOVICH

Marine Resources Division

California Department ofFish and Game

530 E. Montecito Street

Santa Barbara, California 93103

DOUG PRESCOTT

Southwest Fisheries Science Center

National Mmine Fisheries Service, NOAA

8604 Lafolla Shores Drive

LaJolla, California 92038

ABSTRACT

We review and analyze fishery data collected from the California harpoon fishery for

swordfish, which began in the early 1900's. Landings data for 1969-93, logbook data for

1974-93, and size composition data for swordfish landed in 1981-93 are analyzed. Swordfish

landings peaked in 1978 (1,172,000 kg) and decreased to a record low (ll,OOO kg) in 1991.

Landings were less than 200,000 kg in most years. Swordfish landed averaged 149 cm in

length (c1eithrum to fork) or 85 kg dressed weight in 1981-93.

The harpoon fishing season, typically May-December, usually concentrates in the

Southern California Bight off San Diego early in the season and then shifts as far north as

Oregon. Swordfish are usually sighted while basking at the surface in water of 12°-26°C.

Fishing effort peaked in 1979 (12,700 days fished), decreased in 1991 (700 days), and

rebounded slightly in 1993. Catch per day fished fluctuated between 0.14 and 0.93 during

1974-93, and peaked in 1974, 1978, 1985, and 1993, usually 1-2 yr after an El Nino event.

Introduction

In North America, harpoon fishing dates to the use of

harpoons by Indians to catch swordfish, Xiphias gladius,

off the California coast almost 3,000 yr ago (Kronman,

1988). Their vessels were 6.1-m (20-ft) driftwood canoes, and their gear consisted of a 1.8-m (6-ft) foreshaft

tipped with a carved wooden harpoon which bore a

stone point on one end and a curved barb of deer bone

behind (Kronman, 1988).

California's modern-day harpoon fishery for swordfish developed in the early 1900's. The fishery was modeled after the East Coast harpoon fishery, which began

almost 70 yr earlier. Vessels were small sail-powered

sloops or schooners. The harpoon gear was 4.6-5.5 m

(15-18 ft) in length, fashioned from hickory and

tipped-with a bronze dart (Kronman, 1988). The bronze

dart was backed by a tapered socket and a 0.6-m (2-ft)

metal shank attached to the end of a wooden handle. The

design of harpoon gear has remained unchanged except

for minor modifications in the metal used in the shank.

Harpoon fishing continued as the only commercial

fishery that harvested swordfish within 200 mi of the

California coast until 1980, when drift gill net fishing

started in waters off California. The competition from

the more-efficient drift gill nets proved too great for

37
38 NOAA Technical Report NMFS 142 _

the harpoon fishery, and many vessels converted to

drift gill net gear or obtained permits to use both types

of gear. Today, harpoon and drift gill net are the only

commercial fishing gears operating on swordfish in the

area, and only a handful of vessels continue to participate in the harpoon fishery.

This paper reviews and analyzes data collected from

the California harpoon fishery. Landings data are reviewed for 1969-93, logbook data for 1974-93, and size

composition ofswordfish catches for 1981-93.

Data and Methods _

Landings, logbook, and size compositIOn data for

California's harpoon fishery have historically been collected by California Department of Fish and Game

(CDFG) biologists at landing ports as vessels returned

from fishing trips. Locations of landings, logbook

catches, and measured fish were recorded by CDFG

blocks, which are usually lO-minute quadrangles. These

were converted to latitude and longitude and summed

to I-degree quadrangles for the purposes of this report.

Landings

Swordfish landings data have been collected since the

early 1900's (Bedford and Hagerman, 1983). This study

includes landings data for 1969-93, to match the existing logbook and size-composition data sets. This period

includes all of the 1970's, a period of relatively high

catches and increased regulations that significantly impacted the harpoon fishery.

The landings data were compiled from CDFG landing receipts. Commercial fish buyers are required to fill

out a landing receipt for each landing purchased in

California (Hanan et aI., 1993) and submit these receipts to CDFG. Therefore, coverage is very close to

100% for all landings sold commercially. Landings kept

for private consumption are not recorded in the landing totals. A small number of swordfish landings may

also escape the landing receipt system. The landing

receipts contain information on species landed, weight

landed, price paid, and fishing gear used. Other information, such as area of catch, may be included but in

many circumstances is left blank.

Data for 1969-79 include landings reported as catches

by harpoon, spear, and unknown fishing gear (Table

1). Data from 1980 to 1993 include only those landings

specifically designated as caught with harpoon or spear

gear. Landings with unknown fishing gear were included

before 1980 because harpoon was the prevalent gear used

during that time. After 1979, drift gill net gear accounted

for a significant number of swordfish landings, and unknown gear could no longer be assumed to be harpoon.

Landings other than sharks were not included as

harpoon incidental catches (Table 1). Albacore,

Thunnus alalunga; yellowfin tuna, Thunnus albacares;

mackerel, Scombridae; rockfishes, Sebastes spp.; and

other species were often recorded as harpoon landings.

These entries were considered errors in gear-type coding; the catches were most likely made with troll fishing

gear while searching for swordfish.

Logbooks

CDFG implemented a mandatory permit and logbook

system in 1974 (Bedford and Hagerman, 1983). The

original logbook provided space for recording information about a single fishing day on each line. Requested

information included name ofskipper and boat; swordfish permit number and CDFG boat number; date

(month and day) of each entry; CDFG block number;

whether an aircraft was used; whether the fish was sighted

underwater, finning, orjumping; whether the fish was

harpooned; whether it was landed; and estimated

dressed weight in pounds. Space was also included for

any other pertinent remarks.

The original logbook was later modified so that each

page represen ted a single day of fishing (Fig. 1). Fields

were added to record starting and ending times offishing,

time of each entry on the form, sea-surface temperature,

whether sighted fish were pursued, other CDFG blocks

searched, and weather conditions, sea state, and sea color.

Size Composition

Landings of swordfish have been sampled for length

since 1981 under a program originally designed to monitor gill net landings (Odemar 1). Samples were taken by

CDFG biologists as fish were unloaded at various fish

markets throughout the state (Hanan et aI., 1993). No

formal constraints on sample size were established, and

samplers selected as many fish and vessels to sample as

time permitted. Since swordfish were always landed

gutted, headed, and with the dorsal fins and the posterior portions ofthe tail fins removed, samplers recorded

the cleithrum length (CL), the straight length from the

anterior margin of the cleithrum to the fork of the tail.

Lengths were recorded to the nearest millimeter. The

samplers, whenever possible, recorded information on

the weight in pounds of each fish measured, date measured, boat name and number, port and market of

1 Odemar, M. 1982. 1nventol1' of California marine fisheries port

sampling activities. Calif. Dep. Fish Game internal report, 157

p. CDFG, 1416 Ninth St., Sacrament, CA 95814.
Coan et aI.: California Harpoon Fishery for Swordfish 39

Table 1

California harpoon fishery landings (kg). Landings for 1969 to 1979 include landings reponed as unknown fishing geaL

Vnid. indicates sharks not identified to species.

Sharks

Year Swordfish Thresher Mako Blue Hammerhead Soupfin White nid.

1969 459,748 0 0 0 0 0 0 5,230

1970 421,933 0 53 0 0 0 0 0

1971 68,215 0 0 0 0 0 0 0

1972 118,223 0 0 0 0 0 0 0

1973 274,779 0 0 0 0 0 0 382

1974 279,649 0 0 0 0 0 0 1,974

1975 383,658 44 0 0 0 0 0 124

1976 28,936 0 17 0 0 0 0 83

1977 219,055 1,024 192 0 0 0 0 2,839

1978 1,171,655 951 565 0 27 0 0 2,275

1979 226,625 II ,857 311 348 0 0 0 4,936

1980 389,722 2,915 1,486 0 0 0 0 4,336

1981 178,660 0 157 15 69 161 0 1,184

1982 107,580 122 621 0 0 0 0 297

1983 39,796 0 82 0 93 0 0 187

1984 72,992 22 269 0 0 28 0 23R

1985 145,154 0 203 0 55 0 0 0

1986 162,634 55 549 0 43 289 61 69

1987 144,954 0 1,506 0 0 0 227 39,009

1988 123,757 12 1,121 0 61 0 0 22

1989 37,197 0 404 0 0 0 0 0

1990 34,726 33 892 0 70 0 0 0

1991 1l,362 29 540 0 0 0 0 0

1992 44,285 30 1,991 0 0 0 0 0

1993 116,058 0 403 0 0 0 0 0

landing, CDFG block number, and landing weights

(Childers and Halk02). No sampling bias by vessel,

market, area, or month was detected.

Vessels, Gear, and Fishing Strategies _

Vessels that participate in the harpoon fishery are quite

variable but very distinctive. They are usually 6-26 m

(20-87 ft) in length (Holt3), with hold capacities up to

100 metric tons (110 short tons) and main engines of

25-1,300 horsepower. The vessels are equipped with

high masts of 5-12 m (18-40 ft; Kronman, 1988) and a

plank extending 6-9 m (20-30 ft) beyond the bow. The

2 Childers, J., and L. Halko. 1994. Length-frequency database description: California Department of Fish and Game gill net market

samples. .S. Dep. Commer., NOAA, Nat!. Mar. Fish. Serv., Southwest Fish. Sci. Center Admin. Rep. LJ-94-01, 46 p.

3 Holt, S. 1978. Economic analysis of the swordfish harpoon

fishery. Pacific billfish management plan, 47 p. Prepared under

contract no. 78-20 for PFMC. Available from Pac. Fish. Manage.

Coune., 45 S.E. 82nd Dr., Ste. 100, Gladstone, OR 97027-2522.

crow's nest at the top of the mast is usually equipped

with controls to steer the vessel during the pursuit of

swordfish. The planks, while originally made of wood,

are now aluminum or steel conduit and can be raised

during travel and lowered when in pursuit. At the end

of the plank is a pulpit consisting of a metal stand and

railing against which the harpooner can lean.

Harpoon fishing gear has changed little since the

early 1900's. Current harpoon gear consists of a handle

made of metal or wood and approximately 3-5 m long

(10-16 ft), attached to a metal shank approximately 0.6

m long (2 ft), and tipped with a lO-cm (4-inch) bronze

or iron dart. One end of a mainline, 15-46 m (50-150

ft) in length, is attached to the middle of the dart, and

floats and a marker flag are attached to the other end.

Harpoon vessel fishing trips usually are from 3 to 10

days in length and vary according to fishing success,

fish carrying capacity, and preservation capability. Fishing starts with the search. Fish are sighted either finning

orjumping at the surface or swimmingjust beneath the

surface. Sightings are made by the vessel's crew using

binoculars or by assisting aircraft. Since sightings are of

fish on or near the surface, good weather conditions
40 NOAA Technical Report NMFS 142

Time Fishing Started This Day Aircraft Used to Scout Swordfish

lime Fishing Ended This Day This Day: Yes _ No_

1935 Swordfish may be taken with hook-and-line and

harpoon gear.

1971 U.S. Food and Drug Administration (FDA) begins to enforce guideline of 0.5 ppm of mercury

in swordfish.

1973 A permit is required to take swordfish commercially. California Legislature gives regulative authority over the swordfish fishery to the State

Fish and Game Commission (F&GC).

1974 F&GC adopts commercial swordfish regulations

including specific permit qualifications, a logbook requirement, and the notification that airplanes cannot be used to assist a vessel in capturing swordfish after 28 June 1976.

1976 F&GC allows airplane use in locating swordfish,

but not within an 8-km (5-mi) radius of a vessel

operated by a swordfish permittee.

1977 F&GC extends the airplane operating radius to

beyond 16 km (10 mi) of a vessel operated by a

swordfish permittee.

1978 FDA changes limit of total mercury in swordfish

to 1.0 ppm.

Regulations

Modern-day harpoon vessels have added new technology and fishing strategies as they became available,

to increase fishing efficiency. Some vessels employ stateof-the-art navigation equipment, sea-surface-temperature recorders, and sounders to help locate fish. Some

have also been known to use satellite imagery to identify fishing areas. Harpoon vessel operators have also

obtained multiple permits that allow them to fish both

gill net and harpoon fishing gears, and have also been

known to troll jigs between sightings to increase catches

ofswordfish and other commercial species of fish.

Over time, several regulations have been imposed that

directly or indirectly affect the California harpoon fishery (California Fish and Game Code and Title 14 Regulations; Squire and Muhlia-Mel04; Sakagawa5 ). The major regulations are:

No.__

Year__

Month __

Day__

Check One

Fish I

Sea Under- Fish Fish Fish Fish Fish Estimated

Time Block No. Temp. water Finning Jumping Pursued Harpooned Landed Weight

DAILY SWORDFISH LOG

Name of Skipper SW Permit No. _

Name of Boal Boat F&G No.

and calm seas favor fishing. Swordfish are found in seasurface temperatures of 12°-26°C (64°-72°F), and vessels usually start their search in areas where temperatures are within this range.

After a fish is sighted, the vessel's plank is maneuvered over the fish and the striker harpoons the fish.

The handle is pulled free from the dart, the mainline,

marker flag, and floats are thrown overboard, and the

fish is left to tire itself. The vessel is then able to pursue

other fish. After the fish has tired (approximately 2 hr)

the vessel returns to retrieve it. The fish is dressed

(headed, gutted, and fins removed) and stored in ice

for transport to shore. During the early years of the

harpoon fishery, the livers were sometimes kept for sale

because oftheirvitamin A and D content (CDFG, 1949);

this practice is no longer followed as other sources of

vitamin A and D have been developed.

The use of airplanes to assist in the sighting and

harpooning of swordfish started in the early 1970's.

Airplanes both spot the fish and guide the vessels to the

fish. Because conflicts arose between commercial fishermen who used airplanes and sportsmen and other

commercial fishermen who did not use airplanes, a

series of regulations was enacted to limit their use.

8'

w 1---+------1--+--+--+---+---+---+---+------1

~I--+-----1--+-+--+---+---+---+--+-----1

~I--+-----1--+-+--+---+---+---+--+---1

'E1---+------II---+-+--+---+---+---+--+-----1

001---+------11---+-+--+---+---+---+--+-----1

Figure 1

A page from the current California harpoon fishery

logbook.

Weather _

Sea 8IaI8 _

Sea Color

Remarks _

4 Squire, J. L, and A. F. Muhlia-Melo. 1993. A review of striped

marlin (Tetrapturus audax) , swordfish (Xiphias gladius) , and sailfish

(lstiophorus platypterus) fisheries and resource management by

Mexico and the United States in the northeast Pacific Ocean. U.S.

Dep. Commer., NOAA, Nat!. Mar. Fish. Serv., Southwest Fisheries

Science Center Admin. Rep. LJ-93-06, 44 p. (in Eng!. and Span.).

SWFSC, NMFS, NOAA, P.O. Box 271, La Jolla, CA 92038-0271.

'> Sakagawa, G. T. 1994. Supply of swordfish, Xiphias gladius, for

the United States consumer market. International Symposium

on Pacific Swordfish, 11-14 December 1994, Ensenada,

Mexico. Available from G. T. Sakagawa, Southwest Fisheries Science Center, NMFS. NOAA, P.O. Box 271, La Jolla, CA 92038-

0271.
_______________________ Coan et al.: California Harpoon Fishery for Swordfish 41

1980 F&GC prohibits swordfish harpoon permittees

from possessing a gill net on board except for set

gill nets with mesh sizes of 20 cm (8") or less if

they declare on their swordfish permit that they

intend to use such gear.

1984 F&GC allows unlimited airplane use to directly

assist a permittee in the taking of any species of

fish while operating under a swordfish harpoon

permit. FDA changes its regulation to limit methyl mercury content in swordfish to 1.0 ppm.

1985 F&GC allows swordfish harpoon permittees to

have set gill nets of any mesh size aboard if they

declare on their swordfish harpoon permit application that they intend to use such gear.

1987 F&GC allows swordfish harpoon permittees to

have drift gill nets aboard in addition to set gill

nets, if they also possess a valid permit to use

drift gill nets.

Numbers of Vessels and Landings

The number of California harpoon vessels landing

swordfish increased from 63 in 1969, to 309 in 1978

(Fig. 2), decreased to 32 in 1991, and then increased

slightly to 43 in 1993. A sharp decline in 1971 in the

number of vessels participating in the fishery was probably due to the collapse of the swordfish market in that

year as a result of the mercury scare-publicity about

the high levels of mercury in swordfish and health

problems from ingestion of mercury, which discouraged consumers from buying swordfish-and the FDA's

subsequent strict enforcement of the 0.5-ppm mercury

limit. The decline in 1976 was probably due to the ban

on aircraft use, and the general decline since 1980 has

been primarily due to increased competition from drift

gill net operations.

The number of vessels landing swordfish is indicative

of the harpoon fishery fleet size. CPUE during this time

was relatively stable at 0.1-0.9 fish per day, and the

number of harpoon permits showed a trend similar to

that in number of vessels landing swordfish: 164 permits in 1984, decreasing to 43 in 1993.

Harpoon fishery landings in California have been

recorded since 1918 (CDFG, 1949). Records for 1918-

37 combined striped marlin, Tetrapturus audax, and

swordfish landings, since no requirements were in place

to separate the two species. Commercial landings of

striped marlin in California have been prohibited since

the late 1930's.

Records for 1938-68 con tained swordfish landings

only and are assumed to be from harpoon gear, although small amounts of catch from other fishing gears

are probably included. Landings averaged approximately 330,000 kg in 1938-48 and declined to approxi300

260 (f)

--'

220 (f)

w

180

o

ffi 140 en

100

60

1970 72 74 76 78 80 82 84 86 88 90 92

YEAR

Figure 2

Number of California harpoon fishing vessels landing

swordfish during 1969-93.

mately 110,000 kg in 1949-68. Landings increased dramatically in 1968 to 460,000 kg, and reached a record

high of 1,172,000 kg in 1978 (Table 1). After 1978,

landings decreased to a record low of 11,000 kg in 1991

and rebounded slightly to 116,000 kg in 1993. In general, landings seem to be lower during El Nino events

(1972-73,1976-77,1982-83,1991-92) and peak 1-2 yr

thereafter. The same regulations that affected vessel

participation in the harpoon fishery, mentioned above,

also affected annual landings.

The most prevalent incidental landings ofsharks identified to species were thresher, Alopias vulpinus, and

shortfin mako, Isurus oxyrinchus (Table 1). The most

thresher sharks landed in a year was 12,000 kg in 1979;

the most shortfin mako sharks landed was approximately 1,500 kg in 1980 and 1987. Other sharks landed

by harpoon gear include blue, Prionace glauca; hammerhead, Sphyma spp.; soupfin, Galeorhinus zyopterus; and

white, Carcharodon carcharias. The most reported landings of unidentified sharks occurred in 1987 when 39,000

kg were landed.

Logbook Records

Coverage Rates

Annual logbook coverage rates were calculated as the

total annual weight of swordfish reported in logbooks,

divided by yearly swordfish landing weights as given in

Table 1 (Fig. 3). Total annual swordfish weight reported in logbooks was calculated as the total number

of fish reported in logbooks, multiplied by the average

weight (85 kg) of fish recorded in market sampling of

harpoon catches during 1981-93. Annual average
• FINNING

• JUMPING

• UNDERWATER

42 NOAA Technical Report NMFS 142

160

t='

i:5 140 ()

IT:

w 120

100 4:

IT:

w 80 >

o

() 60

o

40

C)

9 20

1975 77 79 81 83 85 87 89 91 93

YEAR

Figure 3

California harpoon fishery logbook coverage rates (logbook catch in weight divided by landed weight) for

1974-93.

weights were not used because of the low sample sizes

in some years. Logbook-estimated weights were not

used because they were missing for as many as 100

landings per yr, combined processed and total weights,

which were difficult to separate, and produced estimates significantly higher than those produced by using average weights from port sampling.

Coverage rates were greater than 120% in 1976, 1977,

and 1984-86; between 80% and 120% in 1979-83 and

1987-92; and less than 50% in 1978 (Fig. 3). Since the

logbook program was mandatory during this time, vessel coverage rates should have been 100%. Coverage

rates not equal to 100% can be attributed to several

factors: 1) use of an average weight to convert numbers

of fish to catch in weight of fish may overestimate or

underestimate actual logbook catches; 2) landings underestimated due to some being classified as unknown

gear; 3) fish kept for personal consumption; and 4)

confusion at markets between gill net landings and

harpoon landings, especially when a permittee had both

drift gill net and harpoon permits. The extremely low

coverage rate in 1978 is difficult to explain and may be

due to a deliberate misreporting of drift gill net catches

as harpoon landings, in an effort to circumvent the prohibition of drift gill net swordfish landings (Bedford, 1987).

Data on Sightings

Swordfish initially sighted by harpoon fishery vessels or

spotter airplanes were reported in logbooks as either

finning at the surface, swimmingjust below the surface,

or jumping. An average of 74% of fish sighted during

10 ,....--------------------,

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1) 3

IT:

2 ::;:

:::J

Z

1975 77 79 81 83 85 87 89 91 93

YEAR

Figure 4

Number ofswordfish sighted at the sea surface finning,

swimming, jumping, or swimming just under the surface (underwater) by California harpoon fishery vessels and reponed in logbooks for 1974-93.

1974-93 were finning at the surface (Fig. 4). The next

most prevalent type of sighting was of fish just under

the surface (19%), except in 1979-82, when jumping

fish were sighted more often (6%). Fish were sighted

finning in especially dominant numbers compared to

fish seen underwater and jumping during 1976-84,

when spotter airplanes were banned. Before 1976 and

in 1984-88, the numbers of finning and underwater

sightings were comparable, and in 1989-92 were virtually the same, probably due to the increased ability to

spot fish just under the surface from airplanes.

Harpoon vessel captains recorded sightings ofswordfish in three types of water color, blue/green, blue, and

green. Swordfish were found most often in blue/green

water in 1974-79, and in blue water in 1980-87 (Fig. 5).

During 1988-93, swordfish were found with the same

frequency in water of all three colors. Blue/green water

is usually associated with high primary production; the

records for this color water seem to parallel increased

swordfish catches and abundance levels of other species of fish in the Southern California Bight during

1974-79 (Squire, 1993).

Swordfish caught in the California harpoon fishery

were found in surface water temperatures of 12°-26°C

(54°-79°F; Fig. 6). Over 50% of the fish were found in

temperatures of 19°-22°C (66°-71°F). In El Nino years,

the range of water temperatures in which the majority

of swordfish are sighted narrows and favors warmer

temperatures of 20°-22°C (68°-71°F). This was very

evident during the strong El Nino of 1982-83 (Fig. 6).

In non-El Nino years, swordfish are sighted in a broader

range of water temperatures, and more are caught in
_______________________ Coan et al.: California Harpoon Fishery for Swordfish 43

54 59 64 69 74 79

SEA SURFACE TEMPERATURE (OF)

1975 77 79 81 83 85 87 89 91 93

YEAR

with temperature regimes during non-El Nino years, when

cooler water mixes throughout the area.

6 Miller, F. 1994. Inter-American Tropical Tuna Comm., 8604 La

Jolla Shores Dr., La Jolla, CA 92037-1508. Pers. commun.

7

U)

"0

c

I1l 6 en

OJ

0 • GREEN ..c::

C 5 • BLUE/GREEN

I

(f) • BLUE u::: 4 0

a:

0

3 (f)

LL

0 2 a:

w

CD

::2:

::J

Z

Figure 5

Number of swordfish sighted in blue/green, green, and blue

water by California harpoon fishery vessels and reported in

logbooks for 1974-93.

20

18

(f) 16 <.9 • 82-83 EL NINO z

f= 14 I • NORMAL

<.9

(j) 12

LL

0 10

IZ

w 8

u

a: 6 ill

a.. 4

2

0

Figure 6

Proportion of swordfish sightings made at different sea-surface water temperatures (OF) from California harpoon fishery

vessels and reported in logbooks for 1974-93. Normal includes all non-EI Nino years. 82-83 EI Nino indicates the effect

of a strong EI Nino on swordfish sightings.

Success and Effort

colder water. This is consistent with oceanographic conditions in the Southern California

Bight, where the California Current extends farther south during non-El Nino years (Miller6).

This extension of the California Current would

result in more mixing of colder water in the area

and, therefore, more days when swordfish would

be sighted in cooler water.

When a swordfish is pursued by a harpoon fishing vessel, the fish often escapes being harpooned

or, if harpooned, may never be landed. In order

to measure the success of each swordfish encounter, vessel captains recorded, for each fish,

whether it was pursued, subsequently harpooned,

and landed. Logbook records show that when

swordfish were pursued, on average 74% were

actually harpooned (Fig. 7). Of those that were

harpooned, 91 % were actually landed. The best

ratios of pursuit to landing success occurred in

1986 and 1989-92 when more than 75% of pursued fish were actually landed.

Annual harpoon fishing effort, as reported in

logbooks, increased from 3,500 days fished in

1976 to a record high of almost 13,000 days in

1979, then declined to a low of approximately

700 days in 1991 (Fig. 8). Airplane-assisted fishing effort accounted for less than 30% of the

total effort during 1974-79, and dropped to 0%

in 1980 and 1983. Between 1984 and 1986, airplane-assisted effort increased rapidly to a peak

of over 1,600 days fished (39%) in 1986, probably in response to the restoration of unlimited

airplane use in 1984. The numbers of assisted

and unassisted days fished since 1989 were approximately the same.

Annually, harpoon fishing effort usually

peaked in August, with high levels of effort extending into the last quarter of the year (Fig. 9).

In El Nino years, fishing effort peaked and concentrated in July and August, with less effort in

the last quarter. Over 70% of fishing effort was

expended between July and October and concentrated in the Southern California Bight during 1974-93 (Fig. 10). Fishing effort usually

started in waters off San Diego early in the season,

and progressed to waters sometimes as far north as

Oregon later in the season. During El Nino years, fishing

effort tended to compress spatially and concentrate in the

Southern California Bight. In non-El Nino years, fishing

effort extended to areas off Oregon, but with relatively

little success. This extension of the fishery is consistent
44 NOAA Technical Report NMFS 142

14

Ul

"0

c

Cll 12 (/)

:::l

0 • HARPOONED .s= 10 !::: • LANDED

I

(j) • PURSUED u::: 8 0

a:

0 6 :s:

(j)

LL

0 4 a:

w

m 2 ::J

Z

0

1975 77 79 81 83 85 87 89 91 93

YEAR

Figure 7

Number of swordfish pursued, harpooned, and landed by

California harpoon fishery vessels, as reported in logbooks for

1974-93.

12

Ul 10 • AIRPLANE "0

c • NO AIRPLANE Cll

(/)

:::l 8 • TOTAL 0

.s=

!:::

0

w 6 I

(j)

u::: 4 (j)

0 2

0

1975 77 79 81 83 85 87 89 91 93

YEAR

Figure 8

Total fishing effort in number of days fished, and fishing effort

with and without the use of airplanes by California harpoon

fishery vessels, as reported in logbooks for 1974-93.

Catches and CPUE

Trends in annual catch (in number offish, as recorded

in logbooks) closely followed trends in annual landings, with low catches of approximately 500 fish in 1976

and 1983 and a record low of 120 fish in 1991. The

highest recorded catch (nearly 7,000 fish) was in 1978.

Recorded fishery catches, like effort, were also highest

in the Southern California Bight, especially in waters

between the California coast and San Clemente and

Santa Catalina Islands (Fig. 11). Catches tended to

concen trate in the Southern California Bight in El Nino

years and extend farther north during non-El Nino years.

Unlike fishing effort, which generally peaked in August,

swordfish catches usually peaked in October, with over

70% of the catch made between July and October (Fig.
_______________________ Coan et al.: California Harpoon Fishery for Swordfish 45

35

0- 82-83 EL NINO

U.J 30 I

(fJ

u:: 25 (fJ

e. 20 fa:

0

LL 15 LL

U.J

fz 10 U.J

u

a:

U.J 5 CL

J F M A M J J A SON D

MONTH

Figure 9

Proportion of fishing effort by month by California

harpoon fishery vessels and reported in logbooks for

1974-93. Normal indicates fishing effort in non-El NiilO

years, and 82-83 EI Nino indicates fishing effort during

the strong El Nino of 1982-83.

12). During EI Nino years, swordfish catches tended to

peak earlier in the year, inJuly and August, with less catch

in the last quarter ofthe year.

Catch-per-unit effort (CPUE, in number of fish per

day fished) was calculated from logbook statistics for

days with airplane assistance, days without airplane assistance, and for total days (Fig. 13). Airplane-assisted

CPUE was higher than airplane-unassisted CPUE except in 1978-83, a period when airplane-assisted effort

was less than 10 days per yr. Combined CPUE fluctuated between 0.14 and 0.93 swordfish per day fished.

The trends in all estimates of CPUE were very similar:

decreasing from 1978 to 1983, increasing to a peak in

1985, decreasing again until 1991, and then increasing

in 1993. CPUE tended to increase 1-2 yr after an EI

NiilO event. In comparison, drift gill net catch rates, in

the same areas, ranged from 1 to 3 fish per day.

Size Composition _

Sampling coverage (number of fish sampled, divided

by the number of fish recorded in logbooks) for size

composition of swordfish catches from the harpoon

fishery sold at fish markets ranged between 0.2% and

7.0% during 1981-93 (Fig. 14). The low sampling coverage was probably due to the higher priority given to

sampling gill-net-caught fish, combined with a low overall monitoring effort which did not adequately cover

the various ports where harpoon vessels landed. The

largest number of fish sampled was in 1984 (about 80

fish) and the smallest in 1990 (only one fish). Because

of the low coverage rates, estimates of length distributions of swordfish by month and by latitudinal band

could not be made. However, because of the close

temporal and spatial proximity of this fishery to its drift

gilI net counterpart, the tendency seen in the drift gilI net

fishery for larger fish to be caught farther north and later

in the season (Hanan et a\., 1993) probably also applies to

the harpoon fishery.

Average CL was calculated for each year and shows a

slight increasing trend, from 140 cm in 1981 to approximately 183 cm in 1990 (Fig. 14). However, because of the small number of individuals sampled, the

estimates are highly suspect during 1989-92. Fish

sampled from harpoon fishery catches during 1981-93

ranged from approximately 62 to 217 cm CL (Fig. 15),

with an average of about 149 cm. In comparison, fish

caught in the California gill net fishery, as expected,

were slightly smaller, averaging only 141 cm.

Discussion

The data collected from the California harpoon fishery

are valuable for monitoring the fishery. While the data

are generally of high quality, some problems can be

identified and improvements made.

Landings data can be affected by various problems

associated with reporting. Reported landings of fish

that would be impossible to catch with a harpoon indicate a problem in the reporting of gear type used to

catch those fish and possibly also swordfish. Also, since

some vessels may have both harpoon and gill net per-
46 NOAA Technical Report NMFS 142 _

30

50 50

1982 1983

[SS 1 - 100 [SS 1 - 100

101 - 500 101 - 500

40 .. 501 - 1,000 40 .. 501 -1,000

• 1,001 - 6,500 • 1,001 - 6,500

30

30 30

20 20

130 120 110 130 120 110W

50 50

1984 1985

[SS 1 - 100 [SS 1 - 100

101 - 500 101 - 500

40 .. 501 - 1,000 40 .. 501 - 1,000

• 1,001 - 6,500 • 1,001 - 6,500

120 110W

20 1...-I-..............l....l.....L...I....I.................l....l.....L...I....I.................l....l..... 20 '--'-..............l....l....l..-L.....l.....I.....l......l....l....l..-L....L....L...L.....l....I.....

130 120 11 0 130

Figure 10

Typical spatial distribution offishing effort by California harpoon fishery vessels reported in logbooks during

normal fishing years, 1984 and 1985, and during a strong El Nino, 1982 and 1983. Spatial distribution of

fishing effort for other years in which logbooks were collected was very similar.

mits onboard during a fishing trip, there will probably

be problems in reporting ofthe appropriate gear. These

problems could be especially frequent during periods

when drift gill net swordfish landings were not allowed

to exceed shark landings. Many of these problems could

be alleviated and the quality of the landing statistics

improved if buyers more carefully verified gear types

used to capture purchased fish.

Rates of logbook data coverage are very high and

therefore can be used to monitor catch rates, seasonal
____________________ Coan et al.: California Harpoon Fishery for Swordfish 47

30

30

20

130 120 110 130 120 110W

50 50

1984 1985

1 - 100 1 - 100

101 - 500 101 - 500

Iiiiiiil 501 - 1,000 40

Iiiiiiil 501 - 1,000 40 • 1,001 - 2,500 • 1,001 - 2,500

30

50 50

1982 1983

1 - 100 1 - 100

101 - 500 101 - 500

Iiiiiiil 501 - 1,000 40

Iiiiiiil 501 - 1,000

40 • 1,001 - 2,500 • 1,001 - 2,500

30

130 120 110 130 120 110 W

Figure 11

Typical spatial distribution of catches by California harpoon fishery vessels reported in logbooks during

normal fishing years 1984 and 1985 and during a strong El NiilO, 1982 and 1983. Spatial distribution of

catches for other years in which logbooks were collected was very similar.

and spatial positioning of the harpoon fishery, and

some environmental conditions that affect fishing success. Some confusion was noted in the reporting of

weights associated with landed fish. While the vessel

captains were instructed to enter their best estimates of

dressed weight for each landed fish, many times these

were unreasonably high and probably actually represented estimates of whole fish weight. A possible solution to this type of confusion would be to distribute an

instruction section with the logbooks. An improvement
48 NOAA Technical Report NMFS 142

J F M A M J J A SON 0

MONTH

Figure 12

Proportion ofswordfish catch (number offish) by month

for California harpoon fishery vessels, as reported in

logbooks for 1974-93. Normal indicates fishing effort

in non-EI Nino years and 82-83 EI ino indicates fishing effort during the strong EI Nino of 1982-83.

in logbook recording of weights of fish landed would

augment and/or verify market sampling results.

Market sampling coverage of harpoon-caught swordfish is low and leads to questions concerning the utility

ofsize data from the sampling program. The quality of

these data could be improved by establishing a formal

Literature Cited

sampling plan that began by establishing sample sizes

necessary to predict lengths of swordfish caught by

year, season, and geographic area.

The harpoon fishery is largely confined to a relatively

small area, the Southern California Bight, which leaves

it vulnerable to changing environmental conditions and

competition from other fishing gears. The effects of

environmental changes were most evident during El

Nino events and resulted in decreasing catches and

CPUE. Competition from the drift gill net fishery since

1980 has resulted in decreases in harpoon catches and

effort. Catch rates in the drift gill net fishery are 2-3

times higher than in the harpoon fishery, drift gill net

vessels use less fuel in finding and pursuing their catch,

and drift gill net vessels can supplement swordfish

catches with catches of sharks. It remains to be seen

what effects recent increases in offshore longline fisheries will have on the harpoon fishery. Therefore, major concerns for the remaining harpoon fleet will probably be the continued availability of the resource in the

Southern California Bight, and the effects of interactions between fisheries and the environment.

Because of the harpoon fishery's inability to move to

other areas and increased competition from other gears,

the outlook for a resurgence of the harpoon fishery

seems unlikely. Recent increases in swordfish catches

by the California harpoon and drift gill net fisheries

(Holts and Sosa, 1994) indicate that the swordfish population may be able to support an even higher catch.

However, due to the low catch rates in the harpoon

fishery and the greater efficiency of the drift gill

net fishery, increases in the harpoon fleet size or

catch do not seem feasible (Sakagawa, 1989).

Therefore, harpoon fishing will probably continue in the Southern California Bight, but as a

form of fishing practiced by a handful of fishers

who continue to pursue the thrill of the one-onone hunt for swordfish.

Bedford, D. W.

1987. Shark management: a case history-the California pelagic shark and swordfish fishery. In S.

Cook (ed), Sharks: an inquiry into biology, behavior, fisheries, and use, p. 161-171. Proceedings of

a conference in Portland, OR, 13-15 October 1985,

Oregon State Univ. Ext. Serv., Portland.

Bedford, D. W., and F. B. Hagerman.

1983. The billfish fishery resource of the California

current. Calif. Coop. Oceanic Fish. Invest. Rep.

24:70-78.

California Department ofFish and Game (CDFG).

1949. The commercial fish catch of California for

the year 1947 with an historical review 1916-

1947. Calif. Dep. Fish. Game. Fish Bull. 74, 267 p.

• AIRPLANE

• NO AIRPLANE

• TOTAL

40

I 35

u

30 u

I

UJ 25 u:::

0

a:: 20 a

s:

UJ 15 Iz

w

U 10 a::

w

Q. 5

0

1975 77 79 81 83 85 87 89 91 93

YEAR

Figure 13

Catch per unit of effort (CPUE) in number ofswordfish caught

per day fished and per days fished with (AIRPLA E) and

without (NO AIRPLANE) airplanes by California harpoon

fishery vessels, as reported in logbooks for 1974-93.

0'

2.8-

(f)

u::: 2.4

o

a: 2.0 UJ

D..

Vi 1.6

u:::

1.2

a:

UJ

co 0.8

::2;

::J

0.4 UJ

::J13 0 L-.,...-.,...--r--r--r--r-~""""""-+--r"....,.......,...-.--r--r---r--,---,,....-r-'
_________________________ Coan et al.: California Harpoon Fishery for Swordfish 49

1981 82 83 84 85 86 87 88 89 90 91 92 93

YEAR

Figure 14

Number ofswordfish sampled and annual estimates of

average cleithrum length (em) for swordfish caught by

California harpoon fishery vessels during 1981-93.

I 180

(f)

u::: 160 LL

0 140 IT: AVERAGE CLEITHRUM LENGTH (CM) w

lD 120 ::;:

:J

Z 100 IT:

0 80

60 I

I-

(9 40 z

w

--' 20

0

Hanan, D. A., D. B. Holts, and A. L. CoanJr.

1993. The California drift gill net fishery for sharks and swordfish, 1981-82 through 1990-91. Calif. Dep. Fish Game.

Fish Bull. 175,95 p.

Holts, D., and O. Sosa-Nishizaki.

1998. Review of the swordfish fisheries in the eastern North

Pacific. In I. Barrett, O. Sosa- ishizaki, and N. Bartoo

(eds.), Biology and fisheries ofswordfish, Xiphias gladius, p.

65-76. u.s. Dep. Commer., NOAA Tech. Rep. NMFS 142.

Kronman, M.

1988. Harpooning: slow but steady improvements in the technology of a timeless skill. Natl. Fisherman, August, p. 53-

57.

Sakagawa, G. T.

1989. Trends in fisheries for swordfish in the Pacific

Ocean. In R. H. Stroud (ed.), Planning for the future of

billfishes: proceedings of the 2nd international billfish symposium, p. 61-80. Natl. Coalition Mar. Consel-v., Savannah, GA.

Squire, J. L.

1993. Relative abundance of pelagic resources utilized by the

California purse seine fishery: results of an airborne monitoring program, 1962-90. Fish. Bull. 93:348-361.

14

0

W

II: 12 ::::>

Cf)

«

w 10

I

Cf)

u.. 8

0

II:

0 6 3:

Cf)

u..

0 4

II:

W

OJ 2

::::>

z

0

71 81 91 101 111 121131141151161171181191201 211

CLEITHRUM LENGTH (CM)

Figure 15

Size distribution (cleithrum length in em) of swordfish sampled from California harpoon fishery vessels during

1981-93.

Spatiotemporal Dynamics of Swordfish, Xiphias gladius,

Landings in the Hawaii-Based North Pacific

Pelagic Longline Fisheryl

GERARD T. DI NARDO' and WILLIAM KWOK

Marine Resource Dynamics and Assessment Program

Joint Institute for Marine and Atmospheric Research

University ofHawaii

1000 Pope Road

Honolulu, Hawaii 96822

ABSTRACT

We characterize the spatial and temporal dynamics ofswordfish landings in the Hawaiibased domestic North Pacific pelagic longline fishery, and develop preliminary size-based

metrics of fishery performance. Between 1991 and 1993, areas of high fishing effort moved

progressively north and west, concentrating in the North Pacific transition zone, along the

subarctic boundary, and in the subarctic frontal zone. Annual weight-frequency distributions were characterized by high interannual variability and changing skewness and modal

frequency. The observed variations in weight result from changes in fleet dynamics rather

than from increasing fishing effort. The continuing decline in the number of small swordfish landed is likely confounded with changes in spatial distribution of the fleet and in

landing practices. Mean swordfish weight increased and interannual variation decreased

with increasing latitude.

Quarterly estimates of mean swordfish landings per unit of effort (LPUE) suggest an

increasing trend accompanied by decreasing intra-annual variability and dampening of the

seasonal signal. LPUE was generally higher for swordfish-targeted trips than for mixedtargeted (swordfish and tuna) trips. Between 1991 and 1993, quarterly swordfish LPUE was

constant for swordfish-targeted trips (mean = 13.5 fish/l,OOO hooks). Between 1991 and

1992, quarterly swordfish LPUE was constant for mixed-targeted trips (mean = 7.0 fish/

1,000 hooks) before increasing to approximately 11.5 fish/l ,000 hooks in 1993. In general,

small swordfish contributed the least to total landings, while medium swordfish contributed

the most. This pattern ofsize-specific contribution to total landings was generally similar in

all quarters. We argue that the differences in computed performance indices are indicative

of differences in fishing strategy between the two trip types.

Introduction

In this paper we characterize the spatial and temporal

dynamics of swordfish, Xiphias gladius, landings in the

Hawaii-based domestic North Pacific pelagic longline

fishery (hereinafter referred to as the Hawaii longline

fishery) and develop preliminary size-based metrics of

fishery performance. Hawaii's longline fishery has recently experienced a period of rapid expansion and

changing fishing strategy. Changes in target species,

fishing methods, and areas fished characterized the

recent fleet expansion.

Since its inception in the early 1900's, the Hawaii

longline fishery has traditionally targeted blue marlin,

Makaira mazara, and tunas, in particular bigeye tuna,

Thunnus obesus, and yellowfin tuna, 1'. albacares (Boggs

and Ito, 1993). However, in recent years (1989-93) the

primary target of the Hawaii longline fishery has gradually shifted to swordfish, and by the end of 1990, swordfish dominated landings (by weight) in the fishery (It02).

• Present address: Honolulu Lab., Southwest Fish. Sci. Cent., Nat!.

Mar. Fish. Serv., NOAA, 2570 Dole St., Honolulu, HI, 96822-2396.

1 A report of the University of Hawaii pursuant to National Oceanic

and Atmospheric Administration Award no. NA37RJ0199.

2 Ito, R. Y. 1992. Western Pacific pelagic fisheries in 1991. U.S.

Dep. Commer., NOAA, Nat!. Mar. Fish. Serv., Southwest Fish. Sci.

Cent. Admin. Rep. H-92-15, 38 p. Honolulu Lab., SWFSC, NMFS,

NOAA, 2570 Dole St., Honolulu, HI 96822-2396.

51
52 NOAA Technical Report NMFS 142 _

Swordfish landings increased from approximately 272

metric tons (t) in 1989 to 6,124 t in 1993 (WPRFMC3).

The reported increase in swordfish landings results

both from a rapid increase in fishing effort directed at

swordfish and from changes in the spatial distribution

of fishing effort. Prior to 1989 most Hawaii longline

fishing effort targeted tuna. In 1993, approximately

28.1 % of Hawaii longline fishing trips exclusively targeted swordfish, 27.9% of the fishing trips targeted a

mixed catch of both tuna and swordfish, and 44% of

the fishing trips exclusively targeted tuna. The number

of longline vessels fishing for swordfish increased from

11 in 1989 to a high of 114 in 1991 before decreasing to

88 in 1993 (Ito et aI., 1998). While most swordfish

fishing effort continues to occur north of the Hawaiian

Archipelago, the spatial distribution of fishing effort

has changed considerably. Areas of high fishing effort

have continually moved farther north and west.

Albeit the magnitude of Hawaii's longline fishery is

small relative to other Pacific pelagic fisheries (Neal et

a\., 1991), Hawaii has become a major supplier offresh

swordfish to United States (U.S.) mainland markets.

Hawaii-based longliners accounted for approximately 15%

of the Pacific-wide harvest and 42% of the total eastcentral Pacific catch (WPRFMC4). The rapid expansion of

the Hawaii longline fishery and its increasing economic

importance necessitate an understanding ofthe dynamics

of this fishery and the sources of variability that affect

indices of fishery performance. This paper is intended to

address these needs by 1) describing the dynamics of the

Hawaii longline fleet, 2) characterizing the size ofswordfish landed in the Hawaii longline fishery from 1989 to

1993, 3) describing spatial and temporal trends in swordfish size statistics, and 4) computing size-based metrics of

fishery performance and identifying factors contributing

to variability in performance indices. The identification of

factors affecting indices is pivotal to the estimation of

standardized performance indices.

Materials and Methods

Data Collection Programs

We used data from three ongoing data collection programs in our analyses: the federal logbook program

and two voluntary shoreside monitoring programs in

3 Western Pacific Regional Fishery Management Council (V\'PRMFC).

1994. Pelagic fisheries of the western Pacific region: 1993 annual

report, 158 p. Western Pac. Reg. Fish. Manage. Coune., 11 fi4

Bishop St., Ste. 1405, Honolulu, HI 96813.

1 Western Pacific Regional Fishery Management Council (V\'PRFMC).

1994. Amendment 7 to the fishery management plan for the pelagic

fisheries of the western Pacific region. Proposed limited entry program for the Hawaii longline fishery, 278 p. Western Pac. Reg. Fish.

Manage. Counc., 1164 Bishop St., Ste. 1405, Honolulu, HI 96813.

Honolulu. Other information pertaining to changes in

fishing strategy was obtained from staff of the Fisheries

Monitoring and Economics Program at the Honolulu

Laboratory of the National Marine Fisheries Service

(:"-JMFS), who provided important qualitative information on trends in fishing operations and fleet characteristics. A brief discussion and characterization of each

data collection program follows.

Federal Logbook Program-To participate in the Hawaii longline fishery, vessels must possess a current

permit and submit logbooks of daily fishing activity.

The federally mandated longline fishing logbook system was implemented in November 1990 and requires

fishermen to submit logbooks to the NMFS Honolulu

Laboratory within 72 hr after a catch is off-loaded. Data

provided by logbooks include gear configuration, fishing position (latitude and longitude), time, and catch

for each longline set within a trip. When the logbook

data are edited by the NMFS, each logbook trip is

assigned a trip number and target-species trip type

(swordfish, tuna, or mixed-species-swordfish and tuna)

based on examination of the logbook data and interviews with the vessel captain or deck boss. When the

captain is unavailable, trip type is determined by analyzing the times of the sets, the number of light sticks

used, the area fished, type of gear fished, and previous

information on trip type for that particular vessel. Operational characteristics of each trip type are outlined

in Table 1. The assigned trip type designation applies

to all longline sets within a trip and is indicative of a

unique fishing strategy. A thorough description of the

logbook system is found in Dollar and Yoshimoto.5

Shoreside Monitoring Programs-Voluntary shoreside

monitoring is conducted at four sites on Oahu. Because

j Dollar. R. A.. and S. S. Yoshimoto 1991. The federally mandated longline fishing log collection system in the Western

Pacific. U.S. Dep. Commer., NOAA, Nat!. Mar. Fish. Serv., Southwest Fish. Sci. Cent. Admin. Rep. H-91-12, 35 p. Honolulu Lab.,

SWFSC, NMFS. NOAA, 2570 Dole St., Honolulu, HI 96822-2396.

Table I

Reported operational characteristics ofthe Hawaii-based

1'\orth Pacific longline fishery. The ranges represent

the 25% and 75% quartiles.

Trip type

Swordfish Mixed Tuna

Hooks 650-800 900-1,020 1,000-1,560

Light sticks 400-850 120-360 0

Set duration (hr) 12-14 11-12 8-10

Sets 9-12 5-7 7-9
_________ Di Nardo & Kwok: Spatiotemporal DynamicE of Swordfish Landings in the North Pacific 53

of rules governing the confidentiality of these data, the

site identities will remain anonymous. For purposes of

this study the sites have been grouped into two homogeneous categories, dealer A and dealer B.

Monitoring of dealer A for pelagic species commenced in 1987 and was initially administered by the

NMFS Honolulu Laboratory. Monitoring in recent years

was facilitated through a joint effort by NMFS and the

State of Hawaii Division of Natural Resources (HDAR).

Monitoring of dealer B commenced in 1989. Data are

provided to NMFS by the dealer, and the NMFS Honolulu

Laboratory is responsible for program administration.

Data collected in the shoreside monitoring programs

include fishing area, date of sale, vessel identification,

the weight of each lot sold, the number of fish per lot,

price per pound paid for each lot (not provided in the

dealer B monitoring program), and dressed condition

(i.e. headed, gutted, and tailed) of fish sold in each

transaction. For swordfish, a lot generally consists of

one fish. In those instances when a lot is two or more

fish, all fish are generally ofsimilar size.

Data Integration and Adjustments

The federal logbook program provides fishing strategy,

catch, and effort data, while the shoreside monitoring

programs provide landings, size composition, and economic data. We integrated data from the data collection programs to provide a more complete description

of trip events, using a two-step process. First, trips that

targeted tuna were deleted. Then, by referencing on

vessel permit number, the remaining strategy and economic data were integrated to create a vessel-specific

transaction file. The logbook program routinely collects vessel permit numbers for each longline set, but

the shoreside monitoring programs do not. However,

the monitoring programs do record fishing vessel names

and corresponding vessel code numbers, which enabled

us to reference the vessel permit numbers. (Vessel code

number is a unique vessel identification number assigned to each vessel which off-loads at either dealer A

or dealer B.)

In the second step, we matched records in the vesselspecific transaction file with specific trips reported in

logbooks. This was accomplished by creating vesselspecific landing intervals (time periods) from logbook

data, associating a trip number with each interval, and

assigning records from the vessel-specific transaction

file to the appropriate intervals. A landing interval represents the window of opportunity for the landing and

selling of swordfish from each trip. The beginning of

the interval was assigned the hauling date of the last

longline set of trip n, and the end of the interval was

assigned the date of the first longline set of trip n + 1.

Table 2

Monthly sampling coverage of pelagic species landings

at dealer A, 1989-93.

Sampling coverage (%)

1989 1990 1991 1992 1993

January 82.6 78.3 81.8 52.2 17.4

February 79.2 79.2 79.2 52.0 16.7

March 85.2 92.6 80.8 50.0 18.5

April 80.0 92.0 84.6 46.2 ]5.4

May 81.5 92.6 81.5 57.7 15.4

June 84.6 96.2 80.0 53.8 ]9.2

July 88.0 96.0 84.6 57.7 15.4

August 85.2 96.3 81.5 38.5 38.5

September 80.0 91.7 83.3 52.0 28.0

October 84.6 96.3 77.8 51.9 30.8

ovember 84.0 88.0 76.0 45.8 36.0

December 84.6 88.9 92.6 28.6 36.0

Records from the vessel-specific transaction file assigned

to an interval assumed the interval trip number, n.

The average position of a trip, used as a measure of

fishing position, was calculated from logbook data by

weighting reported longline set position (latitude and

longitude) by the reported catch of swordfish. All

records from the vessel-specific transaction file were

matched with logbook data; the maximum time between date oflast haul and sales date was 10 days.

For purposes of this study, fishery performance, expressed as mean landings per unit of effort (LPUE;

number of fish landed/l,OOO hooks), and weight-based

performance indices were computed using data collected

at dealers A and B. While data sufficient to compute catchper-unit-effort are collected in the logbook program, we

chose not to use this measure offishing performance.

We restricted our analysis to those samples in which

swordfish were sold either whole or dressed, i.e. headed,

gutted, and tailed. These two market conditions accounted for approximately 95% of all swordfish sold.

Dressed weight (DW) in kg was converted to round weight

(RW) in kg using the formula RW = 1.877(DW)o925,

developed on the basis of measuremen ts of 172 decked

swordfish collected during voluntary swordfish longline

observer and research vessel cruises between 1990 and

1993.

Sampling coverage at dealer A decreased over time.

Accordingly, length frequency data were adjusted upward to reflect a coverage rate of 100%. Between 1989

and 1991, monthly coverage at dealer A ranged from

76% to 96% (Table 2). Monthly coverage was 29%-

58% and 15%-38% in 1992 and 1993, respectively.

Between 1990 and 1993 annual sampling coverage at

dealer B varied from 62% to 91 % (Table 3).
54 NOAA Technical Report NMFS 142

Table 3

Annual sampling coverage of pelagic species landings

at dealer B, 1990-93.

Table 4

Swordfish sampled in Hawaii shoreside monitoring program by dealer, 1989-1993.

Results

Fishing Effort Distribution

RW frequency distributions ofsampled swordfish were

adjusted by multiplying the number offish in the lot by

either the ratio of total number of possible monitoring

days to the number of days monitored for each month

(dealer A), or the ratio of total number of trips offloaded to the total number of trips monitored in that

year (dealer B) .

During 1991-93, areas of higher fishing effort continually moved farther north and west, as shown in Figure 1.

Levels of fishing effort-low, medium, and high-are

based on quartile decomposition of the fishing-effort

frequency distribution. Low represents the first quartile,

high the fourth quartile, and medium the second and

third quartiles. In 1991, much of the fishing effort was

oriented in a north-south direction near the main Hawaiian Islands. By 1993, fishing effort shifted to a northwest-southeast orientation, with increased fishing effort to the northwest. This shift was particularly evident

in quarters 3 and 4.

Shifts in the distribution of target-species trip types

were also observed (Fig. 2). Much of this shift resulted

from a significant northwestward movement of vessels

targeting swordfish, particularly in quarters 3 and 4 of

1993. Data collected at dealers A and B show similar

differences in fishing effort by target-species trip type

(Fig. 3). Vessels off-loading at dealer B primarily targeted swordfish (-93% of trips) while vessels off-loading at dealer A generally targeted a mixed catch (-75%

of trips), implying a difference in fishing strategy according to dealer.

Swordfish samples

Dealer A Dealer B Total

1989 2,966 66 3,032

1990 17,505 5,591 23,096

1991 34,078 12,078 46,156

1992 22,263 12,194 34,457

1993 11,190 20,059 31,249

Total 88,002 49,988 137,990

ing skewness and modal frequency (Fig. 4). Whereas

the descending (right) tails of the distributions appeared

similar over time, the ascending (left) tails showed a

declining trend in the number ofsmall swordfish being

landed, a difference that proved to be significant (2-

sample Kolmogorov-Smirnov test; P<0.05). Between 1989

and 1993, the mean RW of landed swordfish increased

from 48.0-68.0 kg (Fig. 5).

Latitudinal distribution of mean swordfish RW is depicted in Figure 6. Data between the equator and 49°N

were pooled across years and stratified into 10° latitudinal bins. Mean swordfish RW decreased from 52 to 35 kg

between latitudinal bins 1 (00_9°N) and 2 (l00-19°N),

then increased to a maximum mean RW of97 kg in bin

5 (400-49°N). Variability was minimal in latitudinal bin

1, increased to a maximum in latitudinal bin 3, than

decreased with increasing latitude. Similar trends in

the mean and variation of RW by latitudinal bin were

observed annually.

Monthly mean RW by latitudinal bin is shown in

Figure 7. Intra-annual variation in mean RW within

bins decreased with increasing latitude. However, it

should be noted that the number of samples also decreased with increasing latitude. The large seasonal

variation of mean RW observed in bin 3 suggests seasonal movement into and out of that bin. However,

temporal sampling in adjacent bins was sparse, and

migration patterns could not be inferred.

Landed swordfish were generally larger for vessels

targeting swordfish compared to vessels targeting a

mixed catch (Fig. 8). Similar size differences by targetspecies trip type were observed annually and quarterly.

62.4

83.2

Sampling

coverage (%)

1992

1993

Year

90.6

69.5

Sampling

coverage (%)

1990

1991

Year

Swordfish Size Dynamics

Between 1989 and 1993, 137,990 swordfish were sampled

at dealers A and B (Table 4). The perc~nt-frequency

size distribution of swordfish landed in the fishery is

characterized by high intra-annual variability and changSwordfish Landings Per Unit of Effort

Quarterly swordfish mean LPUE (hereinafter referred

to as LPUE) from 1991 to 1993 is shown in Figure 9. An

increasing trend in LPUE is suggested, accompanied by
Di Nardo & Kwok: Spatiotemporal Dynamics of Swordfish Landings in the North Pacific 55

1991 1992 1993

SO·N SO·N SO·N

40·N 40·N 40·N

30·N 30·N 30·N

01 20·N 20·N 20·N

10·N 10·N 10·N

O· O· O·

180· 160·W 140·W 180· 160·W 140·W 180· 160·W 140·W

SO·N SO·N SO·N

40·N 40·N 40·N

30·N 30·N 30·N •

02 2O•

N 20·N 20·N

10·N 10·N 10·N

O· O· O·

180· 160·W 140·W 180· 160·W 140"W 180· 160·W 140·W

SO·N SO·N SO·N

40·N 40·N 40·N

30·N 30·N 30·N

03 2O•N 20·N 20·N

10·N 10·N 10·N

O· O· O·

180· 160·W 140·W 180· 160·W 140·W 180· 160·W 140·W

SO·N SO·N SO·N

40·N 40·N 40·N

30·N 30·N 30·N

04 2O•

N 20·N 20·N

10·N 10·N 10·N

O· O· O·

180· 160·W 140·W 180· 160·W 140·W 180· 160·W 140·W

.Low .Medium DHigh

Figure 1

Quarterly (QI-Q4) distribution of fishing effort by 5° x 5° square in the Hawaii longline

fishery, 1991-93.

decreasing intra-annual variability and modulation of the

seasonal signal. During 1991 and 1992, seasonal signals

were similar: swordfish LPUE was greatest in quarters 1

and 2 and lowest in quarters 3 and 4. In 1993, quarterly

LPUE's were similar, exhibiting little seasonality.

The quarterly LPUE time series was decomposed

into two target-species trip type series: swordfish and

mixed (Fig. 10). Quarterly swordfish LPUE for swordfish-targeted trips was generally higher than that for

mixed-target trips and showed no apparent trend (mean

= 13.5 fish/l,OOO hooks). Between 1991 and 1992, quarterly swordfish LPUE for mixed-target trips showed no

apparent trend (mean = 7.0 fish/ 1,000 hooks). In 1993,

however, quarterly swordfish LPUE for mixed-target

trips increased to 13 fish/ 1,000 hooks in quarter 1

before declining to approximately 9 fish/l,OOO hooks

in quarter 4. Seasonality was apparent in the mixedtarget LPUE series, but not in the swordfish-targeted

series. LPUE was higher during the first half of the year

and lower in the second half of the year.
56 NOAA Technical Report NMFS 142

1991 1992 1993

01

50'N --!--'--'--........-'--'--"'"'-

40'N

30'N

20'N

10'N

50'N --!--'-_'--........--'-_.l..--\-

40'N

30'N

20'N

10'N

0' -+----,--...---,-~-...---+

180' 160'W 140'W 180' 160'W 140'W 180' 160'W 140'W

50'N --!--'-_'--........--'-_.l..--\-

• 10'N

20'N

0' -+----,--...---,----.-...---!-

30'N

40'N

10'N

20'N

0' -+----,--...---,-~-,.---+

50'N --!--'--'--........-'--'--"'"'-

40'N

30'N

0' -+----,--...---,----.-...----l

10'N

20'N

50'N --!--'-_"'--........--'-_.l..--\-

40'N

30'N

02

180' 160'W 140'W 180' 160'W 140'W 180' 160'W 140'W

10'N

20'N

0' -+----,--...---,----.-,---+

30'N

50'N -l---J...----'-

10'N

0' -+----,--...---,----,--...---+

20'N'

50'N --!--'--.........:--'--'--"'"'-

40'N

30'N

10'N

50'N

40'N

30'N

20'N 03

180' 160'W 140'W 180' 160'W 140'W 180' 160'W 140'W

50'N -r---'--.l..-.........---"-"'-----\.

0' +--.-,-...---,----,--,.---+

180' 160'W 140'W

40'N

20'N

10'N

0' +---,-...---,----.-,......-!-

180' 160'W 140'W

30'N

10'N

0' +---,-...------.-,---!-

180' 160'W 140'W

50'N --!---'-_.l..-........--'-_"'---\-

40'N

20'N

30'N

CD 1O'N

40'N

20'N

30'N

04

DMIXED BOTH • SWORDFISH

Figure 2

Quarterly (Q1-Q4) presence-absence distribution of target-species trip types by 5° x 5°

square in the Hawaii longline fishery, 1991-93. Mixed = trips targeted on both swordfish

and tuna; Both = both swordfish- and tuna-targeted trips,

The time series of quarterly LPUE by target-species

trip type was further decomposed into three size-group

series (Fig, 11, 12), The size groups small, medium, and

large were identified from the cumulative distribution

function (CDF) of swordfish weight data (1989-93),

each representing one-third of the total swordfish

sample, The small size group includes swordfish :S;30 kg,

medium includes swordfish >30 kg and :S;100 kg, and

large includes swordfish >100 kg, Size-group-specific

LPUE series for mixed-target trips exhibit similar seasonal behavior and no apparent trend (Fig, 11), However, the relative contribution of each size group varied

quarterly, During 1991 and 1992, quarterly LPUE was

generally similar for different sizes of swordfish, particularly for small and large fish, In 1993, quarterly

LPUE increased for medium and large fish, as did the

relative contribution from medium swordfish, which

dominated landings,
__________ Di Nardo & Kwok: Spatiotemporal Dynamics of Swordfish Landings in the North Pacific 57

1991 1992 1993

40'N

30'N

01 20'N

10'N

0' -1--,.-..---,-........-r--+

50'N -r---'--.:..---'----'--.:..-.,.

40'N

30'N

20'N

10'N

0' -+-----,--,.-...,....----,--,.--+

180' 160"W 140"W 180' 160"W 140"W 180' 160"W HO"W

50'N ~---'--.:..---'-----"-"---.,.

10'N

0' +----,-.....--............-r--+

50'N -r---'--.:..---'-----"-"---.,.

40'N

30'N

20'N

0' -+--"-"--,,,,-"""'--r--+

10'N

20'N

30'N

50'N -!-----'--'---'-----'--'--"'i

40'N

10'N

30'N

20'N'

40'N

02

180' l60'W 140"W 180' 160"W 140"W 180' 160"W HO"W

• 20'N

40'N

50'N -r----"-"---.........----"-.......,.

30'N

20'N

40'N

30'N

50'N -r----'--'---'-----'--.:..---j.

20'N

40'N

30'N

50'N -r----"-"---.........----"--.,.

03

10'N - 10'N 10'N

0' -+-........-.....---",....-...,..---r---+

180' 160"W 140'W

0' +--,.-..--...,-......,--,.--+

180' 160"W 140"W

0' +-,.-.....--............-,---+

180' 160'W l40"W

• 20'N

50'N -r----"-..............---'-......--i40'N

30'N

40'N

20'N

50'N -(-----'--.:..-----'--.:..--1-

30'N

04

10'N - 10'N 10'N

180'

0' +-........-.....---,,....-...,..---r-+ 0' -+----r-.,..........,.---.-,---+

160"W 140"W

0' +-........-.....---,-........-r--+

180' 160"W 140"W 180' 160"W 140"W

OMIXED ~BOTH .SWORDFISH

Figure 3

Quarterly (QI-Q4) presence-absence distribution ofsampled target-species trip types by 5°

x 5° square In the Hawaii longline fishery, 1991-93. Mixed = trips targeted on both

swordfish and tuna; Both = both swordfish- and tuna-targeted trips.

The quarterly LPUE series for medium and large

swordfish caught on swordfish-targeted trips are similar

and are characterized by high intra-annual variability

and an increasing trend (Fig, 12). Quarterly LPUE's for

small swordfish caught on swordfish-targeted trips are

characterized by low inter- and intra-annual variability

and a decreasing trend, Highest landing rates are associated with medium swordfish, followed by large and

small swordfish, A comparison of size-group LPUE series suggests that swordfish-targeted trips generally have

higher landing rates for medium and large swordfish.

In contrast, LPUE for small swordfish is similar for the

two target-species trip types.

These size groups (small, medium, and large) do not

have biological meaning, but were derived from the

CDF of swordfish RW. To help determine biological

impacts of the fishery, we estimated quarterly LPUE

series for mature and immature swordfish, We assumed

a size at maturity of 60 kg for both sexes (Skillman,

1998). Sixty kg is the reported size at maturity for
50

1993

40

1992

30

1991

Year

20

Latitude

1990

10

1989

~1 ~2 ~3 ~4 ~5

o-l,-~---l----f....-----l-----+-----J.

o

60

80

100

160

20

140

oL-~-------_---_---~

20

40

120

Figure 5

Annual mean round weights ofswordfish landed in the

Hawaii longline fishery, 1989-93. The bottom and top

edges of the boxes mark the sample 25th and 75th

percentiles. The whiskers extend to the sample 10th

and 90th percentiles. The line connecting the box

plots is drawn at the means.

160

140

120

OJ

6

:c 100

OJ

'iii

3 80 D

c

:::J

0

'" 60

40

Figure 6

Latitudinal distribution ofswordfish round weight. The

bottom and top edges of the boxes mark the sample

25th and 75th percentiles. The whisker ends mark the

sample 10th and 90th percentiles. The horizontal lines

are drawn at the means.

58 NOAA Technical Report NMFS 142

8

6 1989

4 N =3,032

2

0

0 40 80 120 160 200 240 280

8

6 1990

4 N =23,096

2

0

0 40 80 120 160 200 240 280

8

6 1991

-

c 4 N =46,156 III

2 III

C- o

0 40 80 120 160 200 240 280

8

6 1992

4 N =34,457

2

0

0 40 80 120 160 200 240 280

8

6 1993

4 N =31,249

2

0

0 40 80 120 160 200 240 280

Round Weight (kg)

Figure 4

Annual percent-frequency distribution ofround weight

of swordfish landed in the Hawaii longline fishery,

1989-93.

female swordfish in the Pacific Ocean; male swordfish

mature at a smaller size. Therefore, 60 kg represents an

upper limit.

Quarterly swordfish LPUE by stage of maturity is

shown in Figure 13 for all trips combined. The series

for mature swordfish suggests an increasing trend. Quarterly LPUE for immature swordfish decreased from

1991 to 1992, before increasing in 1993.

Quarterly LPUE's for mature and immature swordfish

caught on mixed-target trips are characterized by similar

increasing trends and seasonal signal (Fig. 14). LPUE was

generally higher during the first half of each year. Quarterly LPUE for mature swordfish caught on swordfishtargeted trips is characterized by high intra-annual variability and increasing trend; it was generally higher than

that for immature swordfish (Fig. 15). Quarterly immature LPUE decreased from approximately 8.5 fish/l,OOO

hooks in 1991 to 3.25 fish/l,OOO hooks in 1992, before

increasing to a mean of 5.0 fish/l,OOO hooks in 1993.

Quarterly mature swordfish LPUE was generally

higher for swordfish-targeted trips than for mixed target
__________ Di Nardo & Kwok: Spatiotemporal Dynamics of Swordfish Landings in the North Pacific 59

Latitudinal Bin 2 Latitudinal Bin 3

140 1991 1992 1993 140 1991 1992 1993

120 _ 120

Ol Ol 6 6

:E 100 :E 100

Ol Ol (j) '(j)

80 80

D D C C

=' 60 =' 60 Q Q

c c 0 40 0 40 Q) Q)

20 20

0 0

1 6 12 1 6 12 1 6 12 1 6 12 1 6 12 1 6 12

Month Month

Latitudinal Bin 4 Latitudinal Bin 5 140 140

1991 1992 1993 1991 1992 1993

120 - 120 Ol Ol 6 6

:E 100 :E 100 Ol Ol (j) '(j)

80 80

D D C C

=' 60 =' 60 Q Q

Figure 7

Monthly mean swordfish round weight by latitudinal bin,

c

g 40

20

OL-_-_-,--L~__..L.,.-__-

1 6 12 1 6 12 1 6 12

Month

c

g 40

20

1 6 12 1 6 12 1 6 12

Month

trips (Fig. 14, 15). In contrast, quarterly LPUE for immature swordfish was similar for the two target-species

trip types.

Discussion

Fleet and Fishing Effort

Changes in the spatial distribution of fishing effort

characterized the recent expansion of the Hawaii

longline fishery. Areas of high fishing effort moved

progressively north and west, concentrating in the North

Pacific transition zone, along the subarctic boundary,

and in the subarctic frontal zone. Much of this change

likely resulted from acornbination of factors including

vessel characteristics and learning. Vessel characteristics relate to a vessel's capacity for distant-water operations, i.e. self-sufficiency, on-board technology, and seaworthiness. During the summer and fall months when

vessels are fishing in the northwestern areas, a fishing

trip could last from 4 to 8 weeks, with 10 days for travel

to and from the fishing grounds. Because of the long

distances traveled and extended periods away from port,

only vessels able to produce ice, that have advanced onboard technology for navigation and locating fish, and

capable of performing most emergency repairs at sea

tend to fish in the northwestern areas.

The observed difference in spatial distribution of

trips targeted on different species illustrates the effects

of fleet characteristics on spatial distribution of fishing

effort. We have shown that vessels targeting swordfish

accounted for much of the northwestward movement

of fishing effort. Prior to participating in the Hawaii

longline fishery, many of these longline vessels fished

for swordfish in the Atlantic Ocean and for salmon and

crabs in the northwest Pacific Ocean. These vessels are

generally capable of producing saltwater ice at sea, are

equipped with a full array of electronics equipment

such as radar and Doppler, carry spare parts for most
60 NOAA Technical Report NMFS 142

180

160

140

Ol

120 :c

0> 0Qj 100

U

c

:J 80

0

C!::

60

40

20

oJ'---------~--~- S M

Trip Type

Figure 8

Swordfish round weight by target-species

trip type for all years combined, 1991-93.

Box plots as in Figure 6. S = swordfishtargeted trip, M = mixed-target trip.

Figure 10

Quarterly swordfish landings per unit effort by targetspecies trip type in the Hawaii longline fishery, 1991-93.

S = swordfish-targeted trip and M = mixed-target trip.

Figure 11

Quarterly size-specific swordfish landings per unit effort for mixed-target trips in the Hawaii longline fishery, 1991-93. L = large swordfish; M = medium swordfish; S = small swordfish.

20

U>

o

o

£

o

o

o 15

:c

;;:::

'"

Q5

.Q

E

:J

oS 10

Q

ill

-'c

:J

5

'"OJ

c

'6

c

o

-'

1991

234

1992

234

Quarter

1993

234

12

U>

0

0

£

0 10 0

0

?

;;::: '"

Q5 8

.Q

E

:J

S 6

§

-

ill

-'c

:J 4

Q5

Q.

'"OJ

c 2 '6

c

0

-'

,;

1991

234

1992

234

Quarter

1993

',,- ---.S

234
__________ Di Nardo & Kwok: Spatiotemporal Dynamics of Swordfish Landings in the North Pacific 61

12

o

o

10

o

o

.r::.

--(J)

:;:: 8

(j)

D

E

::J

S 6 t

.2

Q)

+- '§ 4

(j)

0-

(J)

Ol

c 2

'6

c

.9

., .......

1991

234

1992

234

Quarter

1993

234

10

V) 1991 1992 1993

"'"0 9 0

.r::.

0 8 0

0 "

" :c(J)

:;::

(j)

D 6 '. M

E

::J

C 5

2

Q) 4

+-

C

::J 3

(j)

0-

(J) 2

Ol

c

'6

c

J 0

-J

0

2 3 4 2 3 4 2 3 4

Quarter

Figure 12

Quarterly size-specific swordfish landings per unit effort for swordfish-targeted trips in the Hawaii longline

fishery, 1991-93. L = large swordfish; M = medium

swordfish; S = small swordfish.

Figure 13

Quarterly swordfish landings per unit effort in the Hawaii longline fishery, 1991-93, by maturity phase. M =

mature and I = immature swordfish.

12

o

o

.r::.

olD

o

o

1991 1992 1993

12

V)

"'"o

o

.r::.

o 10 o

o

1991 1992 1993

'eM

.. '

'.

2

8

4

6

(j)

D

E::J

S

t

o

+- 'c

::J

(j)

0-

(J)

Ol

c

'6

c

.9

4 "eM

+- 'c

::J

(j)

0-

(J)

Ol

c 2

'6

c

.9

:c(J)

:;:: 8

(j)

D

E

::J

S 6

Q)

Figure 14

Quarterly swordfish landings per unit effort for mixedtarget trips in the Hawaii longline fishery, 1991-93, by

maturity phase. M = mature and 1= immature swordfish.

Figure 15

Quarterly swordfish landings per unit effort for swordfish-targeted trips in the Hawaii longline fishery, 1991-

93, by maturity phase. M = mature and I = immature

swordfish.

234 234

Quarter

234

234 2 3 4

Quarter

234
62 NOAA Technical Report NMFS 142

on-board electronics and mechanical equipment, and

are more seaworthy than vessels targeting a mixed catch

(Dollar6). In con trast, many of the vessels targeting a

mixed catch are converted shrimp trawlers from the

Gulf of Mexico or small and medium-sized local vessels,

and are generally not designed for distant water operations. Many of these vessels are not capable of producing ice and lack on-board electronic equipment (Ito7).

Some exceptions nonetheless exist.

Distributional changes in fishing effort based on learning result from longliners becoming increasingly familiar with large-scale persistent oceanographic features.

The North Pacific transition zone, subarctic boundary,

and subarctic frontal zone are three such features. These

areas are characterized by multiple fronts (rapid changes

in sea-surface temperature or salinity) with high productivity and distinct endemic species of nekton

(Mishima, 1981; Pearcy, 1991; Roden, 1991). Squid, the

primary prey of swordfish (Stillwell and Kohler, 1985;

Bello, 1991), are known to form dense seasonal concentrations in these areas (Sinclair, 1991). One of the

more abundant species ofsquid endemic to the North

Pacific Ocean is the neon flying squid, Ommastrephes

bartramii (Pearcy, 1991).

Between 1991 and 1993, longline fishing effort gradually moved north and west, with high concentrations in

the North Pacific transition zone, along the subarctic

boundary, and in the subarctic frontal zone. The seasonal distribution offishing effort in 1993 was similar to

the typical seasonal distribution of neon flying squid

(Sinclair, 1991; Gong et aI., 1993; Murata and Hayase,

1993).

While the similarity in seasonal distributions suggest

a possible biological link, Hawaii longliners at best indirectly target squid concentrations. Longline vessels actively search for thermal fronts, where they set the

gear. 8 Podesta et al. (1993) found higher swordfish

catch rates in the vicinity of thermal fronts, but did not

have enough data to link the higher catch rates to other

physical or biological factors associated with frontal

regimes. However, concentrations of neon flying squid

are higher near thermal fronts (Gong et aI., 1993)

which in turn may attract swordfish.

It has been suggested that spatial targeting by Hawaii

longliners may have been influenced by interactions

with vessels participating in the North Pacific high-seas

drift gillnet fishery (Travis9). Reportedly, some long6 Dollar, R. 1994. Honolulu Lab., SWFSC/NMFS/NOAA, 2570

Dole St., Honolulu, HI 96822-2396. Personal commun.

7 Ito, R. Y. 1994. Honolulu Lab., SWFSC/NMFS/NOAA, 2570

Dole St., Honolulu, HI 96822-2396. Personal commun.

8 Fishery Monitoring and Economics Program, Honolulu Lab., Southwest Fisheries Science Center, MFS, OAA, Honolulu, HI 96822-

2396. Unpublished data.

liners would observe the operations of drift gillnet vessels and set their gear in areas associated with large

catches. Presently it is not clear if longliners used drift

gillnet vessels to identity concentrations ofsquid, swordfish, or the location of thermal fronts, but the reported

commensalism represents an interesting form of fishery interaction.

Swordfish Size Dynamics

The observed annual variations in swordfish weight

composition (Fig. 4) most likely result from changes in

fleet dynamics rather than from increased fishing effort. The continuing decline in the number of small

swordfish landed is probably confounded with changes

in spatial distribution of the fleet and in landing practices. As the fleet moved farther west and north, the size

of landed swordfish increased. Because larger swordfish receive a higher unit price than smaller swordfish,

there is an economic incentive to land only the larger

fish (Ito et aI., 1998). Thus, small swordfish, which were

traditionally landed, are caught less frequently due to

the northwestward movement of the fleet, and are often discarded for economic reasons.

Although data to compute swordfish discard rates

are collected through the logbook program, weight of

each swordfish caught is not recorded. Only average

annual discard rates, pooled over all sizes, can be estimated (4.4%-6.6%). However, these rates will be confounded with recent changes in fishing strategy (increased targeting of larger swordfish by longliners and

shifting spatial distribution of fishing effort) and most

likely underestimate discard rates for small swordfish.

The northwestward movement of fishing effort, and

subsequent increase in size of swordfish landed, will

affect the sex ratio of landed swordfish. Results from

Kume and Joseph (1969) in the Pacific Ocean and Lee

and Arocha (1993) in the Atlantic Ocean show that

larger swordfish tend to be female. While there are no

recent swordfish sex-ratio data from the Pacific Ocean,

we have no reason to believe that larger swordfish landed

in the Hawaii longline fishery are not mainly females.

We have shown that intra-annual variation in mean

RW decreases with increasing latitude (Fig. 6). Moreover, intra-annual variability in monthly mean RW within

latitudinal bins decreased with increasing latitude, with

significant seasonal variation in mean RW in bin 3 (Fig.

7). These results, although limited in scope, suggest

seasonal movement of swordfish in the North Pacific

Ocean. However, the direction of movement (north9 Travis, M. 1994. JIMAR, Univ. Hawaii, 1000 Pope Rd., Honolulu, HI 96822. Personal commun.
_________ Di Nardo & Kwok: Spatiotemporal Dynamics of Swordfish Landings in the North Pacific 63

south, east-west, or some combination) cannot be inferred from existing data. While tagging studies in the

Atlantic Ocean suggest north-south movement patterns

(Berkley, 1989), additional data are required before migration patterns in the Pacific Ocean can be identified.

Indices of Fishery Perfonnance

Fishing for swordfish in the Hawaii longline fishery is a

recent phenomenon. The increasing trend in quarterly

LPUE (Fig. 9), accompanied by decreasing intra-annual variability and modulation of the seasonal signal,

exemplifies the effects of learning by longliners in a

developing fishery. Prior to 1993 the catch ofswordfish

was seasonal: higher landing rates in the first and second quarters, followed by lower rates in the third and

fourth quarters. By 1993, however, seasonality in swordfish landings disappeared. Swordfish were being landed at

similar rates throughout the year, suggesting a change in

fishing strategy. We hypothesize that change in strategy to

be the exploitation of temperature breaks which are frequently associated with persistent large-scale oceanographic

features by longliners, the same oceanographic features

important in the seasonal distribution ofswordfish.

The quarterly LPUE's computed for the Hawaiian

longline fishery are among the highest reported for

swordfish in the North Pacific Ocean. Estimates ofswordfish catch-per-unit-effort (CPUE) from the Japanese

tuna longline fishery in the North Pacific Ocean ranged

between 3.0 and 4.0 fish/l ,000 hooks in 1952-62 (Bartoo

and Coan, 1989) and were generally less than 2.0 fish/

1,000 hooks between 1963 and 1980 (Bartoo and Coan,

1989; Ueyanagi et al., 1989). During earlier years (1952-

62), swordfish and albacore were targeted by the Japanese longline fleet, which accounts for the higher CPUE.

Between 1962 and 1963, the target species of the Japanese longline fleet changed to tunas for the sashimi

market, and swordfish became an incidental catch

(Sakagawa, 1989). The lower CPUE in this period most

likely reflects the change in target species.

We have shown that quarterly swordfish LPUE is generally less for mixed-target trips compared to swordfishtargeted trips (Fig. 10). We argue that the differences

in computed performance indices are indicative of differences in fishing strategy. Gear and vessel characteristics differ between the two target-species trip types, and

these differences affect catchability (DiNardo, 1993).

As larger swordfish tend to be female, the increased

targeting of larger swordfish suggests increasing selection for females. Because larger swordfish are more

valuable, it is unlikely that there will be a reversal ofthis

trend. The extent and potential impact ofselecting for

females must be addressed as more data become available; one potential result is recruitment failure. This

necessitates the need for sex ratio data on swordfish

catches and reliable estimates of age at maturity. Because of the potential consequences of selecting for

females, we argue that swordfish fishery performance

indicators in the Pacific Ocean need to be size-based.

Sources of Variability

Assessing the status of swordfish in the Pacific Ocean

requires standardized metrics of fishery performance

from fisheries targeting swordfish, as well as estimates

of population dynamics parameters. Although we identified factors affecting performance indices in the Hawaii longline fishery, our list of factors is not intended

to be exhaustive. Rather, the identified factors represent a point of departure for future research and collaboration. Identified factors include fishing location,

time, fishing strategy, vessel characteristics, fish size,

and oceanographic features.

Additional data on vessel operations and fishing strategy are being collected by fishery technicians aboard

vessels of the Hawaii longline fishery. These data will be

used to identifY additional factors (e.g. vessel captain)

that affect measures of fishery performance, and to

quantifY standardized measures ofswordfish CPU£.

Acknowledgments _

We wish to thank the National Marine Fisheries Service,

Honolulu Laboratory for providing logbook and

shoreside monitoring data. This paper benefited from

comments byJerry Wetherall, Sam Pooley, Michael Seki,

Jeffrey Polovina, Edward DeMartini, Robert Skillman,

and an anonymous reviewer. Maps were constructed

using the Generic Mapping Tools (version 2.1.4) program (Wessel and Smith, 1991). This paper was funded

by a grant!cooperative agreement from the National Oceanic andAtmospheric Administration. The views expressed

herein are those of the authors and do not necessarily

reflect the views of NOAA or any ofits sub-agencies.

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Amer. Geophys. U. 72:441,445-446.
Swordfish, Xiphias gladius, Fisheries of the Eastern North Pacific Ocean

DAVID HOLTS

Southwest Fisheries Science Center

National Marine Fisheries Service, NOAA

Po. Box 271

LaJolla, California 92038-0271

OSCAR SOSA-NISHIZAKl

Centro de Investigacion Cientifica y de Educacion Superior de Ensenada (CICESE)

Apdo. Postal 2732, Ensenada

Baja California, 22800 Mexico

ABSTRACT

Broadbill swordfish, Xiphias gladius, is harvested commercially throughout the area of

its distribution, with catches averaging about 78,000 metric tons per yr. In the North Pacific

it is harvested in both coastal and high-seas fisheries by numerous nations. This paper

provides a description of the swordfish fisheries off the west coasts of the United States and

northern Mexico and summaries of other fisheries in the eastern North Pacific.

Introduction

Broadbill swordfish, Xiphias gladius, is a large migratory

oceanic species widely distributed in all of the world's

tropical and temperate oceans and most major seas. It

inhabits surface waters above 13°C, but seasonally may

enter cooler waters (Nakamura, 1985). The swordfish is

known to descend to depths of 300-500 m, where temperatures are 50

_8°C, presumably for feeding (Carey

and Robison, 1981; Holts et al. l). It is found in greater

abundance in areas of rich production where small

pelagic prey are plentiful, such as in frontal zones and

where water currents merge or where temperature and

salinity gradients occur (Sakagawa, 1989; Sosa-Nishizaki

and Shimizu, 1991). In the Pacific Ocean there are at

least four such areas: the coastal and offshore waters of

the California Current, the Kuroshiro Current offJapan, the Peru Current off northern Chile, and the

current systems east of Australia.

Swordfish is harvested commercially throughout its

area of distribution. It is highly desired, and sold both

fresh and frozen in seafood and sushi markets around

I Holts, D. B., N. W. Bartoo, and D. W. Bedford. 1994. Swordfish

tracking in the southern California bight. U.S. Dep. Commer.,

NOAA, Natl. Mar. Fish. Serv., SWFSC Admin. Rep. LJ-94-15, 9

p. Available from SWFCS, NMFS, 8604 La Jolla Shores Dr., La

Jolla, CA 92083.

the world. Individual swordfish may exceed 500 kg in

the Pacific. Worldwide landings peaked at 81,000 metric tons (t) in 1988 (Table 1), and currently average

about 76,400 t. Total annual catch in the Atlantic Ocean

and Mediterranean Sea averages about 44,000 t, representing 56.8% of the world catch. In these areas swordfish production is declining and the stock(s) appear to be

overexploited. The International Commission for the Conservation ofAtlantic Tunas (ICCAT) therefore set Atlantic

quotas in 1991 to gradually reduce catches to below the

current estimated maximum sustained yield (MSY).

Catches in the Pacific and Indian Oceans, where there is

no international management regime, represent 38.7%

and 4.5% of world production, respectively (Fig. 1).

The north Pacific swordfish resource was considered

stable at the time of the most recent assessments (Sakagawa and Bell, 1980; Bartoo and Coan, 1989; Sakagawa,

1989; Skillman, 1989). However, the data used in these

studies were complete only through 1981. The global

market and product value have remained steady. In

response to continued demand, and reduced supply

from the Atlantic, swordfish catches in the Pacific have

increased. Data assembled by the Food and Agriculture

Organization (FAO) of the United Nations indicate

substantial production increases in all three of its eastern Pacific statistical fishery areas (67, 77, and 87),

especially from the United States (U.S.), Mexico, Chile,

65
66 NOAA Technical Report NMFS 142

Table 1

Swordfish catch (metric tons) for the eastern Pacific

Ocean, entire Pacific, and world (data from Food and

Agriculture Organization, 1986-93).

Eastern Pacific

Northern Central Southern Pacific World

Year Area 67 Ar·~a 77 Area 87 total total

1970 0 6,000 3,600 9,600 40,500

1971 0 2,800 500 3,300 26,678

1972 0 3,602 800 4,402 28,417

1973 0 4,504 2,600 7,104 32,183

1974 0 2,814 904 3,718 25,911

1975 0 2,697 540 3,237 28,819

1976 0 3,908 544 4,452 31,465

1977 0 3,216 832 4,048 33,380

1978 I 3,760 1,119 4,880 39,864

1979 0 3,215 572 3,787 37,992

1980 0 4,308 896 5,204 37,489

1981 8 5,534 900 6,442 38,663

1982 14 4,926 804 5,744 43,716

1983 26 4,168 1,316 5,510 46,587

1984 35 4,794 1,073 5,902 53,517

1985 162 4,995 688 5,845 59,121

1986 25 4,927 1,239 6,191 61,036

1987 28 5,903 2,662 8,593 67,028

1988 74 5,977 5,508 11,559 81,036

1989 86 5,217 6,318 11,621 78,704

1990 30 8,463 6,072 14,565 76,235

1991 4,004 9,390 8,403 21,797 71,639

and other Central and South American countries (Food

and Agriculture Organization, 1986-93; Table I). Many

U.S. commercial swordfish vessels transferred their operations from the Atlantic and Gulfstates to the eastern

North Pacific in 1993. This increase in potential production raised fears that the Pacific stock(s) may also

be vulnerable to overfishing, and created an urgent

need for new assessments utilizing current data Uoseph

et a1. 2).

Imports of swordfish into the U.S. have increased

from less than 1,000 t prior to 1984, to over 4,000 t per

yr in 1985-89. Generally priced well below domestic

market prices, imports have continued to increase to

more than 7,000 t per yr in recent years (1989-92) with

an annual value in excess of $40,000,000 Uacobson3).

Imports from the Pacific Ocean are currently about

67% of total U.S. swordfish imports.

2 joseph,]., W. H. Bayliff, and M. G. Hinton. 1994. A review of

information on the biology, fisheries, marketing and utilization,

fishing regulations, and stock assessment of swordfish, Xiphias

gladius, in the Pacific Ocean. Inter-Am. Trop. Tuna Comm. Int.

Rep. 24,81 p. Available from IATTC, Lajolla, CA 92037-1508.

3 jacobson, R. 1994. Statistics and Market News, Natl. Mar. Fish.

Serv., NOAA, Long Beach, CA 90802. Personal commun.

PACIFIC (30.7%)

SOUTH ATLANTIC (17.4%)

MEDITERRANEAN (19.2%)

Figure 1

Worldwide swordfish production by major ocean system, 1987-92 (data from Food and Agriculture Organization, 1986-93).

This description of the swordfish fisheries off the

west coast of the U.S. and Mexico east of 1400W longitude includes the harpoon, driftnet, and longline fisheries operating out of U.S. west coast ports and the

driftnet and longline fisheries of Mexico, through the

1993 fishing season (Fig. 2). Summaries of the longline

fisheries ofJapan, Taiwan, and Korea in the eastern

North Pacific and that of Hawaii are also presented.

Fisheries _

Japan

Japanese longline vessels began operations in the Pacific in 1952 and were fishing the entire eastern Pacific

between 400 S and 35°N by 1968 (Nakano and Bayliff,

1992; Squire and Muhlia-MeI04 ). Directed fishing effort changed seasonally and annually to target the most

lucrative species of billfish and tunas available. Japanese Pacific-wide swordfish catches varied between

10,000 and 18,000 t and accounted for at least 80% of

Japan's catch of swordfish during 1952-68. The three

areas of the eastern Pacific with the highest swordfish

catch rates were off northern Mexico, east of 120oW; off

northern Chile; and at lOo-15°S and 95°-1IOoW

(Nakano and Bayliff, 1992). Japan has had up to 600

4 Squire,]. L.,jr., and A. F. Muhlia-Melo. 1993. A review ofstriped

marlin, swordfish, and sailfish fisheries and resource management

by Mexico and the United States in the northeast Pacific

Ocean. U.S. Dep. Commer., NOAA, atl. Mar. Fish. Serv., Southwest Fish. Sci. Cent. Admin Rep. LJ-93-06. 44 p. Available from

SWFSC, NMFS, 8604 La jolla Shores Dr., La jolla, CA 92038.
_____________ Holts & Sosa-Nishizaki: Swordfish Fisheries of the Eastern North Pacific Ocean 67

Baja Califoriliil,,-',

Baja Californin S~r\

UNITED STATES

OF AMERICA

Mexito Based

Driftnet Fishery

.'

.'

/

.'

I

.. /. .. ,

.'" ""'I . I / . nternatlona

longline Fisheries

I

'\

\ I

\/

, California Based

Interna~iona~ longline .'/ \ longline Fishery

Fisheries........... .' " "..

.................... 1./ ...... 1"'/ .. --.- . "', _ .. - "'-?_l_~O

.' " Hawaii Based 0/

longline Fishery~/

/

/

/

/

/

/

lOON ....._....I.__/~_....I. ....I...... ..... ..... ..... ....._ ...... lOON

.. - .. - .. - .. _.. - .. _.. - .........,

Figure 2

Swordfish fisheries operating in the eastern North Pacific.

longline vessels operating in the eastern Pacific in a

single year (Sakagawa, 1989).

Japanese longline fishing effort in the North Pacific

increased from 100 million hooks deployed annually in

the 1950's to 230 million hooks by 1967, and has remained above 200 million since. Fishing effort in the

eastern North Pacific increased from approximately

100,000 hooks during the late 1950's to over 20 million

in 1968, and averaged 9.5 million (range 6.4-13.7 million) between 1970 and 1980. This effort was directed

primarily at tuna, although striped marlin, Tetrapturus

audax, and swordfish were targeted around the tip of

the peninsula of Baja California, Mexico. During the

late 1980's, 49%-58% ofJapan's total longline fishing

effort in the Pacific was concentrated in the eastern

North Pacific, north of lOON and east of 140oW.

Substantial numbers of Japanese longline vessels

fished within 12 nautical miles (n. mi.; 22 km) of the

coast of Baja California in 1964, targeting swordfish,

marlins, and sailfish.Japan began targeting bigeye tuna,

Thunnus obesus, in about 1975, using deep longline

technology (Miyabe and Bayliff, 1987; Nakano and

Bayliff, 1992). That technology employs longer floatlines and fewer floats, increasing the distance between

floats and allowing the hooks to fish deeper in the water

column where bigeye tuna are more abundant. Deep

longlining was more commonly used south of lOON and

was used only about 25%-45% of the time off Baja

California.

Conventional Japanese longline fishing effort continued off northern Mexico for swordfish, and the highest catch rates (catch per hundred hooks) were reported from 1975 to 1983 and again in 1986 and 1987

(Miyabe and Bayliff, 1987; Nakano and Bayliff, 1992).

Mexico prohibited longline fishing within its Exclusive

Economic Zone (EEZ) from late 1984 through most of

1985.

Catch of swordfish north of lOON and east of 140 0W

peaked between 1968 and 1973 at an average of nearly

14,200 fish, and represented 9.5% ofJapan's total swordfish catch in the Pacific. Between 1974 and 1980, the

Japanese catch in the eastern North Pacific declined to

4,400 swordfish (3.1 % of their Pacific-wide catch) as a

result oftargeting on other billfish and tunas. The most

recen t data available indicate swordfish catches in 1984

and 1985 were the lowest since the early 1960's.

Japanese longline catch rates for swordfish were highest during the mid-1960's from lOON to 30oN, off Baja
68 NOAA Technical Report NMFS 142 _

California Sur and Mexico and east of Hawaii. Catch

rates were 0.1-0.3 fish per 100 hooks offBaja California

in the 1960's and 1970's and fluctuated from <0.1-0.4

as fishermen switched target species between swordfish

and other billfish off Baja California in the 1980's

(Nakano and Bayliff, 1992). Mexico began enforcing its

EEl in 1978, allowing foreign longline effort within the

EEl on a permit basis only. These permits were limited

to joint-venture operations in 1978-91 and were withdrawn for a period in 1984-85. All longline effort,

foreign and domestic, was abolished within Mexico's

EEl in 1991. During 1981-87, the greatest Japanese

longline catch rates occurred at 30o-35°N and east of

135°W (off Baja California Sur) throughout the year

and west of 135°W in the fall and winter.

Considerable variation exists in the length-frequency

data. Swordfish less than 80 cm and greater than 200

cm, measured from posterior margin of the eye to fork

in tail (EFL) , were most common off Baja California

Sur. Although clear trends were not identified, recruitment into the longline fishery apparently occurs

throughout the year and over a broad area and wide

range of sizes (Nakano and Bayliff, 1992).

Japan's high-seas driftnet fleet did not enter the eastern North Pacific, although it did fish for swordfish,

billfish, and tunas in the South Pacific in 1972-92.

Taiwan

Taiwan's high-seas longline fleet began fishing in the

South Pacific in the 1960's and had expanded into the

North Pacific by 1967. Its fishing effort was primarily

directed at albacore, Thunnus alalunga, and yellowfin

tuna, Thunnus albacares, in the western Pacific. Taiwan's

longline fishing effort exceeded 2 million hooks in

1976, but declined steadily through 1991. Fishing effort

in the eastern North Pacific occurred in only two years

(1980 and 1987) and was directed toward tunas. Incidental swordfish catches were insignificant.

Korea

Korea's high-seas longline fishery targeted on tropical

tunas began in the South Pacific and had expanded

into the eastern Pacific by 1975. Fishing effort in the

North Pacific averaged 10 million hooks from 1975 to

1987 (range 4.5-21.0 million). Most of this effort targeted tuna between lOON and the equator. Effort in the

eastern North Pacific averaged 1.0 million hooks in

1975-87 (range 0.2-3.5 million). Effort decreased after

1984, possibly because of restrictive licensing agreements

within Mexico's EEl. Catches of swordfish were incidental, averaging only 230 swordfish per year (range 0-1,018).

United States

Harpoon Fishery-Fishing for swordfish with hand-held

harpoons began off southern California in the early

1900's. Swordfish (and striped marlin) could be taken

by both recreational and commercial fishermen until

1935, when harpooning for sport was banned by the

California Fish and Game Commission (CFGC). Harpoon fishing remained the primary fishery for swordfish until 1980, when it was essentially displaced by the

driftnet fishery for pelagic sharks and swordfish.

Traditionally the swordfish harpoon fishery extended

seasonally north as far as Oregon and south well beyond

the U.S.-Mexico border. It was, however, concentrated in

warmer waters (l8°-22°C) within the Southern California

Bight from about Santa Barbara to the Mexican border

and out about 60 n. mi. (110 km). The harpoon season

peaks in the summer and fall, when generally mild weather

conditions exist. Changes in climate and current patterns

have influenced the catch distribution (Coan etal., 1998).

Fishing vessels search for swordfish "finning" or basking at

or near the surface. Because fish are usually sighted from

the vessel's mast or from airplanes, calm weather and sea

conditions are critical to locating the fish.

Harpoon vessels average about 6-26 m in length,

with a bow plank of about 6-8 m. They normally operate with a crew of at least two, who search with binoculars for swordfish. When a swordfish is sighted, one

crew member maneuvers the vessel's bow plank over

the fish while the other throws the harpoon from the

end of the bow plank. The catch is often stored on ice

during short trips of a few days.

The number ofvessels with harpoon permits remained

fairly steady prior to 1970. In 1971, levels oftotal mercury

in swordfish exceeded the allowable level of 0.5 ppm.

Local demand dropped for two years, but recovered in

1973. Imports of swordfish were severely restricted for

several years, but domestic swordfish, sold locally, was not

subject to inspection. The level of methyl mercury legally

allowable in swordfish was increased to 1.0 ppm in 1978.

With reduced competition from imports and renewed

consumer acceptance, the number of permits increased

from 150 to over 1,200 by 1980 (Bedford and Hagerman,

1983), although the number ofvessels landing harpooned

swordfish exceeded 300 only in 1978 and 1980.

Harpoon vessels began using aircraft to assist in locating swordfish at or near the surface in 1970. In 1973,

the harpoon was designated the only commercial gear

for swordfish by the CFGC. Aircraft proved extremely

efficient in locating swordfish and improving catches

for those vessels employing their use (Bedford5 ). Air5 Bedford, D. W. 1985. Pelagic shark/swordfish drift gill net

fishery. Calif. Dep. Fish Game Manage. Info. Doc., 74 p. Available

from CDFG, 1416 Ninth St., Sacramento, CA 95814.
_____________ Holts & Sosa-Nishizaki: Swordfish Fisheries of the Eastern North Pacific Ocean 69

craft use was prohibited for a short time in 1976, but its

effectiveness had been demonstrated by both increased

catch rates and landings. Use of aircraft was resumed

but only to locate areas of fish, and aircraft were required to remain at least 5 mi. from the fishing vessel

with which they were working. Legislation was passed in

1980 allowing swordfish taken in the driftnet fishery to

be landed and sold in California. Competition between

the two fisheries became intense, and harpoon fishers

lobbied for and received, in 1984, unrestricted use of

aircraft (Squire and Muhlia-Mel04).

Many of the owners of harpoon and driftnet vessels

obtained dual permits for taking both harpooned and

net-caught swordfish during the same trip. These dual

permittees set their nets at night and spent their days

searching for swordfish to harpoon (Hanan et aI., 1993).

Fishing effort for the harpoon fleet peaked in 1979 at

nearly 13,000 fishing days, and then fell rapidly in 1980-

83 as competition from the driftnet fishery increased.

Days fished by the harpoon fleet have averaged about

1,000 per yr since 1989 (Coan et aI., 1998).

The first sizable harpoon catch, landed in 1927, was

59 t. Landings fluctuated between 100 and 500 t throughout the 1930's and 1940's, then declined to 10-200 t,

where it remained throughout the 1950's and 1960's.

Catches averaged about 320 tin 1970-80 and peaked at

1,172 tin 1978 (Table 2). Between 1981 and 1992 catches

ofharpooned swordfish averaged 92 t, and they increased

to 116 t in 1993 with a fleet ofless than 40 vessels.

Measured swordfish from the harpoon fishery ranged

between 64 and 217 cm alternate length6 (AL) and

averaged 85 kg dressed weight (Coan etaI., 1998). Dressed

weight of swordfish is estimated at 55% of whole body

weight for tax purposes by the California Department of

Fish and Game (CDFG, 1995, Chap. 371, p. 2).

Driftnet Fishery-The driftnet fishery off the coast of

southern California began in 1978, primarily for pelagic sharks. Major changes have occurred in almost

every aspect of this fishery including vessels, gear, fishing techniques, regulations, fishing areas, seasons, and

targeted species. By 1980, Pacific broadbill swordfish

was the target of the fishery. The early success of the

fishery was attributed to the abundance ofPacific swordfish and pelagic sharks (thresher, Alopias vulpinus, and

shortfin mako, /surus oxyrinchus) in coastal waters, popular consumer acceptance of both swordfish and sharks,

and lower operating expenses than in the swordfish

harpoon fishery, primarily due to greater fuel efficiency.

6 Alternate length (AL) for swordfish is measured from the anterior

margin of the cleithrum to the fork of the tail. The regression

equation to convert to EFL (length post-orbit to the fork of the

tail) in centimeters is EFL = 1.09(AL) + 10.13.

Table 2

Reported landings in metric tons by the California

swordfish fisheries, 1970-93, by fishery type. DGN=drift

gill net.

Year Harpoon DGN Other Total

1970 199.3 229.3 428.6

1971 45.2 24.6 69.8

1972 86.4 34.2 120.6

1973 194.9 83.5 278.4

1974 193.7 lOLl 294.8

1975 297.8 94.9 392.7

1976 22.4 15.7 38.1

1977 187.1 44.6 231.7

1978 1,171.7 9.2 1,180.9

1979 222.4 43.8 266.2

1980 389.7 110.2 42.9 542.8

1981 178.6 319.7 20.0 518.4

1982 107.6 629.9 29.4 766.9

1983 39.8 922.4 250.9 1,213.1

1984 73.0 1,488.8 430.4 1,992.2

1985 145.0 1,659.4 552.5 2,356.8

1986 162.6 1,169.1 412.4 1,744.2

1987 145.0 895.7 202.4 1,243.0

1988 123.7 759.2 243.6 1,126.5

1989 37.2 730.1 530.1 1,297.5

1990 34.7 717.4 96.8 849.0

1991 11.3 577.8 120.7 709.7

1992 44.2 898.9 110.8 1,053.9

1993 116.1 905.0 67.3 1,088.4

Continued market demand encouraged development,

and fishers began exploring new areas farther offshore

and as far north as Oregon and Washington, although

few landings were made outside California. Both effort

and catch expanded, reaching highs in 1984 and 1985.

Several fishery-related conflicts emerged in the early

years of this fishery. Commercial swordfish harpoon

fishers feared reduced catches ofswordfish and lobbied

against netting, as did recreational anglers, who were

concerned about striped marlin. A related problem was

the incidental bycatch of marine mammals (Hanan et

aI., 1993; Hanan and Scholl7; Diamond et aI.8).

7 Hanan, D. A., and]. P. Scholl. 1985. Shark drift gill net fishery

observation program (May-June, 1983). In D. A. Hanan (ed.),

California Department of Fish and Game coastal marine mammal

study, annual report for the period July 1, 1982-June 30, 1983,

p. 10--12. U.S. Dep. Commer., NOM, Natl. Mar. Fish. Serv., Southwest Fish. Sci. Cent. Admin. Rep. LJ-85-10C. Available from

SWFCS, NMFS, P.O. Box 271, LaJolla, CA 92038-0271.

8 Diamond, S. L., D. A. Hanan, and]. P. Scholl. 1986. Drift gill

net observations for the 1984-85 fishing season. In D. A. Hanan

(ed.), California Department of Fish and Game coastal marine

mammal study, annual report for the period July 1, 1984-June 30,

1985, p. 9-26 and 45-46. U.S. Dep. Commer., NOM, Natl. Mar.

Fish. Serv., Southwest Fish Sci. Cent. Admin. Rep. LJ~6-25C. Available

from SWFCS, NMFS, P.O. Box 271, LaJolla, CA 92038.
70 NOAA Technical Report NMFS 142 _

Observer programs were mandated by CDFG in 1980

to address the incidental take of marine mammals.

These documented incidental catches during the early

years of this fishery. The CDFG observed hauls from

443 net sets during 1980-85. There were no systematic

observations during the 1986-89 fishing seasons. As mandated by the U.S. Marine Mammal Protection Act (MMPA),

the National Marine Fisheries Service (NMFS) established

an observer program in 1990. Data were recorded by

observers onboard driftnet vessels during obsenTed net

pulls (Hanan et al., 1993; Lennert et al., 1994). Coverage

in observed trips has been 10%-14% since 1990.

The incidental catch of marine mammals was considered relatively high in the developing years of the fishery. Time and area closures around the Channel Islands and along the mainland were successful in reducing that bycatch. Currently, the bycatch of marine mammals in this fishery is apparently low and not compromising any stocks (Hanan et al., 1993). Bycatch of other

species does not appear to be a problem, except possibly for blue sharks, Prionace glauca, which average 10-15

per set. Blue sharks that are not marketable in the U.S.

are discarded at sea Oulian and Beeson, 1998).

The first vessels in the driftnet fishery were converted

from sea bass and halibut set-net vessels, most of which

had wooden or fiberglass hulls. Many harpoon fishers

also converted their vessels for driftnet fishing. Effort

was concentrated around nearshore banks, canyons,

and escarpments, and the offshore islands. As the success of this fishery continued, many of the smaller and

older vessels were replaced with larger steel and aluminum vessels with increased speed and range. Fish hold

space increased, and cooling capabilities evolved from ice

to brine-spray and blast freezers. Several vessels now have

large-capacity ice makers and limit the length of trips to

less than about 3 wk to obtain the best market price.

As the driftnet fishery prospered, the number of

vessels increased and competition for available swordfish became intense. Airplanes were often hired to locate areas offish and to observe catches of other vessels

(Hanan et al., 1993). In 1980, the California legislature

made the driftnet fishery a limited-entry fishery, setting

the maximum number of permits at 150, but allowing

those fishers already involved to continue fishing. The

actual number of permits issued reached a high of 300

in 1985. Driftnet vessels landing swordfish in California

numbered 173 in 1991, 169 in 1992, and 162 in 1993.

There were, however, rarely more than 100 active vessels fishing throughout anyone season.

Drift nets are usually fished 4-10 m below the surface

to allow small vessels to pass over without entangling

them and to avoid catching non-target surface-swimming species. The nets are deployed at sundown and

retrieved in the early morning after a soak of 8-12 hr.

The length of the drift nets is limited to 1 n. mi. (1.8

km). The nets vary in depth between 50 and 100 meshes,

and fish a vertical depth of 15-30 m. The size of each

mesh is limited to a minimum of 40 cm (18 in) although 48 cm (22 in) is more common. The fishing

season originally started on 1 April and ended on 31

January of the following year. To reduce fishing effort

and to protect thresher sharks migrating northward

along the California coast, the season start was pushed

back to 15 August (Hanan et al., 1993).

Swordfish are removed from the net by first cutting

offthe bill and removing the fins. Swordfish (and sharks)

are dressed (head removed, and eviscerated), unwanted

parts discarded, and the carcasses washed with sea water

and placed in the hold at just above freezing (0°-2°C)

until the vessel returns to port. Most swordfish are sold in

local markets (Herrick and Hanan, 1988; Cailliet et al.,

1993; Hanan et al., 1993). Ex-vessel price for swordfish has

ranged from about $4.40 to $8.50 per kg since 1990.

Hanan et al. (1993) summarized the available driftnet data from the California logbook system, landing

receipts, and market sampling program for the 1981-

90 fishing seasons. Logbooks collected from driftnet

skippers under a mandatory logbook system (Huppert

and Odemar, 1986) include catches (number of fish)

by species, date, geographical position, gear and set

data, and various other information, such as vessel registration and permit numbers. Fishing effort is designated in logbooks as number of sets, a set being one

deployment and retrieval of the net.

Landing receipts are collected from commercial fish

brokers each time a vessel delivers its catch to a California market. The receipts report landings in pounds,

along with location and date of catch and type of fishing gear used. Problems associated with reporting of

gear types resulted in the development of criteria to

estimate actual landings of the driftnet fishery (Hanan

et al., 1993). This convention was used in the determination of 1991-93 effort data in this report. Combined

logbook and landing-receipt data provided improved

estimates of effort Oulian and Beeson, 1998; Beeson

and Hanan9) and are used here to estimate effort and

catch for the 1991-93 fishing seasons.

Skipper compliance with logbook reporting regulations was estimated to be greater than 90% (Hanan et

al., 1993; Miller et al. IO). The effort data reported in

Y Beeson, M., and D. Hanan. 1991. Effort estimates of California

p;ill net fisheries: halibut-angel shark set net and shark-swordfish

drift net for the 1990-91 fishing year (April 1, 1990-March 31,

1991). Final rep. NA90AA-HFC401 and NA86-ABD-00201 submitted to atl. Mar. Fish. Serv., Southwest Region, Terminal Island, CA.

IU Miller, D.]., M.]. Herder, and]. P. Scholl. 1983. California

marine mammal-fishery interaction study, 1979-1981. U.S. Dep.

Commer., NOAA, Natl. Mar. Fish. Serv., Southwest Fish. Sci. Cent.

Admin. Rep. LJ-83-13C, 233 p. Available from SWFSC, MFS,

8604 La Jolla Shores Dr., La Jolla, CA 92038-0271.
_____________ Holts & Sosa-Nishizaki: Swordfish Fisheries of the Eastern North Pacific Ocean 71

Table 3

Reported and estimated swordfish catch and effort in

the California driftnet fishery.

Estimated

Effon Catch

(sets) (fish)

D

D

00-499

500 -1,999

2,000 - 4,999

5,000 - 14,999

• 15,000 - 30,000

D

D

30"N

50"N r---=-""""""""-:-------------,

40"N

15,211

11 ,517

16,360

]3,706

4,504

4,752

4,504

5,380

Reponed

Effort Effon Catch

(landings) (sets) (fish)

1981 2,388 6,710 3,871

1982 3,282 10,452 12,925

1983 3,021 11,160 21,878

1984 2,912 9,688 25,725

1985 2,860 9,238 23,062

1986 2,411 11,243 23,454

1987 2,258 8,382 12,690

1988 1,572 6,047 11,289

1989 1,376 6,028 11,511

]990 1,545 4,392 9,367

1991 1,335 4,643 7,771

1992 1,119 3,898 10,460

1993 1,305 5,380 1] ,680

logbooks were therefore assumed accurate. The annual

distribution of effort in the driftnet fishery shifted geographically from nearshore southern California to

northward and offshore. Prior to 1982, fishing effort

during spring was concentrated on sharks in the Southern California Bight, then shifted northward and offshore, targeting swordfish as the season progressed.

During the height of the fishery, effort was concentrated

around the offshore seamounts of central and northern

California, and northward to Oregon and Washington.

Most effort off Oregon and Washington was directed at

thresher sharks, and few swordfish were caught. Because most of these vessels were based in California,

their catches were likewise landed in California.

Total reported annual driftnet effort nearly doubled

in the first 5 yr to a high of 11 ,243 sets in the 1986

fishing season, and subsequently declined to a low of

3,898 sets in the 1992 season. This effort increased in

1993 to 5,380 sets. The decline in effort resulted from

increasing regulations and laws governing the fishery.

Concern about possible overfishing of some pelagic

sharks resulted in the fishing season being shortened in

1985 to 15 August-30 January, and in prohibition of

sets within 75 n. mi. (139 km) of the coast and nearby

islands to avoid the directed spring thresher shark fishery. Effort decreased almost 60% by 1993, corresponding to decreased total landings. Reported driftnet landings increased to a high of 3,500 in the 1983 season,

then decreased steadily to a low of 1,500 in the 1990

season, and have averaged 1,223 during the 1991-93

seasons. Estimates of effort that incorporate NMFS observer data closely correspond to reported effort for the

1990-93 fishing seasons (Table 3).

20"N L-L.......l--'---'--'-...J.......J-...J....-J..-J.......J--'---'--'-...J.......J-...J....-J..-J.......J

130"W 120"W 110"W

Figure 3

Geographical distribution of swordfish catch (number

of fish) reported in CDFG logbooks for the California

driftnet fishery, 1981-93 fishing seasons.

The driftnet fishery catches swordfish mostly in waters off San Diego to San Francisco, and within 500 km

of shore. Catches of swordfish usually peak in October

and November and taper offin December andJanuary.

During the 1981 and 1982 seasons, the areas of highest

catch were in the Southern California Bight. Small

numbers of swordfish were also caught between San

Francisco and the California-Oregon border and within

200 km ofshore. As effort expanded, good catches were

taken offshore of Monterey and San Francisco. Few

catches ofswordfish occurred north of Oregon (Fig. 3).

Logbook data closely followed landings data, showing a peak catch of 25,725 swordfish in the 1984 season

followed by a decrease to 7,771 swordfish in the 1991

season and then an increase to 11,680 in 1993 (Table

3). Mean annual landings were 898 t of swordfish for

the 1981-93 seasons. Average landings for 1990-93

were 775 t, with improved landings in 1992 and 1993

(Table 2). Estimates that incorporate NMFS observer

data indicate that swordfish catch may be under-reported from 15% in 1993 to 38% in 1990 (Julian and

Beeson, 1998).

Swordfish dominated driftnet landings during 1983-

93. Swordfish landings increased from 110 t in the
72 NOAA Technical Report NMFS 142 _

of 35°N averaged 8.6--17.5 cm AL longer than those

caught south of 35°N. CDFG market samplers measured fewer swordfish after 1991, while measurements

by NMFS observers increased (Fig. 4). A large proportion ofswordfish measured by NMFS observers between

1990 and 1993 were caught north of 35°N. Coverage

rates for NMFS observation averaged 5%-28% of reported trips.

Longline Fishery-Traditionally there has been little

longline effort for swordfish along the west coast of the

U.S. and only moderate effort in waters around Hawaii.

In California, only harpoon and driftnet fishing for

swordfish were allowed within the EEZ. Catches ofswordfish taken by high-seas longlining started arriving in

southern California in 1991. Swordfish are rarely landed

by any fishery in Oregon or Washington.

Longline vessels based in Hawaii have fished for a

variety of tunas and billfish since the 1950's. In the

beginning, this was primarily a near-shore, daytime tuna

fishery. In 1987 the Hawaii-based fishery expanded with

technology adapted from the successfullongline swordfish fishery in the Atlantic Ocean, employing night

fishing with chemically-activated light sticks attached

near each baited hook. Expansion was encouraged by

new export markets for fresh tuna in Japan and for

swordfish in the U.S.

This fishery mostly operates west of 140oW, although

some fishing occurs to the east. By 1990, annual swordfish landings in Hawaii hadjumped from <40 t to >1,600 t

(Boggs and Ito, 1993), greatly exceeding landings on

the west coast of the U.S. In 1991, the longline catch of

swordfish totaled 4,500 t and represented 68% of total

landings in Hawaii. Landings exceeded 6,000 t in 1993

and were valued in excess of US$27 million (Ito et aI.,

1998; Skillman, 1998).

Hawaii-based longline vessels targeting only swordfish deployed 6--7 million hooks annually between 1991

and 1993. As the fishery expanded farther than 200 n.

mi. (370 km) from Hawaii, higher catch rates were

obtained to the north and east. Swordfish CPUE varied

between 10 per 1,000 hooks in the most productive

areas to less than 4 per 1,000 hooks nearer the Islands.

Longlining for swordfish in waters off California and

Mexico began prior to 1950. This daytime effort met

with little success, and was banned within California by

the CFGC in 1971, when harpoons were designated the

only legal commercial fishing gear for swordfish in

California.

In the fall of 1993, four longliners arrived in Ventura,

California, from the U.S. east-coast swordfish fishery

and began longline operations for swordfish in the

waters beyond 200 n. mi. They ranged north to 42°N

and westto at least 135°W (Vojkovich and Barsky, 1998).

These vessels had encouraging catches, and by the spring

180

170 A

:E 160 J: NMFS I- ,.-- Cl 150 , Z , W , -l 140 W

I-

< 130 Z

a:

w 120

< 110

100 1980 1982 1984 1986 1988 1990 1992 1994

S 6 0

o. B

5

C

W

a: 4 ::l

C/)

<

w

:;; 3

J:

C/)

u::: 2 NMFS u.

0 ~-~

a: , w ,

III ,

:;;

::l 0 Z 1980 1982 1984 1986 1988 1990 1992 1994

FISHING SEASON

Figure 4

(A) Mean alternate length ofswordfish and (B) smaller

coverage in number of swordfish measured by CDFG

market samplers and NMFS observers, 1981-93.

1980's to a high of 1,659 t in the 1985 season, and then

declined to 578 t by 1991. Landings subsequently increased to 941 t and 897 tin 1992 and 1993, respectively.

Shark landings are a significant product of this fishery,

and actually dominated the catch prior to 1983. Shark

landings have decreased steadily from a high of 1,000 tin

1981 to about 500 t in recent years (Hanan et aI., 1993).

The CDFG market sampling program began in 1981

(Bedford, 1987). Market samplers made routine visits

to primary California fish markets in San Diego, San

Pedro, Santa Barbara, Ventura, Morro Bay, Monterey,

Moss Landing, and the San Francisco Bay area. They

recorded weight and AL for swordfish carcasses delivered for sale.

Swordfish sampled during the 1981-93 seasons

(24,401 fish) measured 37-250 cm AL (mean 144 cm).

Annual mean ranged from 128 to 152 cm (Fig. 4).

Larger swordfish (150-160 cm AL) tended to be caught

off northern California, north of 35°N, with smaller

fish (130-145 cm AL) taken farther south (Hanan et

aI., 1993). At-sea measurements by NMFS observers

between 1990 and 1993 indicate that fish caught north
_____________ Holts & Sosa-Nishizaki: Swordfish Fisheries of the Eastern North Pacific Ocean 73

of 1994 another 15-20 vessels had departed the swordfish fisheries in the Atlantic and Gulf of Mexico for the

west coast. A few local vessels also converted to longline

gear, and by late 1994 nearly 30 California-based longline

vessels were fishing swordfish. They set from 300 to

1,300 hooks per set, depending on location and seasurface conditions. Like the Hawaiian fishery, they set

at night with light sticks and used large squid for bait.

In 1994 it was legal to land longline-caught swordfish

in California only if taken outside the EEZ. Preliminary

data indicate catch was 100 t for the last part of 1993

and nearly 543 t for 1994 (Barskyll). These fish ranged

between 73 and 226 cm AL, and averaged 63 kg dressed

weight (Vojkovich and Barsky, 1998).

In 1994 the CFGC approved a regulation to require

all longline vessels operating beyond the EEZ from

California ports to complete and submit logbooks of

daily fishing activity to the CDFG.

Recreational Fishery-The California recreational fishery for swordfish developed along with that for striped

marlin in southern California about the turn of the

century. Because of the size and strength of swordfish,

anglers still consider them one of the finest of all trophy game fish. Although highly prized by the recreational community, catch is insignificant compared to

the commercial catch in the same areas (Bedford and

Hagerman, 1983).

Swordfish in California was first listed as a game fish

in 1931, and required a sport fishing license issued by

the CDFG. Recreational anglers were allowed the use of

hand-held harpoons as well as sport rod-and-reel fishing tackle until 1971, when the CFGC restricted harpooning to the commercial fishery.

The rod-and-reel season for swordfish can begin as

early as May and continue through December, although

most fish are taken from July to September. Fishing

occurs from about Santa Barbara south at least to the

U.S.-Mexico border, and out to about 100 km. Most

fishing is done during the day from private boats targeting striped marlin. Swordfish is a minor component of

the sport catch of billfish in California, equalling only

1% or less of total marlin catch. Swordfish commonly

fin or bask at or near the water's surface in the area

between the Channel Islands and the coast ofsouthern

California. When anglers sight swordfish, they will offer

them live bait or artificial lures, although swordfish are

usually not receptive to bait presented while basking.

Catch records of swordfish are kept by the various

sportfishing clubs in California. The Balboa Angling

Club, San Diego Marlin Club, and the Tuna Club

(Avalon) are three of the major clubs where anglers

II Barsky, K. 1994. Marine Resources Div., CDFG, 530 E. Montecito

St., Ste. 104, Santa Barbara, CA 93103. Personal commun.

have their swordfish catches recorded and weighed.

Catches have averaged 3-4 fish per yr, except for 1969-

80, when they averaged 30.5 fish, and peaked in 1978

with 127 swordfish reported (Fig. 5). The increased

catches in 1969-80 corresponded to a similar increase

in landings from California's harpoon fishery, and may

have reflected a generally higher abundance of swordfish in southern California waters during that time.

Higher abundances were also reported for the northern anchovy, Engraulis mordax, and bluefin tuna, Thunnus

thynnus, during the same period (Squire, 1993). There

were four EI Nino episodes during this time, and it is

possible that increased catches occur in the years following EI Nino events (Coan et aI., 1998).

The whole weight of recreationally-caught swordfish

is less than the weight of fish taken in the harpoon

fishery. Of 45 swordfish weighed at major sport fishing

clubs between 1981 and 1992, the average whole body

weight was 107.5 kg (range 58.5-177 kg).

The only estimate of recreational fishing effort for

swordfish is from the NMFS's Billfish Angler Survey

(Squire and Muhlia-MeI04; SWFS02,l3). The survey requests individual angler data on fishing effort and catch

of all billfish and swordfish in the Pacific Ocean. The

survey cannot, however, identify effort directed specifically at swordfish. Effort is primarily directed at striped

12 Southwest Fisheries Science Center (SWFSC). 1994. 1993 Billfish Newsletter. U.S. Dep. Commer., NOAA, Nat!. Mar. Fish.

Serv., SWFSC, 9 p. Available from SWFSC, NMFS, 8604 La Jolla

Shores Dr., La Jolla, CA 92083.

13 Southwest Fisheries Science Center (SWFSC). 1995. 1994 Billfish Newsletter. U.S. Dep. Commer., NOAA, Nat!. Mar. Fish.

Serv., SWFSC, 12 p. Available from SWFSC, NMFS, 8604 LaJolla

Shores Dr., La Jolla, CA 92083.

140 r---------------------,

130

120

110

J: 100

en 90 u:

LL 80

70

l:l 60

50

Z 40

30

20

10

o~beo~~~~~!!,..,!!!:....lI....J...-...!.......J..!WJe...:w:.:\,&::~

1~1~1~1_1~1~1~1~1~1~1~

YEAR

Figure 5

Recreational swordfish catch by southern California anglers, as reported by major sportfishing clubs, 1940-93.
74 NOAA Technical Report NMFS 142

Table 4

Reported swordfish effort and catch from the Japanese

longline fishery within the Mexican EEZ, 1961-85.

Table 5

Reported swordfish landings and catch rates for fishing

vessels landing swordfish in the driftnet fishery of

Mexico, 1985-93.

Driftnet Fishery-In 1986 a small fleet of driftnet vessels appeared in northern Baja California. This fishery

was stimulated both by the reduction in longline permits and by the local abundance ofswordfish and other

marketable bycatch products, including several species

of large pelagic sharks. The number of vessels had

grown to 20 by 1990, and to 31 by 1993 (Table 5). These

vessels operate out of Ensenada and are similar in deMexico and joint-venture longline vessels fished coastal

waters. Fishing effort increased within Mexico's EEZ,

averaging 2.4 million hooks in 1981-83. In 1983, a 50-n.

mi. (93-km) sportfishing-only zone was established along

the coast of Mexico to protect billfish, swordfish, and

other popular species and to manage them for the

recreation and tourist industries. Longline permits were

not issued from mid-1984 until late 1985, and effort

decreased (Table 4). Longline permits were again issued in 1987 under stricter regulations, allowing only

about 15 fishing vessels within the EEZ. Operating under new permits, the Japanese/Mexican joint-venture

fleet increased fishing effort to 2.3 million hooks between 1986 and 1988 (Squire and Muhlia-Mel04). All

longline permits for swordfish, billfish, and tunas within

Mexico's EEZ were repealed in 1990. Longline fishing

operations have not been conducted since.

Most of the swordfish and marlin catches from the

joint-venture vessels were shipped to Japan and the

U.S., while other catches were canned or used in domestic markets. The most productive area was 20°-

27°N, east of 115°W.

Longline catches from Mexico'sjoint-venture fisheries peaked in 1982 with 9,275 swordfish (after a low ofl15

in 1978). Catches of swordfish subsequently increased to

at least 5,000 through 1988, before being terminated in

1990 (Squire and Muhlia-Mel04). CPUE fell dramatically

in 1983 and 1984, possibly due to the prohibition of

fishing within the 50-n. mi. sportfishing-only zone.

Catch

Year Hooks (number offish)

1961 74,700 36

1962 429,198 62

1963 502,124 76

1964 10,502,535 20,624

1965 12,797,567 12,235

1966 8,524,654 10,722

1967 7,169,512 6,363

1968 14,393,695 14,770

1969 7,679,938 10,667

1970 7,754,116 14,490

1971 7,269,733 12,092

1972 8,453,797 16,575

1973 8,883,135 12,593

1974 8,365,245 6,214

1975 4,316,486 5,749

1976 7,405,134 11,441

1977 1,844,845 2,997

1978 287,515 115

1979 699,044 233

1980 2,676,935 1,790

1981 1,569,164 3,657

1982 4,601,736 9,275

1983 3,538,430 4,537

1984 1,899,067 1,994

1985 62,984 7

marlin in southern California, and is directed at all billfishes

in Mexico. Effort estimates (catch per angler day) for

swordfish are therefore very low. Anglers fishing in southern California and northern Mexico reported swordfish

catches of 0-0.002 fish per day in 1990-93.

Mexico

Longline Fishery-In 1967, the Mexican government

increased its Exclusive Fishing Zone from 9 to 12 n. mi.

(from 17 to 22 km). Prior to this, foreign commercial

fishing for swordfish, billfish, and tunas was essentially

unrestricted beyond 17 km from the coast. Between

1967 and 1976, Mexico issued permits toJapan's longline

fleet to fish for swordfish, billfish, and tunas off northern and central Mexico, 22 km and further from the

coast. Fishing effort averaged 8.2 million hooks and

catch averaged over 11,000 swordfish per yr during that

10-yr period (Table 4).

Mexico established its EEZ in 1976 and withheld all

longline permits for swordfish, billfish, and tuna between 1977 and 1980, although some fishing continued. Between 1980 and 1984, only vessels registered in

Year

1986

1987

1988

1989

1990

1991

1992

1993

Landings

(metric tons)

286

471

385

407

661

831

552

372

Mean catch

(kg/day)

88.8

250.9

287.6

215.5

115.6

105.7

Vessels

2

3

11

14

21

28

29

31
_____________ Holts & Sosa-Nishizaki: Swordfish Fisheries of the Eastern North Pacific Ocean 75

40

en 35 >

0

Cl 30

Z

25 en

u::

u.

0 20

a:

w

lD 15 - :;:

=>

Z 10 Z

W 5 :;:

0

1988 1989 1990 1991 1992 1993

YEAR

...

1994

900

800

700

>: 600 all<: 500 Z

W 400

e

w 300 =>

c..

() 200

100

0 liIII

1988 1989 1990 1991 1992 1993 1994

YEAR

Figure 6

Total reported fishing effort for the driftnet fishery in

Mexico, 1988-94.

sign and size (18-25 m) to the U.S. driftnet vessels

operatingjust 100 km to the north. The nets are similar

in design to the U.S. drift nets, although they may be up

to 4.5 km long, whereas U.S. nets are limited to 1 n. mi.

(1.8 km). Operational procedures are virtually identical to those in the U.S.

The fishing season usually begins in the waters off

Ensenada in the fall and moves south to central Baja

California between 25° and 27°N during December

and January.

Swordfish landings from Mexican driftnet vessels were

first reported in 1986. They increased steadily to a high

of831 tin 1991, and averaged 535 tin 1988-93 (Table

5). The low catch in 1993 forced some fishing vessels to

look for alternate resources including coastal and pelagic sharks in the Gulf of California. The number of

vessels driftnetting for swordfish in the first half of 1994

fell to 16.

Total driftnet fishing effort for swordfish increased

from about 15 days per mo in 1989 to 20-30+ days per

mo in 1993 (Fig. 6). CPUE increased from about 100

kg/day in 1989 to over 800 kg/day by the end of 1990,

but has generally declined through 1994 (Fig. 7). The

best catches occur in the winter months of OctoberFebruary (Fig. 8)

A coperative program was established by commercial

driftnet fishermen operating out of Ensenada and scientists at Centro de Investigaci6n Cientifica y de

Educaci6n (CICESE), Ensenada, Mexico in 1992. Crew

members and scientists measured 1,412 swordfish during the 1992 and 1993 seasons (Sosa-Nishizaki et aI.,

1993). Most fish were taken from the southern Baja

California peninsula between 25° and 28°N. Mean length

(EFL) was 164 cm and fish length ranged from 60 to

Figure 7

CPUE by month for the driftnet fishery in Mexico,

1988-94. The break in 1989 represents missing data.

20

18

16

>: 14

a 12 ll<:

Z

<t 10 w

e 8

w

=> 6 c..

()

4

2

0 7 8 9 10 11 12 1 2 3 4 6

MONTH

Figure 8

CPUE by month for the driftnet fishery in Mexico,

1988-94.

245 cm. Larger fish were reported taken during March

and October, mostly in waters off Baja California Sur

(Sosa-Nishizaki et aI., 1993).

Recreational Fishery-Recreational fishing for marlin

around the Baja California peninsula is extremely popular world-wide. Angling for swordfish in these waters is

opportunistic and incidental to the large marlin catch.

Although the recreational catch of swordfish is unreported, the greatest catches of swordfish appear to be

off Guaymas and Mazatlan. Swordfish, like marlin, are

included under the existing regulations which allow a

maximum catch of one billfish per day.
76 NOAA Technical Report NMFS 142

Acknowledgments

We thank AI Coan, Fred Julian, Doug Prescott, and

Rand Rasmussen for assistance in data preparation and

analysis of the U.S. fisheries. We also thank Kristine

Barsky, Norm Bartoo, AI Coan, Gerard DiNardo, and

Fred Julian for their valued reviews of the manuscript.

Roy Allen and Ken Raymond prepared the figures.

Literature Cited

Bartoo, N. W., and A. L. CoanJr.

1989. An assessment of the Pacific swordfish resource. In R.

H. Stroud (ed.), Proceedings of the 2nd International Billfish Symposium, Kailua-Kona, HI, 1-5 August 1988. Part 1,

p. 137-151. National Coalition for Marine Conservation,

Savannah, GA.

Bedford, D. W.

1987. Shark management: a case history of the California

pelagic shark and swordfish fishery. In S. Cook (ed.),

Sharks: an inquiry into biology, behavior, fisheries and use,

p.161-171. Oregon State Univ. Ext. Ser., Portland.

Bedford, D. W., and F. B. Hagerman.

1983. The biJlfish fishery resource of the California

current. Calif. Coop. Oceanic Fish. Invest. Rep. 24:70-78.

Boggs, C. H., and R. Y Ito.

1993. Hawaii's pelagic fisheries. Mar. Fish. Rev. 55(2):69-82.

Cailliet, G. M., D. B. Holts, and D. Bedford.

1993. Review of the commercial fisheries for sharks on the

west coast of the llnited States. In]. Pepperell,]. West,

and P. Woon (eds.), Shark conservation, p. 13-29. Proceedings of an international workshop on the conservation

of elasmobranchs, Taronga Zoo, Sydney, Australia, 24 February 1991. Zoological Parks Board of New South Wales,

P.O. Box 20, Mosman, SW, 2088 Australia.

California Department of Fish and Game (CDFG).

1995. Fish and Game Code.

Carey, F. G., and B. H. Robison.

1981. Daily patterns in the activities of swordfish, Xiphias

gladius, observed by acoustic telemetry. Fish. Bull.

79(2) :277-292.

Coan, A. L.,Jr., M. Vojkovich, and D. Prescott.

1998. The California harpoon fishery for swordfish, Xiphias

gladius. In 1. Barrett, O. Sosa-Nishizaki, and N. Bartoo

(eds.), Biology and fisheries of swordfish, Xiphias gladius,

p.37-49. U.S. Dep. Commer., NOAA Tech Rep. NMFS A2.

Food and Agriculture Organization.

1986-93. FAO yearbook of fishery statistics: catches and landings, vol. 68-71. United ations, Rome.

Hanan, D. A., D. B. Holts, and A. L. eoan Jr.

1993. The California driftnet fishery for sharks and swordfish, 1981-82 through 1990-91. Ca. Dep. Fish Game Fish

Bull. 175, 95 p.

Herrick, S. F.,Jr., and D. Hanan.

1988. A review of California entangling net fisheries, 1981-

1986. U.S. Dept. Commer., NOAA Tech. Memo. NMFS

SWFC-108, 38 p.

Huppert, D. D., and M. Odemar.

1986. A review of California limited entry programs. In N.

Mollett (ed.), Fishery access control programs worldwide:

proceedings of the workshop on management options for

the, orth Pacific longline fisheries, p. 301-312. Alaska

Sea Grant Rep. 86-4.

Ito, R. Y, R. E. Dollar, and K. E. Kawamoto.

1998. The Hawaii-based longline fishery for swordfish, Xiphias

gladius. In 1. Barrett, O. Sosa-Nishizaki, and N. Bartoo

(eds.), Biology and fisheries ofswordfish, Xiphias gladius, p.

77-88. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 142.

Julian, F., and M. Beeson.

1998. Estimates of marine mammal, turtle, and seabird mortality for two California gillnet fisheries: 1990-1995. Fish.

Bull. 96(2) :271-284.

Lennert, C., S. Kruse, M. Beeson, and]. Barlow.

1994. Estimates of incidental marine mammal bycatch in California net fisheries forJuly through December, 1990. IntI.

Whaling Comm. Spec. Issue 15:449-463.

"'\iyabe, ., and W. H. Bayliff.

1987. A review of the Japanese longline fishery for tunas and

billfishes in the eastern Pacific Ocean, 1971-1980. InterAm. Trop. Tuna Comm. Bull. 19(1):1-163.

Nakamura, 1.

1985. Billfishes of the world. FAO Fish. Synop. 125, vol. 5,

65 p.

Nakano, H., and W. H. Bayliff.

1992. A review of the Japanese longline fishery for tunas and

billfishes in the eastern Pacific Ocean, 1981-1987. InterAm. Trop. Tuna Comm. Bull. 29(5):187-355.

Sakagawa, GT.

1989. Trends in fisheries for swordfish in the Pacific

Ocean. In R. H. Stroud (ed.), Planning the future of billfishes. Part I, p. 61-80. Proceedings of the 2nd international billfish symposium, Kailua-Kona, Hawaii, 1-5 August

1988. atl. Coalition Mar. Conserv., Savannah, GA.

Sakagawa, G. T., and R. R. Bell.

1980. Swordfish, Xiphias gladius. In R. S. Shomura (ed.),

Summary report of the billfish stock assessment workshop,

Pacific resources, p. 43-55. U.S. Dep. Commer., NOAA

Tech. Memo. NMFS SWFC-5.

Skillman, R. A.

1989. Status of Pacific billfish stocks. In R. H. Stroud (ed.),

Proceedings of the 2nd international billfish symposium,

Kailua-Kona, HI, 1-5 August 1988. Part 1, p. 179-195. Natl.

Coalition Mar. Conserv., Savannah, GA.

1998. Central Pacific swordfish, Xiphias gladius, fishery development, biology, and research. In 1. Barrett, O. Sosa-

\Iishizaki, and . Bartoo (eds.), Biology and fisheries of

swordfish, Xiphiasgladius, p. 101-124. U.S. Dep. Commer.,

NOAA Tech. Rep. NMFS 142.

Sosa-:\ishizaki, 0., P. R. De la Rosa, L. R Castro, C. M. Grijalva, and

V..J. De la Rosa.

1993. Reporte anual 1992 del proyecto; estudio biologico

pesquero del pez espada (Xiphias gladius) y otras expecies

de picudos (marlines y pez vela). Clave Cent. Invest. Cient.

Educ. (CICESE) CTECT 9,306, 44 p.

Sosa-Nishizaki, 0., and M. Shimizu.

1991. Spatial and temporal CPUE trends and stock unit inferred from them for the Pacific swordfish caught by Japanese tuna longline fishery. Bull. Nat. Res. 1nst. Far Seas

Fish. 28:75-90.

Squire,]. L.,Jr.

1993. Relative abundance of pelagic resources utilized by the

California purse-seine fishery: results of an airborne monitoring program, 1962-90. Fish. Bull. 91 (2):348-361.

\'ojkovich, M., and K. Barsky.

1998. The California-based swordfish longline fishery operating beyond the U.S. Exclusive Economic Zone. In 1. Barrett,

O. Sosa-Nishizaki, and N. Bartoo (eds.). Biology and fisheries of swordfish, Xiphias gladius, p. 147-152. U.S. Dep.

Commer., NOAA Tech. Rep. NMFS 142.
The Hawaii-based Longline Fishery for Swordfish, Xiphias gladius

RUSSELL Y. ITO, ROBERT A. DOLLAR, and KURT E. KAWAMOTO

Honolulu Laboratory

Southwest Fisheries Science Center

National Marine Fisheries Service, NOAA

2570 Dole Street

Honolulu, Hawaii 96822-2396

ABSTRACT

This report profiles the Hawaii-based domestic longline fishery for broadbill swordfish,

Xiphias gladius. This fishery grew rapidly during 1989-91, mostly due to the arrival and

participation of recen t entrants. Swordfish became the dominan t species landed by Hawaii's

fisheries in 1990 and the most important in terms of ex-vessel revenue in 1991. In 1993, 88

longliners fishing for swordfish logged 650 trips, fished 7,533 days, set 6.6 million hooks,

and landed 6,000 metric tons ofswordfish with an estimated ex-vessel value of$26.5 million.

Swordfish is delivered as a fresh product. Most swordfish landed in Hawaii is exported to

mainland U.S. cities by air freight.

Introduction

Longlining for broadbill swordfish is a relatively new

fishery in Hawaii. In 1988, the fishing vessel Magic Dragon

began experimentally targeting swordfish using techniques based on the Florida longline fishery. During

1989, a few Hawaii tuna longline and lobster vessels

experimented with longlining for swordfish for at least

part of the year. Good catches by those vessels led to

increased effort as well as national attention (Freeman,

1989).

Domestic U.S.longline vessels from the GulfofMexico

(Gulf vessels) were among the first to join the growing

longline fleet operating from Hawaii (Kawamoto et

al. I ). These new participants initially targeted yellowfin

and bigeye tuna, but in early 1990 some vessels began

targeting swordfish. Longlining for swordfish by many

of the Gulf vessels was discouraging at first due to poor

catches and the high cost of bait and light sticks. Catches

ofswordfish increased as these fishermen became more

experienced.

I Kawamoto, K. E., R. Y. Ito, R. P. Clarke, and A. A. Chun. 1989.

Status of the tuna longline fishery in Hawaii, 1987-88. U.S. Dep.

Commer., NOAA, Natl. Mar. Fish. Serv., Southwest Fish. Cent.

Admin. Rep. H-89-IO, 34 p. Honolulu Lab., NMFS, 2750 Dole St.,

Honolulu, HI 96822-2396.

The decline in Atlantic swordfish landings, catch rate,

and average fish size in the late 1980's (Berkeley, 1989;

Pollack, 1990) as well as prospects of good swordfish

catches in Hawaii influenced many Atlantic swordfish

longline fishermen to relocate to Hawaii. These experienced fishermen from the U.S. east coast began arriving in Hawaii in early 1990. A few longline vessels from

the west coast also entered the fishery at the same time

as Gulf longliners and east coast longliners. In addition, many tuna longline vessels were able to switch to

targeting swordfish with minor modification to gear

and operations.

By the end of 1990, swordfish were the dominant

species landed in Hawaii (lto2) with landings (by weight)

exceeding those of any other species. By 1991, the

monofilament main line, hydraulic reel, and other techniques ofthe swordfish fishery were widespread throughout the longline fleet. The Western Pacific Regional

Fishery Management Council (WPRFMC) passed an

emergency rule in October 1990 to arrest the rapid

growth of the longline fishery. The emergency rule was

replaced by a 3-yr moratorium on new entry in April

2 Ito, R. Y. 1992. Western Pacific pelagic fisheries in 1991. U.S.

Dep. Commer., OAA, atl. Mar. Fish Serv., Southwest Fish. Cent.

Admin. Rep. H-92-15, 38 p. Honolulu Lab., SWFSC, NMFS, 2570

Dole St., Honolulu, HI 96822-2396.

77
78 NOAA Technical Report NMFS 142

1991. The moratorium was to provide a period ofstability during which data could be collected for assessing

the impacts of the increased longline effort on smallboat pelagic fisheries in Hawaii. The longline fishery is

now under a limited-entry plan.

Despite the initial rapid growth, participation ofvessels in the longline fishery declined slightly in 1992-93.

Increasing operational costs from longer trips and lower

swordfish prices were the primary reasons for decreased

activity. Most of the longliners exiting the fishery were

vessels originally from the Gulf and west coast. However, longlining for swordfish is still the largest commercial fishery in Hawaii.

Hawaii has gained the reputation of being an important source of fresh swordfish for U.S. mainland markets. Characteristics and operations of this segment of

the Hawaii-based longline fleet, catch per unit effort

(CPUE), landings, size of fish, and the swordfish market are described here, and data sources and problems

reviewed. We also discuss trends and outlook for this

fishery.

Data and Methods _

Monitoring of longline fleet activity in Hawaii is conducted primarily by the Fisheries Monitoring and Economics Program (FMEP) of the National Marine Fisheries Service (NMFS) Honolulu Laboratory. Hawaiibased domestic longline fishing vessels either target

swordfish or bigeye and yellowfin tuna, or follow a

mixed-species target strategy. Trip types3 contributing

substantial amounts of swordfish are from longliners

targeting either swordfish or mixed species. Longliners

targeting tunas make incidental catches of swordfish

and contribute only a small fraction of total swordfish

catch (Yoshida, 1974; Kawamoto et al. I ). Therefore,

only data from swordfish and mixed-target longline

trips are used in this report. The data originate from

shore-side samples, federal longline logbooks, federal

longline permit applications, voluntary observer reports,

and personal interviews.

Estimates of landings were derived from shore-side

sampling conducted by FMEP in conjunction with the

Hawaii Division of Aquatic Resources (HDAR) during

1989-93, and from a combination of this sampling and

Federallongline logbooks for 1991-93. In the sampling

program, weights ofindividual fish were recorded along

3 Criteria for determining trip type from logbook data are described

in Dollar, R. A. 1994. Annual report of the 1993 longline western Pacific longline fishery. U.S. Dep. Commer., NOAA, Nat!.

Mar. Fish. Serv., Southwest Fish. Cent. Admin. Rep. H-94-06, 38

p. Honolulu Lab., SWFSC, NMFS, 2750 Dole St., Honolulu, HI

96822-2396.

with observations on degree of processing or damage.

Landed swordfish have typically been headed, gilled,

and gutted. The sample weight of each fish was raised

to an estimated whole weight. Raising factors, which

were species-specific, varied from 1.1 to 1.5 depending

on degree of processing or damage. The raising factors

were based on rates used by the seafood industry in

Hawaii.

Numbers of vessels and trips were derived from the

shore-side sampling data for 1989-90 and from federal

logbooks for 1991-93. The federal logbooks were also

the source of detailed information on fishing operation: effort (i.e. vessels, trips, sets, hooks), fishing area,

and CPUE (number caught per 1,000 hooks).

Landings for 1992-93 were estimated as the product

of the number of each species kept, from logbook data,

and the corresponding average weight from shore-side

sample data (It02). Logbook data were not used to

estimate landings in 1991 due to a number of problems

with implementation of the logbook program in the

first year (Dollar4 ). Shore-side sample data were used

for 1991. Logbook data were compared for accuracy

with the shore-side data for total numbers and species

iden tification. Proper species identification for marlins

and total number kept were inaccurate during the first

year (1991). Accuracy in total numbers improved in

1992 and 1993, but improper species identification,

especially for marlins, is an ongoing problem requiring

education of fishermen. 5

Vessel characteristics were summarized from the fishing permit applications of vessels actively longlining for

swordfish. All domestic longline vessels based in Hawaii

have been required to have a federal longline fishing

permit since 1990. Gear and technology, fishing procedures, processing and storage of the catch, and market

information were derived from voluntary observer reports (Dollar6; Dollar et a1. 7) and personal interviews

with industry personnel.

4 Dollar, R. A. 1992. Annual report of the 1991 longline western

Pacific longline fishery. U.S. Dep. Commer., NOAA, Nat!. Mar.

Fish. Serv., Southwest Fish. Cent. Admin. Rep. H-92-11, 26

p. Honolulu Lab., NMFS, 2750 Dole St., Honolulu, HI 96822-

2396.

5 Proper marlin identification has been encouraged by the distribution of informational material by FMEP staff to vessel operators.

6 Dollar, R. A. 1991. Summary ofswordfish longline observations

in Hawaii, July 1990-March 1991. U.S. Dep. Commer., NOAA,

Nat!. Mar. Fish. Serv., Southwest Fish. Cent. Admin. Rep. H-91-09,

13 p. Honolulu Lab., NMFS, 2750 Dole St., Honolulu, HI 96822-

2396.

7 Dollar, R. A., R. Y. Ito, K. E. Kawamoto, and K. C. Landgraf. 1991.

Summary of swordfish longline observations in Hawaii,July-October 1990. U.S. Dep. Commer., NOAA, Nat!. Mar. Fish. Serv.,

Southwest Fish. Cent. Admin. Rep. H-91-03, 10 p. Honolulu Lab.,

NMFS, 2750 Dole St., Honolulu, HI 96822-2396.
______________________ Ito et aI.: Hawaii-based Longline Fishery for Swordfish 79

The Fishery _

Vessel Characteristics

Hawaii-based longliners that

fished for swordfish at least 2

yrduring 1991-93 (N=93) were

typically steel- or fiberglass-hull

vessels with a mean age of 11

and 12 yr respectively (Table

1). Most vessels were 20-24 m

in length, though they ranged

from 8 to 30 m (mean = 20 m;

Fig. 1). Steel-hulled vessels were

slightly larger than fiberglasshulled vessels. All vessels had

diesel engines, with an average

of 460 horsepower (hp; range

200-700 hp).

Fishing Gear and Technology Figure 1

A typical Hawaii-based swordfish longline vessel.

Longlining for swordfish employs hundreds of branch lines

attached to a single main line set horizontally

below the ocean's surface. The monofilament main

line is stored on a large hydraulic-powered reel

(Fig. 2A); over 80 km of main line can be stored

on one reel. Larger vessels may also have an additional main-line reel to store spare main line or to

sometimes set more than one reel of main line.

Monofilament branch lines are stored in plywood

boxes or plastic bins (Fig. 2B). Alternatively, small

spools (hand carts) are sometimes used to store

monofilament branch lines and float lines (Fig.

2C). The most commonly used float is an orange

high-density foam buoy (Fig. 2D). Large polyethylene floats, floats with radar reflectors, radio buoys,

and strobe-light buoys are also used. These buoys and

floats support the main line and aid in locating the

gear. Gear characteristics are detailed in Table 2. With

minor modifications to gear and techniques, vessel operators can set gear to target swordfish, bigeye tuna, or

yellowfin tuna.

Many of the larger vessels use temperature probes,

satellite or global positioning system (GPS) navigation,

automated track plotting, satellite weather imaging, and

communications systems to aid in locating fish. However, some longliners take a low-technology approach

to keep capital and operating costs down.

Longline gear is deployed by spooling the main line

off the reel while maintaining a slight tension on the

drag. A few vessels are equipped with a line shooter to

maintain tension on the main line from the reel to the

Table 1

Characteristics of Hawaii-based swordfish longline vessels

(from lational Marine Fisheries Service, Pacific Area Office

permit data).

Length (m)

Mean age

Hull type Number (yr) Mean Maximum Minimum

Steel 84 11 23 30 16

Fiberglass 9 12 19 24 8

point where it leaves the boat. The depth of fishing is

controlled by a number of factors including branch

line and float line length, weights attached to branch

lines, length ofmain line set between floats, and amount

oftension or slack in the main line. The high frequency

of floats used in longlining for swordfish keeps the

main line close to the surface. The shape of the catenary formed by the main line is not as deep as that

formed when longline gear is set to target bigeye tuna

(Suzuki and Warashina, 1977; Berkeley et al., 1981;

Sakagawa et al., 1987; Boggs, 1992).

Light sticks greatly increase efficiency in catching

swordfish (Freeman, 1989) either by attracting swordfish directly or by attracting swordfish prey (Berkeley et

al., 1981). A chemical light stick is attached to the

branch line about 2 m above the hook (Dollar6). Chemical light sticks glow for up to 12 hr.
~j-'f,.

.. tl

1i'

I

00

Q

z

I"l

::r

:.

I"l

e:.

."

o

"'l

...

z

a:::

;;l

....

Nl

Figure 2

Main components ofswordfish longline gear: (A) hydraulic reel with main line, (B) leader bin with branch lines, (C) hand cart with branch lines, and (D) orange

high-density foam buoy.
_______________________ Ito et al.: Hawaii-based Longline Fishery for Swordfish 81

Table 2

Characteristics of swordfish longline gear used on Hawaii-based longline vessels (Dollarl

).

A

1 Dollar, R. A. 1991. Summary ofswordfish longline observations in Hawaii, July 1990-March 1991. U.S. Dep.

Commer., NOAA, Nat!. Mar. Fish. Serv., Southwest Fish.

Cent. Admin. Rep. H-91-09, 13 p. Honolulu Lab., NMFS,

2750 Dole St., Honolulu, HI 96822-2396.

2 Reference to trade names or commercial firms does not imply

endorsement by the National Marine Fisheries Service, OAA.

Gear

Lines

Main line length

Main line diameter

Estimated distance

between floats

Branch line length

Branch line diameter

Hooks

Hooks per set

Lightsticks

Bait

Characteristics

Monofilament stored on hydraulic

reels

30-80 km

3.0-4.0 mm

90-160 m

13 m

2.1 mm

8/0-10/0 Mustad2

Range 450-1800, mean 724

Cyalume2 (break-activated) and

World Plastics (thaw-activated)

Argentine shortfin squid,

fllex argentinus

B

Figure 3

(A) East coast and (B) Gulfstyle longline gear configurations used by Hawaii-based longliners fishing for swordfish.

Large high-quality Argentine shortfin squid, lllex

argentinus, was the preferred bait, with whole squid hooked

in the mantle. Dyes were sometimes used to color the

squid in an attempt to make them more appealing.

Longline gear, technology, and fishing techniques

used by the Hawaii-based longline fishery for swordfish

originate from the U.S. east coast and the Gulf longline

fisheries. The major differences between the east coast

and Gulfstyles are the number of hooks set between floats

and the frequency at which the light sticks are attached

(Fig. 3). The east coast style of swordfish longlining is

similar to the Florida style, in which 2-3 hooks are set

between floats (Berkeley et a\., 1981); a light stick is attached to each branch line with a rubber band. The Gulf

style is similar to the method oflonglining for yellowfin in

the Gulf of Mexico (Wilson, 1988). The Gulf longliners

set about 3-5 hooks between floats and attach one light

stick for every 3-5 branch lines. Both styles of gear configuration are utilized by Hawaii-based longliners fishing

for swordfish, and both styles are effective.

Fishing Area

Most effort by Hawaii-based longliners fishing for swordfish occurred north of the Hawaiian Islands. Fishing

extended from 50 mi. off the main and northwestern

Hawaiian Islands to far outside the Hawaii Exclusive

Economic Zone (EEZ), with some trips in excess of

2,000 mi. from Honolulu. The northern range of the

fishery approached 500 N, the northernmost distribution of swordfish as described by Bartoo and Coan

(1989). The fishery extended latitudinally from 5° to

48°N and longitudinally from 175°E to 1400W (Fig. 4).

In general, area fished expanded westerly from 1991

through 1993.

As a vessel approaches the fishing grounds, fishermen look for frontal zones where a rapid change in seasurface temperature occurs (Sakagawa, 1989), and exploratory fishing for swordfish is focused in these areas.

Concentrated fishing follows if a productive area is

located. Fishing activity is also affected by moon phase.

Fishermen have remarked that swordfish catch is better

near the full moon, so more fishing occurs then.

The most seaworthy Hawaii-based longline vessels

have the capability to fish in the North Pacific throughout the year. However, the majority of longliners fishing for swordfish traveled farther to fishing grounds

during the summer, when seas were calm, and tended

to fish closer to the Hawaiian Islands in the fall and

winter, when seas become rough. Many longliners also
82 NOAA Technical Report NMFS 142

fish close to Hawaii during the spring months, when

swordfish abundance near the Islands exhibits a seasonal peak (Uchiyama and Shomura, 1974; DollarS).

The high price and increased abundance of bigeye

tuna influences many vessel operators to target tunas

during the winter season.

Figure 4

Geographic area fished by the Hawaii-based longline

fleet fishing for swordfish, 1991-93.

Activity

Gear preparation for setting longline.

Start setting gear (start time varies daily).

End set and clean up (approximately 4 hr to

set gear).

Soak gear overnight and sleep.

Search for light/radio buoy.

Haul gear, process and store fish (approximately 8 hr to haul gear; however, the time to

complete hauling gear depends on amount of

gear set, number of fish caught, and tangles

and breakage in the main line).

2330-0500

0500-0600

0600-1430

1630-1730

1730-1930

2130-2330

Time

Table 3

Typical operating schedule of a Hawaii-based longline

vessel fishing for swordfish.

8 Dollar. R. A. 1993. Annual report of the 1992 longline western

Pacific longline fishery. U.S. Dep. Commer., NOAA, Nat!. Mar.

Fish. Serv., Southwest Fish. Cent. Admin. Rep. H-93-12, 25

p. Honolulu Lab., SWFSC, NMFS, 2570 Dole St., Honolulu, HI

96822-2396.

Fishing Procedures

Swordfish longline gear is usually set during the late

afternoon or evening (Table 3). Setting the gear takes

about 4-6 hr depending on the amount of gear and sea

conditions. Typically, about 48-64 km of longline gear

is set. After setting the gear the vessel either idles near

the end of the longline or travels back to the starting

point of the set. The boat maintains visual and radio

contact with the longline by attaching a strobe buoy

and a radio buoy at the end of the gear. The longline

gear is soaked overnight for 6-10 hr.

Retrieval begins early in the morning. The vessel

approaches and hauls aboard the strobe and radio buoys.

The main line is tied to the main line reel and the haulback process begins. Branch lines are coiled in the bins

or on hand carts. The vessel slows down to haul fish

aboard. Fish are processed and iced down soon after

they are caught. Bait for the next day of fishing is

removed from the freezer and allowed to thaw midway

through the haul-back process. Retrieval time can vary

considerably depending on number of fish caught and

on sea conditions.

1993

1992

1991

160'W 140"W

SO'N

40'N

30'N

20'N

10'N

O'

SO'N

40'N

30'N

20'N

W'N

O'

SO'N

40'N

30'N

20'N

10'N

O'

180'
_______________________ Ito et al.: Hawaii-based Longline Fishery for Swordfish 83

Figure 6

Trips by Hawaii-based longline vessels fishing for swordfish, 1989-93.

9 The area around the northwestern Hawaiian Islands was closed due to

interactions with the Hawaiian monk seal, Monachus schauinslandi,

and near-shore areas around the main Islands were closed due to gear

conflicts with small trolling and handline vessels (Western Pacific

Fishery Management Plan amendments #3 and #5 respectively).

mixed species including swordfish also decreased from

8,331 in 1991 to 7,533 in 1993. However, sets inside the

Hawaii EEZ decreased dramatically, while sets outside

increased (Fig. 7). The main reasons for the shift in fishing

areas were higher swordfish catch rates outside the EEZ,

and emergency federal regulations implemented in 1991,

which closed areas around the Hawaiian Islands?

1991 1992 1993

Year

120

90

til

a.

E

'0 60 Q;

.0

E

:::l

Z

30

Swordfish are headed, gutted, and finned immediately

upon capture. The kidneys are removed and the visceral cavity scraped to remove any remaining slime or

tissue. In general, marlins, tunas, and other fishes are

left whole. Tunas and other pelagic species deteriorate

in quality faster than swordfish, so bycatch is sometimes

released alive or discarded early in the trip. Another

reason for releasing or discarding bycatch is to conserve space for swordfish in the fish hold.

Most vessels have well-insulated, refrigerated fish holds.

In addition, some have on-board saltwater ice makers. Saltwater ice, which is colder than freshwater ice, is used to

chill and store the swordfish. To prevent tunas and other

bycatch from freezing, they are packed in freshwater ice.

The number of Hawaii-based longliners that fished for

swordfish increased more than 10-fold during 1989-93,

from 11 in 1989 to a high of 114 in 1991, and then

decreased to 88 vessels in 1993 (Fig. 5). Of 93 longline

vessels that fished for swordfish in 1991-93, 50 were

originally from the Gulf, 18 from the east coast, 15 from

the west coast, and 10 were Hawaii longline vessels.

Number of Vessels

Processing and Storage of the Catch

Effort

Trips and Sets

The number ofswordfish-targeted and mixed-target trips

increased dramatically from an estimated 43 in 1989 to

1,115 in 1991, and then declined to 650 in 1993 (Fig. 6).

The total number of sets directed at swordfish and at

-Total

- - Outside EEZ .. -Inside EEZ

10000

-------

..... ....

------

1991 1992

Year 1991 1992 1993

Year

1989 1990

7500 (f)

Q)

til (f)

Q;

til -0 til 5000 '"

> Q;

'0 ..0

E

Q; J

Z .0

E 2500 :::l

Z

Figure 5

Hawaii-based longline vessels fishing for swordfish,

1989-93.

Figure 7

Sets made by Hawaii-based longline vessels fishing for

swordfish, 1991-93, inside and outside the Hawaii EEZ.
84 NOAA Technical Report NMFS 142 _

3000

8.0-

-Total

- - Outside EEZ •• ·Inside EEZ

- - - --- . , ,. 4.0-

2.0

.>0::

a

en 6.0

-------- a

..r:::

-a

en

c

,g

::2

CIl

Qj

CIl

Q)

D

E

:::l

Z

23412341234

1991 1992 1993

Figure 8

Quarterly number ofsets made by Hawaii-based longline

vessels fishing for swordfish inside and outside the

Hawaii EEZ, 1991-93.

1991 1992

Year

Figure 9

Hooks set by Hawaii-based longline vessels fishing for

swordfish inside and outside the Hawaii EEZ, 1991-93.

-Outside EEZ

- -Total

•• Inside EEZ

Figure 10

Hawaii swordfish catch per 1,000 hooks inside and

outside the Hawaii EEZ, 1991-93.

----------- --

1992 1993

Year

........

1991

5.0-

15.0

10.0

<u

a.

en

a

a

..c

U

c

<Il

en

:::J

a

..c Hooks

The total number of hooks set by longliners fishing for

swordfish in 1991 was 7.1 million. Hooks set decreased

to 6.5 million in 1992 and remained about the same in

1993 (Fig. 9). The decreased effort was a direct result of

fewer vessels fishing in 1992 and 1993. Slightly more

hooks were set inside than outside the EEZ in 1991, but

more hooks were set on the high seas outside the EEZ

in 1992 and 1993. The average number of hooks set per

vessel per day changed little during 1991-93 (range:

842 hooks in 1992 to 868 hooks in 1993).

Average number ofsets per trip increased from 7.5 in

1991 to 11.6 in 1993. Sets per trip ranged from 5 to 27.

The distance covered on trips and the number of fishing days increased. Transit time to the fishing grounds

varies throughout the year, increasing during spring

and summer (10-12 days) and decreasing during winter (5-7 days). The number of sets was highest during

the second quarter and lowest in the third or fourth

quarter of each year (Fig. 8).

CPUE _

Swordfish CPUE (catch per 1,000 hooks for swordfish

and mixed-target trips) rose from 9.0 in 1991 to 11.9 in

1993 (Fig. 10). Swordfish catch rates were much higher

outside than inside the EEZ. However, fishermen commented that they had to travel farther from Hawaii to

sustain high catch rates.

Swordfish CPUE varied considerably throughout the

year (Fig. 11). CPUE outside the EEZ was consistently

higher than CPUE inside; it peaked in the first quarter

and was lowest in the second or third quarter. CPUE

within the EEZ was highest in the second quarter and

lowest in the fourth quarter. Peak CPUE outside the
_______________________ Ito et al.: Hawaii-based Longline Fishery for Swordfish 85

1989 1990

234

1993

4 1 2 3 4

1992

2

1991

20. -Outside EEZ 800

.. -Inside EEZ

<I) 15.0 6000 0

0

.<: I/J 0 C 0

B 10.0

(;; " 400

'. .;: c- O; .<: :2 ..." 5. U 2000

Figure II

Quarterly swordfish catch per 1,000 hooks by Hawaiibased longline vessels, 1991-93.

Figure 12

Swordfish landings by Hawaii-based longline vessels

fishing for swordfish, 1989-93.

Figure 13

Species composition of landings by Hawaii-based

longliners fishing for swordfish, 1989-93.

marlin (3.3%) and Pacific blue marlin (2.8%). Other

marketable species, mainly mahimahi (dolphin), moonfish, ono, pomfrets, and sharks, contribute a small portion of the landings (all species combined, 6.1 %).

Sharks are the largest portion (by number) oflongline

catch in Hawaii (Dollar4,8.ll), but relatively few are

landed. The estimates of sharks landed were of those

sold fresh, and do not include sharks that had been

finned. Mako and thresher sharks were sold as a fresh

product but nearly all blue and other sharks were released. Since shark fins were not observed in the shoreside sample, the volume and value of shark fins could

not be estimated. The names of pelagic species

EEZ occurred one quarter earlier than peak CPUE

within the EEZ throughout 1991-93.

Landings

Swordfish

It has been estimated that Hawaii-based longliners accounted for about 15% of the Pacific-wide harvest and

about 42% of the total eastern central Pacific catch

(WPRFMCIO). Hawaii-based longline landings of swordfish increased dramatically between 1989 and 1992. In

1990, swordfish became the dominant species landed in

Hawaii's pelagic fisheries (lto2). Estimated landings of

swordfish by longliners fishing for swordfish increased

from about 200 tin 1989 to 6,000 tin 1993 (Fig. 12). Much

of the increase during the past 3 yr is a result offishermen

acquiring more knowledge of the fishery, modifying fishing techniques, and expanding the area offishing.

Species Composition

The swordfish component of total longline landings

(by weight) ranged from 60% in ] 989 to 74% in 1992,

and averaged 68% over the 5-yr period (Fig. 13). Tunas

were the next largest component of total landings. Bigeye tuna (10.8%), yellowfin tuna (6.0%), and albacore

(2.4%) were the most important tuna species represented. Marlin landings were composed mostly ofstriped

Swordfish (67.9%)

Miscellaneous

Tunas (19.6%)

(6.5%)

10 Western Pacific Regional Fishery Management Council. 1994.

Amendment 7 to the Fishery Management Plan for the Pelagic

Fisheries of the Western Pacific Region. WPRFMC, 1164 Bishop

St., Rm. 1405, Honolulu, HI 96813.

II Dollar, R. A. J994. Annual report of the 1993 western Pacific

longline fishery. C.S. Dep. Commer.. NOAA, ;\Iatl. Mar. Fish.

Serv., Southwest Fish. Cent. Admin. Rep. H-94-06, 38

p. Honolulu Lab., SWFCS, , MFS, 2750 Dole St., Honolulu, HI

96822-2396
86 NOAA Technical Report NMFS 142

commmonly caught by longliners fishing for swordfish

are listed in Table 4.

Size of Fish

1990. The modes of these distributions were below the

71-80 kg size class in all years except 1993, when a

mode was observed at 81-90 kg. The modal peaks shifted

by 1-2 size classes each year.

Small and badly damaged (i.e. eaten by sharks or whales)

swordfish have little or no commercial value and are

often discarded at sea or given away to friends at port

upon the vessel's return. Data on these fish were not

available based on the current sampling protocol, and

therefore the shore-side sample was biased towards a

higher number of larger, more marketable fish.

Mean weight of whole swordfish showed a slight net

increase in 1989-93 (Table 5), increasing from 67.0 kg

in 1989 to 81.3 kg in 1992, then decreasing to 80.0 kg in

1993. Weights of individual fish were broadly distributed, with standard deviation exceeding 45 kg. Swordfish landed in 1989-93 (Fig. 14) appeared to have a

higher frequency of large fish than those landed in

1987-88 (It02), prior to the exploitation ofswordfish by

Hawaii-based longliners. The weight-frequency distributions were bi-modal in most years, but uni-modal in

Market _

U.S. swordfish consumption increased dramatically during the early 1980's (Lipton, 1986). Swordfish landed

in Hawaii are either sold by open auction or brokered

by Hawaii seafood dealers; almost all are exported to

the U.S. mainland. Swordfish are chilled with gel ice

packs placed in the gut cavity, individually wrapped in

plastic bags, packed in insulated air freight containers

(LD-3's), and exported via air freight. The cost offreight

and handling ranges from $0.25 to $0.50 a pound.

Some of the more common destinations are Boston,

New York, Los Angeles, and San Francisco.

Currently, the volume ofswordfish consumed in Hawaii is low. Local consumers are not familiar with swordfish, and the demand for the product is low. Most local

sales of swordfish are to restaurants.

Ex-vessel Revenue

Whole weight (in kilograms)

1992

n=34,141

1991

n=46,407

Estimated annual ex-vessel revenue generated by

swordfish rose dramatically from 1989 through

1993, from $980,000 to $26.5 million (Fig. 15).

Ex-vessel revenue for swordfish has been the highest of all fish species in Hawaii since 1991.

Protected Species Interactions _

Average Prices

Estimated ex-vessel prices were based on dressed

weights. The swordfish size categories used by the

seafood market industry are: rats «22.7 kg), pups

(22.7-44.9 kg), and markers (>44.9 kg). Larger

fish receive a higher unit price than smaller fish

(Table 6). In general, mean prices for all sizes of

swordfish were depressed in 1992-93. Estimated

prices for rats and pups decreased from 1990 to

1992-93. Estimated price for markers declined

from a high in 1990 to a low in 1992 and increased slightly in 1993.

>291

1993

n=32,648

1990

n=22,446

1989

n=2,323

91-100 191-200

15

10

5

0

10

5

>- u

c:

Q) 0 :::J

CT

10

c:

Q) 5

.,

Cl. 0

10

5

0

10

5

0

0

Figure 14

Annual weight-frequency distribution of swordfish landed by

Hawaii-based longliners fishing for swordfish, 1989-9~.

Allegations of incidental takes of the Hawaiian

monk seal, Monachus schauinslandi, in the proximity of certain islands and atolls of the northwestern Hawaiian Islands (NWHI), and a rapid
Table 4

Common and scientific names of common pelagic species caught by Hawaii-based longliners fishing for swordfish.

3OT-------------------,

Ito et a1.: Hawaii-based Longline Fishery for Swordfish 87

Table 6

Hawaii ex-vessel swordfish prices (dollars per kg), 1989-

93.

1989 1990 1991 1992 1993

Rats «22.7 kg)

Mean 2.98 4.87 3.33 2.58 2.58

S.D. 1.23 1.15 1.21 1.21 0.95

Pups (22.7-44.9 kg)

Mean 4.67 5.36 5.14 4.28 3.77

S.D. 1.12 1.39 1.12 1.41 1.08

Markers (>44.9 kg)

Mean 5.34 5.47 5.40 4.94 5.07

S.D. 1.17 1.39 1.19 1.39 1.15

1991 1992 1993

Year

1989 1990

Vl

$

o

a

2CH---------=

Coryphaena hippurus

Acanthocybium solandri

Lampris guttatus

Lepidocybiumjlavobrunneum

Alepisaurus spp.

Dasyatis violacea

Alopias superciliosus

fsurus oxyrinchus

Carcharhinus longimanus

Prionace glauca

Carcharhinidae

Thunnus obesus

T. albacares

T. alalunga

T. thynnus orientalis

Katsuwonus pelamis

Xiphias gladius

Makaira mazara

M. indica

Tetrapturus audax

T. angustirostris

lstiophorus platypterus

Scientific name

Billfish

Swordfish

Pacific blue marlin

Black marlin

Striped marlin

Shonbill spearfish

Sailfish

Common name

Tunas

Bigeye tuna

Yellowfin tuna

Albacore

onhern bluefin tuna

Skipjack tuna

Sharks

Bigeye thresher

Shonfin mako

Oceanic whitetip shark

Blue shark

Miscellaneous requiem sharks

Miscellaneous species

Mahimahi (dolphin)

Ono (wahoo)

Moonfish

Escolar

Lancetfishes

Pelagic stingray

Table 5

Mean whole weight and standard deviation (kg) of

swordfish landed by Hawaii-based longline vessels fishing for swordfish, 1989-93.

increase III the number of longline vessels in Hawaii

prompted the WPRFMC to take regulatory action (55

FR 49285, on 27 November 1990). Regulations required

longline vessels to maintain a fishing logbook, to have

permits, and to take an observer if an operator intended to fish in the study zone around atolls and

islands of the NWHI. Based on further reports of monk

seals taken by the fishery, the study zone was closed

permanently to longlining on 18 October 1991 (Regulation 56 FR 52214). According to logbook data, the

area closures around the NWHI appear to have elimiMean

S.D.

1989

67.0

45.9

1990

73.8

51.1

1991

71.3

49.8

1992

81.3

54.9

1993

80.0

51.6

Figure 15

Swordfish ex-vessel revenue from the Hawaii-based

longline fishery, 1989-93.

nated interaction incidents with Hawaiian monk seals.

The area closure resulted in the loss of several banks

where swordfish congregate during the spring months,

a loss felt by many of the smaller longline vessels.

Due to uncertainty over the frequency of turtle interaction with longline gear based on logbook reports, the

low level of authorized incidental take, and greater

than anticipated level of longlining effort, an observer

program was initiated. 12 The main objective of the observer program was to document incidental take ofsea

turtles and to verifY logging of interactions by vessel

operators. Observers began embarking on longline vessels whose captains volunteered to host them in the last

quarter of 1993 (Dollarll ). A regulation issued by the

Secretary of Commerce in January 1994 made it mandatory for all permitted Hawaii-based longline vessels

12 Endangered Species Act Section 7 Biological Opinion Consultation, conducted by NMFS in 1993.
88 NOAA Technical Report NMFS 142

to give notification 72 hr in advance of departUl-e and

to accommodate an observer. The initial authorized

level of total turtle take and mortality was modified

upward in ligh t of the uncertainty regarding the actual

level of incidental take.

The first objective of Amendment 7 to the Fishery

Management Plan (FMP) for the Pelagic Fisheries of

the Western Pacific Region is to regulate effort "... by

limiting potential increases in effort in order to minimize the risk of adverse impacts on the longline fishery,

other fisheries, the stocks, and protected resources such

as sea turtles" (WPRFMCIO). The limited entry and

observer regulations reduce the chance of much higher

levels of effort which might affect turtles, allow NMFS

to more accurately estimate the impact oflonglining on

protected sea turtles, and may temporarily dissuade

NMFS from imposing conservation measures either

under regulations implementing the pelagics FMP, or

under the Endangered Species Act based on the earlier

authorized level of incidental take of sea turtles.

Conclusions

The Hawaii-based longline fishery for swordfish grew at

a rapid pace beginning in 1989 and is now the largest

commercial fishery in Hawaii. This growth has raised

concern regarding over-utilization of the swordfish stock

(WPRFMCIO). However, the rate at which the fishery

has grown in the past 2 yr has slowed in comparison to

1989-91. The number of vessels decreased in both 1992

and 1993. Total fishing effort, in number of sets and

hooks, remained about the same during 1991-93 but

the effort shifted to outside the EEZ. Swordfish CPUE

changed little during 1991-93, but fishermen were making longer trips and fishing farther from Hawaii.

Swordfish landings, ex-vessel revenue, and size offish

have not declined in this new fishery. Indicators presented in this report are helpful in understanding the

swordfish in the central Pacific. However, monitoring

of the Hawaii-based longline fishery must be continued

to see what kind oflong-term impact it has on swordfish

of the orth Pacific.

Acknowledgments _

We would like to thank United Fishing Agency, Pacific

Island Seafood, Norpac Fisheries, and Mai McDowell

for their cooperation and patience with our data coJ]ection efforts. We also appreciate the help ofJo Anne

Kushi'ma of the Hawaii Division of Aquatic Resources

for her assistance in collecting the data and the Fishery

Data Management Program ofthe NMFS Honolulu Laboratory for their efforts in data processing. We would also

like to thank Steven A. Berkeley, Christofer H. Boggs,

Samuel G. Pooley, and Gary T. Sakagawa for their critical reviews and the Honolulu Laboratory's Scientific Services stafffor the preparation of this manuscript.

Literature Cited

Bartoo, . W., and A. L. Coan Jr.

1989. An assessment of the Pacific swordfish resource. In R.

H. Stroud (ed.), Planning the future of billfishes: Proceedings of the 2nd international billfish symposium, KailuaKona, HI, 1-5 August 1988. Part I, p. 137-151. Natl. Coalition Mar. Conserv., Savannah, GA.

Berkeley, S. A.

1989. Trends in Atlantic Swordfish Fisheries. In R. H. Stroud

(ed.), Planning the future of billfishes: Proceedings of the

2nd international billfish symposium, Kailua-Kona, HI, 1-5

August 1988. Part 1, p. 47-60. Natl. Coalition Mar. Conserv.,

Savannah, GA.

Berkeley, S. A., E. W. IrbyJr., and]. W.JolleyJr.

1981. Florida's commercial swordfish fishery: longline gear

and methods. Florida Sea Grant College and Florida Coop.

Ext. Serv., Mar. Advisory Prog. 14,21 p.

Boggs, C. H.

1992. Depth, capture time and hooked longevity of longlinecaught pelagic fish: timing bites of fish with chips. Fish.

Bull. 90:642-658.

Freeman, K.

1989. Lightsticks pull in swordfish despite some problems.

Natl. Fisherman 70(4):54-57.

Lipton, D. W.

1986. The resurgence of the U.S. swordfish market. Mar.

Fish. Rev. 48(3):24-27.

Pollack, S.

1990. Swordfishermen bash council plan at hearings. atl.

Fisherman 70(2): I 2-14.

Sa kagawa, C. T.

1989. Trends in fisheries for swordfish in the Pacific

Ocean. In R. H. Stroud (ed.), Planning the future of

billfishes. Part 1, p. 61-79. Natl. Coalition Mar. Conserv.,

Savannah, GA.

Sakagawa, G. T., A. L. Coan, and N. W. Bartoo.

1987. Patterns in longline fishery data and catches of bigeye

tuna, Thunnus obesus. Mar. Fish. Rev. 49 (4) :57-66.

Suzuki, Z., and Y. Warashina.

1977. The comparison of catches by regular and deep tuna

longline gears in the western and central equatorial Pacific.

Bull. Far Seas Fish. Res. Lab. 15:51-83.

Cchiyama,]. H., and R. S. Shomura.

1974. Maturation and fecundity of swordfish from Hawaiian

waters. In R. S. Shomura and F. Williams (eds.), Proceedings of the international billfish symposium, Kailua-Kona,

Hawaii, 9-12 August 1972. Part 2, p. 142-148. U.S. Dep.

Commer., I OAA Tech. Rep. MFS 675.

Wilson, C. A.

1988. Longlining for yellowfin tuna in the Gulf of

Mexico. Center for Wetland Resources, Louisiana State

Cniv., Louisiana Sea Grant Rep. LSU-G-88-002, 15 p.

Yoshida, H. O.

1974. Landings of billfish in the Hawaiian longline fishery. In

R. S. Shomura and F. Williams (eds.), Proceedings of the

international billfish symposium, Kailua-Kona, Hawaii, 9-12

August 1972. Part 2, p. 297-301. U.S. Dep. Commer., NOAA

Tech Rep. NMFS 675.
Recent Development of Swordfish, Xiphias gladius, Longline Fisheries

near Reunion Island, Southwestern Indian Ocean

FRANGOIS POISSON, EMMANUEL TESSIER, DAVID ROOS, and FRA GOIS RE E

IFREi'.1ER

RueJean Bertho, B. P. 60

97822 Le Port

Reunion Island (Indian Ocean), France

FRANGOIS CONAND

ORSTOM

RueJean Bertho, B.P. 60

97420 Le Port

Reunion Island (Indian Ocean), Fr-ance

ABSTRACT

A substantial increase in French longlining activity targeted on swordfish has been

observed between 5 0 S and 35°S in the western Indian Ocean since 1992. The domestic fleet

increased from one unit in 1991 to 15 in 1994. Other countries active in the area are Taiwan,

with an estimated 150 longliners, and Spain, with five 45-m longliners. Initially concentrated

near the island of Reunion, French activity presently extends to the entire French Exclusive

Economic Zone surrounding Reunion and southward to 26°S.

The catch of the Reunion fleet increased from 41 metric tons (t) in 1992 to approximately 700 t in 1994. In 1994, swordfish represented 65% of the catch (in number); mean

catch was 14 fish per 1,000 hooks, and mean weight of fish was 50 kg. Sales on the local

market are low. The high-quality product is transhipped fresh by air to Europe, and the

lower grade is frozen.

The development of this fishery stresses the need to develop a program in cooperation

with other countries in the southwestern Indian Ocean to improve knowledge of the biology

of swordfish, its relation to the environment, and fishing activity, in order to assess and

manage the stocks in the long term.

Introduction

The domestic swordfish, Xiphias gladius, fishery was virtually nonexistent a few years ago around the island of

La Reunion, an overseas department of France in the

southwestern Indian Ocean. Beginning in 1991, two

factors promoted the rapid development of this fishery.

First, the favorable conditions for swordfish in the southwestern Indian Ocean and the success of the Asian fleet

based on the island inspired a local fisherman to begin

longline trials with a 12-m boat. Second, new tax regulations offering exemption for certain investments in

French overseas departments encouraged fishing companies from the mainland to come to Reunion. Four

16-m longliners based at Pointe des Galets harbor started

operating in 1992, targeting bigeye tuna destined for

theJapanese market. Information on the success of this

fishery spread rapidly. There have since been significant changes in various aspects of the swordfish fishery,

including the evolution of boat and gear characteristics, fishing techniques, fishing grounds and seasonal

activity, target species, and markets.

In 1993, the Institut Fran<;:ais de Recherche pour I'Exploitation de la Mer (IFREMER) began a program in Reunion

to study and monitor the swordfish fishery, analyse the

catch, and improve knowledge on the biology of swordfish and billfish from the southwestern Indian Ocean. The

Institut Fran<;:ais de Recherche Scientifique pour Ie Developpement en Cooperation (ORSTOM) contributes to

this program, specifically by producing weekly surface

89
90 NOAA Technical Report NMFS 142

temperature charts from satellite images. These charts,

which are produced for the Regional Tuna Project, Phase

2, of the Commission de I'Ocean Indien (COl), are distributed to participating countries: Comoros, France, Madagascar, Mauritius, and Seychelles.

This paper describes the swordfish fisheries in the

southwestern Indian Ocean and the data which have

been collected on them, and presents an analysis and

evaluation ofgeographical swordfish distribution, catches,

and catch per unit effort. Along with brief histories of the

fisheries, we describe the fishing strategies of the various

fleets operating in the zone, to examine their fundamental differences and to draw out the positive developments

of the emerging fishery based at Reunion Island.

The Fisheries _

Vessels

Domestic Fleet-The characteristics of the vessels composing the Reunion fleet are summarized in Table 1.

Four companies are represented, operating a total of

15 vessels.

Taiwanese Fleet-The Taiwanese longline fishery is very

active in the Indian Ocean, with probably 150 longliners

operating in the French Exclusive Economic Zone (EEZ)

around Reunion Island. In 1994, 28 vessels received

licenses to fish in the EEZ, on condition that the catch

is landed in Reunion. These vessels are 35-45 m long,

between 145 and 380 horsepower, and have a capacity

of at least 100 metric tons (t), with 18-30 men on

board. A large proportion are equipped with freezing

holds (-60°C).

Spanish Fleet-There is little or no information available on the Spanish fleet. Five 45-m longliners operate

occasionally in international waters in the southwestern

Indian Ocean. These vessels were redeployed from the

Spanish fleet of longliners in the northeast Atlantic.

They arrived on an exploratory cruise at the end of

1993 and in early 1994.

Fishing Gears and Methods

All the Reunion vessels use a system of drifting longline

which utilizes a main spool and a line shooter. The

main line is a nylon monofilament 3.5 or 4 mm in

diameter and approximately 45-80 km long. The line

can be weighted to control its depth in strong currents.

The leaders with hooks (size 8/0 or 9/0) are 10 m long

and 2 mm diameter, and are attached to the main line

with snaps. Depth is controlled by a series ofintermediate floats attached to the main line with leaders of 5-25

m. In addition a larger float is used to separate the

various sections of 60-100 hooks. Between 500 and

1,400 hooks are utilized for each set. The buoys at the

end of the longline are equipped with a strobe light

and a radio system to assist in retrieval. There may be

various modifications to the fishing gear, these being

determined by the requirements ofindividual skippers.

Because swordfish is the target species, the longline

is always set in the evening. Kume and Joseph (1969)

have shown that lines set at night are more productive

for capturing swordfish than lines set during the day. A

line shooter draws the line from the main spool and

controls its setting speed. Clipping ofthe leaders on the

main line and baiting of the hooks takes place progressively during each set. Squid is generally used as bait in

addition to a light stick (Cyalume 1) placed 1 m above

the hook. This whole operation requires three crewI Reference to trade names or commercial firms does not imply

endorsement by the ational Marine Fisheries Service, NOAA.

Table I

Specifications of the longliners of the Reunion fleet.

Company

Number of units

Length (m)

Bunker capacity (m3 )

Crew

Horsepower

Insulated hold (m3)

Ice machine

Regulated hold (0°C/-20°C)

Regulated hold (-40°C)

Compagnie des Longliners Sopesud Pointe de la Table Creole

3 1 8 1 1 1

25 20 16 12 12 12

48 23 13 2.5 2

9 7 6 5 4 4

600 2 x 350 350 200 250 213

120 50 28 20 12 9

yes yes yes no no no

yes yes yes no no no

yes yes yes no no no
_______ Poisson et al.: Swordfish Longline Fisheries near Reunion Island, Southwestern Indian Ocean 91

men on deck and one at the helm. The longline is set in

4-6 hr cruising downwind.

The line is hauled after sunrise. The duration of the

haul depends on the catch and sea conditions. The

number of days at sea varies according to vessel size and

capacity, and weather conditions. Small vessels stay at

sea from 2 to 8 days, while vessels longer than 16 m stay

at sea 7-18 days.

Very little information is available on the fishing

techniques of the Taiwanese fleet. It is known, however,

that the Taiwanese do not use a monofilament longline

and therefore require a large crew. At least 2,000-2,500

hooks are utilised for each set. The target species are

albacore and bluefin, bigeye, and yellowfin tuna. Mackerel is generally utilized as bait.

No information is available concerning techniques

utilized by the Spanish fleet. These are most likely as

described by Rey and Alot (1984).

Onboard Catch Processing

Handling and treatment of the catch depends on the

type of vessel and market requirements. Two processing techniques are utilized: swordfish are headed and

gutted (H&G): head, guts, gills and fins are discarded;

or the fish are gutted only: guts are discarded and the

head is left on, with the gill discarded. The latter treatment is generally carried out on pieces of less than 20

kg. In Reunion, fish destined for export are carefully

and individually processed on board on ice in order to

conserve quality.

On Taiwanese albacore longliners, the entire catch is

placed in _45° or -60°C holds after processing (H&G).

Billfishes are not subject to any particular special treatment. On Taiwanese longliners targeting bluefin, bigeye, and yellowfin tuna ("sashimi boats"), the entire

catch is placed in -60°C holds. Fish are carefully treated

taking into account the special requirements ofsashimi

buyers.

Marketing

Reunion Longliners-In an effort to control the regional market, only local companies are presently allowed to sell on the Reunion market. The portion of

the catch destined for export is processed by a specialized company. Swordfish and tuna loins of 3 kg are

vacuum-packed in temperature-controlled packaging

and air-freighted to Europe.

The Compagnie des Longliners exports its entire

catch, for which purpose it has established ajoint venture with an American company which specializes in

the marketing offresh swordfish and high-quality tuna.

Quality control is carried out before export. The fresh

products are primarily exported to Europe (90%) and

the United States (10%). Fresh fish that are not of

export quality are frozen and exported at a later date to

other markets.

As the result of a flooded market following the first

year of production, there was a sharp drop in the price

in Spain, France, Italy, and Germany. The world demand for fresh swordfish allowed profitable returns of

around US$4 per kilo.

The various strategies for exporting fresh fish by air

from Reunion, including techniques of preservation

and controlled packaging, have been determining factors in the evolution of the industry and have added

value to this limited resource.

Taiwanese and Spanish Vessels-The Star Kist company purchases the catch of the Taiwanese albacore

longliners, which is exported in bulk-freezer vessels to

canneries in Puerto Rico. The sashimi boats transship

their catch in Japanese shuttle vessels equipped with

bulk deep-freezers; it is purchased by traders in Japan.

The marketing of the catch from the Spanish fleet is

undocumented.

Data Collection

Domestic Fleet

Logbooks were distributed to all Reunion longliners to

collect information on fishing positions, number of

hooks per set, light sticks used, fishing gear techniques,

times that line is set and hauled, number of fish caught

by species, and their estimated weights. Environmental

and weather conditions (sea-surface temperature, wind

speed and direction, etc.) are also recorded. The logbooks are collected regularly from the skippers or company managers.

Fishing statistics for Reunion's fleet are determined

on the basis of voluntary declarations of catches by

skippers and companies to the Fisheries Administration. Available data on catches represent the comprehensive results of fishing operations by all registered

companies. The companies must declare the date of

the departure and arrival of each of their vessels as well

as the total catch by species (13 species). In order to

confirm the information received, port sampling and

on-board observer programs are also conducted.

Other Fleets

Authorization to fish in the French EEZ for a period of

one year was granted to 28 Taiwanese longliners in
92 NOAA Technical Report NMFS 142

Quantities Caught

An exhaustive list of species caught was begun by compilation offishing logbooks and

was completed by scientific observers during trips onboard longliners based in Reunion (Table 2). The processing carried

out on the catch by the Taiwanese longliners

makes species identification difficult; however, Lampris guttatus was detected in the

catch.

Fishing Grounds

Species Caught

Figures 1 and 2 show the distribution of the

Reunion longliner fleet in 1993 and 1994.

Each cross represents the starting position

of a set during one fishing day. Figure 3

shows the fishing operations of the 21 Taiwanese longliners in winter 1993 and summer 1994.

Figure 4 shows swordfish catches by the major countries fishing for swordfish in zone

51 of the FAO (300-800 E) during 1984-93

(IPTp2). The increasing catches of swordfish and albacore by the Reunion fleet during 1991-94 are depicted in Figure 5. Increasing targeting on swordfish by the Reunion longliners during 1992-42 is reflected

in Figure 6, which shows the proportions of

major species caught during that time. The

Because the logbooks only cover a portion of fishing

activities, a coverage rate has been established, defined

as the ratio between the number of trips

listed in the logbooks and the estimated

number of total trips by the entire Reunion

fleet. The coverage rate was 24% in 1992,

40% in 1993, and 95% in 1994.

Results and Discussion

declarations from individual countries. No data are

available on the Spanish fishery.

E

E

MAURITIUS

o

+

+

55

+

+

+

+ if

RtUNION

55

MAURITIUS

t 0

+ft~~

REUNION

+

50

MADAGASCAR

"I

MADAGASCAR

l-__.;.- -.--- ,.- ---J s

S L--~;=--------,----------,-----------r

November 1993. This agreement requires that Star Kist

hand over logbooks completed by captains and indicating precise fishing positions, number of hooks per set,

and total catch transhipped at the port of Pointe des

Galets.

Fishing statistics on the Asian fleet are organized and

published by the Indo-Pacific Tuna Development and

Management Programme (IPTP) of the FAO, based on

Figure 1

Distribution of the Reunion longliner fleet in 1993 in summer

(upper) and winter (lo\'.'er). 2 Indo-Pacific Tuna Development and Management

Programe (lPTP). 1994. Indian Ocean and Southeast Asian tuna fisheries data summary for 1994.
_______ Poisson et al.: Swordfish Longline Fisheries near Reunion Island, Southwestern Indian Ocean 93

E

MAURITIUS + 0

+~~ +~,..... REUNION

.,

MADAGASCAR

+ + +

L-_-. -.-- "'lt__-,--- ----r s

Catch Per Unit of Effort

Not only the number, but the size of French

longliners based in Reunion have increased

since 1991 (Fig. 9). Between 1991 and 1994,

both the number of boat days at sea and the

amount of effort, estimated as the number

of hooks set, increased more than 20-fold

(Table 3). The seasonal distribution of effort by the Taiwanese fleet from July 1993

to February 1994 is presented in Table 4.

Effort

monthly variation by species of catch by

Taiwanese longliners is presented by number of fish in Figure 7, and by percentages

in Figure 8.

MAURITIUS

The 1993-94 spatial distribution of swordfish catch per unit effort (CPUE) of the

Reunion longliner fleet is illustrated in Figure 10, and that of the 21 Taiwanese longliners in Figure 11. CPUE by species for the

Reunion longliners (in weight per boat-day

at sea) from March 1992-September 1994

is shown in Figure 12. Monthly CPUE (fish

caught per 1,000 hooks) for swordfish, albacore, and other species) caught by the Reunion and Taiwanese longliner fleets is presented in Figure 13.

Discussion

Reliability of the Data

i

E

++++

+"t+

60

15

Figure 2

Distribution of the Reunion longliner fleet In 1994 in summer

(upper) and winter (lower).

Most companies and skippers have cooperated well with the new system of collecting

catch logbooks, introduced in November

1993. In exchange for the data, complete

confidentiality is guaranteed. Raw (unaggregated) data are not disclosed or published. These logbooks provide very solid information

on the position ofsets, techniques used, environmental

conditions, and number of fish caught by species.

Analysis of the data has shown some limitations to

this system. When total daily catch is compared with the

actual transshipment figures, differences of up to 20%

appear; therefore, the catch estimates provided by the

skippers must be viewed cautiously. There was also discrepancy between data on fishing periods collected by

the Fisheries Administration and by ourselves, for example, the dates of the start and end of fishing trips

were different.

It would be useful in the future 1) to include a

recapitulation table in the declaration forms, in which

the number and weight of fish unloaded would be

summarized by species; 2) to furnish a size-weight conversion table to each skipper in order to improve estimates; and 3) to add to the declaration forms further

required information, such as number of sets per trip

and number of each species caught.
94 NOAA Technical Report NMFS 142

Concerning the catch declarations of Taiwanese

longliners, two types of information are provided, the

number of fish caught and the total tonnage of each

species unloaded. There are many inconsistencies, probably as a result of transshipment at sea and at other ports.

In order to improve the quality of the data it would be

necessary to place observers aboard and to monitor this

fishery on a regional level, over the entire Indian Ocean.

Fishing Grounds and Seasons

..JL1 _---.-__---,---__---.-__--,-__---'1 s

Figure 3

Distribution of 21 Taiwanese longliners during winter 1993 Oul.

93-0ct. 93; upper) and summer 1994 (Nov. 1993-Feb. 1994;

lower).

Domestic Fleet-The fishing grounds of the

Reunion longliners are to the west and south

of Reunion in the French EEZ and in international waters. No longliners are authorized to

fish within a zone of30 nautical miles (n. mi.)

from Reunion, in order to avoid conflicts with

the artisanal tuna fishery.

The period of the most intensive fishing

activity corresponds to austral summer. It appears that the seasonal abundance around

Reunion could be related to the migration of

mature fish, which congregate in this zone

during summer.

The youngest females observed, stage 6 on

the scale ofmaturity (Uchiyama and Shomura,

1974), were observed in the month of 0-

vember; females in the phase of atresia have

been observed in April near Reunion Island.

During the month ofJanuary, swordfish larvae have been observed in the Mozambique

Channel (Kondritskaya, 1970) as well as off

the east coast of Madagascar (Gorbunova,

1969) .

The violent trade winds that characterize

the southern winter limit boats of the domestic fleet, which are not designed for distant

water operations. In addition, the smaller vessels are incapable of manufacturing ice. Thus

during the winter 12-m vessels prefer to pursue demersal fishes on banks off the Mauritian

~landsofRodriguesandSoudan.

The activity of the domestic fleet has significantly evolved in the last 3 years. This is

illustrated by Figures 1 and 2, which show the

progressive spatial extension of fishing. The

catch zone west of Reunion in 1993 expanded

to the southwest in 1994, ''lith maximum catches

between 30 and 60 n. mi. to the west and

southwest, extending southwestward beyond

the 200-n. mi. zone. Figure 12 illustrates

changes in the monthly average catch per

unit effort, which displayed strong seasonal

trends. In 1994 there was no winter decrease

in catch rate, a consequence of progressive

mastery of fishing techniques by the crews.

This promoted a positive balance of accounts

for companies in 1994 and ensured a constant

" ,. 55 6. E i i ! i

1

r" I

I + I + + + ~15 +

I +#

+ + I +

~" + MAURITIUS

+

+~* + D ... -F ++ Q

I +t +.}+ *" REUNION

., ++ + I ++ :++ ++ + -+++++

+ + +

11- +~ ~5 I + + + + + I -W- +

I ~+ Y:: /t/ I ++ -IIj. ... '

I + + + + +t J + + + + + Is + ..... + +~ +++ + I II +t";"

I I 10 -I I

1

I

I

~15

I

MAURiTiuS '0
_______ Poisson et al.: Swordfish Longline Fisheries near Reunion Island, Southwestern Indian Ocean 95

8000

Iii 6000 (j)

c:

c:

g 4000

.r:.

0

ro 2000 0

1985 1986 1987 1988 1989 1990 1991 1992 1993

.FRANCE DJAPAN • KOREA DTAIWAN

Figure 4

Swordfish catch by longliners of the main countries

fishing swordfish in FAD zone 51, 1984-93 (from

IPTp l ).

800 T .-..

+

en 600 , Q) /

C

I

, C /

0 , ..... 400 ,

---- /

...c , () t ... 200 ., ..... , CO .,

: ()

o •

1991 1992 1993 1994

-A-Albacore - --- - Swordfish

Figure 5

Catches of albacore and swordfish by Reunion

longliners,199J-94.

supply of exports to penetrate international markets. The

arrival of more powerful vessels, improvement and mastery of fishery techniques, and the discovery of new zones

of exploitation could all bring further notable changes to

current strategies.

Taiwanese Longliners-The seasonality and fishing

grounds of the Asian fleet are not precisely known.

These vessels are constantly on tht> move, searching for

bigeye, albacore, and bluefin tuna. It seems that this

fleet operates during the austral summer between 10°.

and 25°S, and between 25°S and 35°S during the winter, when they targetjuvenile albacore. No precise data

100

75

C(j)

0 50

ill

a.

25

o '

1992 1993 1994

o swordfish 0 albacore • yellowfin 0 billfish 0 others

Figure 6

Proportions (by number offish) of main species caught

by Reunion longliners, 1992-94.

is available on their activity in the EEZ between 35°S

and 400S. The movements of this fleet are known only

from a sample of 21 boats out of a total fleet of 150 in

the EEZ around Reunion Island and Mauritius between

July 1993 and February 1994. It would appear, according to information obtained by scientists from Seychelles,

Mauritius, Madagascar, and the Comoros, that at least

300 vessels were listed during 1994 in the region southwest of Reunion. 3

Spanish Longliners-Contacts have been established

with the S":J.nish Oceanographic Institute (lEO) and

the European Economic Community (EEC), which

financed the redeployment of vessels [rom the Atlantic

to the Indian Ocean, to obtain more information on

this venture. These 5 vessels seem to obtain excellent

results to the south of Madagascar and in the

Mozambique Channel, but no data are available to

date.

Catch

Reunion Fleet-A considerable and progressive increase

in swordfish landings by the domestic longline fleet was

recorded during 1992, 1993, and 1994, from approximately 1 tin 1992 to 600 tin 1994 (Fig. 5). The number

3 Statistical meeting of the Regional Tuna Project, phase 2 (PTR2)

of the Indian Ocean Commission. Albion, Mauritius,July 1994.
96 NOAA Technical Report NMFS 142

35000 [-

30000 --------

:2$1 25000 -1-------------,

'0Q; 20000 11------------- .0

E

::l I

'"0001 -------- ro 10000 --------- U !

5000 -1------

jul

'93

aug

'93

sep

'93

oct

'93

nov

'93

dec

'93

jan

'94

feb

'94

(J Sharks 0 Marlins 0 Yellowfln • Swordfish II Albacore

Figure 7

Catch (number offish) by species ofthe 21 Taiwanese longliners

between July 1993 and February 1994.

Table 2

Fish species caught by the longliners of the Reunion fleet.

Target species Bycatch species

Swordfish, Xiphias gladius

Albacore, Thunnus alalunga

Yellowfin tuna, Thunnus albacares

Bigeye tuna, Thunnus obesus

Dolphin fish, Coryphaena hippunts

Sailfish, Istiophonts platyptents

Blue marlin, Makaira nigricans

Shortbill spearfish, Telraptu'l1s anguslimslris

Shortfin mako, fsurus oxyrinchus

Oceanic whitetip shark, Carcharinus lon{!;imanus

Scalloped hammerhead, Sphyrna lewini

Smooth hammerhead, Sphyrna zygama

BI ue shark, Prionace glauca

of swordfish caught from March 1993 to December

1994 can reasonably be estimated at 8,000, corresponding to 410 t dressed weight. This increase in the catch

has made this fleet one of the major players in the

Indian Ocean (Fig. 4).

Taiwanese Fleet-Changes In the Taiwanese catch by

species and by month has been calculated from logbook data on fish caught by 21 vessels. In 8 mo, 4,152

swordfish were caught. Representation in weight is not

useful because landing tonnage does not match the

catch, due to long trips and transfers at sea.

Skate, unidentified

Ocean sunfish, Mola mola

Snoek, Thyniloides sp.

Oilfish, Ruveuus sp.

Remora, Remora sp.

Crocodile shark, Pseudocarcharias kamoharai

Silky shark, Carcharinuslalciformis

Spanish Fleet-The Spanish catch cannot be quantified at present.

Effort

Reunion Fleet-During 1991-94 there was a regular

and rapid increase of fishing effort (Table 3). This

seems mainly due to an increase in the national fleet,

which has grown from 1 to 15 vessels in 3 yr (Fig. 9);

increased numbers oftrips and sets, with a transition from

a seasonal to a year-round operation; an increase in the
_______ Poisson et aI.: Swordfish Longline Fisheries near Reunion Island, Southwestern Indian Ocean 97

number of hooks per set; and a major expansion

of the fishing grounds.

Taiwanese Fleet-The effort of the Taiwanese

fleet is known only from the declaration made

by 21 vessels from July 1993 to February 1994,

indicating a probable presence of approximately 150 vessels. These figures would have

to be multiplied by 7 or 8 to give a more

realistic indication of the Taiwanese fishing

effort.

100%

80%

'g

(])

'-' 60%

.e:

.r:::

£

til

(,) 40%

20%

0%

Catch Per Unit of Effort jul

'93

aug

'93

sep

'93

oct

'93

nov

'93

dec

'93

jan

'94

feb

'94

D Sharks D Marlins Cl YelJowfin tuna. Swordfish 0 Albacore

Analysis shows that these zones of high CPUE are all

situated in the southern tropical convergence zone next

to the Agulhas Current in the Mozambique channel

and the Malagasy Southeast Current off Madagascar.

Oceanographers have found several vortices and meanders in the surface circulation, which can generate a

succession of divergence and convergence zones

(Donguy and Piton, 1991; Marsac, 1994). Even if it is

not possible to model these and to explain them at the

Figure 8

Monthly proportions of species caught by the longliners of

Taiwan.

In 1993, the best CPUE for the domestic fleet

was within 70 n. mi. of Reunion (Fig. 10). The

catch in this area ranged between 10 and 15

fish per 1,000 hooks. In 1994, there was an

important increase in CPUE over the whole

fishing grounds, with a zone of optimum catch

distributed around a northeast-southwest axis

50-300 n. mi. from the island. In this zone there were

25-35 captures/I,OOO hooks. For the Taiwanese fleet in

1993-94, the best CPUE on the entire fishing grounds

was 20 fish/l,OOO hooks. This was in a zone situated on

a northeast-southwest axis in the Madagascar EEZ, 100

n. mi. to the southwest of the most productive area

identified by the domestic fleet. Another productive zone

(5-20 fish/I,OOO hooks) appears in the Mozambique channel southwest of Madagascar.

Table 3

Fishing effort of Reunion longliners, 1991-94.

Table 4

Fishing effort of Taiwanese longliners (21 vessels) off

Reunion,July 1993-February 1994.

.12 m 016 m .20 m 025 m

16

14

l/)

....

(lJ 12 c

OJ 10 c

.2

4- 8 0

'-

(lJ 6 .0

E

D :::J 4 c

2

0

1991 1992 1993 1994

Sets

Year Trips Boat days at sea Hooks (x lOS)

1991 20 43 28

1992 59 155 70

1993 142 841 549

1994 173 1,048 690

Year/quarter

1993/3

1993/4

1994/1

155

841

1,048

505

3,586

1,386

Figure 9

Longliners based in La Reunion, 1991-94, by boat

length,
98 NOAA Technical Report NMFS 142

'1

IS

MAURITIUS

0

I

~,s

51 E

0<-10 REUNION

010-15

IZI 15-20

i2l 20-25

.25-35 S '-----,------r-------,-----,-'

'I

Targeting and Bycatch

present time (Petit, 1991), fishermen are successful in

reducing search time and increasing catch rate by using

satellite temperature data to locate convergence zones.

The spectacular increase in catch rate of the domestic fleet (Fig. 12) is largely due to the ability of crews to

improve on American techniques; accurate targeting of

swordfish with techniques including light sticks, setting

at night, adaptation of gear according to the lunar

cycle, and utilization of XBT profiles and bathymetric

data; and more systematic utilization, sinceJuly 1993, of

satellite thermal charts, allowing boats to locate thermal fronts and to position their gear accordingly. These

charts are now considered crucial by the skippers.

Comparison between the domestic and Taiwanese

fleets shows that the catch rates of the domestic fleet

are clearly superior for all species (Fig. 13).

Figures 5 and 6 reveal a change in targeting by the domestic fishery. Swordfish accounted for only 7% of the catch

(in number) in 1992, but 65% in 1994. One will also notice a

progressive drop in the catch of billfishes (marlins, sailfish,

and spearfish; Fig. 6) which underscores the specificity of

the techniques employed. This confirms that it is possible

to exploitswordfish without prejudice to recreational game

fishing activities based on billfish in nearby countries. As

for sharks, by reason of their current weak market value,

only dead individuals are preserved and posted as catches.

Live ones, which are usually more numerous, are released.

Capture ofsharks remains marginal.

Predation after Capture

Predation is weak (<1 %) and seasonal. Nevertheless,

the catch of a set can be totally destroyed by predation,

mainly by sharks, short finned pilot whales, Globicephala

macrorhynchus, and false killer whales, Pseudorca crassidens.

Conclusion

The longline fishery has been operating in the Indian

Ocean for about forty years. This activity was traditionally dominated by Asian fleets until the 1980's.

The French tuna fishery in the Indian Ocean began

with the arrival of a purse seiner fleet from tropical

Atlantic waters. Reunion Island developed a domestic

longline fishery, which was more suited to the exploitation of pelagic resources in oligotrophic subtropical

waters. In the early stages, tax exemptions and the

arrival of fishermen from the mainland created the

necessary incentives for the development of these acFigure 10

Average number of swordfish caught per 1,000 hooks

by Reunion longliners by lOx 10 areas in 1993 (upper)

and 1994 (lower).

tivities. Today, these two factors no longer playa crucial

role. The growing harvest of pelagic resources by Reunion-based fishermen and companies has involved

regional participation and development in three direct

ways: upgrading of the artisanal fishery using new, specially-adapted 12-m longliners; involvement of local investors; and education and training of local fishermen

in longlining techniques.

Some improvements have yet to be undertaken: all

longliners need adequate working space on deck, and

cold storage from O°C to -60°C; and local seafood quality

control services should be improved, in particular to meet

the new standards established by EEC regulations.

In addition, management strategies for swordfish

stocks should be developed and improved, based upon
________ Poisson et al.: Swordfish Longline Fisheries near Reunion Island, Southwestern Indian Ocean 99

iAFRIQ~~ 50 55 60 G5 10 15 E I I I I I I

l"l ~da 25

o <-1

01-2

rs

2-5

Ill! 5-10

Ili!I 10-20

I

!SJ

Figure II

Average number of swordfish caught per 1,000 hooks by 21 longliners of the Tawainese fleet,

by 1° x 1° areas,Jul. 1993-Feb. 1994.

the management problems faced in other geographical

areas. A major program could be structured through

• data collection on catches and transshipments at all

major southern Indian Ocean ports;

• estimation of an index of abundance based on catch

and effort data;

• setting up a biological program to study ageing, reproduction, migration, and behavior;

• data collection on bycatch; and

• study of the potential effects of environmental conditions on the distribution ofswordfish.

Typical swordfish management problems are linked

with the dangers oflocal overexploitation (which should

be controlled at a EEZ and subregional level) in conjunction with global ocean problems, which should

be addressed by a future ad hoc Indian Ocean Tuna

Commission.

Effective control of the longlining fleet should be

set up through a number of geographically-limited

subregional organizations to manage migratory and

long-lived species such as swordfish. Only geographically limited organizations are likely to efficiently

exert control and to be able to enforce edicts of the

larger Indian Ocean Commission. Cooperation will

become more crucial as the catch by the Taiwanese

fleet continues to increase sharply, with no clear control either inside or outside the EEZ's of southwestern Indian Ocean countries.

1000

---. ?

Cl I

::::- 800 I

>.

ro , '"0 600 <> '

1ii II'

<>\ 1\1

0 I

? " ..0

.... 400 I I

a.> \ , a. \ , ..c: \I

<..> 6

-ro 200 <..>

0 N N N N N C') C') C') C') C') C') '<t '<t '<t '<t '<t

q> 0> 0> 0> q> q> 0> 0> 0> 0> q> q> 0> 0> 0> 0>

C') .;, .-:. d> ;; '" .;, .-:. d> ;; '" .;, .-:. d> 0 0 0 0 0 0 0 0 0 0 0 0

- -<>- - Swordfish ---- Albacore

Figure 12

Catch per unit of effort of swordfish and albacore by

the Reunion longliners, March 1992-September 1994.

Acknowledgments _

This study was made possible by financial aid from the

European Economic Community and the local assembly (Conseil General) through the Reunion Centre

d'Appui National (CAN) under PTR2. We are grateful
100 NOAA Technical Report NMFS 142

REUNION

..

8 45

40 0

0

C!. 35

! 30

.E 25

'"

::l

co 20 u

15 ..

~i ;;:: 10 '0 5 .0

E 0 ::l

C .., .., .., .., .., .., .., '" .., '" .., .. .. !" !" !" !" !" !" !" !" !" !" !" !" !" c .0

'" c :a '" Q. 'g > il c .0 .!!, .! Q. co .::. ::l G> e co .!!' .! E co .. c "

-;. .. .. .. .. .. .. !" !" !" !" !" !"

a '" c :a '" Q.

.. .. .::. ::l G> 'g E .. ..

.. 45 TAIWAN ...

0

0 40 0

0 35 o.

8- 30

.E 25

'"

::l 20 :J

.. 15 ;;::

'0 10

5 E

::l

C 0 ... ... ... ... ... ... .. .. !" !" !" !" !" !" !" !"

:a '" Q. 'U > u C .0 ::l G> 0 0 G> .!!, .. .. c .l!! "

o Other species

o Albacore

• Swordfish

Figure 13

Average number of fish of various species caught per 1,000 hooks by

the Reunion longline fleet during January 1993-0ctober 1994 and

the Taiwanese longline fleet duringJuly 1993-February 1994.

to all Reunion companies and longlining fishermen for

their active cooperation. They always have been generous in sharing their knowledge of the fishery.

The authors wish to thank M. Petit, Dominique

Belleme, and Xavier Bernardet from ORSTOM Reunion

for their valuable suggestions and assistance, and are

also very grateful to Joel Najeon de L'Estang for his

help with the English translation.

Literature Cited

Donguy,J. R., and B. Piton.

1991. The Mozambique Channel revisited. OceanoI. Acta

14(6):549-!J58.

Gorbunova, N. N.

1969. Breeding grounds and food of the larvae of the swordfish [Xiphias gladius Linne (Pisces, Xiphiidae) sic]. Probl.

Ichtyol. 9:375-387.

Kondritskaya, S. I.

1970. The larvae of the swordfish (Xiphias gladius) from

Mozambique channel. J. Ichthyol. 10:853-854.

Kume, S., andJ.Joseph.

1969. The Japanese longline fishery for tunas and billfishes

in the eastern Pacific ocean east of 130oW, 1964-1966. Inter-Am. Trop. Tuna Comm. Bull. 13:277-418. [In Engl. and

Span.]

Marsac, F.

1994. Resultats du reploiement d'une bouee derivante dans

Ie canal du Mozambique 14 mars au 28 aout 1994. Rapp.

Cons. Sci., Seychelles, October 1994, p. 4-7.

Petit, M.

1991. Contribution de la teledeteetion aerospaliale al'elaboralion des bases de l'halieutique operationnelle: l'exemple des

pecheries thonieres tropicales de surface (aspect evaluatif).

Doctoral thesis, Univ. Paris VI, 130 p. + 5 annexes.

Rey,J. c., and E. Alot.

1984. Contribucion al estudio de la pesqueria de palangre

del pez espada (Xiphias gladius) en el Mediterraneo

occidental. Int. Comm. Conserv. Atl. Tunas, Coil. Vol. Sci.

Pap. 20(2):428-434.

l'chiyama.J. H., and R. S. Shomura.

1974. Maturation and fecundity of swordfish, Xiphias gladius,

from Hawaiian waters. In R. S. Shomura and F. Williams

(eds.), Proceedings of the international billfish symposium,

Kailua-Kona, HI, 9-12 August 1972. Part 2, p. 142-148. U.S.

Dep. Commer., NOAA Tech. Rep. NMFS-SSRF-675.
Central Pacific Swordfish, Xiphias gladius,

Fishery Development, Biology, and Research

ROBERT A. SKILLMAN

Honolulu Laboratory

Southwest Fisheries Science Center

National Marine Fisheries Service, NOAA

2570 Dole Street

Honolulu, Hawaii 96822-2396

ABSTRACT

The development of the Hawaii longline fishely for swordfish, Xiphias gladius, in the

cen tral North Pacific, which began in 1988, is described. Swordfish landings in the Hawaii

fishery reached 6,000 metric tons in 1993. To put the Hawaii fishery in perspective,

swordfish fisheries and their production in the Pacific and the world are reviewed, along

with swordfish biology and stock dynamics information from the Pacific and Atlantic

Oceans. The fishery monitoring and research strategies of the Honolulu Laboratory are

described, and potential avenues for collaboration are suggested.

Introduction

Prior to 1988, swordfish, Xiphias gladius, was an incidental component of the Hawaii longline fishery targeted

on tuna. The fishery for swordfish expanded rapidly in

1990 and 1991 until swordfish contributed 51 % of

longline landings by weight and 50% by reven ue (ltol).

The Hawaii longline fishery thus became the single

largest swordfish fishery in the central-eastern Pacific

(Skillman et aI., 1993). A few boats based in California

and Alaska have also participated in the central Pacific

swordfish longline fishery. The rapid increase in the

Hawaii fishery and the perception based on events in

the western Atlantic fishery (Beardsley, 1978; Miyake

and Rey, 1989) that the species is more sensitive to

exploitation than other large pelagic fishes (e.g., most

tunas) has led to concerns for the long-term stability of

the Hawaii fishery and the status of the resource in the

central Pacific (WPRFMC2).

1 Ito, R. Y. 1992. Western Pacific pelagic fisheries in 1991. V.S.

Dep. Commer., NOAA, Natl. Mar. Fish. Serv., Southwest Fish. Sci.

Cent. Admin. Rep. H-92-15, 38 p. Honolulu Lab., Southwest Fish.

Sci. Cent., NMFS, Honolulu, HI 96822-2396.

2 Western Pacific Regional Fishery Management Council (WPRFMC).

1993. Amendment 7 to the Fishery Management Plan for the

Pacific Fisheries of the Western Pacific. Western Pac. Reg. Fish.

Manage. Counc., 1164 Bishop St., Rm. 1405, Honolulu, HI 96813.

This paper provides an overview of swordfish fisheries with emphasis on the development of the Hawaii

fishery, a review of swordfish biology and stock dynamics, and a description of monitoring activities and stock

assessment and research strategies at the National Marine Fisheries Service (NMFS) Honolulu Laboratory.

Swordfish Fisheries

Global

Evidence of the harvesting ofswordfish dates to 3,000-

4,000 B.C. inJapan (Ueyanagi, 1974) and to Aristotle's

time (384-322 B.C.) in the Mediterranean (Berkeley,

1989). Commercial harpoon fishing for swordfish began off the northeast coast of North America by the

1870's (Berkeley, 1989); the harpoon fishery in California began in the early 1900's (Beardsley, 1978). Drift

gill nets have today largely displaced the use of harpoons in coastal fisheries, including off California

(Hanan et aI., 1993). High-seas fishing for swordfish

began in the early 1950's when the Japanese longline

fleet began seasonal targeting in the northwest Pacific

(Yamanaka, 1958). Today, subsurface longline gear remains the dominant gear for harvesting swordfish on

the high seas, though much of the take is a bycatch of

tuna fishing. In addition, minor catches occurred in

101
102 NOAA Technical Report NMFS 142 _

90

80

70

.. 60 "tl

C

ca

1Il

:::l

0 50

E.

1Il

C

0 40 lt>.;:

a;

:;; 30

20

10

Pacific

38%

Atlantic

58%

Indian

4%

Figure 2

Swordfish landings by ocean in 1990 (FAG electronic

database).

1980 1985 1990

Year

1970 1975

O+-r"""'r-I"'-r-r"T""r-I"'-r-r"'T""r-T'"T"T"'T""r-T'"T"T""'r-T""T"'I""'"

1965

Figure 1

World swordfish landings (FAG, 1993).

the high-seas driftnet fisheries in the central North

Pacific, which ceased at the end of 1992. World catches

of swordfish remained fairly steady during 1965-80 at

around 30,000 metric tons (t) and then increased

through 1988 to a high of 81,000 t (Fig. 1). Reported

landings declined during 1990-91 for the first time

since 1979.

Pacific

Istiophorids

2%

Swordfish

1%

Although the Pacific Ocean is approximately twice the

size of the Atlantic Ocean, Pacific landings ofswordfish

in 1990 made up only 38% of the reported world catch

(Fig. 2) or approximately 29,000 t (FAO, 1993). The

1990 reported catch in the Atlantic, including the Medi-

, terranean Sea, was about 45,000 t and in the Indian

Ocean only 3,000 t.

In the Pacific, 1990 swordfish landings accounted for

only 1.3% of the harvest oflarge pelagic finfish (Fig. 3).

The fishery for tuna was by far the largest at 2,155,000 t,

while landings of Istiophorid billfishes at nearly 53,000

t were almost double the swordfish landings. However,

there were more landings of swordfish in 1990 than of

Indo-Pacific blue marlin, Makaira mazara, the Istiophorid

with the most landings (22,000 t). The Japanese fishery

(conprised of pelagic longline, driftnet, set net, and, in

Tuna

97%

Figure 3

Catch composition of large pelagic species in the Pacific in 1990 (FAG electronic database).

the early years, harpoon) accounted for 90% or more

oflandings in the Pacific during 1952-60 (Fig. 4). While

Japanese landings, primarily from tuna longline operations, remained relatively stable after 1960, their pro-
____________ Skillman: Central Pacific Swordfish Fishery Development, Biology, and Research 103

30

- 25 .OTHERS (/)

"t:I DUSA

c:

co .MEXICO

III 20 :s .PHIL.I.

0

.s::. DTAIWAN

--(/) 15 DCHILE

c:

0 .JAPAN

I-

(,,) 10

'>:

-C1I

5

0 N r-. N r-. N r-. N r-. It) It) '" '" r-. r-. co co Ol Ol Ol Ol Ol Ol Ol Ol

... ... ... ... ... ... ... ... Year

Figure 4

Area plot of Pacific Ocean swordfish catches by country, 1952-91 (FAa electronic database).

Figure 5

FAa fishel)' statistical areas 67 and 77 in the centraleastern Pacific.

j .-; .. - - , ,,~

f.,..- ...... .~

(~ if .. , , -

- -

H1 1.<:

response to the effects of EI Nino episodes (Fig. 6). For

example, while California and Mexico accounted for

about 35% of the central-eastern Pacific swordfish harvests from 1981 to 1990, California's landings were half

the size of Mexico's landings in 1982, 4 times larger in

1986, and one-tenth as large in 1990.

The high-seas longline fisheries have operated

throughout much of the Pacific; this has been particularly true of the japanese fishery (Fig. 7). Species targeting in this fishery has changed over the years, which

accounts for some of the change in the distribution of

O'

10'S

20'S

30'S

40'S

50'S

60'S

100'E 120'E 140'E 160'E 180' 160'W 140'W 120'W 100'W SO'W

10'N

30'N

20'N

40'N

50'N

60'N

3 Hawaii landings accounted for >10% of total Pacific landings in

1992-95.

portion of the total catch declined to 40% by 1990 with

the addition of other, primarily coastal, fisheries targeting swordfish. With the growth of these other fisheries,

total Pacific landings since 1988 have surpassed the

previous high established by the japanese fishery in

1961. While the United States (U.S.) fishery has grown,

particularly after 1982, it accounted for more than 10%

of the total Pacific catch only three times through 1991

(Table 1), the most current year ofsummary statistics. 3

In the central-eastern Pacific FAO statistical areas 67

and 77 (Fig. 5) ,japan also dominated the fishery in the

early years, accounting for >85% of the reported landings through 1979 (Table 2). The japanese longline

fishery probably was responsible for the majority of

these landings, given that the large-mesh driftnet fishery targeting billfishes and tunas operated primarily in

the western Pacific and generally accounted for <10%

of the Pacific swordfish landings reported by japan

(Ueyanagi eta\., 1989). While landings by Taiwan ranked

third highest in the entire Pacific, their longline landings in the central-eastern Pacific have been less significant; those by Korea were even smaller. After 1979,

landings from the driftnet fisheries based in Mexico

and California increased substantialIy, while landings

by japan, Korea, and Taiwan remained fairly steady.

Large landings in the California and Mexico fisheries

have tended to occur in alternate years, possibly in
104 NOAA Technical Report NMFS 142

effort. Of course, species targeting varies seasonally as

well. Korean longline fishing effort was initially concentrated in the central South Pacific in association with

the albacore fishery and later spread progressively into

the equatorial zone, extending to the coast of Central

America and into the central North Pacific (Fig. 8)

because of targeting on other tuna species. Taiwanese

longline fishing effort was also initially concentrated in

the South Pacific in association with the albacore fishery (Fig. 9) and later spread west to Australia, along

the equator, and into the central and western North

Pacific.

Hawaii

The Hawaii swordfish fishery developed along with the

introduction of longline fishing technology from the

Atlantic Ocean in 1989. Monofilament main line replaced the fiber rope used in tuna longline gear, and

hydraulic reels replaced specialized line haulers. Squid

replaced finfishes as bait, consistent with the known diet

of adult swordfish, although finfishes are a significant

portion of the diet (Palko et a!., 1981). In addition, light

sticks were added to the hook droppers to improve the

swordfish catch.

Table I

Pacific Ocean landings of swordfish in metric tons, 1952-91. "Others" includes Ecuador, French Polynesia, Korea, Peru,

and Tonga. From Bartoo and Coan (1989), updated using FAO's electronic database and FAO (l993). See Table 2 for

updates of U.S. data.

Year Japan Chile Taiwan Philippines Mexico USA Others Total

1952 11,182 157 0 11,339

1953 11,604 85 0 11,689

1954 13,301 77 14 0 13,392

1955 16,220 185 80 0 16,485

1956 12,167 254 163 0 12,584

1957 15,771 250 222 0 16,243

1958 20,815 247 279 0 21,341

1959 19,136 262 265 0 19,663

1960 22,944 273 192 0 23,409

1961 23,636 432 218 0 24,286

1962 14,037 544 23 0 14,604

1963 13,775 300 58 0 14,133

1964 9,703 300 109 0 10,112

1965 11,955 200 300 194 300 12,949

1966 13,283 200 600 277 241 14,601

1967 13,083 200 838 181 1,347 15,649

1968 12,983 200 974 118 855 15,230

1969 15,612 300 1,023 610 1,289 18,934

1970 16,100 200 1,053 1,400 0 400 2,515 21,768

1971 10,400 200 1,033 1,500 0 100 315 13,548

1972 10,400 100 1,005 1,600 2 100 715 13,922

1973 11,100 400 1,987 1,700 4 300 2,015 17,506

1974 10,498 218 1,116 1,84H 6 295 585 14,566

1975 12,361 137 1,239 1,976 0 393 273 16,379

1976 15,843 13 856 1,558 0 39 739 19,048

1977 13,997 32 902 2,103 0 220 685 17,939

1978 14,333 56 779 890 0 1,009 634 17,701

1979 13,091 40 1,060 3,845 7 249 553 18,845

1980 11,953 104 1,459 1,716 380 489 545 16,646

1981 13,078 294 909 1,940 1,575 443 348 18,587

1982 11,350 285 1,107 3,468 1,365 726 348 18,649

1983 12,511 342 1,268 2,974 120 1,195 360 18,770

1984 11,986 103 1,387 2,274 47 2,009 352 18,158

1985 13,083 342 1,429 2,036 18 2,370 148 19,426

1986 14,271 764 1,357 2,089 422 1,585 70 20,558

1987 14,867 2,059 1,540 2,137 550 1,221 194 22,568

1988 15,496 4,455 1,690 4,034 613 1,086 245 27,619

1989 12,367 5,824 3,692 3,756 690 588 263 27,180

1990 11,767 4,955 4,217 3,187 2,650 2,150 474 29,400

1991 9,889 7,255 2,933 3,139 861 5,526 151 29,754
_____________ Skillman: Central Pacific Swordfish Fishery Development, Biology, and Research 105

Table 2

Central-eastern Pacific swordfish catches in metric tons, 1950-93. "Others" includes Korea, French Polynesia, and Tonga.

Non-U.S. data from Bartoo and Coan (1989), updated using FAO statistics for areas 67 and 77 (FAO, 1993). Data for

Hawaii from SWFSC,1 Hamm and Kassman,2 Hamm and Quach,3 lto,4 and WPRFMC5,6 and for the U.S. west coast from

NMFS Southwest Region summaries of Pacific Fishery Information Network data.

Year Japan Taiwan Mexico U.S. west coast Hawaii Others Total

1950 13

1951 17

1952 157 12 157

1953 85 5 85

1954 14 5 14

1955 80 17 80

1956 163 13 163

1957 222 13 222

1958 279 12 279

1959 265 9 265

1960 192 13 192

1961 218 10 218

1962 23 12 23

1963 58 10 58

1964 5,500 0 109 11 5,609

1965 2,700 0 0 194 8 2,894

1966 2,800 0 277 7 3,077

1967 1,900 0 0 181 6 2,081

1968 2,600 0 0 118 5 2,718

1969 4,400 0 0 610 6 5,010

1970 5,600 100 0 400 5 6,]00

]97] 2,700 0 0 ]00 ] 2,800

]972 3,400 ]00 2 ]00 3,602

]973 4,100 100 4 300 0 4,504

1974 2,330 183 6 295 0 2,8]4

]975 2,]39 ]65 0 393 2,697

1976 3,59] 36 0 39 2 242 3,910

]977 2,743 113 0 220 ]9 ]40 3,235

1978 2,6]5 ]08 0 ],009 ]4 29 3,775

]979 2,735 ]81 7 249 ]2 43 3,227

]980 3,299 117 380 489 ]5 23 4,323

]98] 3,38] ]05 1,575 443 9 38 5,55]

1982 2,666 85 ],365 726 18 98 4,958

]983 2,654 ]3] 120 1,195 16 94 4,210

1984 2,589 133 47 2,009 10 51 4,839

1985 2,578 137 ]8 2,370 5 54 5,162

1986 2,792 130 422 1,585 7 23 4,959

1987 3,917 150 550 1,176 45 92 5,930

1988 4,]23 ]60 6]3 ],04] 45 68 6,050

1989 3,566 400 690 316 272 58 5,302

1990 3,556 460 2,650 245 1,905 70 8,886

1991 1,029 4,497

1992 1,548 5,735

1993 1,743 6,124

I Southwest Fisheries Science Center (SWFSC). 1993. Annual and average monthly trends in catch oflarge pelagic species in Hawaii,

1949-78. U.S. Dep. Commer., NOAA, Nat!. Mar. Fish. Serv., SWFSC Honolulu Lab. Admin. Rep. H-83-24, 74 p. SWFSC, 2570 Dole

St., Honolulu, HI 96822-2396.

2 Hamm, D. c., and T. T. Kassman. 1986. Fishery statistics of the western Pacific, vo!. 1. U.S. Dep. Commer., NOAA, Nat!. Mar. Fish.

Serv., Southwest Fish. Cent. Admin. Rep. H-86-04, p. var. Available from SWFSC, 2570 Dole St., Honolulu, HI 96822-2396.

3 Hamm, D. C., and M. M. Quach. 1988. Fishery statistics of the western Pacific, vo!. 3. U.S. Dep. Commer., NOAA, Nat!. Mar. Fish.

Serv., Southwest Fish. Cent. Admin. Rep. H-88-04, p. var. Available from SWFSC, 2570 Dole St., Honolulu, HI 96822-2396.

4 Ito, R. Y. 1992. Western Pacific pelagic fisheries in 1991. U.S. Dep. Commer., NOAA, Nat!. Mar. Fish. Serv., Southwest Fish. Sci.

Cent. Admin. Rep. H-92-15, 38 p. Honolulu Lab., SWFSC, NMFS, 2570 Dole St., Honolulu, HI 96822-2296.

5 Western Pacific Regional Fishery Management Council (WPRFMC). 1993. Pelagic fisheries of the Western Pacific Region 1992

annual report. Western Pac. Reg. Fish. Manage. Counc., 1164 Bishop St., Rm. 1405, Honolulu, HI 96813.

6 Western Pacific Regional Fishery Management Council (WPRFMC). 1994. Pelagic fisheries of the Western Pacific Region 1993

annual report. Western Pac. Reg. Fish. Manage. Counc., 1164 Bishop St., Rm. 1405, Honolulu, HI 96813.
106 NOAA Technical Report NMFS 142 _

10

9

-I/) 8 '0

C

CtI 7 I/)

::J

0 6

.s::.

--- 5 I/)

c

0 4 ....

(,) 3 'i:

-

C1) 2 :lE

1

0

1964 1967 1970 1973 1976 1979

Year

1982 1985 1988 1991

• HAWAII

o CALIF,

• MEXICO

o OTHER

o TAIWAN

.JAPAN

Figure 6

Area plot ofswordfish landings in FAO statistical areas 67 and 77 in the northeast and east-central Pacific (FAO electronic

database).

Swordfish gear is set at dusk and hauled at dawn or

earlier, rather than being set at dawn and hauled at

midday as is typical with tuna gear. This is consistent

with the observation that swordfish in offshore waters

swim near the surface at night and at depth during the

day (Carey, 1990). Swordfish longline gear is configured to fish at depths of 15-25 m, with 2-3 hooks

between floats, whereas tuna gear is rigged to fish at

depths of 150-300 m with 5-15 hooks between floats,

depending on the species being targeted.

If a concentration ofswordfish is found as the gear is

being hauled, some boats will cut the main line, terminate it with a float or radio beacon, set additional gear

in the area, and then continue to haul the remainder of

the gear. Some vessels fish for both swordfish and tuna

on different portions of a trip or even by having some

segments of the gear along the main line configured

for swordfish, and others for tuna.

The longline fishery in Hawaii underwent a gradual

decline in number of boats from the early 1950's to

1975-76, during which time the fleet was reduced by

about 80% (Fig. 10). During 1977-87, the trend reversed and the number of boats roughly doubled. Then,

from 1987 to 1991, the number of boats nearly quadrupled. In April 1991, a moratorium was put into

effect under the authority of a new U.S. federal law, the

Magnuson Fishery Management and Conservation Act.

The moratorium prevented the entry of new boats into

the Hawaii longline fishery and restricted the transfer

of vessel permits. Consequently, in 1992 the number of

boats active in the fishery declined from 140 to 123.

From a single boat in 1988, the estimated number of

boats targeting swordfish on at least one trip per year

increased to 114 in 1991 (Ito, 1998). The swordfish

fleet increased in size when some Hawaii tuna longline

and lobster boats switched to targeting swordfish, and

other boats relocated from U.S. longline fisheries in the

northeast coastal states and the Gulf of Mexico (Itol ).

Prior to 1989, swordfish were an incidental take in

the tuna fishery in Hawaii, with landings averaging 10 t

during 1952-86 (Table 2). Reported swordfish landings increased in 1987 and 1988 to 45 t because of the

large increase in the number of longline boats. The

swordfish fishery began in earnest in 1989, when 11

boats participated in the fishery and landings increased

to nearly 300 t, 500% over the previous high (Fig. 11).

Landings rapidly increased again in 1990 (by 600%)

and then by more modest amounts in 1991, 1992, and

1993 (136%,28%, and 7%, respectively). By 1990, the

Hawaii fishery accounted for 21 % of reported swordfish landings in the central-eastern Pacific. Since California landings were down in 1990, total U.S. landings

accounted for only 24% of total reported landings,

but Mexico and U.S. landings together accounted

for 54%. With 1991 Hawaii landings increasing to

4,500 t, and assuming other catches equal to those in

1990 (more recent data were not available), Hawaii

may have accounted for 40% of the landings in the
_____________ Skillman: Central Pacific Swordfish Fishery Development, Biology, and Research 107

l Number of Hooks

o L.owest 25':'0

o 25~/<) l1elow medIan

120W 100'W 80W

120W 100'W 80'W

140'W

140'W

160"W HOW 120W 100W 80W

160'W

160"W

180"

180'

160'E

160'E

140'E

140'E

A

I-~-"­

I 40'N

O'

c

60"N

50'N

20'S

10'S

20'S

30'S

40'N

10'S

30"N

20'N

10'N

40'S

50'S

60'S ~-+-..L.-'--!..-+--'--f--!--+--'--I--l-.J......1i-----+-.J......1---'--+-.y......L...J--+-'--l--t--L...;.....J

100'E 120'E

50'N

30'S

40'S

60"N '-- --,

30'N

20'N

10"N

O'

0"

40'N

50'S

60'S 1..--"--'--I..--+-i____i-----l---i.....J..-+--'----1.....J..~........,......L-'-_......L_.L...-.. __i______'--....J

100"E 120'E 140'E 160"E 180'

60"N

50"N

Figure 7

Distribution ofJapanese longline fishing effort in (A) 1962-69, (B) 1970-

75, and (C) 1976-l:W.

30"N

20'N

1O"N

60'S t-'--+--t--+--i---'--+-..L.---'---;"'..L.-f-'---'--"----'-.J......1-"--l-.J......1-'--'--'--!--'--'--!-'

100'E 120'E

1O'S

20'S

30'S

40'S

50'S

region. 4 Similarly, projected total U.S.

landings and combined U.S. and

Mexican landings for 1991 may have

accounted for 50% and 60%, respectively, of regional landings (Fig. 6).5

The proportion of swordfish in total pelagic landings in Hawaii has

changed dramatically with the development of the swordfish fishery (Fig.

12). In 1977, the species composition

in the Hawaii pelagic fishery was comparable to that in the Pacific in 1990

(Fig. 3), except that there was more

marlin (9.5% versus 2.4%) and less tuna

(88.2% versus 96.3%). The proportion

ofswordfish had not changed much by

1987, the year prior to the rapid expansion of the fleet (Fig. 12), but the proportion of marlin had increased to

22.2% and tuna had decreased to

74.9%. Subsequently, the proportion

of swordfish increased substantially

while the proportions of tuna and, to a

lesser extent, of marlin declined.

Almost all the swordfish landed in

Hawaii are transshipped fresh to the

U.S. mainland. Some dealers buy only

directly from fishing boats, others do

so on occasion, and the remainder

bid for the fish at the Honolulu fresh

fish auction. Some vessel operators

transship their landings under consignment to dealers on the mainland.

The transshipped product has been

headed, gilled, gutted, and finned (all

fins). Fish below 23 kg are marketed

locally only, and processing is limited

to removing the lobes of the caudal

fin and the bill. Shark- or bird-damaged swordfish are also generally marketed locally. The estimated dockside

revenue generated from swordfish

landings in Hawaii has risen in proportion to catches, reaching nearly

$27 million in 1993 (Table 3).

Examination of the distribution of

Hawaii longline fishing effort became

possible in November 1990 when sub4 In fact, Hawaii catches made up approximately 37% of regional catches in 1991-93

and then declined to 23% in 1995.

5 In fact, U.S. and combined U.S.-Mexican

landings accounted for 38% and 45%, respectively, in 1991; they stayed at about this

level through 1994, then declined to 28%

and 32%, respectively, in 1995.
z

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o

,.,

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Number of Hooks

o Lowest 2501/ 0

o 25°/" below median

25% above median

• Highest 25%

160'W 140'W 120'W 100'W 80'W

10'S

20'S

30'S

40'S

50'S

60'S L-L--..JL-l-...L....l---L...L-l_--J.--'-L..J.._L...L--:....L-L-L-'L-l-'""'----'---L...L-l-L..l....+---L--l.-LJ

100'E 120'E 140'E 160'E 180'

0'

60'N r-B

50'N

40'N

30'N i

20'N

10'N

NumbOI of HOOks

o Lowosl 25'\,

o 25'\. bolow modlul1

II 75"\. abovo modlAn

60'N i ....~"~TV:-li I i I I rf'~ '

50'NI' A ,rl I',+rl'" I;! I! !~~~ 40 N ,( III I I I II I ' I I \ , ,( 1'( , I I tit I ' , . I I:: I~'L c;.... litII t I I I I I 'I I I I 1'\1. Hlll''"st 25~. 30 N I ) )'1 I I I I I II I I I ' , t ' , I ~~- --"rr- rY'ir~ _ ,II;" I I, I I I l I ,I li'~" ): I ',~~

20'N I <..:?J ' ) I I I I I I ' I I I ,.,j I I j I I ' ,I \, .\~ J I.r I:::

)I ! Ii ,I I I I 'I" I I ' Ii, " l'

10'N Y I .iiI I I I I "I I I I I' I I II I~JD)I 'I,~"" I!' III II I'

o (~",,'!- • , J I " I ,~I

, :l-/ ~'" p:- }- - -"':",> , I I I I I

10 S I j-"+--rl' 1,- Ti\"'j. I' , I I ' I I ' 'I/)~JJ\I' I,ll

20'S ! I ,J '''\ I ' ,\ I I I

I \ (' I I 1 I

30'S 'I I ',' I I ' I I

40'S I i 1'-1 " i i 'P i I lp' ,I I ! I i

50S I I I II I I i II ,r, I I I' i

60'S I I

100'E 120'E 140 E 160'E 180· 160'W 140'W 120'W 100'W 80'W

Number of HOOkS

o Lowest 25%

o 250:'0 below median

[J 25% above median

• HIghest 25%

Number of Hooks

o Lowes! 25%

o 25Q/o below median

25% above median

• Hlghe51 25%

160"W 140'W 120'W 100'W 80'W

1- I j j I ; I I I ii' , I I • , I I

120'E 140'E 160'E 180'

0'

10'S

D

50'N

40'N

30'N

20'N

60'N rl-----

50'S

10'N

40'S

20'S

30'S

80'W

, I

I : i I '

1 t

160'E 180' 160'W 140'W 120'W 100'W

,........,.;..;..~ ,f, (71', ,<' I ' - , ,~~ 'I ',- :r~ :I ' , I ..

"~ I

140'E

60'N r -

c

50'N

40'N

30'N

20'N

10'N

0

lO'S

20'S

30'S

40'S

50'S

60'S

100'E 120'E

Figure 8

Distribution of Korean longline fishing effort in (A) 1966-69, (B) 1975, (C) 1977-80, and (D) 1981-87,
DO

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:r

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;.

o' ==

0'

Number of Hooks

o Lowest 25%

o 25% below median

25% above median

• Highest 25%

Number of Hooks

o Lowest25%

o 25%\ below median

Il!!I 25% above median

160'W 140'W 120'W 100'W 80'W

140'E 160'E 180' i60'W 140'W i20'W 100'W 80'W

0'

60'N I

i Il

50'N

40'N

30'N I

20'N

10'N

0'

1O'S

20'S

30'S

40'S

50'S

60'S

100'E 120'E

50'S

60'S L.-I I I I j I I I I j I I i \-j I I I i -\ I I I I ! I I I I I I I i I I

100'E 120'E 140'E 160'E 180'

iO'S

20'S

30'S

40'S

10'N

30'N

20'N

60'N ~.D 50'N

I

40'N

Number of Hooks

o Lowest 25%

o 25% below median

II 25% Above median

• HIghest 25%

160'W 140'W 120'W 100'W 80'W

180' 160'W 140'W 120'W 100'W

10'S

20'S

20'S

30'S

40'S

50'S

60'S I ' I I I I 'I I I ' !! ! !

100'E 120'E 140'E

40'S

50'S

30'S

60'S ! ! I I I I ' I I ' ! I , , ! ' I I I!' I '!

100'E 120'E 140'E 160'E 180'

Figure 9

Distribution of Taiwanese longline fishing effon in (A) 1967-69, (B) 1970-75, (C) 1976-80, and (D) 1981-86.

-

Q

'"
110 NOAA Technical Report NMFS 142

miSSIOn of logbooks became mandatory. During November and December 1990, the fleet was limited to

waters around the main Hawaiian Islands and the southernmost of the northwestern Hawaiian Islands (Fig. 13).

In 1991, effort occurred from latitude 0° to SooN and

from longitude 140 0W to 180°. While the highest level of

effort was again in waters around the main islands and

the northwestern islands, considerable effort was expended south and especially north of the archipelago.

During 1992 and 1993, higher concentrations of effort

extended into the northwestern Hawaiian Islands and

waters to the northwest. Also, the limits of the Hawaii

longline fishery expanded to the north, west, and east.

Effort by the Hawaii fishery reached as far east asJapanese effort through 1980 (Fig. 7), but fell 5° in longitude short ofthe eastward extent of Korean effort (Fig. 8) .

88

Effective management requires knowledge of

various basic aspects of swordfish biology so

that the dynamics of the resource and the impacts of the fishery and management actions

can be assessed.

Population Biology and Dynamics __

The highest catch rates of swordfish in the Hawaii

longline fishery (Fig. 14) occurred in the farthest northwestern and northern areas into which the fishery expanded (Fig. 13). As will be shown in the section on

resource distribution, the areas of high catch rate by

the Hawaii fleet coincide with the central Pacific portion of a region of high catch rate extending from the

western to the central Pacific (Fig. 15). Thus, it appears

that the Hawaii swordfish fishery developed in a region

of resource abundance and that the expansion of the

fishery to the northwest and north was due to the portion of the Hawaii longline fleet targeted on swordfish.

It is also apparent that a considerable portion of the

fishing effort of the Hawaii fleet is still being expended

near the main Hawaiian Islands in the pursuit of tuna.

An examination of indicators of species targeting and

possibly Gulland's (1955) concentration index

could demarcate specific locations ofsegments

of the fleet targeting swordfish or tuna.

93

1:....,' ."

58 63 68 73 78 83

140

120

100

.D 80 E

:J

Z 60

40

20

0

48 53

Year

-Total - - Swordfish

Range and Distribution

Figure 10

Estimated number of Hawaii longline boats, including those

exclusively targeting swordfish. Data from Hawaii Division of

Aquatic Resources, 1948-53, and NMFS logbook data, 1991-93.

6

O+--........---r----r--r--~-....,...-_...-.L,.__-_r__ J 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995

Year

Figure 11

Annual Hawaii swordfish catches, 1950-96. Data from Hawaii

Division of Aquatic Resources and ~\1FS shoreside munitoring.

Swordfish distribution was inferred from the

distribution of Japanese longline catch rates

because the fishing effort for this fishery is

distributed more widely than any other (Fig. 7,

8, 9). These catch rates are for the most part a

measure of the availability and vulnerability of

swordfish adults to gear not used to target

swordfish. As always, the real abundance and

thus distribution of the resource may differ

from what the fishery statistics indicate. Information about fisheries targeting swordfish is

also used here.

Swordfish has a wide distribution in the Pacific, from latitude SOON to 45°S and from the

western margin of the Pacific to the west coasts

of the American continents, based on swordfish catch rates for the Japanese longline fishery during 1962-80 (Fig. 15). In the South

Pacific, catch rates declined toward the southern limit of the effort distribution (Fig. 7), but

in the North Pacific, high catch rates generally

continued up to the northern limit of the effort distribution. The reasons for this differ-
Skillman: Central Pacific Swordfish Fishery Development, Biology, and Research 111

1991 1992 1993 1977 1987 1990

o-l-----L---'--t----

7

60%

6

5

..

l: 4 0

...

u

::; 3

2

2% 10%

Year

IISwordfish • Marlin 0 Tuna

Figure 12

Species composition by weight and by percentage weight of catches by the Hawaii longline

fishery, 1977-93.

conducted in these coastal waters off California and

Mexico. A region appeared off South America with

I Ito, R. Y. 1992. Western Pacific pelagic fisheries in 1991.

C.S. Dep. Commer., NOAA, Nat!. Mar. Fish. Serv., Southwest

Fish. Sci. Cent. Admin. Rep. H-92-15, ~8 p. Honolulu Lab.,

SWFSC, NMFS, Honolulu, HI 96822-2396.

2 Western Pacific Re~ional Fishery Management Council

(WPRFMC). 1994. Pelagic fisheries of the Western Pacific

Region 1993 annual report. Western Pac. Reg. Fish. Manage.

Counc., 1164 Bishop St., Rm. 1405, Honolulu, HI 96813.

200

200

1,100

9,700

22,000

24,270

26,830

swordfish in Hawaii,

C.S. Dollars (thousands)

Table 3

Revenue from longline-caught

]987-93 (Ito!; WPRFM(2 ).

191'7

1981'

1989

1990

1991

1992

1993

Year

ence are not clear; it may be due to the occurrence of

the resource north of the fishery limits, to data aggregation by 5° latitudinal sections, to strong ecological

boundaries, to fleet licensing restrictions, or to some

combination of these.

There were high catch rates in several areas, with

considerable variation in their exten t. The largest, most

consistent region of high catch rates was a broad band

across the North Pacific from Japan eastward to about

140 0W. High catch rates also occurred along the western margin of the Pacific from the equator to the coast

of China; this region extended northeast to Japan and

connected with the North Pacific region in the earlier

periods summarized. Coastal fisheries using harpoon

and other gears also operated in this area. The second

largest region of high catch rates was off Australia,

extending variable distances into the central South Pacific at different times. There appeared to be several

regions of high catch rates off the west coast of the

Americas; one off the coast of California and Mexico

did not extend far enough to the northwest to connect

with the west-cen tral North Pacific region or far enough

south along the coast to connect with another small

region off central America. Drift net fisheries are also
N>

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...,

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'1 Number of Hooks

o Lowest 250;'::.

o 25°,.;, belOW rn~dlan

IE1 25°/<: al)o\le median

• Highesl 25"'/0

-.

120'E 140'E 160'E 180' 160'W 140'W 120'W lOOW 80W

40'S

50'S

20'N ", 1 ~' -: Iii,;,

10Nl'v'~I,~,1 , ..... ,

O l".~ / \'ok.", ~""" j" "

r

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,,~ \)....,J ~~".~,"'-'\*~-~"'- 7--). \,~ '\

'.J.""'':"';_.k--..".;' ~.r",~,~.

10 S ' 'J',<$"I)y,r't-...1~\\ "f~','I

. ' '~I 20'S,;-' , "I

308 : \Tf:'>c-iI ' ))'

, '" I

60'S

100'E

I Ii,

; f

Number of Hooks

o Lowes1 25~,<

o 25% below median

11 25% above median

140'W 120'W 100'W 80'W

1_

160'W

40'r'

60'N "'~T:=-7"';r("- •>-

A J~ '. I " ~',-f i 50'N j-/;:,~.

~v".'\" i~.

:. 1~.1~~. "'

20'N Sf~/ g :J"I' I'j' __ 10'N )'. /~.:~:' .; __ ' ,~, \'.-. f'~~4f~":. :...~.~. . . 0' • l-.J .,..,. '>.. . "'" j' ' .:- '-~? Mfr, : ~. ,'~ ,,~ . 10 Sf.... "\' ~; 20'S -- - ), ,

30'S : :-'11J."-~! ~J.7Y,. ' v: L,..) I, , ii, I , • iI ;. ;

120 i ,E '~40'E lWE

30'1

100'W 80'W

Number of Hooks

o Lowosl25%

o 25% below median

rill 25% above median

• Highest 25%

60'N r;;-- -~~-=rr

50'N I A jr

40'N I' r':~': 1-, .•I,. I ;,"f':. ' j I ) 30'N i,l . ! : i I (J •• 'I ' 1 j c , I

I ..,. r . . I . 1 1

20'N (0.: '. j " ! t '. 1 I I • t

)1~~!lii·ljt·1 ,Ill

10'N - ,I .II' ! I . + 'i 1', • -+" , I I" I I . ;.J 1 I I I ! '/ ~MI" i I 0 .1 t 'I ' " .

0' 'h/i' ~.r.t''..j... J i I~ " '. I.,. 1. 1

. • ih_ "--'f" I I '-,iT'''''''''-'' I ~I l' . I"~-""'~' ....... ; , 10 S -, 1 ;- :t"'? r. I .~ .. i f· '.. I 'i .! I

j 1--l 1/"r-1. '!\\-1·\ ' '.'" I .. J . -'1,;, 1-·, , .v . I: '.. 10, 1 " I I J

20 S I; (- I l FI ' , '1 -1 I'·

1 j '\, I ' j I ' ; I " 30'S 'I." I j ! I I : I I I J :':=-.1,.'~ ).1. I. J'h•.·· 1 J-.J-,- 'i I

40S I • I I I 11!{ 1 t. I 0Y: '. ill 1 I

, • I I I ! I 'I i ' I~f : I' I ii' , 50 S 'I" 1 1 1 I, "., I. I I; , ,I I '

I I

. ,II' I I I' : I'I ' ii' : I I'

: :,

'I

: I ' t 60'S I : I, I 1 . I 1 • I I· 1 I! 1 1 I I' I

100'W 80W 100'E 120"E 140'E 160'E 180' 160'W 140'W 120'W

Number of Hooks

o Lowest 25%

o 25% below median

Ii1 25°/0 above median

• Highest 25%

160'W 140'W 120'W

60'N-, C --_. ~"~'.·,:,c=r-IY,'

1

" .' ..11_ '. f""pt. ,l-I

50'N // '1 . I

:::! rtfT>l j ,;

20'N I q~-h=i '1 rJl:jJ, , . . t , '

10'N h"J., ""'~". ",' '. II' ..i",:.•• f ':.,lJ. ·m','·. "'" .,.i I.' -..1 l'd;r?('" ,'0 I ,. -;- _. " ,

0' ~~ ~~ , 0:, ,.1 -, , I

10'S ~.,~ ..-..~-~,,~·"ti""l'l ... :.1-1=1; 1 Ii, .'ji, 1 .f.

I

-.,.,: I.. " ','

20'S /" "'J1 '\, i ill" r' '.. , f ....t.y. ''i!. '.-f'.:· .', jl : . I '.i..

1

, \ ~' t, r ..~~ I'; ,'.. ,-',:'",- ; , 30'S t~ f" . -. : . i' : - ,-, ,;' t 1 • j ;

50

40:S

S '

',; :T:

.,

~li·:-.'t~01 :' " .. I'. ;.:.' I·~!':·: .. ". .i:,

II

I]' I,.' : -1. i I·· ,:: ',: I:~.' i

60'S : ,. '! i';" I: ' ,;:; 0 I'I':", I,

100'E l20'E 140'E l60'E 180'

Figure 13

Distribution of Hawaii longline fishing effort in (A) November-December 1990, (B) 199\, (C) 1992, and (D) 1993,
VJ

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ec

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:r

Swordfish Catch Rate

o Lowest 25%

o 25%, below median

1m 25°/~ above median

• HIghest 25%

120'W 100'W 80W

120W 100'W 80'W

140'W

140'W

10'5

60'N B A4~':n~tL I, PEi±f'~ j--j.:;. 'f

50'N ' V+---· .- -j,

l< j'HI, I I I"

40'N 1:p:~'r-: iLfl -''''

30'N ~rs'I' 11 !~j ,)-+ t'

20'N "Q ~: ~-, ,..l--J E-t ;l--trrIrrJ

\., • f -- I =1=1 J I I~ITIIIIl

10'N ~ti' -~/l. " ; ,j+, .1't:i,ij

0' _ ", .,,~~J, L~, t ' J', +-; J H'

10'5 ."~-'::" I·~~,qjl-jj-· , ["7' I V'r-~j'\~,-+ 1,_., "1' I 1

205 ] r r' i~, ,- 1-

30'5 _[I\. /' j -'jIf I'h j

40'S ':1 I:f" "bf-fJ', S'J;Y'I " !T

50'5 Iii I i I: 1·1 i :.!-, j t i j I:

60'5 L.Jlc....;·---!..4-·-'-,--,-'-'-,-,--+---,:L.......j......----,-l--,--,-'.l.-l...-It---'--l.

100'E l20'E 140'E l60'E 180' l60W

20'S

30'5

40'S

50'S

60'5 It; I ! I 'I' I [.! i I I i I I ! j I! i i: I I i I

100'E l20'E 140'E 160'E 180' 160'W

60'N )_....,..-

80W

f -,

I

i I

100'W

100W 80'W

Swordflsh Calch Rate

o Lowest 25~/O

o 25% below medIan

C1 25%, above median

• Highest 25%

l20'E 140'E 160'E 180' 160'W 140'W 120'W

40'S

50'S

60~N "_. ·_···..-~~7::'-;~ ...·:~,,-' I "f -

50'N A "'L.

. .I

' ..j~j ! I . i"~. .

1

i .'1__i-"f- ""7~--- L

..;. t.. J. '.:: 1":_1 _ ._ j + 1-:I . Swordfish Catch Rate

40'N .£/p~' I T 1 f 1 i 1. L _' i ~'11 0 Lowest 25%

'7~...0.~.,?!'.l1_.1-.:.-j -j..~. i I "1 i- J _, : LI _ i_ 0 25% below median

30'N . I~.:: J. ;',Y.'.I':'+., 1-:.I J-If.'I -,-I 1-.~- r i - _;. .J L !_t_ I ,~I C\ •III 25%abevemedlan Highest 25%

20'N ,?/~/{j,; . . IT ,-. t 1 , I _ 1 J 1-j 'J L - \' In'!' 'I L I 1 J f- -I' 1 ," j +- ", " I'!. j r' -- -j - -I I ' , 10'N :---,) L :. . r ,of 1 -- J -, ... L I 1 '1 I ,- r ,'1 '.' _ I . I... I· 1-' ,1-' I' ", :./'ro.'.' 1'1'....•-1,-.1·-'.. !-'.. - I-_,._It 1.. I., • '.' Ii 't- o' (.r-' 't.l' ' : 'I ,I., ,!.' J !,' ;.. L' , ! ' 1 I 'I 1

\ :i---/~n,tr~,..::j r.' -1 i- J '-I II-I' 1 L· ,.I 1 j-j'T c LI "!.. ,_ ~~ I ""'-", "'-' 'd 1 j 1 ,I' It - - ,-I J

10'5 _I :;-~{._.;fl''',f'''''f~~-b '<:J • t- i-'ll' Ll -j . I

! -i tf,l"'; lJ\ij'I-['l' r- i--Il r L I -I, T i= 11 r

20'5' ..1j-r. _," ,v' '-..j \1'-I'.-'."'1. -'. J-',"-t -+ ri'," +"l-! J

30'S _I J ' Ii . I-j t- ,). ~'-.'-', J'.'" + 1- '.'.-.'.' .'.' j_' 4'1 ' ¥b. ! '_ j . r i ! i ' I' )--'1'-':' f i i 'Ct-'I "' • 1 litO! ! ! ' . :'J'i I ' I ' I I I , ' , I y,/, ,'I ' • I I ' ; I I' , ,<:( j , , t I ! "I i ' ' " J' ' 60'S I 1 I I I I I , , I i 1 I

100'E I I I I, Ii'I I . 1 i ! I ! I i I I

60'N ------'7',=i~.~~-~-'

C ~-i-l'- "1.... 1·~~11--Ill" "f--........ I"""f--H-j 11 1 .. , X\. 1\1 I "--f-J I, J

50N /~lJ~ Ji-Filfij-' -+I'I_I ! t

40'N <~.. f-- 9;l J 1- ! _I . j. : :DU.~ ,-IlL L t- '~ - 1-

30'N ;' ~\"'l ;- I -I 1 1 1- 1-

.r' I -I I'lL, I, I -I i " 20'N (Q; ~'-: I -; - ! j- i-I -i ,. H'-+-t--t"lI-t-+- i- J 1- - I ,- -!-11 'f-I- - T

10'N y,l.jT" j. j- L I-I l' 1 f-, ,.! -, J 1 • I I "I I I i

. ; t-/(t~'-"'~t l J. j.. i-l·j '1 T,t.: J-l-~ ,"'1'

o ;,w,-"o;!~" 'i-I, -I r - I l'i- -I - " L ", "-.......,,',,;;;."-1 .. .J - L I-r----t-- - , ~,....",._.\._~. I, • f~N' l~'" I J I' I I I 105 ,t.. Jl" - -,f 'e-;' l~'- -I - ). I· . -, 1 - - L I J;;!rf1:, \. '-I '. L. 1.1_1_1"-j ~Li-!.J

20'S i lj' 'oV '\i -IJ .L:·i-,'~1-j '1' L~)_J...:J • - . I"'" . i • I I ' ' f \ 'In -f, t I- !-1 -Ii i L

30'S j -1-. li '-j-Il t-j- ,-i,-,I- r r M~ /_,.1 t,-"",,'I.+ i-I-t J

40'S ! l! j , • 1 .'t~'.• ! i I I n. 'I. ii, I " ! 1 I 'li~I;Vli·I.Y:;,v·.'·! ·1' , i" 1 ' I' ; i It;..! j , ! I '1 I . 1

50'5 I,·!! iii' I , I !. Ii! I I j ,!

! 1 ! ' I I I i I I 1 I I ! I ! I I ! !, 60'S ' I,· I ., . I,!'

100'E 120'E l40'E l60'E 180' l60'W 140'W

Figure 14

Distribution of catch rates (swordfish per 1,000 hooks) for the Hawaii longline fishery during (A) November-December 1990, (B) 1991, (C) 1992, and (D) 1993.

--I.>"
114 NOAA Technical Report NMFS 142 _

U.S. federal law (the Magnuson Fishery Management and Conservation

Act) requires the prevention of recruitment overfishing. Thus, an estimate of size at maturity is necessary

to assess trends and the dynamics of

the mature, spawning component of

the stock. All of the published estimates (Table 4) are based on small

Size at Maturity and Spawning

Stock Structure and Movement

The stock structure of swordfish is

poorly understood. For stock assessment purposes, a single, Pacific-wide

stock generally has been assumed,

with the possibility that there are separate stocks associated with known fishing grounds in the western-central

North Pacific, eastern Pacific, and

western South Pacific (Sakagawa and

Bell, 1980; Bartoo and Coan, 1989;

Skillman, 1989). Only a single swordfish tag recapture has been recorded

in the Pacific. This fish, which weighed

approximately 11 kg when it was

tagged and released from a commercial fishing boat at 29°N, 154°W on

24 April 1992, was recaptured in the

same general area 11 mon ths later at

a weight of 32 kg. Tagging results in

the Atlan tic have indicated that swordfish movement is primarily latitudinal (Berkeley, 1989) and that fish

tagged in the summer tend to return

to the same locale in subsequentsummers (Beckett, 1974).

Progress on the use of genetics to

determine swordfish stock structure

is reported by Grijalva-Chon et al.

(1996) and in the present publication (Alvarado Bremer, Leclerc, and

Ely, 1998; Chow, 1998).

extensions into the central Pacific

along the equator and at middle

southern latitudes, but it never quite

joined with the region extending eastward from Australia. The Chilean fishery also takes place in these coastal

waters off South America.

SwordfISh' Catch Rate I o Lowest 25'7,

o 25% beluw medw.n

f] 25% above median

• Highest 25%

160'W 140'W 120'W 100'W 80'W

160W 140'W 120W 100'W 80W

30'S

40'S

50'S

I 60'S ~-+-W-..L-4....LL..l--+-~e.-L+-.:...-L---l-+--J---'---l-I-----l------'-.L.-'-L-.L-'--'-----l-J

100'E 120'E 140'E 160'E 180' 160'W 140'W 120'W 100'W 80'W

60'N ~--­

50'N I B

i

40'N I

30'N ,

20'N li, I"

10'N ,:"

O'

10'S

20'S

30'S

40'S

50'S

60'S f--'----l---l--'---+---'-+--'--l"'---+---'--r--'---'--t----'------'---l----__+__'

100'E 120'E 140'E 160'E 180'

10"S

1O"S

20'S

Figure 15

Distribution of catch rates (swordfish per 1,000 hooks) for the Japanese

longline fishery during (A) 1962-69, (B) 1970-75, and (C) 1976-RO,

30"S

40"S

20"S

50"S

60"S I-----'--'--l-__l_--'----'-L..-'-_'-'----'-,--'__'-'----'-"'-- ----'

100'E 120'E 140'E 160'E 180'

60'N r --- ~'-_;?~"'r::r.;:r--r-Ti---rT!·"'i"i::J71-,--""F-ii:

, C

50'N j ,

40'N I

30'N I

20'N I

10'N
_____________ Skillman: Central Pacific Swordfish Fishery Development, Biology, and Research 115

Table 4

Estimates of swordfish size at maturity. Values are in the units published by the authors: EFL = eye-fork length, LJFL =

lowerjaw-fork length, and RWT = round weight.

Ocean Sex Smallest mature

Pacific Female 140

83.0

150

Atlantic Female 70

74

160

Male 100

21

90

All mature

235

L65

Size at maturity Units N1 Source2

170 cm EFL 362 1

156.5:1 kg RWT 15 2

170 cm EFL -58 3

cm LJFL G 4

kgRWT G 5

171 cm LJFL NG 6

cm LJFL NG 4

kgRWT NG 5

L13 em LJFL NG 6

I NG = not given.

21 = Kume and Joseph (1969),2 = Uchiyama and Shomura (1974),3 =Yabe etal. (1959),4 = Ovchinniko\' (1970), 5 = PaLko et al. (191'1)

referencing personaL communication from E. Houde, 6 = Hoey et al. (1989) referencing personal communication from R. Taylor.

3 Median between the smallest and largest mature fish in the sample.

sample sizes, and none are based on modern histological techniques necessary to determine maturity in indeterminate spawners, which swordfish may be, and to

estimate fecundity.

For the eastern tropical Pacific, Kume and Joseph

(1969) classified ovary samples collected from theJapanese longline fleet using values of the gonado-somatic

index (GSI), the ratio of gonad weight to the cube of

eye orbit-fork length (EFL). While they stated that

there was no established relationship between GSI and

state of maturation for swordfish, they observed that

there was a cluster of samples with low ovary weights

and GSI values <3.0, which they classified as immature

or undeveloped. Mature fish were defined as having

GSI values ~3.0.

For tht> central Pacific, Uchiyama and Shomura (1974)

classified, according to the most mature ovum stage

present, a small sample of ovaries collected from commercial longline boats operating in the vicinity of Hawaii. The ovum stages identified were primordial, early

developmental, developing, early ripe, ripe, and residual. Taking the occurrence of early ripe or later

stages as indicating maturity, I determined that the

mature fish in their samples ranged from 83.0 to 246.3

kg round (unprocessed or whole) weight (RWf) , with

the median at 156.5 kg RWT.

For the western Pacific, Yabe et al. (1959) plotted

ovary weight versus EFL of samples collected from the

swordfish fishing grounds (30-45° ,1400E-1800). They

observed a cluster of points with small ovary weights,

which they interpreted as immature fish, and a length

range in which ovary weight increased rapidly with body

size. They interpreted this range (150-170 em EFL) as

the size at maturity, and also gave age at maturity as 5-6

years. Sosa-Nishizaki (1990) indicated a similar range

(150-160 cm EFL) using samples collected from across

the Pacific in all seasons.

For the Atlantic Ocean (Table 4), Palko et al. (1981)

provided estimates of size at maturity for female and

male swordfish, referencing Ovchinnikov (1970), without any details of origin of the samples or methods

used. They also provided estimates for swordfish taken

off the southeast coast of the U.S., referencing a personal communication from E. Houde. Also, Hoey et al.

(1989) provided estimates from gonads collected off

the coast of Florida, referencing a personal communication from R. Taylor. These estimates for female and

male swordfish were for the size at which mature fish

were first found, the size at maturity (size at which 50%

of the specimens were classified as mature), and the

size when all specimens in the spawning season were

mature. Miyake and Rey (1989) stated that swordfish

age 4 and above were mature.

Since these estimates were reported in different units

of measure (EFL, lower jaw-fork length, and RWT;

Table 4), I converted them to EFL using research data

collected in the central Pacific to facilitate comparison.

For females, all the estimates except that by Ovchinnikov

(1970) clustered around 150 cm EFL. For males, a

smaller size at maturity was indicated, around 100 Col

EFL, but fewer estimates were available and only for the

Atlantic.

chiyama and Shomura (1974) found that sexually

mature swordfish with developed gonads occurred in

Hawaiian waters from April through July. Swordfish

were rarely present at other times and were generally

small, immature fish. Kume and Joseph (1969) found

that sexually immature female sworpfish were present

in the eastern Pacific in all months, whereas females in

spawning condition were most abundant during March-
116 NOAA Technical Report NMFS 142

July north of the equator and around January south of

the equator.

To evaluate the occurrence of mature swordfish captured with longline gear, Sosa- ishizaki (1990) divided

the Pacific into five areas, one spanning the equator

from 10° to 100 S, and two areas each in the orth and

South Pacific, divided at longitude 1500 W. In the northwest area, spawning appeared to be concentrated in

waters from the Hawaiian Archipelago southward and

occurred during April-July. Spawning was not apparent in the northeast area. In the southeast area, spawning occurred in non coastal pelagic waters during October-January. In the southwest area, spawning was concentrated in the Coral Sea during November-February

and in waters around FUi during May-July. Mature fish

were found in all months in the equatorial area and

exhibited no seasonal trend. Sosa-Nishizaki (1990) believed the equatorial area to be an area of mixing of

stocks from north and south.

Growth

The ability to establish the age of fish allows us to

classify landings by age-class and to model fish growth.

Estimates of growth model parameters can be used in

various age-based and age-structured stock assessment

models (Table 5). Current efforts to age central Pacific

swordfish al-e described in Uchiyama et al. (1998).

All the studies cited in a recent summary of growth

model parameters (Sakagawa and Bell, 1980; updated

by Boggs, 1989) are based on very few samples, and the

estimates should be regarded as provisional. The only

reference for the Pacific was Yabe et al. (1959; Table 5);

from the data they present, the fifth and largest modal

size used to fit the growth model was 148 cm EFL. Thus,

their model is not representative of growth of larger,

older fish. The Japanese swordfish longline fishery in

the ]950's was conducted at night, north of 30° from

140° to 1600 E (Kume and Morita, 1966), and caught

mostly small swordfish.

Similar problems due to lack of data for large fish exist

with several models presented for the Atlantic (Caddy,

1976, ] 977; Berkeley and Houde, 1983; Wilson and Dean,

1983; Tsimenides and Tserpes, 1989). Models by Radtke

and Hurley (1983) and the International Commission for

Conservation of Atlantic Tunas (lCCAT, 1989) were fit

with data from large fish, but data from small fish were not

a,'ailable for the tag recapture model (ICCAT, 1989). The

models from these two sources provided quite different

estimates oflength at age. Ifthe tag recapture model were

accepted as the most reliable, it would suggest that the

otolith ridges used by Radtke and Hurley (1983) to age

fish were formed less often than once a year.

Table 5

Estimates of von Bertalanffy growth parameters and mortality rate for swordfish. Natural mortality rates (1'v1) calculated

from K using the equation of Murphy and Sakagawa (1977). Table derived from Sakagawa and Bell (1980) as updated by

Boggs (1989) and again here using sources 4 and 7.'

Size range 3

Ocean Method .'1/ Sex2 (em) Source I K 1

0 (yr) L_ M

Pacific Length modes L' 61-245 0.124 -1.169 309 0.22

Atlantic Length modes

and vertebrae L' 50-260 2 0.2304 3654 0.21-0.433

Anal ray 275 M 70-270 3 0.19 -~.04 217 0.35

internal zones \64 F O.OY -2.59 340 0.15

Anal ray 427 M 54-~15 4 0.34 -1.22 194 0.64

internal zones 455 F 0.25 -1.52 220 0.47

Otolith 39 .\II 79-209 :; age estimates, no model

internal zones ~9 F 102-290

Otolith 73 M 88-208 6 0.07 -3.94 277 0.12

ridges 195 F SO-~70 0.12 -1.68 267 0.21

Tag recapture 84 C 90-260 7 Gompertz growth model6

I \ = Yabe et al. (1959), 2 = Caddy (1976, 1977), 3 = Berkeley and Houde (19H3), 4 = Tsimenides and Tserpes (1989), 5. = Wilson and

Dean (1983),6 = Radtke and Hurley (19S3), 7 = lCCAT (I~HY).

2 M = male, F = female, l! = unknown or unreported.

3 Pacific and Atlantic size ranges are for eye-fork length and lower jaw-fork length, respectively.

4 These estimates of Kand 1._ from Caddy (1977) do not match the size-at-age groups given in Caddy (lY76).

, Total mortality, Z = 0.1 ~-O.65 and 0.16-0.59 using data fron the harpoon and lonRline fisheries, respectively.

6 Dressed weight (Ibs) = 305.56 exp (-4.6235 exp (-0.305815' Age)), with Age in yr.
____________ Skillman: Central Pacific Swordfish Fishery Development, Biology, and Research 117

In more recent reports, Prince et al. (1988) described

the reading of presumed annual increments on anal fin

rays. However, they could not verify their interpretation of the annual increments using mean monthly

marginal increment widths or mean marginal incremen t ratios. Ehrhardt (1992), in a reanalysis of the

same data, provided statistical evidence that verified

the use of annual increments by Prince et al. (1988).

Miyake and Rey (1989) indicated that the model derived from tagging returns (SEFC, 1987) is the most

accurate available and has been used by ICCAT for

stock assessment. Two problems occur in gathering tag

and recapture data for swordfish: it is difficult and

dangerous to determine fish size prior to release, and

sex of the recaptured fish must be determined when

the fish are dressed at sea. ICCAT (1989) presen ted an

updated model based on tag recaptures, a Gompertz

growth model (Table 5).

Mortality

Few estimates of the instantaneous rates of swordfish

total mortality, Z, natural mortality, M, and fishing mortality, F, have been published, especially for the Pacific.

All available estimates are based on small sample sizes

and many use approximate methods; thus, the estimates are very preliminary. Using the model ofBeverton

and Holt (1956), which requires estimates of the von

Bertalanffy growth coefficients K and L~, the size of

swordfish when recruited to the fishery, and the mean

size ofswordfish in the catch, Caddy (1977) estimated Z

using data from the Canadian harpoon (0.12-0.65)

and longline (0.16-0.59) fisheries. Tagging studies, according to Caddy, could also be used to estimate Z, but

these estimates would be subject to considerable variation caused by immigration and emigration.

All available estimates of the instantaneous rate of

natural mortality, M, were obtained by indirect means.

One estimate of M (0.2-0.4) was inferred from estimates for tunas and considerations of life expectancy

(Caddy, 1977). All other estimates of M were based on

estimates of the von Bertalanffy growth parameter, K,

and an empirical relationship between M and K from

Murphy and Sakagawa (1977). This regression was computed using three data points for bluefin tuna, Thunnus

thynnus, albacore, 1'. alalunga, and yellowfin tuna, 1'.

albacares. Given the concerns about bias in the estimation of growth discussed in the previous section, similar

concerns should be held for estimates of Mbased on K

from these growth models. Estimates of M using this

procedure were first provided by Caddy (1977); were

recomputed utilizing several published estimates of K

by Sakagawa and Bell (1980); were updated by Boggs

(1989); and are updated again here using estimates of

Kin Tsimenides and Tserpes (1989) and ICCAT (1989)

(Table 5). Separate estimates of M for males and females are given by Berkeley and Houde (1983), Radtke

and Hurley (1983), and Tsimenides and Tserpes (1989).

An estimate of M could not be computed for the growth

model from tagged fish in the Atlantic because the

Gompertz model does not include the parameter K.

The single estimate for the Pacific (M = 0.22) was computed by Boggs (1989) using K estimated from data in

Yabe et al. (1959). Most of the estimates in Table 5 fall

within the range inferred from tunas, in spite of the use

of different tissues and size ranges of specimen in determining the growth models.

Caddy (1977) men tions two methods to estimate M

directly, but no estimates using these techniques have

been published. First, he discussed using the catchcurve method, which requires data collected before

heavy exploitation has occurred, but he pointed out

that the method would be difficult to apply because

swordfish stocks are spatially structured by sex and age.

Second, he discussed Suda's method utilizing estimates

of Z and fishing effort at two or more levels of fishing

(Morita, 1977), but no estimates using this procedure

were provided.

No estimates of the instantaneous rate of fishing

mortality, F, have been published for the Pacific. For

the Atlantic, estimates of F by age/size classes have

resulted from stock assessments conducted using virtual population analysis (VPA; Swordfish Assessment

Group, SCRS, 1992). Caddy (1977) suggested using

length-based analysis to estimate fishing mortality, which

requires estimates of L~, M/ K, and exploitation rate, E,

and the existence of a stable size frequency (Jones6).

He also discussed the use of tagging data but provided

no estimates using either of these methods.

In summary, no reliable estimates of Z, F, or M exist

for Pacific swordfish fisheries. While rates can be inferred from studies conducted in other areas, those

estimates also suffer from some of the same problems

described above.

Stock Assessment

In both the Pacific and Atlan tic Oceans, the first attempts to assess the status of swordfish stocks used

Schaefer's (1954) equilibrium stock-production model

or similar models (Pella and Tomlinson, 1969; Fox,

1970). Production models were used because they inLe6 Jones, R. 1974. Assessing the long-term effects of changes in

fishing effort and mesh size from length composition data. ICES

Meeting Doc. eM. 1974/F:33, 12 p. Demersal Fish ( orthern)

Comm., lnt. Counc. Explor. Sea, Palaegade 2-4, DK-1261,

Copenhagen, K., Denmark.
118 NOAA Technical Report NMFS 142

grate the effects of growth, natural mortality, and recruitment into a rate of stock increase that is dependent only on mean stock size. Therefore, production

models have modest data requirements, requiring only

two of the three commonly available fishery statistics,

namely catch, effort, and an index ofstock abundance

(e.g., catch rate). Also, the results from such a model

are simple to understand and to convey to resource

managers. Production models do estimate maximum

sustainable yield (MSY) accurately until MSY is exceeded.

Those attempting to assess the resource in the Pacific

have noted that the predominant fishery, the Japanese

longline fishery, underwent a number of changes in

species targeting, bait, and gear configuration (Bartoo

and Coan, 1989; Skillman, 1989). Prior to 1962 most

swordfish catches resulted from a night-set longline

fishery in the western Pacific targeting swordfish and

using squid as bait. Over the next two years, the Japanese fishery changed to a predominately day-set fishery

targeting tunas and using mixed bait. The tuna fishery

has since undergone considerable expansion, and deep

longlining was introduced in the 1970's to target bigeye

tuna (Suzuki and Warashina, 1977). In 1976, nylon

branch lines began to be used on small longline boats

and by 1989 had become the dominant type of main

line on these boats (Warashina, 1991). Problems have

been experienced with the durabili ty of monofilamentnylon main lines on Japanese distant-water longline

boats (Katsuo-Maguro Tsushin, 1993), but their use

appears to be expanding (Katsuo-Maguro Tsushin,

1994a, b). Data on these changes in gear efficiency a:ld

targeting were not readily available to standardize statistics on the Japanese longline fishing effort, and the

stocks were probably not in equilibrium given the expanded level of fishing. Thus, little confidence has

been placed in the results of equilibrium production

models even when such modeling was attempted, e.g.

an MSY of 18,000-20,000 t (Sakagawa and Bell, 1980;

Skillman, 1989). The conclusion in the latter two papers and in Bartoo and Coan (1989) was that the fishery

had not overexploited the stock, catch rates had remained relatively stable over time, and the resource was

in good condition. It should be noted that Pacific landings (Table I) have increased considerably and by 1991

had exceeded previous estimates of MSY by some 8,000-

10,000 t. 7

Similar problems with time series of nonstandardized

fishing effort were encountered in attempting to assess

Atlantic stocks using equilibrium stock-production models (Kikawa and Honma, 1981; Farber and Conser,

1983). Therefore, Atlantic researchers turned in 1985

to the use of age-structured assessment models, bei By 1995, Pacific catches exceeded these MSY estimates by 10,000-

12,000 t.

cause these depend only on age-composition data and

estimates of growth, natural mortality, and fishing mortality in the terminal year of the fishery (Conser et aI.,

1986). A VPA model was used to estimate stock size and

fishing mortality at age, with the best estimates in the

earlier years of the time series, because VPA is a backward-sequencing procedure. With the addition of average weight-at-age data, estimates of stock biomass, surplus production, and female spawning-stock biomass

also became available. Such information helped in the

evaluation ofwhether the Atlantic fishery in the course of

its development had a significant impact on the stock.

Estimates from VPA were often analyzed with agebased models, e.g. estimated yield per recruit was used

to estimate spawning-stock bi0mass per recruit. Over

the next several years, different formulations of the

VPA model and different means of tuning the model

were used to deal with uncertainties in estimates of

growth (particularly for older fish and also by sex) and

natural mortality (Restrepo, 1991; Restrepo and Powers, 1991; Hiramatsu, 1992; Restrepo et aI., 1992). These

assessments were also used to deal with differences in

size composition estimation among different fisheries

and the lack of data on sex composition of landings.

Since so much ancillary information was being incorporated to tune the VPA to handle these problems and

obtain better estimates, an integrated approach called

ADAPT was employed with the VPA (Conser and Powers, 1990; Restrepo et aI., 1991; Mohn, 1992; Powers

and Restrepo, 1992; Hiramatsu, 1993; Gavaris8).

However, Conser et al. (1992) noted that the abandonment of stock-production models for the ADAPTVPA approach may not have been wise for several reasons. First, growth models that adequately modeled the

growth of older age groups had not been developed.

Second, logistical sampling problems had precluded

the developmen t of age-length keys, thus requiring the

use of cohort slicing to estimate catch-at-age using sizefrequency data, landings data, and growth models.

Third, since the causal mechanism for the observed

preponderance of females at larger sizes had not been

determined, it was unclear whether to incorporate sexually dimorphic growth, differences in natural mortality by

sex, differences in availability by sex, orsome combination

of these or other possible causes in the assessments.

Because of these problems, interest in the use of

stock-production models was renewed, but this time in

nonequilibrium (or dynamic) versions. In contrast to

VPA, time-series estimates (e.g. biomass) from a stockproduction model are estimated more accurately at the

B Gavaris, S. 1988. An adaptive framework for the estimation of

population size. Can. Atl. Fish. Sci. Ad\'. Comm. Res. Doc. 88/29,

12 p. Marine Fish Div., Dep. Fisheries and Oceans, St. Andrews,

:".B., EOG 2X1 Canada.
____________ Skillman: Central Pacific Swordfish Fishery Development, Biology, and Research 119

end of the time series because a forward-sequencing

computational procedure is used. Vaughan and Scott

(1991) compared the performance of three models:

the equilibrium logistic production model (Schaefer,

1954); the Pella and Tomlinson (1969) generalized

model, with an adjustment for nonequilibrium (Fox,

1975); and Schnute's (1977) dynamic logistic model.

While catch in a given year is a function of effort in the

same year in the equilibrium stock production model,

catch in the current year is a function of effort in the

same year plus catch and effort in the previous year in

Schnute's model. Vaughan and Scott (1991) found that

an MSY estimate was highest for the equilibrium model

and lowest for the dynamic model, as expected. Estimates based on the model with nonequilibrium adjustment were close to the dynamic model, but generally

higher. Conser et al. (1992) proposed using Shepherd's9

nonequilibrium stock-production model and provided

a statistical basis for estimating the parameters. The

dynamic nature of this model is based on biomass in a

given year as a function of biomass at the start of the

previous year, plus net production and catch. Another

nonequilibrium model (ASPIC, a surplus-production

model incorporating covariates) has been developed

that is similar to the Pella and Tomlinson (1969) model

but uses an analytical solution to the yield equation

rather than a numerical solution (Prager, 1992, 1993b;

PragerlO). Prager (1992) noted that since the model is a

forward solution, it can be modified to handle different

patterns of fishing or data collection as easily as with

simulation models, which is a benefit also noted by Methot

(1989, 1990) in discussing his stock-synthesis model. Thus,

ASPIC can use several data series, e.g. catch-and-effort

data from different gears or different periods in a fishery.

Auxiliary population-biomass estimates or other information can be used to tune the model. Also, bootstrapping

can be used to construct approximate nonparametric

confidence intervals (Prager, 1993a).

Issues and Problems _

With the recent development of swordfish fisheries in

the Pacific, a number ofissues and problems have arisen

pertaining to fishery management, biological research,

and data collection.

9 Shepherd, J. G. 1987. Towards improved stock-production

models. Int. Counc. Explor. Sea (lCES) Working Group on Methods of Fish Stock Assessment, Working Pap. 6, 16 p. ICES,

Palaegade 2-4, DK-1261, Copenhagen, K., Denmark.

10 Prager, M. H. 1993. User's manual for ASPIC: a stock-production model incorporating covariates, program version 3.30. U.S.

Dep. Commer., NOAA, Nat!. Mar. Fish Serv., Southeast Fish. Sci.

Cent., Miami Lab. Doc. MIA-92/93, no. 55, 31 p. SEFSC, NMFS,

Miami, FL.

Fishery Management

Under U.S. federal law, fishery management actions for

U.S. waters are initiated by regional councils and implemented by the NMFS. Deliberations and resultant management actions taken by the Western Pacific Regional

Fishery Management Council (WPRFMC) and the NMFS

indicate three primary fishery management concerns associated with the swordfish fishery in the central Pacific:

Stock Dynamics and Overf"Ishing-The size of the harvest

of the expanding central-eastern North Pacific longline

fishery directed at swordfish could possibly cause

overutilization (harvesting beyond MSY) or even recruitment overfishing. The expansion ofthis fishery and coastal

fisheries also targeting swordfish has changed the nature

of the Pacific swordfish fishery; previously, the vast majority of swordfish were taken incidental to tuna fishing

operations. A species targeted by a number offisheries is

more likely to become overfished than one taken incidentally, although bycatch can result in overfishing. Harvesting of subadults by some segments of the Hawaii fishery,

and probably other fisheries as well, could lead to yieldper-recruit concerns, but this issue has not been raised, at

least formally, in the Hawaii fishery. Relevant U.S. domestic management actions are the Fishery Management Plan

for Pelagic Species in the Western Pacific Region and the

first amendment to the plan, which specified an objective

definition of recruitment overfishing.

Incidental Take of Protected Species-In U.S. fisheries, this is regulated by domestic law (Endangered Species Act). The take of marine turtles reported by the

Hawaii-based longline fishery exceeded the allowable

limits set for the fishery before the expansion in fleet

size or targeting on swordfish had occurred. Because of

this, consultations under the Endangered Species Act

were conducted in 1994. The impact ofsuch bycatches

on protected species and their prevention is IDcreasingly becoming a fisheries management issue.

Bycatch-Sharks (primarily blue shark, Prionace glauca)

comprise the largest catch of the Hawaii-based swordfish longline fishery, although landing numbers have

been low. Some finning of blue shark occurs, but estimates of landings in round weight are not currently

available. Reported landings of whole sharks have consisted primarily of mako, Isums spp., and thresher, Alopias

spp., but have been a very small proportion oftotallongline

landings. The incidental hooking ofsharks may become a

managemen t issue if the take becomes large and if fishery

or ecological impacts become significant.

The Pacific Regional Fishery Management Council

(PRFMC) and the North Pacific Regional Fishery Management Council have not developed a fishery manage-
120 NOAA Technical Report NMFS 142

ment plan for swordfish or similar pelagic species. The

states ofWashington and Oregon do not allow driftnet- or

longline-eaught fish to be landed, while California allows

driftnet fishing but not longline fishing in waters off its

coast. However, Oregon is in the process of permitting

driftnet fishing (Hanan I1 ).12 At present, there is no administrative mechanism for coordination of U.S. swordfish management in the central and eastern Pacific, although the PRFMC could serve that role on the U.S. west

coast. In the North Pacific there is no regional fishery management body with the authority to manage swordfish.

Biological Knowledge

As discussed above, swordfish biology in the Pacific is

poorly known, and estimates of population parameters

necessary for stock assessment are generally lacking.

Although some of these shortcomings are addressed in

this symposium, no formal or informal arrangement

exists for assessing priori ties and facili tating the coordination of research among nations and scientists to improve our knowledge of this species.

Fishery Monitoring

Data collection activities are driven by local interests and

historical practices. Landings data on the U.S. west coast

are maintained in a database by the Pacific Marine Fisheries Commission, but data formats are not standardized

between states supplying the data. Alaska does not routinely collect landings data from the longline boats fishing

in the central North Pacific. The Honolulu Laboratory, in

collaboration with American Samoa, Hawaii, Guam, and

the Northern Mariana Islands, maintains a landings database, but it contains little data on swordfish other than for

Hawaii. No regional or more broadly based arrangement

between nations exists to coordinate data-eollection activities for swordfish or provide a forum for exchanging or

accessing data. Thus, in general, statistics necessary to

assess the status of swordfish in the Pacific are either

unavailable or inaccessible on a timely basis.

Honolulu Laboratory Research

Fishery Monitoring

The Honolulu Laboratory's swordfish fishery monitoring

program aims to estimate production from the Hawaii

II Hanan, D. A. 1996. Marine Resources Division, California Department of Fish and Game. SWFSC, P.O. Box 271, La Jolla, CA

92038-0271. Personal commun.

12 In 1996, regulatins were passed in Oregon allowing both the use

of drift nets and the landing of longline-caught fish.

fishery and collect data on the associated fishing and

marketing sectors. This program is briefly described here.

Production-The weigh t ofindividual swordfish landed,

ex-vessel revenue, and price are collected as part of a

shoreside monitoring program conducted in conjunction with the State of Hawaii's Division of Aquatic Resources (Ito et a1., 1998).

Interaction with Endangered Species-A mandatory observer program for the Hawaii longline fishery was established in 1994 by the NMFS Southwest Region to collect

data on interactions of marine turtles with longline gear.

Biological Sampling-Observers from the mandatory

program also collect swordfish otolith, fin, gonad, and

stomach samples; determine the sex of swordfish retained; collect detailed data on catches and discards;

and record length measurements for all fishes brought

on board. Biological sampling also takes place on Honolulu Laboratory research cruises.

Cooperative Efforts-The following possible cooperative efforts have been discussed:

• Establish an ad hoc working group to facilitate and

coordinate the collection and exchange of fishery

data (weight of landings, effort and catch data, and

fish sizes) for the swordfish fisheries based in Hawaii,

California, Oregon, and Alaska.

• Establish a regional ad hoc working group with members from Japan and other distant-water fishing nations, Mexico, and the U.S. to facilitate sharing of

data for stock assessment purposes.

Vessel Specifics-For Hawaii longline boats, data on

vessel specifications, crew size, and the type and amount

of gear carried are obtained from federal fishing permit applications. Personal interviews provide additional

information (Ito et a1., ] 998).

Effort and Catch-Submission of logbooks became

mandatory for Hawaii longline boats in November 1990,

according to the second amendment to the Fishery

~lanagement Plan for Pelagic Species of the Western

Pacific Region. These logbooks provide data on fishing

effort expended daily by latitude and longitude, resulting catches by species, discards, fishing gear, and vessel

operations. In addition, for longline boats fishing out of

California ports, an industry association has developed a

volun tary logbook which is being considered for adoption

by California and the PRFMC (Hanan4).13 The La Jolla

13 .-\s of 1996, California requires the submission of logbooks by

longline boats landing in the state.
____________ Skillman: Central Pacific Swordfish Fishery Development, Biology, and Research 121

Laboratory obtains summary logbook data for the highseasJapanese, Korean, and Taiwanese longline fisheries,

although data after 1990 are not available from Japan.

Oceanography Research

The goal of the Honolulu Laboratory's biological research on swordfish is to provide estimates of parameters needed for stock assessment modeling and to

model the effect of gear characteristics on swordfish

catch rates. Fishery oceanographic research will examine the effect of major oceanographic phenomena, e.g.

El ino, on swordfish distribution and catch rates.

Age and Growth-Efforts to refine estimates of age will

continue by evaluating alternative light and electron

microscope procedures and by attempting to validate

ageing procedures. Sampling protocols will be revised

to improve coverage of the size range of swordfish

harvested by the Hawaii fleet and of the spatial range of

the fishing fleet.

Size at Maturity-Sampling protocols will be developed

to improve the collection ofsamples from the commercial longline fishery so that the precision of size-atmaturity estimates may be improved.

Fishery Oceanography-One approach will examine

the effect of temperature gradients, as deduced from

satellite data, on swordfish distribution and catch rates.

Another will involve the use of satellite altimetry data

on a mesoscale. Timely access to high-quality fisheries

data and satellite oceanographic data will facilitate such

research.

Stock Structure-The Honolulu Laboratory will continue to facilitate genetic research on swordfish by providing opportunities to scientists from across the Pacific

to use the Laboratory's research vessel and to obtain

samples.

Possible Cooperative Research-The following cooperative research has been proposed:

• Comparison of ageing techniques used by different

scientists by exchanging swordfish hard parts collected

from different segments of the Pacific fishery. This

would also facilitate the identification of differences

in regional growth, if they exist, better than independent research efforts.

• Archival tagging in fisheries across the range of the

species would provide an opportunity for experiments

to compare the effects of different oceanographic

environments on movement.

• Joint acoustical tracking of swordfish in geographically-separated fisheries with differing oceanographic

regimes would provide for more extensive testing of

swordfish habitat preferences than tracking in any

single fishery location.

Stock Assessment

The Honolulu Laboratory's stock assessment strategy

involves a series of assessment techniques designed to

progressively improve our understanding of resource

dynamics. Almost all studies would benefit from, and in

many cases require, cooperation and collaboration with

researchers from across the Pacific to improve the quality of biological and fishery information and improve

access to information.

Production Modeling-Once current, comprehensive

statistics are available, initial efforts to assess the status of

swordfish will employ dynamic stock-production modeling.

Yield per Recruit-Yield-per-recruit models will be employed to provide preliminary estimates of the effect of

harvesting young fish, particularly by some segments of

the Hawaii fleet.

Simulators-Stock and harvest simulators should be

developed early on to guide stock-assessment and datacollection activities by predicting potential impacts of

continued fishery development on stock dynamics.

Age-structured Modeling-Age- (or length-) structured

stock-assessment models will be used to determine in

more detail the impact of the fishery on the stock, e.g.

the spawning component.

Spatial-Temporal Dynamics-The spatial and temporal variation of swol'dfish size in the catches of the

Hawaii fleet will be compared to the results from the

landings-based report in this symposium (Di ardo and

Kwok, 1998). This and possibly other types of research

will make it possible to standardize fishing effort statistics for the Hawaii longline fleet.

Possible Cooperative Research

• Cooperation between nations will be required to standardize effort statistics, due to changes in the highseas longline fisheries ofJapan, Korea, and Taiwan,

the expansion of coastal fisheries, and the development of new fisheries using longline and other gear.

A standardized time series of fishing effort statistics

is needed to conduct unbiased production-model

assessments.
122 NOAA Technical Report NMFS 142

• The use of nonequilibrium production models capable of including geographically-separated fisheries

in a single model should provide better understanding of stock dynamics and more useful parameter

estimates than fits using composite data.

• Because age- and length-structured models are dependent on age- or size-composition data from all

geographically-separated segments of the fishel), at

least cooperative development of the data sets is

needed. Collaborative utilization of these data in fitting the models would be the best way of resolving

data problems and would facilitate a common understanding of the resource status.

• Examination of the spatial and temporal dynamics of

swordfish size distribution (DiNardo and Kwok, 1998)

could best be extended by collaboration among investigators with access to comparable size data from other

geographically-separated or overlapping fisheries.

Acknowled~ents __

1 am grateful to Norman Bartoo, Gerard T. DiNardo,

Doyle A. Hanan, Russell Y. Ito, and Jerry A. Wethe:rall

for their review of earlier versions of this paper. Geographical charts were generated using the computer

program Generic Mapping Tools, version 2.1.4 (Wessel

and Smith, 1991).

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Standardized CPUE of North Pacific Swordfish, Xiphias gladius,

in the Japanese Large-mesh Driftnet Fishery

KOJI UOSAKI

Tuna Ecology Section, Pelagic Fish ResouTces Division

National ReseaTch Institute ofFaT Seas Fisheries

Fisheries Agency ofJapan

7-1, Orido 5-chome, Shimizu

Shizuoka 424-8633, Japan

ABSTRACT

The CPUE of swordfish, Xiphias gladius, caught by the Japanese large-mesh driftnet

fishery in the North Pacific in 1977-92 was standardized using a General Linear Model to

obtain an index of annual abundance. The factors included in the analysis were year,

quarter, area, and catch rates of albacore, Thunnus alalunga, skipjack tuna, Katsuwonus

pelamis, and striped marlin, TetraptuTUs audax. The catch rates of striped marlin and swordfish were highly correlated. No trend in abundance over time was found.

Introduction Materials and Methods

The Japanese large-mesh driftnet fishery commenced

in the nineteenth century in the coastal waters ofJapan

and then expanded widely in the North Pacific. By the

1970's the fishery had reached the South Pacific. Swordfish, Xiphias gladius, is one ofthe important species caught

by this fishery. The annual catch of swordfish by this

fishery in the North Pacific has ranged from 1,000 to

3,500 metric tons (t) since 1973, and has constituted

about 10%-20% of the total swordfish catch by Japanese North Pacific fisheries. In addition to swordfish,

the Japanese large-mesh driftnet fishery harvests considerable numbers of albacore, Thunnus alalunga, skipjack tuna, Katsuwonus pelamis, and striped marlin,

Tetrapturus audax, in the North Pacific.

Most indices of abundance are based on catch per

unit effort (CPUE). To be a reliable indicator, CPUE

must be standardized to account for factors that can

affect the estimation of abundance. A General Linear

Model (GLM) has often been used to standardize CPUE

of the tuna longline fishery (e.g. Turner, 1987; Miyabe,

1988). In this study the CPUE of swordfish caught by

the Japanese large-mesh driftnet fishery was standardized using a GLM in order to investigate trends in

swordfish abundance in the North Pacific.

Catch and fishing-effort data used in this analysis were

obtained from Japanese large-mesh driftnet fishery statistics for 1977-92, based on logbooks and compiled at

the National Research Institute of Far Seas Fisheries.

These data include fishing date and position, mesh

size, net length, and catch in numbers by species. Mesh

size was recorded to the nearest centimeter. About 54%

of the fishing effort was made using nets with 18-cm

mesh; about 97% of the effort was made with nets of

mesh size 15-21 cm. Mesh-size data were aggregated for

purposes of this study in 3 categories: <17 cm, 17-19

cm, and >19 cm. Logbook data were aggregated by

year, month, lOx 10 area, and mesh-size category. CPUE

was calculated as catch in number per 10 km of net. In

order to exclude outliers, records aggregated from less

than four fishing days were excluded from the analysis.

Swordfish CPUE was standardized for the effects of

year, fishing season, area, mesh size, and targeting (Table

1). Fishing season was categorized by the quarter of the

year. Five fishing areas were defined based on the spatial distribution of nominal swordfish CPUE (Fig. 1, 2).

It is known that the species targeted by the fishery

change by season and area. The CPUE's for these species were used to account for targeting effects. Four

125
126 NOAA Technical Report NMFS 142 _

20·NL__'_ -'--__~====J::=========::=:i __'__.._JL _'__ __'_JO·N

2

3

4

5

120·E 140· 160· 180· 160· 140· 120·W

Figure I

Fishing areas 1-5 used in the GLM analysis of swordfish CpeE in the Japanese large-mesh drif~net fishery in the North

Pacific, 1977-92.

Table 1

Variables examined in the GLM for standardization ofswordfish CpeE of the Japanese large-mesh driftnet fishery in the

orth Pacific.

Variable Type Description Level

Year

Quarter

Area

Mesh size

CP E of striped marlin

CPUE ofskipjack tuna

CPUE of albacore

classification

classification

classification

classification

classification

classification

classification

1971-92

1-4

1-:5

less than 17 cm, 17-19 cm, 19 cm and larger

In(CPlJE)<-1.2, -1.2-0.3, 0.3-1.5, ~1.5

In(CPl.'E) <1.6, 1.6-3.4, 3.4-4.6, ~4.6

In(CPUE) <-0.4, -0.4-2.9, 2.9-4.5, ~4.:5

16

4

5

4

4

4

4

In[CPUE(SWD) + 0.05] =

I.l + Y + Q + A + M +S(i) .. .+ ITER + E

categories were defined for each species such that, for

each species, each category included approximately

the same number of observations. It was assumed that

the relative abundance and distribution of these species in the North Pacific did not change significantly

during 1977-92.

The GLM used was:

AlC = X In(MSE) +2Y

where X is the number of observations, MSE is mean

square error, and Y is the number of parameters estimated (Sakamoto et a\., 1986). Model fit improves as

AlC decreases. Analyses were conducted using SAS version 6.09 (SAS, 1989).

effect ofspecies i, i= (ALB, SIg, STM);

two-way interaction;

error term - N (0,0'2).

S(i)

INTER

£.

The natural logarithm of CPUE(SWD) + 0.05 was

used instead ofCPUE(SWD) in order to include observations for which there was fishing effort but no catch

of swordfish. The constan t, 0.05, was selected based on

an examination of the distribution of swordfish nominal catch rates and such that the constant would be

small relative to observed values of nominal CPUE(SWD)

(Fig. 3). Fitted model selection was made using Akaike's

swordfish; Information Criterion (AlC):

albacore;

skipjack tuna;

striped marlin;

intercept;

effect of year;

effect of quarter;

effect of subarea;

effect of mesh size;

where SWD

ALB

SKJ

STM

I.l

y

Q

A

M
Uosaki: Standardized CPUE of North Pacific Swordfish in the Japanese Large-mesh Driftnet Fishery 127

50'N

40'N

30'N

20'N

140'

50'N

40'N

30'N

20'N

140' 120'W

180' 160' 140' 120'W

"",'':"rtr:'

'''''.,. ,;;""r- IS

120'E 140' 160'

30'N

50'N

40'N

20'N

SO'N

40'N

30'N

140'

20'N

Figure 2

Distribution of the nominal catch rate ofswordfish (fish per 10 km of net) by the Japanese large-net driftnet fishery in the

North Pacific, 1977-92.
128 NOAA Technical Report NMFS 142

Results and Discussion

First the main-effects model, which included all main

effects but no interaction terms, was examined to identifY the effects to be considered for inclusion in the

fitted model. Only mesh size was not significant (F,

p=0.094). Each of the remaining main effects was then

sequentially added into a model which included year

030

0.25

0.20

c

a

015 Q.

E

a

U

0.10

0.05

00 1._- -4 -2

InICPUE(SWD)+O 051

Figure 3

Distribution of In (CPUE + 0.05) of swordfish in the

Japanese large-mesh driftnet fishery in the North Pacific, 1977-92.

effect, in the order of larger to smaller F values. A

summary of the A OVA results, with AlC values, is

shown in Table 2 (A). The model that provided the best

fit as measured by AlC (ModelS) included Y, Q, A,

S(STM), S(SKJ), and S(ALB)

Next, interaction terms were added to ModelS in a

procedure analogous to that just described for main

effects. All combinations of two-way interactions were

attempted, except interactions with species effects. A

summary of the A OVA results, with AlC's, is shown in

Table 2 (B). The results indicated that none of the

models with interaction terms provided a significant

improvement. Thus, the chosen model was:

In[CPUE(SWD) +0.05] =

J1 + Y + Q + A + S(STM) +S(SKJ) + S(ALB) + E.

The ANOVA table for the final model is shown in

Table 3, and the distribution of standardized residuals

is shown in Figure 4. All terms in the model were

significant at the p ~O.OOOI level, i.e. at levels at least

500 times the standard p-value of 0.05. At the same

time. the correlation coefficient for the final model was

1

2 = 0.22. These results are not surprising given the

large data set (5,633 observations) (Draper, 1984). The

fact that the significance levels of the regression coefficients were so high indicates that the results may be

considered not only significant but useful (Draper and

Smith, 1981). In comparison, the results ofGLM analyses of swordfish CPUE of the Japanese longline fishery

in the North and the South Pacific had r2 = 0.53 and

r2 = 0.47, respectively (Nakano, 1998).

Table 2

Summary of ANOYA's, with Akaike's Information Criterion (Ale). Effects Y, Q, A, S(SKJ), S(STM), and S(ALB) indicate

year, quarter, area, and CPUE's of skipjack tuna, striped marlin. and albacore, respectively. Number of observations =

5,633.

Model o. of parameters R-square C.V. MSE F value AIC

A. Main-effects models

(I) YS(STM) 20 0.151 -544.69 1.771 55.58 1,438.62

(2) YS(STM) Q 24 0.161 -541.83 1.753 51.12 1,420.84

(3) YS(STM) Q S(SKJ) 28 0.195 -530.88 1.683 56.46 1,328.95

(4) YS(STM) QS(SKJ) A 33 0.216 -523.91 1.639 55.20 1,274.27

(5) YS(STM) QS(SKJ) A S(ALB) 37 0.222 -522.11 1.627 51.54 1,265.49

B. Models with interaction terms

(5) + Y*Q lOl 0.262 -510.42 1.555 26.34 1,282.65

(5) + Y*A 117 0.261 -511.07 1.559 23.94 1,320.90

(5) + Q*A 57 0.234 -518.48 1.605 39.79 1,271.33

(5) + Y*QY*A 181 0.298 -500.31 1.494 18.52 1,344.80

(5) + Y*Q Q*A 121 0.276 -506.15 1.530 24.31 1,281.58

(5) + Y*A Q*A 137 0.273 -507.68 1.539 22.08 1,328.35

(5) + Y*QY*A Q*A 201 0.315 -494.49 1.460 18.34 1,327.57
_____ Uosaki: Standardized CPUE of North Pacific Swordfish in the Japanese Large-mesh Driftnet Fishery 129

The GLM for standardizing catch rate ofswordfish by

driftnet might be further improved by addition of factors related to the environmen t and/or characteristics

of the gear other than mesh size. For example, it is

known from acoustic telemetry (e.g. Carey and Robison,

1981) that during hours of darkness swordfish spend

significant periods of time at shallow depths. It is also

known that swordfish are, not surprisingly, effectively

targeted with longline gear that is fished with shallow

hook depths at night. Therefore, including factors that

account for the vertical distribution of swordfish, as

well as the time of day of sets and the fishing depth of

the net, might improve the model.

It was somewhat surprising that the effect of mesh

size was not significan t. In general, fishermen select

mesh size to effectively target specific species. In the

04

03

0

u 02

01

00

-4 -2

Standardized residual

Figure 4

Distribution ofstandardized residuals of the fitted GLM.

case of the Japanese large-mesh driftnet fishery, it was

believed that gillnets with larger mesh sizes were selective for billfish, and smaller, for tunas. However, these

results did not support that hypothesis.

Relationships between standardized swordfish CPUE

and Q, A, S(STM), and S(SKJ) are shown in Figure 5. It

is apparent that swordfish CPUE was greatest in the

third quarter, moderate in the first and fourth quarters,

and lowest in the second quarter. It is also apparent

that CPUE in Area 5 was remarkably higher than in the

other areas. Swordfish CPUE increased with S(STM)

and S(SIg), but not with S(ALB). This suggests that

swordfish, striped marlin, and skipjack have similar distribution patterns and tend to be caught in the same

times and places.

Standardized swordfish CPUE, with upper and lower

95% confidence bounds, is shown by year in Table 4.

Annual CPUE has varied widely during 1977-92. It was

highest (1.2-1.3) during 1978-80, but declined significantly in 1981 and 1982, and stayed at around 0.55

during 1982-84. After that, CPUE fluctuated between

about 0.50 and 1.16. Based on these analyses, the relative abundance ofswordfish in the North Pacific during

1990-92 was about 54% of that seen during the period

of highest abundance (1978-80).

Nominal and standardized swordfish CPUE, scaled by

1977-92 average nominal and standardized CPUE, respectively, are shown in Figure 6. As expected, due to the

reduction of variance provided by the GLM, fluctuations

in standardized CPUE are smaller than those in nominal

CPUE. The nominal and standardized CPUE series were

tested for trend using regression analysis; no trend in

relative abundance was found (df = 14, Student's 1=-1.10

and -1.80, p= 0.29 and 0.093, respectively).

Nominal CPUE values include noise and may include

bias caused by variation in artificial and natural factors

Table 3

ANOVA for the fitted model for standardization of swordfish CPUE in the Japanese large-mesh driftnet fishery in the

North Pacific, 1977-92. R-square =0.222; C.V. =-522.11

F value P> F

15.03 0.0001

45.72 0.0001

39.69 0.0001

127.97 0.0001

37.93 0.0001

13.86 0.0001

Source DF Sum of Squares Mean Square

Model 31 2,600.52 88.89

Error 5,601 9,115.60 1.63

Corrected total 5,632 11,716.12

Source DF Type lIT SS Mean Square

y 15 366.94 24.46

Q 3 223.23 74.41

A 4 258.36 64.59

S(STM) 3 624.80 208.27

S(SKJ) 3 185.19 61.73

S(ALB) 3 67.66 22.55

F value

51.54

P>F

00001
130 NOAA Technical Report NMFS 142

"" 2.0 <oJ ..

= ;:> "

ti Z1.5 "C = " E .~ "'" 1.0 "Co

"C:; -

; ~O.5

<Jl -""

0:: 0.0

4

tl.5

Jj

1.0

E

"'"

0

iO.5

"" 0.0

4

2

2

3

Area

3

4 5

4

<oJ tl.5 ,...-------------,

;:>

0..-

1.0

.~"Co

:0.5

;;

en 0.0

Skipjack tuna

2

Albacore

3 4

Figure 5

Relationships between standardized CpeE of swordfish and Q, A, S(STM),

S(SKJ), and S(ALB). Dotted lines indicate 95% confidence bounds.

Table 4

Standardized CPUE and 95% confidence bounds for North Pacific swordfish caught by the Japanese large-mesh driftnet

fishery, 1977-92. Unit is fish per lO-km net length.

Standardized Upper Lower Standardized Upper Lower

CPUE bound bound CPUE bound bound

1977 1.02 1.27 0.82 1985 0.97 1.14 0.82

1978 1.21 1.43 1.01 1986 0.79 0.93 0.68

1979 1.21 1.48 0.98 1987 1.04 1.23 0.87

1980 1.32 1.58 1.09 1988 0.78 0.89 0.68

1981 0.83 0.95 0.72 1989 1.16 1.33 1.01

1982 0.57 0.67 0.48 1990 0.75 0.84 0.66

1983 0.57 0.66 0.49 1991 0.54 0.62 0.47

1984 0.50 0.58 0.43 1992 0.73 0.84 0.64

that affect the fishing event. Standardizing CPUE with a

GLM may remove biases that result from variations

such as those in fishing seasons and fishing grounds. In

order to ensure that reliable estimates of the relative

abundance and status of swordfish stocks in the North

Pacific are available, the results of this study should be

compared with the results of other such investigations

to ensure that any conflicts in results may be further

investigated and the reasons for any noted differences

resolved.
_____ U osaki: Standardized CPUE of North Pacific Swordfish in the Japanese Large-mesh Driftnet Fishery 131

2.0

-+- Std.CPUE

--nomLCPUE

1.5

W

:J

a..

0

"'0 1.0

Q)

ro

u

C/)

0.5

0.0

77 79 81 83 85 87 89 91

Figure 6

Nominal and standardized CPUE of swordfish, scaled by average 1977-92 nominal and

standardized CPUE, respectively, for the Japanese large-mesh driftnet fishery in the North

Pacific. Dotted lines indicate 95% confidence bounds for standardized CPUE.

Acknowledgments _

I would like to thank Yuji Uozumi and Hideki Nakano,

National Research Institute ofFar Seas Fisheries, for useful

advice regarding improvements in the manuscript. I also

thank Michael G. Hinton, Inter-American Tropical Tuna

Commission, for his critical reading of the manuscript.

Literature Cited _

Carey, F. G., and B. H. Robison.

1981. Daily patterns in the activities of swordfish, Xiphias

gladius, observed by acoustic telemetry. Fish. Bull.

79 (2) :277-292.

Draper, . R.

1984. The Box-Wetz criterion versus H2. J. R. Statist. Soc.

Ser. A 147(1):100-103.

Draper, N. R., and H. Smith.

1981. Applied regression analysis. 2nd ed. John Wiley &

Sons, New York, 709 p.

Miyabe, N.

1988. Estimation ofstandardized CPUE for the Atlantic swordfish using the data from the Japanese longline fishery. Int.

Comm. Conserv. Atl. Tunas, Coli. Vol. Sci. Pap. 2Y:183-1!J4.

'akano, H.

1998. Stock status of Pacific swordfish,Xiphias gladius, inferred

from standardized CPUE of the Japanese longline fleet using general linear models. In I. Barrett, O. Sosa-Nishizaki,

and N. Bartoo (eds.), Biology and fisheries of swordfish,

Xiphias gladius, p. 195-209. U.S. Dep. Commer., NOAA

Tech. Rep. NMFS 142.

Sakamoto, Y., M. Ishiguro, and G. ){jtagawa.

1986. Akaike information criterion statistics. KTK Scientific

Publishers, Tokyo, 290 p.

SAS Institute.

1989. SAS/STAT user's guide, version 6, 4th ed., vol. 2. SAS

Institute, Cany, NC, 846 p.

Turner, S. C.

1987. Catch rates of bluefin tuna in the Japanese longline

fishery recorded by United States observers. Int. Comm.

Conserv. Atl. Tunas, CoIl. Vol. Sci. Pap. 26(2):323-338.

Review of the Japanese Swordfish, Xiphias gladius,

Fisheries in the Pacific Ocean

YOJI UOZUMI and KOJI UOSAKI

Tuna Ecology Section, Pelagic Fish Resources Division

National Research Institute ofFar Seas Fisheries

Fisheries Agency ofJapan

7-1, Orido 5-chome, Shimizu

Shizuoka 424-8633,Japan

ABSTRACT

The Japanese catch of swordfish peaked at about 24,000 metric tons (t) in 1961;

thereafter the catch decreased sharply to about 10,000 t in 1964. Since the mid-1960's it has

been stable at 10,000-15,000 t. The catch by the Japanese longline fishery represents more

than 90% of the total Japanese swordfish catch. The driftnet and harpoon fisheries accounted for a small portion of the total catch.

Over the same time period, the Japanese longline fishery expanded operations widely

in the Pacific Ocean, but most of the swordfish catch was from the northwest Pacific. A

minor portion was from the waters off California, Peru, and the Tasman Sea. The driftnet

fishery operated mainly in the central North Pacific, but stopped operations in the high seas

after the UN resolution in December 1992 for a moratorium on large-scale drift net in the

high seas. The harpoon fishery operated in the coastal waters around Japan; its catch

continues to decrease.

Introduction Price of Swordfish and Other Billfishes

inJapan _

The swordfish catch by Japanese fisheries accounted

for more than 80% of the total swordfish catch in the

Pacific Ocean in the 1950's and 1960's. The Japanese

swordfish catch has remained stable, but other countries such as U.S.A., Philippines, and Chile have increased

their catch in recent years (Table 1). Therefore the percentage of the total catch represented by the Japanese

catch has declined, especially in the 1990's, when it decreased to 30-45%. However, the Japanese catch is still

the largest by a single country. Catch and effort data from

theJapanese fisheries, especially the longline fishery, have

been used for the stock assessment of swordfish in the

Pacific Ocean because of their wide areal coverage and

long history (Sosa-Nishizaki and Shimizu, 1991).

This paper offers a description of the historical catch

of swordfish by Japanese fisheries and its geographical

distribution of catch, effort, and CPUE, based on annual statistics published by the Statistics and Information Department of the Japanese Ministry of Agriculture, Forestry, and Fisheries, as well as on logbook data

compiled by the National Research Institute of Far Seas

Fisheries.

Figure 1 shows the historical changes in average price

for some tunas and billfishes (frozen and round fish) at

major fishing ports in Japan from 1967 to 1992. The

prices of bluefin and southern bluefin tunas were much

higher, but the prices of albacore and skipjack much

lower than those shown here. Average prices of frozen

tunas and billfishes increased markedly during the 1970's,

mainly due to technological improvement in freezers which

increased the quality of fish meat used for sashimi. Japanese longliners began outfitting their vessels with freezers

capable ofquick-freezing fish to below -55°C. The fish are

then stored in holds at below -40°C (Ueyanagi et a\.,

1989). The prices of tunas and billfishes kept under these

conditions were higher in the sashimi market. Prices stabilized after 1980, except for bigeye tuna.

The price of swordfish was less than 300 yen/kg

before 1970, increased rapidly to around 700 yen/kg in

the late 1970's, peaked at about 900 yen/kg in 1984,

and has since decreased gradually. Its price was about

average among the species of billfishes and tunas shown

in Figure 1.

133
134 NOAA Technical Report NMFS 142

1 ,

1991

,

,

I,

I I I I

1979 1983 1987

Year

1971 1975

/\ • 1

./ \ 1\ ' / \' 1

/ ' '\ ./ \ /.: '/

/".J ',' .

/ ." , ,

/' ,.,'

./ ... ~.

~.-~. /-'.,. ~. .

- - - Bigeye

--Yellowfin

- - - Striped marlin

--Swordfish

..... ·Blue marlin

1400

1200

1000

C 800 CO>

?:

CO>

(j 600

'C

Q.;

400

200

0 ~-'

1967

Figure 1

Average price of tunas and billfishes (for frozen and round fish, per kg) at major

fishing ports in Japan, 1967-92.

MajorJapanese Swordfish Fisheries

The Japanese swordfish catch in the Pacific Ocean increased during the 1950's and peaked at about 24,000

metric tons (t) in 1961 (Fig. 2). The catch decreased

sharply to about 10,000 tin 1964, then fluctuated between 10,000 and 15,000 t in the 1970's and 1980's. The

catch by the longline fishery represented more than

90% of the total throughout the years observed. The

driftnet and harpoon fisheries accounted for only a

small portion of the total swordfish catch. Catch by

other fisheries such as the purse seine and baitboat

fisheries was negligible and incidental.

Longline Fishery

The total effort of the Japanese longline fishery in the

Pacific Ocean increased rapidly from the late 1950's to

the mid-1960's and remained stable until the mid-1970's

(Fig. 3). The effort increased again in the late 1970's,

but has been stable since about 1980, with some fluctuations.

Albacore and yellowfin tunas dominated the longline

catch during the 1950's and 1960's, but the catch of

albacore decreased rapidly during the late 1960's and

early 1970's (Fig. 3). Mter about 1970 the catch of

bigeye tuna increased gradually, with some fluctuations.

The catch of swordfish by the longline fishery increased rapidly in the 1950's, then decreased drastically

until 1964. Since then the catch has been stable. The

catch of striped marlin also increased rapidly in the

1950's and was at record levels from 1964 to 1970, a

decade after the swordfish catch had begun its decline.

The striped marlin catch decreased during the early

1970's and has fluctuated until the present. The catch

of blue marlin followed a trend intermediate between

those of swordfish and striped marlin. The catch of

swordfish has been the largest of the billfish catches

since 1983, though only 10% the size of the bigeye tuna

catch. Generally swordfish has been caught as a bycatch

species, especially in waters distant from Japan, except

for a minor local longline fishery which targets swordfish in Japanese coastal waters.

By the 1960's,Japanese longline fishery had expanded

throughout the tropical and subtropical Pacific; efforts

were concentrated in the waters offJapan and in western tropical waters (Fig. 4). In the 1970's, technological

improvements in freezing made it possible for longliners

operating in distant waters to target southern bluefin

and bigeye tunas and to sell them in the Japanese

sashimi market. As a result, efforts were concentrated

in eastern tropical Pacific waters to target bigeye tuna

and in New Zealand-Australian waters to target southern bluefin tuna, in addition to former fishing grounds.

In the 1980's and 1990's (up to 1992), effort increasingly concentrated in the eastern tropical Pacific and

New Zealand-Australian waters. The most striking feature of the recent two decades was the significant increase of efforts in the eastern tropical Pacific, which is
Uozumi & Uosaki: Japanese Swordfish Fisheries in the Pacific Ocean 135

Table 1

Catch (metric tons) ofswordfish in the Pacific Ocean by country, 1952-93. Numbers in parentheses are percentage of the

total which the Japanese catch represents. Data from IATTC (1994) and FAD (1995).

Year Japan Chile Philippines USA Taiwan Mexico Other Total

1952 11,182 (98.6) 157 11,339

1953 11 ,604 (99.3) 85 11,689

1954 13,301 (99.3) 14 77 13,392

1955 16,220 (98.4) 80 185 16,485

1956 12,167 (96.7) 163 254 12,584

1957 15,771 (97.1) 222 250 16,243

1958 20,815 (97.5) 279 247 21,341

1959 19,136 (97.3) 265 262 19,663

1960 22,944 (96.1) 456 192 273 23,865

1961 23,636 (95.8) 394 218 432 24,680

1962 14,037 (94.2) 297 23 544 14,901

1963 13,775 (96.8) 94 58 300 14,227

1964 9,703 (93.2) 300 109 300 10,412

1965 11 ,955 (92.3) 200 194 300 0 300 12,949

1966 13,283 (91.0) 200 277 600 0 241 14,601

1967 13,083 (83.6) 200 181 838 0 1,347 15,649

1968 12,983 (86.3) 135 118 974 0 833 15,043

1969 15,612 (82.9) 300 610 1,023 0 1,289 18,834

1970 11,301 (66.4) 200 1,400 558 1,053 0 2,515 17,027

1971 9,182 (73.8) 200 1,500 91 1,149 0 315 12,437

1972 8,846 (70.7) 100 1,600 157 1,095 0 714 12,512

1973 9,644 (62.6) 400 1,700 363 1,278 0 2,015 15,400

1974 9,517 (70.4) 218 1,848 383 1,170 0 385 13,521

1975 11,274 (73.3) 218 1,976 510 1,120 0 273 15,371

1976 15,843 (83.0) 13 1,558 49 886 0 738 19,087

1977 13,997 (78.2) 32 2,103 301 789 0 684 17,906

1978 14,333 (89.0) 56 890 1,536 693 0 634 18,142

1979 13,091 (69.8) 40 3,845 346 873 7 553 18,755

1980 11 ,953 (73.2) 104 1,716 706 932 380 544 16,335

1981 13,078 (69.9) 294 1,940 674 803 1,575 347 18,711

1982 11,350 (61.3) 285 3,468 726 984 1,365 347 18,525

1983 12,511 (67.7) 342 2,974 1,195 979 120 360 18,4Rl

1984 11,986 (67.2) 103 2,274 2,009 1,056 47 352 17,827

1985 13,083 (69.7) 342 2,036 2,370 775 18 148 18,772

1986 14,271 (71.7) 764 2,089 1,585 692 422 69 19,892

1987 14,867 (65.9) 2,059 2,137 1,221 1,540 550 195 22,569

1988 15,496 (56.1) 4,455 4,034 1,086 1,690 613 246 27,620

1989 12,367 (45.5) 5,824 3,756 588 3,692 690 265 27,182

1990 11,341 (39.3) 4,955 3,187 2,150 4,097 2,650 447 28,827

1991 9,936 (35.6) 7,255 3,139 4,597 1,645 861 501 27,934

1992 15,619 (44.5) 6,379 4,256 5,948 1,300 1,160 446 35,108

1993 15,458 (45.2) 4,712 4,633 6,981 1,525 806 97 34,212

one of the most important fishing grounds of bigeye

tuna in the world.

The geographical distribution of swordfish catch is

shown in Figure 5. In the 1960's, the catch was concentrated in waters offJapan. In later decades, the swordfish

catch was increasingly concentrated off California and

Peru, and in the Tasman Sea. The catch in the orth

Pacific was more than 90% of the total in the 1960's, but

decreased gradually to around 70% in the 1970's and

1980's. In the 1990's (up to 1992), it decreased to 60%.

Figure 6 shows the distribution of nominal mean

CPUE for swordfish (catch in number per 1,000 hooks)

in each decade. High CPUE's were observed between

25° and 45°N in the North Pacific, off California and

Peru-Chile, and in the Tasman Sea. There were low

CPUE's in tropical waters.
136 NOAA Technical Report NMFS 142

1956 1960 1964 1968 1972 1976 1980 1984 1988 1992

o

1952

5000

25000

• Others

I!!ICoastal LL

l!ll Longline

o Driflnet

20000 • Harpoon

'"c: 15000

S

.S

.:::

10000 U

Figure 2

Swordfish catch by Japanese fisheries in the Pacific Ocean by type of fishery, 1952-92.

Driftnet Fishery

The Japanese large-mesh driftnet fishery, called "oomeami" or "oome-nagashiami" and officially registered as

"Billfishes and Others Drift Gillnet Fishery," commenced

in the 19th century in the coastal waters of Japan

(Watanabe; 1 Uozumi2). The modern large-mesh driftnet

fishery started in the early 1970's and gradually expanded to offshore waters in the North Pacific. From

1983 to 1990, some of these vessels operated in the

South Pacific (Nakano et al.;3 Uozumi 2). Swordfish has

traditionally been targeted by the driftnet fishery in the

coastal waters ofJapan, but it has also been caught as a

valuable bycatch species in the high seas of the Pacific

I Watanabe, Y. 1991. A review oftheJapanese large-mesh driftnet

fishery in the north Pacific. In Scientific review of North Pacific

high seas driftnet fisheries, Sidney, B.C., Canada, l1-14June E'91.

Report for presentation to the L'nited Nations pursuant to resolutions 44/225 and 45/197, app. 6, vol. I, 13 p. Available from hst.

of Ocean Sci., P.O. Box 60UO, 9860 W. Saanich Rd., Sidney, B.C.,

V8L 4B2 Canada.

Uozumi, Y. 1993. The historical review of the Japanese largemesh driftnet fishery in the North Pacific Ocean. 13th North

Pacific albacore workshop, La Jolla, CA, 8-14 December

1993. NPALBI3/11, 15 p. Available from IATTC, Scripps Inst.

Oceanogr., La Jolla, CA 92037-1508.

:l Nakano, H., Y. Watanabe, and Y. Nishikawa. 1989. Preliminary

rep0rl of albacore catch by Japanese large-mesh driftnet fishery in

the south Pacific. Second South Pacific albacore research workshop, 5 p. Available from Secretariat of the Pacific Community,

B.P. 0-5, Noumea, New Caledonia.

where Japanese large-mesh driftnetters targeted albacore and/or skipjack tuna.

North Pacific-Figure 7 shows historical trends in

driftnet catches of major species in the Pacific Ocean.

The total catch increased rapidly in the 1970's and

fluctuated between 15,000 and 23,000 t in the 1980's.

In the 1990's the catch decreased rapidly, and the operations of the driftnet fishery in the high seas of the

North Pacific have ended since December 1992, following a UN resolution for a moratorium on large-scale

high seas driftnetting.

During the 1970's, billfishes accounted for the major

part of the total driftnet catch. After about 1980, the

catch of albacore increased rapidly and became the

largest part of the catch. The catch ofskipjack increased

beginning in the mid-1980's, and became the major

species in the driftnet catch after 1990.

Swordfish driftnet catch peaked at 3,500 t in 1976

and then decreased gradually through the years, with

some fluctuations. The catch of swordfish has been

around 1,000 t annually in recent years. It is assumed

that the swordfish catch decreased substantially after

1992, since driftnet operations are now restricted to the

200 nautical miles around Japan.

The geographical distribution of the mean fishing

effort (total length of fishing gear) is shown in Figure 8

by 3-yr period from 1977-91, based on logbook sampling statistics.
__________________ Uozumi & Uosaki:Japanese Swordfish Fisheries in the Pacific Ocean 137

- - - Bluefin+suthern bluefin ---Albacore - Bigeye - - - - - - Yellowfin

8884 92

-Swordfish

---Striped marlin

- - - - - -Blue marlin

56 60 64 68 72 76 80

L_'--'--"---'-'_.L-l- 1-"-1---'-1--'----'--I-'1--".-".'-'-'---'--I--'--'-'--"--'1-'-1---'-'--'-'_1'--'1--"-"-1-'-'--'-'--'---'1--'1-"-'-'-'_l-l..-L....J ---.L..-J

600

C

500

..,

Q

C 400 .c

[i:'"

... 300 0

B 200 :s

;Z

100

0

52

Year

Figure 3

Catch and effort of the Japanese longline fishery in the Pacific Ocean, 1952-92. (A) number of hooks

set, in millions, (B) catch of tunas, and (C) catch of swordfish and marlins. Note different scales.
(.>0 -

00

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20 ON

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0°

> 'iRRR L-..... 'I' I ., I' }'" 1980~' ~j • (= 'iRRR ,.,......... I . : • (= ?RRR ••••••••...••• 0 • •• \ • '•• lJ '(=lRRR~re ••••••• ·• •••••• ····1\" , ~j(= 'iRR ••••••••••.•••• 0 ••••••• • \.~ .1< = 1RS 'L'. . .~- - + = B : I" •••• • ••••••.." .:.. .••••••••r.,' ,~'.::I

I , ""~'- ---@ -..,-

=--. t ·~·I· ..,:.•• 1••••••1•••...... ',' .... ,.-- .' ...... .. . . •••••••••••••••••••• o Q .... .. • .. ••••••••••••••

. '. .....••.....

.... \

20 0 S • ':"':: ::.-

. .

20 'N

40 'N

Figure 4

Geographical distribution of mean annual fishing effort (in thousands of hooks) by the Japanese longline fishery in the Pacific Ocean, by decade.
120'E150'E 1 8 0 0

1 50 'W 120'W 90 0

W 120'E 150'E 180' 150'W 120'W 90 0

W

.. ,.~::,:::::

o - . ~. .... ... o :' ~ , ,"' ,~" .1. _I_ .1 •• 1 •• 1 •• 1 • • 1_11

" '1· .,. '1' '1' '1' '1' '1' ......................t)

". '1' '1' '1'

"'lO"'"

0' '~.... , \J : ... -.,o' .:

4 O' N tl~m -t\li"=-'~";"'--':;+~·'~-1'--+--+'--f-:.--:_+-+:-\'t-T,-rllr1 r·<~!AAA'. •••••• <- ~~~ . , , " .<= lA8"

, §.~ = 8 .•. • • • • • ." ..

2 0 N I\l: :~: : : .,' . '1' . . . ~'-l--I'---+---+-

····~~~~li "'I 9i" .. , ., .•. t.1. '1'

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• <= :; AAA -'~--=-l":"":=+----=.J~±:--+--+-+- ,.<=?AAA •

'"" • <= 1AAA • ~~<= 'iA~ .1<= lA8

: + = 8 • . "

:\'f"r;" . ~. ~I: .~. , . 2 0 oN

40 'N

Figure 5

Geographical distribution of mean annual swordfish catch (in thousands of fish) by the Japanese longline fishery in the Pacific Ocean, by decade.

c:

o

N

s:2,

ll:'

c:

o

'"

:::

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.. - .. ,'1' ... '1+ +1 "'!'¥ .-t- •••••••••••••••1)

a 0 • + •••••••••

• ••••••• 1 •• 1 ••

> ."AAA l!" ' , , r 1990s IF'

• ( 'iAA ---1;...... .. f.:.,....:.-J-:.-.+~-+-+-+,--t-:-+\t--'-j-,Tln 4 0 0 N • < ?AAA J" ••• • • • • • . . . . . . . . ';. '. lJ .< lAAA";'••••••••.•••••••••• 'r'\~ "

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, + = 8 "1' . • . . • . . . • , .. ,....... r h A'~ 0'

20 Nt<i, '11 .,,, , " ·'-o~h· ~,)I .. '

1980s lr>

. ... .. ..... -~

o0 .. ~... .. .. .. .. .. .. • .. .. •• .. .1) .. .. .. .. .... .. .. .. .. .; .. . .. .

... . . . . ......

- .

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4 0 N • <= ?AAA 'y~ ••• • • • • . . . • • • • • .• \ c '. , lJ,

• < 1AAA '~ ••••••••.••••••••••.1\" ' ;-' < :'lA~ , "~l' f( \ ';\

. < lA81 + 8·············· • _

, •••••••• ·r·)!( I ....~·

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2 0 0S rtrrltWrn#wnm ..

40 0S I

2 0' S r--t7r-r-Mb-;i~~~:-+4-=++-+-+--i-~D

\>0

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-....

o

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120'E 150'E 180' 150'W 120'W 90'W

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~> ? ,'. .'T 1970s • < ? ••·.

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·.. ....r•• • • . ·. • (

'iJ ·. :~9v

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O'

40' S

40'N

20 'N

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tit. '1' '1' • • • • • • • • • • • • • J '1' '1' '1' '1' JI ·r· ALi\} I" Q M ·V(~··,·

o R~~~~~~< o ••••::::::::::~:= l ·,r.P'iIA...·;·····: c -ii-.•••••••••••• \

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, ........ . . . .. . .........•.

t~h-""

• (= '--- <= . <= .1

2 0 ' Ni-/ = 8 -:-'t-:'--t-=--.t=-=t--t=--t-.:.t=-:..p,'-+-+-~~+~hft...::~ \1'•• •• " "," • .. • • . .. ~~l· .~.. . .... . . . ....•.... ..

40' N

• 40'S ' + •••••

. .. . ..-

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. .. . . . ... . . .. . . . . . . . . . . . + .......... ~~ ••••••••••••

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.. .... . ...

40 'N

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- ~~~= I ' - • <= 1 , • <= . S ""'v-l__i

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· <= ,1

K;.=.~ :. . . .. ., .... t. ll~ . ....'. .. .1.. .. .... -....

40 DN

20 'N

0'

20' S

40' S

Jt> ? ;./ •• T 1990s 1 ~< ? •••

.< 1, ••·.·.·.· .·.• •• •• \ , • < ,S •

•••• •••• • •••••• • o • '---+. ( ? • + \" •••••••• ••• • • o • ·. '~ "(\ ,< ,1 ••

-\ ."" 1~·. + = 8 •.• • • ·.·. i';;...";

0: ~~: ~: , .. ·.·.·.· . ..'''~R' . :.10' ... .. · . · ..-. · . · . · . · . · . • 0 ·.· .· ·;', + • ·. • •• • • • .~rr f-J ~-.,;. ~. + • ·.·.·.·. • • r... , ,,\ • ·. /" f\ 0.0 . ·. ·.·.·.·.· . • •

I~ ·. · D

'.' -;;." .'.•• • • • •·.•• ( I.: . · .' •• . .. . • •• ••• • • • •• · .. L....r'""4 II • •• ·.

• · ·.. -- ·.•• • (

\j · . ~.~ .. l

Figure 6

Geographical distribution of mean annual swordfish CPUE (number/1,000 hooks) of the Japanese longline fishery in the Pacific Ocean, by decade.
_________________ Uozumi & Uosaki:Japanese Swordfish Fisheries in the Pacific Ocean 141

• Swordfish 0 Striped marlin • Blue marlin Cl Sailfish Albacore Other tunas II!I Skipjack

25000

20000

"-'

r:::

0 15000 ....

.5

.::::

u

.... 10000

U

5000

o

1972 1976 1980

Year

1984 1988 1992

Figure 7

Catch by the Japanese driftnet fishery in the Pacific Ocean by species, 1972-92.

In 1977-79, fishing effort was mainly focused on the

waters west of 180°, offTohoku region and in the East China

Sea. In 1980-82, fishing effort expanded to the eastern North

Pacific, but the main fishing area was still in the western area.

In 1983-85 and 1986-88, the distribution of effort was

similar to that in 1980-82, but the main fishing area was

shifted slightly to the east (1700E-1700W). In 1989-91, the

mean distribution pattern was similar to those in previous

years, but fishing effort was concentrated in the offshore

waters of the Tohoku region in addition to the area between 1700E and 1700W. In this period, the interannual

distribution of fishing effort changed due to socio-economic conditions. After 1991, fishing efforts in the high

seas decreased rapidly and effort was again concentrated

in the waters inside the Japanese 200-m EEZ.

The distribution of swordfish catch (mean catch in

number/yr) by driftnetting in the North Pacific is shown

in Figure 9 by 3-yr period. The catch was concentrated

in the waters offJapan before 1985. In 1986-91, the

concentration of catch was in waters to the northwest of

Hawaii. These changes reflect the changing patterns of

effort distribution.

The distribution ofswordfish CPUE (number/l0 km

of gear) in 1989-91 is shown in Figure 10. Areas of high

CPUE are scattered all over the operation area, with no

area of concentration.

South Pacific-Driftnet operations in the South Pacific

commenced in 1983. From 7 to 20 vessels operated

before 1988; the number of vessels peaked at 64 in

1988, and decreased to 19 in 1989. The operations of

the driftnet fishery in the south Pacific have stopped

since July 1990, following the UN resolution.

The swordfish catch in the South Pacific was only

1%-2% the size of the albacore catch there. It is estimated that the swordfish catch was about 220 tin 1988,

when the number of vessels peaked. In other years, the

catch ofswordfish is estimated at less than 50 t.

The distribution of driftnet fishing effort, swordfish

catch, and CPUE in the South Pacific are shown in

Figure 11. Most fishing effort was concentrated in the

central area of the Tasman Sea, but some effort was

expended on the eastern waters off New Zealand. Swordfish catch was also concentrated in the central Tasman

Sea. But swordfish CPUE was higher in the waters east

of New Zealand than in the Tasman Sea. The discrepancy between the distributions of catch and CPUE was

mainly due to the fact that the driftnet fishery targeted

mainly albacore, with swordfish only a bycatch species.

Harpoon Fishery

A harpoon fishery directed at billfishes operates in the

coastal waters ofJapan. Swordfish is one of the major

target species in the harpoon fishery, next to striped
142 NOAA Technical Report NMFS 142

I. 1,"1",,1.

1989-91

160 'W

160'W

1 B O'

1 B O'

.........

.......... ......

1 60' E

tlt /'

,......• ........ . . .. . .......-... . ..................... ..........•.. ·-41·····_··· ....::.*.:~::~~ ...":::.:;;;:::::::.:~.:::::.:::::. :: . ..........._.. . . ........... . . ........_. .. ............. . .. .. , _ _.. . . ...............

140'E 160'E

1 40' E

..

,~::m tlt ' 1986-88

~~ ~~~ 11:/ .... .'

l);~:;J1J~~A,.:>Eili~:~~~~~i~;:~::::::.~;;;~?;;::;· ............................................ . , :..::::::::::.~::::::::::::::::::::::::":.: ..::::.. 4iI'" ..

• * .•== *

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, ) lAAA

(: IAAA

• (: fiAA • (: nA , (: 1AA

• (: fiA

• : e

U

".,

20 'N

30'N

40 'N

20 'N

30 'N

1977-79

1980-82

160 'W

160 'W

1 B 0'

1 60' E 1 B O'

.. .. .... . .. _.. ............................ ... . ..

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................ .. 4·.-....········· . ....... . _..• ... ..•........•.•-.- . ..........._ . ~...... • ...-.•••••• 0 •••••••• '0 .0.

...-.-. . .................................... . ................................................

140'E 160'E

1 40' E

1AAA

1AAA tlt

1AAA

1AAA ~\

1 4 O' E 1 6 O' E 1 B O' 1 6 O'W r""':'T"'".,.,.,...I;;A~~"'T"",.,.,...,.j~·.p.I,'"', ~I~""""'~Frll:;'~"""'"rnT~

1AAA tlt 1983-85

.• (:(= ?!iA 'AA ~:' ~/ .

:.;~~~~A'-~~f ~JiHjjUgS:~~~~:;~~::::::.:: . \ I ~~~::~:!:::.:.::. ':.:'.: .:.: .:"

1), ::::::::::::::::::::::::::.:::::::=~:::~::::: : : " . •• ! --••••_ .

• : .' +0 .~.:::~~~~•••:::~:::.::••

..........................

40 'N

20'N

40 'N

4 O'N

20'N

30'N

30 'N

30'N

Figure 8

Geographical distribution of mean annual fishing effort (mean total length of gear in km) for the Japanese driftnet fishery

by 3-yr period, 1977-91.

marlin. The fishing grounds are located around Izu

and off the Sanriku area of northern Honshu Island.

The average fishing vessel is less than 20 gross t.

Total annual catch from the harpoon fishery fluctuated between 2,500 t and 4,500 t during the late 1950's

and 1960's (Fig. 12). The annual swordfish catch was

about 250 t until 1957, fluctuated between about 800

and 1,900 t until 1970, and then dropped precipitously

to under 500 t, where it has remained. The decrease in

catch by the harpoon fishery was mainly due to the

decrease in number of fishing vessels.
Uozumi & Uosaki: Japanese Swordfish Fisheries in the Pacific Ocean 143

'"o

"

o

1986-88

1989-91

.::::.!:._. ... 1 40' E

20 'N

30'N

40 'N

20 'N

30'N

"

o

1977-79

160'E 1 80' 160'W

~: :..::::': . ..................- . ._ . •.._-_.._ _.. _. .~:.:_~::~~:::..::. ........................................ ..........- ......

40 'N

30 'N

"

2 0 • NL,.Lu'~.,""I..~I.~,""I.. .. '"'I,,~,,I.Uul=ili..u~u.U.L'"'-"-u.u.L0u.u.Lu.u.L"";:

",....,,,......'T""""'"1~4,.fC0'"'·,.;:E~,.,.,.;,.1,..;.,6 ~E~~,:;.,1...;:8j"T>1O"'·T='~lTc6~t"'P~·.,.,W,.,..,.,n"T'T=

• ~~ ~~~ / 1983-85

;~ i:: ll.:< -._-- _.... :+;~~~:...;:i:~:~~;-:::::::~~~~~~~:::;;:i:j:~:·::

U ,.':::::::::~:::::::::.:::::::...-:.- ':":''': .:..: ........... -. - . , -..::::::.:'" :.:::::::::::::::::::.-:::::::::::::.:::::: ....: " .0 _ _... ._•••. _. - . --- _._ _.._..- _.._.._.- -

. - -:-':.::::::::::::::::::::::::::-. -::=~:::-::. . ..._ - .....

20 'N

40 'N

40'N

30 'N

30 'N

Figure 9

Geographical distribution of mean annual swordfish catch (number of fish) in the North Pacific by the Japanese driftnet

fishery by 3-yr period, 1977-91.
144 NOAA Technical Report NMFS 142 _

140 ° E ] 6 0 ° E 1 80° 1 60 oW

40 0N

30 oN

20 oN

t

• <=~= R

:~/ 1/' ...

• <= R' .~.

• <= 11 .~..;._ ~:_ --::: • <= ._.... _.. ++ .'_0+ ••

8

' •••••• ++-I _ _~

+= +\ q\ t ....-+

{)' .::::::::::::: :~:;.-:=-=_: ..::::-:::-:::+...+ -

. ::::.~~~:~t:~~~~::::::~~~~~~~~~~l:i;..++ ......::.... :wr:: ... ,I +:..-:.__.::::::.. .::::::::;::~ ...-. ++ ..

....... ............... ...• . . .

•

Figure 10

Geographical distribution of mean annual swordfish CPUE (number per

10 km of gear) by the Japanese driftnet fishery during 1989-91 in the

North Pacific.
___________________ Uozumi & Uosaki:Japanese Swordfish Fisheries in the Pacific Ocean 145

1 6 O·W

..._....

...... .. ....••....... .....••.......

1 6 O· E 1 8 O·

.,111111

'ill II II

?'illll

1111111

'illll

?'iB

B

45 ·S

4 0 • S +-~-+-1----"".

,~

• <

· ( 35·S .<

+

Effort

1 6 O· E 1 8 O· 1 6 O·W

.._... ..+. .. +

...

....--........

.............+

• ~= 1 <=

• <= • <= • <=

+ =

40·S .....

35· S

45· S

Catcb

1 6 0 0E 1 80· 160 ·W

, ~= I <= ? • (= 1

• <= 'i 3 5 0

S . <= .1

+ = B

4 5· S

..

•

•••

•

•

....

-

•

CPUE

Figure 11

Geographical distribution of accumulated effort (total length of gear in

km), catch in number, and mean CPUE (number per] 0 km of gear) for

Japanese driftnet fishery operations from 1983 to 1990 in the South

Pacific.
146 NOAA Technical Report NMFS 142

5000

4500

4000

'" 3500 c

B 3000

.5 2500 ..c

t.J 2000 ....

U'" 1500

1000

500

0

1954 1962 1970

Year

1978

• Tunas

Other marlins

o Striped marlin

Swordfish

1986

Figure 12

Annual catch by the Japanese harpoon fishery in the Pacific Ocean, 1954-92.

Literature Cited

Food and Agriculture Organization of the United Nations (FAO).

1995. Catches and landings, 1993. FAO yearbook of fishery

statistics, vol. 76, 687 p. FAO, Rome.

Inter-American Tropical Tuna Commission (IATTC).

1994. A review of information of the biology, fisheries, .rarketing and utilization, fishing regulation, and stock assessment of swordfish in the Pacific Ocean. Inter-Am. Trop.

Tuna Comm., 79 p. Available from IATCC, Scripps Inst.

Oceanogr., La Jolla, CA 92037-1508.

Sosa-0Iishizaki, 0., and M. Shimizu.

1991. Spatial and temporal CPUE trends and stock unit inferred from them for the Pacific swordfish caught by the

Japanese tuna longline fishery. Bull. Far Seas Fish. Res.

Lab. 28:75-90.

Ueyanagi, S., R. S. Shomura, Y. Watanabe, andJ. L. Squire.

19R9. Trend in the fisheries for billfishes in the Pacific. In

R.H. Stroud (ed.), Planning the future of billfishes. Part 1,

p. 31-46. Natl. Coalition Mar. Conserv., Savannah, GA.
ABSTRACT

MARIJA VOJKOVICH and KRISTINE BARSKY

The California-based Longline Fishery for Swordfish, Xiphias gladius,

beyond the U.S. Exclusive Economic Zone

147

ow the Marine Region of the CDFG.

Until 1979, swordfish landings in California averaged

about 200 metric tons (t) annually. Since 1983 California swordfish landings have averaged approximately

1,200 t annually; in 1985 they peaked at 2,400 t (Dewees,

1992) .

Recently, a California-based high-seas longline fishery has developed. While these vessels do not fish in

local waters, they unload their catch and reprovision in

California ports. In 1993 the California Departmen t of

Fish and Game (CDFG) began dockside sampling and

tracking of longline landings, and began to develop a

logbook program. This paper provides a description of

the California-based longline fishery, landings, species

composition, size composition oflanded swordfish, and

anecdotal bycatch information. The defacto management scenario is also presented. We do not discuss the

health of the Pacific swordfish stock(s) or the implicaMarine Resources DivisionJ

California Department ofFish and Game

530 E. Montecito Street, Suite 104

Santa 8m-bam, California 93103

Swordfish, Xiphias gladius, provides a popular seafood

which is recognized worldwide. Known for its white

meat and mild taste, swordfish is the focus of many

commercial fisheries. Approximately 22% of the world

supply of swordfish is purchased by consumers in the

United States (Sakagawa, 1990). Imports of swordfish

into the U.S. have risen from nearly 500,000 lb in 1980

to over 15 million lb in 1989 (Bouchelle et aI., 1991).

To meet a portion of this market demand, fleets from

Japan, Taiwan, and the United States target swordfish

and tunas (Scombridae) year-round in the northeastern Pacific.

California-based fishermen have harvested swordfish

in nearshore waters since the early part of this century.

Hand-held harpoon was the predominant gear type

until the late 1970's, when drift gill nets were found to

be effective in catching large quantities of swordfish.

Introduction

Between 1991 and 1994, the number of California-based longliners fishing for swordfish beyond the U.S. Exclusive Economic Zone increased from 3 to 31. Recreational fishing

groups raised concerns regarding the impact of the fishery on swordfish, shark, tuna, and

marlin stocks. The California Department of Fish and Game established a sampling program to document species composition of longline landings and size composition of the

swordfish catch, and collected anecdotal information about fishing methods and bycatch.

In 1991-94, swordfish accounted for 59%-79% by weight of all landings by the fishery.

Tunas were II %-24% of the catch, and the remainder was pelagic sharks, opah, dolphin,

and escolar. Sampled swordfish were 6-277 k~ dressed weight (l3-6lJ Ib). Fish <50 kg

(<110 Ib) accounted for nearly 48% by number, those >100 kg (>220 lb) only about 17%.

Bycatch included striped marlin, turtles, birds, and marine mammals, although there are no

estimates of take.

The State of California is the current management authority for this fishery; re~ulations comprise requirements for commercial fishing licenses, provisions governing prohibited species (striped marlin), and logbook reporting requirements similar to those for the

Hawaii-based high-seas longline fishery. Discussions among the Fishery Management Councils for the Pacific, -orth Pacific, and Western Pacific Regions have not yet resulted in a

fishery plan for Pacific swordfish.
148 NOAA Technical Report NMFS 142 _

tions of catching protected species and slow-growing,

low-fecundity sharks, nor do we consider the cumulative effects of multinational exploitation on any of these

stocks. These issues are important, complex, and beyond the scope of this paper.

The Fishery _

From 1991 until late 1993, only 3 high-seas longline

vessels fished in waters beyond the U.S. Exclusive Economic Zone (EEZ) for swordfish and tunas and landed

their catch in southern California. In late August 1993,

longline vessels from the Gulf of Mexico began arriving

in southern California. They quickly established a local

infrastructure that supplied fuel, bait, gear, ice, and

fish offloading and transportation services. In 1994 a

total of 31 vessels landed swordfish and tunas taken

beyond the U.S. EEZ.

The California-based longline fleet operates far offshore, precluding small vessels from participating. Vessels are mostly steel hulled and at least 18 m (60 ft) in

length. Vessels are of both forward and stern cabin

design. Crew sizes range from 5 to 7 depending on

vessel size and operating procedures.

Generally, fishing trips are 3 wk in duration, although

accidents and breakdowns may cause much shorter

trips. Most vessels do not have built-in refrigeration

equipment and are thus limited in their time at sea.

The fish are iced and are sold as "fresh".

From 1991 through 1994, it was difficult to gather

information about longline fishing areas. Because there

was no formal reporting requirement, exact locations of

sets could not be ascertained. Discussions with captains or

their representatives generated only very general geographic information. One vessel captain indicated that he

usually fished around latitude 21 ON and longitude 121°W,

and others reported fishing as far north as 42°N and as far

west as 135°W. Comments like "we are fishing in the same

area as the Hawaii-based longline fleet" were common.

We assumed that the vessels fished beyond the U.S. EEZ

wherever they found promising signs of fishing success,

within an economically feasible radius of port. Seasonal

patterns oflandings were unclear due to the short tenure

of this fishery in California (Table 1).

Vessels in the California-based longline fleet target

both swordfish and tunas, especially bigeye, Thunnus

obesus. Typically, vessels fish 24-72 km (15-45 mi) of

600-lb to 1200-1b test monofilament mainline per set.

Mainlines are rigged with 22 m (72 ft) swiveled gangions

at approximately 61-m (200-ft) intervals, and buoyed

every 1.6 km (1 mi). Anywhere from 800 to 1,300 hooks

are deployed in a set. Large squid, Illex spp., are known

to be used for bait; variously colored light sticks are also

used. The mainline is deployed in 4-7 hr and left to

Table 1

Landings by California-based longline vessels fishing

beyond the U.S. EEZ, by month, 1991-94.

1991 1992 ]993 1994

January I 2 ] 3

February I 3 I 9

March 0 I 2 19

April I I ] ]3

May I I 0 IS

June 0 0 ] 17

July 0 2 I 6

August 0 I 4 16

September ] 0 4 5

October 3 0 5 17

November I I 6 17

December 3 I 10 17

Total 12 13 36 154

drift unattached for 7-10 hr. Radio beacons are attached to the gear for recovery. Retrieval requires 7-10

hr. Fishing takes place primarily during the night, when

more swordfish are available in surface waters (Carey

and Robison, 1981).

Longline-caught fish are sold both to wholesale fish

dealers and to an auction house. Local California fisheries, distant offshore fisheries, and imports from Hawaii, Chile, and Taiwan all influence the ex-vessel price

of swordfish. Longlined swordfish landed in California

averages $8.00 per kg ($3.65 per Ib). This compares to

nearly $11.00 per kg ($5.00 per Ib) for harpooned

swordfish, and roughly $6.00 per kg ($2.75 per Ib) for

gill-netted fish. Swordfish, like most other commercially-landed fishes, are often graded by size and quality, and the price adjusted accordingly.

Landing Data _

Information for this paper was derived from two sources:

the CDFG Marine Fisheries Statistical System,2 which

compiles data from landing receipts, and dockside sampling. Data from the landing receipt system include

date of landing; vessel, captain, and dealer identification; port of landing; gear type; fishing area; species;

pounds; and price paid.

Swordfish landings in California (from all gear types)

have fluctuated between 500 t and 2,400 t since 1980

(Fig. 1). Landings of longline-caught swordfish ranged

from 28 t (61,000 Ib) in 1991 to 497 t (1,095,000 Ib) in

2 Y1arine Fisheries Statistical Unit, California Department of Fish

and Came. 330 Colden Shore, Ste. 50, Long Beach, CA.

Cnpublished data.
Vojkovich & Barsky: California-based Longline Fishery beyond the U.S. Exclusive Economic Zone 149

2500

2000

III

c:

0 1500 .....

0

'':::

..... 1000 CD

::::E

500

0

198019811982 198319841985198619871988198919901991199219931994

Year

Figure 1

California swordfish landings in metric tons by all gear types, 1980-94.

1994 (Table 2). During 1991-93, longline swordfish

landings grew from 4% to 8% of total swordfish landings. In 1994, longline landings were more than 5 times

those in 1993, and accounted for 43% of California

swordfish landings. Until recently, and since 1982, the

drift gill net fishery produced more than 90% of California swordfish landings. 2

Species composition of longline landings was determined from landing receipt data. Swordfish were 59%-

79% of landings by weight, 4 species of tunas contributed 11 %-24%, and sharks represented 3%-11 % (Table

3). Other marketable bycatch included opah, Lampris

regius, dolphin, Coryphaena hippurus, and escolar,

Lepidocybium flavobrunneum. Relatively few sharks (in

proportion to those caught) have been marketed from

this fishery. The major shark bycatch is blue shark,

Prionace glauca, which has not been successfully marketed in the U.S., although in 1994 one large landing

was purchased by a dealer on speculation.

Sampling Data _

Data collected dockside included date of landing, vessel name and number, species, and individual weight

and/or length. Choosing which swordfish to weigh and/

or measure was done using a random number table to

avoid biasing the sample, because fish were often packed

in the hold by size. Length measurements (mm) of

dressed fish were made with calipers from the middle

of the cleithrum to the fork in the tail (CF). Individual

weights (lb) were obtained as fish were offloaded and

recorded for the landing receipt.

Table 2

Landings in metric tons by California-based longline vessels

fishing beyond the U.S. EEZ, 1991-94.

1991 1992 1993 1994

Swordfish 27.5 28.8 10l.3 496.7

Bigeye tuna 4.0 4.7 27.0 31.5

Albacore 0.5 <0.1 2.6 20.3

Bluefin tuna 0.1 0.5 3.5 5.1

Yellowfin tuna 0.1 0.0 6.3 4.0

Unspecified tuna 0.3 0.4 0.8 4.3

Mako shark 0.9 3.6 6.3 13.3

Thresher shark 0.1 0.6 1.4 12.8

Blue shark 0.0 0.0 0.0 7.5

Unspecified shark 0.0 0.0 0.7 \.4

Dolphin <0.1 0.7 \6.\ 27.6

Opah 0.8 0.5 3.9 7.3

Escalar 0.4 0.4 1.7 4.3

Total 34.7 40.2 \71.6 636.1

From January 1991 through December 1994, a total

of 215 landings was made by California-based longline

vessels fishing outside the U.S. EEZ. Sampling coverage

ranged from 8% to 50% (Table 4).

Nearly 1,500 CF length and 2,100 weight (dressed)

measurements were made of longline-caught swordfish. Swordfish length ranged from 73 to 226 cm and

weight from 6 kg (l3Ib) to 277 kg (611 Ib) (Fig. 2, 3).

The mean length and weight were 136 cm and 63 kg

(139Ib), respectively. Approximately 13% ofthe landed

fish were smaller than 25 kg (55Ib), 35% were between

25 and 50 kg (110 Ib), and 17% were heavier than 100
150 NOAA Technical Report NMFS 142 _

Table 3

Species composition (percentage by weight) of landings by

California-based longline vessels fishing beyond the U.S. EEZ.

Columns may not sum to 100% due to rounding.

]99] 1992 1993 1994

Swordfish 79 72 59 78

Bigeye tuna 12 12 16 5

Albacore ] <1 2 3

Bluefin tuna <1 1 2 1

Yellowfin tuna <l 0 4 1

Unspecified tuna 1 I <1 1

Mako shark 3 9 4 2

Thresher shark <I 2 1 2

Blue shark 0 0 0 I

Unspecified shark 0 0 <l <1

Dolphin <1 2 9 4

Opah 2 1 2 I

Escolar 1 1 1 I

kg (220 lb). The relation between weight (lb) and

length (mm) developed from those fish for which both

measurements were obtained is

Dressed weight = 0.00000013415 X CF2 87896.

Bycatch _

No observer program existed for the California-based

longline fishery, and bycatch was not documented. However, captains and crew members reported to samplers

that they caught unmarketable species, and we have

seen a home videotape showing striped marlin,

Tetrapturus audax, bird, marine mammal, and turtle

bycatch.

Management

The rapid growth of this fishery captured the attention

of local recreational fishing interests. They voiced concern that the longliners would increase fishing pressure

on stocks of swordfish, tunas, and sharks. They were

also concerned about the bycatch of striped marlin (a

billfish species prohibited from commercial sale in California), birds, marine mammals, and turtles. The recreational fishing groups claimed that the west coast

high-seas longline fishery would result in the same declines in swordfish, tunas, and sharks as on the Atlantic

and Gulf coasts. They demanded that the Federal or

State government "do something"

about the increased longline fleet in

California.

California commercial fishing law

presently governs the California swordfish fishery. Drift longline gear is not

provided for and is therefore illegal in

California waters. Because the Pacific

Fishery Management Count:il (PFMC)

has not developed a Fishery Management Plan (FMP) for large pelagic species (i.e. swordfish and striped marlin)

for the west coast, California fisheries

jurisdiction extends beyond State waters. Thus all California gear, season,

size limit, and bag limit laws apply to

waters within 200 mi of the coast. If, or

when, an FMP is developed for large

pelagic species within the PFMC's jurisdiction, that plan would preempt

California law.

Another high-seas longline fishery for

pelagic species, including swordfish and

tunas, is based in the Hawaiian Islands

longline vessels

95 115135 155 175 195 215 235 255

Dressed length (em)

75

1475

136 em

55

n =

x =

15 35

o.L---r---r--r-......1---+JL..Il~...............~'-&.+ I.....I"_......--i

5

15

20 .,....-----------------------,

Figure 2

Length (cleithrum to fork) frequencies of swordfish sampled from the

California-based longline fleet during 1991-94.

199] 1992 1993 1994

Boats 3 2 8 31

Landings 12 13 36 153

Landings sampled I 6 lR 41

Sampling coverage R% 46% 50% 270/<

Table 4

CDFG sampling of California-based

fishing beyond the V.S. EEZ.

10 Gl

U

.....

Gl

n.

>.

u

[:

Gl

::J

tT

Gl

.....

.....
______ Vojkovich & Barsky: California-based Longline Fishery beyond the U.S. Exclusive Economic Zone 151

9-r-----------------------,

Figure 3

Weight (dressed) frequencies ofswordfish sampled from the Californiabased longline fleet during 1991-94.

x = 63 kg

n = 2137

75 100 125 150 175 200 225 250 275 300

Dressed weight (kg)

50

Update-One Year Later _

Many of the vessels from the Gulf and Florida coasts

that were based in California during 1994 have left.

During most of 1995 only 4-6 vessels fished for more

than one trip from a California port, although 22 vessels

did make at least one longline landing. During the latter

portion of the year, five vessels from the Hawaiian fleet

began operations in California. They decided to temporarily base their fishing operations in California because

of the higher price realized from the sale of their fish.

Representatives from the WPRFMC and the PFMC

met a number of times concerning an FMP for Pacific

swordfish. At a final meeting in October 1995 the PFMC

decided they could not support the WPRFMC's bid for

lead councilor primary data repository. The PFMC did

commit to improved data collection, and fully supported

international management of this highly migratory species. However, they refrained from committing to a

swordfish management plan for the U.S. west coast or

any additional management measures. The NPFMC initially supported WPRFMC's bid as lead council, but has

since reconsidered and hasn't yet determined which

management approach it will support.

The CDFG is continuing to sample landed catch and

to monitor developments within the fishery. Landings

data and fleet dynamics information is being forwarded

to the PFMC. Logbook implementation is scheduled

for the summer of 1995.

25

2

o

8

4 Q)

3 Q)

0...

>, 7 u

[:

Q) 6 ::;]

tT

5 ....

3 Western Pacific Regional Fishery Management Council (WPRFMC).

1994. Management of U.S. Pacific fisheries: single council designation. Concept paper dated 22 September 1994. presented to the

Pae. Fish. Manage. Coune. and North Pac. Fish. Manage. Coune.

WPRFMC, 1164 Bishop St., Rm. 1405, Honolulu, HI 96813.

and takes place both within and beyond

the Hawaiian EEl. The Western Pacific

Regional Fishery Management Council

(WPRFMC) has developed an FMP for

large pelagic species and has authorized

a limited-entry longline fishery with a

vessel cap in the Hawaiian EEl. This

prohibits non-permitted domestic vessels from fishing within the EEl and

landing fish in Hawaii. All fishing for

large pelagic species by foreign vessels

is prohibi ted in the EEl of the Western

Pacific Region.

The WPRFMC in 1994 asked the

PFMC and the North Pacific Fishery

Management Council (NPFMC) ifitmay

act as lead council for the management

of large pelagic species (swordfish and

other billfishes) and serve as the primary repository of data for the west coast

high-seas longline fleet (WPRFMC3). The

WPRFMC feels that the swordfish stock is

one of the most important components

of their region's longline fishery and

that they need data from all fishery sectors to effect

responsible management. On the other hand, the PFMC

has been petitioned by several Pacific fishermen's organizations and a fish marketing group to keep management within its own jurisdiction. The councils have not

reached a decision, but are preparing a workshop on

the issue for March 1995.

Although California does not allow longlining within

the EEl, it does allow longlined fish to be landed. The

state requires all boats, and fishermen who land fish, to

be properly licensed. In addition, striped marlin cannot be landed; that species has been set aside as a

recreational-only species since the mid-1930's. In late

1994, the State of California Fish and Game Commission enacted regulations requiring all vessels participating in the high-seas longline fishery, and landing their

fish in California, to fill out daily fishing logs.

Recreational fishing interests have openly expressed

concerns about the longline fishery to CDFG, PFMC,

and the media (Tefft, 1994). They sought legislation in

1994 to limit the number of vessels, establish a permit

fee, institute an observer program, and require vessels

to carry transponders (vessel-position indicators). Although they were unable to get a bill introduced during

the 1994 legislative session, they are actively seeking

similar legislation for 1995.
152 NOAA Technical Report NMFS 142

Recreational fishing interests were again unsuccessful in 1995 in getting a bill through the California

legislature to control the longline fleet. They are still

committed to being fully involved in the management

process for swordfish.

The logbook required by the state of California was

developed along the lines of the one used by the NMFS

in the Hawaiian fishery. Logbooks were distributed to

participants of the California-based fishery beginning

in August 1995. Data on fishing locations, fishing effort

and catch, and bycatch will now be available through

the logbook program. No observer program has been

mandated.

The California-based longline swordfish fishery remains dynamic, and we anticipate more movement of

vessels in and out of the area due to changing·availability of this highly migratory species and the search for

new fishing grounds, reasonable port costs, and lower

transshipment costs.

Acknowledgments _

We thank Bill Craighead and Ken Trinh of Hi-Seas Fish

Company for their cooperativeness and generous details

of the fishery and markets, Bruce Mournier and Bill

Irwin for their video documentation of the longlining

process, and the vessel captains and crews who shared

their fishing information. We also thank the many reviewers who took the time to give us constructive feedback.

Literature Cited

Bouchelle, E. L., E. Thunberg, C. Adams, and]. L. SealeJr.

1991. In Tropical and subtropical fisheries technological conference of the Americas. Proceedings of the 15th annual

conference, p. 262-274. Florida Sea Grant Pub!. SGR-I05.

Carey, F. G., and B. H. Robison.

1981. Daily patterns in the activities ofswordfish, Xiphiasgladius,

observed by acoustic telemetry. Fish. Bul!. 79(2):277-292.

Dewees, C. M.

1992. Swordfish. In California's living marine resources and

their utilization, p. 148-150. W. S. Leet, C. M. Dewees, and

C. W. Haugen (eds.), Calif. Sea Grant Pub!. UCSGEP-92-12.

Sakagawa, G. T.

1990. Trends in fisheries for swordfish in the Pacific

Ocean. In R. H. Stroud (ed.), Planning for the future of

billfishes. Proceedings of the second international billfish

symposium, p. 61-80. Nat!. Coalition Mar. Conserv., Savannah, GA.

Tefft, R.

1994. Straining the SEA? In Sea Mag., September, 6 p.
Review of Swordfish, Xiphias gladius, Catch

in the Western Pacific Ocean

PETER G. WILLIAMS

Oceanic Fisheries Programme

South Pacific Commissionl

B.P. D5

Noumea, New Caledonia

ABSTRACT

Swordfish in the western Pacific Ocean are taken almost entirely as incidental catch by

longline vessels in the tuna fishery, which is the largest anywhere in the world. Rare catches

have also been reported by pole-and-line and purse-seine vessels; and there is growing

interest in targeting on swordfish. This paper presents what is known of swordfish catch in

the western Pacific tuna fisheries, based on data submitted to the Oceanic Fisheries

Programme.

Introduction

The western Pacific Ocean (WPO) currently supports

the largest industrial tuna fishery in the world; catch in

the statistical area of the Secretariat of the Pacific Community (SPC; formerly the South Pacific Commission])

was estimated at 931,685 metric tons (t) in 1993

(Lawson2). Skipjack is the most important of the four

major tuna species in the fishery, accounting for 59% of

the 1993 catch by weight, followed by yellowfin (31 %),

bigeye (4%), and albacore (4%). Purse seine gear was

responsible for 79% of the total catch, pole-and-line

gear for 7%, longline gear 13%, and troll gear 1%.

Rare catches of swordfish have been reported by

pole-and-line and purse-seine vessels. However, by far

the majority of swordfish taken in the western Pacific

Ocean has been incidental catch by longline vessels.

The development of the Hawaiian longline fishery into

a primarily targeted swordfish fishery during the past 6

yr has been well documented; this fishery has provided

useful information to the developing fisheries targeted

on swordfish in the SPC statistical area. There has been

growing interest in targeting swordfish by longline vessels operating in the waters ofAustralia, New Caledonia,

I Renamed Secretariat of the Pacific Community in 1998.

2 Lawson, T. 1994. South Pacific Commission tuna fishery

yearbook. Oceanic Fisheries Programme, S. Pac. Comm. Available

from Secretariat of the Pacific Community, B.P. D5, oumea,. ew

Caledonia.

New Zealand and, more recently, Fiji, although this

effort is very minor in comparison to overall longline

effort in the region.

This paper presen ts what is curren tly known ofswordfish catch in the western Pacific tuna fisheries, based on

data submitted to the Oceanic Fisheries Programme of

the SPC. For convenience, this paper subdivides the

SPC statistical area, mainly due to the various fisheries

involved, into the western tropical Pacific (lOON-lOOS),

the western subtropical Pacific (100S-35°S, and the

area to the north of 15°N), and the western temperate

Pacific (35°-45°S) (Fig. 1). Few data have been received for the northernmost portion of the western

subtropical area, which is therefore not discussed in

this paper.

Western Pacific Longline Fisheries _

Two types of longline vessels fish in the WPO. Large

distant-water vessels (typically >100 gross metric tons)

from Japan, Korea, and Taiwan are capable of fishing

far from their home ports, with usual trips of >1 mo,

and up to 1 yr for vessels that use at-sea transshipment.

Other, smaller vessels, used specifically for shorter fishing trips, are based near their fishing areas, and make

trips from a few days to 2 wk in duration. These smaller

vessels have established home ports in SPC member

countries and territories. They typically use ice and

supply fresh, chilled fish to sashimi markets, as opposed

153
154 NOAA Technical Report NMFS 142 _

.;~

Figure 1

The SPC statistical area, showing the western tropical Pacific

(WTP), western subtropical Pacific (WSP and WSPn), and western

temperate Pacific (WTeP) subdivisions used in this paper, and

200-mi economic zones of SPC member countries.

• • •

not expected to occur on the distant-water vessels, which

normally have adequate freezer storage for most of

their catch. The difficulty in monitoring the levels of

swordfish discard via logsheets has meant that some

reliance must be placed on data collected by observers,

although observer data coverage is insufficient at this

stage.

Figure 2

Spatial distribution of fishing days reported on logsheets for

longline vessels in the western Pacific, ] 978-92.

- 0

One of the prime responsibilities of the Oceanic

Fisheries Programme (OFP) of the SPC is the

maintenance of the Regional Tuna Fisheries Database (RTFD). The source of data in the RTFD is

primarily daily catch logsheets from domestic and

foreign vessels fishing in the Economic Zones (EZ)

of SPC member countries. The coverage of logbook data held in the RTFD is dependent on fleet

and area, and is therefore poor in some instances.

Lawson J provides some indication oflogbook data

coverage.

As the prime aim of the RTFD is to gather data on

catches of tuna species that are commercially important to the longline fishery, quite often data on bycatch

(e.g. swordfish) has been lacking. One significant difference between the two types of longline vessel is the

amount of discarded bycatch (e.g. swordfish), which is

to the larger distant-water vessels, which utilize on-board freezers to supply frozen fish to

normally lower-priced markets. The general

decline in the past 5-10 yr in the number of

large distant-water vessels, and the increase

in activities involving smaller vessels based in

SPC member countries, are attributed primarily to efforts to capitalize on higher sashimi

prices for fresh, chilled fish and to related

improvements in airfreight availability.

Longline activity in the western temperate

Pacific is seasonal and occurs primarily in

waters offsoutheastern Australia and around

New Zealand (Fig. 2), where southern bluefin tuna, Thunnus maccoyii, and yellowfin tuna,

T albacares, are the prime target species. Seasonality in the subtropical fisheries is less pronounced; fishing occurs off the east coast of

Australia as an extension of activities in the

western temperate area, in the northern waters of New Zealand, New Caledonia, Fiji,

Tonga, Cook Islands, French Polynesia, and

Vanuatu, and in the international waters bordering these areas. The prime target species

in subtropical waters are yellowfin tuna, albacore, T. alalunga, and bigeye tuna, T. obesus. The

tropical area contains the majority of western Pacific longline activity; the target species are almost

exclusively bigeye and yellowfin tuna. One of the

most significant developments among western Pacific longliners during the past 15 yr is the trend

to set gear deeper in order to target bigeye tuna,

which demand a higher price than yellowfin on

the sashimi market.

Data Collection _
__________________ Williams: Review of Swordfish Catch in the Western Pacific Ocean 155

Table I

Annual incidental swordfish catch and nominal CPUE (number per 1,000 hooks) from longline vessels operating in the

western Pacific Ocean, 1978-94, from logbook data held in the RTFD.

Areas of the western Pacific

Tropical Subtropical Temperate All areas

% of total % of total % of total Catch

Year Catch (no.) catch CP E Catch (no.) catch CPUE Catch (no.) catch CP E (no.)

1978 30 0.18 0.05 2 0.23 0.10 0 0.00 0.00 32

1979 668 0.10 0.02 1,095 3.01 0.55 0 0.00 0.00 1,763

1980 2,223 0.18 0.05 6,838 4.14 0.98 5,822 2.69 0.30 14,883

1981 3,123 0.26 0.05 18,422 3.40 0.78 6,469 2.73 0.28 28,014

1982 6,862 0.53 0.11 25,849 5.46 1.14 7,214 3.48 0.39 39,925

1983 3,312 0.31 0.08 14,035 2.72 0.83 4,226 2.33 0.29 21,573

1984 7,380 0.61 0.11 15,571 2.85 0.68 3,974 2.45 0.48 26,925

1985 10,466 0.79 0.14 20,049 2.75 0.82 4,056 3.44 0.67 34,571

1986 4,926 0.69 0.12 20,179 3.81 0.96 5,276 3.84 0.81 30,381

1987 5,986 0.79 0.12 21,296 3.66 1.06 4,979 3.25 0.65 32,261

1988 7,197 0.86 0.14 28,098 3.11 0.87 4,827 2.71 0.61 40,122

1989 8,399 0.78 0.12 18,333 3.07 0.73 7,498 2.53 0.55 34,230

1990 7,587 0.73 0.10 14,047 2.18 0.58 4,497 2.66 0.46 26,131

1991 5,103 0.62 0.09 12,815 2.99 0.78 5,115 3.47 0.42 23,033

1992 7,049 0.66 0.11 13,804 3.32 0.91 6,426 4.71 0.57 27,279

19931 14,696 1.76 0.20 6,865 1.03 0.36 2,463 2.37 0.43 24,024

19941 8,296 2.36 0.28 387 0.95 0.28 80 3.32 0.48 8,763

1 Data incomplete.

The absence of specific questions (e.g. the use of

light sticks) on logsheets has also made it impossible to

determine if some primary or secondary targeting of

swordfish occurs in western Pacific Ocean longline fisheries. Further, it is possible that specific fishing strategies have indirectly increased the catch of swordfish

(e.g. shallow-set targeting of bigeye near the full moon),

but the lack of information on logsheets has meant that

such practices can not be quantified. The abovementioned problems should be taken into account in

considering the information presented in this paper.

Observer programs that have operated out ofAustralia (since 1979) and ew Zealand (since 1986) provide

some indication of the level of swordfish catch and

discard in the western temperate Pacific. In the tropial

waters of the western Pacific, the observer program of

the Micronesian Maritime Authority of the Federated

States of Micronesia currently provides the only monitoring of longline activity in an area with considerably

more effort. Unfortunately, relevant data from observer

programs have yet to be provided and/or compiled, so

they receive limited mention in this paper.

Swordfish size-composition data have been collected

from port sampling operations established in SPC member countries since 1992. Length and weight measurements of dressed swordfish have been collected from

longline vessels unloading in the ports of the Federated

States of Micronesia and Marshall Islands. The majority

ofswordfish landed at these ports have been measured

from the anterior base of the pectoral fin to the caudal

fork; unfortunately, there is no conversion factor available for equating these dressed weights with whole

weights of swordfish taken by small-scale longline operations in the same area. In contrast, swordfish catch

reported on the logsheets of distant-water vessels operating in temperate waters of the western Pacific, tends

to be given as filleted rather than trunk weight; in this

case, a coarse raising factor has been employed to account for this.

Swordfish Catch _

Incidental Longline Catch

Table 1 shows annual swordfish catch, percentage of

total catch, and CPUE for longline vessels operating in

the SPC statistical area, based on logsheet data held in

the RTFD, which is incomplete (for example, it excludes some fishing in international waters). Table 2

provides estimates of total swordfish longline catch in the

western Pacific based on all data available, including
156 NOAA Technical Report NMFS 142

aggregated data provided by the distant-water fishing

nations ofJapan (since 1962), Korea (since 1975), and

T~iwan (since 1967) that have not been included in this

paper. Swordfish catch data contained in the data set

fromJapan have already been described elsewhere (e.g.

Sosa-Nishizaki and Shimizu, 1991).

The subtropical area of the western Pacific produces

the highest catch rates and catch volume (Fig. 3, 4).

Since the early 1980's, annual CPUE for the western

subtropical Pacific has fluctuated between 3 and 11 fish

per 10,000 hooks (Fig. 4; the apparent drop in swordfish CPUE and catch for 1993 and 1994 for the subtropical area is attributed to catch data for those years

not having been submitted at the time of compilation).

Peaks in CPUE in the subtropical and temperate areas

correspond with ENSO (El Nino-Southern Oscillation)

events in 1982-83, 1986-87, and 1991-92.

Table 2

Estimates ofswordfish catch from longline vessels fishing in the western Pacific for 1989-92. The estimation

procedure is given in Bailey et al. (1996).

Catch

Year Number Weight (metric tons)

1989 57,190 3,043

1990 82,235 4,364

1991 52,568 2,712

1992 59,270 3,213

-.~---~- ; " . . . ·1

", ....

Figure 3

Distribution of nominal CPUE for swordfish taken by longline

vessels in the western Pacific, 1978-92.

Catch rates for the western tropical Pacific have

steadily increased during the last 10-15 yr (Fig, 4); this

has coincided with a tendency for longline vessels to set

their gear deeper in order to increase the catch of

bigeye tuna. The marked increase in swordfish CPUE

in this area during 1993 and 1994 is believed to result

from 1) better reporting on logsheets by longline vessels as a result of increased observer and port sampling

activities; 2) the increase in number ofsmaller longline

vessels operating out of ports of SPC member countries; and 3) (related to 2) fishing methods that have

indirectly led to increased swordfish bycatch. Unfortunately, not enough information is currently available to

quantify these effects.

There is a strong seasonal pattern in the western

subtropical and temperate areas, with higher swordfish

catch rates during the austral winter and spring (Fig.

5). Sosa-Nishizaki and Shimizu (1991) describe seasonal trends in swordfish catch rates in other areas of

the Pacific; similarities between the temperate waters of

the northwest Pacific and the southwest Pacific can be

expected. Analysis ofJapanese longline CPUE in the

Pacific Ocean using the Generalized Linear Model

(GLM) method shows similar, clear seasonal changes

in CPUE in the temperate areas of both hemispheres

(Nakano, 1994). In contrast, there is no apparent seasonality in swordfish catch rates in the western tropical

Pacific (Fig. 5).

Observer data made available to the Oceanic Fisheries

Programme indicate that swordfish are rarely discarded

on distant-water vessels and they appear to be the most

resilient of the billfish species (Bailey et al., 1996).

Targeted Longline Catch

There has been some limited targeting of swordfish in the waters ofAustralia and New Zealand. In

Australia, feasibility trials utilizing chemical light

sticks have been successful. However, the marketing ofswordfish in Australia is currently restricted

by regulations prohibiting the sale of this species

if it con tains more than 0.5 ppm mercury.

Limited trials in targeting swordfish with longline gear have recently been conducted in American Samoa and New Caledonia. Promising catches

were taken during the New Caledonia trials and a

market study is currently being undertaken.

In late August 1994, some vessels that had targeted swordfish in the Hawaiian longline fishery

commenced exploratory fishing in southern Fiji

waters centered on 20oS. Nine vessels were operating at the end of November 1994, with average

swordfish catch rates of 7 fish per 1,000 hooks

during the first months of operation, plus large
___________________ Williams: Review of Swordfish Catch in the Western Pacific Ocean 157

6 7 10 11 12 Month

o +---1--+---+--+---+--+---+--+-----+--;------"

1

Size Composition _

Swordfish taken by longline vessels in tropical waters

appear to have a narrower range of weights than those

taken in more temperate waters (Fig. 6). Most of the

dressed catch that has been sampled in the western

tropical Pacific falls in the range 30-50 kg (95-125 cm

pectoral fin-fork length).

Unfortunately, no data are currently available to determine whether discarding practices in the tropical

area may account for the absence of smaller swordfish

seen in port sampling there (Fig. 7). It is known that

processing procedures are different between areas and

between fleets, but it will not be possible to accurately

compare size composition data from different sources

until further information on the various processing

procedures employed has been gathered and conversion factors for relating dressed to whole weight can be

calculated. Figure 8 shows the length-weight relationship of swordfish caught in tropical waters and measured during port sampling.

swordfish were taken (presumably from one school) by

a Japanese pole-and-line vessel in Kiribati waters in

November 1990. The reported average weight of2 kg is

consistent with information on the expected spawning

period (March-July) in the central Pacific Ocean, and

with observations on the period between spawning and

the appearance ofjuvenile swordfish in other fisheries

(Nakamura, 1985).

A few swordfish have also been taken as bycatch in

the now-defunct New Zealand purse seine skipjack fishery (Bailey et al., 1996).

Figure 5

Seasonal swordfish CPUE (numbers per 10,000 hooks)

in the longline fisheries of the tropical (WTP) , subtropical (WSP), and temperate (WTeP) areas of the

western Pacific Ocean, 1978-94. Source: RTFD.

...~~

WTP '-.

3 12

2.5 10

2

w

~15 w

::>

0 Q.

<)

0

<Xl a N .... CD <Xl a N .... ..... <Xl <Xl <Xl <Xl <Xl (J) (J) (J) (J) (J) (J)

12

10

8

w

~6

0

4

2

0

<Xl a N .... CD <Xl a N .... ..... <Xl <Xl <Xl <Xl <Xl (J) (J) (J) (J) (J)

J

:34+

3 -ld

t I I I I I I

<Xl a N .... CD <Xl a N .... ..... <Xl <Xl <Xl <Xl <Xl (J) (J) (J) (J) (J)

Year

Figure 4

Annual swordfish CPUE (numbers per 10,000 hooks)

for longline vessels in the tropical (top), subtropical

(middle), and temperate (bottom) areas of the western

Pacific, 1978-94. Source: RTFD.

incidental catches of dolphin (mahimahi) and other species. It is reported that up to 20 vessels may eventually

operate in this fishery, and the potential for the development of a targeted swordfish fishery appears good.

There has been only one report of swordfish catch by

pole-and-line fishing to date. Approximately 0.1 t of

Incidental Swordfish Catch from Other Tuna

Fisheries
158 NOAA Technical Report NMFS 142

Conclusions

Swordfish are an important bycatch of the western Pacific

longline tuna fisheries. Logsheet programs, portsampling,

and observer data provide some relevant information,

and this paper provides some insight into the distribution

ofswordfish catch by longline vessels throughout the SPC

statistical area. However, it should be noted that no attempt was made to determine standardised CPUE, and

caution is advised in inferring indices of abundance.

There appears to be some potential for targeted swordfish fisheries in areas of the western Pacific (e.g. Fiji),

although it appears certain that marketing logistics will

be the driving force in any such implementation.

The OFP is about to undertake a 5-yr project, funded

by the European Union, referred to as the South Pacific

Regional Tuna Resource Assessment and Monitoring

Project (SPRTRAMP). The prime aims of this project

will be to establish a regional scientific observer data

collection program, and to provide assistance in further development of port sampling activities throughout the region. The project should increase our knowledge of swordfish in the western Pacific Ocean by

providing

• Standardized length and weight data from port sampling operations.

• Observer-collected information on longline targeting practices, swordfish length, weight, and biology,

and levels of swordfish discard.

8000 ,----------------------,

7000

6000

5000

E 4000

z 3000

2000

1000

o

o

Weight (kgs) Length(em)

20 40 60 80 100 120 140 160 180 200

1800,..-------------------.,

1600

1400 "

1200

1000

§ 800 z 600 "

200 400 "~,~~~~~~~~~~=a.I!!I. J o

o

Figure 7

Length frequency distribution ofswordfish taken in longline fisheries of the western tropical Pacific, 1992-94, from

sampling in ports ofSPC member countries. Length measured from anterior base of pectoral fin to caudal fork.

Weight (kgs)

Length (em)

50 100 150 200 250

400

200

o0 I---~-'•.....::..:::..=-+-------~------I

o

200 0

180 a

160 a • - 1400 • !If'" 1200

100 0 • Cl 800 "iii

3: 600

Figure 8

Length-weight relationship for swordfish taken in

longline fisheries of the western tropical Pacific, 1992-

94. Length measured from anterior base of pectoral fin

to caudal fork. Source: size composition data collected

in ports of SPC member countries.

Figure 6

Weight composition of swordfish catches in the tropical

(top), subtropical (middle), and temperate (bottom) areas of the western Pacific for 1984 (lowest curve) through

1992 (highest curve). Source: RTFD logsheet data for days

where only 1swordfish was recorded on a logsheet. Weights

have been rounded to nearest 10 kg and no allowance has

been made for weight loss due to processing.

800 ,---------------------,

700

600

500

E 400

z 300

200

100 "

o

o 20 40 00 100 120 140 100 100 200

Weight (kgs)
_____________________ Williams: Review of Swordfish Catch in the Western Pacific Ocean 159

• An improved longline logsheet form for better collection of data on targeting practices.

Literature Cited

Bailey, K. ., P. G. Williams, and D. G. Itano.

1996. By-catch and discards in the western Pacific tuna fisheries: a review of SPC data holdings and literature. Oceanic

Fish. Progr. Tech. Rep. 34.

Nakamura, 1.

1985. Billfishes of the world: an annotated and illustrated

catalogue of marlins, sailfishes, spearfishes and swordfishes

known to date. FAO Fish. Synop. 125(5),65 p.

Nakano, H.

] 998. Stock status of Pacific swordfish, Xiphias gladius, inferred from standardized CPUE of the Japanese longline

fleet using general linear models. In 1. Barrett, O. SosaNishizaki, and N. Bartoo (eds.), Biology and fisheries of

swordfish, Xiphias gladius, p. ]95-209. U.S. Commer.,

NOAA Tech. Rep. NMFS ]42.

Sosa-Nishizaki, 0., and M. Shimizu.

1991. Spatial and temporal CPUE trends and stock unit inferred from them for the Pacific swordfish caught by the Japanese tuna longline fishery. Bull. Far Seas. Fish. Res. Lab. 28.

Distribution and Stock Assessment of Swordfish, Xiphias gladius,

in the Eastern Pacific Ocean from Catch and Effort Data

Standardized on Biological and Environmental Parameters

MICHAEL G. HI TON and RICHARD B. DERISO

Inter-American Tropical Tuna Commission

8604 LaJolla Shores Drive

LaJolla, California 92037-1508

ABSTRACT

Catch and effort data for swordfish, Xiphias gladius, caught in the eastern Pacific Ocean

(EPO) by longline fisheries in 1971-92 were standardized using a new model that incorporates biological and environmental data. Distributions of relative abundance by 2° latitude x

5° longitude areas and bimonthly periods as well as relative annual abundances (1962-92)

for the entire EPO are presented. Stock structure ofswordfish in the EPO was examined on

the basis of biological, standardized catch rate (CPUSE), and genetic data. Results support

existence of a stock with distribution centered in the southern EPO. Whether there exists a

stock centered in the northern EPO is unclear. Reproductive activity was identified in the

north central EPO and in the vicinity of Baja California, Mexico. Length-frequency distributions and CPUSE indicate significant migration of swordfish in the northern EPO. Thus,

though there may be a stock centered in the northern EPO, the region is regularly

frequented by swordfish moving across the geographical limits of this study. The DerisoSchnute delay-difference model was used to examine stock-structure hypotheses and to

estimate average maximum sustained yield (AMSY) and optimum effort (OE). Model

results did not differentiate between an EPO open to or closed to migration, and the

estimates of AMSY «8,400 metric tons) and OE (<156 x I 07 average hooks) were sensitive to

whether there was migration across 1500 W. Independent estimates for the southern stock

were not possible. Preliminary analyses of recent data indicate that catch rates are continuing to decline, but that they remain above those expected at AMSY. Further examination of

stock structure and status should be conducted as more data become available.

Introduction

The first part of this study applies a new general

method for standardization of fishing effort (Hinton

and Nakano, 1996) to data from longline fisheries capturing swordfish, Xiphias gladius, in the eastern Pacific

Ocean (EPO). Catch-per-unit-of-effort (CPUE) statistics provide the core knowledge of swordfish distribution and abundance, and the key source of these statistics in the Pacific is the Japanese longline fisheries.

Japanese longline CPUE statistics have provided the

basis of all major investigations of Pacific swordfish, and

this study was no exception. CPUE is particularly valuable to fisheries investigations because it often provides

the sole measure of presence and abundance. Nominal

CPUE (CPUNE) is proportional to mean abundance if

population or fishing effort is homogeneously distributed and if all uni ts of effort are equal and proportional

to the rate of fishing, conditions that are seldom

achieved (Ricker, 1975).

The use oflongline CPUE is problematic. Among the

several problems encountered when standardizing

longline effort across the broad geographical and temporal scales necessary for study of swordfish relative

abundance and distribution patterns are 1) the fishery

is directed at tunas (Ueyanagi, 1974; Suzuki, 1989); 2)

small portions of the fishery were historically directed

at swordfish (Kume and Joseph, 1969); 3) Japanese

logbook records do not indicate target species (Squire

and Suzuki, 1990); and 4) there have been significant

changes in longline gear design and fishing configuration, in particular the advent of deep-longline gear,

that make it necessary to standardize longline effort on

a species-specific basis (see e.g. Suzuki et aI., 1977;

161
162 NOAA Technical Report NMFS 142

Suzuki, 1989). Shomura (1980) noted that for longline

gear, the underlying assumption that catch rate is proportional to average stock abundance is sensitive to

"changes in the construction or deployment of [the]

gear, shifts in fishing strategy or target species, and

changes in [vulnerability] of the fish to the gear. ..."

The underlying condition that results in violation of

the assumption that longline CPUNE is proportional to

average stock abundance is that longline gear is deployed across environmental conditions that limit the

distribution ofspecies caught by the gear. The fact that

such limits exist has long been recognized (Blackburn,

1965; Green, 1967; Hanamoto, 1974; Sharp, 1978; Sund

et ai., 1981). Geographical and seasonal effects have

been incorporated into models to explain variability in

CPUE (e.g. Honma, 1974; Allen and Punsly, 1984;

Punsly, 1987; Suzuki, 1989; Punsly and Deriso, 1991;

Nakano, 1998). However, Punsly and Nakano (1992)

noted that in their GLM model (used to standardize

longline hook rates for yellowfin and bigeye tuna to

estimate annual abundance) the "depth of the fish,

resulting from variations in vertical thermal structure

(Green, 1967), oxygen level, or food availability could

have a greater effect on hook rates than does abundance."

While these problems may appear daunting, information on conditions limiting the distribution of a

species, on distribution of limiting conditions in the

environment, and on longline gear configuration, when

used together, provide the means to surmount most of

these problems and form a basis for effort standardization. This study illustrates the general method ofHinton

and Nakano (1996) by developing standardized estimates of CPUE and presenting estimates of relative

abundances for swordfish in the EPO.

The second part of this study examines the structure

and status of swordfish stocks in the EPa by using

biological and abundance data and applying a delaydifference model to standardized CPUE data. Published

stock assessments of Pacific swordfish have been derived largely from simple production models fitted using equilibrium techniques to catch and effort data

from longline fisheries, a procedure known to yield

biased and unreliable results (Hilborn and Walters,

1992). Delay-difference models are in the class of biomass dynamic models, which include these simpler stock

production models (Hilborn and Walters, 1992), but

specifically incorporate process models, which introduce information about growth, recruitment, and Sl:.fvival not explicitly included in the simpler models. The

parameters of delay-difference models are readily interpretable in a biologically realistic sense, which is not

the case for parameters of the simpler models. Delaydifference models provide this level of interpretation

and sophistication without requiring the full details of

population age composition required by age-structured

models such as virtual population analysis. Thus, delaydifference models represent a compromise between

complex fully age-structured models and overly simplistic production models. We refer those interested to

Hilborn and Walters (1992), in which each of these

model categories and their applications are afforded

significant description and review.

Data and Methods _

The development of longline fisheries in the EPa has

been documented byJoseph et al. (1974). By 1963 most

of the region was being fished, and by 1968 virtually the

entire area bounded by 400 N and 400 S latitudes was

exploited. Suzuki (1989) noted that initially longline

gear was configured to fish the upper layers of the

ocean using from four to six or seven hooks per basket

(HPB), and the primary target species was yellowfin

tuna, Thunnus albacares. However, since 1974 significant portions of the effort have shifted from shallow to

deeper ocean zones to more effectively target the deeperswimming and more valuable bigeye tuna, T. obesus

(Suzuki, 1989). Deep longline gear, which has about 8-

15 HPB, fishes to maximum depths of about 200-300

m, compared with about 150 m for regular longline

gear. This is a significant difference in terms ofvariability in hydrographic across the depth of the gear and

across areas and time.

Catch and Effort Data

Catch and effort data from Japanese and Mexican

longline fisheries were used in this study. The Japanese

longline fishery catch and effort data were collected by

the Japanese government from over 90% of registered

Japanese-flag longline vessels fishing in the Pacific. These

logbook data were subsequently compiled by the National Research Institute of Far Seas Fisheries, Shimizu,

Japan. Formats of available fishery data were 1) total

catch and effort estimates for 5° latitude by 5° longitude (5 x 5) strata by month; 2) 5 x 5 catch and effort

estimates by month by HPB; and 3) catch and effort

estimates for 1° latitude by 1° longitude (1 xI) strata

by month. These data were processed as described in

Hinton and Nakano (1996). Note that the HPB data

were used to estimate hook fishing depth (Suzuki et ai.,

1977; Wright, 1980; Gong et ai., 1989; Hinton and

Nakano, 1996), which was required to estimate vertical

distribution of effort and its relationship to the distribution ofswordfish in the environment.

Data from Mexican-flag longline vessels were logbook data from 1980-87 collected by the Inter-American Tropical Tuna Commission, which for each set
_______ Hinton & Deriso: Distribution and Stock Assessment of Swordfish in the Eastern Pacific Ocean 163

included date and time, position, number of hooks

fished, and catch in numbers and/or weight. The data

did not include detailed information on HPB, as this

was not recorded in the logbooks. Although several of

these vessels were fishing under the direction of Korean fishing masters, the majority were under the direction ofJapanese fishing masters. We also note that this

fishery was previously a Japanese regular longline fishery that targeted marlins (Squire and Muhlia-Melo1).

Thus the Japanese HPB distributions were used to estimate HPB distribution for the Mexican data. In those

area/bimonthly period combinations lacking Japanese

data, the regular gear configuration with HPB of 4-7

was assumed (see Hinton and Nakano, 1996). Prior to

pooling with the Japanese data, the data from Mexican

logbooks were summarized by 2° latitude by 5° longitude (2 x 5)stratum by bimonthly period (Jan-Feb, ... ,

Nov-Dec) by HPB.

Estimates of the total catch of swordfish in the EPa

during 1954-87 were obtained from data compiled in

Joseph et al. 2 These data were used in fitting the DerisoSchnute delay-difference model. Final estimates of total catch for more recent years were not available.

Hydrographic Data

Distributions of temperature relative to mixed layer

temperature (MLT), expressed as isotherms [MLT -

(1°,2°, ... , l7°C)] for 2 x 5 strata by bimonthly period

during 1971-87, were developed from temperature-atdepth (TZ) data (White3) with depth resolution of (0,

20, ... ,80, 120, ... , 240,300,400 m),asdescribed in

Hinton and Nakano (1996). In cases where TZ data

were lacking for a specific area and bimonthly period,

the pertinent climatology was used. Finally, of nearly

16,850 observations in the 2 x 5 by bimonthly period

data, in about 700 cases TZ data were not available in

the White3 database. In those cases, isotherm depths

were estimated using the 5 x 5 by quarterly period TZ

climatology of Mizuno and Yakinawa (1991). For those

I Squire, j. L., and A. F. Muhlia-Melo. 1993. A review of striped

marlin (Tetmpturas audax) , swordfish (Xiphias gladius) , and sailfish

(TstiophoTUS platypteTus) fisheries and resource management by

Mexico and the United States in the northeast Pacific Ocean. U.S.

Dep. Commer., NOAA, at\. Mar. Fish. Serv., SW Fish. Sci. Cent.

Admin. Rep. LJ93-06. 44 p. SWFSC. NMFS. Box 271, Lajolla, CA

92038.

2 joseph, j., W. H. Bayliff, and M. G. Hinton. 1994. A review of

information on the biology, fisheries, marketing and utilization,

fishing regulations, and stock assessment of swordfish, Xiphias

gladius, in the Pacific Ocean. Inter-Am. Trop. Tuna Comm. lnt.

Rep. 24.81 p. IATTC, Scripps Inst. of Oceanography. La jolla,

CA 92037-1508.

3 White, W. 1995. Scripps Institution of Oceanography. La jolla,

CA. Personal commun.

bimonthly periods and 2 x 5 areas that overlapped the

quarterly periods, or overlapped the 5 x 5 areas in the

Mizuno and Yakinawa (1991) data, the averages of the

TZ data from the overlapping quarterly periods or areas were used to estimate isotherm depths.

Vertical Distribution: Time at Temperature

It was assumed that the vertical distribution of the swordfish population is limited by temperature relative to

MLT (~t). Such constraints are commonplace; for example, ~t limits marlin distribution (Brill et aI., 1993),

and both temperature and oxygen limit tuna distribution (Brill, 1994). Carey (1990) found that swordfish

are able to regulate rates of heating and cooling of

muscle tissue so that muscle cools slowly during ventures into colder waters and heats rapidly during recoveries in warmer water. The ability to control muscle

temperature is also found in tunas (Brill, 1994) but not

in marlins (Block et aI., 1992). Swordfish eye and brain

temperature are controlled by a heater organ (Carey,

1982; Block, 1990), tissue that is found in all billfishes

(Block, 1991). In the case of swordfish, this heater

organ is capable of maintaining elevated brain and eye

temperatures over long periods in cold water. Thus,

while temperature may be expected to limit swordfish

distribution, other factors, such as ambient oxygen concentration and behavioral response to light levels (Carey

and Robison, 1981), also may be limiting factors.

The vertical distribution of the swordfish population

was estimated from plots offish depth-at-time with overlaid isotherm profiles (Carey and Robison, 1981; Carey,

1990). These data were from five swordfish, four of

which were tagged in the northwestern Atlantic (Carey

and Robison's fish 7, and Carey's fishes 9, 10, and 11)

and one ofwhich was tagged offBaja California, Mexico

(Carey and Robison's fish 6). They ranged in size from

about 32 to 140 kg.

Japanese longline operations targeting tunas operate

the gear during the day (Kume and Joseph, 1969;

Ueyanagi, 1974), and the data for the Mexican fishery

contained only sets made during daylight hours. The

Japanese currently set longline gear at night for swordfish only in areas nearJapan (Miyabe4 ). Therefore, only

swordfish tracking records for the sunrise-to-sunset period were used.

Following Hinton and Nakano (1996), the data were

scanned and digitized, and then pooled to obtain species-specific estimates of time at temperature relative to

MLT for ~t = (0, _1°, -2°, .... , -l70 C). The distribution was significantly different from a uniform distribu4 Miyabe, N. 1995. National Institute of Far Seas Fisheries,

Shimizu,japan. Personal commun.
164 NOAA Technical Report NMFS 142 _

Effort Standardization

Then catch within any depth zone (j) ofsubregion (i) is

C(i,j) = q/ N(i,-) x p(j) x!,,(i,j) x [A(i) x h(i,j)]-l

Fishing effort was standardized by the method developed in Hinton and 1 akano (1996), which utilizes

information on the distribution of habitat and on the

distribution of a species within that habitat.

a region (area) of the ocean;

index of subregions of A, such that

for i = (1, ... , n), A(-) = LA(i);

depth (m) of the water column in A;

index of depth zones, such that

for h(i,j) andj= (1, ... , n), h(i,-) = Lh(i,j);

volume, such that V(i) = A(i) x h(i);

nominal (unstandardized) fishing effort;

effective (standardized) fishing effort;

catchability coefficien t wi th units [V] / [j];

catch in numbers or weight;

number or biomass of fish; and

proportion ofthe population in a depth zone,

such that for j= (1, ... , n), p(-) = L p(j).

h

}

v

in

!e

qv =

C =

N=

P =

Let A

Maturity

tion (X2=17, p<O.OOOI); the percentage of time spent

within a 1°C temperature bin ranged from about 1% to

17%. The distribution thus obtained translated directly

into a distribution of population in temperature-space

(Fig. 1) under the assumption that the sampled fish

were representative of the species.

Data not available for inclusion in this initial analysis

were obtained in 1986 on a swordfish, estimated to be

about 90 kg, tracked off San Clemente Island, California (Holts et al."). During the 24-hr tracking period, it

showed a vertical distribution with respect to temperature which was similar to the distributions of the fish for

which data are included here.

Data collected from 1,079 swordfish sampled aboard

Japanese fishing and research operations during 1971-

92 were examined. Summaries of the 1971-87 data

have been published (Miyabe and Bayliff, 1987; akano

and Bayliff, 1992) and procedures of data collection

are detailed therein.

The gonad index (GI; Hinton et aI., 1997) was estimated as

GI = In(gonad weight in grams)

In (eye-fork length in centimeters)

which, with some simplification, can be rewritten as

wherej,(i,j) =!,,(i,j) x p(j) x h(i,j)-l.

As noted in Hinton and Nakano (1996), average

density of the population in A( i) is estimated using

C(i,-) and !,,(i,j) weighted by factors that are proportional to the fraction of the population in h( i,j) and

inversely proportional to volume, i.e. factors proportional to population density in volume V(i,j). Effort

outside the range of the population does not bias this

density estimate, for example when hooks on a longline

are fished outside the depth range of a species and are

included in estimates of catch rates based on total hooks

fished. Further, the estimate of average density is applicable not just to the sampled zones, but rather to the

subregion, which is important since longline hooks often

may not sample the entire depth range of a species.

In this application of the method to swordfish, the

resolution was 2° latitude by 5° longitude and bimonthly

period; thus these were the spatial-temporal dimensions within which C(i,-) and in(i,-) were estimated.

The distributions of in(i,j) were estimated from the

gear configuration data. Habitat h(i,j) ofswordfish was

delimited by 1°C increments in temperature relative to

MLT, and p(j) was estimated using results from ultrasonic depth telemetry studies.

9 11 13 15 17

/H(0C)

>- 75

U

a:

w

ll.

50

;::

:s:>

::;:

:>

u

Figure I

Cumulative percentage ofswordfish at temperatures L'.!

below the temperature of the mixed layer, as determined by acoustic telemetry.

5 Holts, D. B., N. W. Bartoo, and D. W. Bedford. 1994. Swordfish

tracking in the southern California Bight. U.S. Dep. Commer.,

NOAA, 1 atl. Mar. Fish. Serv., SW Fish. Sci. Cent. Admin. Rep. lJ94-15,9 p. SWFSC, NMFS, Box 271, LaJolla, CA 92038.

100-r------------------;;r-,
Hinton & Deriso: Distribution and Stock Assessment of Swordfish in the Eastern Pacific Ocean 165

-von Bertalantfy

. - . Brody

200

150

:E

en£ 100

250~-----------------,

where a and ,8 are parameters of a Beverton-Holt curve

(Ricker, 1975). On the basis of length-frequency data

for swordfish in the EPO (Shingu et aI., 1974; Miyabe

and Bayliff, 1987; Nakano and Bayliff, 1992), individuals were considered fully recruited to the fishery at an

eye-fork length of about 100 em, which corresponds to

a weight of about 10 kg and an age of about 2 yr. Thus,

recruitment was lagged by 2 yr (k = 2) with respect to

spawning stock biomass.

The Brody coefficient p = 0.9999 (-1) (Fig. 2) was

estimated as follows. Length at age was first determined

from a von Bertalanffy growth curve for swordfish from

the Pacific (Yabe et aI., 1959). These lengths at age

were then converted to weights at age with the Kume

andJoseph (1969) weight-length relationship for whole

swordfish in the EPO. These weight-at-age estimates

provided the basis for estimating p by the method of

least-squared difference between the square roots of

these estimates and the square roots of weights at age

predicted by the Brody growth curve. Finally, it was

considered that a reasonable range on which to consider survival rate, [, was about 0.62-0.81 (Boggs, 1989).

The parameters of the DSM were estimated by fitting

model predictions of annual catch rates to "observed"

rates based on catch per unit of standardized effort

(CPUSE) and catch per unit of nominal effort (CPUNE)

for 1962-87 (recall that the standardized data were not

available prior to 1971, nor were final estimates of total

catch available for the 1988-92 period). The "observed"

annual catch rates are actually estimates based on the

effort and weight of catch from individual 2° latitude by

5° longitude areas, A( i). These areal CPUE observations were combined into an annual index of catch

rate, CPUSE(t) or CPUNE(t), for the EPO using area

weighting (Quinn et aI., 1982).

B(t) = (1 + p) x [ x S( 1- 1) - P X [2 x

[S(t-I)xS(/-2)/B(/-I)] +}~[B(/-k)]. (1)

w(a+ 1) = w(a) + p[w(a) - w(a-I)]

We used the Deriso-Schnute delay-difference model

(DSM; Hilborn and Walters, 1992) to investigate the

status of swordfish stocks in the EPO. Delay-difference

models have as their basis the fact that population

biomass (B) at a given time I may be written as the sum

of the biomass of individuals surviving from time (1-1)

to I, plus the biomass resulting from growth of the

survivors from (I - 1) to I, plus the biomass of individuals that enter the population at time I:

Stock-assessment Model

where N(a./) = number of individuals of age aat time t,

w(a) = average weight of an individual of age a; and k is

the age of recruits at entry into the population.

The basic assumptions of the DSM were 1) recruitment

to the population occurred over a short period (knifeedge recruitment); 2) the survival rate from natural causes

(l) was a constant for all fish recruited to the population;

3) spawning occurred at the start of each year, with fishing

occurring after spawning and with natural mortality negligible during that period; and 4) the average weight at age

was determined by a Brody growth model:

B(t) = Lw(a) x N(a,t) + w(k) x N(k,/)

Incorporating process models for weight at age and

recruitment, this may be written as

B(/) = B(survivors from (1-1) to I) + B(survivors'

growth from (1-1) to I) + B(recruits at I)

where p is the Brody growth coefficient. We applied the

simplified version of this model, which has the constraint w(k -I) = 0, as given in Deriso (1980).

Define S( I) as the biomass of adults that survive the

fishery and FBas the biomass of recruits as a function of

the adult biomass. Then, substituting the Brody curve

solutions for the w(a) and simplifying, the full model is

given by

With FB as defined, this formulation is for a closed

population. An alternative formulation would include

an additional term, R, added to the right side of Eq. (1)

to account for net flux resulting from immigration and

emigration ofswordfish in the EPO. We considered the

following two models for recruitment:

FB[B(/- k)] = ax B(/- k)/I+[,8x B(/- k)] and

FB[B( 1- k)] = a x B(t - k) / 1+[,8 x B( 1- k)] + R

50

10 12 14 16 18 20

Age (years)

Figure 2

Brody growth model approximation ofswordfish weight

at age modeled by a von Bertalanffy growth function.
166 NOAA Technical Report NMFS 142

Fishing with deep longline gear began in the western

Pacific Ocean in about 1975. During the first few years

following its introduction, deep longline gear was used

primarily in the western Pacific Ocean, with its use

spreading over time to various other regions of the

Pacific. In the first few years of the standardized series,

1971 to about 1977, there was little or no use of this

gear in the EPO. The impact of effort standardization

on the annual indices of CPUE was examined by first

scaling the standardized and nominal CPUE series by

their respective averages for 1971-87, computing the

differences of the paired observations, and then testing

this series of differences for trend. The Theil distnbution-free test for slope (Hollander and Wolfe, 1973)

indicated a significant trend in these differences

(Kendall's K; n=17, p=0.003), which results from increasing values of annual CPUSE (Wilcoxon signed

rank; n=ll, p=0.002) starting in about 1976. When the

catch rate series for 1988-92 were included in these

analyses, the trend in the differences was insignificant

(Kendall's K; n=22, p=0.13). The 90% confidence

intervals for the annual abundance indices based on

CPUSE were estimated using the bias-corrected and

accelerated (BC.) bootstrap method (Efron cLnd

Tibshirani, 1993) with 5,000 replicates and a resample

size equal to the number of observations in a year, and

these intervals included the observed values of CPUNE.

In 1973 the difference in the scaled values of CPUSE

and CPU E was insignificant. It was therefore judged

acceptable to use CPUNE for the earlier period in

analyses of annual abundance. The final catch-rate series used in fitting the DSM consisted of annual CPU E's

for 1962-72 and, for 1973-87, of annual CPUSE's, scaled

by the ratio of average CPU E for 1971-92 to ~he

respective average CPUSE. Fishing effort for this catchrate data series is hereafter referenct'd in units of average hooks.

The error structure for delay-difference models involves two sources, the process error arising from the

modeling of biological processes with a population dynamics model, i.e. error associated with using approximates for (true) growth, recruitment, and survival functions, and measurement error which arises from the

independent estimates of catch rates (in this case the

CPUSE (t) and CPU E(t) data), against which the delay-difference model predictions are fitted during the

estimation of model parameters. The process and measurement errors were assumed to have log-normal distributions with parameters (0, (j2). Process errors were

included in the model as multipliers of annual recruitment. Measurement errors were the difference between

the log-transforms of the observed and predicted catch

rates. We should note that the predicted catch rate

follows the assumption of Hilborn and Walters (1992,

p. 345) and others that ex Jjl = 1 - e-qE.

Model fit was determined using the Microsoft Excel

(version 5.0a) solver and maximizing concentrated likelihood, CL = -(n/2) * In(SSE) - u, where n is the

number of observations of process and measurement

error, SSE is the sum of the squared process and measurement errors, and u is a constant. Parameters estimated were I, a, f3, q, and, in the open population

structure, R Prior to 1964 much of the EPO was not

fully exploited by longline fisheries, so it was assumed

that the biomass ofswordfish in the EPO was at carrying

capacity in 1962 and 1963, the first 2 yr used in fitting

the model, and B(t) for these years was set to the model

prediction of carrying capacity.

Results

Distribution

The average annual distribution of swordfish in the

EPO, as determined from relative density of CPUSE, is

shown in Figure 3. Principal zones of high abundance

are found from the coast of South America to 150oW,

400 '-- .....J.... ---l ----I

1500

c=J 12223 _

1 2 3 4 5

Figure 3

Annual average swordfish catch per unit of standardized effort (CPUSE) in the eastern Pacific Ocean, 1971-

li7. Area rankings are 1: CPUSE =0 and decile 1; 2: deciles

2-4; 3: decile 5; 4: deciles~; and 5: deciles 9-10.
Hinton & Deriso: Distribution and Stock Assessment of Swordfish in the Eastern Pacific Ocean 167

between about 100S and the southern extent of the

coverage of the longline fishery data; and from the

coast of North America to ISOoW along a zone of about

10° latitude bounded on the southern side by a line

running from 200N at the coast to about 28°N at ISOoW.

Other regions of high average annual abundance are

located near the coast of Central America, from about

8° I to 16°N; westward from the coast of South America

to about 900-9SoW between about 60S and 2°N; and in

a region of about 6° latitude along the Inter-Tropical

Convergence Zone between about 120° and 13SoW.

Underlying this picture of zonal distribution ofswordfish in the EPO are seasonal distributions that vary

significantly from the annual average. Average distribution during January-February (Fig. 4) is similar to the

average annual distribution just described, but differs

in several key respects. The southernmost zone of high

abundance was shifted westward by about SO_10° of

longitude. Relative abundance is intensified in the northern zone, that reaching from IS00W to the region nealBaja California, and there is a slight southerly extension in the extent of high abundance near the coast of

Mexico. There is also a broader and more intense distribution ofswordfish in the equatorial regions.

Swordfish clearly shift southward in both hemispheres

during March-April (Fig. S) as compared to JanuaryFebruary. The southern boundary of the northernmost

zone shifts from about 28° to 24°N at IS00W, and

becomes contiguous with the region of high abundance

off Baja California during this period. The northern

boundary of the southern zone shifts from about 80S to

12°S. In addition, the southern region of high abundance extends to the coast of South America at about

12°-14°S. There is a coincidental intensification and

widening of the distribution of high abundance in the

equatorial regions.

By May-June (Fig. 6), swordfish in the southern EPO

are concentrated in an area from the coasts of Peru and

northern Chile westward to about 900

-9SoW. Swordfish

are widely dispersed in the northern EPO. The equatorial zone of high concentration has shifts northwal-d

and is no longer clearly separated from the northernmost zone in waters west of about 1200W. The southern

boundary of the northernmost zone has shifted south40°

120° 90°

400 l.- -L... ....L --l

150°

CJ~~~_

1 2 3 4 5

90°

~­4 5

120°

CJ~

123

400 '-- ....L.. ---I --.I

150°

Figure 4

Average swordfish catch per unit ofstandardized effort

(CPUSE) in the eastern Pacific Ocean for JanuaryFebruary, 1971-87. Area rankings are 1: CPUSE = 0

and decile 1; 2: deciles 2-4; 3: decile 5; 4: deciles 6-8;

and 5: deciles 9-10.

Figure 5

Average swordfish catch per unit ofstandardized effort

(CPUSE) in the eastern Pacific Ocean for \1arch-April,

1971-87. Area rankings are 1: CPl'SE = 0 and decile 1;

2: deciles 2-4; 3: decile 5; 4: deciles 6-R; and 5: deciles

9-10.
168 NOAA Technical Report NMFS 142 _

40°1....- ....I- -.J'--__-----'

150° 120° 90 0

CJ~~~_

1 2 345

Figure 6

Average swordfish catch per unit ofstandardized effort

(CPUSE) in the eastern Pacific Ocean for May-June,

1971-87. Area rankings are 1: CPUSE = 0 and decile 1;

2: deciles 2-4; 3: decile 5; 4: deciles 6-8; and 5: deciles

9-10.

ward from about 28°N (in January-February) to about

l4°N. The region of high concentration off Baja California now extends southward to Costa Rican waters

(about 10° ), and about 10°_15° of longitude westward of the coast of the Americas.

During July-August (Fig. 7), high concentrations of

swordfish in the southern EPO extend from the coast to

about lloo-1l5°W, a westward shift of about 10° longitude in comparison to the May-June distribution. This

region of high concentration extends south to about

300 S in the region of 800-95°W. A narrow strip of high

abundance is found at about 16° -12°S from the coast

to about 145°W. There is also high abundance in the

equatorial region in an area bounded by the coast of

South America from about 4°S to 4°N and extending

westward to 85°-95°W. The contiguous zone of high

abundance along the coast of the Americas is again

reduced to core regions around Baja California and off

the Central American coast from about 10° (Costa

Rica) to 16°N (Guatemala). In the northern EPO the

distribution of swordfish is less cohesive than in earlier

months, and the southern boundary of the northern40°=-------:-:'-:-------.1...------1

150° 120°

CJ~~~_

1 2 3 4 5

Figure 7

Average swordfish catch per unit ofstandardized effort

(CPl'SE) in the eastern Pacific Ocean forJuly-August,

1971-87. Area rankings are 1: CPUSE = 0 and decile 1;

2: deciles 2-4; 3: decile 5; 4: deciles 6-8; and 5: deciles

9-10.

most zone has shifted northward to about 24°-26°N,

separating from a zone of high abundance at about 6°_

lOON from 130 0 -150 0 W.

By September-October (Fig. 8), the zone of high

abundance in the northwestern portion of the EPO has

fully dissipated. Zones of high abundance in the region

about Baja California, extending offshore about 5° of

longitude, and in the Guatemala-Costa Rica region

persist. There continue to be two zones of relatively

high abundance in the equatorial region, one in an

area bounded by the coast of South America from

about 4°S to 4°N extending westward and northward to

95°-100 0W and 6°N, and the other in the central to

western EPO, at about 1200 -145°W and 6°_16°N. The

dominant features in September-October are the northward shift of the southernmost zone of high abundance

from south of about 12°S and the development of a

contiguous region of high abundance lying south of

about 8°_100 S and stretching across the EPO from the

coast of South America to 150 0W.

During November-December (Fig. 9) there again

appears a region of higher abundance in the north-
Hinton & Deriso: Distribution and Stock Assessment of Swordfish in the Eastern Pacific Ocean 169

40° L..:-:-------L-------L---_--J

150° 120°

c:::=J (LZl _

1 2 3 4 5

Figure 8

Average swordfish catch per unit ofstandardized effon

(CPUSE) in the eastern Pacific Ocean for SeptemberOctober, 1971-87. Area ran kings are I: CPUSE = 0 and

decile I; 2: deciles 2-4; 3: decile 5; 4: deciles 6-8; and 5:

deciles 9-10.

westernmost portion of the EPO between about 135°

and 150 0W and 32° and 38°N. This area of high abundance is not contiguous with the region of high abundance about B~a California, as in January-February.

There are also southward shifts of about 2°_4° latitude

in the northernmost boundary of the high abundance

zone in the southern EPO (from about 8°_100 S to

about 100-12°S), and in the southern boundary of the

area of high abundance along the coast of Mexico near

Baja California.

Stock Status

The results of fitting the DSM model with net immigration/emigration (R) are shown in Fig. 10. A one-to-one

relationship between land R exists, which made it

necessary to bound solutions using the range of likely

values of natural survival rate, l, i.e. 0.62-0.81 (see prior

discussion). Over this range, values of CL ranged from

52.8 to 50.9; however there is no significant difference

between these values (X2=1, p=0.17), and a null hypoth400 '-- ...J.... --J'--__-----I

150°

c:::=J Itm _

1 234 5

Figure 9

Average swordfish catch per unit ofstandardized effon

(CPUSE) in the eastern Pacific Ocean for NovemberDecember, 1971-87. Area rankings are I: CPUSE = 0

and decile I; 2: deciles 2-4; 3: decile 5; 4: deciles 6-8;

and 5: deciles 9-10.

esis would not reject any of the solutions bounded by

these l. Within these bounds on l, the estimated values

of average maximum sustained yield (AMSY) and associated optimum effort (OE) ranged from 8,400 to 4,000

metric tons (t), and from 156 x 107 to 86 x 107 average

hooks, respectively.

At l = 0.62, the fit of the model with R was achieved

with significant contributions from both process and

measuremen t error (Fig. 11). This is con trasled by the

results at l = 0.81, in which the fit was achieved by

attributing almost all error to measurement. However,

the difference in the estimated trends in abundance, as

given by the series of the natural logarithms of predicted CPUE in these two fittings of the model, were

not significantly different (Hollander distribution-free

test for parallelism [Hollander, 1970]; n=26, p=0.23)].

In fitting the model without R, i.e. R = 0, CL decreased monotonically from 52.7 to 51.1 over the range

of lfrom 0.62 to 0.81, and as in the model that included

R, there was no significant difference between these

minimum and maximum values of CL (X2=1, p=0.21),

which fall within the range of values of CL obtained
170 NOAA Technical Report NMFS 142 _

15000

Ia: 10000

o

(f)

:.::

o

o

I

o

o

g 5000

o

+

\ +~

.-.

......., ==:== +~

.... ....

60.0

59.3 a

o

o

I

:J

LJj

:.::

:J

z 58.6 ....J

57.9

0.5 0.6 0.7

NATURAL SURVIVAL RATE

0.8 0.9

Figure 10

Results offitting a Deriso-Schnute delay-difference model with Beverton-Holt recruitment

and an immigration/emigration term (l/E, in metric tons, t) to catch rates of swordfish

from the eastern Pacific Ocean. Vertical lines mark natural survival rates of 0.62 and 0.8I.

OE = optimum effort (average hooks). AMSY = ayerage maximum sustained yield (t).

1.0,---------------------------,

-2.5 +-+---if-+-+--+-+-+---if-+-+-+-+-+---if-+-+-+-+-t-l-+-+-+-+-t-l-+-+--+-+-H

1964 1967 1970 1973 1976 1979 1982 1985 1988 1991

YEAR

with R"#- O. Thus a null hypothesis would

not reject any of the solutions bounded

by these l. Within these bounds on l,

the estimated values of AMSY and the

associated OE for the model without R

were 7,200-1,000 t, and 80 x 107 to 7 X

107 average hooks, respectively.

Model fits obtained using the CPUNE

data series for 1962-87 were somewhat

similar to those described above. In this

case, over the range of l from 0.62 to

0.81, for the model with R the estimated values of AMSY and associated

OE ranged from 6,900 to 5,600 t, and

from 113 X 107 to 86 X 107 average

hooks, respectively. For the model without R, the estimated values were 1,000-

200 t and 6 x 107 to 1 x 107 average

hooks, respectively.

These models and results were tested

by generating simulated data using various series of fishing effort, which provided wide ranges of catch and catch

rates (e.g. Ludwig and Walters, 1989),

and the parameter estimates obtained

...

,, "' M.E

••,., \ ...., -... 10- ~- • • •• ) " ........, J / ,. • \ / ' ." .. ,--"" \. ,., ··..0\-.· ""0'

f '\1 P.E. \ /.... J _J _, V

0.5

-2.0

Figure 11

Indices of abundance from the Deriso-Schnute delay-difference model

with natural survival rate of 0.62, fitted to 1962-87 abundances from

CPUSE for swordfish in the eastern Pacific Ocean, and measurement

(M.E.) and process (P.E.) error.

a:

o

a:

ffi 0.0 ....

o

o

z

-0.5

u

z

..

o

z

::::> -1.0

.."'

....

o

-1.5 u

i5
_______ Hinton & Deriso: Distribution and Stock Assessment of Swordfish in the Eastern Pacific Ocean 171

by fitting the model with the original data. These simulations gave maximum estimates of AMSY and OE of

7,000 t and 107 x 107 average hooks, and 1,000 t and

6 x 107 average hooks for the R * 0 and the R = 0

models, respectively. These values compare well with the

results obtained from the initial fitting and parameterestimation procedures.

Discussion

Distribution and Stock Structure

Information used by fisheries scientists to define the

boundaries of stocks of fish include data on relative

abundance, size and spawning condition of individual

fish, distribution oflarval fish, genetics, and movements

as determined from tagging. The boundaries determined from this basic research (Brown et aI., 1987)

may then be employed in studies that estimate the

status of a stock with respect to conservation and management objectives. Prior to proceeding, we must address the meaning of the term stock.

The least useful definition of stock, from a management or conservation point of view, is "the part of a fish

population which is under consideration from the point

ofview of actual or potential utilization" (Ricker, 1975).

For example, strictly interpreted this definition may

exclude portions of a population that contribute to

the presence and level of the stock, i.e. a stock may

consist only ofjuveniles whose existence derives from

the reproductive success of those surviving utilization,

but the survivors are not considered part of the stock.

The environment and fishing in any part of the range

of a fish population affect the subsequent abundance

and distribution of the species throughout its range,

giving this narrow definition little value within our current framework of knowledge in oceanography and

fisheries science. Application to management or conservation questions requires that a stock be a "selfsustaining component of a particular species" (Sinclair,

1988). So defined, a stock has biological and genetic

significance (Sinclair, 1988), which provides a basis for

measures (Brown et aI., 1987) commonly used to differentiate among stocks. However "in all cases some indications of significant degree of physical separation at

spawning is [sic] required to support biological bases

for separate stocks" (Brown et aI., 1987). To the extent

that relative abundance data accurately depict the spatial and temporal distribution of a stock, the stock is a

function of nature and not an abstraction (Sinclair,

1988).

Various stock structures have been proposed for

swordfish in the Pacific Ocean. Sakagawa and Bell

(1980), and more recently Bartoo and Coan (1989)

using data through 1980, employed annualized estimates of relative abundance based on CPUNE data to

estimate the distribution of swordfish stocks in the Pacific. Each included an EPO stock in their three-stock

hypotheses. The ability ofsuch annualized data to accurately reflect the spatial and temporal distribution of

stocks that may exhibit migratory behavior is doubtful.

Using CPUNE data with monthly resolution, SosaNishizaki (1990) and Sosa-Nishizaki and Shimizu (1991)

hypothesized a more complex stock structure. However

at the core of their determination were the independent seasonal trends in the extensions of local relative

abundance about centers of high abundance, with the

result that their definition of stock was in essence that

of Ricker (1975) noted above. Noting the need for

increased biological information, Sosa-Nishizaki (1990)

concluded

I think that these four different areas can represent different stocks, not in the complete biological sense, but as fishery management units. In other

words, the stocks thus agreed upon were in the

sense of defining a manageable resource not to

define the borderline ofmovements ofindividuals,

nor do stocks intend to be referred to [as] isolated

genetic units, as was stated for the management of

Atlantic swordfish populations (Miyake and Rey,

1989) .

Although this four-stock hypothesis may prove of

questionable value in defining and achieving management or conservation objectives, such initial hypotheses may provide a sound basis for further research

(Brown et aI., 1987). This hypothesis includes two stocks

centered in the EPO, one centered off B~a California,

and another centered off the west coast of South

America; we will examine this hypothesis as if these

were proposed as self-sustaining stocks.

Sosa-Nishizaki (1990) and Sosa-Nishizaki and Shimizu

(1991) reported seasonal variation in the extent of

distribution of the swordfish stocks about the centers of

distribution, but with one exception, that of contiguous

northern and southern EPO distributions of swordfish

during the boreal autumn and winter, they noted that

the distributions "always seemed to be separated." However, there remained some question concerning these

hypotheses, as Sosa-Nishizaki (1990) cautioned that misleading conclusions might be reached as a result of his

estimation of relative abundance using the CPUNE statistics, and that catch and effort data analyzed on spatial scales with higher degrees of resolution might lead

to alternate hypotheses or conclusions. In their analyses, Sosa-Nishizaki (1990) and Sosa-Nishizaki and

Shimizu (1991) used three ranges of average monthly

CPUNE measured within 5° latitude by 5° longitude
172 NOAA Technical Report NMFS 142

areas. Our use of standardized rather than nominal

statistics and a higher degree of spatial resolution (2°

latitude by 5° longitude) are responsible for the differences between our results and those of Sosa- ishizaki

(1990) and Sosa-Nishizaki and Shimizu (1991).

The stock of swordfish in the northern EPa was

essentially separated through the entire year from the

stock in the southern EPa: the zones of relatively low

abundance seen in Figure 3 shift latitudinally, but are

generally maintained throughout the year. This is in

contrast to Sosa-Nishizaki and Shimizu's (1991) ob5ervation of a continuous distribution of swordfish from

the northern to southern EPa during the boreal fall

and winter months (their Figures 4-1 Oanuary] and 4-6

[November-December]) .

We found that the Baja California stock of SosaNishizaki (1990) andSosa-NishizakiandShimizu (1991)

was not isolated from other stocks in the Pacific, specifically the northwestern-central Pacific stock of these

authors, of Sakagawa and Bell (1980), and of Bartoo

and Coan (1989). Our results (Fig. 4, 5) suggest that

the distribution ofthe northwestern-central Pacific stock

becomes contiguous with Sosa-Nishizaki and Shimizu's

(1991) Baja California stock during January-February

and March-April each year. As well, the fact that

throughout the year the equatorial zone of high abundance (discussed below) extends to the westernmost

geographical limits of this study (1500

W) indicates that

there may be significantly more contact between these

two stocks than we have noted here. These results do

not confirm that the Baja California and northwesterncentral Pacific stocks do not exist as separate reproductive units, only that there exist areas and times during

the year in which the stocks may mingle. This is critical

because "as long as fish from different breeding areas

mingle during a portion of the fishery they have to be

managed as a unit" (Brown et aI., 1987).

Previous studies of the reproductive condition of

swordfish have not indicated the presence of individuals in spawning condition in the Baja California regIon

(Ramon and Castro-Longoria6). Shingu et al. (1974)

found that high values of gonad indices were fOlnd

only in high-seas areas, indicating that "spawning is

limited to the more offshore waters." Larval surveys

(Nishikawa et aI., 1985) near Baja California have been

limited, with observations recorded for only the January-March period at only two locations in the reg:on

from 10° to 200N and from the coast of Mexico to

1200W, and neither location was in the immediate vi6 Ramon, D., and R. Castro-Longoria. 1994. Sex composition and

maturity of swordfish, Xiphias gladius, caught in the drift gill net

fisheries of the U.S. and Mexico. Paper presented at Symposium

on Pacific swordfish, Ensenada, Mexico, December 1994. Available from D. Ramon, NMFS Southwest Fisheries Science Center,

8604 La Jolla Shores Dr., LaJolla, CA 92037-1508.

cinity of Baja California. Samples collected at these

locations did not include larval swordfish. It has been

demonstrated (Hinton et aI., 1997) that in general the

methods that have been used to estimate the reproductive condition of female swordfish are likely not to

identity reproductively active individuals. Our analyses,

employing the new method of Hinton et al. (1997),

indicated that swordfish were reproductively active in

the vicinity of Baja California during May-August.

Our results (Fig. 4, 7-9) and, though not described

therein, those of Sosa-Nishizaki and Shimizu (1991)

indicate an apparently isolated center of relatively high

abundance off the coast ofCentral America from about

10° to 16°N. Our analyses indicate that the distribution

centered off Baja California extends southward along

the coast of North and Central America during the

boreal spring and early summer (Fig. 5, 6), and becomes contiguous with this more southerly region of

higher abundance. This connection was not evident in

Sosa-Nishizaki and Shimizu (1991).

Sosa-Nishizaki (1990) and Sosa-Nishizaki and Shimizu

(1991) found an equatorial zone of high abundance in

the EPa from October through January. Their studies

indicated that in most other months this distribution

consisted of two high-abundance areas, one between

South America and about 1000W, and the other between about 115° and 1500W. Sosa- ishizaki and

Shimizu (1991) noted their inability to resolve an equatorial zone of high abundance and more northerly or

southerly areas of high abundance. We found a clear

and persistent zone of relatively high abundance of

swordfish throughout the year in the equatorial region

extending to 1500W. The zone showed north-south

seasonal movement, and was generally located between

about 4°S and lOON. This equatorial region of high

abundance was consistently separated from more southerly cen ters of high abundance by the previously-noted

zone of low abundance. Further, there appears to be

clear separation of the high-abundance zone in the

southern EPa from waters west of 1500

W during much

of the year, and therefore from the swordfish stock

centered in the southwestern Pacific (Sosa-Nishizaki,

1990; Sosa-Nishizaki and Shimizu, 1991). Thus, our

findings provide support for the hypothesis of a separate swordfish stock with distribution centered in the

southern EPa.

Integrity of the equatorial zone was not maintained

with respect to stocks found in the northern EPa. SosaNishizaki (1990) noted that the Baja California stock

appeared to be contiguous with the equatorial region

of high abundance between about 120° and 1400W

during November-December. Figures 4 and 9 suggest

that during November-February the region of high

abundance around Baja California is contiguous with

the equatorial-centered region of high abundance be-
_______ Hinton & Deriso: Distribution and Stock Assessment of Swordfish in the Eastern Pacific Ocean 173

tween about 115° and 1300 W. This connection did not

extend into March-April.

In addition to relative abundance data, information

from tagging experiments may be used in defining

stock boundaries. Previous tag recovery information

from the Atlantic has indicated that swordfish may undertake extensive migrations, which may be regular

and include migrations between spawning and feeding

areas (Carey and Robison, 1981). Billfish tagging efforts in the Pacific have, until recently, been primarily

those of recreational fishermen through the ational

Marine Fisheries Service Cooperative Marine Game Fish

Tagging Program. These efforts did not result in significant placement of tags on swordfish, but more recently

commercial fishermen operating longline gear in the

central Pacific have begun placing tags on small swordfish (Holts7).

There have been insufficient tag returns to adequately

describe movements ofswordfish in the Pacific, but our

finding that the northwestern-central Pacific stock and

the Baja California stock mingle is supported by the

recent recovery of a swordfish tagged on 1 May 1993

northeast of the Hawaiian Islands at 28°20'N, 149°08'W

and recovered offSan Clemente Island, California, USA,

at 32°03'N, 118°29'W on 1January 1995 (Holts8 ). If one

assumes that the location of tagging was central to the

travel of this individual, then its ambit could easily have

included positions at least as far west as 1700W, and

certainly as far north as 40° and as far south as the

equator. Further, this recovery had locations and timing of tag placement and recovery which were consisten~ with seasonal movement of swordfish from the

northwestern Pacific to Baja California, as discussed

below.

Length-frequency data (Miyabe and Bayliff, 1987;

Nakano and Bayliff, 1992) also support our hypothesis

of mingling of swordfish stocks in the northern EPO.

From October to December about 95% offish sampled

from the EPa region north of 20 0 N and west of 120 0 W

were less than 145 cm in length. The range oflengths of

individuals in this region duringJanuary-June was about

80-240 em, with 30% or more of individuals greater

than about 180 em. Kume andJoseph (1969) estimated

the average annual growth in the EPO of swordfish

between 62 and 165 cm at about 38 em per yr, or less

than 10 em per quarter. Thus, growth would not be a

reasonable explanation for the observed increase in numbers of larger fish, and individuals must have migrated

into the region during the first quarter of the year.

7 Holts, D. B. 1994. 1994 billfish newsletter. U.S. Dep. Commer.,

NOAA, Nat!. Mar. Fish. Serv., SW Fish. Sci. Cent., 9 p. Available

from SWFSC, NMFS, P.O. Box 271, LaJolla, CA 92038.

8 Holts, D. B. 1995. 1995 billfish newsletter. U.S. Dep. Commer.,

NOAA, Nat!. Mar. Fish. Serv., SW Fish. Sci. Cent., 12 p. Available

from SWFSC, NMFS, P.O. Box 271, LaJolla, CA 92038.

There were four regions from which larger individuals might migrate into this northern and westerly region of the EPO: 1) more westerly regions of the northern Pacific, 2) the Baja California region, 3) the equatorial zone of high abundance, and 4) waters beyond the

northern extent of these fisheries. There is insufficient

information available to evaluate the presence, abundance, or status of swordfish north of regions in the

EPO in which these fisheries occur; however, the lack

of significant fisheries for swordfish in those waters

suggests that their presence has been found to be minimal. The length data presented by Sosa-Nishizaki (1990)

were not summarized in a manner that identified lengths

of individuals from waters west of 1500W by area and

time so that comparisons to information from the EPO

might be made. Thus, of these four regions, samples of

lengths ofswordfish (Miyabe and Bayliff, 1987; Nakano

and Bayliff, 1992) were available to us only from regions 2 and 3, and only in region 2 were larger fish

present during the period preceding the first quarter

of the year, when they appeared in the northwestern

EPO.

In the Baja California region, catches of swordfish

ranged in length from about 80 to 250 cm during

October-December and from about 100 to 200 em

during January-March (Miyabe and Bayliff, 1987;

Nakano and Bayliff, 1992). The high abundance of fish

less than 180 cm in length in the Baja California region

during the first quarter suggests that any movement of

larger fish from the region was independent of the

available food supply. A movement of larger fish westerly or to the south during this period, as previously

discussed, would be consistent with movement to a

region suitable for spawning (Matsumoto and Kazama,

1974; Nishikawa and Ueyanagi, 1974), as the 23,SOC

sea-surface temperature isotherm extends from about

28°N at 1500W to 20° at 145°W, thence easterly to

about 121°W, whence it runs northeasterly to intersect

the Baja California peninsula at about 26°N, 113°W

during ovember-December; and duringJanuary-February it runs from about 22°N at 1500W to 17°N at

145°W, thence easterly to about 135°W, whence it runs

northeasterly to intersect the mainland of Mexico at

about 23°N, 108°W (Robinson and Bauer, 1976).

In an effort to determine how far south larger individuals might have gone following emigration from the Baja

California region, we re-examined the data on lengths of

swordfish summarized by Miyabe and Bayliff (1987) and

Nakano and Bayliff (1992) to determine the distribution

of the measurements by time and area. These length data

were collected by port samplers in Japan and by crew

members of training and research vessels, but the positions of capture are known only for data from swordfish

sampled by the vessel crews. The data obtained by port

samplers can generally be located to 5° (or 10°) latitude
174 NOAA Technical Report NMFS 142

by 10° (or 20°) longitude. We found that the number of

samples by area was such that we could not with certainty

determine distributions of length frequencies within a

zone extending across the EPO from 10° to 20 0N on a

bimonthly basis. However, data (Kume andJoseph, 1969;

Miyabe and Bayliff, 1987; Nakano and Bayliff, 1992) indicate that few, if any, ofthese larger individuals move south

of lOoN during the first quarter. This is not surprising,

given the fact that they would encounter regions suitable

for spawning well to the north.

Following the January-March period, the range of

swordfish lengths in the Baja California region increased

from 110-200 em to include lengths less than 80 em

and up to about 260 em (Miyabe and Bayliff, 1987);

however the relative abundance of larger individuals

was significantly less than during October-December.

Again, although estimated growth rates are insufficient

to explain the renewed presence of large individuals,

recruitment from local reproduction or migration would

explain the renewed presence of smaller fish in the region. The question is, from whence do these individuals

come when they enter the Baja California region?

It seems likely that the larger fish were entering or

returning to the Baja California region from more westerly regions of the EPO. The smaller fish, those less

than 110 em, may be progeny of reproductive efforts in

the vicinity of Baja California, or they may have entered

the EPO as part of the apparent migration of individuals from the more westerly portions of the North Pacific, even tually reaching the waters off Baja California.

They also may have moved north from the more southerly equatorial region of high abundance. The equatorial region of the EPO is known to be a region of high

productivity throughout the year (Chavez and Barber,

1987), and on the basis of the high frequency ofsmaller

swordfish in length-frequency distributions for the region, Kume andJoseph (1969) identified it as a region

offeeding and growth for immature swordfish. Considering that smaller fish leaving this area for waters off

Baja California would, in essence, be investing energy

to move from one highly-productive region to another,

it seems more plausible that the influx ofsmaller fist to

the region of Baja California during the second quarter

of the year may be traced either to local reproduction,

or to the western North Pacific, as discussed below.

A zone of high abundance lying north of 200

N and

west of 1200W first appeared early in the NovemberApril period north of about 32° at 135°-1500

W (Fig.

9). Monthly catch-rate data (Sosa-Nishizaki, 1990) show

that a zone of high abundance spreads across the entire

. orth Pacific, from Japan to the EPO, during this period. In the EPO, this zone of high abundance expanded eastward and southward, until in January-February it extended from 150° to 1200

W and south to

about 26°N. At this point it was nearly contiguous with

the zone of high abundance about Baja California, and

by the end of March-April a single zone of high abundance extended northward ofa line from about 24°N at

150 0W to about 18°N at the coast of Mexico (Fig. 5). By

May-June the continuity of these two zones was breaking down and the southern boundary of the northwestern center of high abundance had shifted south to

about 14° to 18°N between 150° and 135°W, respectively (Fig. 6). During the subsequentJuly-August period, regions of relatively high swordfish abundance

were found widely scattered within the area north of

200N and west of 1200W (Fig. 7). If the tagged fish

previously noted was in fact undertaking an annual

migration from the central North Pacific to the EPO,

then the information obtained from this individual supports migration as inferred from these data.

Squire and Au (1990) found that the "high-catch-rate

areas off Mexico are areas of at least temporary accumulation or aggregation" of striped marlin, Tetrapturu5

audax, into a region of high productivity and food

supply (Hanamoto, 1974) and that the "movements of

larger fish may be related to maturity and, thus, to

spawning seasons and spawning areas." Our findings

suggest that the region of high abundance ofswordfish

in the vicinity of Baja California may be both the center

of a stock's distribution and a feeding and growth region, as is the case for striped marlin.

Studies of the distribution of values of swordfish gonad indices in the eastern Pacific have been made by

Kume and Joseph (1969), Shingu et al. (1974), Miyabe

and Bayliff (1987), Sosa-Nishizaki (1990), Sosa-Nishizaki

and Shimizu (1991), and akano and Bayliff (1992).

Such studies have not indicated a clear separation of

areas with high indices in the northern and southern

hemispheres (Sosa-Nishizaki and Shimizu, 1991). The

results from these studies and our analyses of GI data,

when examined with respect to the -relative abundance

estimates described herein, show that spawning activity

is closely associated with high-abundance zones in the

four regions of the EPO in which mature females in

spawning condition have been found, i.e. the Baja California, northwestern (north of about 200 N and west of

about 1200W), equatorial, and southern regions of high

abundance we have described.

Kume and Joseph (1969) presented quarterly gonad

index data at a resolution of 1° latitude and 1° longitude. The regions of high average values that they identified fall clearly in either the equatorial or southern

zones of high abundance. The other earlier studies

presented data at a resolution of 5° latitude and 5°

longitude, making comparisons difficult and necessitating reanalysis of the GI data. Our re-examination of the

data indicated that regions of the EPO with individuals

in spawning condition were clearly separated throughout the year. Of the 105 combinations of 2° latitude by
_______ Hinton & Deriso: Distribution and Stock Assessment of Swordfish in the Eastern Pacific Ocean 175

5° longitude area and bimonthly period in which individuals with Gl ~I.375 were found, 6 were within and 1

was adjacent to either the Baja California or the northeastern zone of high abundance, 51 were within the

bounds of the equatorial or southern zones of high

abundance, and 26 were in areas immediately adjacent

to one of these latter two zones. This indication of

physical separation at spawning supports the hypothesis (Sosa-Nishizaki, 1990; Sosa-Nishizaki and Shimizu,

1991) of a separate swordfish stock in the southern

EPO, and is consonant with our previously-noted finding, founded on CPUSE, that the southern stock is

isolated from other stocks of the EPO.

Data on the distribution of genotypes of nuclear or

mitochondrial DNA in a population may provide measures of the degree to which, over periods spanning

many generations, stocks have been separated during

spawning, and therefore may be useful to investigations

of stock structure (Ferris and Berg, 1987). For various

reasons (see Avise et aI., 1987), mitochondrial DNA

(mtDNA) is frequently used to investigate the structure

of populations (e.g. Graves and McDowell, 1994). Significant differences in the distribution of mtDNA genotypes among stocks would provide positive evidence of

previous reproductive isolation and stock structure, but

homogeneous distributions of genotypes across hypothesized stocks does not indicate the absence of stock

structure. This is because only a few individuals per

generation (on the order of tens, regardless of population size) need reproduce with members of other stocks

to prevent genetic drift and maintain homogeneity of

mtDNAin the population (Allendorf and Phelps, 1981;

Slatkin, 1987). These numbers of individuals are trivial

in comparison to the large number of individuals with

homogeneous vital rate parameters and a high degree

ofreproductive isolation which underlies the stock structure of a population (Graves9). Further, mtDNA inheritance is not linked to inheritance of nuclear DNA, and

there may be differences in population structure as inferred using mtDNA and nuclear DNA (Harrison, 1989).

Studies of mtDNA from swordfish in the Atlantic

Ocean and the Mediterranean Sea (Magoulas et a\.,

1993) indicate that distinct stocks exist in these oceans,

and the genotypes found in these stocks are different

from those found in swordfish in the Pacific Ocean

(ChowlO). Grijalva-Chon et a\. (1994) failed to reject

the null hypothesis that there was a single stock of

swordfish in the North Pacific, and stated that "there is

sufficient gene flow across the North Pacific to prevent

genetic [mtDNA] differentiation," but it is important

9 Graves,]. E. 1995. Virginia Institute of Marine Science, College of

William and Mary, Gloucester Point, VA. Personal commun.

10 Chow, S. 1995. National Research Institute of Far Seas Fisheries, Shimizu,Japan. Personal commun.

to remember that, as discussed above, this does not

demonstrate that stocks do not exist in the north Pacific, only that there is mingling among any stocks.

Given the amount of genetic variation reported by

Grijalva-Chon et al. (1994), and even greater variation

noted in more recent studies (by Alvarado-Bremer and

Ely, Rosel and Block, and Chow), samples ofswordfish

from geographic locations have been far too small to

estimate distributions of genotypes with any degree of

precision (Gravesl ]). Consequently, it would be premature to make a definitive statement regarding the genetic basis of swordfish stock structure in the North

Pacific, although it is likely that significant differences

in genotypic distribution will be seen among geographically distan t locations when adequate samples have been

obtained (Gravesll).

The information and analyses presented to this point

support the hypothesis (Sosa- ishizaki, 1990; SosaNishizaki and Shimizu, 1991) ofa swordfish stock with

its center of distribution in the southeastern Pacific

Ocean, and they do not reject the hypothesis (SosaNishizaki, 1990; Sosa-Nishizaki and Shimizu, 1991) of a

swordfish stock cen tered in the northeastern Pacific

Ocean in the vicinity of Baja California. They suggest

that the waters near Baja California may be a feeding

and growth region for swordfish stocks that spawn elsewhere and are distributed more broadly in the North

Pacific Ocean, and that swordfish are reproductively

active in the region. The failure of Grijalva-Chon et al.

(1994) to identify the presence of stock structure in

swordfish in the North Pacific is not surprising in light

of the small number of individuals required to maintain genetic homogeneity, and their failure to reject a

null hypothesis should not form the basis for restricting

or terminating basic research into the stock structure of

North Pacific swordfish. In fact, their findings, taken in

conjunction wi th those of Sosa-Nishizaki (1990), SosaNishizaki and Shimizu (1991), and this study indicate

that further basic research is required. As part of this

research, investigation of the geographical limits of the

distributions of swordfish stocks in the EPO should be

conducted over a region extending to the west of the

150 0W limit of this study.

Stock Status

Sakagawa and Bell (1980) and Bartoo and Coan (1989),

among others, have examined the status of swordfish

stocks in the Pacific. Sakagawa and Bell (1980) did not

estimate AMSY for the stocks of their three-stock hy11 Graves,]. 1996. Virginia Institute of Marine Science, The College of William and Mary, Gloucester Point, VA. Personal

commun.
176 NOAA Technical Report NMFS 142 _

pothesis, but using production-model analyses they estimated that under a single-stock hypothesis the annual

AMSY for swordfish stocks in the Pacific was about

20,000 t. While cautioning that fisheries should be monitored for changes in technology and fishing practices

that might result in catches exceeding AMSY, they concluded that stocks ofswordfish were "capable ofsustaining increased yields with increased effort." Bartoo and

Coan (1989) did not estimate AMSY values, but examining catch-rate trends for swordfish in the entire Pacific (the single-stock hypothesis) and within the three

regions identified by relatively high average annual

catch rates (the three-stock hypothesis), they concluded

that there was no indication "that the stock(s) have

been exploited heavily enough to cause a noticeable

decline in CPUE through 1980." Sosa-Nishizaki (19£0)

and Sosa-Nishizaki and Shimizu (1991) did not determine the status of specific stocks because data were

unavailable, but referencing the findings of Sakagawa

and Bell (1980) and Bartoo and Coan (1989), and

following a review of FAO catch statistics, they concluded "that the general situation in the Pacific swordfish resources [is] stable." These analyses of the status

ofswordfish stocks have at their core either an ill-fitting

production model (Squire, 1981) or simple examirations of trends in catches and catch rates.

Analyses of stock status may be designed to provide

information not only on the estimates of AMSY and OE

commonly sought by fisheries managers, but also to provide some measure of the acceptability of the underlying

stock structure hypotheses. The value ofsuch a design has

been discussed (see Brown et al., 1987), and studies along

these lines were recommended (Sakagawa and Bell, 1980)

for swordfish stocks in the Pacific. Our analyses are the

first to our knowledge which were specifically structured

to differentiate between the likelihoods of various stockstructure hypotheses for swordfish in the EPO.

The results offitting the Deriso-Schnute delay-difference model with recruitment represented as (Modell)

a function of adult biomass (the Beverton-Holt component) and (Model 2) as a function of both adult biomass and a linear term expressing net migration were not

significantly different based on observed values of CL.

Model 1 represented a system closed to significant

transboundary migration, and Model 2 represented a

system open to migration. Thus, these results did not

distinguish between the hypotheses that (a) there exists

a single stock ofswordfish with its distribution centered

in the EPO and approximately bounded by the American continents and 1500

W (e.g. a geographically-discrete southern or northern stock, or a stock with a

distribution spanning the EPO) and (b) there exists a

single stock ofswordfish as in (a) but the EPO region is

also frequented by swordfish stocks with distributions

extending well beyond 150oW.

Ideally an estimate of stock status could be made for

each hypothesized stock, and results could be compared to aid in determinations of stock structure. In

this case that approach was not possible for swordfish

stocks in the EPO for several reasons. Historical reporting of total swordfish catch has been on the basis of

large statistical reporting areas which are unrelated to

boundaries of hypothesized stocks. A positive note is

that it was recently agreed among regional fisheries

agencies that are responsible for obtaining and maintaining data for high-seas fisheries that catch and effort data

should be made available on a stock basis, and at finer

resolutions if possible (Anonymous, 1994). Estimates of

population parameters may be used to identify stocks

(Skillman, 1989); however there are few estimates of rates

ofgrowth, recruitment, and mortality ofswordfish (Boggs,

1989) and those estimates from the Pacific were obtained

without reference to hypothesized stock structure. Thus,

these estimates were employed to bound plausible model

solutions (natural mortality) or were assumed to be homogeneous (fishing mortality, growth, and recruitmen~

model parameters) within stocks in the EPO.

The estimate of AMSY for swordfish in the EPO from

all plausible solutions was less than about 8,400 t, and

the optimum effort was 156 x 107 average hooks or less.

In comparison, during 1980-85 swordfish catch in the

EPO averaged about 6,300 t. In 1987 the catch reached

about 9,200 t, exceeding the maximum estimate ofAMSY

by about 10%, but the effort required to make this catch

was only about 41 x 107 average hooks. This indicates that

catch rates at that time were higher than they would be

once the biomass of the population was reduced to that

expected at AMSY. Due to the lack of a direct estimate of

the abundance ofswordfish in the EPO, as well as the lack

of biological data necessary to examine estimates and

variability of population parameters such as changes in

age-specific reproductive capacity, it was not possible to

identify whether swordfish in the EPO have high abundance but low productivity, or whether they are relatively

low in abundance and high in productivity.

Since 1987 the catch of swordfish in the EPO has

steadily increased, reaching about 18,000 tin 1992 and

1993. the last years for which relatively complete catch

data are currently available. Estimates of AMSY and OE

obtained by us should be used with caution, because

the history of declining catch rates along with increasing fishing effort in the EPO provides us with the most

tenuous of data series (Hilborn and Walters, 1992) with

which to model the dynamics of the swordfish population. Preliminary examination of more recent catch

and effort data from the Japanese longline fishery

(UosakiI 2) indicate that catch rates have continued to

12 Uosaki. K. 1995. National Research Laboratory of Far Seas Fisheries, Shimizu.Japan. Personal commun.
Hinton & Deriso: Distribution and Stock Assessment of Swordfish in the Eastern Pacific Ocean 177

decline, though they still exceed those to be expected

at AMSY, and that AMSY and OE may be slightly higher

than the estimates we obtained herein. As the more

recent data are finalized, they should be incorporated

into analyses of the status ofswordfish stocks in the EPO.

Until such analyses are completed, it is not possible to

estimate the current level ofswordfish stocks in the EPO

with respect to the level to be expected at AMSY.

Acknowledgments _

We thank the Japanese government and the scientists

of the National Research Institute of Far Seas Fisheries

(NRIFSF), Shimizu,Japan, for fisheries data made available to the Inter-American Tropical Tuna Commission.

We thank Warren White for hydrographic data. William H. Bayliff provided a most helpful review and comments. I (Hinton) thank the members of my doctoral

committee at Scripps Institution of Oceanography: Richard H. Rosenblatt, Paul E. Smith, Richard B. Deriso,

David M. Checkley, Dean H. Roemmich, and Richard

T. Carson; and Hideki Takano of the NRIFSF.

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Standardizing Swordfish, Xiphias gladius, Longline Catch

per Unit of Effort Using General Additive Models

PIERRE KLEIBER and NORMAN BARTOO

Southwest Fisheries Science Center

National Marine Fisheries Service, NOAA

PO. Box 271

LaJolla, California 92038-0271

ABSTRACT

Catch per unit of effort in the Japanese longline fishery for swordfish in the Pacific

Ocean was analyzed using General Additive Models (GAM's). Twenty years of catch and

effort data were standardized using various GAM's which incorporated variables of time,

proportion ofswordfish in the catch, and month of catch. Separate analyses were conducted

for various areas.

A modeling exercise was conducted to discover whether it is effective to use the

proportion of swordfish in the catch as a proxy for targeting of swordfish by the fishery.

Results showed that under some systematic trends in abundance of either swordfish or

bycatch species, real catch-per-unit-effort trajectories for swordfish were mis-estimated;

without independent external data, this method of analysis applied to this data set has a

high risk of misin terpretation.

Introduction _

The Japanese longline fishery for swordfish in the Pacific Ocean has the broadest combination ofspatial and

time coverage of all the fisheries catching swordfish.

Swordfish in the Japanese longline catch is and has

been both a target species and a valuable incidental

catch. The Japanese longline catch-and-effort data series is considered to be the most complete single data

set covering the range of tunas and billfish in the Pacific and as such has been used to draw inferences on

tuna and swordfish stocks (Bartoo and Coan, 1989).

An important feature of the Japanese longline fleet

operations is that the target species varies and with it

the fishing strategy, such as time of day, time of year,

geographic location, depth of set, type of bait, and use

of ligh tsticks. Such factors are highly likely to affect the

power of the gear to attract and capture swordfish.

However, not all of these factors are reported in the

data set. This paper examines the use of proportion of

swordfish and other species in the catch as an indicator

of targeting, as an approach to standardizing catch per

unit of effort (CPUE).

Data Selection _

The data used were catch, in number offish, and effort,

in number of hooks, as reported by the Fisheries Agency

ofJapan (1963-82) for the fishing years 1960-80. The

data were summed by 5° x 5° square by month, yielding

approximately 60,000 records. Two spatial stratifications of the data were used: a Pacific-wide examination

including all areas of catch, and four regions selected

because they had fisheries targeting swordfish and were

relatively high-catch areas (Bartoo and Coan, 1989;

Fig. 1).

CPUE Standardization

The reason for standardizing CPUE is to remove from

the data any variation due to effects other than fish

abundance. This is usually accomplished by some sort

of multivariate statistical technique with CPUE as a

dependent variate explained by a suite of independent

variates, including time (e.g. Punsly and Deriso, 1991).

To the extent that the independent variates other than

181
182 NOAA Technical Report NMFS 142

time account for all variation in CPUE due to things

other than variation in abundance and random noise, the

time effect estimates the u'ajectory of abundance in time.

In our analysis we used a general additive model

(GAM) technique (Chambers and Hastie, 1992). This

technique allows numerical independent variables to

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_________ Kleiber & Bartoo: Standardizing Catch per Unit of Effort Using General Additive Models 183

have nonlinear effects on the dependent variable as determined by a

smoothing algorithm (Cleveland,

1979). Therefore the effect of an independent variable is not tied to a particular mathematical function but instead is constrained only by the smoothing algorithm.

Our simplest model, in which we entered time as a non-linear variable, is

given by

Table I

Deviance (%) in swordfish CPUE in different areas explained by the

models. All tests were significant at P<O.OOOOOI.

Deviance explained

Test orthwest North-cen tral East Southwest Total

Modell add lo(t) 2 12 6 4 0.3

Model 2 add lot?) 66 91 82 84 80

Model 3 add factor(M) 72 93 83 88 81

where P is the arcsine transform of the proportion of

swordfish in the catch.

To investigate seasonal variability within years, we

used a third model given by

where factor(M) is the month entered as a categorical

(factor) variable. To enter M as a continuous, numerical variable, we would like it to be a circular variable

(i.e. withJanuary and December adjacent to each other

in the same way as all other pairs of adjacent months).

However, we could not find a way to do that with the

software we had to work with.

We did not progress to further models with additional independent variables, such as environmental

variables, because specific, set-by-set data other than

catch were not available. Broader-scale indices could

have been used, such as average temperature or the

southern oscillation index, but there is a danger that

such variables affect swordfish abundance rather than

where £ is a small value (0.1) to handle the case where

there is zero catch, and lo(t) is a local regression (LOESS;

Chambers and Hastie, 1992) smoothing function of

time given as the year and decimal fraction thereof (e.g.

85.5 for 1July 1985). In this and other cases the LOESS

functions were of degree 1 and span parameter 0.5.

Because the data do not contain direct information

on species targeted, we used a proxy variable consisting

of the arcsine transform of the swordfish catch as a

proportion of the total catch of tunas and swordfish.

The arcsine transform of a variate is the inverse sine of

the square root of the variate. It is applied to proportions to spread out the values approaching zero and

one, that is, values near the ends of the range of values

that a proportion can take (Sokal and Rohlf, 1969).

Our second model is given by

Modell:

Model 2:

Model 3:

10g(CPUE + £) = a + lo(t)

10g(CPUE + £) = a + lo(t) + 10(P)

10g(CPUE + £) = a + lo(t)

+ 10(P) + factor(M)

catchability. They would therefore obscure rather than

reveal the abundance signal that we wished to elucidate

from the CPUE data.

Standardization Results _

We first tried to detect a Pacific-wide abundance trend.

Because the whole data set was too large for the software to accommodate in a single analysis, we chose a

random subsample of approximately 10% ofthe records.

Using Modell, which had time as the only independent variate, a gentle, approximately 15-yr cycle was

evident (Fig. 2A). The model explained only a small

percent of the raw deviance, yet its statistical effect was

still significant (Table 1). With Model 2, which added

the proxy targeting variable, the temporal effect was

smoothed into a steady decline from 1960 to 1980

(Figure 2B). The targeting variable P had a positive

effect which leveled off at high values of P (Figure 2C).

Thus, as would be expected, CPUE tends to increase

with increasing proportion of swordfish in the catch.

Repeated subsamplings did not change these results

materially.

To allow for the possibility that swordfish abundance

in the different regions would vary independently, we

conducted separate analyses of 4 regions within the

Pacific (Fig. 1). A large number (65%) of the longline

records from the tropical regions, where swordfish is

not targeted but is retained, were eliminated (Bartoo

and Coan, 1989). In this case the software was able to

handle all the data in each region. Using Modell,

different patterns of temporal variation were indeed

apparent (Fig. 3): an overall declining trend in the

northwest and north-central Pacific, a rising trend in

the southwest Pacific, and a rise followed by a fall in the

northeast Pacific. Under Model 2, the addition of our

proxy variable for targeting changed the picture somewhat (Fig. 4). The temporal effect was flattened and the

span (maximum - minimum) was reduced, particularly

in the north-central and the southwest regions. Model 2

showed a more or less decreasing time trend in all
184 NOAA Technical Report NMFS 142

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60 65 70

Year

75 80

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Model 2

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ex>

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Year

75 80

--- ------------- --- ;?r-----------------------------------------

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------------------- ex>

OL-~-----------~----------~-----------~--.-J 0.0 0.5 1.0 1.5

asin(sqrt(Prop))

Figure 2

Results from GAM analysis of a random subsample of swordfish CPUE data from the Japanese

longline fleet, 1960-80. (A) year effect with Modell; (B) year effect with Model 2; (C) effect of

proxy targeting variable with Model 2. Dash~d lines indicate ± 2 standard errors.

regions from 1960 to 1980, the trend in the southwest

region being the reverse of that shown in Model 1.

The functional effect of the proxy targeting variable

Pwas monotone increasing in all regions except in the
__________ Kleiber & Bartoo: Standardizing Catch per Unit of Effort Using General Additive Models 185

North-Central

70 75 80 60 65

Year

North-West

60 65

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East

60 65 70

Year

75 80 65 70 75

Year

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Figure 3

Year effects in four regions analyzed independently under Model 1. Dashed

lines indicate ± 2 standard errors.

North-Central

60

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Year

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South-West

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Figure 4

Year effects in four regions analyzed independently under Model 2. Dashed

lines indicate ± 2 standard errors.

northwest, which showed a downward trend for high

values of P (Fig. 5). In all cases the targeting effect was

more pronounced over the range examined than the

effect of time over 20 yr.

When residuals were plotted around the time function for Modell in the northwest region (Fig. 6), it was

obvious that very little of the deviance in the data is

explained by the model, as is true for all the regions
186 NOAA Technical Report NMFS 142

0.5 1.0 15

asin(sqrt(Prop)

North-Central

0.0

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N

,..----------------,

... ------ ....... ,.;,;/;,.-'--"'''' ... t3 North-West Q)

rB~ c:n~

c

~~c:n~

Co

1--'"a

°a LO-.0---0-.5----1.-0---1~5---l

asin(sqrt(Prop)

0.5 10 1.5

asin(sqrt(Prop)

East

0L..- --'

0.0

,

, ' , , , , , ,,"

,,;~<;;;;

>'

South-West

0.0 02 04 06 08 1.:1 12

asin(sqrt(Prop)

° L..- --'

Figure 5

Effects of proxy targeting variable in four regions analyzed independently

under Model 2. Dashed lines indicate ± 2 standard errors.

(Table 1). The model fit was still significant statistically,

due to the large number of data points, for all regions

but the southwest. With addition of the targeting variable (Model 2), much more deviance was explained by

the model, between 66% and 91 % (Table 1), and the

span of the residuals was reduced by 3 orders of magnitude in the northwest (Fig. 6). Seasonality in the residuals was also revealed, which was not picked up by the

time-effect function, 10 (t). We could have attempted to

capture this variability by setting the LOESS span parameter to a much smaller value than 0.5. However, we

chose to let lo(t) focus on interannual variability, and

added a month variable (Model 3) which accounted for

most of the seasonality and reduced the span of residuals by another order of magnitude (Fig. 6). The month

effect showed a minimum in the summer and a maximum in the winter in the northwest region; the basic

shapes of the time-effect and targeting-effect functions

in Model 3 were not appreciably different from Model

2 (Fig. 7; d. Fig. 4, 5).

For the north-central and southwest regions, similar

results to those in Figures 6 and 7 were observed in the

reduction of the span of residuals when progressing

from Model 1 to 2 to 3, and in the seasonality revealed

by Model 2 residuals and captured by the month effect

in Model 3. As would be expected, seasonality in the

southwest was 6 mo. out of phase with the two northern

regions. As expected for a region that spans the equator, the eastern region revealed no seasonality. Therefore in this case there was no reduction in span of

residuals by Model 3 beyond that achieved by Model 2.

Simulation Modeling _

An important question about our analyses is whether

the proxy targeting function is really doing its job.

Ideally this function would be sensitive only to the relative emphasis that fishermen are putting on catching

swordfish rather than other target species. While the

proportion of swordfish in the catch would seem to

reflect the targeting of swordfish relative to other species, it would also be expected to reflect the abundance

of swordfish relative to other species.

With a simple simulation model, we investigated this

and other possible problems inherent in a proxy targeting variable that uses catch of other species. The model

produces synthetic CPUE data for swordfish and for an

alternate, non-target species which is a composite of all

tuna species caught. In the model, 2,500 fishing sets are

distributed throughout 20 yr of simulated time, the

date of each set being randomly chosen from a uniform

distribution. For each set a random choice is made,

according to a probability level, sprob, which is the probability that a set targets swordfish. The value ofsprob can

either be held constant or can be varied with the date of

the set. The mixture of swordfish and non-swordfish

sets, therefore, is either more or less constant (being
__________ Kleiber & Bartoo: Standardizing Catch per Unit of Effort Using General Additive Models 187

co

b

t--

b

Model 1

LO _b

u~

ffi~ ro~

Q)(')

>-b

..

g

60 65 70 75 80

Year

0

0

0

0

0

0

0

0

0 Model 2

0

0 _0

u~

Q)

5J

~o

"'0

~~

60 65 70

Year

75 80

g,---------------------------------------------------.

o

o

o

o

o Model 3

60 65 70

Year

75 80

Figure 6

Time effect shown by residuals in northwest region under (from top to bottom) \1odels 1, 2, and 3.
188 NOAA Technical Report NMFS 142

subject to stochastic variation) or it has additional variation with time governed by the variation in sprob. The

catchability of swordfish is assumed to be 100 times

m

o

'"o

greater for swordfish sets than for non-swordfish sets,

whereas the composite catchability of other species is

assumed to be twice as great for non-swordfish sets than

-------....

.... _-------------

60 65 70

Year

75 80

,..,.------- ----------~--- ,,-:.-:.---:.-- ---- ----------------.

/.~~~,,- ----- ,,- .. >- >-

Of)

o

:;L-~------------~-------------~-------------~--

00 0.5

asin(sqrt(Prop)

1.0 1.5

N

o

-----.... ----.... .... ----- .... .... .... .... .... .... .... .... .... .... ....

.... ....

.... ....

.... " .... .... .... .... " .... .... .... .... .... .... .... .... .... .... " .... .... ".... .... ....

',', ,'1 , '-_____ I

.... --- " ,'-- - - - .... .... - - - - - "

----'

2 6

Month

8 10 12

Figure 7

Year, targeting, and month effects in northwest region under Model 3. Dashed lines indicate ± 2

standard errors.
__________ Kleiber & Bartoo: Standardizing Catch per Unit of Effort Using General Additive Models 189

for swordfish sets. The milder response of the composite (other) species catchability to targeting reflects theassumption that some other species are likely to be

more vulnerable to swordfish sets and some to nonC\l

o

.... .... .... .... .... .... .... .... .... ... ------

A

,--------------------------

------ ---- -------------------------- a>

o ... ... ... ......

o 5 10

Time

15 20

B

C\l

--------- ----------

-----------------------------------

o

a>

o

o 10

Time

15 20

o

C\l

c

o L-~----~----~---~---~-----~---~----....__J

0.0 0.2 0.4 0.6 0.8

asin(sqrt(Prop))

1.0 1.2 1.4

Figure 8

GAM analysis ofsimulated data with constant abundance ofswordfish, constant abundance of other

species, and constant targeting probability. (A) Year effect under Modell; (B) year effect under Model 2;

(C) effect of proxy targeting variable under Model 2. Dashed lines indicate ± 2 standard errors.
190 NOAA Technical Report NMFS 142

Figure 9

Targeting probability, sprob, as a function of time in "

GAM analysis of simulated data. Points are actual proportions ofsets chosen to target swordfish by l-yr intervals in one of the simulations.

swordfish sets. Both catchabilities are subjected to lognormal stochastic error. The abundance of either swordfish or the composite (other) species can be held constant or forced to follow any arbitrary trajectory in time.

The synthetic data consist of catches (catchability times

abundance) ofswordfish and other species for each set.

We produced synthetic data sets for a variety of combinations of variability in swordfish abundance, other

fish abundance, and swordfish targeting probability,

sprob. The data sets were then subjected to Modell and

Model 2 GAM analyses. We did not trouble with Model

3 because we were interested in interannual rather

than seasonal variability.

Figure 8 shows GAM results for a situation in which

swordfish abundance, other fish abundance, and sprob

are all held constant. Though the time effects in both

Model 1 and Model 2 are not completely flat, attention

to the confidence regions shows little indication of a

time trend in swordfish abundance in either case. However, the width of the confidence region is reduced in

Model 2, reflecting an innate correlation between the

dependent variable (swordfish CPUE) and the targeting variable due to the fact that swordfish catch is used

in calculating both variables.

To investigate the effect of a change in targeting we

forced the targeting probability, sprob, to vary with time

as in Figure 9. The proportion of sets chosen to target

swordfish is also shown for each year. The GAM results

for this situation (Fig. 10) show a dramatic drop in

apparent swordfish abundance under Modell, as wOl.ld

be expected. The addition of the targeting variable in

Model 2 only partially accounts for the change in tarC>

<0'"

is

"

8.~ eO

0-

(;

Z'

B"":

]'10

e

0-

N

<0

°<0

0 10

Time

15 20

geting. Thus even in this ideal situation, that is, no

changes in the abundance of other species, the proxy

targeting variable is only partially successful in correcting a false drop in apparent swordfish abundance.

When the abundance of other fish change over time,

the problems are even worse. Figure 11 shows GAM

results from a scenario in which swordfish abundance is

constant, and targeting is constant, but the abundance

of other species drops by a factor of 10 over the 20 yr of

simulation. The Modell results show some variation,

but within the confidence region. However, the time

effect in Model 2 indicates a dramatic drop in apparent

swordfish abundance. In this case the proxy variable

creates a false drop in apparent swordfish abundance

that did not exist without the proxy variable.

From these results and the results of many other

simulations, it is evident that is it possible to simulate

almost any scenario of misleading indications of trends

in fish abundance from CPUE data, with or without

standardization using a proxy targeting variable. Therefore it is clear that there is very limited information

about targeting contained in data on the proportion of

different species in the catch.

Discussion

In order to standardize swordfish CPUE, we wanted to

accoun t for variation in fishing strategy that targets fishing

effort either toward swordfish or toward other species. We

used the proportion of swordfish in the catch as a proxy

variable for targeting, but our modeling results show that

it cannot be relied upon to correct for targeting effects in

the CPUE time series. Therefore the declining overall

swordfish CPUE (Fig. 2) cannot be unequivocally interpreted as indicating a decline in swordfish abundance.

Our analyses ofseparate regions eliminated much of the

non-swordfish longline effort in equatorial regions, but

the fishelies in those regions remained multi-species fishelies. Some measure of confidence might be taken in

results for three of the regions from the fact that the

patterns of variation in time are essentially identical with

and without the targeting variable (Fig. 3, 4). However,

given the simulation results, caution is called for, and the

reversal in the time trend for the southeast region depending on the model used must be viewed with extreme

caution. The fact that the targeting variable was able to

greatly reduce the residual deviances (Fig. 6) could in

large part be due to the inherent correlation between

swordfish CPUE and the targeting variable.

To adequately analyze catch and effort data from

multi-species fisheries such as the Japanese longline

fleet, there is a great need for information that is directly relevant to targeting, e.g. depth of set, time of

day, and use of light sticks. Provision for such data on
Kleiber & Bartoo: Standardizing Catch per Unit of Effort Using General Additive Models 191

-------------.

A

10 15 20

Time

... ... ... , , ,,

,

,, , , , ,, ,, , , , , , , ,, ,, ,, , , , , , , , , ...

--

5

-------------- N'"

0

N

0""': '" Q)

mQ)

~~

'"0

0

0

0

"'.--_----------------------------------------------,

'" B o

'"

------------------- ----- ------ --....

... ...

'"o

... ... , ... -------------.

---------------- o

0L...~---------~_---------~---------~---------~- o 5 10

Time

15 20

u

2'"

W

'"

C

~<.O

[!>

>-'"

o

0.0 0.2 0.4 06 0.8

asin(sqrt(Prop))

1.0 1.2

Figure 10

GA~ analysis ofsimulated data with constant abundance ofswordfish, constant abundance of other

species, and declining tar~eting probability. (A) Year effect under Modell; (B) year effect under

~odel 2; (C) effect of proxy targeting variable under ~odel 2. Dashed lines indicate ± 2 standard

errors.
192 NOAA Technical Report NMFS 142

A

------ -- ------

---------

----

... ...

.,

o

-----.....

<D

o

o 5 10

Time

15 20

--- B ---

u

[J~ '"

",-

E

i=

.,

o

<D

o

--------------

o 10

Time

15 20

o

'"

'"N c

, , ,, , , , ,/

,/

,/

,/

,/,/

o

L-~--------~--------~--------~

0.0 0.5 1.0 1.5

asin(sqr1(Prop))

Figure 11

GAM analysis of simulated data with constant abundance of swordfish, declining abundance of

other species, and constant targeting probability. (A) Year effect under Modell; (8) year effect

under Model 2; (e) effect of proxy targeting variable under Model 2. Dashed lines indicate ± 2

standard errors.
__________ Kleiber & Bartoo: Standardizing Catch per Unit of Effort Using General Additive Models 193

log sheets will improve the future situation, but will not

fix the existing published time series. Because these

time series cover extended time periods (20-30 yr) they

are potentially of great.value, but they would be immensely more valuable if accompanied by targeting

data. It may be the case that unpublished (and not

computer-encoded) data relevant to targeting is stored

away in attics or basements somewhere. Though difficult

and time consuming, a data "rescue" effort among fusty

shoe boxes and the like might be highly rewarding.

Literature Cited

Bartoo, N. W., and A. L. CoanJr.

1989. An assessment of the Pacific swordfish resource. In R.

H. Stroud (ed.), Planning the future of billfishes: research

and management in the 90's and beyond. Part I, Fishery and

stock synopses, data needs and management, p. 137-

151. Natl. Coalition Mar. Conserv., Savannah, GA.

Chambers,j. M., and T.j. Hastie.

1992. Statistical models in S. Wadsworth and Brooks, Pacific Grove, CA, 608 p.

Cleveland, W. S.

1979. Robust local weighted regression and smoothing

scatterplots. j. Am. Stat. Assoc. 74:829-836.

Fisheries Agency ofJapan.

1963-82. Annual reports of effort and catch statistics by area

on Japanese tuna longline tishery, 1960-1980. Dep. Res.

Develop., Fish. Agency ofJapan.

Punsly, R. G., and R. B. Deriso.

1991. Estimation ofthe abundance of yellowfin tuna, Thunnus

albacaTes, by age groups and regions within the eastern Pacific ocean. Inter-Am. Trop. Tuna Comm. Bull. 20:99-

131.

Sokal, R. R., and F. j. Rohlf.

1969. Biomeu)'. Freeman, San Francisco, CA, 776 p.

Stock Status of Pacific Swordfish, Xiphias gladius,

Inferred from CPUE of the Japanese Longline Fleet

Standardized Using General Linear Models

HIDEKI NAKANO

Pelagic Fish Resources Division

National Research Institute ofFar Seas Fisheries

Fisheries Agency ofJapan

5-7-1 Orido, Shimizu

Shizuoka 424-8633, Japan

ABSTRACT

Swordfish catch has increased significantly in recent years in the Pacific Ocean. The

Japanese longline fishery is the largest fishery for swordfish in the Pacific in terms of catch,

although swordfish is a secondary target species. The historical fishing grounds, seasons,

and gear of the Japanese longline boats have changed in response to shifts in target species

and fishing strategies of the fishermen. Standardized swordfish catch per unit of effort

(CPUE) of the Japanese longline fishery was analyzed for three hypothetical stocks: North

Pacific, southwest Pacific, and southeast Pacific, using a Generalized Linear Model. The

factors considered in the model were year, season, area, gear configuration, and target

species. CPUE decreased over time in the North and southeast Pacific, and increased in the

southwest Pacific. In the southeast Pacific, the catch increased from 2,000 to 10,000 metric

tons in recent years, while CPUE declined 30%.

Introduction

Swordfish, Xiphias gladius, is a large pelagic species

found in tropical, subtropical, and temperate waters of

the world oceans and adjacent seas (Nakamura, 1985).

The world catch of swordfish increased from about

30,000 metric tons (t) in the late 1960's to about 70,000

t in the late 1980's (FAO, 1961-93). In the Pacific

Ocean, the swordfish catch increased from about 10,000

tin 1952 to 25,000 tin 1962, then decreased to 10,000 t

in 1964 (Fig. 1). Catches have since increased, reaching

about 34,000 t in 1993. The recen t rapid increase in

catch was due to Chile and Mexico (Barbieri et a!.,

1994; Holts and Sosa-Nishizaki, 1994). The United States

catch also increased following a shift of fishing effort

from the Atlantic to the Pacific due to fishery restriction in the Atlantic by the International Commission

for the Conservation ofAtlantic Tunas (Holts and SosaNishizaki, 1994). Thus, concern is appropriate for the

status of swordfish stocks in the Pacific, where the relevant information is poor.

Since the Japanese catch ofswordfish has historically

been the largest portion of total swordfish catch in the

Pacific Ocean, previous researchers have usedJapanese

longline catch rates as indices of swordfish abundance

35000

30000

25000

20000

"5

" 15000 U

10000

5000

o

1952 1957 1962 1967 1972 1977 1982 1987 1992

Yenr

Figure 1

Annual swordfish catch in the Pacific in metric tons,

1952-92.

(Sakagawa and Bell, 1980; Bartoo and Coan, 1989).

Sakagawa and Bell (1980) reported on the condition of

swordfish stocks in the Pacific using Japanese longline

data and equilibrium-production model analysis for both

195
1200

E1500E 180° 1500W1200W 900W

196 NOAA Technical Report NMFS 142

a single Pacific-wide stock and for a threestock hypothesis. They concluded that the

stock was not overexploited. Bartoo and Coan

(1989) revised this stock assessmen t using updatedJapanese longline data and reached the

same conclusion, i.e. none of the examined

data indicated too-heavy exploitation. This

analysis was conducted using updated Japanese catch and effort data, and examines the

hypothesis that recent increases in catch have

impacted the stocks.

Materials and Methods

400N

20 0N

20°8

40°8

0= 10 V', ~-~.

..- '1J = 2 0= 1 r/l£9 00 0 0 0 0 0 T .~\~ 0 / 0 0 0 0 0 0 ° 'rt

~, 0 0 0 0 0 ° 0 d ( 1, ...

. fl· -tr "'" V?,'fl .. ° ° J r"¥" I~ 0 0

t~\ . I ° 0 '&., f--

o ~o ° . i ' 0 I-- I No 0 0 v... ' [ 0 0/

I I '0 c'v. I ° i J

! i ! "

Stock Structure Figure 2

Average swordfish epeE (number caught per 1,000 hooks) from

Japanese longline data, 1952-92.

The stock structure ofswordfish in the Pacific

Ocean is not well known. Sakagawa and Bell

(1980) first suggested two hypotheses based

on the distributions of larvae and of the long-term

annual mean catch rates of the longline fishery. Those

hypotheses were 1) a single, Pacific-wide stock, and 2)

three separate stocks with centers of concentration in

the northwest, southwest, and east Pacific Ocean. For

reference, the average distribution of unstandardized

catch per unit of effort (CPUE) of swordfish taken by

the Japanese longline fishery is shown in Figure 2. SosaNishizaki and Shimizu (1991) examined the spatial

distribution of monthly mean CPUE for swordfish, and

proposed four stocks in separate regions of the Pacific:

1) offJapan, in the northwest and central Pacific, 2) off

the Baja California Peninsula, 3) off the west coast of

South America, and 4) off the east coast of Australia

and north of New Zealand. The principal difference

from the Sakagawa and Bell (1980) hypothesis is that

the four-stock hypothesis divides the eastern Pacific

into northern and southern regions. Recent genetic

analyses of swordfish indicate that Atlantic and Pacific

stocks differ, and also suggest that there is no genecic

separation between the northern and other Pacific stocks

(Chowl ). Furthermore, the CPUE for the presumed

single stock (Sakagawa and Bell, 1980) was similar to

trends in CPUE from the northwestern Pacific, due to

overwhelming data from the large Japanese swordfish

fishery there. Therefore, three stock units are assumed

here: 1) a North Pacific stock in the area north of lOON,

2) a southwest stock ranging south of lOON and west of

140oW, and 3) a southeast stock, in the area south of

I Chow, S. ]994. Genetic comparision between the western and

eastern Pacific swordfish (Xiphias gladius) by PCR-RFI.P analysis on

D-Ioop region of mitochondrial DNA. Paper presented at the

international symposium on Pacific swordfish, Ensenada, Mexico,

1994. Available from S. Chow, National Research Institute of Far

Seas Fisheries, 5-7-1 Orido, Shimizu, Shizuoka, 424-R633,Japan.

lOON and east of 140oW. Even if there is only one

southern stock, division of the South Pacific into smaller

regions will serve to monitor local depletion, which is

important in light of the rapidly increasing catches in

the southeast Pacific.

Standardization of CPUE

For the Japanese longline fishery operating in the Pacific, the major target species were yellowfin, Thunnus

albacares, and albacore, T. alalunga, tunas in the early

period and more recently bigeye, T. obesus, and southern

bluefin, T. maccoyii, tunas. With the exception of a very few

vessels which target swordfish (Uozumi and Uosaki,

1998), swordfish is not the target of the longline fishery,

but it is an important component of the catch. Nominal

swordfish CPUE oftheJapanese longline fishery probably

has been affected by historical and seasonal changes of

fishing grounds, fishing gear, and target species. Therefore, it is difficult to interpret it as an index of stock

abundance without standardization for various factors.

The General Linear Model (GLM) (Draper and

Smith, 1966) approach to analysis of variance is used to

obtain standardized abundance indices. Robson (1966)

was the first to use a GLM for standardization of fishing

effort. Gavaris (1980) first published this application in

a readily-accessible journal; Allen and Punsly (1984)

and Punsly (1987) describe the method in detail.

The logbook data of the Japanese longline fishery as

compiled by the National Research Institute of Far Seas

Fisheries (NRIFSF) were used for the analysis. These

data cover more than 90% of the total number of sets,

and include information on year, month, day, location,

number of hooks, and swordfish catch in number until
Nakano: Stock Status Inferred from CPUE Standardized Using General Linear Models 197

Table 1

Independent variables in General Linear Models used to standardize swordfish CPUE from the Japanese longline fleet. YR = year, QT =

quarter, AR = area, SP = species targeted, BET = bigeye tuna, ALB = albacore, YFT = yellowfin.

1952-75 1975-92

Variable Mean Range nits Type Variable Mean Range Units Type

orth Pacific

YR 63.5 52-75 year class YR 79.2 75-92 year class

QT 2.5 1-4 quarter class QT 2.5 1-4 quarter class

AR 5.5 1-10 50 x 50 class AR 4.5 1-8 50 x 50 class

SP(BET) 2.5 1-4 log (CPUE + 1) class GEAR 2.5 1-4 hooks per basket class

SP(ALB) 2.5 1-4 log (CPUE + 1) class SP(BET) 2.5 1-4 log (CPUE + 1) class

SP(YFT) 2.5 1-4 log (CPUE + I) class SP(ALB) 2.5 1-4 log (CPUE + I) class

SP(YFT) 2.5 1-4 log (CPUE + 1) class

Sou thwest Pacific

YR 63.5 52-75 year class YR 79.2 75-92 year class

QT 2.5 1-4 quarter class QT 2.5 1-4 quarter class

AR 4 1-7 50 x 50 class AR 3 1-5 50 x 50 class

SP(BET) 2.5 1-4 log (CPUE + 1) class GEAR 2.5 1-4 hooks per basket class

SP(ALB) 2.5 1-4 log (CPUE + 1) class SP(BET) 2.5 1-4 log (CPUE + 1) class

SP(YFT) 2.5 1-4 log (CPUE + 1) class SP(ALB) 2.5 1-4 lo~ (CPUE + 1) class

SP(YFT) 2.5 1-4 log (CPUE + 1) class

Southeast Pacific

YR 63.5 52-75 year class YR 79.2 75-92 year class

QT 2.5 1-4 quarter class QT 2.5 1-4 quarter class

AR 2 1-3 50 x 50 class AR 2.5 1-4 50 x 50 class

SP(BET) 2.5 1-4 log (CPUE + 1) class GEAR 2.5 1-4 hooks per basket class

SP(ALB) 2.5 1-4 log (CPUE + 1) class SP(BET) 2.5 1-4 log (CPUE + 1) class

SP(YFT) 2.5 1-4 log (CPUE + I) class SP(ALB) 2.5 1-4 log (CPUE + 1) class

SP(YFT) 2.5 1-4 log (CPUE + I) class

1975. Additional information on fishing gear was added

beginning in 1975, because fishermen began to change

their gear configuration, e.g. the number of hooks between floats (Suzuki eta!., 1977), to target deep-swimming

bigeye tuna. Since then the Japanese fishermen have

tended to set their hooks deeper and deeper each year.

Thus two data sets were used for this analysis. One

consisted of data aggregated by year, month, and 5°

square, extrapolated to 100% coverage for 1952-75

(raised data). The other consisted of data aggregated

by month and 5° square, and included the number of

hooks between floats, for 1975-92 (unraised data). In

general, the greater the number of hooks, the deeper

the depth ofthe hooks. For considering historical trends

in CPUE, both data sets were used by adjusting the

results of unraised data in 1975 to the resul ts of raised

data in the same year. CPUE was calculated as catch in

number of fish per 1,000 hooks. Strata with fewer than

20,000 hooks (raised data) and 3,000 hooks (unraised

data) were arbitrarily excluded from the analysis to

avoid possible problems created by small sample sizes.

Japanese longline fisheries usually use 2,000 to 3,000

hooks per set; fewer hooks represent fewer sets.

The model used for this analysis was

CPUEijklm = J1 X YR; x QTj X ARk x

GEAR, x SPm x INTER x E

where CPUEijklm is the catch rate obtained In year i,

quarter j, area k, and gear class t, for target species m; J1

is the overall mean catch rate; YRj is a year factor; QT. is

a season factor; ARk is an area factor; GEARI is a g~ar

factor; SPm is a factor of target species; INTER is any

combination of 2-way interaction terms between main

effects; and E is a (0, 0 2) error term.

Taking natural logarithms of both sides, we obtain

the linear statistical model

In CPUEjjklm = In J1 + In YR j+ In QTj + In ARk +

In GEARI + In SPm + In INTER + In E.

In order to include strata in which there was fishing

effort but no catch of swordfish, (CPUE + 1) was used

instead of observed CPUE. The mean, range, units of

measure, and type of variables used in the model are

summarized in Table 1. Main effects of the model in-
198 NOAA Technical Report NMFS 142

o

205

405

40N

o

205

405

120E

120E

HOE

HOE

160E

160E

160

1BO

160W 140W 120W 100W BOW

160W 140W 120W 100W BOW

60W

60W

Figure 3

Geographical areas used in this analysis of nonhern, southwest, and southeast Pacific swordfish stocks during 1952-75 (above) and 1975-92 (below.)

clude year, quarter, area, and log-transformed CPUE of

bigeye, albacore, and yellowfin tuna for 1952-75. Logtransformed CPUE was categorized into four levels (CPUE

= 0, 0 < CPUE < 1.0, 1.0 CPUE < 2.0, and CPUE 2.0)

Hoey et al. (1989) used the proportion of swordfish

catch to total catch in U.S. swordfish fishery statistics as

a main effect in standardizing orth Atlantic swordfish

CPUE, since the U.S. swordfish fishery is a mixed species fishery targeted on various species. Miyabe (1994)

used log-transformed CPUE of other species as a bycatch effect to obtain standardized CPUE of Atlantic

bluefin tuna from Japanese longline fishery statistics.

Since swordfish is a sub-target species for the Japanese

longline fishery in the Pacific Ocean, log-transformed

CPUE's of other species were used in this analysis as a

main effect to account for targeting.

Based on mean swordfish CPUE levels, the three

stock areas were divided into ten and eight geographical blocks in the North Pacific, seven and five blocks in

the southwest Pacific, and three and four blocks in the

southeast Pacific for 1952-75 and 1975-92, respectively

(Fig. 3). Differences among the blocks are mainly due

to the different fishing grounds of the Japanese longline

fishery in the t\¥0 periods. Gear configuration, taken as

the number of hooks bet\¥een floats, was included as an

additional main effect for the data of 1975-92. Sets with

4-20 hooks between floats were observed in the data.

Following Uozumi and akano (1994), these were categorized into 4 levels: 4-7, 8-11, 12-15, and 16-20

hooks between floats, to avoid problems created by lack

of information in the data set. All GLM analyses were

made using SAS version 6.08 (SAS, 1989).
Nakano: Stock Status Inferred from CPUE Standardized Using General Linear Models 199

2.5 4

Residual

-3.5 -2 -as

a

2.5 4

Standardized CPUE at the four levels of each main

effect for the North Pacific stock is shown in Figure 5.

Main effects and in teractions were statistically significant in the final model (Table 2). Seasonal differences

were observed in the standardized CPUE for both time

periods: the first quarter had the highest CPUE, and

the third had the lowest. In areas I, 2, and 5, east of

Assessment of Effects

Residual

-3.5 -2 -0.5

a

Figure 4

Distribution of standardized residuals from the fitted models for each swordfish stock and time period.

Results and Discussion

North,1952-1975 North, 1975-1992

30 30

Final Models

25 25

Forward stepwise regression and 20 20

the value of the squared multiple E E

correlation were used to select 15 IS

c..." c..." the best models. After several tri- 10 10

als, the final model and combination of factors for north, southwest, and southeast stocks were a a

chosen. For all stocks during -4 -2.5 -1 0.5 2 3.5 -4.5 -3 -1.5 a 1.5

1952-75, the factors included in Residual Residual

the final models were

Southwest, 1952-1975 Southwest, 1952-1975

In(CPUE + 1) = YR + QT + AR +

45 40

SP(BET) + SP(ALB) + SP(YIT) +

40 35

QT x AREA + E

35 30

30 25

E 25

and for 1975-92: " 20

20 c...

15

IS

north: In(CPUE + 1) = YR + 10 10

QT + AR + GEAR + SP(BET) + 5

SP(ALB) + SP(YIT) + a a

QT x AREA + E -4 -2.5 -I 0.5 2 3.5 -4 -2.5 -1 as 2 3.5

southwest: In(CPUE+ 1) =YR+ Residual Residual

QT + AR + GEAR + SP(BET) +

Southeast, 1952-1975 Southeast, 1952-1975 SP(ALB) + SP(YFT) + 30 30

QT X SP(YIT) + E

25 25

southeast: In(CPUE+ 1) =YR+

QT + AR + GEAR + SP(BET) +

20 20

SP(ALB) + SP (YIT) + "" IS 15

QT " x AREA + E. c... c..

10 10

Interactions including year, e.g.

YR x AREA or YR x QT, were not

examined due to insufficient data.

These interactions should be considered in future research if data

become available.

The results of the A OVA indicated that all final models were

statistically significant (Table 2-

4). The squared multiple correlations in the final models were 0.53

and 0.47 for the north, 0.45 and 0.39 for the southwest,

and 0.32 and 0.20 for the southeast for 1952-75 and

1975-92, respectively, which means that the models

explain 53%-20% of the variability in the data. It is

possible that other factors not included in the model

may explain the rest of the variability. Histograms of

overall distributions of standardized residuals for the

final models are not extremely different from normal

distributions (Fig. 4).
200 NOAA Technical Report NMFS 142 _

1952-75

Source OF Sum of squares Mean square F P>F

Model 71 2,253.772 31.74327 184.81 0.0001

Error 11,457 1,967.832 0.17176

Corrected total 11,528 4,221.605

Squared multiple correlation= 0.533866 C.V. = 0.80772 Root MSE = 0.41444 Mean = 0.51309

Source OF Ty_:>e III SS Mean square F P>F

YR 23 79.7J77 3.46595 20.18 0.0001

QT 3 27.0770 9.02565 52.55 0.0001

AR 9 353.2747 39.25274 228.54 0.0001

SP(ALB) 3 33.1365 11.04549 64.31 0.0001

SP(BET) 3 86.4296 28.80988 167.74 0.0001

SP(YFT) 3 32.2016 10.73388 62.49 0.0001

QTxAR 27 272.7557 10.10206 58.82 0.0001

1975-92

Source OF Sum ofsquares Mean square F P>F

Model 60 4,582.521 76.37535 567.32 0.0001

Error 38,314 5,157.981 0.13462

Corrected total 38,374 9,740.502

Squared multiple correlation = 0.47046 C.V. = 0.97082 Root MSE = 0.36691 Mean = 0.37794

Source OF Type III SS Mean square F P>F

YR 17 54.4091 3.2005 23.77 0.0001

QT 3 8.3407 2.7802 20.65 0.0001

AR 7 471.9310 67.4187 500.79 0.0001

GEAR 3 380.2856 126.7619 941.60 0.0001

SP(ALB) 3 289.6523 96.5507 717.19 0.0001

SP(BET) 3 278.8754 92.9584 690.50 0.0001

SP(YFT) 3 68.1805 22.7268 168.82 0.0001

QTxAR 21 481.2105 22.9147 170.21 0.0001

Japan, high CPUE's were observed. Gear effects were

negatively correlated with swordfish CPUE: CPUE decreased if fishing gear was set deeper. Several types of

gear were used in the areas near Japan. For instance,

some 10ngline gear had many hooks between floats,

and yet it was fished as shallow gear targeting albacore.

Thus there were several gear configurations, which could

not be accounted for in standard categories of longline

gear depth. Therefore it is premature to draw a definitive conclusion as to gear efficiency. Species effects

were generally negative for the northern stock, with the

exception of a relatively strong effect from bigeye CPUE

in 1952-75.

Standardized CPUE at the levels of each main effect

during 1952-75 and 1975-92 for the southwest stock is

shown in Figure 6. Main effects and interactions were

statistically significant in the final model (Table 3).

Strong area effects were seen in areas 6 and 7 during

1952-75, and in area 4, which includes the Tasman Sea,

during 1975-92. The effects of bigeye CPUE were positively correlated with swordfish CPUE in both time

periods.

Figure 7 shows main factor effects for the southeast

stock. Main effects and interactions were statistically

significant in the final model (Table 4). Strong seasonal changes in CPUE were observed in the southeast
Nakano: Stock Status Inferred from CPUE Standardized Using General Linear Models 201

Table 3

Results of the ANOVA for the southwest Pacific swordfish stock.

1952-75

Source OF Sum of squares Mean square F P>F

Model 59 312.4885 5296414 179.1 0.000]

Error 12,775 377.7889 0.029573

Corrected total 12,834 690.~773

Squared multiple correlation = 0.4527 C.V. = 1.03516 Root MSE =0.17197 Mean =0.16613

Source OF Type III SS Mean square F P>F

YR 23 10.2493 0.44562 1:,.07 0.0001

QT 3 5.7028 1.90095 64.~8 0.0001

AR 6 108.4591 18.07652 611.26 0.0001

SP(ALB) 3 I~. 1909 4.06363 137.41 0.0001

SP(BET) 3 4.2749 1.42498 48.19 0.0001

SP(YFT) 3 0.6899 0.22999 7.7R 0.000]

QTxAR 18 25.8629 1.43683 48.59 0.0001

1975-92

Source OF Sum of squares Mean square F P>F

Model 44 893.357 20.30358 514.92 0.0001

Error 35,180 1,387.166 0.03943

Corrected lOtal 35,224 2,280.523

Squared multiple correlation =0.391734 C.V. = 1.19072 Root MSE =0.19857 Mean =0.16677

Source OF Type III SS Mean square F P>F

YR 17 123816 0.72833 18.47 0.0001

QT 3 12.1535 4.05119 IU2.74 0.0001

AR 4 312.8623 78.21556 1,983.63 0.0001

GEAR 2 2.6686 1.33432 33.84 U.0001

SP(ALB) 3 3.4264 1.14216 28.97 O.UOOI

SP(BET) 3 4.2153 1.40512 35.64 0.U001

SP(YFT) 3 5.2359 1. 74531 44.26 0.0001

QT xSP (YFT) 9 12.4345 1.38162 35.04 0.0001

stock. Of the area effects, those in area 1, the equatorial

eastern Pacific, during 1954-75, and in area 4, off Peru,

during 1975-92, were the strongest observed. The effects of bigeye CPUE were positively correlated with

swordfish CPUE. There was a difference in bigeye effect between the North and South Pacific: it was negative in the north, but positive in the south. More detailed study of the cause of this inconsistency is needed

in the future.

Various attempts have been made to standardize

CPUE for longline fisheries with mixed target species

(Hoey et aI., 1989; Miyabe, 1994). Here and in Miyabe

(1994) the log-transformed CPUE of other species was

used as a main effect. However, there may be problems

with this practice. Although excluding the target species effect showed similar trends in annual standardized CPUE, there is the possibility that the factor may

be related to abundance rather than to targeting, i.e. it

may simply reflect changes in relative abundance or in

relative temporal and spatial distributions ofspecies. A

reasonable approach should be developed in the future

to account for fishing strategy in standardizing the CPUE

of non-target species.

Some interactions, e.g. that between quarter and )'ellowfin (QT x SP(YFT)) for the southwest Pacific, and

various quarter-area interactions (QT x AR) were signifi-
202 NOAA Technical Report NMFS 142

Table 4

Results of the A IOVA for the southeast Pacific swordfish stock.

1\:152-75

Source OF Sum uf squares Mean square F P>F

Model 41 34.732 0.847134 33.71 0.0001

Error 3,003 75.476 0.025134

Corrected total 3,044 110.209

Squared multiple correlation =0.315151 C.V. =0.59786 Root 'viSE =0.15854 Mean =0.26553

Source OF Type 11I SS Mean square F P>F

YR 21 3.23000 0.153810 6.12 0.0001

QT 3 5.81158 1.937194 77.08 0.0001

AR 2 10.74744 8.373722 333.17 0.0001

SP(ALB) 3 0.17807 0.059357 2.36 0.0695

SP(BET) 3 0.88302 0.294343 11.71 0.0001

SP(YFT) 3 0.62972 0.209908 8.35 0.0001

QTxAR 6 2.76630 0.461050 18.34 0.0001

1975-\:12

Source OF Sum of squares Mean square F P>F

Model 44 368.406 8.37287 183.4 0.0001

Error 32,509 1,484.143 0.045653

Corrected total 32,553 1,852.549

Squared multiple correlation =0.198865 C.V. =0.87135 Root 'viSE =0.21367 Mean =0.24521

Source OF Type III SS Mean square F P>F

YR 17 61.2459 3.6027 78.91 0.0001

QT 3 127.4766 42.4922 930.76 0.0001

AR 3 98.6999 32.8999 720.65 0.0001

GEAR 3 0.9401 0.3133 6.86 0.0001

SP(ALB) 3 4.8031 1.6010 35.07 0.0001

SP(BET) 3 14.9572 4.9857 109.21 0.0001

SP(YFT) 3 1.0301 0.3453 7.57 0.0001

QTxAR 9 91.5053 10.1672 222.71 0.0001

cant. Other interaction terms could not be examined due

to insufficient data. In the case of the QT x AR interaction,

area effects probably differ by quarter due to the migration of fish, which might be seen in the quarter-species

interaction. For example, a significant QT x SP(YFT)

interaction would mean that the CPUE ofyellowfin tuna

changes over time, which could be caused by migration.

Trends in Standardized CPUE

Standardized CPUE and 95% confidence intervals for

the three swordfish stocks are shown in Figure 8. CPUE

In the North Pacific peaked in 1958, then decreased

until 1968, and has increased since. CPUE in the southwest Pacific showed an increasing trend until 1987,

followed by a moderate decrease. CPUE in the southeast Pacific showed an increasing trend until 1977,

decreased until 1984, then increased until 1987, and

has decreased since then. These trends may indicate

changes in abundance of swordfish in each region.

However, Punsly and Nakano (1992) pointed out that

even these standardized hook rates may be unrelated to

abundance. For example, annual variation in swordfish

vulnerability to longlines due to variability in the depth

of the fish, resulting from variations in vertical thermal
Nakano: Stock Status Inferred from CPUE Standardized Using General Linear Models 203

0.6 0.5

0.5 <ol 0.4 <ol

=> =>

"" "" U 0.4 U 0.3

] ]

:c 0.3 :c... ... " 0.2 " ." "C 0.2 c c

" Vi" Vi 0.1

0.1

0 0

2 3 4 2 3 4

Quarte r AIbaco re

1.2 0.7

I.l

I 0.6

<ol 0.9 <ol

=> => 0.5 "" 0.8 U U"" ." 0.7 ." ... 0.4 ::: " 0.6

0.5 0.3 ..

." ."" ;; 0.4 c

" 0.2 Vi 0.3 Vi

0.2 0.1

0.1

0 0

1 2 3 4 5 6 7 8 9 10 2 3 4

Area B ige ~·e

0.6 0.6

0.5 0.5 <ol <ol

=> =>

"" 0.4 "" 0.4 U U

." " ::: 0.3 ... 0.3

"

-= .)(........ ." 0.2 c 0.2 ;;

Vi Vi" 0.1 0.1

0 0

2 3 2 3 4

Gear Yellowfin

---"-1952-1975 ... )( ··1975-1952

Figure 5

Standardized CPUE at each level of the main effects for the I onh Pacific

swordfish stock, 1952-75 and 1975-92.

structure, oxygen level, or food availability, could have

a greater effect on hook rates than does abundance.

Swordfish Catch in the Pacific

Annual catches ofswordfish from each region are shown

in Figure 9. The catches of all nations except Japan

were taken from FAO fishery statistics yearbooks (FAO,

1961-92). Japanese swordfish catches were calculated

from catch and effort statistics compiled by RIFSF by

multiplying the average weight (calculated from lengthfrequency data) for various time and area strata by

number of fish caught in these strata. These estimates

were summed to obtain catches byJapanese fisheries in

the north, southwest, and southeast areas.

The catch of swordfish in the north increased from

14,000 tin 1952 to 20,000 tin 1960, decreased to 7,000
204 NOAA Technical Report NMFS 142

0.4 0.4

'-l '-l

:J 0.3 :J 0.3

u"" U"" ." )( ... ."

.~" " 0.2 .!:i 0.2 ." ."

... ... ."

" ."

" C C

" 0.1 .. 0.1

en 00

0 0

2 3 4 2 3 4

Quartc r Albacore

0.4

'-l '-l

:J :J 0.3

U"" U"" •• )If •• ' ., •

." ."

.:::" 0.5 "" 0.2 ."

... .. .. .. ." ."

C C .. " 0.1 en en

0 0

2 3 4 5 6 7 2 3 4

Area Bigcyc

0.3 0.4

'-l --- ......x•. :J -'.c :J 0.3 r--- U"" "" 0.2 U ." ."

•"!::: "

... 0.2

"E .. 0.1 ." C C

" " 0.1 en en

0 0

2 3 4 3 4

Gear V.llnwfin

-1952-1975 -_·x·_· 1975-1992

Figure 6

Standardized CPlJE at each level of the main effects for the southwest

Pacific swordfish stock, 1952-75 and 1975-92.

tin 1964, then gradually increased to 18,000 tin 1990.

Changes in standardized CPUE for the North Pacific

were almost parallel to changes in catch, although the

Japanese longline effort was stable at about 120 million

hooks during this time.

The swordfish catch in the southwest Pacific gradually increased to 2,000 t in 1972, and has fluctuated

about this point since that time. Both catch and CPUE

in this area show comparable trends after the mid1960's. The fishing ground was expanding to the south

before 1980. Since then, catch and CPUE have tended

Lo stabilize in this area.

In the southeast Pacific, swordfish catch increased

from about 100 t in the 1950's to 1,000-2,000 t in the

1960's. Catches then fluctuated between about 1,000

and 4,000 t, until they began increasing again in about

1987, increasing to about 10,000 t in 1991. This rapid

increase was due to the Chilean catch, which increased
Nakano: Stock Status Inferred from CPUE Standardized Using General Linear Models 205

0.4 0.3

;:l

'" 0.3 ;:l

'"c.. c.. U 0.2 U -·x·-

.!:!" 0.2 .~"

.. .. .. .. 0.1 c

.. .. 0.1 x- ii5 ii5

0 0

2 3 4 2 3 4

Quarte r Albacore

0.4 0.4

'";:l 0.3 ;:l

'" 0.3 c.. c..

u u

-= -= " "

" .!:S 0.2 0.2 :;; -=.. .. .. .. -= -=c c .. .. 0.1 0.1

ii5 ii5

0 0

2 3 4 2 3

Area Bigeye

0.3 0.3

'" '" ....... x· ....· .... ·x. ;:l ...... w- ......... 'X .•• -_. ;:l

c.. c.. U 0.2 U 0.2

-= -= .~" .!:::" -=..

..

-= 0.1 -=" 0.1 c c

" .. ii5 ii5

0 0

2 3 4 2 3 4

Gear Yellowfin

-1954-1975 .. ·x· ·1975-1992

Figure 7

Standardized CPUE at each level of the main effects for the southeast

Pacific swordfish stock, 1952-75 and 1975-92.

from 342 t in 1985 to 7,255 t in 1991. Such rapid

increases in catch, concomitant with decreasing CPUE,

should be carefully monitored.

Standardized Effective Effort and Catch

The relation between standardized effective effort and

catch in each region is shown in Figure 10. Estimates of

effective effort were obtained by dividing total catch by

standardized CPUE. Effective effort does nol appear lO

correlate with catch in the 1 orth Pacific, whereas the

relation exhibits a linear trend in the southwesl Pacific.

It seems that the abundance of the southwest stock is

under the MSY level; it is the most stable of the three

stocks hypothesized here. Judging from the trend in

CPUE and the low level of catch, the fishery for sword-
206 NOAA Technical Report NMFS 142

North

:: r, ".

'E 0.4 s

:c

; 0.3

""c

0.2

0.1

o

1952 1957 1962 1967 1972 1976 1981 1986 1991

0.5

Southwest

_ 0.4

Q"

U

"" 0.3 ;!

0.2 .. c

..

Vi

57 62 67 72 77 82 87 92

0.1 [

o -'-'.L.L...L..L---'--'-'-L-'---'-'---'-'L-'-.L.L--'-'-~L-'--'--'---'-'----,---"'-'--,--"---'----'--'-''--'---.L.L--'--'

52

Southeast

0.5

_ 0.4

Q"

U

"" 0.3

:c

0.2 c

..

Vi

0.1

o

57 62 67 72 77

YEAR

82 87 92

Figure 8

Annual standardized CPL'E from Japanese longline fisheries data, and

95% confidence intervals, for each Pacific swordfish stock. ;'\ote differing x scales.

fish appears to be in a developing stage in the southwest

Pacific. Tn the southeast Pacific, the relation between

effective effort and catch was different before and after

1980. Standardized CPUE has decreased in the southeast Pacific since about 1977, while catch has drastically

increased since about 1986. However, there is a possibility that CPUE trends in this region indicate changes

in local abundance and are not representative of overall stock status in the region. The swordfish fishing

grounds of South American fleets are very small and

concentrated nearshore. Even for a high-seas fishing

country like Japan, swordfish fishing grounds in the

South Pacific are much smaller than those in the North

Pacific, being concentrated in the Tasman Sea and off
Peru. Therefore, the CPUE of the Japanese longline

fishery may represent local stock reductions or increases

in the South Pacific. Different approaches, such as nonequilibrium production or delay difference models (e.g.

Hinton and Deriso, 1994), should be applied in future

assessments of the status of swordfish stocks.

Conclusion _

Average standardized CPUE from recent years, 1983-

92, was compared with that of earlier periods, 1952-61

for the north and southwest stocks, and 1961-67 for the

southeast stock. CPUE decreased from 0.46 to 0.38 in

the North Pacific and from 0.26 to O.lR in the southeast

Pacific, and it increased from 0.26 to 0.36 in the southwest. In the southeast Pacific, the catch increased rapidly from about 3,000 t to about 10,000 t in recent years.

This stock should be carefully monitored because of

the observed declining CPUE coupled with an increasing catch, which may be indicative of a decrease in

abundance. In addition, since swordfish catches have

increased in the North and southeast Pacific Ocean in

recent years, fishery activities and abundance indices of

stocks on both a wide and a local area basis should be

carefully monitored.
208 NOAA Technical Report NMFS 142

North

25000

60

20000

f=' 15000 ;§,

..c

... a 10000

5000

63

o

o 10000 20000 30000 40000 50000 60000 70000

2500

500

3000

4000 6000 8000 10000

Southwest

o 2000

o

'5

...

U 1000

f=' 2000

;§, 1500

Southeast

12000

10000

8000

1:i 6000

"

U 4000

2000

o

92

o 10000 20000 30000 40000 50000 60000 70000

Hooks

Figure 10

Relation between standardized effective effort for swordfish and swordfish catch

in each region of the Pacific Ocean. Numerals indicate years. Note differing x

and y scales.

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1984. Catch rates as indices of abundance of yellowfin tuna,

Thunnus albacares, in the eastern Pacific Ocean. Inter-Am.

Trop. Tuna Comm. Bull. 18(4):301-379.

Barbieri, M. A., C. Canales, V. Correa, M. Donoso,

A. Gonzalez Casanga, B. Leiva, A. Montiel, and E. Yanez.

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H. Stroud (ed.), Planning the future of billfish, research

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Draper, N. R., and H. Smith.

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Gavaris, S.

1980. Use of a multiplicative model to estimate catch rate

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data standardized using biological and environmental

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1989. Catch per unit effort information from the U.S. swordfish fishery. Int. C:omm. ConselY Atl. Tunas, Coil. Vol. Sci.

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Miyabe, N.

1994. Trends of CPUE for Atlantic bluefin caught by the

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19(3):265-306.

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Mitochondrial and Nuclear DNA Analyses in the Study of Swordfish,

Xiphias gladius, Population Structure

JAIME R. ALVARADO BREMER, GILLES M. LECLERC, and BERT ELY

FISHTEC Genetics Laboratory

Department ofBiological Sciences

University ofSouth Carolina

Columbia, South Carolina 29208

ABSTRACT

We review two complementary approaches to the genetic differentiation of swordfish

populations. The first involves direct sequencing of PCR-amplified fragments of the mitochondrial genome. A 300-base-pair (bp) fragment of the ATPase 6 gene yielded relatively

low values of nucleotide sequence divergence and haplotypic diversity. In contrast, analysis

of a 330··bp nucleotide sequence, corresponding to the hypervariable left domain of the

mitochondrial control region, confirmed that mtDNA harbors a large amount of variation.

Very high values of haplotypic diversity were obtained for samples from the North Pacific,

Atlantic, and Mediterranean, with at least 68 mtDNA types among 109 individuals. The

phylogenetic relationship of haplotypes revealed the presence of two highly divergent

clades. Monte Carlo simulations suggested heterogeneous frequency distributions of mitochondrial types in North Pacific (n=25), Atlantic (n=39), and Mediterranean (n=45) samples.

Phylogeographic analysis revealed that certain mtDNA lineages are found almost exclusively in the Atlantic, while others are ubiquitous in all oceans.

The study of mtDNA gives only a partial view of genetic population structure because it

reflects primarily the history of maternal lineages. Therefore, to study nuclear DNA we

developed a genomic library ofseveral anonymous loci. To facilitate screening large samples,

we employed PCR-based assays combined with restriction analysis. In addition we report the

development of PCR primers that target the growth hormone gene and may have a wide

range of application.

Introduction

Current management practices for most large pelagic

species offish are subject to both national and international controversies, primarily because of the dramatic

decline in the catches of many species, including swordfish. The international commissions in charge of regulating fisheries, of which most major fishing nations are

signatories, have been criticized for making erroneous

assumptions regarding the state of fish stocks.

Among the most controversial issues is the structure

of stocks. Hypotheses about stock structure have often

been established without sufficient knowledge about

the biology of the species in question. This issue is

further complicated by differences in the interpretations of the term stock. Ideally, a stock is an intraspecific

group of randomly-mating individuals with temporal or

spatial integrity (Ihssen et al., 1981). Unfortunately, to

what extent management units fulfill the conditions of

random mating and temporal and spatial genetic integrity is extremely difficult to assess in most cases.

Recently, genetic studies have been used to test hypotheses on stock structure ofseveral scombroid fishes.

These studies include some based on allozyme electrophoresis (Ward et al., 1995) and several focused on

mitochondrial DNA polymorphisms. Mitochondrial

studies include restriction fragment length polymorphism studies (RFLP) (e.g. Graves et al., 1984; Graves

and Dizon, 1989; Scoles and Graves, 1993; Graves and

McDowell, 1994, 1995) and direct sequencing of PCRamplified portions of mtDNA (Finnerty and Block,

1992). The advan tages of using the mitochondrial genome in the study of population structure have been

summarized by Avise et al. (1987) and Moritz et al.

(1987). RFLP analyses have been conducted on swordfish populations in the Atlantic Ocean (Alvarado

211
212 NOAA Technical Report NMFS 142

Bremer, 1992), the Mediterranean Sea (Magoulas et

al., 1993), and the North Pacific (Grijalva-Chon et al.,

1994). Both the North Atlan tic and the global population structures of the swordfish have been examined

using direct sequencing of the mitochondrial genome

(Alvarado Bremer, 1994; Alvarado Bremer et al., 1995a,

b). In the first portion of this paper, we review the

major findings on swordfish stock structure reported in

these papers. We emphasize the advantages and limitations of using sequence data of the mitochondrial control

region to study the population structure ofswordfish.

The second portion of this paper focuses on the

analysis of nuclear DNA variation. Because mtDNA is

almost exclusively maternally inherited, it provides evidence primarily for female population structure. If patterns of distribution and migration are similar between

sexes, mtDNA data may provide an accurate description of the geographic structure of the species. However, when the rates of dispersal of males and females

differ significantly, the conclusions derived from mtDNA

data apply only to maternal lineages. Because there is

ample evidence of significant differences in distribution and behavior between male and female swordfish

(Palko et al., 1981), we decided to also assess the variation contained in the nuclear genome to offer a more

complete scenario of the population structure ofswordfish.

Mitochondrial DNA Sequence Data _

The development of the polymerase chain reaction

(PCR) (Saiki et aI., 1985, 1988) has made it possible to

amplify and directly sequence relatively large stretches

of DNA from a variety of organisms. The protocols and

primers employed to amplify and sequence portions of

the swordfish mitochondrial genome (Alvarado Bremer,

1994) are given in Appendix 1. These control region

primers appear to be universal for fishes, and are routinely used in our laboratory to amplify and sequence

the hypervariable portion of the genomes of a wide

variety of fish species (Alvarado Bremer and Ely, unpublished results).

There are appreciable differences in the mutation

rate of different portions of the swordfish mitochondrial genome (Alvarado Bremer, 1994). Only five variable positions, which define four distinct types, were

found in an approximately 300-base-pair (bp) nucleotide sequence of the ATPase 6 gene from a sample

which included six Atlantic and four Pacific individuals

(Table 1). In contrast, in a 630-bp control region sequence from the same sample we identified nine distinct genotypes defined by 47 variable positions. More

than 70% ofthe variable positions in the control region

were found in a nucleotide sequence roughly 280 bp

Table 1

Bases found at polymorphic sites in a 300-bp sequence

of the ATPase 6 gene surveyed among 6 Atlantic and 4

Pacific swordfish (from Alvarado Bremer, 1994). CAN =

Georges Bank, Nova Scotia; PAC = Pacific Ocean. T =

thymine, C = cytosine, G = guanine, A = adenine.

Position

Specimens 54 102 138 240 255

21 (CAN) T G G T C

19 (CA~) C A A C C

10,11,15,22 (CAN);

6S, 16S, 20 (PAC) C G G T C

JLC5S (PAC) C G G T A

long and adjacent to the tRNA proline gene (Alvarado

Bremer, 1994). The analysis of 330 bp including this

hypervariable segment from 109 individuals collected

in the Pacific (n=25), Atlantic (n=39), and Mediterranean

(n=45) (Alvarado Bremer et aI., 1995b) confirmed the

presence of two highly divergent lineages. These two lineages, referred to henceforth as clade I and clade II, are

separated by a total of ten fixed differences: 1 transversion, 2 insertions or deletions (indels), and 7 transitions.

one of the 68 characterized genotypes was present

at a high frequency. A test of geographic heterogeneity

in haplotype frequency distribution using Monte Carlo

simulations (Roff and Bentzen, 1989) revealed that the

Pacific, Atlantic, and Mediterranean samples were significantly different (P<0.05; Fig. 1). However, within oceans

there is evidence that extensive mixing has occurred.

While statistical analysis of frequency distribution,

such as Monte Carlo simulations of chi-square values

(Roff and Bentzen, 1989) and G-tests of independence

(Sokal and Rohlf, 1981), give valuable information about

the heterogeneity of populations, additional insight

into the present distribution of genotypes can be obtained through the analysis of their phylogenetic relationship (Fig. 2). For instance, the phylogeographic

information shows that certain lineages have an uneven

distribution. The largest observed difference results from

the absence of members of clade 11 in the Pacific Ocean

and the high proportion of members of this clade in

the Mediterranean Sea and the eastern North Atlantic.

Less obvious, but equally important, is the uneven distribution of certain clade I lineages in the Pacific and

Atlantic samples. A total of22 genotypes, which include

37 individuals, derive from the branch emerging from a

single node (labeled A in Fig. 2) and represent almost

exclusively Atlantic and Mediterranean samples. Only

one of these individuals was collected in the Pacific

Ocean (genotype 43). The branch emerging from this
____ Alvarado Bremer et al.: Mitochondrial and Nuclear DNA Analyses in the Study of Population Structure 213

Figure I

Frequency distribution of swordfish genotypes in sampling regions used in this

study. Sampling areas were: I, Pacific Ocean (PAC); II, northwest Atlantic (NWA);

III, northeast Atlantic (NEA); IV, South Atlantic (SAT); and V, Mediterranean

(MED). The frequency of three major families of mtDNA lineages are represented in

the pie charts as follows: alpha, light grey; beta, dark gl"ey; and theta (clade II), black.

node is short and it is supported by only one fixed

difference, a transition from adenine to guanine at

nucleotide position 127. Some of the lineages in this

group share an additional transition from cytosine to

thymine at nucleotide position 133, whereas others share

a transversion change from cytosine to guanine at nucleotide position 180.

Most Pacific genotypes (97%) emerged from the basal

branches of clade 1. However, some Mediterranean and

Atlantic lineages emerged from these basal branches as

well. Thus clade I appears to consist of two families of

haplotypes: one which is ubiquitous and another which

consists primarily of Atlantic and Mediterranean

samples. The presence of two differentially distributed

groups oflineages is consistent with the phylogeographic

patterns described for the highly divergent mtDNA lineages of both blue marlin and sailfish in the Atlantic

and Indo-Pacific Oceans (Graves and McDowell, 1995).

The present asymmetric distribution of mtDNA types

for these two species represents the differential migration of females from the Indo-Pacific into the Atlantic.

A similar uni-directional migration oflineages may have

taken place in swordfish. There is evidence that substantial east-west gene flow has taken place in the North

Pacific (Grijalva-Chon et aI., 1994; but see GrijalvaChon et aI., 1996). In the absence of barriers, movement from the Indian Ocean to the South Atlantic may

be occurring at the present time.

Identification of Nuclear DNA Markers __

Nuclear DNA markers can provide information that

cannot be obtained from the analysis of mtDNA. For

population studies, assays of nuclear markers must be

easy to perform and adaptable for use with large numbers of samples. To meet these criteria, we developed

assays based on PCR amplification of sample DNA,

followed by an RFLP analysis. We used two approaches

in the development of these assays, the analysis of DNA

regions containing microsatellites, and the development of PCR primers based on the DNA sequences of

known genes. Both approaches allowed us to identify

intraspecific variation that can be easily surveyed In

large samples.

Microsatellite regions generally vary in size due to

differences in the number of repeat units in the

microsatellite sequence (Beckman and Weber, 1992).

These differences can be observed by analyzing the

products of PCR amplification on a DNA sequencing

gel. However, these gels are cumbersome and require

the use of radioactivity or a fluorescent marker to detect the variable DNA bands. To provide a simpler

assay, we screened PCR products for the presence of

restriction-site polymorph isms. We reasoned that

stretches of DNA containing microsatellite sequences

were likely to contain other variation as well. For striped

bass, Marone saxatilis, we found that in two of three cases
214 NOAA Technical Report NMFS 142

A

26(MED,NEA,NWA)

,--t-- 34 (SAT)

35(MED)

36(MED)

,--H----- 37 <NWA)

14<NWA)

38<NWA)

17<NWA) L- 22(MED,NEA,SAT)

.---- 3ca <NEA)

0---- 6 (SAT)

.---------- 8 (SAT)

16(NWA)

13(NWA)

39(MED)

'----- 4ca (MED)

99%

I

------1===~:;;~~~- 41 (NWA ) I 43<PAC)

'---- 9(NEA,NWA)

1ca(NWA)

12(NEA,NWA)

42(NWA)

23<NEA)

r-. -i1_~32=--:.<S=-A~T ) I - 49(PAC)

.------i---:-:::-:-~.5 (PAC) 18<NWA)

5r<l<PAC)

.-------- 51 <PAC)

52<MED)

21<MED,NEA,SAT)

'------------- 53 <MED)

,-------- 31 <NEA, PAC)

'------- 48 (PAC)

15<NWA)

---e::=c 27<NWA,SAT)

7<NEA)

54<NWA)

-jr------ 55(NWA)

'-.----- 56 <PAC)

,----- 4<PAC)

57<PAC)

l(PAC)

58<PAC)

'------- 59 (PAC)

6ca(NWA)

,------ 61 <PAC)

62<PAC)

46<PAC)

,--- 3<PAC)

- 47<PAC)

28<SAT)

.------ 2(PAC)

29(NWA)

33<SAT)

1 44 <PAC) . 45<PAC)

"

II

99%

'"

.----------1 24 (NEA ) 25(NEA)

11(NWA)

'----------- 64 <NWA )

19(MED,NEA)

2ca(MED)

Figure 2

Neighbor joining tree calculated from Tamura-1'\"ei distances (modified from Alvarado Bremer

et a\., 1995b) using the computer program MEGA (Kumar et a\., 1993). Numbers on the tips of

the branches correspond to the swordfish mtD!"A haplotypes defined by Alvarado Bremer et a\.

(1995b). They are followed by a list of areas where this genotype was found (PAC = Pacific

Ocean; NEA = northeast Atlantic; NWA = northwest Atlantic; SAT = South Atlantic; MED =

Mediterranean). Branch lengths are proportional to genetic distances. The branches separating

clades I and II are supported by confidenct probability (CP) values >99%. The length of branch

A was supported by CP values of 97% using Kimura 2-parameter distances (Kimura, 1980).
____ Alvarado Bremer et al.: Mitochondrial and Nuclear DNA Analyses in the Study of Population Structure 215

Table 2

Growth hormone cDNA sequence sources. Consensus primers: GH-U24 5'ACCARCGNCTSTTCWMCATCGCNGT3' (forward); GH-U25 5'ACCTTGTGCATGTCCTTCTTGAAGCA3' (reverse).

examined, a polymorphic

restriction site was located

within the amplified region.

We therefore assayed population samples by digesting

PCR products with the appropriate restriction enzyme and examining the resulting bands by ethidium

bromide staining after agarose gel electrophoresis.

Preliminary results with

striped bass from South

Carolina rivers indicate that

allele frequencies at one of

these loci differ in samples

from different rivers. This

approach is currently being

applied to clones containing swordfish nuclear DNA.

Accession number

(CenBank/EMBL)

K03050

MI9999

M22731

M22732

S54890

S78253

X06735

X06962

X13670

X14305

X15055

X60475

Fish species

Oncorhynchus keta

Oncorhynchus kisutch

Oncorhynchus mykiss CHI

Oncorhynchus mykiss CH2

Spants aurata

Morone saxatilis

Thunnus thynnus

Pagrus major

Cyprin us carpio

Salmo salar

Paralichthys olivaceus

Hypophthalmichthys molil1ix

Sequence length

(base pairs)

1,120

1,201

1,171

1,212

958

928

911

906

1,158

1,169

831

1,170

Fish Growth Hormone Primers

A second successful strategy for developing nuclear

DNA markers is to design primers for PCR amplification based on the DNA sequences of known genes. We

designed primers based on published sequences of the

growth hormone (GH) genes of several fish species

(Table 2). The growth hormone gene was chosen because the coding portions of the gene (exons) are

highly conserved through a wide range of fish species.

However, interspecific comparisons reveal that exons

are flanked by introns ofvariable length and number. It

is in these non-coding portions of the gene that intraspecific variation is most likely to be found. We compared the nucleotide sequences of GH genes from 11

fish species (Table 2) to determine a consensus sequence, which was then used to design primers capable

of amplifying fish GH genes. We used these primers

successfully to amplify the GH gene from both striped

bass and swordfish nuclear DNA. Subsequent analyses

have revealed a restriction-site polymorphism which

can be used to discriminate striped bass from other

species of Morone. Experiments are underway to determine whether a restriction-site polymorphism can be

identified for swordfish.

Summary _

We have shown that nucleotide sequence analysis of the

D-Ioop region of mtDNA can be used to characterize

genetic variation in swordfish. A phylogenetic analysis

of the resulting haplotypes demonstrated that the distribution of mtDNA lineages differs among swordfish

populations from the Pacific Ocean, Atlantic Ocean,

and Mediterranean Sea. We also developed PCR-based

RFLP assays that can be used to examine the distribution of alleles of nuclear genes among fish populations.

Acknowledgments _

This work was supported by FISHTEC Grant R/FT-Ib

and is FISHTEC Contribution umber 95-5. We thank

Iman Naseri for expert technical assistance. John M.

Dean of USC gave us invaluable advice with regards to

sampling. We thank the members of the Bluewater

Fishermen's Association and the National Marine Fisheries Service (NMFS) Southeast Fisheries Science Center for help in providing samples of Atlantic swordfish;

Tony Geisman for help in providing Pacific swordfish

samples; and]. M. de la Serna, Blanca Garcia, Manuel

Quintans, and in particular Jaime Mejuto from the

Instituto Espanol de Oceanografia (lEO) and Gregorio

De Metrio from the University of Bari for help in obtaining northeast Atlantic, South Atlantic, and Mediterranean swordfish.

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Appendix: Procedures

Universal Mitochondrial Primers

The universal primer set for the ATPase 6 gene that we

used for amplification and sequencing was designed by

Oliver Haddrath of the Royal Ontario Museum, using

as reference the salmonid ATPase 6 sequence in Thomas and Beckenbach (1989) and the published mitochondrial sequences of chicken and frog. The set consists of the light-strand primer Al (5'ATG AAC CTA

AGC TTC TIC GAC CAA TI-3') and a heavy-strand

primer A2 (5'ATA AAA AGG CTA ATT GTT TCG AT3'), beginning at positions 9240 and 9673, respectively,

of the chicken mitochondrial genome.

Double-stranded amplification reactions were carried

out in 25-,u1 volumes containing 67 mM Tris-HCl (pH

8.8), 50 mM KCI, 1.5-2.0 mM MgCI2, 10 mM

mercaptoethanol, 0.1 % Triton l X-I00, 1 unit of Taq

polymerase, 200,uM of each dNTP, and 8 picomoles of

each primer. The template was 1 ,ul of purified mtDNA

1 References to trade names or commercial firms do not imply

endorsement by the National Marine Fisheries Service, NOAA.
____ Alvarado Bremer et aI.: Mitochondrial and Nuclear DNA Analyses in the Study of Population Structure 217

or total DNA extractions. The reactions were subject to

38 cycles of the following temperature profile: 93°C for

45 sec, 50°C for 45 sec, and 72°C for 90 sec, in a thermal

cycler (Perkin-Elmer/Cetus). The amplified product

was visualized with a UV transilluminator; approximately

1 III of a gel region containing amplified DNA was

collected and dissolved in 1 ml of sterile deionized

water heated at 55°C for 5 min. Exactly 1 III of this

solution was used as a template for single-strand amplification in a 100 III volume containing the same reactants as double-strand amplification, but reducing the

concentration of one primer by 100 times. The cycling

profile was the same as in the double-stranded amplification, with the exception that the annealing temperature was increased to 52°C. Single-stranded amplified

product was purified by selective isopropanol precipitation (Sambrook et aI., 1989). Sequencing of singlestranded DNA was done using a Sequenase kit (United

States Biochemical).

Control Region Primers2

Two swordfish-specific primers were designed: L15998-

PRO (5'-TAC CCC AAA CTC CCA AAG CTA-3') and

H00585-PHE (5'-CAG TGT TAA GCT TTA ACT AAG

CT-3'), placed in the tRNApro and tR Aphe, respectively. PCR amplifications using this primer set were

carried out in 25-111 reactions subjected to 35-38 cycles

of 93°C for 1 min, 52°C for 1 min, 72° for 90 sec, and a

final extension at noc for 5 min. The primer H235 (5'-

CGT GTG CAC TCT GAA ATG TCA-3') was used with

Ll5998 to amplify a fragment approximately 545 bp

2 Alvarado Bremer (1994).

long which included the left domain and most of the

central domain. Similarly, the primer L318 (5'-GTC

ATT GAA GGT GAG GGA CA-3') was used with the

oligonucleotide H00585 to amplify a 510-bp fragment

corresponding to the central and right domains. Because the amplified products overlapped, the complete

sequence of the central domain was obtained in both

directions for five specimens that had extremely divergent profiles for the left and right domains. A fifth

(heavy) primer, CSBDH (5'-TGA ATT AGG AAC CAG

ATG CCA G-3'), located in the conserved block D of the

central domain of the control region, was used in combination with primer Ll5998-PRO. This primer combination is universal and has been used successfully to

amplify a wide variety ofspecies offish genetic material.

The cycling profile began with an initial denaturing

step of 5 min at 94°C, followed by 34-36 cycles of

denaturing at 94°C for 45 sec, annealing at 55-59°C for

45 sec, and extension at noc for 1 min. The final

extension was at 72°C for 5 min.

Amplification of Growth Hormone Genes

PCR conditions were optimized with a PCR-Optimizer

kit (Invitrogen, Inc.). About 20 ng of uncut genomic

DNA was added to a Ix PCR mixture consisting of 60

mM Tris-HCl, pH 9.0; 2 mM MgCI 2; 0.5 ,uM of each

primer; 200 ,uM of each dNTP; and 1.25 units of

AmpliTaq DNA polymerase (Perkin Elmer). PCR amplification was carried out on a 50-,u1 aliquot, and consisted of initial denaturation for 6 min at 94°C followed

by 36 cycles in a thermal cycler (denaturation: 1 min at

94°C; annealing: 1 min at 57°C; extension: 3 min at

n°C), and a final incubation for 10 min at noc to

ensure maximum full-length product formation.

Protecting the Reproductive Value of Swordfish, Xiphias gladius,

and Other Billfishes

DAVIDW.AU

Southwest Fisheries Science Center

National Marine Fisheries Service, }\'OAA

P,O. Box 271

LaJolla, California 92038-027J

ABSTRACT

The intrinsic rate of population growth (r) and the reproductive value of females at

given age (v) are estimated for swordfish, Xiphias gladius, and other billfishes to determine

how protecting reproductive value affects population sustainability. The procedure used

involves the standard demographic equations and standard assumptions regarding densitydependent changes in vital rates from basic deterministic population dynamics. It appears

that to ensure population sustainability of swordfish and blue marlin, age at first capture

should be high enough to protect the first 1-2 mature age classes, but need not protect the

most reproductively valuable, older females. For striped marlin and sailfish, however, the

most valuable females may need protection.

Introduction

An argument frequently raised regarding the management of billfishes is that large, mature individuals, especially females, should be protected for their valuable

reproductive capability. That very large and fecund

females are valuable to their populations is intuitively

obvious, and especially so if they are scarce or solitary,

as adult billfishes usually are. In addition, female

billfishes grow rapidly to sizes that are larger than males

of the same age (see Boggs, 1989) and tend to be

outnumbered by males on the spawning grounds (Hopper, 1990); this suggests they constitute a particularly

valuable reproductive resource. Some protection of

these females would obviously be beneficial-but to

what extent?

The purpose of this paper is to estimate the reproductive value of billfish females to their populations,

using the demographic formulae of Lotka (1907) and

Fisher (1958). How a population's potential for increase is affected by protecting females below the most

reproductively valuable age will be examined. This involves first estimating the population's intrinsic rate of

increase when it is near the size that produces maximum sustainable yield, and then using that estimate to

determine reproductive value and the effects of protection. The focus will be on the commercially important

swordfish, Xiphias gladius, but the cases for blue marlin,

Makaira mazara, striped marlin, Tetrapturus audax, and

sailfish, Istiophorus platypterus, will also be evaluated for

perspective.

Classical demographic analyses are not much used in

studying the dynamics of fishes other than sharks (e.g.

Cailliet, 1992; Cailliet et aI., 1992; Cortes, 1995), because most teleosts have extremely low larval andjuvenile survival rates which are very difficult to measure.

Proposed survival schedules are therefore not very convincing for these fishes. However, the demographic

relationships allow this difficulty to be circumvented, as

will be shown.

Methods

Estimating Life History Parameters

Estimates of age at maturity (a), maximum age of reproduction (w), and instantaneous natural mortality

(M) are basic for a demographic analysis. These parameters were estimated from the biological characteristics

of billfishes taken in the eastern Pacific. Age at 50%

maturity (a) was estimated as the age at which a species' gonad index increased rapidly to values greater

than 3 (see Eldridge and Wares, 1974; Miyabe and

219
It states that recruitment into a population must come

from offspring, with contributions from older females

discounted at rate r relative to those from younger

females because they have less time to contribute to

population growth. In terms ofsurvival to maturity (La)'

lx equals la(l/la) = lae-M(x-a) for x ~a. Thus Equation (1)

becomes

density-dependent compensation occurs in a population as a response to reduction by fishing. Lotka's equation (more correctly, the Euler-Lotka equation) expresses the fundamental relation between survival from

birth to age x (i.e. l), mx

' a, and w, and rate of population growth, r, of a stable-aged population. The term

stable-aged means that all population segments (e.g.

age classes) are growing at the same rate, the abundance ratio of anyone segment relative to another

remaining the same. Lotka's equation may be written

(e.g. Stearns, 1992, Chapter 2, p. 20-38)

220 NOAA Technical Report NMFS 142

Bayliff, 1987; Nakano and Bayliff, 1992). Maximum reproductive age (w) was obtained from converting maximum sizes observed historically in the longline fisheries

(Shingu et aI., 1974; Miyabe and Bayliff, 1987; akano

and Bayliff, 1992) to age (von Bertanlanffy growth parameters as listed by Boggs, 1989; Table 1). Maximum age :v is

difficult to estimate from growth relationships without

underestimation, and very old fish are expected to be

rare, especially in an exploited population; therefore ~he

calculated maximum ages were arbitral;ly increased by

10% to estimate unexploited w for this analysis. Natural

mortality was obtained from this age, w, using Hoenig's

(1983) relationship for fishes (In M = 1.46 - 1.01 In w).

To estimate fecundi ty (m), size at age was converted

to weight at age using length-weight relationships as

given by Kume andJoseph (1969) for swordfish and by

Wares and Sakagawa (1974) for the other billfishes.

Fecundity-weight relationships are best known for

swordfish (106 advanced mode ova = 2.725 + 0.015 * adult weight in kg; Uchiyama and Shomura, 1974); that

relationship, which is nearly identical to one reported

for sailfish (Eldridge and Wares, 1974), was used for all

species considered here. There is no quantitative information on batch frequency of spawning among the

billfishes. The final fecundities calculated were divided

by 2 to obtain age-specific estimates of female newborn

per adult female, i.e. mx

'

w

L,lxe-Ixmx = 1.0.

x==a

w

l -M(x-a) -IX = 1 0 a.L..Je e m x .

x=a

(1)

(2)

Estimating Intrinsic Rate of Increase

The intrinsic rate of population increase (r) is estimated here by incorporating the standard concept that

which can be solved for r if mx

' M, and la are known.

Our interest is finding nvhen the population is most

productive, i.e. at the size that produces maximum

sustainable yield (MSY). Theory and experience (e.g.

Shepherd, 1982; Kimura, 1988; Clark, 1991) suggest

Table 1

Growth and life history parameters of billfishes.

Species Sex2

Swordfish U

Blue marlin F

Striped marlin

Sailfish

Von Benanlanffy ~rowth Life history

parameters] parameters

L (em) K (yr-]) '0 (yr) ex5 (yr) w6 (yr) M 7 (yr-I )

309 0.124 -l.J fi9 5 20 0.21

4873.4 0.116 -0.161 4 II 0.38

275 0.264 4 9 0.47

232 0.472 3 8 0.53

] From Boggs (l989).

2 u = Unidentified/unreported sex; F = female. l.' ~rowth rate used for striped marlin because F growth rate did not accommodate the

largest size observed.

3 Corrected from value listed by Boggs (1989).

" After age 8. size at age was based on a freehand-drawn curve rather than predictions from ~rowth parameters. because the largest blue

marlin in the E. Pacific longline catch (332 cm) was much smaller than the reponed maximum size (about 389 cm).

5 Age at 50% maturity.

6 Maximum reproductive age.

7 Natural mortality derived from In M = 1.46 - 1.01 In w (Hoenig. 1983).
_______________ Au: Protecting the Reproductive Value of Swordfish and Other Billfishes 221

and similarly for S, (e.g. Caughley, 1977). Gathering

those terms and substituting Sx gives

It measures that female's relative contribution to future

population growth, again discounting for the lesser

effect that contributions made at older ages will have.

Equation (5) is more meaningfully expressed in terms

of the standing population, which is the abundance at

hand and the focus of fishermen's interest. Then vx

would be a measure of the reproductive output of ages

x and older in the population, normalized by the relative abundance at age x. The standing relative abundance of fish at each age x (designated S) in such a

population is

that MSY usually occurs in teleosts at population sizes

between 1/2 and 1/5 of initial biomass, usually closer

to the smaller fraction. A fishing mortality (F) with

values between M and 2M (total mortality Z = (F + M) =

2M to 3M) would reduce an exploited population to

approximately between 1/2 and 1/3 of its initial numerical size. In terms of biomass the reduction would

be greater (Beverton and Holt, 1957), though it may

not be if growth is density-dependent (Beverton I).

Therefore, this range of Fshould conservatively bracket

the MSY population size and will be used here for that

purpose.

With this fishing mortality emplaced, total reproductive output would be reduced and the population would

decline. If, however, the decline ends at a level that is

sustainable, there must be density-dependent compensation such that Equation (2) describing the smaller,

now stationary (r = 0) population is satisfied. Under

total mortality Z (= 2M or 3M) this compensation is

assumed here to result from an increase in the survival

of immature fish, to (say) survival la z.

Equation (2) then becomes, with 'r= 0, or

w

V x = l/Sx LS,m,

f=x

(6)

iii

la,Z L e-z(x-a)mx =1.0

x=a

(3)

ii'

V x = l/(SjSa)L(S,ISa)m,

I=x

(7)

I Beverton, R.J. H. 1994. Montana, Old Roman Rd., Langslone,

Gwenl, NP6 2]U, U.K. Personal commun.

The reproductive value (V) of a female at age x from a

stable-aged cohort can be written (Fisher, 1958)

from which la z can be estimated as the reciprocal of the

summation t~rm, given that the other parameters are

specified. Estimation of la z enables specification of the

particular adult survival s~hedule of a population at its

Z-reduced size. The actual, age-specific survival rates of

pre-adult fish need not be of concern.

If fishing mortality is removed (F = 0) and if I z a,

holds, this stationary population will begin growing,

eventually at a rate here designated rz. This is the rpotential at the MSY population size, and it is found by

iteratively solving for r

zfrom Equation (2), now written

i.e. reproductive value in terms of the standing abundance of age-a fish (Sa)' Values of Vx can be readily

calculated for any age X;::: a in a population with fishing

mortality removed, using the abundance ratio S/Sa =

(ljla) (e-I x/e-ra) = e-(M+,)(x-a) (and similarly for (S/Sa)' At

the MSYpopulation size, ris the rzestimated previously.

Evaluating Effects of Protection

Reproductive value in a population capable of increasing at rate r, and therefore with survival la (designated

la ) and relative abundance S at age a (S = I ('-Ia), " a,1 a,l a,1

can be protected to ensure that the population's rate of

increase remains at least equal to r', where r' r. This

protection can be obtained by raising the age at first

capture to compensate for reduced r'. Lotka's equation

would still remain satisfied, but now by the reproductive output from the protected ages alone. Operationally, a certain r' is assumed, and then the age to which

protection needs to be extended (x,,) for obtaining that

r' is found.

To determine this age (x,,) for an r'less than or equal

to a given r, survivalla,I must first be determined. From

Equation (5), reproductive value at age 0 (vo) equals

1.0, because its expression is then equivalent to Lotka's

equation (since 10 = 1.0). Also So = 1.0, from Equation

(6). Thus, using Equation (7), va becomes

(5)

(4)

w

-I(t-x)(l / I ) vxL.".e , x m,.

I=x

x=a

w

I -M(x-a) -rzx - 1 0 a,ZL.".e e mx - ..

Estimating Reproductive Value
222 NOAA Technical Report NMFS 142

Table 2

Fecundity (m) schedules, in 106 female newborn per

adult female at each age x, for four species of billfish

From age-length relationships calculated by von

Bertanlanffy equations (see Boggs, 1989). Length-·

Weight relationship for swordfish is log W = -4.675 +

2.961 log L (Kume and Joseph,] 969). L-W for other

billfishes as described by Wares and Sakagawa (1974).

Fecundity-weight relationship as per l'chiyama and

Shomura (1974): 106 advanced-mode ova = 2.725 + 0.015

kg adult weight; mx is the final fecundity divided by 2.

Age Swordfish

Blue

marlin

Striped

marlin Sailfish

Table 3

Estimates of intrinsic rate of increase (rz) for several

species of billfishes. lo.z is survival to maturity at age a,

where Z = 2M or 3M (to bracket the mortality level at

which MSY likely occurs); r 2M and r]M are the correspondi ng r estimates.

ex w M {"2M la,3M r

2M '3M

Species (yr) (yr) (yr-I ) (x 10-6) (x 10-6) (yr-I) (yr- 1)

Swordfish 5 20 0.21 0.142 0.201 0.076 0.118

Blue marlin 4 11 0.38 0.216 0.298 0.104 0.159

Striped marlin 4 9 0.47 0.306 0.388 0.090 0.135

Sailfish 3 8 0.53 0.385 0.472 0.107 0.158

and Sa I can now be found as the reciprocal of the above

summ~tion term. Finally, L is found from Sa using a,1 ,r

Equation (6).

With La.r determined, and additionally assuming that

r'is to be ensured, va or Lotka's equation (Equation 8)

is written

'" =s '" -(,W+,)(t-a) =10 a.r£..Je m/.

/=a

x,

S '" -(.\1+I')(/-a) =1 0 a,I' £..Je m/,

I=a

'" Vo = Sa" I (S//Sa )m/

/=a

Values for survival to maturity which bracket the likely

range for the MSY condition, i.e. La,z with Z = 2M or 3M

from Equation (3), are listed in Table 3 along with the

resulting r estimates. The latter, which are the rz from

Equation (4) using the La z survival values, are 0.08-

0.12, 0.10-0.16, 0.09-0.14', and 0.11-0,16 per yr for

swordfish, blue marlin, striped marlin, and sailfish respectively. These ranges correspond to the Z = 2M and

Z= 3M estimates. An example of this computation for r,

as well as for reproductive value and age to protect

(described next), is given in Table 4.

Results

Life History Parameters

Intrinsic Rate of Increase (r)

Age at maturity ex was estimated as 5, 4, 4, and 3 yr and

maximum reproductive age was 20, 11,9, and 8 yr for

swordfish, blue marlin, striped marlin, and sailfish respectively (Table 1). The natural mortality M estimates were

0.21, 0.38, 0.47, and 0.53 respectively for these same

billfishes. Fecundity mx estimates are as listed in Table 2.

If all fish are taken above age xr" the population would

still increase at rate r' since Lotka's equation is still satisfied for rate r'; if no fish are taken (all ages are protected)

the population would increase at its native rate r, which is

here estimated by rz: In the analysis to follow, r' is set to

zero to investigate the protection needed to ensure that

the population is at least stationary at the MSY level.

(9)

(8)

1.67

1.74

1.80

Ul2

1.85

1.87

1.89

2.07

2.24

2.38

2.50

2.60

2.07

2.49

2.99

3.50

4.01

4.54

5.01

5.42

2.04

2.24

2.45

2.65

2.89

3.0'1

3.24

3.41

3.58

3.72.

3.86

3.99

4.11

4.22

4.31

4.40

o

I

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

where S ,= L e-I'a and x ' is the upper summation age a," OJ'" ...

to be found that satisfies the equation. The condition

described is thus that of a population capable of increasing at rate rbut now increasing at rate r'.

Reproductive Value (vxl

The above estimates of rsuggest that it would be useful

to examine reproductive value for populations at the
Au: Protecting the Reproductive Value of Swordfish and Other Billfishes 223

MSY size that are assumed to have native

rates of r in the range of the values estimated. Accordingly, V x was calculated from

Equation (7) with r = 0.07-0.13 for swordfish, and wi th r = 0.08-0.16 for the other

billfishes.

The resulting reproductive value curves

for billfishes peak at the age of maturity ex or

later, as Vx curves always do. But the age of

maximum V x is much larger than ex if fecundity increases greatly with further age, as with

the long-lived swordfish, and also blue marlin. The Vx curves begin with a value of 1.0 at

age 0 (vo = 1.0 as previously explained) and

end at zero after age w. They are shown only

after age ex in Figure 1. Among the billfish

species, the high-fecundity swordfish has the

highest levels of vx' and sailfish the lowest.

Within any species, V x is seen to be reduced

and to peak later as r increases. This is because increased r means higher survival to

maturity, and this depreciates vxand slows its

rise with age. The correct V x curve for a species may be considered as lying approximately

midway between the curves depicted.

Protection Age

15

10 (!)

o

x

.;

5

0

0

10

8

(!) 6 0

x

.; 4

2

0

0

0.07

0.13

5

2 4 6 8

20

10 12

25

14

Figure 1

Intersection of proteetion age (xo) curves (dashed) with reproductive value (v) curves (solid). Each Vx curve is for the specified

assumed level of population, r. The Xo curves specify the ag-e at first

capture that would ensure the r= 0 condition (population at least

stationary). Note the chang-e ofscales in comparing swordfish with

the other billfishes.

The ages (x,,) up to which protection would

ensure an r' rate of increase (from Eq. 9)

are shown in Figure 1 by the ages at which

dashed Xo lines cross appropriate V x curves

(here, r' = 0, so x,. = Xo for ensuring a justsustainable population). Thus the protection

age or age at first capture is 7-8 yr for swordfish, considerably short of the peak Vx age at

13-14 yr. But for the shorter-lived, apparently higher-r sailfish, Xo is between 4 and 5

yr, approximately the same age that gives

peak vx'

Discussion

Strictly speaking, the demographic analyses presented

here pertain to populations that have become stableaged, although any real population probably never

achieves that state. Even so, the demographic approach

is useful, because Lotka's equation captures robust features of demography and thus predicts long-term, underlying effects that are at least qualitatively correct

(Stearns, 1992, chapter 2, p. 20-38). Vandermeer

(1968), who also derived Equation (7) through a more

involved argument, concluded the same. In defense of

AGE (years)

the demographic approach in fisheries work, it is worth

noting that Murphy's (1967) sardine study is one of the

better known demographic analyses in the ecological

literature.

Reproductive value (v) and its protection is naturally of interest in conservation considerations. Fisher

(1958) first noted in 1930 that natural selection acts

through vx

' and reproductive value has since been the

subject of numerous discussions of long-term evolutionary dynamics, e.g. Goodman's (1982) explanation

of how optimal life histories maximize vx

' In terms of

reproductive value, an optimal predator or fishery

should avoid or protect the most valuable V x ages and

harvest mainly juveniles (MacArthur 1960), notwithstanding the loss from taking individuals hefore they
224 NOAA Technical Report NMFS 142

Table 4

Example of a computation to determine r, ux' and age to protect, x," for swordfish when total mortality Z equals 2M.

Swordfish population parameters are a =5 yr, w =20 yr, M =0.21 /vr, and Z=2M =0.42/yr.

Determining x" for

Determining r Determining v, when r= 0.07 r' = 0 when r = 0.07 10

x I m v

(yr) Via (x 10-6) (X 106) SjSa (S/Sa)m, (X {06) 5.JSa la(Sx ISa)11Ix Cumul

(I) (2) (3) (4) (5) (X )06) I(S,ISa)mx (6) (7) (8) (9)

5 1.0000 0.1420 2.04 1.0000 2.0400 10.5500 10.5500 1.0000 0.2744 0.2744

6 0.6570 0.1151 2.24 0.7558 1.6930 8.5100 11.2596 0.8106 0.2442 0.5186

7 0.4320 0.0933 2.45 0.5712 1.3994 6.8170 11.9345 0.6570 0.2165 0.7351

8 0.2840 0.0756 2.65 0.4317 1.1440 5.4176 12.5495 0.5326 0.1898 0.9249

9 0.1860 0.0613 2.86 0.3263 0.9332 4.273b 13.0971 0.43] 7 0.1661 1.0900

19

20

0.0028

0.00]8

0.0061

0.0000

4.31

4.40

0.019H

0.0150

0.0853

0.0660

0.15J3

0.0660

7.6414

4.4000

0.0529

0.0429

0.0207

0.0254

I Age in years.

2 Relative survival is IJ la = e -llx- aJ.

:1 Survival to age x is I, = la{lJ la)' where (from Equation 3) la = I/I(l/ la) m, = J17.0425 = 0.1420 x 10-6

" Fecunditv at age x.

5 Relative standing abundance at age x =SJ Sa =e-(M + »(,- a), where r = 0.07 (from the estimate of r = 0.0763 in note 10).

6 Reproductive value at age x. v, = II (SjSa) I(S,ISa) 111, = rrevious column lcolumn 5 = I~0(5jSa) 11Ix I (SjSa) (see Equation 7).

7 Relative standing abundance at age x when r' =0 is S, I Sa = r(M + ,'J (" - a) = e-'\/( ,- a).

These are the terms of Equation 9 when r= 0.07 and .,-' = 0, for then (from Equation 6) Sa." = la" = Salr"a where Sa = 1/10.550 (from

Equation 8) and r,a= r O.7(:,). Thus la., (here designated i

a ) = 0.1345 X 10-6

9 Cumulative sum of previous column from age 5 to age x, according to Equation 9.

JO Summing from x = 5 to 20 yr, Il,m, = 1.9884; Ixl,m, = 18.9736; I (l./Ia)m, =7.0425; I(SJSa) In, = 10.5550.

Generation length T = Ixl,In,/Il,m, = 18.9736/1.!J884 = 9.5420 vr. Thus r = (In II,m)1 T = (In 1.9884)19.5420 = 0.0720/yr. Or, .,- =

0.0763/yr by iterative solution of Lotka's equation (Eq. 1).

The age x,. to which protection must be extended to ensure r' = 0 is given in the lasl column ("Cumul") where the cumulative sum becomes

1.0 (see Equation 9). This occurs at an interpolated age ofS.4 yr (or 8.9 yr if column values are considered to occur at midpoints of age).

have realized most of their growth. For a given population r, reproductive value at any age is proportional to

fecundity and inversely proportional to survival. Thus

the few surviving large adult billfishes acquire high vx'

The approach used here is simple and essentially

requires solution of Lotka's equation, which is equivalent to finding the dominant eigenvalue of a

population's Leslie matrix. The assumptions employed

are from ordinary, deterministic population dynamics.

Even the assumption that all compensation effects are

through increases in la and that mx is unchanged is not

unusual, for any actual 1nx changes can be considered as

manifested through changes in la' Such la-compensation has been demonstrated in groundfish populations

(Myers and Cadigan, 1993) and is implicit in consta:ltrecruitment fishery models.

Accuracy of the Vx estimates presented here depend

strongly upon the accuracy of the rand 1nx estimates. The

former is most sensitive to the estimates of age Ct, which, as

here, must at least appear reasonable in terms ofother life

history parameters. More problematical are the 1nx schedules, which are derived from rather sketchy information.

There can be little doubt, however, that fecundity increases rapidly ""ith age in the fast-growing swordfish and

blue marlin, thus setting those two species apart.

This analysis shows that the age to which protection

should be extended to ensure a population is at least

stationary (r' = 0) is much lower than the age of maximum v, in the reproductively more valuable, longerlived swordfish, more so than in the other species,

especially striped marlin and sailfish. Protecting swordfish lip to age xr' = Xo would therefore exclude protection for the most valuable vxages (valuable for enabling

an r rate of increase), but without endangering the

population. On the other hand, the protection ages for

striped marlin and sailfish do include the peak V x ages,

so those ages are needed to ensure that their populations remain sustainable. Of course if the objective

were to ensure a condition of r' > 0, e.g. to allow stock

rebuilding, then the xr' lines would cross the Vx curves to

the right of the lines shown in Figure 1, i.e. the protection ages (ages at first capture) would have to increase.

The demographic analysis here is more fundamental

than the similar spawning-stock biomass per recruit

(SSB/R) analysis (see Gabriel et aI., 1989). Both derive

from the same population theory. SSB/R can be used
Au: Protecting the Reproductive Value of Swordfish and Other Billfishes 225

to determine whether present recruitment or survival

to recruitment is adequate for stock rebuilding, although

the findings can only be as definite as the stock-recruitment (5-R) relationship employed. That S-R relationship can be provided by demographic analysis by using

an estimate ofthe rate ofincrease at the population size

that produces MSY (i.e. rz with Z= 2M or 3M), as in this

study. Noting that any such population that is stableaged, as well as any of its segments, has potential to

grow at annual rate e'z - 1, it is in principle only necessary to find an S-R curve that describes an MSY exploitation rate equal to that annual rate. Ifrecruitment (R) is

defined as recruits to age at maturity a, (i.e. Ra ), then

this S-Ra relationship will determine the stock size produced by any mortality Z (and the converse), as established by the point on that S-Ra curve where the Ra:S

survival diagonal with slope equal to fa z (from Eq. 3)

crosses that curve. '

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populations. Math. Biosci. 59:77-93.

Shingu, C., P. K. Tomlinson, and C. L. Peterson.

1974. A review of the japanese longline fishery for tunas and

billfishes in the eastern Pacific Ocean, 1967-1970. Inter-Am.

Trop. Tuna Comm. Bull. 16(2):65-230 (in Engl. and Span.).

Stearns, S. C.

1992. The evolution of life histories. Oxford Univ. Press,

New York.

Uchiyama,J. H., and R. S. Shomura.

1974. Maturation and fecundity of swordfish from Hawaiian

waters. In R. S. Shomura and F. Williams (eds.), Proceedings

ofthe international billfish symposium. Part 2, p. 142-148. U.S.

Dep. Commer., NOAA Tech. Rep. MFS SSRF-675.

Vandermeer,J. H.

1968. Reproductive value in a population of arbitrary age

distribution. Am. Nat. 102(928):586-589.

Wares, P. G., and G. T. Sakagawa.

1974. Some morphometrics of billfishes from the eastern Pacific

Ocean. InR. S. Shomura and F. Williams (eds.), Proceedings

of the international billfish symposium. Pan 2, p. 107-120.

U.S. Dep. Cammer., NOAA Tech. Rep. MFS SSRF-675.

Report Generation and Data Display from the NMT Archival Tag

MICHAEL BARTHELOW,* PHILIP EKSTROM, and STA MOBERLY

Northwest Ma'rine Technology, Incorporated

PO, Box 427

Ben Nevis Road

Shaw Island, Washington 98286

ABSTRACT

The Northwest Marine Technologyl ( MT) Archival Tag promises to provide researchers with fisheries data never before obtainable, Implanted in a large pelagic fish such

as a tuna or swordfish, the tag records depth, internal and external temperature, and light

intensity every two minutes for up to 10-12 yr.

The tag employs three separate logs: a time series log, which stores measurements every

128 sec., a day log containing daily summaries, and a histogram log which records a tally of

the number of times each possible value was measured in each data channel. While the time

series log may overflow on a long mission, resulting in lost data, the day log and histogram

logs cannot overflow, and will preserve information from the time the tag was initialized,

Software supplied with the kit runs under MS-DOS on an IBM-compatible personal

computer, and allows the user to communicate with the tag and read its data, Software

currently under development allows the user to browse a graphical representation of the

Archival Tag data, zooming in and out on the details, and print, save to disk, and export the

graphs to other WindowTM applications,

Introduction

Tag Description

The Northwest Marine Technology! (NMT) Archival

Tag is designed to be attached to or implanted in a

large pelagic fish such as a tuna or swordfish to determine and record its position and key environmental

variables every day for a period of years, When recovered and interrogated it will yield position data along

with statistical summaries of all data measured and a

detailed time series record of a portion of the mission,

The tag is housed in a stainless steel cylinder 16 mm

in diameter and 100 mm long (Fig, 1), A thin, flexible

measurement stalk 2 mm in diameter (stalk length can

be customized but is nominally 200 mm) is attached to

one end; when the tag is implanted the stalk extends

through the skin of the animal to trail in the water. The

end of the stalk houses a light sensor and a sensor for

external temperature. A pressure sensor and a sensor

for internal temperature are in the body of the tag,

The tag makes direct measurements of temperature

internal and external to the fish, pressure, and narrowband blue-green light intensity, As first proposed by

NMT in 1987, the tag perfoms onboard data processing

to reduce memory requirements, Depth is inferred from

pressure, Temperatures at standard depths are interpolated, A measure of water clarity is computed from

depth, light intensity, and time of day; the tag utilizes

water clarity and depth data to extrapolate to noontime

light intensity at the surface. Times of sunrise and sunset are inferred from light intensity as corrected for

depth, and used to determine longitude; latitude is

determined from sea temperature at standard depths

(Smith and Goodman, 1986).

Temperature measurements, light intensity, and

depth are recorded in a "time series log" every 128 sec.

The tag extracts from each day's data, and records in a

* Present address: 1337 Port Stanley Rd" Lopez Is" WA 98261.

I Reference to trade names or commercial firms does not imply

endorsement by the National Marine Fisheries Service, OAA,

227
228 NOAA Technical Report NMFS 142

+G'---- ~'F= I. 100 mil' .1

Figure I

The NMT archival tag.

"day log," the comparatively small amount of information required to fix position, plus some additional diagnostic information. The day log is compact enough so

that it can log every day of a multi-year mission and

never lose data for lack of memory space.

Either NMT or the user can handle the tasks ofinitially

setting parameters and of reading data from a recovered

tag. Host software running on an IBM-eompatible personal computer communicates with the tag through an

adapter to do either task. The data file from a recovered

tag is initially in compact binary form, maximum size

257 Kbytes, which is easy to handle and store. A second

program translates the compact data record into a set of

printable reports. A third program (under development)

provides graphical display of the data for easy browsing,

and generates various kinds of graphical output.

Data Logs

Day Log

The day log is the primary position record, and holds a

12-byte entry for each day of a mission. Primary quantities recorded are the times of sunrise and sunset, and

the temperatures at the surface and at 61 m (200 ft)

and 122 m (400 ft) depth. These standard depths can

be changed as a user option. The record also contains

some engineering information and a cross-reference to

the day's data in the time series log. Seven years' worth

of storage space is allocated to the primary day log.

Even after this initial log space fills up, no day log

entries are lost. Instead the log is expanded into space

otherwise used for time series records, converting time

series log into day log. This overwrites 1.6 days (1,100

records) of the oldest time series for every additional

year of mission beyond 7 yr.

Histogram Log

The most compact data summary is a set of histograms

which tally the number of occurrences of every possible

data value in each measurement channel. These tallies

include all measurements taken since the tag was initialized. For example, the histograms can provide information on the extreme values of depth and temperature ever measured and on the fraction of time the

animal spent, say, below 250 m depth.

Time Series Log

The remaining memory, 215 Kbytes, is devoted to a

time series log containing 4-byte records of raw data.

The user may specify the rate at which data are recorded by setting the time series log interval (N). Measurements are always taken every 128 seconds, 675 times

per day; the user can choose to record one out of every N

of these measurements. For example, if he chooses to

record every seventh measurement (N= 7), a new record

will be added about every 15 minutes.

The time series log has two parts. Section A fills up

with the first data measured and does not change thereafter. Next section B fills up, but when it is full, new

data begin to overwrite the oldest data in that section.

Thus the time series log preserves the very first data measured, and the last data measured. The user may choose

how much of the available space to devote to each section.

Tag Communication Kit _

Tags arrive with the clock and all parameters set as

requested, and are ready to use. There is no way to turn

them off, so it is not possible to release an inactive tag.

NMT's Archival Tag Communication Kit contains the

necessary hardware and software to communicate with

the tag and read its data. The two software applications

supplied with the kit, HOST.EXE and READABLE.EXE,

run under MS-DOS on an IBM-compatible personal

computer. This communication kit has been successfully tested on a wide variety of computers, including

very old and slow machines.

Using HOST.EXE, the user may adjust the tag's parameters to customize its operation for the mission at

hand and to clear the logs just before the tag is released. When the tag is recovered at the end of a mis-
Barthelow et aI.: Report Generation and Data Display from the NMT Archival Tag 229

sion, HOST.EXE is used to download the stored data

from the tag into a compact data file.

The data download yields a compact binary file, size

257 Kbytes or less, intended for easy storage on the

floppy disk of the minimal portable computer which is

likely to be available in the field. READABLE.EXE is

used to translate the compact binary data into a set of

formatted text files which are easily printed or imported into any word processing program. The reports

contain control codes which allow the user to easily

write a custom program to read the reports from disk

and perform further processing of the data.

Graphical Display

A program called DATAPLOT, presently under development, displays the log contents graphically. This program runs under WindowsTM and allows the user to

browse through the three logs, zooming in on areas of

interest. Individual graphs can be printed directly or

saved as Windows metafiles for import into other Windows applications.

Summary _

The NMT archival tag is more than a simple data logger. It has sensors carefully adapted to solve the real

problems of fixing the position of pelagic fish. It performs data processing and keeps a day log which is

compact enough so that it never loses position information due to data overflow. Finally, it is part of a complete system of hardware and software which presents

data to the user in a convenient and ready-to-use form.

Literature Cited

Ekstrom, P.

1994. Archival tags: present and future. Paper presented at

45th annual tuna conference, Lake Arrowhead, California,

May 23-26.

Smith, P., and D. Goodman.

1986. Determining fish movements from an "archival tag":

precision of geographical positions made from a times series of swimming temperature and depth. U.S. Dep.

Commer., OAA Tech. Memo. NMFS-SWFC-60, 13 p.

Age Determination of Swordfish, Xiphias gladius L., from Waters off

Baja California, Mexico, Using Anal Fin Rays and Otoliths

REINA CASTRO-LONGORIA* and OSCAR SOSA-NISHIZAKI**

Centro de Investigaci6n Cientifica y de Educaci6n Superior de Ensenada (CISESE)

Apartado Postal 2732

Ensenada, Baja California

22800 Mexico

ABSTRACT

Age was estimated based on otolith (sagittae) microstructure and on cross sections of

the second ray from the first anal fin from 255 swordfish collected on board commercial

drift gill net vessels operating off Baja California during 1992 and 1993. We were able to

successfully analyze 47% of otoliths examined. Annular counts ranged from 204 to 1,329

assumed daily rings (0.55-3.64 yr). Ninety-two percent of the anal-fin second rays were

readable; estimated ages ranged from 0+ to 9+ for females and 0+ to 7+ for males. Based on

the ray sections, 2- and 3-yr-old fish of both sexes were most frequent. Otolith age and age

from second ray sections from the same fish (n=56) were highly similar for the first 2 yr

(86% and 77% respectively); in older fish, similarity was <60%. Based on our results, as well

as studies ofswordfish in other oceans, we highly recommend the use of cross sections of the

second ray from the first anal fin to determine ages of swordfish in the Pacific Ocean.

Introduction

The determination of age in fishes is crucial to understanding their population dynamics and the impact of

exploitation. Age-composition data provide fundamental insight into fish biology and stock productivity, and

allow the estimation of basic parameters for describing

growth, mortality rates, and recruitment.

Attempts at aging swordfish, Xiphias gladius, have been

made using several methods, including modal analysis

of length frequencies and examination of hard parts

such as vertebrae, otoliths, and dorsal and anal-fin ray!

sections (Yabe et aI., 1959; Berkeley and Houde, 1983;

Radtke and Hurley, 1983; Wilson and Dean, 1983; Prince

et aI., 1987; Megalofonou and De Metrio, 1989;

Tsimenides and Tserpes, 1989; Cavallaro et aI., 1990;

Megalofonou et aI., 1990a, b; Ehrhardt, 1992; Tserpes and

Tsimenides, 1995; Ehrhardt et aI. 2). However, discrepancies exist among the different methods used to study

growth and age (Ehrhardt, 1992).

• Present address: Departmento de Investigaciones Cientfficas y

Tecnol6gicas de la Universidad de Sonora, Rosales y Ninos Heroes

S/ , Hermosillo, Sonora, 83000 Mexico.

•• Mailing address: Ecologfa Marina, CICESE, P.O. Box 434844, San

Diego, CA 92]43.

Most swordfish age determination studies have dealt

with Atlantic populations. Berkeley and Houde (1983)

analyzed the age ofswordfish using anal-fin ray sections

and proposed that the observed annuli could be annual

marks. Radtke and Hurley (1983) analyzed the external

features of otoliths and proposed that superficial ridg-es

represented annual marks. Wilson and Dean (1983)

analyzed otolith (sagittae) microstructures that they

thought were daily rings and external features assumed

to be annual increments. They also analyzed anal-fin

ray sections from the same fishes, and found a good

agreement (91 %) between ages based on presumed

annual growth increments in sagittae and ages based

on annular bands on the fin ray sections. Prince et al.

(1987) intended to validate the accuracy of the fin ray

method for estimating swordfish age and growth, usingmarginal increment analysis, but their results did not

provide sufficien t evidence to validate the method.

Ehrhardt (1992) used previously-reported data and ap1 Several authors ha\'e used the term "fin spines." However, swordfish fins lack spines, going by the diagnostic features reported by

akamura (] 983, ]985).

2 Ehrhardt, N. M., R. Robins, and F. Arocha. ]995. On the age

and growth of the swordfish in the northwest Atlantic. Int. Comm.

Cons. Atl. Tunas Working Document SCRS/95/99, 23 p. ICCAT,

Estebanez Calderon 3, E-28020, Madrid, Spain.

231
232 NOAA Technical Report NMFS 142

plied statistically more robust protocols to test the seasonal formation of marginal increments in anal fin ray

sections. He found a significan t difference in growth of

marginal increments between seasons, with the maximum during summer, and concluded that rings in anal

fin rays indicate annual events. Ehrhardt et al. 2 validated the use of these annual marks in anal fin rays of

northwest Atlantic swordfish, using the same statistical

algorithm as Ehrhardt (1992) and newly-collected data.

Tserpes and Tsimenides (1995) analyzed swordfish

age and growth in the eastern Mediterranean using

anal-fin ray sections. Their marginal increment analysis

demonstrated that growth bands are deposited annually in fish 2-5 yr of age. However, they stated that these

results constituted only partial validation ofthe method,

which can not be considered successful until all reported ages of each population have been validated

(Beamish and McFarlane, 1983).

In the Pacific, only a few swordfish aging studies have

been done. Yabe et al. (1959) described the age composition and growth of swordfish caught in the western

Pacific, based on modal analysis of length frequencies.

Uchiyama et al. (1998) used hard parts, including rays

of the first dorsal and first anal fins, vertebrae, and

sagittae, for aging swordfish in the central north Pacific. They stated the necessity of validating the use of

annuli on rays, vertebrae, and sagittae, and daily growth

increments on sagittae.

In 1986, a swordfish drift gill net fishery commenced

in waters offBaja California, Mexico. Between 1988 and

1993 the landings averaged 535 metric tons (t) (Holts

and Sosa-Nishizaki, 1998). Due to the recent development of this fishery, it lacks a science-based management scheme. In order to produce the necessary information, a cooperative program was established in 1992

between the commercial drift gillnet fishermen and

scientists at CICESE. This study is part of that effort.

The objectives of this research were to use the internal morphology of sagittal otoliths to age swordfish

caught off Baja California, and to compare the results

with those from the analysis of growth bands in first

anal fin rays from the same fishes. Using these methods, we describe the age composition of the commercial fishery catch in the area.

Materials and Methods

Swordfish (n=366) were sampled on board commercial

drift gillnet vessels operating in waters off Baja California, Mexico (between 22°N, 109°W and 32°N, 118°W),

during 1992 (January-December) and 1993 (OctoberDecember). Postorbital eye-fork length (EFL) to the nearest centimeter was measured on board. Samples of heads

for otolith extraction (n=166), first anal fins for excision

of the second ray (n=255), and gonads for sex discrimination (n=255) were brought to the laboratory for analysis.

Semicircular canals were removed from the cranial

cavity and preserved in 95% ethanol. Complete otoliths

(right or left sagittae) were later removed from the

tissue, cleaned in 5.23% sodium hypochlorite (Wilson

and Dean, 1983), rinsed in distilled water, and dried in

an oven at 40°C for 24 hr. In 34 cases the heads did not

contain the inner ear organs, and the otoliths from 14

fish were lost due to handling, hence 118 sagittae were

recovered from the 166 fishes.

Weights of the sagittae were measured to the nearest

microgram using an electronic Mettler UM33 ultramicrobalance. Right and left sagittae mean weights were compared. The relationship between otolith weight and

EFL was described by a power function. All comparisons of data were performed with the Student's t test,

analysis of covariance, or analysis of variance, using a

significance level of ex = 0.05 for statistical inferences.

External morphology of a subsample of 10 sagittae

was examined with a scanning electron microscope

(SEM) using the method of Radtke and Hurley (1983).

Because the external surface of the rostrum of these

otoliths lacked the ridge formation reported in the

literature (Radtke, 1983; Radtke and Hurley, 1983), we

did not use this method of age determination.

The internal microstructure of the sagittae was examined by two methods. First, a subsample ofthree sagittae

were embedded in epoxy resin and sectioned in the

transverse plane on a Buehler Isomet saw (Wilson and

Dean, 1983). This method was also discarded because

of the difficulty in obtaining good otolith sections.

A second method was used following Laurs et al.

(1985). After cleaning and without further preparation, the otoliths were placed on a culture microslide

filled with immersion oil to improve transparency and

resolution and viewed through a compound microscope at magnifications of 100, 400 and 1000x, using

transmitted light. This treatment revealed marks similar to daily increments described in other species (Fig.

1). Counts of increments were made on either right or

left sagittae along the major axis of the rostrum, where

the definition ofincrements was best (ordinarily at 1000x).

The counting path was usually not linear, due to otolith

topography, and frequent refocusing was necessary.

One experienced reader counted increments twice

in a random subsample of otoliths (n=54) to assess

counting precision. The precision of age estimates was

calculated using the Index of Average Percent Error

(IAEP) (Beamish and Fournier, 1981).

To verify ages estimated from sagittal otoliths, assuming that the marks we counted represented daily incre3 Reference to trade names or commercial firms does not imply

endorsement by the National Marine Fisheries Serivce, NOAA.
Castro-Longoria & Sosa-Nishizaki: Age Determination of Swordfish Using Anal Fin Rays and Otoliths 233

Figure 1

Light micrograph of daily increments along the rostrum of an otolith (sagitta) of swordfish, Xiphias gladius, from Baja California, Mexico. Scale bar = 8 ~m.

ments, we compared them with ages estimated from

sections of the second ray of the first anal fin from the

same fish. The second ray was separated from the fin,

cleaned in hot water, and air dried. All cross sections

(about 1 mm thick) were cut with a Buehler Isomet saw

at a point which was 10% of the total ray length from

the condyle base to the tip of the ray, where growth

patterns were observed more clearly. Sections were read

by the two authors three times under a stereomicroscope at either 6 or 12x magnification, depending on

ray size, using transmitted light. A series of opaque and

hyaline annuli were observed (Fig. 2), as described by

Jolley (1977) and Berkeley and Houde (1983). The

light annulus (hyaline zone) was counted as an annual

mark (jolley, 1977). Here also the 1APE was calculated

to assess precision.

During the aging process, the readers did not have

any information about the length of the fish. All readings for both hard parts were done randomly and reading repetitions were spaced by one month.

The increments counted on each otolith were divided by 365 to obtain age in years. Ages from fin rays

were expressed as the number of complete annuli, and

the marginal increment was not considered.

For comparisons between readings of otoliths and fin

ray sections, an index ofsimilarity, S, was applied:

S=~(I00), Ai +Bi

where Ci = number offish assigned the same age class

i by both otolith and fin ray readings,

Ai = number of fish of age class i according to

the otolith reading, and

Bi number of fish of age class i according to

the fin ray reading.

Results

Swordfish females ranged from 85 to 245 cm in EFL,

while males were from 79 to 239 cm (Fig. 3). Females

caught in the Baja California swordfish fishery were

significantly larger than males (F=16.6, P<O.OOl).

The otoliths from females weighed 0.50-2.75 mg

(n=87), while those from males weighed 0.25-1.75 mg

(n=27). No difference between the lllean weights ofleft

and right otoliths was observed (t=0.95, P=0.34). The

relationship between fish EFL and otolith weight (OW)

is represented by the following equations (Fig. 4):

Females: OW =0.1196 exp(OOI33xEFL), R2 =0.792 (n=88)

Males: OW = 0.1831 exp(OOl08XEFL), R2 = 0.76 (n=27).
234 NOAA Technical Report NMFS 142 _

Figure 2

Transverse section of a first anal-fin ray viewed under transmitted light, showing two annual increments (1,2). The sample was

from a swordfish, Xiphias gladius, male of 138 cm EFL. Scale bar =

1.5 mm.

35

30

E: 25

>-

u

<: 20 ..

:>

15

u. 10

70 90 110 130 150 170 190 210

o FEMALE

.MALE

230

The slopes of the log-transformed EFL-OW regressions for females and males were significantly different (P<O.OOl).

We were able to successfully analyze 56 (47%)

of the 118 otoliths sampled. Annular counts

ranged from 204 to 1,329 apparent daily rings

(0.55-3.64 yr). No significant difference was

found between mean values of two increment

counts (t=0.40, P=0.68), and the precision of

age estimates (IAEP) was 6%.

The rest of the otoliths (n=62) were hard to

read, either because only a portion of the rostrum could be discerned, or because the space

between increments decreased toward the edge

of the otolith in older fish, where our highest

magnification (lOOOx) was insufficient to observe them.

Ray sections were easier to handle, prepare,

and read than otoliths. Two hundred and thirtyfour (92%) second rays from the 255 first anal

fins sampled were analyzed successfully (61

males and 173 females). Samples were considered unreadable (n=21) if there was no agreement between readers due to the presence of

multiple bands (as described by Berkeley and

Houde, 1983) or because growth bands were

unclear, especially for the first several growth

marks which were sometimes obscured by vascularization in the central matrix. We found

12% IAEP when the age determinations of the

two readers were compared.

Estimated ages from ray sections ranged from

0+ to 9+ for females and from 0+ to 7+ for males.

The highest age frequencies were observed for

fishes of 2 and 3 yr old for both sexes (Fig. 5).

Ages estimated from otoliths and second ray

sections from the same fish (n=56) were

highly similar for 1-yr-old and 2-yr-old

fish (86% and 77%, respectively), but

similarity for older fish was less than 60%

(Fig. 6). The age frequency distributions

based on the two structures are shown in

Figure 6, where the otolith age distribution appears to be more right-skewed (predominately younger) than that from fin

rays. Otoliths showed a tendency to underestimate age compared to fin ray sections

in fishes 2 yr or older (Fig. 7), assuming fin

ray counts to be more accurate.

Eye· fork length (c m )

Figure 3

Length frequency distribution ofswordfish, Xiphias gladius, males (n=84)

and females (n=282) from Baja California, Mexico.

Discussion

Our results demonstrate that otoliths

grow proportionally in weight with body
Castro-Longoria & Sosa-Nishizaki: Age Determination of Swordfish Using Anal Fin Rays and Otoliths 235

FEMALE

2.50

2.00

300

300

200

200

MALE

-- : : - .- .- ;;. ::-

:-

100

/

z

--

: -

-

Eye - fork length (em)

o 100

o

2.50

0.00

3.00

2.00

0.50

1.50

0.50

0.00

1.00

1.00

1.50

-C)

E

-....,

J:

C)

CIJ

J:

....,

.-

...., o

o

Figure 4

Relationship between otolith weight and eye-fork length

(EFL) by sex for swordfish, Xiphias gladius, from Baja

California, Mexico.

includes distinguishing them from false marks); and

the ability to convert accurately a count of marks to an

absolute age, the demonstration of which is considered

validation of an aging method (Francis et aI., 1992).

The confirmation of agreement in results between two

aging methods, i.e. verification (Wilson et a!., 1983),

offers a good estimation of ages that have not been

validated, providing confidence in a given interpretation (Casselman, 1983). The term verification has also

been defined as "a term usually used in reference to the

precision of estimated age" (Hill and Calliet, 1990).

The agreement in this study between presumed annuli in fin rays and daily rings in otoliths enables us to

verify the anal-fin-ray method of determining age in

northeast Pacific swordfish, at least for fishes younger

than 3 yr old. The use of anal-fin ray sections for aging

3.00

.- ,- ,-

size, following a exponential function with different

trends by sex. As was reported by other authors (Radtke

and Hurley, 1983; Wilson and Dean, 1983; Uchiyama et

aI., 1998), our resul ts show that otolith in ternal microstructures can be treated as daily increments to estimate swordfish age. Our data show consistent microstructure increments along the rostrum plane in otoliths

from 1- and 2-yr-old swordfish; precision was unsatisfactory for older fish. Other studies have reported the use

of otoliths to estimate the age offish up to 9 yr old (e.g.

Radtke and Hurley, 1983). Our inability to age older

fishes may have been due to our difficulty in discerning

the growth path along the rostrum of the otolith or to

inadequate sample preparation.

Counting external ridges along the rostrum ofsagittae

was proposed as a method of age estimation for swordfish by Radtke and Hurley (1983) and for Istiophorids

by Radtke (1983). Radtke and Hurley (1983) used an

SEM to study otoliths of Atlantic swordfish and found a

maximum age of 14 yr for males and 32 yr for females.

According to our study, the applicability ofthat method

may be questionable due to the lack of consistent external ridge formation. This problem was also reported by

Wilson and Dean (1983). Furthermore, Hill and Calliet

(1990) found high variability in Pacific blue marlin age

estimates, using an SEM to study otolith external morphology. They compared otolith age estimates with ages

determined by dorsal and anal fin techniques, and

concluded that the high variability of sagittal otolith

age estimates may reflect problems in interpretation of

ridges in regions of acute calcium overburdening, overlapping ridges, or multiple ridges within a large ridge.

Their results show how difficult the application of this

technique can be. Thus, at least for swordfish, we do

not recommend using otolith external morphology for

age estimation.

Growth patterns observed in anal-fin ray sections were

similar to those previously described for Atlantic (Berkeley and Houde, 1983), Aegean (Tsimenides and

Tserpes, 1989), and eastern Mediterranean swordfish

(Tserpes and Tsimenides, 1995). The use of anal-fin ray

sections as a source of age information for commercial

fishery catches of swordfish has the advantages that

growth patterns can be clearly seen and samples can be

easily obtained without altering the commercial value

of fish. Nevertheless, the core of the fin rays in older

fish can undergo resorption and become vascularized,

obscuring and even eliminating the first growth zone in

some specimens. The presence of multiple bands may

also be a problem, but can be easily overcome with

experience (for an extensive discussion see Tserpes

and Tsimenides, 1995).

Three conditions are necessary for accurate age estimation: the existence of a periodic mark in some body

part; the ability to identify these marks reliably (which
236 NOAA Technical Report NMFS 142

30

25

e:. 20 ,.,

c.>

a; 15

:::>

<T

10 \L.

o FEMALE (n=173)

.MALE (n=61)

o 4

Age (years)

Figure 5

Age frequency distributions estimated by anal-fin ray sections of swordfish, Xiphias gladius, from Baja California, Mexico.

Figure 7

Comparison between ages assigned on the basis of

otoliths and anal fin ray sections for swordfish, Xiphias

gladius. The number of fish at each point is indicated.

The bisector line represents 100% agreement.

3 4

•

•

6

3

2

Age from anal ray

1·1.99 2·2.99 3-3.99 4-4.99

Age class

0·0.99

4

30 _OTOLITH 90 c::JRAY

-o-SIMILARITY 80

25 3 70 :§ 20 60 _ (5

,., 0 u 50 ;: c: 15 ." E 2

":J

cr 40 E ... e 30 en ll) ... 10 Ol

<l: 20 1

10

Figure 6

Age frequency distribution of swordfish, Xiphias gladius, estimated by otoliths and anal-fin ray sections from

the same fish. Values of the index of similarity (5) between ages estimated from the two structures are also

shown.

swordfish has previously been partially validated (for

the case of one to five growth bands) by means of

marginal increment analysis for swordfish from the

northwest Atlantic and Mediterranean (Ehrhardt, 1992;

Ehrhardt et aI., 1995; Tserpes and Tsimenides, 1995).

Taking into consideration the verification of the fin ray

section method, and the partial validation ofthis method

in other papers, we highly recommend the use of anal-fin

ray sections as a reliable method for aging Pacific fish.

The age frequency histogram (Fig. 5) shows that the

commercial catch in Baja California was dominated by

young male and female fishes (2-3 yr). This could be

an indication that fishes under 2 yr old are not fully

recruited to the fishery. This result is similar to the

catch composition reported by Berkeley and Houde

(1983) and Wilson and Dean (1983) for the northwest

Atlantic more than 10 yr ago. The difference seen in

the sample between maximum age of females (9+ yr)

and of males (7+ yr) (Fig. 5) could be a result of

temporal-spatial difference in catchability or of a difference in lifespan. Further studies should be carried out

in order to understand the population dynamics of the

swordfish resource in this region.

Acknowledgmen~ ___

We would like to acknowledge the Swordfish Fishery

Section of the National Fishing Industry Chamber

(CA AI PES), especially their on-board observer,
Castro-Longoria & Sosa-Nishizaki: Age Determination of Swordfish Using Anal Fin Rays and Otoliths 237

Ruben De la Rosa, who helped in the collection of the

samples. We thank Gregory Hammann and two anonymous reviewers for their useful comments at an early

version of this paper. Support of this research was provided by a scholarship to the senior author from the

Consejo Nacional de Ciencia y Tecnologfa.

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Genetic Comparison of Pacific and Mediterranean Swordfish,

Xiphias gladius, by RFLP Analysis of the Mitochondrial D-Ioop Region

SEINE CHOW

National Research Institute ofFar Seas Fisheries

5-7-1 Orido, Shimizu

Shizuoka 424-8633,Japan

ABSTRACT

The mitochondrial DNA D-loop region of swordfish, Xiphias gladius, was amplified by

the polymerase chain reaction (peR), and the amplified DNA fragments (1,950 base pairs)

were subjected to restriction fragment length polymorphism (RFLP) analysis to investigate

genetic differentiation among geographically distant samples. Four endonucleases (Alu I,

Dde I, Hha I, and Rsa I) detected high levels of RFLP's in western (n=45) and eastern (n=35)

North Pacific samples. Estimated diversity (h) was 59.9% and 56.1 % (Alu I), 44.0% and

39.2% (Dde 1),42.1 % and 21.4% (Hha I), and 60.4% and 64.0% (Rsa I) for western and

eastern samples, respectively. In contrast, no RFLP was detected with Hha I and Rsa I in the

Mediterranean sample (n=34). Frequency distributions of the restriction patterns in all

endonuclease digestions were significantly different between the Mediterranean and Pacific

samples, while no significant differences were observed between western and eastern Pacific

samples. Much higher haplotypic diversity was observed in the Pacific (92.0%-94.4%) than

in the Mediterranean (70.2%) samples, indicating that little genetic exchange has occurred

between the two populations.

Introduction

Restriction fragment length polymorphism (RFLP) analysis of the whole mitochondrial DNA (mtDNA) molecule

has been used to investigate genetic diversity within and

between local samples ofswordfish, Xiphiasgladius (GrijalvaChon et al. 1994; Katoulas et aI., 1995). Katoulas et al.

(1995) showed that genotype frequencies were significantly different in samples of swordfish from the Gulf of

Guinea and from the eastern Atlantic (off Gibraltar) and

Mediterranean (Greece, Italy, and Spain), suggesting the

existence of genetically different stocks in the Atlantic. In

contrast, no genetic heterogeneity was observed between

swordfish samples from the eastern, central, and western

North Pacific (Grijalva-Chon et aI., 1994).

Recently, a direct nucleotide sequencing method

based on the polymerase chain reaction (PCR) has

been introduced and applied to further investigate genetic differentiation within and between swordfish populations (Finnerty and Block, 1992; Alvarado Bremer et

aI., 1996; Rosel and Block, 1996). In particular, Alvarado

Bremer et al. (1996) and Rosel and Block (1996) reported that the left domain of the mtDNA D-Ioop region of the swordfish is hypervariable. They compared

swordfish samples from the Atlantic, Mediterranean,

and Pacific on the basis of sequence variation, and

reported that mtDNA haplotype frequencies were significantly differen t.

This study reports on intraspecific RFLP in the Dloop region of swordfish mtDNA amplified by PCR.

Genetic comparisons were made among two Pacific

samples and one Mediterranean sample ofswordfish.

Materials and Methods

All swordfish samples included both adults and juveniles. The western North Pacific sample (n=45) was

caught by the Japanese commercial longline fleet and

was collected at the landing site in Yaizu City, Japan,

during November 1991-February 1992. Muscle dissected

from the fresh fish was transferred on ice to the laboratory of the National Research Institute of Far Seas Fisheries (NRIFSF), where DNA extraction was carried out.

The eastern North Pacific swordfish sample (n=35)

was caught by the Mexican commercial fleet using drift

gillnets from November 1991 to February 1992. Crude

DNA extracted from these fish was kindly provided by

239
240 NOAA Technical Report NMFS 142

O. Sosa-Nishizaki and J. M. Grijalva-Chon, Centro de

Investigacion Cientifica y de Education Superior de

Ensenada (CICESE), Mexico.

The Mediterranean sample (n=34) was collected by

A. Di Natale of Aquastudio, in Italy, in 1994. A small

piece of tissue dissected from frozen muscle was preserved in ethanol and transferred to the laboratory.

DNA extraction and PCR amplification procedures

are described elsewhere (Chow and Inoue, 1993; Chow

et aI., 1993; Grijalva-Chon et aI., 1994). Primersequences

for amplifying the mitochondrial D-loop region were

from Palumbi et al. l ; the nucleotide sequences were

CB3R-L: 5'-CATATTAAACCCGAATGATATTT-3, and

12SAR-H: 5'-ATAGTGGGGTATCTAATCCCAGTT-3'.

The PCR products were electrophoresed in 1% agarose

gel to confirm amplification, whereafter the amplified

samples were directly digested by the restriction endonucleases and electrophoresed through 2%-2.5% agarose gel (Biogel, Bio 101, La Jolla, CA2) followed by

ethidium bromide staining and photography. Diversity

(h) was calculated using the frequencies of restriction

patterns and haplotypes (Nei, 1987). The G test of

independence (Sokal and Rohlf, 1981) was employed

to compare frequencies of restriction patterns "nd

haplotypes between samples.

Results

RFLP Analysis

The western North Pacific sample was tried with 15

endonucleases, of which 7 detected polymorphisms

(Table 1). Since 4 of the 7 (Alu I, Dde I, Hha I, and Rsa

I) detected relatively high polymorphisms in this sample,

these 4 endonucleases were used to analyze the other 2

samples. The electrophoretic profiles of all detected

restriction patterns (alphabetically labeled) are shown

in Figure 1. The observed number of restriction patterns was 4 in Alu I and Dde I, 3 in Hha I, and 6 in Rsa I

digestions.

Comparisons between the Samples

Frequencies of the restriction patterns in each endonuclease digestion ofswordfish mtDNAare shown in Table

2. In the Alu I digestions, pattern A was common and

occurred at a similar frequency in all samples. Frequencies of patterns Band C were similar in western and

I Pa:umbi, S., et. al. 1991. The simple fool's guide to PCR, versiOl! 2.0. Dep. of Zoology, Univ. Hawaii, Honolulu.

2 Reference to trade names or commercial firms does not imply

endorsement by the National Marine Fisheries Service, OAA.

Table I

Polymorphisms and genetic diversity, h, in mtDNA from

western Pacific swordfish (n=45).

Sequence No.

Endonuclease at site Variation) individuals h2 (%)

Alu! AG'CT P 45 59.9

BsaJ! C'CNNGG M 14 0.0

Bsl! CCN5'N2GG M 22 0.0

BstU! CG'CG M 14 0.0

Dde! CTNAG P 45 44.0

Hae III GG'CC M 22 0.0

Hha! GCG'C P 45 42.!

Hinf! G'ANTC M 22 0.0

Mbo! 'GATC M 14 0.0

Mse! rTAA P 18 9.1

Nla III CATG' P 45 38.0

Rsa! GrAC P 45 60.4

Sau 961 G'GNCC M 22 0.0

SaFl CCNGG M 10 0.0

Taq! rCGA P 18 24.7

1 P = polymorphic; M= monomorphic.

2 After Nei (1987).

eastern North Pacific samples, but the Mediterranean

sample had a much lower frequency of B and a higher

frequency of C than the Pacific samples. In the Dde I

digestion, C was common in all samples; A was not

observed in the Mediterranean sample; and Dwas much

more frequent in the Mediterranean than in the Pacific

sample. Similarly, for Hha I digestion the Mediterranean sample was monomorphic (h= 0), while a moderate level ofvariation was observed in the Pacific samples

(h = 42.1 % for the western and 21.4% for the eastern

sample), The largest difference between the Pacific

and Mediterranean samples was observed in the Rsa I

digestion. The Mediterranean sample was monomorphic for this endonuclease digestion, as all individuals

examined possessed pattern C. In contrast, the Pacific

samples were highly polymorphic (h = 60.4% and 64.0%

for the western and eastern samples, respectively).

A G test of independence indicated that the frequency distributions of the restriction patterns were

significantly different between the Pacific and Mediterranean samples for all digestions (P«0.05). In contrast, no significant difference was observed between

the western and eastern North Pacific samples.

An analysis ofthe composite haplotypes derived from

the restriction patterns of all 4 endonuclease digestions

also demonstrated differences between the samples. All in

all, 24 haplotypes were observed among 113 individuals

(Table 3). Twenty and thirteen haplotypes were found in

the western and eastern Pacific samples, respectively, while

only five were observed in the Mediterranean sample.
________________ Chow: Genetic Comparison of Pacific and Mediterranean Swordfish 241

Alu I

ACA BDCC A

Hha I

BACA BC BB

Dde I

CCABCDAC

Rsa I

ADC BEF CAB

Figure 1

Restriction patterns of the swordfish mitochondrial D-Ioop fragment digested by four endonucleases.

Restriction patterns were alphabetically labeled. The leftmost lane in each electrophenogram is l-kb

o A ladder (Gibco, BRL).

Haplotypic diversity estimates (H; Nei, 1987) reflected

the skewed number of haplotypes in the Mediterranean

sample. Thus, the eastern and western Pacific samples had

much higher diversity (94.4% and 92.0%, respectively)

than the Mediterranean sample (70.2%).

This difference was amplified when only Hha I and

Rsa I restriction fragment patterns were considered

(Table 4). Eight and five haplotypes were found in the

western and eastern Pacific samples, respectively, and

only one (Be) was observed in the Mediterranean

sample. The haplotypic diversities were 77.6% and 71.5%

for the western and eastern Pacific samples, respectively, while that of the Mediterranean was O. The dif~

ference in haplotype distribution between the Pacific

and Mediterranean samples was highly significant

(P«O.OOl). These results indicate that there is little

gene flow between the swordfish populations of the

Pacific Ocean and the Mediterranean Sea.
242 NOAA Technical Report NMFS 142

Table 2

umber (% frequency) of restriction patterns in each of four restriction endonuclease digestions of mtDNA from three swordfish samples, and calculated genetic

diversity, h (after ei,1987).

North Pacific

Endonuclease Patterns Western Eastern Mediterranean

Alu J A 29 (57.8) 21 (60.0) 18 (53.0)

B 9 (20.0) 10 (28.6) I (2.9)

C 9 (20.0) 4 (I 1.4) 14 (41.2)

D I (2.2) 0 (0.0) 1 (2.9)

nl 45 35 34

h 59.9 56.1 56.4

DdeJ A 7 (15.6) 6 (17.6) 0 (0.0)

B 1 (2.2) 0 (0.0) 0 (0.0)

C 33 (73.3) 26 (76.5) 27 (79.4)

D 4 (8.9) 2 (5.9) 7 (20.6)

nl 45 34 34

h 44.0 39.2 33.7

Hila I A ]0 (22.2) 4 (11.8) 0 (0.0)

B 33 (7'\.3) 30 (88.2) 34 (100.0)

C 2 (4.5) 0 (0.0) 0 (0.0)

nJ 45 ~4 34

Il 4~.1 21.4 0.0

Rsa I A 17 (37.8) 15 (42.9) 0 (0.0)

B (6.7) 3 (8.5) 0 (0.0)

C 23 (51.] ) ]5 (42.9) 34 (100.0)

D 0 (0.0) 2 (5.7) 0 (0.0)

E 1 (2.2) n (0.0) 0 (0.0)

F 1 (2.2) 0 (0.0) 0 (0.0)

nl 45 35 34

Il 60.4 64.0 0.0

J n = number of individuals examined.

Discussion

Evaluation ofintraspecific haplotypic diversity via RFLP

analysis is very sensitive to the numbers of endonuc1eases used and individuals sampled (Nei, 1987), and

RFLP analyses appear to miss many nucleotide substitutions (Beckenbach, 1991). Therefore, comparisons of

haplotypic diversity between species via RFLP analysis

are much less meaningful than spatio-temporal comparison of values within species. Especially for genetic

stock analysis, it is much more important to find a way

to detect diagnostic variation.

PCR-RFLP analysis is well suited for analyzing large

numbers of specimens because it is quite simple and

less costly than conventional restriction analysis of

mtDNA via Southern blotting or with direct nucleotide

sequencing. This technique has been used to detect

genetic polymorphisms in the mitochondrial ATPase

gene of albacore, Thunnus alalunga, using a large number of individuals (n=620; Chow and Ushiama, 1995).

Examination and selection of a target gene region and

the length of the amplified fragments are critical for

PCR-RFLP analysis (Chow and Inoue, 1993; Chow et a\.,

1993). Alvarado Bremer et a\. (1995, 1996) demonstrated that the D-Ioop region of swordfish mtD A is

extremely polymorphic, using nucleotide sequence

analysis. In the present study, RFLP analysis of the

amplified swordfish D-Ioop region was able to detect a

considerable amount of genetic variation. In addition,

the haplotypic diversity obtained by using a limited number of endonucleases was higher than that obtained by

restriction analysis of the entire mtDNA molecule (see

GI-ijalva-Chon et a\., 1994; Katoulas et aI., 1995).

The present results coincide with those of previous

studies. Samples from the Pacific were found to be

genetically homogeneous (Grijalva-Chon et a\., 1994)

using RFLP analysis on the entire mtDNA molecule,

whereas large differences in haplotypic distributions
Chow: Genetic Comparison of Pacific and Mediterranean Swordfish 243

Table 3

Number of composite haplotypes (% frequency) in mtDNA from three swordfish

samples. Four columns of the haplotype represent four endonucleases: Alu I, Dde I,

Hha I, and Rsa I, from left to right.

North Pacific

Clone Haplotype Western Eastern Mediterranean

I AAAA 3 (6.7) 3 (8.8) 0 (0.0)

2 AAAC 2 (4.5) 0 (0.0) 0 (0.0)

3 AABC 0 (0.0) 3 (8.8) 0 (0.0)

4 AABE I (2.2) 0 (0.0) 0 (0.0)

5 ABBA I (2.2) 0 (0.0) 0 (0.0)

6 ACAA 2 (4.5) I (2.9) 0 (0.0)

7 ACAC 3 (6.7) 0 (0.0) 0 (0.0)

8 ACAF I (2.2) 0 (0.0) 0 (0.0)

9 ACBA I (2.2) 3 (8.8) 0 (0.0)

10 ACBB 2 (4.5) 2 (5.9) 0 (0.0)

lJ ACBC 6 (13.3) 7 (20.6) 11 (32.4)

12 ADBA 3 (6.7) I (2.9) 0 (0.0)

13 ADBC 1 (2.2) 0 (0.00) 7 (20.6)

14 BCBA 3 (6.7) 4 (11.8) 0 (0.0)

15 BCBB I (2.2) 0 (0.0) 0 (0.0)

16 BCBC 5 (1l.] ) 4 (11.8) I (2.9)

17 BCBD 0 (0.0) 2 (5.9) 0 (0.0)

18 CACA I (2.2) 0 (0.0) 0 (0.0)

19 CCBA 1 (2.2) 2 (5.9) 0 (0.0)

20 CCBC 6 (13.3) 1 (2.9) 14 (41.2)

21 CCCA 1 (2.2) 0 (0.0) 0 (0.0)

22 CDBB 0 (0.0) 1 (2.9) 0 (0.0)

23 DCBA 1 (2.2) 0 (0.0) 0 (0.0)

24 DCBC 0 (0.0) 0 (0.0) I (2.9)

Total 45 34 34

Hl(%) 94.4 92.0 70.2

1 Haplotypic diversity (Nei, 1987).

Table 4

Comparison of composite haplotype frequencies between three swordfish samples on

the basis of restriction patterns in digestions by Hha I and Rsa I endonucleases.

North Pacific

Clone Haplotype Western Eastern Mediterranean

1 AA 5 (11.1 ) 4 (11.8) 0 (0.0)

2 AC 5 (lJ.] ) 0 (0.0) 0 (0.0)

3 BC 18 (40.0) 15 (44.1) 34 (l00)

4 BE I (2.2) 0 (0.0) 0 (0.0)

5 BA 10 (22.2) 10 (29.4) 0 (0.0)

6 AF I (2.2) 0 (0.0) 0 (0.0)

7 BB 3 (6.7) 3 (8.8) 0 (0.0)

8 BD 0 (0.0) 2 (5.9) 0 (0.0)

9 CA 2 (4.4) 0 (0.0) 0 (0.0)

Total 45 34 34

Hl(%) 77.6 71.5 0

1 Haplotypic diversity (Nei, 1987).
244 NOAA Technical Report NMFS 142

were observed between Pacific and Mediterranean

samples using nucleotide sequence analysis, as reported

by Alvarado Bremer et al. (1996) and Rosel and Block

(1996). Thus, regardless ofthe methods employed, millNA

analysis may be quite powerful for the detection of genetic

differen tiation among geographically distinct populations.

Further PCR-RFLP analysis is underway on swordfish

samples from other locations in the Pacific as well as the

North and South Atlantic and Indian Oceans. The results

may be useful in clarifYing the global population structure

of this highly migratory and cosmopolitan fish.

Acknowledgments _

I would like to thank A. Di Natale of Aquastudio, Italy,

and O. Sosa-Nishizaki and J. M. Grijalva-Chon, Centro

de Investigacion Cientifica y de Education Superior de

Ensenada, Mexico, for generously sharing their swordfish specimens for this study. Z. Suzuki, Y. Uozumi, and

H. Nakano of the National Research Institute of Far

Seas Fisheries are also acknowledged for reading the

manuscript.

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gladius. Mol. Ecol. 4:473-41'1.

'\;ei. :'II.

19H7. Molecular evolutionary genetics. Columbia Uni,·.

Press, :--Jew York.

Rosel, P. E., and B. A. Block.

19'J6. Mitochondrial control region variability and global

population structure in the swordfish, Xiphias gladius. Mar.

BioI. 125:11-22.

Sokal, R. R., and F. J. Rohlf.

1981. Biometry. W. H. Freeman,. ewYork.
Food and Feeding Habits of Swordfish, Xiphias gladius L.,

offWestern Baja California

UNAI MARKAIDA* and OSCAR SOSA-NISHIZAKI*

Departamento de Ecologia Marina

Centro de lnvestigacion Cientifica y de Educacion Superior de Ensenada

(CICESE)

Apartado Postal 2732

Ensenada, Baja California

22800 Mexico

ABSTRACT

Stomach contents of 173 swordfish caught off the west coast of Baja California in eight

commercial fishing trips during 1992 and January 1993 were analyzed. Cephalopods dominated the stomach contents over the first four trips, off southern Baja California: 85% by

number, 90% by weight, and 96% by frequency of occurrence. The species composition in

the diet was constant during the four trips; ommastrephid squid, Sthenoteuthis oualaniensis,

was the most important prey. Fishes dominated the diet in the last four trips, off northern

Baja California: 62% by number, 84% by weight, and 65% by frequency of occurrence. The

fish species composition varied during the four trips, mesopelagic species being the most

important. Significant differences were found in the numerical composition of prey species

between the eight trips.

Values of a fullness weight index indicated that swordfish eat equal quantities off

northern and southern Baja California. However, differential digestion could be masking a

greater quantity of feeding off the southern area, where swordfish reach sexual maturity

during migration. Swordfish feed mostly alone on schooling prey, and appear to be efficient

and opportunistic predators whose diet indicates prey abundances in the environment. This

may allow swordfish to be used as an efficient biosampler. Swordfish trophic level off

western Baja California varies between 4 and 4.5.

Introduction

The swordfish, Xiphias gladius Linnaeus, is a large, pelagic, predatory fish distributed worldwide in tropical

and temperate waters, and between 50 0N and 35°S in

the Pacific Ocean (Nakamura, 1974). Almost half the

total catches of this species occurs in the Pacific (Holts

and Sosa-Nishizaki, 1998), and the western Baja California coast is a major fishing zone (Sakagawa, 1989).

Studies of swordfish food habits have been made

mainly in the North Atlantic and Mediterranean Sea,

where some authors reported cephalopods (mainly

ommastrephids) as the most important prey (see historical summary by Toll and Hess, 1981; Stillwell and

Kohler, 1985; Bello, 1991; Guerra et aI., 1993). However, other studies found fishes to be the principal

component of stomach contents (Tibbo et aI., 1961;

Scott and Tibbo, 1968, 1974; Moreira, 1990; Clarke et

aI., 1995). Few authors have focused on seasonal and

geographical changes in swordfish diet (Maksimov, 1969;

Stillwell and Kohler, 1985; Hernandez-Garda, 1995).

The trophic ecology of the swordfish in the Pacific

Ocean is poorly known; observations on its food habits

have been made as part of more extensive studies.

LaMonte and Marcy (1941) and LaMonte (Hubbs and

Wisner, 1953, p. 130) found only squid in the stomach

contents ofswordfish caught offChile. Nakamura (1949)

reported cod, rockfish, and myctophids as swordfish

prey in a study of tuna and billfish biology and fisheries.

Yabe et al. (1959), studying swordfish biology in the

western Pacific, found mostly zooplankton and pelagic

fish larvae in the guts of ten larval swordfish; squids,

* Mailing address: Ecologia Marina, CICESE, P.O. Box 434844, San

Diego, CA 92143, U.S.A.

245
246 NOAA Technical Report NMFS 142 _

fishes, and amphipods in twenty young swordfish; and

mainly squid, fishes, and crustaceans in six adult swordfish. De Sylva (1962) identified 24 jumbo squids,

Dosidicus gigas, in five of seven female swordfish stomachs examined during a study of dinoflagellate bloom

off northern Chile, and concluded that feeding occurs

near the surface. He also reported that Pacific bonito,

Sarda chiliensis, are eaten by swordfish. Wisner (de Sylva,

1962, p. 276) reported that the stomach contents of

swordfish off southern California indicated feeding on

rather deepwater fishes.

Fitch and Lavenberg (1971), in a study of California

marine fishes, found that most swordfish off California

had fed on anchovies and cephalopods (squid) and

other fishes such as hake,jack mackerel, and shortbel1y

rockcod. A few stomachs contained deep-sea fishes such

as lanternfish, barracudinas, pencilsmelt, and other

oddities. Frey (1971) enumerated northern anchovies,

squid, hake,jack mackerel, rockfish, barracudinas, black

smelt, ribbonfish, and shrimp as swordfish prey off

California, and considered whether swordfish may undergo ontogenic change in feeding habits, foraging at

greater depths with age.

Mearns et al. (1981) analyzed the stomach contents

of 17 swordfish caught near the Channel Islands, California, as part of a study of the trophic structure of

marine ecosystems. In 15 individuals that contained

food, northern anchovy and Pacific hake each accounted

for over 40% of the index of relative importance, the

remainder being almost entirely fish tissue. Seki (1993)

studied the stomachs of 22 swordfish caught north of

the Hawaiian Archipelago to examine predator-prey

relationships with a squid, Ommastrephes bartramii. The

cephalopod fauna was composed of 0. bartramii (40.9%),

Sthenoteuthis oualaniensis (18.3%), Thysanoteuthis rhombus (31.8%), and unidentified ommastrephid (13.6%).

Yatsu (1995), in a paper on the ecology of slender

tuna in the South Pacific Ocean, reported mainly unidentified fishes and cephalopods from the stomachs of

19 swordfish. Barbieri et al. (1998) found that longtailed

hake, Macruronus magellanicus, and jack mackerel,

Trachurus murphyi, were the most important prey

(60% each) in 55 swordfish stomachs caught off Chile.

Squids, Dosidicus gigas and Loligo gahi (15%), fish remains (15%), and shrimp, Heterocarpus reedi (10%)

occurred less frequently.

The purpose ofthis paper is to increase knowledge of

the food and feeding habits ofswordfish caught off the

western Baja California coast.

Materials and Methods

The stomachs of 173 swordfish were obtained by swordfish drift gillnet vessels based in El Sauzal harbor,

Ensenada, during eight commercial trips along the western coast ofBaja California. A description of this fishery

is given by Holts and Sosa- Jishizaki (1998). The first

four trips were made off southern Baja California between 23°58' and 29°38'N from February to August

1992, and the last four off northern Baja California

between 29°10' and 32°21'[ from October 1992 to

January 1993 (Fig. 1, Table 1). Stomachs were preserved by an observer on board the vessels in 10%

buffered formalin, and their contents transferred to

70% ethanol in the laboratory. The eye-fork length of

each swordfish was measured to the nearest centimeter

and its sex was determined. Weights were estimated

using allometric relationships calculated by CastroLongoria (1995).

Identification of pelagic fishes in the stomach contents was based on external anatomy or vertebral charTable I

Dates of collection and number, size, sex, and stomach condition of swordfish sample caught during 1992 and January

1993 off Baja California.

Eye-fork length (cm) Sex Number ofstomachs

Trip Date N Range "'lean SD Female 'vlale L'nid. Contents Empty Evened

1 29 February-21 March 1992 28 88.9-233.7 156.0 3R.1 21 7 23 2 3

2 5-22 April 1992 18 9Y-200.6 160.7 35.9 16 2 17 1

3 29June-16July1992 22 93.9-220.9 166.4 34.4 22 22

4 28July-7 August 1992 26 88.9-223.5 164.5 32.2 22 4 22 4

5 17-27 October 1992 33 111.7-218.4 162.3 33.4 23 9 32 I

6 10-13 'ovember 1992 8 ]]6.8-210.8 157.1 35.7 7 I 8

7 10-22 December 1992 26 76.5-208.2 166.1 31.3 IY 5 2 24

8 14-20 Jan uary 1993 12 116.4-203.2 156.8 27.1 9 3 II

Pooled 173 76.5-233.7 161.9 33.4 139 31 3 159 9 5
Markaida & Sosa-Nishizaki: Food and Feeding Habits of Swordfish off Western Baja California 247

Figure 1

Swordfish fishing- area off western Baja California. l'\umbers

indicate locations where 173 swordfishes analyzed for this

study were caught during eight fishing trips (see Table 1 for

collection dates and numbers).

the pooled stomachs stabilizes represents the minimum

sample size needed to describe the diet.

A fullness weight index was calculated for each swordfish as the relationship between the weight (g) of the

stomach contents and the total body weight (g) of the

swordfish multiplied by 10,000. This index removes

bias caused by the effect of predator size; it is frequently

used to determine feeding behaviour (Hyslop, 1980).

The mean fullness weight indices for the eight trips

were compared using ANOYA after testing for normality and homogeneity of variance of the data. Empty

stomachs were taken into account in sample size estimation and fullness weight index calculations.

The index of relative importance, IRI = (%N + %W)

x %FO (Pinkas et aI., 1971) was represented graphically for only those taxa that accounted for more than

1% of IRIon a trip.

A G-statistic contingency table analysis (Crow, 1982) was

used to test for differences in diet composition between

trips, employing the number of individuals in each prey

taxon. Prey species were pooled in ecologically similar

groups to increase the number of observed frequencies in

each cell of the contingency table. In the R x C contin110°

•

+

5'¢

% ~. • 6

• 334

.. 25° 3 ..

PACIFIC

OCEAN

[slade

G/uululu,pe

I Rosenblatt, R. H., C. Klepadlo, and H.J. WalkerJr. 1994. Scripps

Marine Vertebrates Collection, Scripps Institution of Oceanography, 8604 La Jolla Shores Drive, La Jolla, CA 92037-1508. Personal commun.

2 Hochberg, F. G. September 1994. Dep. of Invertebrate Zoology, Santa Barbara Museum of Natural History, 2559 Puesta del Sol

Road, Santa Barbara, CA 92105-2936.

actenstIcs (Clothier, 1950). Well-preserved mesopelagic fishes were identified by R. H.

Rosenblatt, C. Klepadlo, and H.J. Walker, Jr.,l

and the vertebrae from these specimens were

used to identify the bony remains of other specimens. Cephalopods were identified mainly from

beaks, using available keys (Pinkas et aI., 1971;

Wolff, 1984; Clarke, 1986) and a reference collection, under the supervision ofF. G. Hochberg.2

Fish otoliths were not used to quantify diet in

this study, as only those belonging to Pacific

hake remained complete, even though buffered

formalin was used to fix samples. This is not

surprising, since otoliths of a related family, Gadidae, are among the most durable Oobling and

Breiby, 1986; Pierce et aI., 1993; HernandezGarda, 1995).

Percent number (%N), weight (%W), and frequency of occurrence (%FO) (Cailliet, 1976)

were quantified for each prey species or group

of species in the diet, including trace amounts,

not including everted stomachs. Counts of fish

remains were based on the maximum number of

vertebrae possible per species, or by counting

heads or tails. The larger of the two counts of

upper and lower beaks was taken as the minimum number of cephalopods represented

(Perrin et aI., 1973). Prey remains were weighed

to the nearest 0.1 g. Although weight and volume measures give the same information

(Cailliet, 1976), weight was preferred because it

is more accurate and less time consuming. umber and weight of prey were calculated pooling the

contents of all stomachs from the same trip.

In order to assess whether collected stomachs were

sufficient to describe adequately the diet of swordfish,

the minimum sample size for each trip was estimated by

plotting a general form of Bernouilli's diversity index

against number of pooled stomachs, as described by

Hoffman (1979):

where Hk is the diversity in k pooled stomachs, Nk the

number of individuals in those stomachs, and Nki is the

number of individuals of the ith species in k pooled

stomachs. The point where the cumulative diversity of
248 NOAA Technical Report NMFS 142 _

Eye-fork length class (em)

Results

were found (one-way ANOYA; F7,162=0.317, P=0.94) after tests for normality (Kolmogorov-Smirnov; n=l70,

dmax=0.07583, P>0.20) and homogeneity of variance

(Levene; F7,162=0.692, P=0.677) were made. The sample

included 139 females, 31 males, and 3 undetermined.

Frequencies of females were not significantly different

between trips (X2=1.690, df=7, P>0.95). Nine stomachs

were empty, 5 everted, and 159 contained food remains. Information about the samples is summarized in

Table 1.

Hoffman's (1979) graphic method suggested an ideal

sample size of about 20 stomachs, or 25 in the case of

the first trip (Fig. 3). Diversity of trips 6 and 8 didn't

reach the stability point, because few samples were

taken during these trips. We concluded that samples

were of sufficient size to describe the food habits of

swordfish except for trips 6 and 8. The second trip

showed a drop in diversity due to the thirteenth stomach, which had 23 flying purple squid, the dominant

species.

The fullness weight index was not calculated for eight

swordfish because three were not measured for length

and five had everted stomachs. The log-transformed

mean and standard deviation of the index for each trip

are shown in Figure 4. There were no significant differences between trips (one-way ANOYA; F7,157=0.768,

P=0.61), after transformed data were tested for normality (Kolmogorov-Smirnov; n=165, dmax=0.7039, P>0.20)

and homogeneity of variance (Levene; F7,157=1.355,

P=0.227).

The remains of 1,108 cephalopods belonging to 3

orders and at least 19 species, and 709 teleosts belongn=170

,-

- - -,-

I--

I--

-

o

60

A80 100 120 140 160 180 200

lh220 240

5

15

=go 10

20

Figure 2

Eye-fork length distribution of 170 swordfish analyzed

in this study.

Swordfish sizes ranged from 76 to 233 cm eye-fork

length (Fig. 2). No differences in size between trips

gency table, R was the number of pooled prey categories

and C the number oftrips.The test was performed repeatedly, removing less likely variables, as prey category or trip,

from the contingency table when a significant difference

was obtained, and testing again with the remaining variables until no significant difference was obtained.

0.0

o 5 10 15 20 25 30 35

Number of pooled stomachs (k)

1.0 A 1.0 B

0.8 0.8

0.6 0.6

0.4 .=1 0.4 .=5

.=2 .=6

0.2 ... =3 0.2 ... =7

T=4 T=8

6

.......

o

Cl)

;>

.~

...-<

;:l

§

U 0.0

o 5 10 15 20 25 30

Number of pooled stomachs (k)

Figure 3

Bernouilli's diversity index plotted against the number of pooled stomachs from each trip in A. southern

Baja California and B. northern Baja California.
Markaida & Sosa-Nishizaki: Food and Feeding Habits of Swordfish off Western Baja California 249

Figure 4

Log-transformed mean and standard deviation of the fullness weight

index for each trip that collected swordfish stomachs off Baja California, 1992-93.

0.6 -- -- -- -~ -~

0.2

2 3 4 5 6 7

Trip number

ing to more than 8 orders and 16 species were found in

the stomach contents (Table 2). An unidentified ray

was the only elasmobranch found.

Offsouthern Baja California, cephalopods accounted

for the major part of the swordfish diet composition

(85%N, 90%W, 89%FO) (Fig. 5, Table 3). Ommastrephid squids dominated the diet by all counts, and

flying purple squid, Sthenoteuthis oualaniensis, was the

major prey species (44%N, 40%W, 64%FO). Jumbo

squid, Dosidicus gigas, was the second most important

ommastrephid species (15%N, 6%W, 48%FO). Gonatids

were the second most important family, represented by

Gonatus berryi and G. californiensis. Ancistrocheirus lesueurii

and Thysanoteuthis rhombus followed in frequency of

occurrence. Argonauta spp. were the only octopods with

some importance in the swordfish diet. Unidentified

cephalopod remains accounted for a large proportion

of weight in the diet and were mainly composed of

squid mantles without beaks. However, it is likely that

most of this belonged to the Ommastrephidae family.

Pacific hake, Merluccius productus, was the most important fish prey in %N and %W; it occurred only in

February-March. An unidentified Stromateoidei had

some importance in %FO during June-July.

Fish was the most important component in swordfish

diet off northern Baja California (62%N, 83%W,

64%FO) (Fig. 6, Table 4). Unlike squids, important fish

species varied by trip. Pacific hake, the fish that occurred in the greatest percentage of the samples (11 % ,

15%W, 48%FO) was relatively important only in October and December (trips 5 and 7). Duckbill barracudina,

Paralepis at/anticus; pearleye, Scopelarchidae; king-ofDeviation

Methodology in marine predator diet studies has improved notably in recent years due to

studies on marine mammals (Pierce and

Boyle, 1991; Pierce et aI., 1993) and advances in the iden tification of cephalopod beaks (Clarke, 1986).

Secondary prey, those ingested by primary prey, may be mistaken for food

items of the predator (Perrin et aI., 1973) .

Remains of the pelagic red crab, Pleuroncodes planipes, were determined to be

secondary prey originating from Pacific

hake and king-of-the-salmon. Three species of euphausiids were found in stomachs of duckbill barracudina. These crustaceans were also considered to be secondary prey of swordfish, and they were

not taken into account in the analysis of

stomach contents. One swordfish stomach contained a whole Octopoteuthis

deletron in the open stomach of a king-ofthe-salmon, and also a pair of beaks of

another squid; it was impossible to discern whose prey the beaks represented.

Discussion

8

the-salmon, Trachipterus altivelis; and jack mackerel,

Scomberjaponicus, varied greatly in importance in different months. Pacific sardine, Sardinops sagax caeruleus,

occurred only in January 1993 (trip 8). Larger prey,

such as king-of-the-salmon and cutlassfish, Lepidopus

fitchi, were important by weight but not by number.

Sixteen individual cutlassfish were found in a stomach

during November (trip 6), accounting for almost all

the stomach-content weight for that month. Northern

anchovy, Engraulis mordax; frigate and bullet tuna, Auxis

spp.; Panama lightfish, Vinciguerria lucetia; and unidentified Species A each appeared in only one month.

California needlefish, Strongylura exilis, and dusky

pencilsmelt, Microstoma microstorna, also each appeared

in only one month, in northern Baja California, but

their IRl's were always less than 1%.

Contingency table analysis showed highly significant

differences between trips in numerical diet composition when the following prey groups were tested: Pacific hake, pelagic fishes, mesopelagic fishes, and cephalopods (G=1682, d.f.=21, P<O.OI). In general, fish and

cephalopod proportions were significantly different

between all trips (G=616, d.f.=7, P<O.OI). No significant

differences were obtained in the proportion of

ommastrephids (flying purple squid and jumbo squid)

between the four trips off southern Baja California

(G=4.54, d.f.=3, P>O.OS).

-- --

-~

-- -~

-~

I

-~

I ±Stnnd

o Meau

-,--

2.6

x 2.2

.g

.s;

.<:

OJ) 1.8 .

w

W

<U

-= 1.4 ::2

-0

§

;j

"

On

o

-'
250 NOAA Technical Report NMFS 142

1

%N

2

40

%W60

80

60

%N 40

20

40

%W60

Sthenotellthis

February 21-March 21, 1992

n =25

-

April 5-22, 1992

n = 18

.~

3 ~'\'> '"" ....OJ

80 .....

CZI ~~v. ~, ." ,}' .~ 0 toO f .~

60 o . IV'\''> v<:1 ~Oj %N ~I...CZI S~ ~" " ~v 40 s-'C' !-. .~,

f:,' ,,<:1 ,,<:1 .~

o ,,0 :11:' 20 d" ~"'i "v ~& (j~

I

0 =-+---- ----- -

20

40

%W60

June 29-July 16, 1992

n = 22

4 -

80

Sthenotelltllis 60

%N .t!1'-

VJ 40 0

..!E 20

0 f----

-:= ----- --

20

40

%W60

DosidicliS

July 28-August 7,1992

n =26 o 20 L.L..J

%FO

Figure 5

Percent composition of swordfish stomach contents collected off southern Baja

California during 1992: number (% ), weight (%W), and frequency of occurrence (%FO) of prey groups that accounted for more than 1% of index of

relative importance. n = number of stomachs with food remains.
Markaida & Sosa-Nishizaki: Food and Feeding Habits of Swordfish off Western Baja California 251

5 80

40

%w - 60· October 17-27, 1992

n = 33

20

60

%N 40

6 80

7

40

%w60

80

60

%N 40

November 10-13,1992

n=8

o ------- ------ ----- ------- -------- -

20

8

40

%w60

80

1

60

%N 40

40

%w60 January 14-20, 1993 L...--

n = 11

December 10-22, 1992

n = 25

o 20 '--'-.J

%FO

Figure 6

Percent composition ofswordfish stomach contents collected off northern

Baja California during 1992 and January 1993: number (% ), weight

(%W), and frequency of occurrence (%FO) of those prey groups that

accounted for more than 1% of index of relative importance. n = number

of stomachs with food remains.
252 NOAA Technical Report NMFS 142

Interpretation of the fullness weight index should

consider the differential digestion of different prey; it

has been reported that cephalopods are digested faster

than fishes (Bigg and Fawcett, 1985; Olson and Boggs,

1986). Therefore, the fullness weight index for swordfish caught off southern B;;ya California could be underestimated, as they contained a greater weight of

cephalopods than those caught off the northern coast

(Fig. 5, 6). Due to the lack of information on differential rates of gastric evacuation in swordfish, we are not

able at this point to discern whether differential digestion may be hiding significant

differences between the fullness weight indices for northern and southern Baja California swordfish. It is probable that swordfish

females eat more as they mature during their

migration to the south; Kume and Joseph

(1969) and Bedford and Hagerman (1983)

suggested that swordfish migrate along California and Baja California coasts, and CastroLongoria (1995) found initial stages of mature gonads in female swordfish off southern Baja California. Frontal zones of high

productivity where swordfish tend to concentrate (Sakagawa, 1989), such as the western Baja California coast, provide swordfish

with rich food resources for sexual maturation while they migrate toward the tropics.

Previous studies have noted that the diet

of swordfish varies by geographic area

(Maksimov, 1969; Hernandez-Garda, 1995)

depending upon the prey species present in

the area (Tibbo et aI., 1961; Scott and Tibbo,

1968). This would explain the great differences observed in the diet of swordfish off

western Baja California. The variability in

food habits found in our study could not be

explained by sex or size.

The fact that merluciids, gadids, paralepidids, and scombrids have been described

as the most important fish prey species of

swordfish (Tibbo et aI., 1961; Scott and Tibbo,

1968,1974; Mearns et aI., 1981; Stillwell and

Kohler, 1985; Moreira, 1990; HernandezGarda, 1995; this study) indicates the great

abundance of these groups in the coastal

pelagic ecosystems where swordfish are usually caught. The fish species composition in

the diet of swordfish caught in oceanic waters seems to be different (Yabe et aI., 1959;

Maksimov, 1969; Hernandez-Garda, 1995;

Clarke et aI., 1995), although more studies

of the oceanic ecosystem are needed. Ommastrephids have been described as the most

important cephalopod prey in other regions

TELEOSTEI

CLLJPEIFORMES

Clupeidae

Etrttrneus teres*

Sardinops sar;ax caeruleus*

Engraulididae

Engraulis mordax

OSMERIFORMES

Microstomatidae

A1icrostorna rnicrostoma*

Bathylagidae

Bathylagus sp*

STOMIlFORNIES

Photichthydae

Vincig1.terria htcetia*

Stomiidae

fdiacanth1.ts antrostornus*

AULOPIFORMES

Scopelarchidae*

Synodontidae

Synodus lucioceps*

Paralepididae

Paralepis at/anticus

Alepisauridae

Alepisaurus ferox

LAMPRIDIFORMES

Trachipteridae

Trachipterus altivelis*

GADIFORMES

Merluciidae

Merluccius /Jroduct1.ts

BELONIFORMES

Belonidae

Stronr;ylum exdis*

Scomberesocidae

Cololabis saira*

PERCIFORMES

Carangidae

TrachurttS syrnmftricus*

Trichiuridae

LfPidopus fitchi*

Scombridae

Auxis spp.

Scomberjaponicus*

Stromateoidei

ElASMOBRA:-.lCHIl

RAJIFORMES*

CEPHALOPODA

TEUTHOIDEA

Ommastrephidae

Dosidicus gigas

Sthenoteuthis oualaniensis

Gonatidae

Gonatopsis borealis*

Gonatus berryi*

Gonatus wlifomiensis*

Thysanoteuthidae

Thysanoteuthis rhombus

Ancistrocheiridae

Ancistrochei111s lesueurii

Onychoteuthidae

Onychoteuthis banksii

Onychoteuthis spp.

Histioteuthidae

Histioteuthis heteropsis*

Histioteuthis hoylei (=H. doJleini)

Mastigoteuthidae

Mastigoteuthis dentata*

Mastigoteuthis spp.

GrimaJditeuthidae

Grirnalditeuthis bonplandi

Ocropoteuthidae

Octopoteuthis deletron*

Pholidoteu th idae

Pholidoteuthis boschrnai*

OCTOPODA

Argonautidae

A19onauta argo?

Argonauta spp.

Bolitaenidae

Japetella diaphana*

Alloposidae

Haliphron at/anticus

Octopodidae

Octopus rubescens*

VAMPYROMORPHA

Vampyroteuthidae

Varnpyroteuthis in[emalis*

Table 2

Prey species or taxa (*=new record for swordfish diet) identified in

the stomach contents of swordfish caught off Baja California during 1992 and January 1993.

Probably some of the smaller prey were, in fact, secondary prey of the swordfish. However, smaller prey were of

low importance in the swordfish diet, and we feel that

this problem caused little bias.

Back-calculation of cephalopod weights using the

lower rostral lengths of beaks was not conducted in :his

study because it is well known that beaks can remain

undigested in stomachs for much longer periods of

time than fish otoliths and bones (Bigg and Fawcett,

1985; Hernandez-Garda, 1995).
Markaida & Sosa-Nishizaki: Food and Feeding Habits of Swordfish off Western Baja California 253

Table 3

Prey species by number, weight, and frequency of occurrence in 84 stomachs of swordfish caught off southern Baja

California.

Taxon Number % Weight (g) % Frequency %

TELEOSTEI 136 15.16 3,034.2 10.00 27 29.67

Merluccius productus (Pacific hake) 81 9.03 1,658.4 5.51 11 12.08

Unidentified Stromateoidei 17 1.89 285.2 0.94 8 8.79

Scomberjaponicus (Pacific mackerel) 4 0.44 259.2 0.86 3 3.29

Trachipterus altivelis (king-<Jf-the-salmon) 4 0.33 169.1 0.56 4 4.39

Alcpisaurusjerox (longnose lancetfish) 2 0.22 128.9 0.42 2 2.19

Lepidopus fitchi (cutlassfish) 2 0.22 50.9 0.16 2 2.19

Engraulis mO'rdax (northern anchovy) 5 0.55 5.0 0.01 1 1.09

Synodus lucioceps (California lizardfish) 2 0.22 320.0 1.06 1 1.09

Pamlepis atlanticus (duckbill barracudina) 1 O.ll 21.0 0.06 I 1.09

Auxis spp. (frigate or bullet tuna) 1 0.11 18.5 0.06 1 1.09

Tmchurus symmetricus Uack mackerel) 1 0.11 13.8 0.04 I 1.09

Scopelarchidae (pearleye) 1 0.11 0.7 0.00 1 1.09

Microstoma mic1'Ostoma (dusky pencilsmelr) I 0.11 0.1 0.00 1 1.09

Unidentified Teleostei 14 1.56 103.4 0.34 8 8.79

CEPHALOPODA 761 84.83 26,971.9 89.69 81 89.01

Sthenotcuthis oualanicnsis (flying purple squid) 396 44.14 11,982.7 39.84 59 64.83

Dosidicus gigas Uumbo squid) 137 15.27 1,977.9 6.57 44 48.35

Unidentified Ommastrephidae 5 0.55 0.8 0.00 5 5.49

Gonatus benyi 67 7.46 11.7 0.03 34 37.36

Gonatus californiensis 42 4.68 568.4 1.89 24 26.37

Ancistrocheirus lesueurii 18 2.00 3.5 0.01 14 15.38

Thysanoteuthis rhombus 22 2.45 452.8 1.50 14 15.38

Mastigoteuthis dentaUt 7 0.78 0.3 0.00 2 2.19

Mastigoteuthis spp. 2 0.22 0.2 0.00 2 2.19

Histioteuthis heteropsis 6 0.66 0.7 0.00 2 2.19

Histioteuthis Jurylei (;H. doflcini) 1 0.11 0.2 0.00 I 1.09

Grimalditeuthis bonplandi 2 0.22 0.6 0.00 2 2.19

Pholidoteuthis boschmai 1 0.11 0.2 0.00 1 1.09

Unidentified Teuthoidea 4 0.44 0.4 0.00 3 3.29

Argonauta spp. 43 4.79 49.2 0.16 12 13.18

Haliph1'On allanticus 3 0.33 0.2 0.00 2 2.19

Octopus rubesccns 3 0.22 0.1 0.00 2 2.19

Unidentified Octopoda 1 0.11 0.1 0.00 1 1.09

Vampy1'Oteuthis injernalis 1 0.11 0.1 0.00 I 1.09

Cephalopoda remains 11,920.9 39.64 40 43.95

UNIDENTIFIED REMAINS 64.9 0.21 2 2.19

TOTAL 897 30,071.0 91

of the world (Tibbo et aI., 1961; Scott and Tibbo, 1968,

1974; Maksimov, 1969; Toll and Hess, 1981; Stillwell

and Kohler, 1985; Moreira, 1990; Bello, 1991; Guerra et

aI., 1993; Seki, 1993; Hernandez-Garda, 1995) in both

coastal and oceanic pelagic ecosystems.

The use of the "sword" for disabling or killing prey has

been recorded by previous workers (Bigelow and

Schroeder, 1953; Tibbo et aI., 1961; Scott and Tibbo,

1968; Stillwell and Kohler, 1985). In this study, most prey

showed evidence of being slashed or cut. Whole king-<lfthe-salmon (as large as 160 cm) were folded in the stomach due to cuts. Small prey such as Argonauta spp. showed

no damage and probably had been ingested whole.

Predation upon schools of fish (Scott and Tibbo,

1968; Stillwell and Kohler, 1985; Bello, 1991) and cephalopods (Toll and Hess, 1981; Guerra et aI., 1993; Seki,

1993) has been previously noted. As many as ten individuals of the same species, namely, Pacific hake, Pacific sardine, andjack mackerel, occurred in some stomachs. As many as 44 lower beaks from flying purple squid

were found in another stomach. A Bray-Curtis index of

similarity (Ludwig and Reynolds, 1988) was calculated for

the number of prey species shared by all possible swordfish pairs caught during the same night. It did not show

any congruence, suggesting thatswordfish feed alone upon

prey schools that are patchily distributed.
254 NOAA Technical Report NMFS 142

Table 4

Prey species by number, weight, and frequency of occurrence in 75 stomachs of swordfish caught off northern Baja

California.

Taxon Number % Weight (g) % Frequency %

TELEOSTEI 573 62.21 41,200.5 83.16 49 63.63

Merlueeius produetus (Pacific hake) 103 J1.18 7,378.7 14.89 37 48.05

Paralepis aLlantieus (duckbill barracudina) 1:19 11.83 1,643.1 3.31 27 35.06

Scopelarchidae (pearleye) 91 9.88 736.4 1.48 25 32.46

TraehipttmtS altivelis (king-of-the-salmon) 33 3.58 21,458.1 43.31 21 27.27

Sardinops sagax caeruleus (Pacific sardine) 55 5.97 2,125.7 4.29 7 9.09

Traehurm symmetricus (jack mackerel) 24 2.60 991.6 2.00 7 9.09

Unidentified Species A 23 2.49 99.4 0.20 7 9.09

Auxis spp. (frigate or bullet tuna) 12 1.30 1,552.9 3.13 7 9.09

Strongylura exilis (California needlefish) 8 0.86 216.5 0.43 7 9.09

Mierostoma microstoma (dusky pencilsmelt) 38 4.12 156.3 0.31 6 7.79

Scomberjaponicus (Pacific mackerel) 4 0.43 181.1l 0.36 3 3.89

Lepidopus fitchi (cutlassfish) 17 1.84 4,298.1 8.67 2 2.59

Vinciguerria lucetia (Panama lightfish) 13 1.41 3.1 0.00 2 2.59

Engraulis mordax (northern anchovy) 6 0.65 3.8 0.00 2 2.59

Etrumeus teres (round herring) 2 0.21 156.2 0.31 2 2.59

Bathylagus sp. (blacksmelt) 3 0.32 16.5 0.03 2 2.59

AlepisaUTUS ferox (Iongnose lancetfish) 1 0.10 73.6 0.14 1 1.29

Cololabis saira (Pacific sauri) I 0.10 61.2 0.12 I 1.29

Idiaeanthus antrostomus (Pacific blackdragon) 1 0.10 12.0 0.02 1 1.29

Unidentified Stromateoidei 1 0.10 0.5 0.00 1 1.29

Unidentified Teleostei 21l 3.04 35.0 0.07 15 19.48

ELASMOBRANCHIi

Rajiformes 0.10 128.5 0.25 1.29

CEPHALOPODA 347 37.67 7,804.3 15.75 57 74.02

UllOE TIFIED REMAI S 406.9 0.82 12 15.58

TOTAL 921 49,540.2 77

Swordfish can feed at great depth during diurnal

vertical migrations (Carey and Robison, 1981), and has

demonstrated great ability to catch powerful prey (Toll

and Hess, 1981). As an opportunistic predator whose

diet reflects the presence and abundance of its prey,

swordfish could be used as a biosampler which would

aid us in obtaining information about other potential

commercial resources off western Baja California, for

example, jumbo squid and Pacific hake.

Mearns et al. (1981) assigned a trophic level of 3.97

to swordfish in the Southern California Bight, based on

stomach content analysis in which northern anchovy

accounted for almost half of the diet. Planktivorous

fishes were not found to be important components of

the swordfish diet in other studies. On the contrary,

squids and mesopelagic carnivorous fishes seem to be

more commonly reported, resulting in a somewhat

higher trophic level. Assuming that the trophic levels of

more important prey (Fig. 5, 6) fluctuate between 3

and 3.5 (Mearns et aI., 1981; Yang, 1982; Brodeur and

Pearcy, 1992), swordfish's trophic level off the western

Baja California coast would vary between 4.0 and 4.5.

The prey of swordfish are shared by numerous other

predators in the eastern Pacific Ocean, as shown in

Appendix Table 1 and 2. A comprehensive study of the

marine predator assemblages that populate these waters is lacking.

Acknowledgments _

The authors are greatly indebted to R. de la Rosa, who

obtained the samples on board fishing vessels, as well as

to all those fishermen who collaborated on sampling.

R. Castro-Longoria began the analysis of the stomach

contents. F. G. Hochberg was decisive in cephalopod

beak identification and his attention at Santa Barbara

Museum of atural History is acknowledged. M. R.

Clarke identified two of the cephalopod beaks. R. H.

Rosenblatt, C. Klepadlo, H.J. WalkerJr., and F. GalvanMagana helped in the identification of fish remains.

Thanks are also due to G. Hamman, R.J. Olson, and an

anonymous reviewer for the revision and helpful commen ts on a earlier draft ofthis man uscript, which greatly
Markaida & Sosa-Nishizaki: Food and Feeding Habits of Swordfish off Western Baja California 255

contributed to improve it. This paper constitutes part

of the M.Sc. thesis of the senior author, in the course of

which he enjoyed a Spanish-Mexican (CSIC-CONACyT)

exchange scholarship which A. Guerra collaborated in

obtaining.

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and harbour seal on the British Columbia coast. Bull. Fish.

Res. Board Can. 146,52 p.

Stillwell, C. E., and N. E. Kohler.

1985. Food and feeding ecolo~ of the swordfish Xiphias Kladius

in the western North Atlantic Ocean with estimates of daily

ration. Mar. Ecol. Prog. Ser. 22: 239-247.

Stroud, R. K., Fiscus, C. H., and H. Kajimura.

1981. Food of the Pacific white-sided dolphin, LaKfnorhil1rhus

obliqllidens, Dall's porpoise, Phocoenoidps dalli, and northern

fur seal, Callorhinus ursinus, off California and Washington.

Fish. Bull. 78(4):951-959.

Tibbo, S. ., L. R. Day, and W. F. Doucet.

1961. The swordfish (Xiphias gladius L.), its life-history and

economic importance in the northwest Atlantic. Bull. Fish.

Res. Board Can. 130,47 p.

Toll, R. B., and S. C. Hess.

1981. Cephalopods in the diet of the swordfish, Xiphias gladius,

from the Florida Straits. Fish. Bull. 79(4):765-774.

Trikas, T. C.

1979. Relationship of the blue shark, Prionare glaura, and its

prey species near Santa Catalina Island, California. Fish.

Bull. 77(1):175-182.

Wolff, C. A.

J984. Identification and estimation of size from the beaks of

18 species of cephalopods from the Pacific Ocean. C.S.

Oep. Commer., NOAA Tech. Rep. NMFS 17, 50 p.

Yabe, H., S. Ueyanagi, S. Kikawa, and H. Watanabe.

1959. Study on the life-history of the swordfish, Xiphias gladius

Linnaeus. Rep. Nankai Reg. Fish. Res. Lab. 10: 107-J.~O.

Yang,J.

1982. A tentative analysis of the trophic levels of North Sea

fish. Mar. Ecol. Prog. Ser. 7:247-252.

Yatsu, A.

1995. The role of slender lUna, Allothllnnlls fallai, in the pelagic ecosystems of the South Pacific Ocean. Jpn.J. Ichthyol.

41(4):367-377.
258 NOAA Technical Report NMFS 142

Appendix Table I

Predators in the Eastern Pacific of teleost fishes found in the diet ofswordfish caught off Baja California. Where a source

identifies a predator as having a prey similar to that i:1 column 1, this prey is shown in parentheses.

Prey

Merluccius productus

Trachipterus altivelis

Paralepis atlantica

Sardinops sagax

Trachurus symmetl'icus

Auxisspp.

Engraulis mordax

Lepidopus fitchi

Vinciguerria lucetia

Scopelarchidae

Stromateoidei

Predator (Similar prey) [Source l . 2]

Alepisaurus richardsoni; Anoplopoma fimbria; Ophiodon elongatus; Galeorhinus zyopterus; white shark, Carcharodon

cal'Charias; Pacific electric ray, Torpedo californiws [5]. Common thresher, Alopias vulpinus [21]. Blue shark,

Prionace glauca [13, 22, 31]. Bluefin tuna, Thunnus thynnus; albacore, Thunnus alalunga; Pacific bonito, Sarda

chilensis [26]. Striped marlin, Tetrapturus audax [1]. Sea birds [22]. Pinnipeds, odontocetes [7,9, 10, 19,21,22].

Alepisaurus ferox [28]. Pacific white-sided dolphin, Lagenorhynchus obliquidens [30]. Northern fur seal, Callorhinus

ltrSinus [23, 29]. Spinner dolphin, Stenella lonf!irostris (Trachipterus fukuzakii) [25]. Albacore (Trachipterus sp.)

[20]. Bigeye tuna, T1!unnus obesus [6]. Yellowfin tuna, Thunnus albacares [3].

Bigeye tuna; albacore [17, 26]. Albacore (Paralepididae) [15, 20]. Yellowfin tuna [3]. Spotted dolphin, Stenella

attenuata; spinner dolphin [11,25].

Striped marlin, Tetrapturus andax [1, 8, 14, 27]. Blue marlin, Makaira nigricans [1]. Dolphinfish, Coryphaena

hipp1ll'uS [2].

Albacore; bluefin tuna; Pacific bonito [20,26]. Yellowfin tuna [3]. Striped marlin [8, 14]. Blue shark [31]. Mako

shark, !surus ox)'rinchus [21]. Northern fur seal; Steller sea lion, Eumatopias jubatus [24, 29]. California sea lion,

Zalophias californirus [19].

Yellowfin tuna [3, 6, 16, 21]. Skipjack, Katsuwonus pelamis [3, 21]. Bigeye tuna [6]. Albacore; spotted dolphin

[25]. Dolphinfish [2]. Striped marlir-; blue marlin [I]. Striped marlin (A. thazard) [8]. Silky shark, Carcharhinus

falciforrnis [21].

Albacore; bluefin tuna; Pacific bonito [4,20,21,26]. Yellowfin tuna; skipjack [3]. Striped marlin [8, 14]. Other

teleosts [22]. Pacific mackerel, Scomber japonicus; California barracuda, Sphyraena argentea; common thresher

[21]. Blue shark [13,21,22,31]. Sea birds [22]. ?'Iorthern fur seal; Pacific white-sided dolphin; Dall's porpoise,

Phocoenoides dalli; common dolphin, Delphinus delphis [9, 22, 24, 29, 30]. California sea lion [10, 19,21,22].

Bluefin tuna; skipjack [3]. Albacore (Trichiuridae) [15]. Yellowfin tuna; skipjack [3]. Striped marlin [8].

Yellowfin tuna; skipjack [3]. Albacore [20,26]. Tunas; dolphins, Stenellaspp. [11,18]. Sailfish, Istiophorus platypterus [8].

Spinner dolphin [11]. Alepisaurus; opah, Lampris ref!ius; albacore; salmon, Oncorhynchussp. (Benthalbella liguidens) [12].

Albacore (Stromateidae) [15]. Yellowfin tuna [3]. Pacific bonito [26]. Striped marlin; sailfish [8]. Spinner

dolphin; spotted dolphin [25].

I [1] Abitia-Cardenas et aI., 1997, [2] Aguilar-Palomino et aI., 1998, [3] Alverson, 1963, [4] Bernard et aI., 1985, [5] Best, 1963, [6] Blunt,

1960, [7] Condit and Le Boeuf, 1984, [8] Evans and Wares, 19n, [9] Fiscus, 1979, [10] Fiscus and Baines, 1966, [11] Fitch and

Brownell, 1968, [12] Fitch and Lavenberg, 1968, [13] Harvey, 1989, [14] Hubbs and Wisner, 1953, [15] Iversen, 1962, [16]juhl, 1955,

[17] Kajimura, 1969, [18] Lavenberg and Fitch, 1966, [19] Lowry et aI., 1990, [20] McHugh, 1952, [21] Mearns et aI., 1981, [22]

Morejohn et aI., 1978, [23] Perez and Bigg,2 [24] Perez and Bigg, 19R6, [25] Perrin et aI., 1973, [26] Pinkas et aI., 1971, [27] RamfrezGonzalez, 1979, [28] Roedel, 1938, [29] Spalding, 1964, [30] Stroudetal., 1981, [31] Trikas, 1979.

2 Perez, M. A., and M. A. Bigg. 1983. Food habits of northern fur seals (Callorhinus ursinus) offwestern North America. Unpubl. rep.

of 26th meeting of the North Pacific Fur Seal Commission, Seattle, WA, 103 p., 28 figs. Natl. Mar. Mamm. Lab., Natl. Mar. Fish. Serv.,

NOAA, 7600 Sand Point Way'. E., Seattle, WA 98115-0070.
Markaida & Sosa-Nishizaki: Food and Feeding Habits of Swordfish off Western Baja California 259

Appendix Table 2

Predators in the eastern Pacific Ocean of cephalopods found in the diet of swordfish caught off Baja California. Where a

source identifies a predator as having a prey similar to that in column 1, this prey is shown in parentheses. Prob. = prey

identified as probable for this predator.

I [1] Abitia-Cardenas et aI., 1997, [2] Aguilar-Palomino et aI., 1998, [3] Alverson, 1963, [4] Antonelis et aI., 1994, [5] Blunt, 1960, [6)

Clarke, 1986, [7] Clarke and MacLeod, 1980, [8] Clarke and Trillmich, 1980, [9] Clarke et aI., 1976, [10] Condit and LeBoeuf, 1984,

[11] Evans and Wares, 1972, [12] Fiscus, 1982, [13] Fiscus et aI., 1989, [14] Galvan-Magana et aI., 1985, [15] Galvan-Magana et aI., 1989,

[16] Hacker, 1992, [17] Hacker, 1994, [18] Harvey, 1989, [19] Imber, 1978, [20] Iversen, 1962, [21JJuhl, 1955, [22] LOWl)'et aI., 1990, [23]

McHugh, 1952, [24] Mead et aI., 1982, [25] Mearns et aI., 1981 [26] Morejohn et aI., 1978, [27] Okutani and Tsukada, 1988, [28] Perrin et

aI., 1973, [29] Pinkas et aI., 1971, [30] Ramirez-Gonzalez, 1979, [31] Stroud et aI., 1981, [32] Trikas, 1979.

Prey

Sthenoteuthis oualaniensis

Dosidicus gigas

Gonatus berryi

Gonatus californiensis

Gonatopsis borealis

Thysanoteuthis rhombus

Onychoteuthis borealijaponicus

Onychoteuthis banksii

Histioteuthis heteropsis

Histioteuthis haylei (=H. doJleini)

Algonauta spp.

Predator (Similar prey) [Source l ]

Yellowfin tuna [3, 14, prob. 28]. Striped marlin [1]. Tunas [27]. Galapagos fur seal, Arctocephalus

galapagoensis [prob. 8]. Spinner dolphin; spotted dolphin [prob. 28]. Sperm whale, Physeter macrocephalus

[prob. 9]. Pigmy sperm whale, Kogia Ineviceps; Dall's porpoise (Ommastrephidae) [26].

Albacore; bluefin tuna [29]. Yellowfin luna [3, 14, prob. 27]. Bigeye lUna [5, 21]. Dolphinfish [2].

Striped marlin; blue marlin [1]. Blue shark [18, 32]. orthern fulmar, Fulmarus glacialis [26). Northern

elephant seal, Mimunga angustimstris [4]. Spinner dolphin; spotted dolphin [prob. 28]. Sperm whale [9, 13].

Albacore [29 in 19]. orthern elephant seal [4]. Sperm whale [13]. Yellowfin (Gonatus sp.) [14]. Blue

shark; sea birds; northern elephant seal; California sea lion; northern fur seal; pigmy sperm whale; Dall's

porpoise; Pacific white-sided dolphin [12, 18,22,26,31]. Northern fur seal (Gonalidae) [12].

Hubb's beaked whale, Mesoplodon carlhubbsi [24 in 6].

Albacore; bluefin luna [prob. 29]. Northern elephant seal [4, prob. 10, prob. 17]. Northern fur seal

[12]. Pacific while-sided dolphin [31]. Short-finned pilol whale, Globicephala macmrh)'nchus [prob. 16].

Sperm whale [13, prob. 7 in 13].

Bigeye tuna [5]. Yellowfin luna [3, 14]. Tunas [27]. Blue shark (Thysanoleulhidae) [32]. Pigmy sperm

whale [26].

Yellowfin [14]. Albacore; bluefin tuna; Pacific bonito [29]. Blue shark [18,32]. Sea birds [26]. California

sea lion [22, 26]. Northern elephant seal [4, 10, 17]. Pacific while-sided dolphin; Dall's porpoise;

northern fur seal [12,25,30]. Hubb's beaked whale [24]. Short-finned pilol whale [16]. Pigmy sperm

whale [26]. Sperm whale [13].

Yellowfin luna [3]. Albacore [23]. Tunas [27]. Smooth hammerhead, Sphyrna zYf<aena [15]. Galapagos

fur seal [8].

Albacore [29]. Blue shark [26,32]. Hammerheads, Sphyrna spp. [15]. Northern elephant seal [17].

Short-finned pilot whale [16]. Sperm whale [13]. Blue shark (Histioteuthis sp.) [18, 31]. Yellowfin luna;

spinner dolphin; spotted dolphin [28]. Northern elephant seal [4]. Sperm whale [9, 13].

Nonhern elephant seal [4]. Short-finned pilol whale [17]. Sperm whale [13].

Yellowfin tuna (A. pacifica) [3]. Blue shark [18]. Albacore; bluefin tuna (A. nouryi) [29]. Yellowfin tuna

(A. cornuta) [3]. Bigeye tuna; yellowfin tuna; skipjack (Algonauta spp.) [3,5, 14,25]. Albacore [20].

Dolphinfish [2,30]. Striped marlin; blue marlin; sailfish [I, 11,30]. Pigmy sperm whale [26].

A Preliminary Assessment of the Use of Hard Parts

to Age Central Pacific Swordfish, Xiphias gladius

JAMES H. UCHIYAMA, ROBERT A. SKILLMAN,

JEFFREY D. SAMPAGA, and EDWARD E. DEMARTINI

Honolulu Laboratory

Southwest Fisheries Science Center

National Marine Fisheries Seroice, NOAA

2570 Dole Street

Honolulu, Hawaii 96822-2396

ABSTRACT

We describe the results of preliminary work that contributes to ongoing studies of the

age and growth ofswordfish, Xiphias gladius, in the central Pacific. Multiple hard parts (first

dorsal and first anal fin rays, caudal vertebrae, and otolith sagittae) were evaluated for their

suitability as ageing structures. Proportional relations were observed between counting-path

dimensions of various hard parts (width of fin rays, depth of vertebral cones, and length of

sagittae) and eye-fork length ofswordfish. Age estimates (counts of presumed annuli) were

evaluated within and among tissues and between pairs of readers.

A provisional growth model is presented for swordfish in the Hawaii longline fishery,

based on presumed annuli observed in cross sections of the second ray of first anal fins. The

validations of annuli on fin rays and sagittae, and of daily growth increments on sagittae, are

indicated as key topics for continuing studies. Validation of annuli should include analysis

of marginal growth increments on both fin rays and sagittae collected at expanded spatial

and temporal scales. Complementary research needs are identified, emphasizing an expanded

mark-recapture program to provide specimens needed for conclusive age validation.

Introduction

The age and growth ofswordfish, Xiphias gladius, stocks

in the Atlantic Ocean have received much attention

(Ovchinnikov, 1970; Beckett, 1974; Berkeley and Houde,

1983; Radtke and Hurley, 1983; Wilson and Dean, 1983;

Prince et aI., 1988; Ehrhardt, 1992; Turnerl ), because

the status of these stocks has been assessed primarily

with age-structured stock assessment models (Megrey,

1989; Miyake and Rey, 1990). Age-structured rather

than surplus production models have been used, at

least until recently (Cosner et a!., 1992; Prager, 1992),

because high-quality effort statistics were unavailable

for all segments of the fleet. In addition, the size and

1 Turner, S. 1986. Further examination of the marginal increments observed by Berkeley and Houde in cross sections of anal

spines from swordfish. U.S. Dep. Commer., NOAA, Natl. Mar.

Fish. Serv., Southeast Fisheries Center Swordfish Workshop Working Paper 86/4, 5 p. SEFC, 75 Virginia Beach Dr., Miami, FL

33149.

sex composition of landings varied considerably among

different national fleets because of differential targeting.

In the Pacific Ocean, swordfish is not as heavily exploited as in the North Atlantic (Sakagawa, 1990), and

Pacific swordfish stocks are presently believed to be under-exploited (Bartoo and Coan, 1990; Skillman, 1990;

NOAA, 1993). Yet concern has been raised during recent deliberations ofthe Western Pacific Fisheries Management Council (WPFMC) that management restrictions in the Atlantic and continued market demand

could result in considerable expansion of the Pacific

fishery and a rapid decline in Pacific stock (WPFMC2).

Dependency on age-structured stock assessment modeling may be expected also in the Pacific because of

similar problems with the availability of comprehensive

fishing-effort statistics, and differences in fishing strat2 Western Pacific Fishery Management Council. 1994. Amendment to the fishery management plan for the pelagic fisheries of

the Western Pacific Region. Western Pae. Fish. Manage. Coune.,

1164 Bishop St., Rm. 1405, Honolulu, HI 96813.

261
262 NOAA Technical Report NMFS 142

35° ,-------r----,----,----,

Longitude West

o TC9101

'7 TC9203

o TC9303

160°

o

,0

a.~

Hawaiian ,.....

Islands V

1650 1700

15° '-- -'-- ..L..... --'- ,

175°

20°

Figure I

Location of longline sets on Townsend Cromwell cruises

TC-9101, TC-9203, and TC-9303.

vessel Townsend Cromwell on cruises TC-9101 (10 January-15 February 1991), TC-9203 (13 April-7 May 1992),

and TC-9303, Leg I (12 March-8 April 1993). We hereafter refer to these three series of collections as 1991,

1992, and 1993, respectively. The longline gear was set

around 2000 and retrieved the following morning at

0700. Retrieval of the longline was usually completed

by noon. Dead swordfish and some live fish needed for

very fresh tissue samples were brought aboard ship.

Most viable swordfish were i~ected with oxytetracycline

(-600 mg/fish), marked externally with a stainless steel

dart tag (Squire, 1974), and released for use in future age

validation studies based on time-marked recaptures.

For fish brought aboard ship, eye-fork length (EFL,

the distance from posterior edge of orbit to fork of tail)

was measured to the nearest 0.1 cm. Sex was assessed

macroscopically while dressing the fish, and gonad

samples were collected and fixed in 10% formalin (seawater-buffered). Sex was later re-evaluated by microscopic examination of standard histological preparations (Harris' hematoxylin stain, eosin counterstain).

Several tissues were collected and frozen for processing

and subsequent estimation of age at the Honolulu Laboratory. Fin rays and otoliths were taken in part because

prior studies (Berkeley and Houde, 1983; Radtke and

Hurley, 1983; Wilson and Dean, 1983) suggested their

potential usefulness in ageing swordfish. Future availability was also a criterion in the selection of tissues.

The caudal peduncle containing terminal vertebrae,

for example, can be easily collected from landed car-

-C

.....

I...

o

Z

Q) 25° -0

:::J

30°

egy between geographically-separated fisheries. The

adequacy of age-structured models is of course dependent on accurate and precise estimates of age and growth

rates.

Data are generally lacking on growth of Pacific swordfish. Yabe et al. (1959) analyzed the length frequency

distribution of swordfish landed in the western North

Pacific during 1948-56; and Sakagawa and Bell (1980)

estimated the von Bertalanffy growth function (VBGF)

Kfrom these data. Kume and Joseph (1969) examined

length frequency distributions of swordfish from the

eastern Pacific. The ages ofswordfish from the Mexican

fishery have recently been estimated by counting presumed annuli on cross sections of anal fin rays and

presumed daily growth increments (DGI's) on otoliths

(Castro-Longoria and Sosa-Nishizaki, 1998).

The validation of annuli and DGI's is crucial for any

ageing study. To date, only Ehrhardt (1992) and Tserpes

and Tsimenides (1995) have been able to provide partial validation of swordfish ages using anal fin rays.

Wilson and Dean (1983) verified, but did not validate,

counts of DGI's and annuli on cross sections ofsagittae

from the same swordfish, as did Radtke and Hurley

(1983) for counts of DGI's and of external ridges on

sagittae. All these comparisons were limited to Atlantic

and Mediterranean swordfish. Since neither annuli nor

DGI's have been validated for Pacific swordfish, validation of these methods is of the utmost importance in

the Pacific, as elsewhere.

Because current knowledge of swordfish growth is

insufficient to support age-structured stock assessment,

the Honolulu Laboratory of the Southwest Fishery Science Center initiated a program to describe size-at-age

relations for swordfish in the central Pacific. In this

paper, we report our progress to date in estimating the

age of swordfish caught by the Hawaii longline fishery.

We first evaluate the basic suitability of various hard

parts as ageing structures based on proportionate growth

of counting paths on tissues and of fish length, and we

evaluate the related issue of variation in tissue preparations among individual fish. We then compare age estimates by the same reader and between age readers, and

among different tissues from the same fish. A provisional growth model is next presented, and work in

support of age validation is described. Lastly, key topics

for future research are identified.

Specimen Collection

Hard parts were obtained from swordfish caught north

and west of the Hawaiian Islands (Fig. 1) by monofilament longline gear fished from the NOAA research

Methods and Materials
__________ Uchiyama et aI.: Assessment of the Use of Hard Parts to Age Central Pacific Swordfish 263

Table I

umber of counts made by each of three readers on various tissues (one specimen of each) used to age swordfish, for each

of the three (1991, 1992, and 1993) series of collections. 01, 02, 03 =dorsal fin rays 1-3; AI, A2, A3 =anal fin rays 1-3.

Cuunts by re-ader and year

Reader A Reade-r B Re-ader (;

1991 1992 1993 1991 1992 199~ 1991 IYtJ2 19t]:~

Rays

01 3 4

02 3 4 :'\

03 3 4 3

Al 3 4 3

A2 3 4

A3 3 4 :'\

Vertebrae l 1 I

Sagittae

Rostral ridges 3 4 3

Postrostral bands 3

Daily growth increments 10 10 10 10

casses. The skull, with otoliths, and the anterior portions

of the first dorsal and first anal fins can be collected by

observers or by fishers during onboard processing-.

Preparation and Examination of Specimens

The counting of presumed annual marks (hereafter

referred to as annuli) was done by three readers with

different types and levels of experience. Reader A had

the most experience at reading material from different

species and tissues. Reader B read greater numbers of

specimens for this study, except for vertebrae and band

counts on the postrostrum of otolith sagittae (described

below). Reader C, experienced in using a computerized optical image analyzer to age hard parts, used an

image analyzer to count annuli. The number of counts

made on each tissue type by each of the three readers is

summarized in Table 1. All repeat counts of presumed

annuli on fin rays, and of t'idges and bands on sagittae,

were made a month apart without knowledge of fish

size or of previous counts on that part, to assure independence among readings.

Rays-Because the terminology of swordfish fin morphology is obscure, we first define our usage. The first

dorsal (hereafter called dorsal) and first anal (anal)

fins of swordfish have both unbranched and branched

rays. The first two or three rays in these fins are unbranched, have right and left sides joined by a medial

suture, and have an opened gap in their bases (Fig. 2).

These structures thus match Summerfelt and Hall's

(1987) definition of soft rays, even though the lInbranched rays of swordfish haye been variously called

spines, spiny rays, or spinous rays. one of the dorsal or

anal fin rays ofswordfish appear to he scgmen ted.

The rays of dorsal and anal fins were separated from

their fins, cleaned of tissue, and dried in a dehydrator

at about 52°C for 24-48 h. For each fin ray collectecl in

1993, length was mcasurecl to the nearest mm along its

convex cephalad surface from a proximal point on its

basc to its distal tip (Fig-. 2) using a fabric measuringtape. After cross sections were cut from the ray (described below), the distance between base of the ray

and the point at which the ray was cut was also measured. For 1992 and 1993 specimens, ray widths were

measured to the nearest 0.1 mm with a dial caliper on the

proximal side of the point at which the ray was first cut.

Using an Isomet3 low-speed saw, a first cut was made

across the ray proximal to the point at which its left and

rig-ht sides converg-ed posteriorly (Fig-. 2). Then 3-5 sections about 1 mm thick were cut successively toward the

ray tip (distal end) so that the first section included the

point at which the left and rig-ht sides converged. Sections were mounted on a glass microscope slidc using a

synthetic mounting- medium (Flo-texx) and examined

without further preparation. Counts of annuli were

made using a dissecting- microscope at 12x magnification with reOected lig-ht against a black backg-round.

Annuli were defined as alternating pairs of opaque

and translucent bands. These concentric bands ran

continuously ancl in parallel along the lateral circumference of the sectioned ray from the an tcrior to poste-

:< Reference to trade names or commercial firms does not imply

endorsement by the National Marine Fisheries Service, NOAA.
264 NOAA Technical Report NMFS 142

Figure 2

Truncated caudad view of a curved swordfish

fin ray, illustrating position at which ray was

first cut for cross sections used in ageing. Also

indicated are the proximal and distal points

between which the length of ray was measured along its cephalad surface.

rior side of the medial suture, but were absent along

the relatively flat-sided medial suture (Berkeley and

Houde, 1983; Tsimenides and Tserpes, 1989, Fig. 1). 1l

was assumed that one pair of bands had formed each

year. Multiple bands sometimes occurred, but could be

distinguished from true annuli, in that the opaque

bands of neighboring annuli remained distinct from

one another around the entire lateral circumference of

the section, including the region of the medial suture.

Conversely, multiple bands converged on one another

near the suture; they were counted as a single annulus.

Another type of opaque band ("false check") sometimes

occurred, but was not counted. False checks did not

extend to the region of the medial suture and usually

varied greatly in band width. An opaque band at the

edge was scored as a "plus" growth and not a year mark.

...1'.-+----

OPENED BASE

DISTAL TIP

MEDIAL SUTURE

FIRST CUT

PROXIMAL POINT

(FOR RAY

MEASUREMENT)

Vertebrae-Flesh around the 23rd and 24th (caudal)

vertebrae was removed, and vertebrae were separated

with a knife. Vertebral annuli were defined as concentric alternating pairs of opaque and translucent bands

within cartilaginous tissue on the anterior and posterior cones of vertebral centra. Annuli were counted

once by unaided eye before vertebrae were processed

further. The vertebrae were then boiled, all remaining

soft tissue was removed, and they were dried in a dehydrator at 52°C for 24-48 h. Both anterior and posterior

depths of cones (perpendicular distance from the open

end of the cone to the apex) were measured to the

nearest 0.1 mm using a dial caliper.

Otoliths-The semicircular canals, located lateral to

the spinal cord's foramen in the skull, were extracted

using watchmaker's forceps. Using a dissecting microscope at 6x, the sagitta (largest of the three otoliths)

was teased out of the sacculus with size 00 insect pins.

The sagitta was then cleaned oftissue under 25x magnification using pins and a fine-tip brush, and stored in

75% EtOH.

Length ofsagittae was measured by placing complete

sagittae, antirostrum side down, in the well ofa culture

slide. The ventral profile was viewed through a video

camera mounted on a dissecting microscope and its

length measured with an image processor. End-to-end

line segments were measured along the middle of the

profile, from the tip of the rostrum to tip of the

postrostrum (Fig. 3).

Sagittae were further prepared in one of two ways. A

sagitta for which DCI's were to be enumerated (Radtke

and Hurley, 1983; Wilson and Dean, 1983) was glued

onto a microscope slide, sulcus (medial) side down.

The exposed surface of the rostrum was sanded lightly

with 600-grit silicon carbide paper with frequent inspections until DCI's became visible in the sagittal plane

from the core to the distal tip of the rostrum. The

sagitta was then mounted in Euparal under a cover

slide. All apparent DCI's were enumerated from the

core to the tip of the rostrum using a compound microscope at 600x with transmitted light. In a preliminary

comparison of counts of DCI's on the rostrum,

antirostrum, and postrostrum of sagittae, DCI counts

on the rostrum were always highest. We assumed that

these highest counts were most representative and thereafter counted DCI's on the rostrum only. Mter a number of practice coun ts, we decided on using the average

of ten consecutive counts to estimate specimen age.

DCI counts were divided by 365 to convert to years.

External ridges have been observed on the proximal

surface of sagittae rostrums for northwest Atlantic

(Radtke and Hurley, 1983), but not southwest Atlantic

(Wilson and Dean, 1983) swordfish. We additionally

observed alternating pairs of opaque and translucent
__________ Uchiyama et aI.: Assessment of the Use of Hard Parts to Age Central Pacific Swordfish 265

Figure 3

Diagrammatic curved ventral profile of a swordfish sagitta. Dashed

line represents a series of end-toend straight line segments drawn

by an image processor and used to

estimate total length of the sagitta.

bands on the postrostrums of sagittae (heretofore unreported for swordfish); these also may represent annual marks. A sagitta for which rostral ridges and

postrostral bands were to be enumerated was mounted on

a microscope slide, sulcus side up, in Euparal without any

processing. Ridges and bands were counted using a dissecting microscope at 25x with reflected light.

Data Analysis

Tissue-EFL Relations-Proportionality between EFL

and the growth axis of hard parts used for ageing was

evaluated by product-moment correlation. The relation between width of fin rays and EFL was examinedfor males and females separately. Depth of vertebral

cones was related to EFL for the sexes combined because sex is indeterminable for fish in the landed catch.

The relation between sagitta length and EFL also was

examined for the sexes combined because the number

of intact otoliths available for measurement was small.

Position of Sections-Preliminary observations suggested much variability among fin rays and individual

fish in the location at which the left and right sides of

rays joined at their medial suture. Hence, unavoidable

variation existed in the position at which fin ray sections were cut. To evaluate the extent of this variation,

we expressed the distance between the base of the ray

and its first cut as a percentage ofthe total length ofthe

ray, and compared coefficients of variation (CV = SD/

mean X 100%) among the six different rays.

Precision of Readers-The precision of ages estimated

by each of two readers (A and B) was evaluated as

average percent error (APE, Beamish and Fournier,

1981). APE values were calculated for repeat counts of

annuli on fin ray cross sections, for bands on

postrostrums ofsagittae, and for rostral ridges on sagittae

of all 1992 specimens. Although Reader B made four

readings of the hard parts, only B's last three readings

were used so that B's APE's would be comparable to

Reader A's APE's which were based on three readings.

Comparisons among Readers-To compare counts of

annuli among readers, the count of one reader was

regressed on a second reader's count for the same

tissue using ordinary least squares. Data included all six

different rays from the three collection series. The significance of each pairwise comparison was evaluated by

Student's t test of whether the regression slope equaled

zero (i.e. whether reader counts were related). The

equivalence of counts between readers was similarly

tested by hypothesizing slope = 1. Only the last of the

repeat counts by Readers A and B, and Reader C's single

count, were used. Comparisons were made for all three

pairwise reader combinations. Analogous comparisons

among readers were made for counts on vertebrae.

Comparisons among Tissues-To evaluate whether the

counts made on the six different rays equivalently estimated age, we used Friedman's two-way ANOVA by

ranks (Daniel, 1978). This test analyzed the difference

in counts (responses) among rays (treatments) for each

swordfish (block). The null hypothesis tested was that

counts were equal among rays, within fish. These data

consisted of the last series of repeat coun ts by Reader A

for 1992 and 1993 specimens.

Age-Length Relation-Reader A's last series of counts

for second anal rays of 1992 specimens, and A's single

count of second anal rays from 1993, were used to

calculate VBGF parameters. Nonlinear regression using Marquardt's algorithm and Statgraphics version 5.0

(Statistical Graphics Corp., 1991) was used to obtain

least squares estimates of parameters. Parameters were

estimated by sex and for all fish pooled.
266 NOAA Technical Report NMFS 142 _

Results

Table 3

Correlation (r) between swordfish eye-fork length

(EFL) and the depth of vertebral cones for anterior

and posterior faces of the 23rd (V23) and 24th (V24)

vertebrae.

Table 2

Correlation (r) between swordfish eye-fork length

(EFL) and cross section width of the first, second, and

third rays of the first dorsal (Dl, D2, D3) and first anal

(AI, A2, A3) fins.

Males

r 0.614 0.694 0.740 0.891 0.665 0.725

:v 26 29 29 19 27 26

p <0.001 <0.001 <0.001 <0.001 <0.001 <0.001

Females

r 0.866 0.942 0.967 0.843 0.891 0.940

N 30 34 33 21 30 31

P <0.001 <0.001 <0.001 <0.001 <0.001 <0.001

Dorsal fin rays

A2 A3

Anal fin rays

01 02 03 Al

Precision of Readers

Location of Sections on Rays

In general, all tissues that we examined satisfied the

minimum requirement of proportionality between

counting path of hard part and body size of fish. Correlations between width of ray at point of cut and EFL

were significant for all six different rays (Table 2).

Relation between depth of vertebral centrum and EFL

were also significant (Table 3), as was that between EFL

and length ofsagitta (r=O.69, N=25, P<O.OOI).

Proportionality of Tissues and EFL

The distance from the base at which the left and right

sides of the ray converged (relative to length of the ray)

decreased from the first to the third ray for dorsal and

anal fins (Table 4). The third rays of dorsal and anal

fins were the least variable (Table 4).

The APE's of repeat counts of annuli for the six different fin rays, for external ridges on the rostrums of

sagittae, and for bands on the postrostrums of sagittae

were calculated for Readers A and B (Table 5). Values

were consistently less for Reader A than for Reader B.

Counts of ridges on the rostrum and of bands on the

postrostrum were less precise than counts of annuli on

rays. Values for the second ray of dorsal and anal fins

were less than for other rays (Table 5).

Comparisons between Readers

V23 V24

Anterior Posterior Anterior Posterior

0.959 0.920 0.965 0.894

IV 48 48 69 70

p <0.0001 <0.0001 <0.0001 <0.0001

by both Readers A and B, and the mean difference in

coun ts between readers did not significantly differ from

zero (t=I.413, d.f.=4, P=O.23).

When we employed Student's t test to compare counts

of annuli by different readers for the 6 different fin rays

pooled, all regressions were significant, indicating that

readings by different readers were related (Table 6).

However, each of the regressions had a slope significantly different from 1, indicating a significant difference within each pair of readers (Table 6). Reader

counts on specific rays were therefore examined to

iden tify where disagreements occurred. Differences were

significant for the first ray of both dorsal and anal fins,

but never significant for the second ray of either fin for

any pairwise reader comparison (Table 7).

Results of reader comparisons were variably conclusive for the other hard parts examined. All regressions

of counts on vertebrae by different readers were significant, but all differences in counts between readers also

were significant (Table 8). Only five sagittae were read

Comparisons of Tissues

Reader A's last counts of annuli clearly differed among

the 6 different rays (Friedman's two-way ANOVA,

X2=34.8, d.f.=5, P<O.OOl). Counts ranked lowest for the

first ray of dorsal and anal fins (average rank = 3.11)

and highest for the second ray of the anal fin (average

rank = 3.88), but this apparent maximal contrast was not

significant (Friedman's a posteriori multiple comparison

test; Po::O.10; Daniel, 1978, p. 231). Mean counts ranged

from a minimum of2.62 for the first ray ofthe dorsal fin to

a maximum of 3.26 for the second ray of the anal fin.

Reader B's average DCI counts on sagittae of 1992

and 1993 specimens were converted to years for comparison with annuli in rays and vertebrae from the same

fish (Table 9). Estimated ages based on DCI's and on
__________ Uchiyama et al.: Assessment of the Use of Hard Parts to Age Central Pacific Swordfish 267

Table 4

Summary statistics for relative position of the first cross section of fin rays for swordfish specimens collected in 1993.

Coefficient of variation, CV == (SD/mean) x 100%.

Dorsal fin rays Anal fin rays

DI D2 D3 Al A2 A3

Relative position (%)

CV 16.7 22.4 18.2 23.7 29.4 19.2

Mean 35.4 25.9 17.6 33.3 22.1 18.2

SD 5.9 5.8 3.2 7.9 6.5 3.5

Maximum 48.0 38.5 25.0 59.5 42.3 26.6

Minimum 22.0 15.3 10.7 15.4 11.9 11.0

Ray length (em)

Maximum 16.0 39.0 54.5 10.7 36.0 36.5

Minimum 3.3 6.9 19.5 2.8 8.5 13.0

o. rays measured 41 42 42 41 42 40

Table 5

Precision of repeat counts (APE == average percent

error) for individual specimens of swordfish collected

in 1992. N == number ofspecimens.

Reader A Reader B

N APE N APE

Dorsal fin rays

Dl 29 12.18 29 22.20

D2 28 5.97 28 16.98

D3 29 10.39 29 27.01

Anal fin rays

Al 29 9.76 29 21.22

A2 30 9.06 30 17.58

A3 26 7.25 26 15.28

Sagittae

Ridges 29 20.62 7 77.36

Postrostral bands 28 14.45

annuli generally agreed among the 12 relatively small

and young fish for which comparison was possible

(r==0.89, P<O.OOI), although DGI's appeared somewhat

under-counted (Table 9).

Provisional Growth Model

A provisional estimate ofthe VBGF equation for cen tral

North Pacific swordfish with sexes combined was

L, == 321 [1 _ e-O.14 (t+ 1.3)]

Growth curves fit to EFL-at-age for males and females

broadly overlapped, at least for ages 4 or less; seven of

nine fish aged 6 and older were females (Fig. 4).

Table 6

Comparisons between readers of counts of presumed

annuli on all six different swordfish rays.

Test of Ho: slope == I

Regression

Readers N coefficient SE P

Avs B 502 0.913 0.0162 5.34 <0.001

Avs C 353 0.891 0.0129 8.43 <0.001

B vs C 345 0.890 0.0179 6.14 <0.001

Validation

A total of only 28 apparently viable swordfish were

caught on the 1991 (10 fish), 1992 (9), and 1993 (9)

cruises; each was injected with oxytetracycline, tagged,

and released. None of these marked fish has been recaptured as of October 1995.4

Discussion

Tissue-EFL Proportionality and Variability

All hard parts that we evaluated for ageing swordfish

grow proportionally with body size. Berkeley and Houde

(1983) and Tsimenides and Tserpes (1989) similarly

observed proportionality between the width of second

anal fin rays and body length ofswordfish. Our findings

of proportionality between sagitta length and body

length, though, seem to be the first to date for any

billfish. This should not be surprising, as our study is

4 Nor as of September 1998.
268 NOAA Technical Report NMFS 142

Table 7

Comparisons between readers of counts of presumed

annuli on each of six different swordfish fin rays. D =

dorsal, A = anal.

Table 8

Comparisons between readers of counts of presumed

annuli on swordfish vertebrae.

Regression

Readers Ray N coefficient SE

Test Ho: slope = 1

Regression

Readers N coefficien t SE P

Avs B 47 0.963 0.0279 1.33 >0.1

Avs C 33 0.937 0.0418 1.50 >0.2

B vs C 14 0.927 0.0564 1.30 >0.2

Table 9

Matched estimates of the number of presumed daily

growth increments (DGI's, converted to years) on

sagittae and the number of presumed annuli on cross

sections of rays and vertebrae of the same swordfish.

Counts of annuli agreed across all hard parts examined

for these 12 fish.

Avs B

Avs C

B vs C

Test for H o: slope = 1

p

Dl 74 0.753 0.0472 5.25 <0.001

D2 88 1.011 0.0356 -0.32 >0.5

D3 87 1.059 0.0348 -1.68 >0.1

Al 76 0.740 0.0492 5.28 <0.001

A2 95 1.033 0.0371 -0.88 >0.2

A3 82 1.000 0.0307 <0.001 >0.9

Dl 50 1.128 0.0268 -4.78 <0.001

D2 65 1.042 0.0366 -1.16 >0.2

D3 56 1.115 0.0299 -3.85 <0.001

Al 43 1.106 0.0310 -3.42 <0.001

A2 77 0.927 0.0402 1.82 >0.05

A3 62 1.045 0.0344 -1.30 >0.2

Dl 50 0.653 0.0533 6.50 <0.001

D2 65 0.962 0.0281 1.37 >0.1

D3 54 0.950 0.0356 1.41 >0.1

Al 42 0.713 0.0522 5.49 <0.001

A2 73 1.052 0.0407 -1.28 >0.2

A3 61 0.877 0.0383 3.21 <0.001

EFL

(cm)

DCI

(yr)

Presumed

annuli

I F = female, M = male, U = unrecorded, I = immature.

Dorsal and Anal Fin Rays-Counts of annuli sometimes

varied greatly among the different fin rays of individual

fish, especially for large specimens (>165 cm EFL).

easy, and fins can be obtained in large quantities because

they are discarded as swordfish are dressed at sea. Lastly,

the second ray of the first anal fin has precedence in

studies of Atlantic and Mediterranean swordfish (Berkeley and Houde, 1983; Prince et aI., 1988; Tsimenides

and Tserpes, 1989; Ehrhardt, 1992; Tserpes and

Tsimenides, 1995; Turner! ). The second ray of the first

anal fin is the most logical choice if fin rays are used to

age swordfish, even though there are inevitable complications in using fin ray sections, as there are with other

hard parts, for ageing studies. Difficulties in interpreting annuli on swordfish fin rays and other hard parts

are discussed in the sections that follow.

apparently the first to use a series ofshort straight-line

segments to approximate distance along the major axis

of a billfish sagitta. The sagitta becomes progressively

more curved in large billfish (Radtke and Hurley, 1983),

and describing its length by a single straight-line measurement disproportionately underestimates the length

of larger sagittae in older fish.

Some potentially useful ageing tissues can be prepared and measured with less variability than others.

Among the fin rays that we examined, for example, cuts

for cross sections can be most precisely located on the

second and third rays of dorsal and anal fins.

Tissue Suitability for Ageing

Additional factors such as reader precision, agreement

among readers, and preparation efficiency are also important criteria when choosing tissues to use for ageing.

The APE ofrepeat counts of annuli was consistently lowest

for the second ray of both the dorsal and anal fin. Counts

made using the second ray of dorsal and anal fins also

did not differ between readers, whereas counts clearly

differed between readers for other fin rays. On average,

counts of annuli did not differ between the second and

third rays of either dorsal or anal fins. Second rays

typically are the widest and usually have the deafest

bands. In general, the preparation offin ray cross sections

and the counting of annuli on ray sections are relatively

76.8

80.7

82.5

88.6

95.3

105.8

107.4

107.5

116.0

140.9

141.3

165.6

[

1

M

M

F

M

F

F

M

F

F

U

0.85

0.78

0.75

0.95

0.85

1.37

1.36

1.47

1.31

1.55

1.69

2.52

1

1

1

1

1

2

2

2

2

3

3

3
__________ Uchiyama et al.: Assessment of the Use of Hard Parts to Age Central Pacific Swordfish 269

250

6-

~O

200 E

()

'--"

.£.

-+-

rn 0

c

Q) 150

.::::t.

0 Male Female '+-

I 6:. Q)

0 - - _. 0 6:. ..........- 6:.

w 100 ....• ...

All

L ex> 321 em

50 k 0.14 -1

yr

to -1.3 yr

a

a 2 3 4 5 6 7 8 9

Age group (yrs)

Figure 4

Von Bertalanffy growth curves (VBGF's) for adult male (n=33) and female (n=40) swordfish

collected in 1992 and 1993. Provisional estimates of VBGF parameters (L~, K, and to) are

noted for all (n=77) fish, including three immatures and one of undetermined sex. Age

estimates were based on presumed annuli counts on cross sections of the second anal ray.

Second rays ofdorsal and anal fins sometimes appeared

to have more bands than adjacent rays. Higher counts

may represent mistaken inclusion of multiple bands or

false checks. Berkeley and Houde (1983) and

Tsimenides and Tserpes (1989) both observed multiple

bands on swordfish fin rays, but (like ourselves) only

counted the more prominent bands as annuli.

Loss of early annuli is theoretically a problem whenever living tissues such as fin rays are used to estimate

age. Neither Berkeley and Houde (1983) nor Tsimenides and Tserpes (1989) rigorously adjusted their fin

ray counts for potential loss of annuli due to internal

resorption. Tsimenides and Tserpes (1989) in part

elected to use the second anal ray because external

wear (erosion) did not seem to be a problem and

because the vascularized matrix (core) of the second

ray is small. Under-counting can be an important problem if early-formed annuli are missing due to resorp-
270 NOAA Technical Report NMFS 142 _

tion in the core offin rays; back-calculating the location

of resorbed first annuli has been modestly successful

for other billfishes (Hill et aI., 1989). Loss of the first

and second annuli may not be a problem when fin rays

are cut (as we have done, Fig. 2) at a moderate distance

above the base, thereby potentially minimizing the effects of internal resorption and external wear. The

general agreement that we found between DGI's and

annuli counts for the same fish (Table 9) suggests that

first annuli were present in our ray preparations, although these comparative data were limited to young

fish for which resorption and wear may be less or not a

problem. Further studies are needed that compare

counts of annuli between sections of fin rays cut at

various distances above the base and cut at the more

conventional location (base) of the same fin ray, particularly for old fish.

Vertebrae-It is possible to obtain a large number of

age estimates requiring no tissue preparation by counting bands on vertebral centra oflanded swordfish. However, the use ofvertebrae for ageing poses several problems. When counts of annuli on centra were compared

to counts on rays, higher counts sometimes occurred

on vertebrae, suggesting the presence ofmultiple bands

or false checks. Since pairing of adjacent bands does

not occur on centra, we had no objective basis for

adjusting counts. Counts also sometimes differed between the anterior and posterior cones of the same

vertebra. The last pair of bands to form on the cartilaginous faces of centra can easily be damaged or lost when

vertebrae are separated with a knife or scalpel. Bands

on swordfish vertebrae have previously been investigated by Beckett (1974), with similarly inconclusive

results.

Otoliths-The potential of using DGI's on sagittae to

estimate swordfish ages has been demonstrated by

Radtke and Hurley (1983) and Wilson and Dean (1983).

However, several unresolved problems exist. A major

difficulty in using otoliths is the care needed to extract

and prepare the tiny (1-5 mm long), delicate sagitta.

To obtain age estimates, the long fragile rostrum must

be extracted and prepared intact. Also, more time is

required to count DGI's than to count annuli. Furthermore, increment widths near the tip of the rostrum

may be too narrow to be resolved by light microscopy

(Campana and Neilson, 1985), requiring scanning electron microscopy. Light microscopic counts of the relatively broad DGI's that form during rapid early growth

may be the best way to age larval and young-of-year

juvenile swordfish (Megalafonou et aI., 1995), however.

The ridges reported by Radtke and Hurley (1983) on

the rostrums ofsagittae of northwest Atlantic swordfish

have now also been observed on sagittae of central

Pacific swordfish. Since rostral ridges are surface structures, the angle at which rostrums are viewed affects

their counts. Identifying the first and last ridges can be

subjective because these ridges are sometimes less developed than others, and an obvious potential bias exists for underestimating ages. Conversely, we observed

some specimens for which ridge counts were higher

than counts of annuli on other tissues from the same

fish. Ridges did not appear to form pairs or groupings

on these latter specimens, so there was no obvious basis

for objectively adjusting counts. The use ofrostral ridges

on sagittae for estimating ages of swordfish merits further study.

We also observed bands on the postrostrums of

sagittae that possibly could be used to estimate age.

However, counts of these bands were usually higher

than counts on other tissues of the same fish. As with

vertebral bands and otolith ridges, these postrostral

bands did not appear to form pairs or groupings whose

numbers could be objectively adjusted downwards.

Postrostral bands on swordfish sagittae appear to be

among the least reliable time markers and we discourage their use.

Age Validation

Ehrhardt's (1992) and Tserpes and Tsimenides's (1995)

edge analyses of annuli on anal fin rays of Atlantic and

Mediterranean swordfish, respectively, remain the only

partially successful attempts to date at validating swordfish ages based on a hard part. Wilson and Dean (1983)

and Radtke and Hurley (1983) only verified their results when they found agreement between counts from

different preparations or tissues. We have similar verification based on a general agreement between estimates

from second and third rays from dorsal and anal fins,

caudal vertebrae, and otolith ridges and DGI's. To date

we have been unable to validate our results, however,

because no oxytetracycline-marked fish have been recaptured. Thus far we also lack a comprehensive time

series of specimens necessary for an analysis of the

seasonal progression of marginal growth increments

on ageing structures. Insufficient seasonal samples seriously limited Ehrhardt's (1992) study.

Provisional Growth Model

We are reasonably confident that our estimates of age

in whole years for swordfish collected in 1992 and 1993

neither over- nor under-estimate ages by significant

fractions of a year. Even though the fin rays used for

this analysis were collected during a limited period of

the year (March-May), a translucent zone was always
__________ Uchiyama et al.: Assessment of the Use of Hard Parts to Age Central Pacific Swordfish 271

present on the edges of ray cross sections of the youngof-year and age-l fish, indicating completion or nearcompletion of the last annulus. Some edges ofray cross

sections of older fish (~2 yr) were translucent, but most

were partly translucent and opaque or still fully opaque

(Uchiyama, unpublished observation). Our current

study offin rays emphasizes the timing and duration of

opaque and translucent band formation for most early

age groups of central North Pacific swordfish.

Yabe et al. (1959) consistently identified four length

modes (73, 102, 128, and 148 cm EFL) for swordfish

caught during 1948-56 in the western North Pacific.

Our provisional growth curve for swordfish of both

sexes in the central North Pacific generally agrees with

these length modes, if the second, third and fourth

length modes of Yabe et al. (1959) correspond to fish

ages 1+ (18 mo), 2+ (30 mo), and 3+ (42 mo). Our

curve estimates a length of74 cm in about 7 mo, 104 cm

in 18 mo, 132 cm in 30 mo, and 157 cm in 42 mo (Fig.

4). Our estimate of the VBGF parameter, K = 0.14, for

the sexes pooled is similar to the K = 0.124 estimated by

Sakagawa and Bell (1980) using Yabe et al.'s (1959)

progression of length modes and L~ = 309 cm, graphically estimated using Walford's (1946) method. Our

growth curve describes an average growth increment of

about 28 cm/yr for swordfish between 74 and 157 cm

EFL, compared to Yabe et al. 's (1959) estimate of about

25 cm/yr for swordfish of 73-148 cm EFL from the

western North Pacific. Using length frequency data for

swordfish caught in the eastern Pacific, Kume and Joseph (1969) estimated growth rates of 38 cm/yr for fish

of 62-165 cm EFL.

These general agreemen ts between length modes

and estimates of the VBGF parameter, K, are limited to

only the first several apparent age classes entering their

respective fisheries. Clearly, additional data for both

small (young-of-year and yearling) and very large (>200

cm EFL) fish are needed to adequately describe the

shape of the VBGF growth curve. The von Bertalanffy

parameters K and L~ are inversely related, and L~ is

greatly influenced by data that lie near and on the

asymptote of the curve (Southward and Chapman,

1965).

Kume and Joseph (1969) further concluded that females grow faster and larger than males among eastern

Pacific swordfish. Also, based on size frequency distributions, female swordfish in the eastern Atlantic appear to grow faster and larger than males (Beckett,

1974). The hard-part ageing studies of Berkeley and

Houde (1983), Radtke and Hurley (1983), and Wilson

and Dean (1983) all suggest or indicate faster growth

rates for female swordfish in the western Atlantic, as did

analogous studies by Tsimenides and Tserpes (1989)

and Megalofonou et al. (1991) ofswordfish ofthe Mediterranean and Aegean Seas. Our data likewise suggest

that male growth starts decelerating earlier, perhaps

because males mature at smaller sizes or younger ages

in the Pacific as well as the Atlantic (Taylor and Murphy,

1992; Arocha et aI., 1994). Greater numbers of large

(>165 cm EFL) specimens of both sexes are needed

before we can adequately evaluate possible sexual dimorphism in the growth and mortality rates of Pacific

swordfish.

Research Needs

Since the end of summer 1993, observers have been

placed aboard commercial longline vessels operating

from Honolulu, and these observers have collected anal

fins and otoliths for our ageing studies. These samples

will enable us to expand our studies over a broader

geographical area and obtain greater numbers of large

fish. In addition, better seasonal coverage should result

than can be accomplished with our single research vessel.

A larger-scale tagging program with a more efficient

system for tagging and recovering tagged fish is necessary for validation. Greater involvement of the fishing

industry, other U.S. agencies, and foreign investigators

would vastly improve the chances of recapturing timemarked fish. On research cruises, we have learned how

to select and handle swordfish during the tag application process to maximize apparent viability, and these

findings need to be implemented on observer and cooperating fishermen cruises. A more accurate method

for estimating size of fish at the time of tag release also

still needs to be developed.

Acknowledgments _

We thank S. Kim for measuring lengths of sagittae and

H. Williams for measuring depths of vertebral cones

and band widths on cross sections of fin rays. We also

thank R. W. Gauldie, B. Kikkawa, M. K. Lowe, and S.

Smith for critical comments on an early draft of this

manuscript.

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SYMPOSIUM PARTICIPANTS]

Jaime R. Alvarado Bremer

Department of Biological Sciences

University of South Carolina

700 Sumter St.

Columbia, SC 29208, U.S.A.

jaimeab@biol.sc.edu

David W. Au

Southwest Fisheries Science Center

National Marine Fisheries Service, NOAA

P.O. Box 271

La Jolla, CA 92038-0271, U.S.A.

david.au@noaa.gov

Maria Angela Barbieri

Universidad Cat61ica de Valparaiso

Escuela de Ciencias del Mar

Facultad de Recursos Naturales

Avenida Brasil 2950

Casilla 1020,Valparaiso, Chile

mabarbie@ifop.c1

Kristine Barsky

Marine Region

California Department of Fish and Game

530 East Montecito Street, Room 104

Santa Barbara, CA 93103, U.S.A.

73711.2713@compuserve.com

Norman Bartoo

Southwest Fisheries Science Center

National Marine Fisheries Service, NOAA

P.O. Box 271

La Jolla, CA 92038-0271, U.S.A.

norm@wallyworld.ucsd.edu

William Bayliff

Inter-American Tropical Tuna Commission

c/o SIO

8604 LaJolla Shores Drive

La Jolla, CA 92037-1508, U.S.A.

Steven A. Berkeley

Hatfield Marine Science Center

Oregon State University

2030 S. Marine Science Drive

Newport, OR 97365-5292, U.S.A.

Reina Castro-Longoria

C[CESE

Apdo. Postal 2732

Ensenada, Baja California

22800 Mexico

rcastro@guayacan.uson.mx

I Current addresses.

Albert Caton

Fisheries Resources Branch

Bureau of Rural Sciences

P.O. Box Ell

Kingston, ACT 2604, Australia

albert.caton@brs.gov.au

Seinen Chow

National Research Institute of Far Seas

Fisheries

5-7-1 Orido, Shimizu

Shizuoka 424-8633,Japan

chow@enyo.affrc.gojp

Atilio L. CoanJr.

Southwest Fisheries Science Center

National Marine Fisheries Service, OAA

8604 La Jolla Shores Drive

La Jolla, CA 92038, U.S.A.

coan@nokaoi.ucsd.edu

Fran~ois Conand

ORSTOM

Rue Jean Bertho, B.P. 60

97420 Le Port

Reunion Island (Indian Ocean), France

fconand@univ-reunion.fr

James Cook

Western Pacific Regional Fishery Management Council

I [64 Bishop St., Suite 1405

Honolulu, HI 96813, U.S.A.

Richard Deriso

Inter-American Tropical Tuna Commission

c/o SIO

8604 La Jolla Shores Drive

La Jolla, CA 92037-1508, U.S.A.

Gerard T. Di Nardo

Honolulu Laboratory

Southwest Fisheries Science Center

National Marine Fisheries Service, NOAA

2570 Dole St.

Honolulu, HI 96822-2396, U.S.A.

gdinardo@honlab.nmfs.hawaii.edu

Bert Ely

Department of Biological Sciences

University of South Carolina

700 Sumter St.

Columbia, SC 29208, U.S.A.

ely@bioJ.sc.edu

David Evans

MRAG Ltd.

27 Campden Street

London W8 7EP

United Kingdom

Manuel Grijalva-Chon

C[CESE

Apdo. Postal 2732

Ensenada, Baja California

22800 MEXICO

Robert Harman

Western Pacific Regional Fishery Management Council

1164 Bishop St., Suite 1405

Honolulu, HI 96813, U.S.A.

Michael Hinton

Inter-American Tropical Tuna Commision

c/o SIO

8604 LaJolla Shores Drive

LaJolla, CA 92037-1508, U.S.A.

mhinton@ucsd.edu

David B. Holts

Southwest Fisheries Science Center

. ·ational Marine Fisheries Service, OAA

P.O. Box 271

La Jolla, CA 92038-0271, U.S.A.

dhol ts@fantasia.ucsd.edu

Russell Y. [to

Honolulu Laboratory

Southwest Fisheries Science Center

National Marine Fisheries Service, NOAA

2570 Dole SI.

Honolulu, HI 96822-2396, U.S.A.

russell. ito@noaa.gov

FredJulian

Southwest Fisheries Science Center

National Marine Fisheries Service, I OAA

P.O. Box 271

La Jolla, CA 92038-0271, U.S.A.

Pierre Kleiber

Southwest Fisheries Science Center

National Marine Fisheries Seryice, NOAA

P.O. Box 271

La Jolla, CA 92038-0271, C.S.A.

pkleiber@honlab.nmfs.hawaii.edu

275
276 NOAA Technical Report NMFS 142

Michael Laurs

Honolulu Laboratory

Southwest Fisheries Science Center

ational Marine Fisheries Service, NOAA

2570 Dole St.

Honolulu, Hawaii 96822-2396, U.S.A.

mlaurs@honlab.nmfs.hawaii.edu

Unai Markaida

CICESE

Apdo. Postal 2732

Ensenada, Baja California

22800 MEXICO

umarcaid@cicese.mx

Stan Moberly

P.O. Box 99488

Seattle, WA 98199-0488, U.S.A.

stan.moberly@nmt-inc.com

Hideki Nakano

National Research Institute of Far Seas

Fisheries

5-7-1 Orido, Shimizu

Shizuoka 424-8633,Japan

hnakano@enyo.affrc.gojp

Donald A. Petersen

Southwest Region

National Marine Fisheries Service, NOAA

501 West Ocean Boulevard, Suite 4200

Long Beach, CA 90802-4018, U.S.A.

don_petersen@-nmfs-LB

Fran.;:ois Poisson

IFREMER

Rue Jean Bertho, B.P. 60

97822 Le Port

Reunion Island (Indian Ocean), France

ifremer@dns.guetali.fr

Russell G. Porter

Pacific States Marine Fisheries Commission

45 SE 82nd Dr., Suite 100

Gladstone, OR 97027-2522, U.S.A.

Darlene Ramon

Southwest Fisheries Science Center

National Marine Fisheries Service, NOAA

P.O. Box 271

La Jolla, CA 92038-0271, U.S.A.

Fran.;:ois Rene

IFREMER

Rue Jean Bertl:o, B.P. 60

97822 Le Port

Reunion Island (Indian Ocean), France

ifremer@dns.guetali.fr

Gary Sakagawa

Southwest Fisheries Science Center

National Marine Fisheries Service, NOAA

P. O. Box 271

La Jolla, CA 92038-0271, C.S.A.

gary_sakagawa@-nmfs-Ll

Gerald P. Scott

Southeast Fisheries Science Center

National Marine Fisheries Service, NOAA

75 Virginia Beach Drive

Miami, Florida 33149-1003, U.S.A.

scotl_gerry@nmfs-sefc

Robert A. Skillman

Honolulu Laboratory

Southwest Fisheries Science Center

National Marine Fisheries Service, NOAA

2570 Dole St.

Honolulu, Hawaii 96822-2396, U.S.A.

rskillma@honlab.nmfs.hawaii.edu

Oscar Sosa-Nishizaki

CICESE

Apdo. Postal 2732

Ensenada, Baja California

22800 MEXICO

ososa@cicese.rrx

Richard B. Stone

Highly Migratory Species Management

Division (F/CM4)

ational Marine Fisheries Service. NOAA

1315 East West Highway

Silver Spring, MD 20910-3283, U.S.A.

Paul Taylor

Maf Fisheries, Greta Poi n t

P. O. Box 297

Wellington, New Zealand

James H. Uchiyama

Honolulu Laboratory

Southwest Fisheries Science Center

ational Marine Fisheries Service, NOAA

2570 Dole St.

Honolulu, HI 96822-2396, U.S.A.

james.uchiyama@noaa.gov

Koji Uosaki

National Research Institute of Far Seas

Fisheries

7-1, Orido 5-chome, Shimizu

Shizuoka 424-8633,Japan

uosaki@enyo.affrc.gojp

Yuji Uozumi

National Research Institute of Far Seas

Fisheries

7-1, Orido 5-chome, Shimizu

Shizuoka 424-8633,Japan

uozumi@enyo.affrc.gojp

Marija Vojkovich

Marine Region

California Department of Fish and Game

530 E. Montecito St., Ste. 104

Santa Barbara, CA 93103, U.S.A.

74763.1265@compuserve.com

Jerry Wetherall

Honolulu Laboratory

Southwest Fisheries Science Center

National Marine Fisheries Service, NOAA

2570 Dole St.

Honolulu, HI 96822-2396, U.S.A.

jwethera@honlab.nmfs.hawaii.edu

Michael C. White

Marshall Islands Marine Resources

Authority

Ministry of Resources and Development

Majuro 96960, Marshall Islands