tu 

NOAA Technical Memorandum NMFS 

+ 

July 1981 

STATUS REPORTS ON 

WORLD TUNA AND BILLFISH STOCKS 

NOAA-TM-NMFS-SWFC-15 

U.S. DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric Administration 

National Marine Fisheries Service 

Southwest Fisheries Center 
TABLE OF CONTENTS 

.......................... 2 Introduction 

A Synopsis of the Tuna and Billfish Status of Stocks Report. .. 5 

STATUS OF STOCKS REPORT 

At1 antic Ocean 

Yellowfin tuna. 9 

Bigeye tuna. ....................... 34 

Skipjack tuna ....................... 55 

Southern albacore ..................... 78 

Northern albacore ..................... 87 

...................... 

Indian Ocean 

Tunas.... ....................... 99 

Bill ........................ 118 fishes. 

Pacific Ocean 

Eastern tropical yellowfin tuna .............. 143 

Eastern tropical skipjack tuna. .............. 163 

Western skipjack tuna ................... 182 

Western yellowfin tuna. .................. 196 

Southern a1 bacore ..................... 212 

Northern albacore ..................... 228 

Northern bluefin tuna ................... 246 

Swordfish ......................... 256 

Striped, blue, and black marlins. ............. 277 

Appendix: List of Conference Attendees. ............ 391 
-2- 

INTRODUCTION 

The National Marine Fi sheries Service's Southwest Fi sheries Center

(SWFC) second Workshop on Tuna and Billfish Research was held at the Sa

Clemente Inn, San Clemente, California, on December 15-17, 1980. Th

report summarizes the results of that workshop and reproduces the report

on the status of tuna stocks that were presented at the workshop. 

A total of 26 persons participated in the meeting, including 24 fro

the SWFC and two from the NMFS Office of International Affairs. A list o

attendees and their organizational affiliation is given in the Appendix

David Mackett, Planning Officer for the SWFC, was the Workshop Coordinator. 

The purpose of the Workshop was to review the situation regarding 

number of tuna and billfish stocks of importance to the U.S. and to improv

the Center's near-term and long-range research plans. Before the Worksho

began, 16 Status Reports written by SWFC staff and collaborators, coverin

some 25 different species or stocks of Atlantic, Pacific, and Indian Ocea

tuna and billfish, were distributed to the participants. These report

give a short description of the fishery, present an overview of the natu

and degree of U.S. and foreign interest in the fishery, and discuss th

current status or condition of the stocks. Recommendations for furthe

also given. The Status Reports include most of the world's tuna stocks o

direct and indirect interest or importance to the U.S. commercial an

recreational fishermen, canning industry, and consumers. The full repor

are presented in this document. 

analyses, data collection, or research programs regarding the fishery ar

Authors presented highlights of their reports to the Worksho

participants and questions and comments were solicited from the group. I

addition to the Status of Stocks Reports, the Director of the Office o

International Fisheries Affairs presented an overview of the status o

international tuna fishery problems and the state of international an

bilateral negotiations concerning them. On the basis of the reports

presentations, discussions, and rapporteurs' summaries, the Cente

Director, Honolulu Laboratory Director, and the Chief of the Ocean

Fisheries Resources Division (OFRD) , meeting as the Tuna Program Boa

(TPB), made a number of decisions regarding future SWFC program emphas

and direction. These decisions were discussed in the Workshop an

subsequently assignments were given to SWFC staff for completing an

documenting the work pl ansl. 

The Workshop concentrated on the stock assessment and fisher

evaluation aspects of the Center's tuna research program, but some tim

a1 so was devoted to a discussion of the tuna-environment interactio

'The first Workshop was held September 11, 1979, at the same location. 
-3- 

studies. The presentations and discussions were held in the context 

framework shown in Figure 1, which depicts the elements contributing to 

overall goal of the Center's tuna research program, i .e. , the del iver

tuna resource management information and advice to NMFS, Departmen

State, U.S. Commissioners of international commissions, U.S. delegates 

negotiators participating in bilateral or international negotia

missions, and fisheries managers in both the international and nati

arenas. 
-4- 

SWFC TUNA PROGRAM: FUNCTIONAL MODEL 

VIRONMENT 

OF PROGRAM 

MANAGEMENT 

TUNA PROORAM 

PACK AGl W 

INFOIADVI 

I 

UNA STOCK 

ASSESS- SYSTEMS ECONOMICS 

DATA 

TUNA- COLLECTION ENVIRONMEHT a DATA 

INTERACTION 'MANAGEMENI 

p%%-"tq CAPABl Ll T Y 

Figure 1. The SWFC's Tuna Program is geared to the delivery of tuna 

management information and advice to U. S. Commissioners 

and U.S. negotiators. Several functions must be performed 

to deliver the information required for good management 

decisions; these functions include stock assessments, 

economic analysis, data management, analysis of fish environment interactions and a system analysis function that 

ties the specialized information together. Research in 

any or all elements may be required to improve overall 

quality; management of the program, because of its diversity and complexity, is given special consideration. 
-5- 

A SYNOPSIS OF THE TUNA AND BILLFISH STATUS OF STOCKS REPORTS 

CQ 

The current evaluation of the status of tuna stocks and tuna fish

is based on a large number of foreign and domestic data sources, 

analyses performed by NMFS scientists or by international or fo

fishery agencies. Many of the evaluations presented here are the re

of international fishery workshops in which NMFS/SWFC scien

participated. Expert judgement is required in choosing the analy

techniques to be applied and in interpreting the results; therefore, 

has been taken in setting forth the results of each analysis in ord

indicate its reliability and to point out where weaknesses in the da

techniques may exist. This is especially indicated in light of pos

discrepancies in the data or inconsistencies in the outcome or conclu

of simil ar analyses. 

The papers presented herein summarize the avail ab1 e informatio

conclusions to be dr,awn for some 25 species or stocks of the world's 

and billfish. In several cases it is not known whether a specie

represented by a single breeding population or by two or more sepa

breeding stocks. Whenever prevail ing opinion or overwhelming eviden

present to strongly suggest the presence of separate stocks, we 

separated the analyses and results accordingly and presented thes

separate papers, e.g,., south and north Atlantic albacore. However, in 

cases where there is some evidence to suggest that two or more stoc

the same species may be present, or where it is of interest to invest

the hypotheses of separate stocks, we have performed the analyses 

both the single and multiple stock hypotheses (if sufficient data e

and have presented the results in a single paper, e.g., Pacific swo

or Atlantic skipjack. 

A summary of the reasonable conclusions to be drawn from the cu

status of stocks is given in Table 1. Each species or stock is eval

in terms of whether or not catches could be increased by (1) s

increasing the effort expended, or (2) instituting certain manag

measures. These overly simp1 ified categories are modified somewhat b

information presented in the matrix. (NOTE: The reader shou

cautioned that, in order to give a quick overview, most of the quali

remarks about the re1 iabil ity of these conclusions have been stripped 

the original text as it was lifted from the detailed status of stock p

and placed in the table.) 

The question arises as to why the SWFC performs tuna stock assess

and fishery evaluations when the U.S. fishery seems to be relat

heal thy economical ly and opportunities for tuna fishery devel opmen

fairly well identified. Often a remark about the difficulty 

uncertainty of suclcess of international negotiations accompanies 

question. 

The answer to why this work is required lies in the analysi

comparison of (1) the tuna fisheries' value to the United States, (2
-6- 

Table 1. 

Conclusions to be Drawn from the Status of Tuna Stocks 

Concerning the Level of Annual Sustainable Catches 

Relative to Current Effort and Possible 

Management Measures 

Increase in catch likely 

with about optimum with an increase in with change in 

SpecieslStocklFishery Increase in catch likely Catch at or near MSY 

effort be i ng 

expended under 

current fishery 

management 

effort management provisions 

ATLANTIC OCEAN 

Yellowfin Catch near MSY 

especially in eastern 

Atlantic creased surface effort 

Eastern Atlantic, no; western 

Atlantic, possibly with inUncertain 

Bigeye Yes, an annual 11,000 to Some increase to be expected No 80,000 mt increase is likely with increase in age of first 

capture 

Skipjack Yes, MSY cannot be calculated 

but information suggests 

potential yield higher than Unknown 

current catch especially in 

western Atlantic. 

Yes, increases of from 6,000 No, yield-per-recruit already 

to 10,000 mt seems Dossihle hirlh at 7.7 kg for lonq-line 

Unknown 

Albacore, S. Atlantic - 

Albacore, N. Atlantic Near MSY with current Small increase in average Yes, but only with severe 

age structure of catch annual catch likely with restrictions on surface 

increased effort, but fisheries 

recruitment highly variable 

so probably not prudent to 

increase effort substantially 

INDIAN OCEAN 

A1 bacore 

Bigeye 

Appears fully exploited 

Unknown Lightly exploited, but 

actual potential unknown 

Yes, especially by surface 

fisheries 

? 

Ye1 1 owf i n Long1 ine catch appears 

to be at maximum 

Skipjack ? 

B1 ue marl in 

? 

Possibly, but there may be 

errors in total catch estimates 

which would affect conclusion 

Striped marlin Some small increase appears 

possible __ 

Unknown Black marlin Appears to be fully or 

over-exploited 

Increase in catch appears 

1 i kely 

Yes, potential yield much 

higher than maximum annual 

catch thus far 

Swordf i s h 

Sailfish 

PACIFIC OCEAN 

Yellowfin, E. Pacific No, recent catches and 

effort above MSY and 

optimum with current 

age structure 

Skipjack, E. Pacific 

No Yes, increasing the age of firs

capture would yield substantial 

improvements in total catch 

over time 

Increases in catch likely 

with increased effort, 

especially if smaller 

fish are caught without 

affecting recruitment 

Some increase in surface 

fishery catches possible; 

total yield may increase 

Yellowfin, W. Pacific Yes, especially for 

longline 
-7- 

Table 1. (cont.). 

- Skipjack, W. Pacific Stock appears under- - 

exploited 

Albacore, N. Pacific Subs tan tial gains 

unlikely with fishery 

in present configuration 

of long1 ine and surface 

effort 

- 

Bluefin, N. Pacific 

Swordfish 

Blue marlin 

Recent catches are near 

MSY 

IU 0 No 

Black marlin Appears fully Possibly, but large increases 

exploited probably not sustainable 

Striped marl in Catches near MSY Modest increases in effort 

may increase yield on 

Pacific-wide basis 

Potential increases possible, 

currently being evaluated 

Western Pacific-eastern 

Pacific catches have declined 

substantially but at present 

cause and therefore cure are 

unknown. Analyses will be 

performed 

Fishery Management Plan (FMP) 

being developed under Pacific 

and Western Pacific Fishery 

Management Councils. 

Preliminary Fishery Management 

Plan (PMP) in effect 

Unknown, stock appears 

"overfished" 

Unknown 

Unknown 
-8- 

existing and potential threats to diminishing that value seriously, and (3) 

the costs of developing and using information and analysis to preserve that 

value and to mitigate or avoid problems. 

First, let us investigate the value of tuna fisheries to the Pmerican 

citizen, consumer, worker, businessman, and taxpayer. Estimates put the 

total annual retail value to the United States (in the form of canned 

products of U.S. catches and foreign (whole) fish imports for canning) at 

$1,288,000,000 - nearly $1.3 billion annually. 

The existing and potential threats to the maintenance of this $1.3 

billion annual value to the U.S. are varied and complex. This value, which 

is based on a living renewable resource, is threatened with diminution from 

inadvertent or willful overfishing by foreign or domestic fisheries - 

perhaps in pursuit of small short-term gains at great long-term costs to 

future Americans. Major threats to preserving this value can occur if U.S. 

fishermen are denied access to fishing grounds within the fishing or 

economic zones established by foreign countries - fish caught by U.S. 

fleets are an important factor in avoiding a "fish OPEC" situation. 

Similar threats to limit the world's total supply of tuna (which supports 

the U.S. supply of imported fish for processing in American canneries) can 

occur on a multi-national scale. Thus, the success of the tuna fisheries 

of Japan, Korea, and Taiwan are of interest to the U.S. as well. The fact 

is that all the tuna stocks and fisheries of the world are linked, if not 

by principles of nature and the biological responses of the tuna resource 

to fishing and environmental changes, then by the complexities of 

international economics, demographics, and markets on a global scale. 

The U.S. tuna fishery - its supply, harvest, processing, and marketing 

- is carried out within the world-wide multi-national arena of foreign 

affairs. On the international scale, one cannot negotiate fishing access 

to foreign waters, negotiate international conservation measures, or 

negotiate for 1 ong- term 1 arger annual benefits in pl ace of small er 

diminishing short-term gains without being prepared, and ?wing prepared 

means being informed. Information about the world's tuna ss~cks an+ the 

world's tuna fisheries is vital to the effort to preserve the msourc;r: and 

the valuable U.S. tuna industry and its products for the benefit of all 

Americans. 

The annual cost incurred by the SWFC in obtaining information on tuna 

resources and the fishery is $1.2 million - about 15% of the Center's 

budget and less than one-tenth of one percent (0.01%) of the annual value 

of the U.S. fishery. 

David J. Mackett 

Workshop Chairman 

Southwest Fisheries Center 

La Jolla, California 
STATUS REPORTS ON 

WORLD TUNA AND BILLFISH STOCKS 
-9- 

STATUS REPORT: ATLANTIC YELLOWFIN TUNA 

Atilio L. Coan, Jr. 

Southwest Fisheries Center 

Oceanic Fisheries Resources Division 

La Jolla, California 

ABSTRACT 

The status of Atlantic yellowfin tuna stocks remained unchanged fro

1979 to 1980. Production model analyses indicate that the stocks are b

fished at high levels, especially in the eastern Atlantic. 

fishing effort with the fishery operating within its present geographic

boundaries is unlikely to produce substantial gains in yield. 

Increase in 

In 1973, a minimum size regulation was adopted for Atlantic yellow

tuna to decrease fishing mortality on small fish and to increase yield-p

recruit (YPR). 

occurred for some fisheries since the adoption of the regulation. 

gains may be less than predicted due to discarding of undersized fish. 

relatively constant. 

stocks should be carefully monitored. 

Analyses indicate that a slight increase in YPR has 

These 

Estimates of recruitment to the Atlantic yellowfin fishery have he

Rased upon these assessments, Atlantic yellowfin t
-1 0- 

I. DESCRIPTION OF THE FISHERY 

Atlantic yellowfin tuna are caught by multispecies fisheries located 

throughout the tropical regions of the Atlantic Ocean; skipjack and bigeye 

tunas are also caught. Three principal fishing methods are used in these 

fisheries: purse seine, baitboat, and longline. Analyses of Atlantic 

ye1 lowfin tuna fisheries usually consider fisheries in two geographical 

regions: an eastern Atlantic fishery and a western Atlantic fishery, 

divided at 30" W longitude (Figure 1). 

I.A. History of the Fishery 

I .A.1. Eastern At1 antic Fi shery 

Baitboats from France and Spain started the eastern 

Atlantic surface fishery for yellowfin tuna in 1955 and purse seiners 

entered the fishery in the early 1960's. 

1957 with the Japanese long1 ine fleet. 

in the eastern Atlantic surface fishery and 6 countries participate in the 

1 ongl ine fishery. 

The longline fishery started in 

Currently, 14 countries participate 

The major participants in the eastern Atlantic 

fisheries are the French-Ivory Coast-Senegalese-Moroccan (FISM) , Spanish, 

Korean/Panamanian, and U.S. fleets. 

eastern Atlantic yellowfin tuna catches during the period 1975 to 1979 

(Figure 2a). 

These fleets caught 90% of the average 

I .A.2. Western At1 antic Fi shew 

catches in the Gulf o 

Surface fisheries for 

from time to time off 

catches have been sma 

The yellowfin tuna fishery in the western Atlantic, 

started by the Japanese in the 1950'~~ is primarily a longline fishery. 

Catches are concentrated in areas off Brazil and Venezuela, with some 

Mexico and off the U.S. east coast (Figure 1). 

yellowfin tuna in the western Atlantic have existed 

Venezuela and off the U.S. east coast, but the 

1 (highest reported catch is 5,000 mt). 

The major participants 

are Korea/Panama, Japan, Venezuela, Cuba, 

accounted for 88% of the total western At 

period 1975 to 1979 (Figure 2b). 

n the western Atlantic fishery 

and the U.S. These fleets 

antic yellowfin catch during the 
-I I100" 80" 60" 40" 20" O0 20" 40" 

60" 

40" 

20" 

0" 

20" 

40" 

60" 

Figure 1. Areas of the Atlantic Ocean currently or historically fished 

for yellowfin tuna. Densely hatched areas indicate areas of 

greatest fishing intensity. 
-1 2- 

SPAIN 29% 

F ISM 45% 

OTHER 10% 

KOREA / PAN AM A 10% 

USA 6% 

JAPAN 17% TUSA 6% 

7 

OTHER 12% 

KOREAiPANAMA 49% 

Figure 2. a) Major participants in the eastern Atlantic surface and longline fishery for yellowfin tuna, 1975 to 1979. 

b) Major participants in the western Atlantic surface and longline fishery for yellowfin tuna, 1975 to 1979. 
-1 3- 

1.6. Trends in Catch and EFfort 

.- 

I .B.1. Eastern At1 antic Fishery 

Catches of yellowfin tuna for the eastern Atlantic 

longline fishery peaked in 1973 at 25,000 mt, then decreased gradually to 

an estimated 5,000 mt in 1980 (Figure 3a). Surface fishery catches, in 

contrast, increased from 36,000 mt in 1966 to a record high of 110,000 m

in 1979. Estimated surface catches in 1980 decreased to 95,000 mt 

( prel iminary estimates). 

Estimated fishing effort for the eastern Atlantic 

longline fishery from 1967 to 1977 is shown in Figure 4a. Effort increa

to a high of 91 million hooks in 1973, then decreased to 43 million hook

in 1977. Estimated fishing effort for the eastern Atlantic surface fishe

from 1967 to 1979 was estimated by dividing the total eastern Atlantic 

surface yellowfin catch by catch-per-unit-effort for the FISM fleet, the 

major harvester (Figure 4b). 

standard days absence (SDA) in 1967 to 57,000 SDA in 1979. 

Surface fishery effort increased from 8,000 

1.6.2. Western Atlantic Fishery 

Catches from the western Atlantic longline fishery 

have fluctuated between 7,000 mt and 15,000 mt during the period 1966 to 

1980 (Figure 3b). 

4,700 mt in 1978 to a low of 600 mt in 1976. 

Surface fishery catches have fluctuated from a high o

Estimated effort for the western At1 antic long1 ine 

fishery increased from 25 million hooks in 1967 to 65 million hooks in 

1973, then fluctuated between 46 and 58 million hooks from 1974 to 1977 

(Figure 5). 

At1 antic. 

No estimates of surface effort are available for the western 

I.C. Value of Catch 

The 1979 U.S. average ex-vessel price for yellowfin tuna was 

$893/mt for fish less than 3.2 kg and $1,047/mt for fish greater than 3.2 

kg. 

Atlantic longline and surface yellowfin tuna catch (130,OO mt) was 

approximately $126 million. The western Atlantic catch (11,100 mt) was 

worth approximately $11 million. 

Based on an average price of $970/mt, the value of the 1979 eastern 
-1 4- 

A 

tit5 

I 

0 

l0 

Y 

a 

8 

h 

rr) 

2 

t5 

I 

0 

l0 

Y 

a 

I L" 

- SURFACE 

loo/ ---- LONGLINE 

Of I I I I I I 

1966 1968 1970 1972 1974 1976 1978 1980 

YEAR 

1966 1968 1970 1972 1974 1976 1978 1980 

YEAR 

Figure 3. a) Total catch of yellowfin tuna using surface and longline fishing gear in the eastern Atlantic, 1966 to 

1980. 

b) Total catch of yellowfin tuna using surface and long- 

line fishing gear in the western Atlantic, 1966 to 

1980. 
-1 5- 

A. 

I ea 

80 

6a 

40 

20 

0 

1967 I969 1971 1973 I975 I977 

YEAR 

B. 

rl 

n 

8 

Ir) 

- 

I 

4 

69 

W 

IQ! 

0 

L 

k 

W 

a 

..- 

78 

60 

50 

48 

30 

20 

la 

0 

1967 I969 1971 I973 I975 1977 I979 

YEAR 

Figure 4. a) Fishing effort (number of hooks) on yellowfin tuna from 

the eastern Atlantic longline fishery, 1967 to 1977. 

b) Fishing effort (standard purse seine days absence, SDA) 

on yellowfin tuna from the eastern Atlantic surface 

fishery, 1967 to 1979. 
-1 6- 

70 

68 

sa 

40 

30 

20 

10 

0 

I967 I969 1971 1973 

YEAR 

I975 1977 

Figure 5. Fishing effort (number of hooks) on yellowfin tuna from 

the western Atlantic longline fishery, 1967 to 1977. 
-1 7- 

I .D. Current Management of the Fishery 

Yellowfin tuna fisheries in the Atlantic Ocean are managed 

cooperatively by the 19 member nations of the International Commission f

the Conservation of Atlantic Tunas (ICCAT). 

yellowfin minimum size regulation in July 1973 that states 

The Commission adopted a 

'I. . .that the Contracting States take the necessary measures 

to prohibit any taking and landing of yellowfin tuna weighing 

less than 3.2 kg. 

Notwithstanding the above regulation, the Contracting 

States may grant tolerances to boats which have incidentally 

captured yellowfin weighing less than 3.2 kg, with the condition that this incidental catch should not exceed 15% of the 

number of fish per landing of the total yellowfin catch of 

sa i d boats . 'I 

The size regulation was adopted to decrease fishing mortality o

young ye1 lowfin tuna and increase yield-per-recrui t. ,,-- 

11. NATURE AND SIGNIFICANCE OF U.S. AND FOREIGN 

PARTICIPATION IN THE FISHERY 

c 

The U.S. interest in Atlantic yellowfin tuna is concerned with: 1) 

harvesting by our domestic fleet, 2) processing of domestic and foreig

catch, 3) consumption of the canned product, and 4) maintaining a relia

and steady market for yellowfin through conservation measures. 

Only part of the U.S. tropical tuna fleet, predominately an eastern 

tropical Pacific industry, fishes in the Atlantic Ocean. These vessels 

usually enter the fishery in the summer soon after the yellowfin tuna 

regulatory area (CYRA) in the eastern tropical Pacific is closed to 

yellowfin fishing, and usually return to the Pacific by December. 

fleet is composed mainly of large purse seiners. 

vessels that annually participate in the fishery peaked in 1972 (40 

vessel s) , dropping to 12 vessel s in 1979 (Figure 6a). 

fished in the Atlantic in 1980. 

peaked in 1969 (18,791 mt) and has averaged 7,400 mt from 1967 to 1979 

(Figure 6b). 

approximately $3 million (the entire industry catch was 141,000 mt worth 

$137 million). 

two species are not separated in preliminary figures) was 8,500 mt. 

The 

The number of U.S. 

Only 6 U.S. vess

The yellowfin catch of these vessels 

The 1979 U.S. Atlantic yellowfin catch of 3,200 mt was wo

Preliminary U.S. catch of yellowfin and bigeye in 1980 
-1 8- 

A 

N 

U 

H 

B 

E 

R 

0 

F 

v 

E 

S 

E 

L 

S 

B. 

C 

A 

T 

C 

ti 

n 

E 

T 

R 

I 

C 

T 

0 

N 

S 

I I I 1 I 1 

I968 1970 I972 t 974 I976 I978 

YEAR 

THOUSANDS 

I968 1970 I972 I974 1976 I978 

YEAR 

Figure 6. a) Total fishing effort in number of U.S. vessels 

fishing in the Atlantic Ocean, 1967 to 1979. 

b) Total catch of yellowfin tuna for U.S. vessels 

fishing in the Atlantic Ocean, 1967 to 1979. 
-1 9- 

,- U.S. imports of Atlantic yellowfin and bigeye tuna averaged 

approximately 12,000 mt during 1970 to 1979 (yellowfin and bigeye impor

are not reported separately). 

mt) was approximately $8 mill ion. Virtually a1 1 domestic and imported 

catches of Atlantic yellowfin tuna are packed and consumed in the U.S. 

Annual total consumption of At1 antic yellowfin tuna is approximately 15

mt worth about $14 million. 

The value of the 1979 imported catch (7,8

Future participation by U.S. and foreign vessels in the Atlantic 

yellowfin fishery is difficult to determine. 

the current status of the stocks, the FISM and Spanish fleets should 

continue to dominate surface catches, and the Korean/Panamanian and 

Japanese fleets should dominate 1 ongl ine catches. 

off South Africa and Brazil may increase foreign participation. Future 

U.S. participation is partially dependent on catches in the CYRA and the 

outcome of regulatory measures in this area. 

present, U.S. participation should not increase from that in 1980 (6 

vessels). The U.S. fleet in 1978 to 1980 increased their fishing activ

in the western Atlantic off Venezuela. Whether this increase will cont

in 1981 is unknown. 

Based on past performance 

New fisheries devel o

If conditions remain as 

111. STATUS OF THE STOCKS 

1II.A. Stock Structure 

No conclusive evidence is available on Atlantic yellowfin tuna 

stock structure. 

western At1 antic have been observed and larval studies have identified 

important spawning areas off Brazil and in the Gulf of Guinea. 

show lower gonad indices for yellowfin tuna off Brazil than in the east

Atlantic, leading to the hypothesis of separate eastern and western sto

in the Atlantic Ocean. Since this evidence is inconclusive, analyses h

employed both single and two stock hypotheses. 

Separate longline catch rate maxima in the eastern an

Studies 

Recent catches of yellowfin tuna off Cape Agulhas, South Afric

have raised the question of whether these fish were from an Indian Ocea

popul ation or an At1 antic Ocean popul ation. Additional studies are nee

to answer this question. 

The hypothesi s of separate ye1 1 owfin stocks avail ab1 e to surfa

and longline gears has been suggested. Current evidence, although not 

conclusive, indicates that there is a high seasonal and annual correlat

of CPUE indices between the two gears. Therefore, until new evidence i

available, fish caught by surface and longine gears are provisionally 

thought to be of the same stock. 
-20- 

I I1 .B. Stock Assessment and Fishery Eva1 uation 

I I1 .B.1. Trends in Catch-per-Uni t-Effort 

The only avail ab1 e At1 antic-wide catch-per-uni t-effort 

Since 

(CPUE) series is for the longline fishery (Figure 7a). 

decreased from 0.9 fish per hundred hooks in 1967 to 0.4 in 1975. 

1975, CPUE estimates have fluctuated between 0.4 and 0.6 fish per hundred 

hooks. 

CPUE estimates 

The best available eastern Atlantic CPUE series is for 

the FISM purse seine fleet. 

absence (SDA) in 1969 to 1.9 in 1979 (Figure 7b). 

CPUE decreased from 6.2 mt/standard day 

III.B.2. Results of Production Model Analysis 

No definite evidence on stock structure exists; 

therefore, production model analyses used to assess stock status have been 

performed under two stock structure hypotheses: 1) total Atlantic stock, 

and 2) separate eastern and western Atlantic stocks. Data from each stock 

structure have been analyzed with three production models: 1) the 

asymptotic model, where m = 0, 2) the Gompertz model, where m approaches 1

and 3) the logistic model, where m = 2. 

parameter of the fitting equation. 

In each case, m is the skewness 

III.B.2.a. Total Atlantic stock 

Based on the degree of fit index (r2), 

the m = 0 (r2 = 0.995) production model best fits the data (Fi ure 8). 

models are essentially the same. Therefore, the choice of the most 

appropriate model is impossible at this time. While the m = 0 model 

imp1 ies that sustainable catch theoretically never decl ines at very high 

levels of effective fishing effort, it is clear that, at some high level o

effective fishing effort, the stock will become so depressed that 

recruitment and sustainable catch will decline. It is not known at what 

level of fishing effort this will occur and caution must therefore be 

exercised when drawing conclusions from higher effort levels beyond the 

1 imi t s o f the avail able data. 

However, the r2 values for the m = 1 (r2 = 0.992) and m = 2 (r 4 = 0.992) 

Estimates of maximum sustainable yield 

(MSY) of yellowfin from the total Atlantic stock range from 119,000 mt to 

144,000 mt depending upon the model being used (Figure 8). MSY occurs at 

an optimum effort (f*) of 51,000 standard days absence (SDA) for the m = 2 

defined for the m = 0 model. 

model , and at 54,000 SDA for the m = 1 model. Optimum effort is not 

The preliminary estimate of the 1979 catch 
-21 - 

A. 

v) 

Y 

0 

0 

X 

\ 

X 

v) 

H 

c 

4 

D fn 

\ 

tx 

0.8 

0.6 

0.4 

0.2 

0 

1967 1969 1971 1973 197s 1977 

YEAR 

8. 

io 

8 

6 

4 

2 

0 

1967’ I969 1971 1973 I975 1977 I979 

YEAR 

Figure 7. a) Catch-per-unit-effort (number of fish/100 hooks) from 

the Atlantic longline fishery for yellowfin tuna, 

1967 to 1978. 

seine days absence) from the eastern Atlantic surface 

fishery for yellowfin tuna, 1967 to 1979. 

b) Catch-per-uni t-effort (metric tons/standard purse 
-22- 

120- 

100- 

80- 

I .-. 0 c 

X 

I 

0 

t0 

Y 

a 

60- 

40- 

\ m= 1 

i m=2 

0,' I I I I I I I I 

10 20 30 40 50 60 70 80 0 

EFFORT (X lo3 SDA) 

Figure 8. Equilibrium yield curves generated from data of the total 

Atlantic surface and longline fishery for yellowfin tuna, 

1964 to 1979. 
-23- 

*- 

(130,000 mt) is within the range of MSY estimates and is at an effort le

of 68,000 SDA. 

III.B.2.b. Separate eastern and western 

Atlantic stocks 

Production model analyses were performed 

assuming separate east and west stocks. 

eastern Atlantic data sets: 

and 2) data from the surface fishery only. 

The models were applied to two 

1) data from the surface and longline fishe

The m = 0 model best fits data sets 1 and 

2 where r2 = 0.990 and 0.972, respectively. 

between 94,000 and 133,000 mt, depending on the model and data set chos

(Figures 9 and 10). Optimum effort is 43,000 to 46,000 SDA for the m = 

model, and 49,000 to 52,000 SDA for the m = 1 model. The 1979 catch is 

116,300 mt for data set 1 and 109,500 mt for data set 2. Current fishin

effort levels are 13 to 24% greater than fk. 

Results suggest that MSY i

As with the total Atlantic stock data, r2 

values for the m = 1 and m = 2 models were only slightly different than 

the m = 0 model. Therefore, MSY estimates are presented for all three 

model s because objective criteria for choosing among the different mode

are unavailable. If m = 1 or m = 2 is true, and the fishery is current

operating under equil ibrium conditions, then any increase in effective 

fishing effort will not result in any notable increase in sustained yie

If m = 0 is true, however, increases in effective fishing effort can re

in increased sustained yield and decreased CPUE. 

The models were fitted to data from the 

longline fishery in the western Atlantic. Results give MSY values rang

from 16,000 mt to 22,000 mt at effort levels of 25 million and 35 mill

hooks (Figure 11) for the m = 1 and m = 2 models, respectively. Curren

catches are at or below MSY and current levels of fishing effort are ab

those giving MSY. The results suggest that total catch by the longline 

fishery in the western Atlantic will not increase with increased fishin

effort. 

III.B.3. Results of Yield-per-Recruit-Analysis 

Yield-per-recrui t analyses performed on the 

hypothesized eastern Atlantic stock indicate that increases in yield-pe

recruit to the fishery as a whole can be obtained with an increase in s

at-first-capture or a moderate increase in fishing effort (Figure 12). 

outcome is different for the different gears: the longline fishery wou

gain in yield-per-recruit by any increase in size-at-first-capture up t

about 120 cm; the purse seine fishery would gain by any increase in siz

at- fi rst-capture. 
-24- 

EFFORT (xio3 SDA) 

Figure 9. Equilibrium yield curves generated from data of the eastern 

Atlantic surface fishery for yellowfin tuna, 1969 to 1978. 
-25- 

_- 

II20 

100 

- 

tH 

ro 80 0 

X 

7 

v 

6 60 

a 

t0 

4c 

2c 

C I I I I I I I I 

0 10 20 30 40 50 60 70 80 

EFFORT (x io3 SDA) 

Figure 10. Equilibrium yield curves generated from data of the 

eastern Atlantic surface and longline fishery for 

yellowfin tuna, 1964 to 1979. 

.- 
-26- 

EFFORT (X lo6 HOOKS) 

Figure 11. Equilibrium yield curves generated from data of the 

western Atlantic longline fishery, 1956 to 1977. 
-27- 

- 1975 FISHERY, M = 0 8 

480 - 

- 

I60 - 

- 

I40 - 

- 

- 

- 

120 - 

100 - 

80 - 

- 

60 - 

- 

40 - 

Ill IIIIIIIII I I I I I I 11 1'1 111'1 I 

00 02 04 06 08 10 12 14 16 18 20 22 24 26 28 30 

EFFORT MU LT I P LI E R 

.- 

Figure 12. Yield-per-recruit isopleths for the eastern Atlantic surface 

and longline fishery in 1975. Natural mortality M=0.8. 
-28- 

The situation with respect to changes in minimum 

landing size is more complex. 

the benefits to the fishery as a whole will occur as predicted by the 

yield-per-recruit model. On the other hand, if small fish continue to be 

caught, and are discarded dead, there may be little or no increase in 

effective size-at-first-capture, and therefore, no benefit. Available dat

show that Japanese Tema-based baitboats apparently discarded 1,130 mt of 

undersized yellowfin in 1977 while landing only 2,488 mt. Higher rates of 

discarding were noted for two trips of Tema-based baitboats accompanied by 

Ghanaian technicians in 1978 (6,660 mt). Therefore, the actual yield-perrecruit to the fishery may be less than predicted. 

If fishermen avoid catching small fish, the

I I I .B.4. Resul t s o f Spawner/Recrui tment Analysis 

No spawner/recrui t re1 ationshi ps have been defined for 

At1 antic ye1 1 owfin tuna. 

of yellowfin tuna to the eastern Atlantic fisheries. Estimates of 

recruitment to age 1 in the 1965 to 1968 year-classes varied between 12 

million and 26 million fish. 

relatively constant at approximately 24 m i l l i o n f i s h (Figure 13). 

trends in recruitment are evident. 

Studies were conducted which analyzed recruitmen

The 1969 to 1972 year-classes have held 

No 

Increased catches over the past decade do not appear to 

have had an adverse effect on recruitment. However, the catch-per-uniteffort of the longline fishery has decreased, suggesting that the spawning 

stock has declined. In view of this trend and of the increased catches of 

large fish by purse seiners, the size of the spawning stock and the 

possible effect on subsequent recruitment need to be monitored. 

III.B.5. Results of Other Analvses/Simulations 

None avail ab1 e. 

1II.C. Current Evaluation of Stocks and the Fishery 

Regardless of the stock structure assumed, Atlantic ye1 lowfin 

tuna stocks are heavily fished, particularly in the eastern Atlantic. 

Given the present geographical distribution of the fishery and pattern of 

fishing by different gears, it is unlikely that appreciable increases in 

yield can be achieved by increasing the amount of fishing effort. 

Increases in total catch which have occurred in recent years are largely 

due to the effect of geographical expansion of the area of fishing in the 

eastern tropical Atlantic. It is not known to what extent a further 

expansion can be achieved, or what further increases in catch might result 

from such an expansion. 
-29- 

50 

45 

40 

35 

30 

25 

20 

15 

10 

1966 1968 

YEAR CLASS 

1978 197

Figure 13. Estimated recruitment to age 1 of yellowfin tuna from the 

eastern Atlantic Ocean by year of birth, 1965 to 1972. 
-30- 

Total yield to the fishery partially depends on the sizes of 

Conversely, increased fishing on small 

fish caught. 

increase yield up to a point. 

ye1 1 owfi n woul d tend to decrease the total 1 ong- term yiel d. 

Any increase in the effective size-at-first-capture should 

1II.C 1. Effects of Regulations 

On the basis of several studies, ICCAT, in 1973, 

adopted a min mum size limit on Atlantic yellowfin of 3.2 kg or 55 cm. 

was estimated that under the then-current fishing pattern, this would 

either give a small increase in yield-per-recruit (YPR) or, if undersized 

fish were discarded dead, would not affect the YPR. Since the regulation 

was adopted, the fisheries have changed dramatically: 

have increased greatly and have shifted to larger fish, catches of both 

baitboats and longliners have decreased, and there has been a s h i f t t o 

smaller fish by the baitboats. 

It 

purse seine catches 

Analyses were conducted to assess the amount of change 

Results indicated that YPR 

The longline fishery experienced a 57% reduction in 

in YPR since the adoption of the regulation. 

for the entire fishery increased anywhere from 3 to 18% since the adoption 

of the regulation. 

the baitboat fishery a 45% decrease. 

yield-per-recrui t was probably due to increased competition from purse 

seine fisheries. 

was due to increased effort on larger fish. The baitboat's decrease in 

yield-per-recruit was due to reduced effort on large fish and increased 

effort on very small fish. 

e q u i l i b r i u m y i e l d - p e r - r e c r u i t , the purse seine fishery a 55% increase, and 

The longline fishery's decrease in 

The purse seine fishery's increase in yield-per-recruit 

The regulation may also have resulted in increased 

occurrences of undersized yellowfin tuna being landed as bigeye tuna, and 

increased dumping of dead undersized fish at sea. Several ICCAT member 

countries have initiated research to quantify the extent of discards at 

sea, to describe in detail the areas where juvenile yellowfin tuna are 

available, and to describe the interaction between juvenile yellowfin and 

juveniles of other tuna species. 

A size regulation on bigeye tuna, similar to that on 

yellowfin tuna has also been adopted by ICCAT members to increase the 

yield-per-recruit of bigeye tuna and to reduce the landing of undersize 

yellowfin tuna as bigeye. 

small yellowfin tuna are being evaluated by ICCAT's Juvenile Tuna Working 

Group. 

looking at different alternatives to the current size limit. 

Additional measures to reduce the taking of 

The Group has identified areas of high juvenile tuna catches and i
-31 - 

*- 

IV. STATUS OF CURRENT RESEARCH NEEDS AND EFFORTS 

1V.A. Major Research Problems 

1) The growth relation of yellowfin tuna, particularly during th

juvenile period, needs to be better defined. Age composition of the catc

is an important input to cohort analyses and therefore important for 

accurate estimates of recruitment and fishing mortal i ty. 

this research would lead to better, more accurate estimates and, therefor

better management advice. 

Completion of 

2) The existence of a spawner/recruit relationship for yellowf

tuna needs to be investigated. 

better understanding of the status of Atlantic yellowfin tuna stocks. 

Completion of this research would lead to 

3) Verification is needed of the various stock structure 

hypotheses: single stock of longline and surface-caught yellowfin, mixin

of an Indian Ocean stock with Atlantic yellowfin, and separate eastern a

western Atlantic stocks or a single Atlantic stock. 

stock structure issue would lead to more accurate assessments of the sta

of Atlantic yellowfin tuna. 

Clarification of the 

4) Alternative management schemes for reducing the catch of sm

yellowfin tuna should be analyzed. A1 though the current management schem

has increased yield-per-recruit as intended, small yellowfin tuna continu

to be landed by some purse seine and baitboat fisheries that are 

experiencing difficulties in implementing the 3.2 kg size 1 imit. 

5) Continued research on the relationship between environmenta

parameters and abundance, availabil ity, and vu1 nerabil i ty of At1 antic 

yellowfin tuna is needed. 

on sea surface temperature. 

estimates, verification of the technique may be critical. 

Current abundance estimates are partially bas

Since production models are based on these 

IV. B. Current Research Efforts 

Current At1 antic ye1 1 owfin tuna research is concentrated on the 

foll owing subjects: 

1) Trends in fishery statistics: catch, effort, CPUE, and size

frequency (SWFC) . 

2) Development of new fisheries and their relation to stock 

structure ( I CCAT) . 
-32- 

3) Fecundity of yellowfin tuna off southern Brazil (ICCAT). 

4) Relationsip between occurrences of yellowfin tuna and sea 

surface temperature (SWFC) . 

5) Techniques to estimate economic value of the eastern Atlantic 

surface fi shery (SWFC) . 

6) Status of stocks: production models, yield-per-recrui t 

(SWFC) . 

7) Management problems, a1 ternative management schemes, sampl ing 

probl ems (SWFC) . 

IV. C. Future Research Needs 

Future research on Atlantic yellowfin tuna should center on the 

following activities: 

1) Refining and extending studies of alternate management 

schemes. Discrepancies in the data sets and procedures used in initial 

analyses should be resolved. 

mu1 tispecies catches, yield-per-recruit, economics, etc. , should be 

considered. 

Effects of different management schemes on 

2) Investigating the re1 ationships between environmental 

parameters and abundance, availability, and/or vu1 nerabil ity of stocks. 

3) Investigating the interaction between surface and long1 ine 

gear. 

IV.C.1. Suggested Approach and Methods 

1) U.S. single-set data should be evaluated for possible 

use in improving knowledge of species composition and fish size composition 

of schools. A model should be developed to predict movements of the fishery 

due to different management alternatives and to predict benefits to the 

fishery, yield-per-recrui t, undersize catches, and mu1 tispecies catches, 

based on fishery, economic, and environmental assumptions. 

2) Data sets from other geographical regions, or 

utilizing other species, could be used to test the technique of using sea 

surface temperature to separate effort by species, for example. 

1V.D. Status of SWFC Data Base 

Data on Atlantic yellowfin tuna at the Southwest Fisheries Center 

are currently considered adequate for population assessments. There are 
-33- 

c-. 

problems in the data sets and analytical data procedures being used, 

however, which need to be resolved: 

1) Data set and procedures used in alternative management sche

need to be reviewed and standardized. 

2) A plan to assure that the SWFC data system is supplied with

or notified of, all changes to data sets must be developed. Methods of 

choosing which samples should be used in the case of duplicate sampling 

fleets must be standardized, 

3) Growth in size of the current data sets and the need for m

interactive processing necessitate a reevaluation of the current data ba

system for cost reasons. 

and use of other file structures is now being investigated. 

Most of the data have been converted to the B7

The following data will be required in the future: 

1) French length-frequency samples by smaller than 5 x 10-degr

2) U.S. Atlantic single-set data extracted from IATTC data bas

areas to use for alternate management scheme analyses. 

and placed on the SWFC bases. 

3) Continued sampling of transshipments to Puerto Rico for 

species and size composition. 

4) Data reflecting more complete coverage of the Korean baitbo

and Spanish purse seine fisheries. 
-34- 

STATUS REPORT: ATLANTIC BIGEYE TUNA 

by 

Atilio L. Coan, Jr. and Wesley Parks 

Southwest Fisheries Center 

Oceanic Fisheries Resources Division 

La Jolla, California 

ABSTRACT 

Recent total annual Atlantic catches of bigeye tuna have averaged 

41,000 mt. Major participants in the fishery include Japan, Korea, Spain

and the USSR. 

catches have been less than 500 mt. 

The U.S. takes bigeye along with yellowfin and skipjack tu

in its eastern Atlantic tropical tuna purse seine fleet. Recent U.S. 

The stock structure of bigeye tuna in the Atlantic is uncertain. 

Hypotheses include a single At1 antic-wide stock and separate north and 

south stocks. Catch-per-unit-effort shows sl ight decreasing trends. 

Production model analysis estimates MSY in the range of 52,000-123,00

mt. Recent catches are below MSY. Recent estimated effort levels are 25 

to 50% less than optimum effort. 

fishing patterns, increasing age-at-first-capture would slightly increase 

equi 1 i b ri um yi el d- per- recrui t . 

Analyses suggest that with current 

The International Commission for the Conservation of At1 antic Tunas 

adopted a minimum size limit of 3.2 kg for bigeye tuna in 1979. 

regulation, intended to increase yield-per-recrui t, has not been in effe

long enough for its effectiveness to be assessed. 

The 
-35- 

I. DESCRIPTION OF THE FISHERY 

Bigeye tuna are distributed throughout the Atlantic Ocean between 50" 

N and 40" S latitudes (Figure 1). 

concentrated in the west at 40" N latitude and in the east at 20" N 

latitude. South Atlantic catches are concentrated in the west at 30" S 

latitude and in the east at 10" S latitude. 

Catches in the north Atlantic are 

I.A. History of the Fishery 

The Atlantic fishery for bigeye tuna began in 1956 when the 

Japanese longline fleet expanded operations from the Pacific into the 

Atlantic Ocean. Longline continues to be the principal gear capturing 

bigeye. 

have taken a greater proportion of the catch (from 17% in 1972 to 37% in 

1978). The surface fishery for bigeye tuna is a multi-species fishery 

which also takes yellowfin and skipjack. 

However, in recent years surface gears (purse seine and baitboat) 

The major participants in the north Atlantic fishery are the 

Japanese, Korean, Spanish, and Portuguese fleets. These fleets together 

caught 80% of the average north Atlantic bigeye catch during the period 

1975 to 1979 (Figure 2a). r"L. 

The major participants in the south Atlantic fishery for bigeye 

tuna are the fleets of Japan, Korea, Russia, and Taiwan. These fleets 

caught 74% of the south Atlantic catch of bigeye during the period 1975 to 

1979 (Figure 2b). 

I.B. Trends in Catch and Effort 

I .B.1. North At1 antic Fi sherv 

Catches for the north Atlantic longline fishery peaked 

1974 at 26,000 mt and decreased to approximately 10,000 mt in 1979 (Figure 

3a). Catches for the surface fishery also peaked in 1974 at 13,000 mt and 

averaged 10,000 mt during the 1975 to 1979 period. 

north Atlantic longline and surface fishery catch is 21,400 mt. 

the north Atlantic reached a peak of 165 million hooks in 1975, then 

decreased to 85 million hooks in 1977 (Figure 4a). 

Is1 and bai tboat fleet however, remained re1 atively constant (10,000 days a

sea) during the 1975 to 1978 period (Figure 4b). 

The provisional 1980 

Fishing effort (in number of hooks) for bigeye tuna in 

Effort for the Canary 
-36- 

100" 80" 60° 40" 20" O0 20° 40" 

60" 

40" 

20" 

0" 

20" 

40" 

60" 

Figure 1. Areas of the Atlantic Ocean currently or historically fished 

for bigeye tuna. Densely hatched areas indicate areas of 

greatest fishing intensity. 
-37- 

OTHER 

SPA1 N 

PORTUGAL 

USSR 

OTHER 

KOREA 20% 

JAPAN 26% 

TAIWAN 13% 

KOREA 19% 

7 i’ JAPAN 23% 

Figure 2. a) Major participants in the northern Atlant 

longline fishery for bigeye tuna, 1975 to 

b) Major participants in the southern Atlant 

longline fishery for bigeye tuna, 1975 to 

c surface and 

1979. 

c surface and 

1979. 
-38- 

50 

40- 

A 

rr) 

30- 

II 

I 

0 

Y 

50 T I 

- S U R FAC E 

e--- LONGLINE 

SURFACE 

LONG L I NE 

- 

- - -- 

10- 

0 

0 :-- I I I I I I 

1968 I970 1972 I974 I976 I978 

YEAR 

e/------f-- 

\- - ' - - /* 

'. 

_--- ____- ---- - - --- I I 

YEAR 

Figure 3. a) Total catch of bigeye tuna from surface and longline 

gears fishing in the northern Atlantic, 1968 to 1979. 

b) Total catch of bigeye tuna from surface and longline 

gears fishing in the southern Atlantic, 1968 to 1979. 
-39- 

A. 

200 

rcB. 

E 

F 

f 

0 

R 

T 

I975 1976 1977 

YEAR 

I978 

Figure 4. a) Fishing effort in hooks for the longline fishery in 

the northern Atlantic, 1960 to 1977. 

b) Effort in days at sea for the Canary Island baitboat fleet, 1975 to 1978. 
-40- 

1.6.2. South Atlantic Fishery 

Bigeye catches for the south Atlantic longline fishery 

peaked in 1971 (20,000 mt), then gradually declined to 12,000 mt in 1979 

(Figure 3b). Surface fishery catches peaked in 1974 (6,000 mt) and, afte

a brief decline, remained relatively constant at 5,000 mt between 1977 and 

1979. 

catch is 13,600 mt. 

The provisional 1980 south Atlantic long1 ine and surface fishery 

South Atlantic longline effort increased from 7 millio

hooks in 1960 to 94 million hooks in 1976 (Figure 5). No reliable measur

of effort is available for the surface fishery. 

I.C. Value of Catch 

In the United States, yellowfin and bigeye tunas are marketed at 

the same prices: 

kg and $1,047/mt for fish greater than 3.2 kg. Based on an average price 

of $970/mt, the value of north Atlantic bigeye caught by all fisheries in 

1979 was $21 million; the total south Atlantic bigeye catch was worth $16 

million. The total 1979 U.S. bigeye catch was worth approximately 

$200,000. 

$893/mt (1979, average ex-vessel ) for fish less than 3.2 

I.D. Current Management of the Fishery 

In 1979,the International Commission for the Conservation of 

Atlantic Tunas (ICCAT) recommended to their member nations that they adop

a minimum size limit regulation for bigeye tuna. The regulation states: 

"That the Contracting Parties take the necessary measures 

to prohibit any taking and landing of bigeye tuna (Thunnus 

obesus) weighing less than 3.2 kg until December 31,1983. 

Notwithstanding the above regulations, the Contracting 

Parties may grant tolerances to boats which have incidentally captured bigeye tuna weighing less than 3.2 kg with 

the condition that this incidental catch should not exceed 

15% of the number of fish per landing of the total bigeye 

catch of said boats." 

This size regulation was adopted to 1) increase yield-per-recruit 

of bigeye tuna by reducing fishing mortality on small fish, and 2) reduce 

the misreporting of small yellowfin tuna in landings as bigeye tuna. The 

U.S. adopted these regulations for bigeye tuna in early 1981. 
-41 - 

fi 

in 

Y 

0 

0 

S 

a 

u) 

c 

X 

W 

Ie 

0 

L 

LL 

W 

w 

> 

H 

0 

W 

LL. 

LL 

w 

200 

150 

100 

50 

0 

1968 1962 1964 1966 1968 1970 1972 1974 1976 

YEAR 

Figure 5. Effective effort in hooks for the longline fishery in 

the southern Atlantic, 1960 to 1977. 
-42- 

11. THE NATURE AND SIGNIFICANCE OF U.S. AND FOREIGN 

PARTICIPATION IN THE FISHERY 

United States tuna processors utilize domestic and foreign-caught 

bigeye tuna for canning as light meat tuna. The highest recorded U.S. 

Atlantic bigeye tuna catch (865 mt) occurred in 1974 (Figure 6). In 1979, 

the U.S. catch was 200 mt. The amount imported is difficult to determine 

since bigeye and yellowfin tuna are not separated in import reports. The 

preliminary U.S. catch of yellowfin and bigeye in 1980 (preliminary figure

do not separate catches of the two species) was 8,500 mt. 

U.S. participation in the Atlantic fishery (which is a multi-specific 

tropical tuna fishery catching bigeye, yellowfin, and skipjack tuna) is no

expected to increase above 1980 levels (6 vessels). Future foreign 

participation in the fishery is difficult to estimate with any degree of 

certainty but is not anticipated as long as the fisheries continue 

operating within their current geographical boundaries and current fishing 

methods. 

111. STATUS OF THE STOCKS 

1II.A. Stock Structure 

Bigeye tuna are distributed throughout the Atlantic Ocean (Figure 

1). Scientists have hypothesized separate north and south Atlantic stocks. 

Evidence for this includes a decline in hook rates in the equatorial 

Atlantic and preliminary evidence of separate spawning areas, one in the 

northern and one in the southern tropical areas. 

Recapture of bigeye tuna tagged in the eastern Atlantic indicate 

that the fish generally remained in areas of tagging off Dakar and PointNoire, except for a single fish that exhibited northward migration from the 

Gul f of Guinea to the area off Dakar after one year. 

either a single or separate northern and southern stocks is inconclusive, 

two hypotheses are used in stock assessments: 

and 2) two independent stocks separated at approximately 5' N latitude. 

Since evidence of 

1) a single Atlantic stock, 
-43- 

2000 

1500 - 

1000 - 

T 

0 

N 

S r”” 

1968 1970 1972 1974 I976 1978 

YEAR 

Figure 6. Total catch of bigeye tuna for U.S. vessels fishing in 

the Atlantic Ocean, 1968 to 1979. 
-44- 

I11 .B. Stock Assessment and Fishery Evaluation 

I I I . B . 1 . Trends i n Ca tc h- per-Un i t- Ef f or t 

Annual bigeye tuna hook rates were estimated from 

Japanese longline fleet catch/effort data (Figure 7). 

the northern and southern At1 antic exhibit similar gradually decreasing 

trends except for differences in peak hook rate years. 

in 1974 in the northern Atlantic and 1969 in the southern Atlantic. 

Hook rates in both 

Hook rates peaked 

No reliable CPUE estimates are available for surface 

f i sheries . 

III.B.2. Results of Production Vodel Analysis 

The 1 ogistic (~2) , the Gompertz (m approaches 1) , and 

the asymptotic (m=O) production models have been used to assess the status 

of Atlantic bigeye tuna. Because division of the stocks is uncertain, 

analyses have been performed under hypotheses of a single Atlantic stock 

and separate north and south Atlantic stocks. 

III.B.2.a. Total Atlantic stock 

The latest available analysis uti1 ized data 

The m=O model 

The 1978 

for the total Atlantic fishery for the period 1961-1978 (Figure 8). 

Estimates of equil ibrium maximum sustainable yield (MSY) ranged from 

51,900mt to 60,100 mt for m=2 and m=l models, respectively. 

gave an MSY estimate of 123,200 mt. . any of the three models as best. 

estimated effective effort was 25% to 50% less than the optimur; effort if*) 

corresponding to MSY for the m=2 and m=l models, respectively. 

effort for the m=O model is undefined. The 1979 catch was approximately 

42,000 mt. No estimate of effective effort is available for 1979. 

Objective criteria fail to indicate 

The 1978 catch was 45,700 mt. 

Optimum 

I I I .B .2. b. Separate north and south 

Atlantic stocks 

Bigeye tuna fishery data were separated into 

northern and southern fisheries and production models fit to each data set.. 

The models were applied to data representing the northern fishery for the 

period 1961-1978. 

41,100 mt for the m=1, 89,600 mt for the m=O model (Figure 9). 

catch was 25,200 mt at an estimated effective effort 45% to 64% less than 

f* for the m=2 and m=l models, respectively. The 1979 catch was 

approximately 22,100 mt. 

Estimates of MSY were 35,200 mt for the m=2 model, 

The 1978 
-45- 

0.8 

H 

0 

0 0.6 

K 

R 

A 

T 0.4 E 

0.2 

8 

- NORTH 

1961 1963 1965 1967 1969 1971 1973 1975 1977 

YEAR 

Figure 7. Hook rates (number of fish/100 hooks) for bigeye tuna 

caught by longliners in the northern and southern 

Atlantic Ocean, 1961 to 1978. 
-46- 

r 

60 - 

EFFECTIVE EFFORT IN lo6 HOOKS 

Figure 8. Equilibrium yield curves for bigeye tuna in the whole 

Atlantic Ocean, 1961 to 1978. 
-47- 

40 

30 

I I 

50 100 150 200 250 

EFFECTIVE EFFORT IN IO6 HOOKS 

m=O 

m = 1.0 

m = 2.0 

50 100 150 200 250 

EFFECTIVE EFFORT IN IO6 HOOKS 

Figure 9. Equilibrium yield curves for bigeye tuna in the northern 

Atlantic Ocean, 1961 to 1978. 
-48- 

These models were also applied to data from 

the south Atlantic fishery. 

model, 25,500 mt for the m=l model, and 49,000 mt for the m=O model (Figu

10). 

than f* for the m=2 and m=l models, respectively. The 1979 catch was 

approximately 20,100 mt. 

Estimates of MSY were 21,000 mt for the m=2 

The 1978 catch was 20,500 mt at an estimated effort 3 to 41% less 

III.B.3. Results of Yield-Der-Recruit Analysis 

Yield-per-recruit analyses have been used in the past t

assess the status of bigeye tuna stocks, and were the basis of the size 

limit proposal in 1979. 

Working Group on Juvenile Tropical Tunas. Results confirmed that 

increasing size-at-first-capture from approximately 0.9 kg (30 cm fork 

length) to 3.2 kg (54 cm) would increase yield-per-recruit to the fishery

especially at higher levels of effort (Figure 11). 

A new analysis was performed in 1980 by ICCAT’s 

I I I. B .4. Resul ts of SDaWner/ReCrUi tment Anal vsi s 

Recruitment to age-1 for year-classes 1967 to 1973 was 

estimated (Figure 12). Only longline data from the total Atlantic fisher

were considered. Depending on the natural mortal ity rate chosen, estimat

vary moderately and no general trend is apparent. 

I11 .B.5. Results of Other Analvses/Simulations 

None available. 

1II.C. Current Evaluation of Stocks and the Fishery 

Results of the production model analyses indicate that Atlantic 

bigeye tuna are currently being fished below levels corresponding to MSY. 

All models indicate that increases in yields are available with increases 

in effort. 

impossible to select the appropriate model and MSY. 

Until the fishery operates at higher effort levels it is 

Any i nc rease i n si ze- a t- f i rst-capture shoul d increase yi el d- perrecruit to the fishery. The feasibility of increasing size-at-firstcapture for the baitboat fleets, however, is questionable. Since these 

fleets take small bigeye tuna with catches of skipjack, any increase in 

size-at-first-capture may result in decreased skipjack catches. 

increases in catches of small bigeye should result in decreases in yieldper-recrui t. 

Continue
-49- 

25 

20 

n 0, 15 

V 

5 

rn= 0 

ril = 1.0 

m = 2.0 

I I i 

50 100 150 

EFFECTIVE EFFORT IN IO~HOOK

Figure 10. Equilibrium yield curves for bigeye tuna in the southern 

Atlantic Ocean, 1961 to 1978. 
-50- 

5.0 

4.0 

3.0 

2.0 

1.0 

11 12 13 14 15 16 

41.3 

22.7 

9.8 

2.6 

i 

0.5 1.0 1.5 2.0 2.5 3.0 

FISHING MORTALITY MULTIPLIER 

Figure 11. Equilibrium yield-per-recruit (kg) for Atlantic 

bigeye tuna for combinations of age- (weight)- 

at-first-capture and multiples of fishing 

mortal i ty . 
-51 - 

,- 

A 

I 

v) 

H 

LL 

61 

W 

c 

X 

W 

tz 

W 

I: 

IH 

3 

tY 

0 

W 

tY 

c10 

1967 1968 1969 1970 1971 

YEAR CLASS 

1972 19

Figure 12. Estimated recruitment to age 1 for Atlantic bigeye tuna 

under two assumed values of natural mortality, M. 
-52- 

III.C.l. Effects of Regulations 

The current size regulation for b 

in force long enough to assess its specific effects 

size 1 imit should increase yield-per-recruit to the 

geye tuna 

Theore t 

f i she ry . 

has not been 

cally, the 

At its 1980 meetina, ICCAT's Working Group on Juvenile 

Tropical Tunas assessed the effects of area-time closures designed to 

protect small yellowfin and bigeye tunas, and thus increase yield-perrecruit. Potential gains to yellowfin-bigeye catches were contrasted to 

possible losses to catches of skipjack tuna in multi-species surface 

fisheries. 

and bigeye tuna in excess of 50 mt were identified (Figure 13). Twentythree area-month combinations were chosen for detailed examination. The 

following conclusions were made: 

Six fishing areas having combined monthly catches of yellowfin 

1) Ignoring losses to catches of skipjack tuna, closing any or a 

combination of these strata would result in a maximum gain of 10% to 

ye1 1 owf i n- bigeye catches. 

2) Assuming that skipjack tuna not taken in closed strata would be 

taken in other areas or at later times, an overall gain in at least yieldper-recruit of bigeye and yellowfin would result from closures. Yield-perrecruit to bai tboats would decrease while yiel d-per-recrui t to purse 

seiners, which catch a broader size range of fish, would increase. 

3) It was assumed that any skipjack tuna not taken would be lost, and 

that these 1 osses woul d particul arly affect bai tboats. 

data were insufficient to predict skipjack losses, the consensus of the 

Working Group participants was that losses to skipjack catches would exceed 

gains to ye1 lowfin/bigeye catches. 

area-time closures investigated would probably result in a decrease in the 

combined catch of ye1 lowfin, bigeye, and skipjack tuna. 

A1 though avail ab1 e 

The Group concluded that imposing the 

IV. STATUS OF CURRENT RESEARCH NEEDS AND EFFORTS 

1V.A. Major Research Problems 

The uncertainty of the composition of the Atlantic bigeye stock 

structure makes it difficult to evaluate and assess the effect of the 

fishery upon this tuna. Analyses of models and determination of MSY, 

therefore, can only be regarded as "best guesses." 

minimum size limit regulation has not been in effect long enough to 

determine its effect upon the fishery. 

In addition, the ICCAT 
-53- 

.- 

e 

Figure 13. Areas investigated for effect of time-area 

closures by Juvenile Tuna Working Group. Areatimes listed are strata investigated in detail. 
-54- 

1V.B. Current Research Efforts 

Current Atlantic bigeye tuna research is very limited. 

the SWFC has concentrated on evaluation of available data for cohort, 

yield-per-recrui t, and recruitment analyses; areas where small bigeye and 

yellowfin tunas are caught are also being identified. 

Research a

1V.C. Future Research Needs 

IV.C.l. Suggested Approach and Methods 

The following projects should be undertaken in -?der to 

improve management of the fishery: 

1) Re-estimate popul ation parameters: 1 ength-weight re1 ation, growth 

rates (particul arly for small fish) , and mortal i ty rates. 

2) Investigate stock structure to include the relationship of 

currently hypothesized northern and southern stocks, and the relationship 

between longline and surface-caught bigeye tunas. 

3) Eva1 uate the adequacy of current data to analyze yiel d-per-recrui t 

and spawner/recrui t. 

4) 

yellowfin tuna on bigeye tuna. 

of fish should be determined and considered in any management scheme for 

yellowfin or bigeye tunas. 

Investigate the impacts of alternate management schemes for 

The extent of mixing of species and sizes 

1V.D. Status of SWFC Data Base 

All currently available Atlantic bigeye tuna data reside on SWFC 

data bases. Available fishery data (catch, catch/effort, and size 

composition) for the 1 ongl ine fishery are minimally adequate for stock 

assessments, but those for the surface fishery are sparse and inadequate 

for assessments. Additional biological data are needed for both long1 ine 

and surface fisheries in order to assess population parameters and evaluate 

stock structure problems. 

a1 though improving, continues to be a problem. Species-composi tion 

sampling at all landing and transshipment ports should be continued to 

a1 1 eviate thi s probl em. 

Misreporting of bigeye tuna as yellowfin, 
-55- 

STATUS REPORT: ATLANTIC SKIPJACK TUlEjA 

by 

Richard H. Evans and Norman Bartoo 

Southwest Fi sheries Center 

Oceanic Fisheries Resources Di vision 

La Jolla, California 

ABSTRACT 

Eastern Atlantic skipjack tuna stocks are currently fished at a high 

level (100,000 mt in 1980) while western Atlantic stocks are fished at a 

low level (9,000 mt in 1980). CPUE indices for both the French-Ivory 

Coast-Senegal-Morrocan and Tema-based fleets, which are quite different a

show no clear trend over time, are not considered to be adequate estimato

of abundance. A v a i l a b l e evidence indicates that neither western or easte

Atlantic skipjack stocks are overfished at this time, and both stocks may 

effectively support increased fishing effort. This seems especially true 

for the western Atlantic, where a developing fishery off Brazil accounted 

for 80 percent of the western Atlantic catch in 1980. 

*cr 
-56- 

I. DESCRIPTION OF THE FISHERY 

I.A. History of the Fishery 

Skipjack tuna fisheries began to develop in the eastern Atlantic 

about 1955 when baitboats from France and Spain moved into the area off 

Dakar (Figure 1) to fish for yellowfin tuna. 

1960 was operative year-round between the Canary Islands and Point Noire. 

Purse seiners entered the fishery in the early 1960's. Carrying capacity 

of the combined purse seine and baitboat fleets has increased steadily 

through the 1960's and 70's and currently stands at more than 60,000 mt 

(Table 1). Principal participants in the fishery are the FISM (French, 

Ivory Coast, Senegal and Moroccan) and Tema-based bai tboat fleets ( the 

latter including Japan, Korea, Panama and Ghana), and the FISM, Spanish, 

and U.S. purse seine fleets (Table 2, Figure 2). These fleets, which 

exploit yellowfin, bigeye, and skipjack tuna, have increased their combine

effort continually since 1968. 

This fishery expanded and by 

Skipjack tuna catches in the western Atlantic are quite small 

(less than 10% of the total) compared to the eastern Atlantic. 

the principal participants in this fishery were baitboats from Cuba and 

purse seiners from the United States (Figure 3) fishing in the Caribbean. 

Until 1980

In 1980. catches bv Brazilian baitboats off Brazil were estimated at 7,000 

mt or about 80% ofthe projected 1980 catch for the western Atlant 

1.6. Trends in Catch and Effort 

During the period 1969-1979, catches of skipjack in the to 

Atlantic varied between 60,000 and 117,000 mt (Figure 4). 

was projected to be 109,000 mt. 

The 1980 catch 

C. 

a1 

I.B.l. Eastern Atlantic Fishery 

Catches in the east,ern Atlantic fluctuated between 26,300 

mt and 113,200 mt during 1969-1979. 

eastern At1 antic bai tboat and purse seine fleets has increased steadily 

since 1968 (Figure 5). 

seiners fishing in the eastern Atlantic has fluctuated between 9 and 40 

ships, with 12 U.S. purse seiners fishing in the eastern Atlantic in 1979 

(Figure 6). Fishing effort on skipjack tuna in the eastern Atlantic, as 

indexed by data for the FISM purse seine fleet, increased markedly (Figure 

7) from less than 30,000 standard days fishing (SDA) in 1972 to more than 

65,000 SDA in 1973. Since then, FISM skipjack effort has fluctuated 

between 40,000 and 60,000 SDA per year. The level in 1979 was about 58,00

SDA days per year. 

The carrying capacity of the combined 

During this period, the number of U.S. purse 
-57- 

.-- 

25" W. 20" W. 15" W. loo W. 5"W. 0" 5" E. loo E. 

Figure 1. Area in the eastern tropical Pacific where skipjack tuna 

fisheries began to develop around 1955. 
-58- 

v) I 

-0 

c 

(d 

I I L 

S a, 1: 

I' a, 

v) 

a, 

v) 

L 

3 

a 

L 

0 

% 

CI 

v) 

c 

0 

c, 

N 

2 

or + 

v) 

3 

a, 

5 

I- 

- 

n 

SY? \9-! 

M-VI 

# 

.* 
-59- 

r- 

'UI 

a rl 000 

BJ Cot-3te-i . ... 3 N 93 -4 

0 

0 

e 

0 

b 

0 

0 

O 

b 

0 

cu b 

0 

# 

0 

0 

M 

n 

r3 

4 

b 

? 

N 

b 

a 

0: 

5 

n 

4) 

9 

r\l 

b 

'r 

d 

e 

a 

VI 

0: 

-l 

L\I 

(3 

*J 

u 

7- 

3 
-60- 

SPA 

JAPAN 

KOREA 

-GHANA 

FIS 25.1% 

u. s. 5.5% 

OTHER 4.8% i 

PORTUGAL 3.7% 

IN 25.990 

15.0% 

7. I Oh 

5.9% 

Figure 2. a) Percentage of annual catch by country for eastern Atlanti

skipjack tuna 1975-79. Average annual catch is 86,539 mt
-61 - 

CUBA 

u. s. 

12.1 

20.6 

% 

Figure 3. Percentage of annual catch by country for western Atlantic 

skipjack tuna, 1975-79. Average annual catch is 3,361 mt. 
-62- 

'T ti 0% AN DS 

128 

100 

C 

A 

T 

C 

H 80 

M 

E 

T 

R 

I 

C 

T 40 

0 

N 

S 

60 

20 

0 

1966 1968 1970 1972 1974 1976 1978 198

YEAR 

Figure 4. Total and U.S. skipjack tuna catch for the eastern 

Atlantic, 1966-80. 1980 value is estimated. 
-63- 

n 

8 

m 

- 

x 

tz 

v 

>. 

tH 

0 

G 

a 

0 

a 

1968 1970 1972 1974 1976 1978 1988 

YEAR 

Figure 5. Carrying capacity of the baitboat-purse seine fleet in 

the eastern Atlantic, 1968-80. 1980 value is estimated. 
-64- 

59 

N 413 

U 

M 

B 

E 

U 

0 

F 

V 

S 

s 

E 

L 

S 

30 

E 20 

18 

0 

1 I I I I I 

1968 I970 1972 1974 1976 I978 

YEAR 

Figure 6. Number of U.S. purse seiners fishing in the eastern 

Atlantic, 1968-79. 
-65- 

THCUSANDS 

- 

78 i 

E 60 50 1 I \/ V 

I 1 l0 0 1- I I I 

1969 197 1 1973 I975 1977 197

YEAR 

Figure 7. Fishing effort for skipjack tuna in standard days 

fishing per year for the eastern Atlantic, 1969-79. 
-66- 

I .B.2. Western Atlantic Fishery 

Skipjack catches in the western At1 antic have fluctuated 

markedly in recent years. From 1966 through 1972, the catch varied from 

1500 mt to 2700 mt, with a slight downward trend over time (Figure 8). 

Since 1972 the catch trend has been generally upward, increasing much mo

sharply in 1978 with the addition of the Brazilian catch. 

The United States fleet has traditionally been only 

marginally involved in the western At1 antic skipjack tuna fishery. The 

U.S. catch peaked at 1700 mt in 1978, then declined to 730 mt in 1979. No 

fishing effort data are available for the western Atlantic. 

I.C. Value of Catch 

In 1979, skipjack tuna weighing less than 1.8 kg brought an avera

of $635/mt in the U.S., while skipjack larger than 1.8 kg brought $771/mt

Assuming an average of $703/mt, the value of the 1979 eastern Atlantic 

catch (75,600 mt) was in excess of $53 million. The U.S. portion of the 

catch had a value of more than $3.9 million. At the average 1980 U.S. 

price ($952/mt), the 1980 eastern Atlantic skipjack catch (99,900 mt) had 

an estimated value of more than $95 million. 

Based on an average value of $703/mt, the 1979 western Atlantic 

catch of skipjack had a value of more than $2.4 million. 

of this catch had a value of $574,000. 

an estimated value of about $8.9 mil 1 ion ($952/mt). 

The U.S. portio

The 1980 western Atlantic catch h

In 1978 United States tuna processors imported more than 50,000 

of Atlantic skipjack which, at an average value of $632/mt, had a value o

more than $31 million. 

I.D. Current Management of the Fishery 

There are presently no ICCAT or U.S. regulations for Atlantic 

skipjack tuna in effect. It should be noted that ICCAT minimum size 

regulations are in effect for both Atlantic yellowfin and bigeye tunas. 

Since these tunas are taken in a multispecies fishery with skipjack tuna 

the eastern At1 antic, these regulations impact the skipjack tuna fishery. 
-67- 

C 

A 

T 

C 

H 

M 

E 

T 

R 

I 

c 

T 

0 

N 

S 

1966 1968 1970 I972 1974 I976 I978 198

YEAR 

Figure 8. Total and U.S. skipjack tuna catch for the western 

Atlantic, 1966-80. 1980 value is estimated. 
-68- 

11. NATURE AND SIGNIFICANCE OF U.S. AND FOREIGN 

PARTICIPATION IN THE FISHERY 

I1 .A. Eastern At1 antic Fishery 

Significant United States participation in the Atlantic skipjac

tuna fishery began in 1967 with three U.S. tuna purse seiners fishing of

Africa. Their success attracted other U.S. seiners to the eastern Atlan

fishery. In 1972, 40 American tuna seiners in the eastern Atlantic fish

caught 12,000 mt of skipjack tuna. Since then American participation ha

fluctuated between 6 (1980) and 37 vessels (1975). 

(21,200 mt) was taken in 1973 by 29 purse seiners. 

projected to be 2,700 mt, 3% of the eastern Atlantic total. 

the skipjack tuna catch in the eastern Atlantic is made by FISM and Tema

based baitboats and FISM seiners. Their catch is expected to account fo

50% of the 1980 total catch. Spanish purse seiners are expected to catc

about 32% of the 1980 total. In recent years, the catches of Angola, 

Portugal, and the USSR have increased. Two Soviet purse seiners are 

reported to have fished in the Gulf of Guinea in 1980. 

The largest U.S. cat

The 1980 U.S. catch 

The bulk of 

I I .B. Western Atlantic Fishery 

Fishing by U.S. seiners in the western Atlantic has been primar

by seiners transiting between the Gulf of Guinea and Puerto Rico or the 

eastern tropical Pacific. Since 1975, however, U.S. seiners have spent 

more time searching for skipjack in the western Atlantic, and have 

accounted for almost 20% of the total (Figure 3) through 1979. The catc

of both Cuba and the U.S., who together took 88% of the total catch, hav

been relatively constant in recent years (1971-77). 

been almost exclusively from the Caribbean. 

These catches have 

A new fishing area off Brazil and Argentina is currently being 

Catches for this area totaled 670 mt 

This figure jumped to 1900 mt in 1979 and was projected to be 70

This new area is quite large and appears to have potentia

exploited by Brazilian baitboats. 

1978. 

mt for 1980. 

for increased exploitation. 

111. STATUS OF THE STOCKS 

Due to the nature of the fishery (i .e. , primarily surface gears 

exploiting only one young age group) , population assessment techniques 

uti1 ized for other tuna species give inconclusive results for skipjack. 

the International Skipjack Year program currently being coordinated by 

ICCAT. 

The need for further information to assess stock status is emphasized by 
-69- 

I I I. A. Stock Structure 

Little is known about the structure of Atlantic skipjack tuna 

stocks. A separate east-west stock has been hypothesized and indeed 

skipjack catch has been traditionally segregated into eastern and weste

Atlantic components. Results of tagging programs in 1980 by the United 

States in the Caribbean, the Spanish in the Canary Islands, and the 

Japanese in the Gulf of Guinea should provide information bearing on th

probl em. 

I I1 .B. Stock Assessment and Fishery Eva1 uation 

I I I. B . 1 . Trends- i n-Ca tc h- per- Un i t-E f fort 

Available skipjack tuna catch-per-unit-effort (CPUE) 

estimates for the eastern Atlantic include those for the FISM and Temabased fleets. These estimates are dissimilar because they are based on 

different units of effort. In addition, neither of these eastern Atla

CPUE estimates provides a valid index of abundance because skipjack 

availability varies markedly from year to year. 

complicated by some vessels, including FISM fleet units, fishing skipja

only in times of low yellowfin/high skipjack availability. 

Tema-based fleet CPUE indices, are, however, the only information avai

for inferring skipjack abundance in the eastern Atlantic. 

This problem is furthe

The FISM an

The FISM estimate is considered to be the most 

representative of the two eastern Atlantic CPUE estimates and is prese

in Figure 9. 

tons per fishing day, with no apparent trend over time. 

CPUE for 1969-1979 fluctuated between one and three metr

No CPUE index currently exists for the western Atlan

III.B.2. Resul ts of Production Model Analysis 

Plots of fishing effort, catch, and CPUE from the FIS

purse seine fleet in the eastern Atlantic are presented in Figure 10. 

Attempts to fit the production model to these data have failed to produ

viable relation between surplus production and effort. Due to spotty 

fishing effort and small catches in the western Atlantic (9,000 mt 

annually) , production model analysis for western At1 antic has not been 

attempted. 
-70- 

10 

C 8 

P 

U 

E 

t.1 6 

E 

T 

R 

I 

C 

T 

0 

N 

S 

4 

2 

0 

1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 

YEAR 

Figure 9. Average catch-per-unit-effort (CPUE) for skipjack 

tuna in the eastern Atlantic, 1969-79. 
-71 - 

-8 

-6 

-4 

-2 

C 

A 

T 

c 

H 

H 

E 

T 

R 

I 

C 

T 

0 

N 

§ 

I20 

100 

80 

68 

40 

20 

0 

10 

69 

10 

1 I 1 I 1 1 I 

10 20 30 40 50 60 70 80 

EFFORT (SDFI THOUSANDS 

Figure 10. a) Relation between catch (mt) and effort (SDFstandard days fishing) 1969-79. 

b) Relation between CPUE (mtjSDF) and effort 

(SDF) 1969-79. 
-72- 

III.B.3. Results of Yield-per-Recruit Analysis 

A yiel d-per-recrui t analysis for eastern At1 antic 

skipjack was performed at the second ICCAT workshop on juvenile tunas held 

in Brest, France, in 1980. 

participants noted that uncertainties associated with identification of 

year-cl asses due to year-round spawning of eastern At1 antic skipjack made 

the resultant analysis questionable. This analysis (Figure 11) indicates 

that for high and low levels of skipjack tuna recruitment there is little 

benefit to be expected from an increase in the age-at-first-capture. 

In formulating the analysis, the workshop 

III.B.4. Results of Spawner/Recruitment Analysis 

No spawner/recrui t analysis is avail able for Atlantic 

skipjack tuna stocks. 

III.B.5. Results of Other Analvsis Simulations 

None avail able. 

1II.C. Current Evaluation of Stocks and the Fishery 

Sk 

high level 

yield from 

the potent 

especially 

pjack tuna in the eastern Atlantic are currently fished at a 

while western Atlantic skipjack are fished at a low level. 

the stock(s) is unknown, but available information suggests tha

a1 yield is larger than current catch levels indicate, 

in the western Atlantic. 

The 

IV. STATUS OF CURRENT RESEARCH NEEDS AND EFFORTS 

Major research activities for At1 antic skipjack tuna are currently 

underway in conjunction with ICCAT's International Skipjack Year Program. 

To date they include tagging of skipjack and collection of data for 

maturity/fecundity studies, ageing studies, stomach analysis, and 

environmental studies. Further research and data collection by ICCAT 

participants are planned for 1981 in these areas and in the areas of 

exploratory fishing, improved fishery statistical sampl ing, and larval 

studies. 
-73- 

HIGH RECRUITMENT 7, 

3.0 - - 5.39 

50 

2.5 - 

2.0 - 

1.5 - - 1.33 

X I 

I I I .o 0.48 

0 1 2 3 

LOW RECRUITMENT 

3.0 

2.5 

2.0 

I .5 

I .o 

FISHING MORTALITY MULTIPLIER 

Figure 11. Equilibrium yield-per-recruit for Atlantic skipjack 

for two hypothetical recruitment levels (A - high 

recruitment of 356 x 106 fish; B - low recruitment 

of 14.3 x 106 fish) for combination of fishing m rtality multiplier and age (weight at first capturey. 

X = present situation. 
-74- 

1V.A. Major Research Problems 

1) Improved skipjack tuna fishery statistics must be collected to 

a1 low accurate assessment of stock condition and development of management 

strategies. This applies to traditionally fished areas as well as areas 

with developing fisheries (such as off Brazil and Ascension Island). 

2) No reliable index of abundance currently exists for eastern 

Atlantic skipjack stocks. CPUE indices computed from data for FISM and 

Tema-based fleets use different units of effort and therefore cannot be 

compared. 

proportional to skipjack abundance because vessels fish for this species 

only in times of low yellowfin availability. 

exists for eastern or western Atlantic skipjack fisheries. 

In addition, CPUE for the FISM fleet is not thought to be 

No viable abundance index 

3) Minimum size regulations for bigeye and yellowfin tuna affect 

skipjack tuna fisheries because all three species may be captured in the 

same time/area. The impact of these regulations on skipjack fisheries 

needs to be assessed. 

a1 ternate management schemes for conserving yellowfin and bigeye (e.g. 

time/area/cl osures) . 

Such assessment can be used to infer the efficacy o

1V.B. Current Research Efforts 

1) Improved estimates of the skipjack length/weight relation, 

natural mortal i ty, and growth have been devel oped. 

2) A preliminary assessment of the effects of minimum size 

regulations for bigeye and yellowfin on skipjack catch has been performed. 

3) Sex ratios and age at maturation of skipjack landed at Dakar 

(1977-79) have been determined. 

4) Migration patterns for skipjack dart-tagged and tetracyclinemarked in the Canary Islands (1979-80) have been examined. 

5) Skipjack caught south and southeast of Brazil between 1978 and 

1980 have been examined to determine length/weight and gilled-gutted 

weight/weight re1 ationships. 

6) School species composition and aggregation phenomena 

associated with tuna schools in the Gulf of Guinea (1979-80) have been 

examined. 

7) Current status of Atlantic skipjack stocks have been assessed 

using production model analysis techniques. 
-75- 

8) The use of sea surface temperature as an index for 

partitioning fishing effort on skipjack and yellowfin tuna has been 

examined. 

9) The economic value of eastern Atlantic tuna fisheries has be

assessed. 

1V.C. Future Research Needs 

Proposed future research projects are 1 isted below, together with 

suggested methods of study and sources of information. 

IV.C.l. Suggested Approach and Methods 

need to be examined to verify or establish suitable CPUE indices for 

eastern At1 antic skipjack tuna stock( s) . same techniques to catch/effort data for the western Atlantic should then 

be assessed. 

1) Catch/effort data from FISM and Tema-based fleets 

The feasibility of applying thes

2) Distribution and migration patterns of At1 antic 

skipjack stocks need to be examined using tag return results from ISY 

_n tagging programs. 

3) Growth and stock structure of eastern and western 

Atlantic skipjack stocks need to be compared using data to be collected by 

ISY programs (e.g., length/frequency data for skipjack captured off Brazi

Ascension Island, and in the Gulf of Guinea). 

4) Location, seasonality, intensity, and physiologica

triggering mechanisms related to skipjack spawning need to be examined. 

5) Preliminary assessments of interactions of small 

yellowfin, bigeye, and skipjack have been performed. 

data used in these assessments need to be re-examined and preliminary 

results verified or a1 tered as required. 

The techniques and 

6) Environmental data taken during the SWFC skipjack 

tagging cruise in the Caribbean should be compared with skipjack school 

sightings to determine if these results agree with published 

environment/availabil ity relations for other geographic areas. 

7) The identification of skipjack habitat vulnerable t

surface fishing gear off Brazil and Argentina (Figure 12) in 1979 preceded 

the establishment of a substantial fishery in that area in 1980. 

seasonal and areal fluctuations of this habitat area need to be examined. 

The 
-76- 

.. 

' 9:. 

.. 

.. 

.. 

.. 

.. 

.. 

Figure 12. Annual mean contours of maximum depth of skipjack tuna 

habitat. Hatched areas indicate habitat depths of less 

than 50 meters. 
-77- 

8) An assessment of potential skipjack biomass in the 

area indicated in (7) above should be undertaken to determine if the area 

can support a substantially larger fishery. 

1V.D. Status of SWFC Data Base 

La Jolla Laboratory data bases for Atlantic skipjack tuna contain 

all available fishery data. Ancillary marine environment data bases 

necessary for the studies proposed in (61, (71, and (8) of Section IV.C.l. 

are at PEG. 
- 78- 

STATUS REPORT: SOUTH ATLANTIC ALBACORE 

by 

Norman Bartoo 

Southwest Fisheries Center 

Oceanic Fisheries Resources Division 

La Jolla, California 

ABSTRACT 

Annual catches from the south Atlantic albacore stock have remained 

near 22,000 rnt for the last few years. Current annual effort levels are 

near 100 million hooks, the level reached in 1972. Available evidence 

indicates that the stock is currently producing catches about 25% below 

estimated MSY and that a relatively high yield-per-recruit of about 7.7 

is being realized. The south Atlantic albacore fishery supplies about 4

of the U.S. annual consumption through imports. 
-79- 

I. DESCRIPTION OF THE FISHERY 

A1 bacore in the Atlantic Ocean are distributed from approximately 50

N to 40" S latitude although most catches come from temperate waters 

(Figure 1). 

I.A. History of the Fishery 

The south Atlantic fishery began in 1956 when longliners, 

principally from Japan, began fishing in the Atlantic. Japan dominated t

industry from 1956 through the mid-1960's. 

have greatly increased their share of the catch (Figure 2). 

Since then Taiwan and Korea 

1.8. Trends in Catch and Effort 

Albacore catches in the south Atlantic rose steadily from 20 mt i

1956 to an early peak of 36,000 mt in 1966. 

recorded catch in 1967, the catch rose erratically to a record high of 

42,000 mt in 1972. Since 1972 the catch has been in the 20,000 to 23,000 

mt range (Figure 31, with a reported catch in 1979 of 22,000 mt. 

effort has increased from near zero in 1956 to a peak of 100 plus million 

effective hooks in 1972 and 1973. 

remained high, near 100 million hooks. 

Following a 45% drop in 

J.-- Longlin

Since 1973, effective effort has 

I.C. Value of Catch 

Reliable ex-vessel price data for foreign fleets are not readily available. 

U.S. fishermen), the south Atlantic a1 bacore catch averaged about $36 

million per year from 1973 to 1977. 

mil 1 ion. 

Assuming a value of $1,800 per mt (the approximate price paid 

The 1979 catch was worth about $40 

8 

I.D. Current Management of the Fishery 

There are no international fisheries management measures currentl

in force for the south Atlantic albacore stock. 

c 
-80- 

looo 80° 60° 40° zoo O0 20° 40° 

Figure 1. General distribution of albacore in the Atlantic (bold hatch

and location of fisheries (fine hatching). 
-81 - 

SOUTH STOCK 

TAIWAN 82% 

KOREA 16 

Figure 2. Percentages of south Atlantic albacore catches taken by 

major f i s hery part i c i pants . 
-82- 

Figure 3. Comparison of annual catch of south Atlantic albacore by 

longline fishery to Atlantic total (north stock surface, 

south stock longline, and north stock longline fisheries)
-83- 

I . NATURE AND SIGNIFICANCE OF I S. AND FOREIGN 

PARTICIPATION IN THE FISHERY 

The U.S. does not actively participate in the south Atlantic albaco

commercial fisheries, but is interested in the south Atlantic albacore 

stock. The U.S. is a signatory to the ICCAT convention and as such has 

indicated its willingness to conserve the Atlantic tuna stocks. 

longline, is imported into the U.S. for domestic consumption. This 

imported Atlantic albacore accounts for about 40% of the total annual U

albacore consumption. 

oceans and domestic catches. For comparison, the U.S. domestic fishery 

provides about 15 to 20% of the albacore consumed in the U.S. The U.S. 

currently consumes about 45% of the world's total albacore catch. 

About 45% of the total Atlantic albacore catch, mostly caught by 

The remaining 60% comes from imports from other 

111. STATUS OF THE STOCKS 

1II.A. Stock Structure 

This analysis assumes that the Atlantic a1 bacore population is 

composed of north and south stocks separated at the equator. The assum

stock separation is based primarily on longline catch rates which declin

near the equator. Secondary support is given by the different reaction

the longline CPUE, both north and south, to increased fishing pressure 

the north. 

1II.B. Stock Assessment and Fishery Evaluation 

III.B.l. Trends in Catch-per-Unit-Effort 

The south stock is fished only by longline. The catc

per-unit-effort for the stock shows an expected gradual decline followi

peak value in 1960 (Figure 41, indicating a reduction in adult abundanc

Longline effort has increased from near zero in 1956 to a peak of 100 p

million effective hooks in 1972 and 1973. Since 1973 effective effort 

remained high, near 100 million hooks. 

III.B.2. Results of Production Model Analysis 

Results of production model analysis for the south st

(Figure 5) indicate an estimated MSY in the 28,000 to 32,000 mt range. 

catch in recent years has been below this level although catches in the 
-84- 

Figure 4. Catch-per-unit-effort for Atlantic albacore longline 

fisheries on the south stock. 

Jy/ 1961- I975 DATA 

I 

I956 - I975 DATA 

-56 I I I I I 

20 40 60 80 IO0 I20 

NOMINAL FISHING EFFORT ( MILLIONS OF HOOKS 1 

Figure 5. Production model results for south Atlantic albacore. 
-85- 

*- 

late 1960's and early 1970's were close to MSY. 

mt was below MSY, with effort levels below that required for MSY. 

The 1979 catch of 22,000 

111.9.3. Results of Yield-per-Recruit Analysis, 

The south Atlantic fishery is producing a yield-perrecruit of about 7.7 kg. 

virtually no increase in yield-per-recruit is likely to occur by 

maintaining fi shi ng effort and increasing si ze-at- f i rst- capture. 

Furthermore, increases (up to 40%) in effort with the same size-at-firstcapture will produce 1 i ttle change in yield-per-recrui t Val ues. 

Because of the nature of the longline fishery, 

III.B.4. Results of Spawner/Recruitment Analysis 

No spawner/recruit relationship has been established fo

this stock. Estimates of recruitment to age 3 from the 1960 to 1966 year

classes (from cohort analyses) show relatively constant values of about 3

mill ion fish per year. 

I11 .B.5. Results of Other Analyses/Simul ations 

None avail ab1 e. 

1II.C. Current Evaluation of Stocks and the Fishery 

Evidence avail able for the south At1 antic a1 bacore stock indica

the stock is currently being expldited about 25% below MSY. 

appears to be producing a yield-per-recruit which is near the maximum fo

the mode of fishing used. 

The stock 

No problems with recruitment have been found. 

IV. STATUS OF CURRENT RESEARCH NEEDS AND EFFORTS 

1V.A. Major Research Problems 

The south Atlantic albacore stock has shown no immediate research 

needs although the representativeness of longline CPUE as an indicator of 

stock abundance should be investigated. 

1V.B. Current Research Efforts 

The current U.S. research effort on south Atlantic albacore is 

1 imi ted to monitoring the research efforts of foreign scientists through 

I CCAT . 
-86- 

1V.C. Future Research Needs 

As stated, the representativeness of longline CPUE as an indicato

of stock abundance should be investigated. 

1V.D. Status of SWFC Data Base 

The data base for south Atlantic albacore at SWFC is adequate and 

up-to-date. New data are supplied by ICCAT as available. 
-87- 

.- 

h 

STATUS REPORT: NORTH ATLANTIC ALBACORE 

Norman Bartoo 

Southwest Fisheries Center 

Oceanic Fisheries Resources Division 

La Jolla, California 

ABSTRACT 

The north Atlantic albacore stock is fished by longline and surface 

gears. 

1960. Longline catches in 1979 were 11,000 mt. Available evidence 

indicates that MSY is about 60,000 mt, which is 10% to 15% above recent 

years' catches. Yield-per-recruit to the north Atlantic a1 bacore fisheri

is about 3.8 kg, with some increase possible with fishery changes. 

Recruitment indices indicate that spawning stock is low and recruitment 

highly variable. 

Surface catches (38,000 mt in 1979) have declined about 25% since 

The fishery appears to be heavily exploited. 
-88- 

1. DESCRIPTION OF THE FISHERY 

A1 bacore in the Atlantic Ocean are distributed from approximately 50" 

N to 40" S latitude, although most catches come from temperate waters 

(Figure 1). 

I .A. History of the Fishery 

, The north Atlantic albacore fishery developed as a surface fishery 

(troll and baitboat) in the Bay of Biscay in the 1920's and continued as 

such until 1956 when an At1 antic-wide 1 ongl ine fishery devel oped. 

surface and longline fisheries have operated continuously from 1956 to the 

present . 

Both 

Six relatively separate a1 bacore fisheries (and participants) can 

be identified in the north Atlantic: 

1) Surface (France and Spain) troll fishery - 2-5 year-old fish, 

2) Summer live-bait (Spain) fishery - 2-6 year-old fish, mostly 

mostly juveniles in the Bay of Biscay to the Azores. 

juveniles in the Bay of Biscay. 

3) Autumn live-bait (France and Spain) fishery - 5-12 year-old 

adults, from Spain to the Azores since 1974. 

4) Year-round (Spain and France) live-bait fishery - 5-12 year-old 

adults, from the Iberian Peninsula to the Canary Islands, since 1970. 

5) Winter (Taiwan) longline fishery - 4-7 year-old young adults, in 

the northern At1 antic. 

6) Summer (Korea) longline fishery - 5-12 year-old adults in the 

northern At1 antic. 

A total of 10 countries, Taiwan, Cuba, France, Grenada, Japan, 

Korea, Norway, Portugal, Spain, and Trinidad, have reported north Atlantic 

albacore catches to ICCAT. The vast majority of the reported recent years

catches have been made by France, Spain, and Taiwan in the fisheries noted 

above (Figure 2). 

I.B. Trends in Catch and Effort 

' 

gear, and year are available from and summarized by the International 

Commission for the Conservation of Atlantic Tunas (ICCAT). Trends in catc

by year are shown in Figure 3. 

Data on catch for the longline and surface fisheries by country, 

The fishery began about 1920 with reported 
40" 

20" 

0" 

20" 

40" 

60" 

Figure 1. General distribution of albacore in the Atlantic (bold hatchi

and location of fisheries (fine hatching). 
-90- 

NORTH STOCK 

TAIWAN 

Figure 2. Percentages of north Atlantic albacore catches taken by 

major fishery participants. 

50% 
-91 - 

90 

80 

70 

- 60- 

Iz 

50- 0 

x 

0 

I 40- 

0 

t 

a 

0 30- 

20 

IOc 

- 

- ATLANTIC ALBACORE 

- 

SURFACE- NORTH 

- 

____------- 1--- 

0/1 I I , I I I I 1 I I I , I I I I , I I 1 I I 1 

"L 

Figure 3. Comparison of annual catch of north Atlantic albacore by 

fishery (longline and surface) to Atlantic total (includes 

south longline fishery). 
-92- 

catches near 10,000 mt. 

rose to 41,000 mt in 1956. 

50,000 mt range from 1956 to 1967, then dropped to 27,000 mt during 1967 t

1973. 

maintained the general downward trend started in 1960. The surface fisher

apparently concentrates on albacore of ages 1, 2, and 3 years. In 1979 th

surface fisheries took 38,000 mt. 

Catches increased slowly at first, then rapidly 

Catches from 1974 to 1978 again rose near 34,000 mt but generally 

Surface catches fluctuated in the 40,000 to 

Longliners began fishing for north Atlantic albacore in 1956 with 

catches of only a few tons. Catches rose steadily to a peak of 15,000 to 

16,000 mt in the 1963 to 1965 period. After the 1965 catch year (Figure 

31, longline catches dropped to the 5,000 to 8,000 mt range through 1969. 

By 1971 the catch rose to 11,000 mt, then declined to 6,000 mt in 1972. 

The 1973 to 1978 catches were somewhat higher, ranging from 9,000 to 24,00

mt with an average catch of 17,000 mt. The longline fishery apparently 

concentrates on adult albacore of age 5 and older. The 1979 longline catc

was 11,000 mt. 

The enti re north At1 antic a1 bacore fishery produced yields from 

10,000 mt ir, 1920 to 41,000 mt in 1956, with a peak of 69,000 mt in 1964. 

The entire 1958 to 1965 period experienced fluctuating catches from 41,000 

to 69,000 mt, averaging about 55,000 mt per year. 

while fluctuating, have generally declined to the 45,000 to 55,000 mt 

range. In 1977, 1978, and 1979 the catches were 52,000 mt, 48,000 mt, and 

48,000 mt, respectively. 

Longline effort has continuously increased from near zero in 1956 

to about 65 million effective hooks in 1973. Since 1973 the effort has 

remained generally constant, near 60 million hooks. Standardized surface 

effort grew from about 18,000 fishing days in 1920 to about 92,000 fishing 

days in 1967. Since 1967, surface effort has declined about 40%, to abou

55,000 fishing days. 

Since 1965, the catche

I.C. Value of Catch 

No reliable data are available on the foreign ex-vessel values fo

the catch. However, in 1980 the U.S. albacore fishermen received about 

$1800 per mt (ex-vessel). Based on this price, the 1977, 1978, and 1979 

north Atlantic albacore catches are valued at about $90 million, $86 

mil 1 ion, and $87 mill ion, respectively. 

I.D. Current Management of the Fishery 

No international fisheries management measures are currently in 

effect for the north Atlantic albacore stock. 
-93- 

.- 

11. NATURE AND SIGNIFICANCE OF U.S. AND FOREIGN 

PARTICIPATION IN THE FISHERY 

The U.S. does not actively participate in the Atlantic albacore 

commercial fisheries but is interested in the Atlantic albacore stocks. 

The U.S. is a signatory to the ICCAT convention and as such has indicated 

its willingness to conserve the Atlantic tuna stocks. 

About 45% of the total Atlantic albacore catch, mostly caught by 

longline, is imported into the U.S. for domestic consumption. This 

imported Atlantic albacore accounts for about 40% of the total annual U.S

albacore consumption. The remaining 60% comes from import from other ocea

and domestic catches. By comparison, the U.S. domestic fishery provides 

about 15 to 20% of the albacore consumed in the U.S. The U.S. currently 

consumes about 45% of the world's total albacore catch. 

111. STATUS OF THE STOCKS 

I I I .A. Stock Structure 

This analysis assumes that the At1 antic a1 bacore population is 

composed of north and south stocks separated at the equator. The assumed 

stock separation is based primarily on longline catch rates which decline 

near the equator. 

of the longline CPUE, both north and south, to increased fishing pressure 

in the north. 

Secondary support is given by the differential reactio

111.6. Stock Assessment and Fishery Evaluation 

111.6.1. Trends in Catch-per-Unit-Effort 

Catch-per-unit-effort (based on catch/100 hooks) for th

longline fishery on north stock has followed a gradual and continuous 

decline (Figure 4). Catch-per-unit-effort (based on weight) for the majo

surface fisheries shows a slight downward trend (Figure 5). 

111.6.2. Results of Production Model Analysis 

A production model analysis for the logistic growth 

assumption was presented in 1980 by ICCAT (Figure 6). 

that Maximum Sustainable Yield (MSY) is about 60,000 mt at near or slight

above current effort levels. Catches in 1979 were about 48,000 mt. 

Results indicate 
- 94- 

- I .! 

)r 

0 

-0 

Q, 

Q 

v) 

L 

5 I.( c 

.- 0 

I 

t 

v 

O.! 

W 

3 

0 

a 

O.( 

Figure 4. Catch-per-uni t-effort for At1 antic a1 bacore 

longline fisheries on northern stocks. 

BA I T BOAT 

I I I I I I 1 I 1 I I 1 I 1 

65 70 75 

YEAR 

Figure 5. Catch-per-unit-effort for the north Atlantic 

baitboat and troll fisheries. 
-95- 

n 

tz 

0 

0 

0 c - 

Y 

I 

0 

I0 

a 

NORMALIZED EFFORT 

Figure 6. Production model results for north Atlantic albacore 

24 - 

- 

20 - 

1957 

0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0 4.4 4.8 

P INDEX 

Figure 7. Relationship between parent (P) stock and recruitment (R) 

levels for north Atlantic albacore. 
-96- 

III.B.3. Results of Yield-Der-Recruit Analvsis 

Fisheries on the north Atlantic stock were realizing 

yield-per-recruit of about 3.8 kg in the 1970'~~ with a size-atrecruitment of about 40 cm. Maintaining the current effort levels and 

increasing size-at-first-capture to about 65 cm should produce about a 

increase in yiel d-per- recrui t. Thi s si ze-at-recrui tment , however , wi 11 

1 ikely impact the existing surface fisheries severely. Maintaining the 

current size-at-recruitment and increasing or decreasing effort up to 2

will produce no significant changes in yield-per-recruit. 1980 ICCAT 

results indicate that changes in the surface fisheries patterns may be 

increasi ng yi el d- per-recrui t. 

III.B.4. Results of Spawner/Recruitment Analysis 

Analysis of spawner and recruit indices for the north 

stock in recent years has caused concern at ICCAT. 

spawning stock indices appear to be about 15% to 20% as great as those 

observed in the late 1950's (Figure 7). Indices of recruitment show a 

possible declining trend with increasing variability. 

measured by CPUE indices dropped from a value of about 16 in 1957 with 

relatively little estimated variance, to a mean value of about 12 in th

last 5 years with variance increasing five-fold. 

probability of a year-class failure may be as high as 10% to 20%. 

Current levels of 

Recruitment as 

Recent work indicates 

III.B.5. Results of Other Analyses/Simulations 

None avail ab1 e. 

1II.C. Current Evaluation of Stocks and the Fishery 

The avail ab1 e analyses indicate that the north At1 antic a1 bacor

stock appears to be fished near MSY. 

maximum value, owing to substantial amounts of small fish in the catch. 

However, little change appears possible without large changes in the 

structure of the fisheries. The decline in recruitment (related to the 

yield-per-recrui t) and apparent increases in variability, make a year-c

failure, as measured by the recruitment index, a real possibility. 

Yield-per-recruit is not near a 

IV. STATUS OF CURRENT RESEARCH NEEDS AND EFFORTS 

1V.A. Major Research Problems 

1) Effort needs to be standardized to determine its effect on 

production model resul ts. 
-97- 

c2) 

evaluated with regard to assumed parameters, and variability and bias in 

basic data. 

The robustness of current stock assessment techniques must 

These should indicate whether more conclusive management advice 

and recommendations are possible, using existing model/data combinations

1V.B. Current Research Effort 

1) Conventional stock assessments of foreign fisheries are bein

2) 

analyzed, using production model, spawner/recrui t, and cohort analyses. 

about spawner/recrui t re1 ationships. 

Work is being done on the estimation of confidence intervals 

1V.C. Future Research Needs 

IV.C.l. Suggested Approach and Methods 

1) The effects of changing effort standardization 

methods on production model results can be examined using available data 

and a variety of standard and new analytical methods. 

2) The robustness of current assessment techniques wi

avail ab1 e data can be investigated using Monte Carlo and sensitivity 

analyses. Results of this research are applicable to all species. 

1V.D. Status of SWFC Data Base 

The data base for north Atlantic albacore at SWFC is adequate an

up-to-date. New data are suppl ied by ICCAT as avail able. 
- 99- 

.- 

STATUS REPORT: TUNAS IN THE INDIAN OCEAN 

Fletcher V. Riggs 

iSouthwest Fisheries Center 

Honol ul u , Hawaii 

ABSTRACT 

The status of stocks of four species of tuna (albacore, bigeye, 

yellowfin, and skipjack) in the Indian Ocean were analyzed. 

estimated annual catch of albacore in the Indian Ocean has fluctuated 

widely 

14,600 mt. 

assessment suggests no gain in yield-per-recruit from harvesting the 

younger fish as fishing effort moved into more southerly waters. 

stock appears fully harvested and there appears to be no reason for conc

over the future of the stock at this time. 

Since 1962 

between 10,000 and 28,000 mt. The estimated catch for 1978 was 

MSY lies between 15,000 and 20,000 mt. A yield-per-recruit 

This 

Estimated annual catch of bigeye tuna in the Indian Ocean reached a 

high of 48,600 mt in 1978. 

reliable prediction of MSY. 

effort and did not reach an asymptote. 

1 ightly exploited. 

A production model analysis did not produce 

The yield curve showed increasing catch wit

This stock appears to be only 

Yellowfin tuna in the Indian Ocean are fished by surface and longlin

gears. 

exhibited a general upward tend. The estimated total catch for 1978 was 

62,500 mt. 

data suggest an MSY for that fishery of around 40,000 mt. Due to rather 

inaccurate total catch estimates, however, MSY may be higher. It is 

unlikely that longline catch could be increased appreciably above the 

current level. 

increased landings of yellowfin tuna by surface fisheries. 

undeveloped. 

trend. Estimated catch for 1978 was 32,600 mt. There have been no 

quantitative assessments of the Indian Ocean skipjack tuna stock. 

Estimated annual catch fluctuated widely from 1952 to 1978 but 

Production model analyses based on available long1 ine fisher

However, it is generally felt that there is a potential 

The surface skipjack tuna fishery in the Indian Ocean is relatively 

Catches have fluctuated from 1965 on a generally rising 
-1 00- 

I. DESCRIPTION OF THE FISHERY 

I .A. Hi story of the Fishery 

Commercial 1 ongl ine fishing for a1 bacore (Thunnus a1 a1 unga) , bigey

tuna (T. obesus) , and yellowfin tuna (T. a1 bacaresE%-%e Indian Ocean, 

startea afterorld War I I a1 though exEloratorv fishing .," by JaDanese vesse

in the early 1930's had indicated-the presence"of tunas in the eastern 

Indian Ocean. Intensive commercial longline fishing in the Indian Ocean 

began in 1952 in the eastern sector and rapidly expanded westward to reac

the African coast by 1956 (Figure 1) (Nakamura et al. 1956; Ki kawa et al. 

1969). Countries currently maintaining longline fleets in this area 

include Japan, Korea, Taiwan, U.S.S.R., and Sri Lanka. Vessels from 

Australia, India, Madagascar, Maldives, Pakistan, Sri Lanka, Democratic 

Republic of Yemen Seychelles, and Oman catch surface yellowfin tuna (Wetherall et a1 . f 1. 

The surface skipjack tuna (Katsuwonus pelamis) fishery in the 

Indian Ocean is still relatively undeveloped. Vost of the catches of 

skipjack tuna, and a smaller but growing proportion of the catches of 

yellowfin tuna, are made in localized fisheries along the coastline of the 

The origins of these fisheries are obscure and their historical accounts 

are few and fragmentary.. 

by trolling gear, drift nets, and pole-and-line. Use of the pole-and-line 

method dates back to 1919 in Sri Lanka and in Minicoy, Laccadive, and 

Maldive Is1 ands to 1909 (Sivasubramaniam 1965). 

skipjack tuna catches in the Indian Ocean include Australia, Comoros, 

Indonesia, Japan, Korea, Maldives, Mauritius, Seychelles, and Sri Lanka 

(Food and Agriculture Organization of the United Nations [FAO] 1979). 

various countries bordering the ocean and around the many island groups. 

In Sri Lanka (Ceylon), skipjack tuna are taken 

Countries reporting 

I.B. Trends in Catch and Effort 

Albacore - The estimated annual catch in the Indian Ocean rose fro

100 metr7c tons (mt) in 1952 to 17,700 mt in 1962. 

estimated annual catch fluctuated widely, reaching a high of 28,200 mt in 

1974 (Table 1 and Figure 2). 

From 1962 to 1978, the 

'Weatherall, J. A., F. V. Riggs, and M. Y. Y. Yong. 1979. Some 

production model analyses of tuna and billfish stocks in the India 

Ocean. SWFC Admin. Rep. H-79-7, Nat. Mar. Fish. Serv., NOAA, Honolulu, 

Hawaii, 12 p. Prepared for the Workshop on the Assessment of Selected 

Tunas and Billfish Stocks in the Indian and Pacific Oceans, Shimizu, 

Japan, 13-22 June 1979. 
-1 01 - 

I I 

30" 40" I 

I I I I I I 

lo 60" 70" 80" 90" 100" llOo 120" 

Fi'gure 1. The expansion of Japanese longline fishing grounds in the 

Indian Ocean. (Adapted from Kikawa et al. 1969). 
-1 02- 

Table 1.--Estimated total catches of tunas in the Indian Ocean. 

Year A1 bacorel Bigeye tuna1 Ye1 lowfin tuna1 Skipjack tuna

1952 

1953 

1954 

1955 

1956 

1957 

1958 

1959 

1960 

1961 

1962 

1963 

1964 

1965 

1966 

1967 

1968 

1969 

1970 

1971 

1972 

1973 

1974 

1975 

1976 

1977 

1978 

0.1 

1.1 

2.8 

3.3 

4.8 

4.7 

6.3 

10.4 

11.1 

15.4 

17.7 

12.6 

18.1 

12.4 

17.3 

23.7 

17.4 

21.9 

15.2 

10.2 

11.7 

22.1 

28.2 

11.2 

14.9 

11.4 

14.6 

1.5 

3.6 

8.0 

10.3 

14.0 

13.3 

12.8 

10.4 

17.0 

15.5 

19.9 

14.2 

19.0 

20.1 

26.4 

26.9 

38.7 

27.4 

24.8 

22.8 

18.1 

16.0 

27.7 

39.7 

29.8 

36.8 

48.6 

~~ 

8.9 

13.3 

25.1 

47.1 

65.5 

37.3 

27.6 

26.8 

42.5 

37.4 

55.1 

29.4 

30.1 

34.5 

56.8 

44.8 

88.1 

61.7 

42.6 

50.9 

47.4 

41.2 

43.5 

51.4 

56.4 

70.5 

62.5 

13.2 

16.0 

18.1 

16.6 

18.7 

29.7 

31.4 

20.1 

25.1 

41.3 

36.2 

38.4 

30.3 

32.6 

IData for albacore, bigeye tuna, and yellowfin tuna for 1952-77 

from FA0 in press and for 1978 from FA0 1979. 

2Data for skipjack tuna for 1965-69 from FA0 1974, for 1970-72 

from FA0 1976, for 1973 from FA0 1977, and for 1974-78 from FA0 

1979. 
-1 03- 

&=- 

YEARS 

Figure 2. Estimated total catch of albacore in the Indian Ocean 

(Data from Table 1.) 
-1 04- 

Bigeye tuna - The estimated annual catch increased steadily from 

1,500 mt in 1952 to 38,700 mt in 1968, then declined temporarily to 16,000 

mt in 1973. 

high of 48,600 mt (Table 1 and Figure 3). 

Annual catch estimates after 1973 rose sharply to the 1978 

Yellowfin tuna - The estimated annual catch fluctuated widely from 

1952 to 19/8 b ut suggests a general downward trend. Years with relatively 

high catches include 1956 (65,500 mt), 1968 (88,100 mt), and 1977 (70,500 

mt) (Table 1 and Figure 4). 

Skipjack tuna - The catch fluctuated with a generally rising trend 

from 13,200 mt in 1965 to a peak of 41,300 mt in 1974; it then declined to 

32,600 mt in 1978 (Table 1 and Figure 5). 

Reliable statistics of nominal effort are available only for 

Japanese and Taiwanese 1 ongl ine vessel s (Figure 6). 

to a high of 126 million hooks in 1967, followed by a general decline to 6

million hooks in 1978. 

rapidly to 53 million hooks within the first 3 years, then experienced a 

gradual decline to 34 million hooks in 1973. Taiwanese effort then rose 

again sharply, reaching its highest value of 57 million hooks in 1974; it 

then declined to 26 million hooks in 1977. 

Japanese effort rose 

The effort by Taiwan, beginning in 1967, rose 

Although not included in Figure 6, an increasing proportion of th

total longline effort in recent years may be attributed to Korean vessels. 

Japanese longline effort shifted away from yellowfin tuna in earlier years 

to albacore, then bigeye tuna, and is currently targeted on southern 

bluefin tuna, - T.thynnus. 

I.C. Value of Catch 

No information on the value of catch is available. Presumably mo

of the tunas caught in the longline fishery are landed in Japanese, Korean

and Taiwan ports. 

I.D. Current Management of the Fishery 

None of the tunas in the Indian Ocean is under management. 

11. NATURE AND SIGNFICANCE OF U.S. AND FOREIGN 

PARTICIPATION IN THE FISHERY 

There is no known current U.S. participation or direct investment in 

the Indian Ocean tuna fisheries. A quantity of tuna landed by foreign 
-1 05- 

#- 

YEARS 

Figure 3. Est mated total catch of bigeye tuna in the Ind 

(Data from Table 1.) 

an Ocean. 
-1 06- 

loo ,lll.,,,(/,,ll,,,lll,, /Ill 

Figure 4. Estimated total catch of yellowfin tuna in the 

Indian Ocean. (Data from Table 1.) 
-1 07- 

1 1 1 1 I 1 I I I I 

1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 

YEARS 

Figure 5. Skipjack tuna catch in the Indian Ocean. 

(Data from Table 1 .) 
-1 08- 

(I) 

0 

X 

Ul Y 

0 

z 

P 

e 

c a

w lL 

-I 

a 

z 

I 

0 z

0 I I I I 

I962 1964 1966 1968 I970 1972 1974 I976 1978 

YEARS 

Figure 6. 

longline vessels in the Indian Ocean. 

Fisheries Agency of Japan, Research Department 1980 and Taiwan 

data courtesy of R. T. Yang, National Taiwan University, Taiwan

Republic of China. 

Nominal effort in lob hooks by Japanese and Taiwan 

(Japanese data from 
-1 09- 

interests, however, may be imported into the U.S.; the actual volume or 

value is unknown. 

The significance of the tuna fisheries in the Indian Ocean relative 

other oceans to nations with long-range longline fleets may be reflected 

the proportion of total nominal effort that is expended in the Indian 

Ocean. For the Japanese longline fleet, 15% of the total hooks set were 

the Indian Ocean in 1978; for the Taiwan fleet the most recent figure wa

25% in 1976. This is in contrast to the middle and late 1960’s with 

relatively higher values of 27% for Japan and 50% for Taiwan. 

111. STATUS OF THE STOCKS 

1II.A. Stock Structure 

It was assumed at the 1979 Shimizu Workshop (Food and Agriculture 

Organization of the United Nations [FAO], in press) that there are singl

stocks of albacore and bigeye tuna in the Indian Ocean. The yellowfin tu

resource was believed ‘to be composed of either two stocks (east and west 

about 100” E longitude) or a single stock. No information on skipjack tu

stock structure was available for this report. 

I11 .B. Stock Assessment and Fishery Evaluation 

III.B.l. Trends in Catch-per-Unit-Effort 

Abundance indices have been recently computed for India

Ocean albacore, bigeye tuna, and yellowfin tuna over the period from 195

to 1976 (Wetherall et al., see footnote 1). 

The abundance index for albacore tripled in the first 

few years of the fishery, but subsequently declined steadily to less tha

10% of its peak value (Figure 7). The abundance index for bigeye tuna h

fluctuated moderately but generally shows an overall downward trend since 

1952. The apparent abundance in recent years, however, is still about 50

of its initial value (Figure 8). 

has show a steady decl-ine since 1954 to levels about 15% of the initial 

Val ues (Figure 9 1. 

The abundance index for yellowfin tuna 

Catch-per-unit-effort statistics are not available fo

Indian Ocean skipjack tuna. 
-1 10- 

/\ ALBACORE 

EFFECTIVE EFFORT 

1955 I960 1965 1970 1975 

YEARS 

Fiaure 7. Estimated total catch (lo3 MT). relative abundance 

hGoks), and effective effort ( lo6 hooks)-for Indian Ocean albacore. 
-111- 

I

1

1

Figure 8. Estimated total catch (lo3 MT), relative abundance (kg/100 hoo

and effective effort (lo6 hooks) for Indian Ocean bigeye tuna. 
-1 12- 

200 

Is0 

I60 

- 140 :: 

0 

0 

I 

120 8 

loo - 

z Bow 

- 

\ 

11 0 

i 

2 

V 

605 m 

a 

40 

20 

0 

400 

360 

320 

280 ;; 

8 

Y 

0 

240 *o 

t- 

- - 

200 E 

W LL 

160 $ 

0 W LL 

120 

80 

40 

0 

Figure 9. Estimated total catch (lo3 MT), relative abundance (kg/100 hooks

and effective effort (IO6 hooks) for Indian Ocean yellowfin tuna. 
-1 13- 

III.B.2. Results of Production Model Analysis 

Production model analyses have been applied to Indi n Ocean lbacore, bigeye tuna, and yellowfin tuna data (Kume and Morita 9 , 

Suzukij, and Wetherall et a1 . , see footnote 1). No assessment studies have 

been done on skipjack tuna. 

A1 bacore - A MSY (maximum sustainable yield) between 

15,000 and 20,000 mt was suggested by production model analyses. 

curve appeared to be asymptotic and there was little change in the catch 

although effort doubled from 1966 to 1974. 

A yield 

Bigeye tuna - A production model analysis did not 

produce a reliable prediction of MSY. 

catch with effort; effort. levels were not high enough to indicate a maximum 

or asymptotic yield. 

The yield curve showed increasing 

Yellowfin tuna - Production model analyses based on 

available data suggested an MSY of around 40,000 mt. However, because 

total catch estimates are rather inaccurate, it may be premature to 

pinpoint an MSY for this fishery, except to indicate that it is thought to 

be between 40,000 and 60,000 mt. 

III.B.3. Results of Yield-per-Recruit Analysis 

A yield-per-recrui t assessment of Indian Ocean a1 bacore 

by Suda (1973) suggested no gain in yield-per-recruit from harvesting the 

younger fish as fishing effort moved into more southerly waters. 

I I I. B .4. Resul t s o f SDawner/Recrui tment Anal vsi s 

Stock size indices by age for Indian Ocean yellowfin tuna 

have been calculated under the one- and two-stock hypotheses (Suzuki, see 

footnote 3). No relationship between stock and recruitment was evident. 

2Kume, S., and Y. Morita. 1979. Brief review of the fishery biology 

of bigeye tuna in the Indian Ocean and its stock assessment. Prepared 

for the Workshop on the Assessment of Selected Tunas and Billfish 

Stocks in the Indian and Pacific Oceans, Shimizu, Japan, 13-22 June 

1979. 

3Suzuki, Z. 1979. Stock assessment of yellowfin tuna in the Indian 

Ocean exploited by tuna 'longline fishery. 

the Assessment of Selected Tunas and Billfish Stocks in the Indian and 

Pacific Oceans, Shimizu, Japan, 13-22 June 1979. 

Prepared for the Workshop on 

"CI 
-1 14- 

I11 .B.5. Results of Other Analyses/Simulations 

None available. 

1II.C. Current Evaluation of Stocks and the Fishery 

A1 bacore - The Indian Ocean a1 bacore stock appears to be fully 

harvested. 

there appears to be no reason for concern over the future of the stock at 

this time. 

The consensus at the Shimizu Workshop (FAO, in press) was that 

Bigeye tuna - The Indian Ocean bigeye tuna stock appears to be 

only lightly exploited. 

potential exists for surface fisheries on this species. 

It is impossible at this time to assess what 

Yellowfin tuna - It is unlikely that longline catch of Indian 

Ocean ye1 1 owfin tuna could be increased appreciably above the current 

level. However, it is generally felt that there is a potential for 

increased landings of this species by surface fisheries. 

increased surface fishery might reduce the abundance of yellowfin tuna 

available to longliners, the total catch would probably increase. 

While an 

IV. STATUS OF CURRENT RESEARCH NEEDS AND EFFORTS 

1V.A. Major Research Problems 

Several research needs were identified at the 1979 Shimizu Workshop 

(FAO, in press). 

Yellowfin tuna - Studies were recommended to 1) analyze, under 

various hypotheses, the sensitivity of stocks, catch, etc., because an 

adequate data base will not be available for some time; 2) estimate 

coefficients of mortality, particularly in relation with fishing effort; 3

determine changes in effectiveness of fishing gear, particularly in 

relation to total fishing effort; 4) apply production model analyses to 

the catch in terms of number of fish and fishing effort, because a) the 

size freauencies are functions of fishing intensity, and b) there is an 

uncertainty in applying a fixed age-size key to estimate the age 

composition; and 5) determine hypothetical yields for various new fishing 

stratagies. 

Bigeye tuna - It was recommended that a study of the population 

relationship of bigeye tuna in the Banda Sea and in the Indian Ocean be 

carried out. 

priority. 

Research on population parameters was not considered of high 
-1 15- 

Albacore - The workshop recommended that an effort should be made 

to determine precisely which data are missing and needed for minimally 

sophisticated stock assessments such as production models and cohort 

analyses. 

Skipjack tuna - Aside from localized studies, research on this 

species has been almost nil. 

1V.B. Current Research Efforts 

There are currently no research efforts by the SWFC on Indian Ocea

tunas. Details of research being done by other agencies are not available 

for this resport. 

1V.C. Future Research Needs 

There is an overall need to enhance and strengthen the Pacific and 

Indian Ocean tuna data base and to monitor fishing activities and 

developments in these areas more closely. 

c The Shimizu Workshop (FAO, in press) pinpointed the following dat

needs: 

1) More accurate estimates of yellowfin tuna catch, particularly for 

the surface fisheries. 

2) Yellowfin catch, effort, and size-frequency data by temporalspatial strata for yield-per-recrui t and stock structure studies. 

3) Improved data from that segment of the longline fishery which 

targets on yellowfin, albacore, and bigeye tuna: the available analyses, 

based on data from the Japanese longline fishery, are now inadequate 

because Japanese long1 iners now target on southern bluefin tuna. 

4) Fishing effort #and other biological data for the yellowfin and 

bigeye tuna surface fisheries. 

5) Unpublished albacore catch and effort data thought to exist in 

government and industry files. 

6) Improved catch (and effort data for skipjack tuna in the various 

local ized surface industries. 
-1 16- 

1V.D. Status of SWFC Data Base 

Data on Indian Ocean tunas maintained and currently used at the 

Honol ul u Laboratory consist of Japanese and Taiwanese 1 ongl ine catch and 

effort statistics. 

are avail able but questions on interpretation have precluded use. 

Some catch and effort data for Korean longline vessels 

LITERATURE CITED 

Food and Agriculture Organization of the United Nations. 

1974. Catches and landings, 1973. FA0 Yearbook Fish. Stat. 36, 

590 p. 

1976. Catches and landings, 1975. FA0 Yearbook Fish. Stat. 40, 

334 p. 

1977. Catches and landings, 1976. FA0 Yearbook Fish. Stat. 42, 

323 p. 

1979. Catches and landings, 1978. FA0 Yearbook Fish. Stat. 46, 

372 p. 

In press. Summary report of the Workshop on the Assessment of 

Selected Tuna and Billfish Stocks in the Pacific and Indian 

Oceans, Shimizu, Japan, 13-22 June 1979. FA0 Fist?. Rep. 

Fisheries Agency of Japan, Research Department. 

Annual report of effort and catch statistics by area on 

Japanese tuna longline fishery, 1978. Fish. Agency Japan, Res. 

Dep., 241 p. 

1980. 

Kikawa, S., T. Koto, C. Shingu, and Y. Nishikawa. 

1969. Status of tuna fisheries in the Indian Ocean as of 1968. 

Far Seas Fish. Res. Lab., S. Ser. 2, 20 p. 

Nakamura, H., Y. Yabuta, and K. Mimura. 

1956. Longline fishing grounds in the Indian Ocean. Indo-Pac. 

Fish. Counc., Proc., 6 Sess., Sect. 2 and 3: 220-238. 
-1 17- 

,- 

Si vasubraman i am, K . 1965. Exploitation of tunas in Ceylon's coastal waters. Bull. 

Fish. Res. Stn., Ceylon 18: 59-73. 

Suda, A. 

1973. Observation on the recent status of tuna longline fishery in 

the Indian Ocean. Far Seas Fish. Res. Lab., S. Ser. 7: 41-70. 
-118- 

STATUS REPORT: BILLFISHES IN THE INDIAN OCEAN 

Howard 0. Yoshida 

Southwest Fisheries Center 

Honol ul u, Hawai i 

ABSTRACT 

Billfishes are caught primarily as a by-catch on longline gear set to 

catch tunas in the Indian Ocean. Most of these billfishes appear to be 

sold in Japan where striped marlin brings the highest price, followed by 

swordfish, blue marlin, and black marlin. Tentative results from 

production model analyses indicate that no significant increase in total 

yield can be expected for blue and black marl in, whereas striped marl in 

yields could increase with increased effort. 

do not appear to be adversely affected by current levels of fishing 

efforts. Additional statistics must be collected from the fleets of 

participating nations to give a clearer picture of stock status in these 

waters. 

Swordfish and sail fish stock 
-1 19- 

I. DESCRIPTION OF THE FISHERY 

I.A. History of the Fishery 

c 

The billfishes (blue marlin, Makaira nigricans, striped marlin, 

Tetrapturus audax, black marl in, M. indica, swordfish, Xi phias gladius, 

sail fish, Ismorus platypterus,amrtbill spearfish, T. 

angustirostris) are widely distributed and have generally siiiiil ar 

distributions in the Indian Ocean (Figure 1). Billfishes are caught on

incidentally by longliners because the target species in the Indian Oce

are the various tunas. Major participating fleets include those of Jap

Taiwan, and Korea, although Tanzania and the U.S.S.R. also report billf

catches from the Indian Ocean to the FA0 (Food and Agriculture Organiz

of the United Nations 1977). Indonesian vessels and sport fishermen in 

South Africa, Kenya , Seychell es, and western Austral ia probably catch a 

small amount of billfishes. 

According to Ueyanagi (1974) , the Japanese long1 ine fishery ar

the Lesser Sunda Islands began expanding into the Indian Ocean in 1952 

(Figure 2). By 1956, Japanese vessels were fishing in African coastal 

waters and by 1958, they had reached the northern limit of the Indian 

Ocean. Subsequent expansion was southward. By 1964, longline operatio

had reached 40" S latitude, the southern limit of billfish distribution

Further southward expansion was solely for the southern bluefin tuna. 

Longline boats of Taiwan and Korea began fishing in the Indian Ocean in 

1954 and 1967, respectively (Honma and Suzuki 1972). 

I.B. Trends in Catch and Effort 

The estimated total bill fish catch from the Indian Ocean amoun

to 7,804 mt (metric tons) in 1975 and 7,062 mt in 1976 (Wetherall et a

The catch is listed by species, country, and year in Table 1. 

catch, relative abundance, and effective effort are available from 1952 

1976 (Table 2). 

Data fo

'Wetherall, J. A., F. V. Riggs, and M. Y. Y. Yong. 1979. Some prod

tion model analyses of tuna and billfish stocks in the Indian Ocean. 

SWFC Admin. Rep. H-79-7, Natl. Mar. Fish. Serv., NOAA, Honolulu, Hawa

12 p. Prepared for the Workshop on the Assessment of Selected Tunas 

Billfish Stocks in the Indian and Pacific Oceans, Shimizu, Japan, 13-2

June 1979. 
-1 20- 
-1 21 - 

I 

cn 

LL 

Q 

0 

cn 

- 

a 

9 
-1 22- 

0) 

0 

v 

#3 

0 .r 

c, 

51: 

0 

V 

I 

I 
-1 23- 

Figure 2.--The expansion of Japanese longline fishing grounds in the 

Indian Ocean. (Adapted from Kikawa et al. 1969). 
-1 24- 

Table 1 .--Estimated annual catches (metric tons) of billfishes of 

the Indian Ocean by species and country, 1975 and 1976. 

B1 ue Striped B1 ack 

Country marl in marl in marl in Swordfish Sai 1 fish 

1975 

Japan 700 900 500 700 2 00 

Taiwan 447 344 192 291 51 1 

Korea 1,130 870 495 244 280 

1976 

Japan 300 5 00 200 300 2 00 

Taiwan 343 81 9 78 371 261 

Korea 872 2,082 198 398 140 
-1 25- 

-X 

CnaJ 

JI 

OL 

GO 

c,i 

ul 

wm 

IO 

I- 

.- 

OOOOOOOOOOO-UU-~O~

oooaooooooomuium6w~~mmo

m m 7 o y U.N. N-" ma u w o m m u n m u (0 h m - 

......... .. 
-1 26- 

Blue marlin catches rose to a high of 4,980 mt in 1956, fluctuate

Striped marlin catches reached a high of 4,729 mt in 196

between 4,980 and 2,634 mt from 1956 to 1970, and dropped to 1,515 mt in 

1976 (Figure 3). 

and have since varied between 1,117 and 3,401 mt (Figure 4). 

catches increased to a peak of 2,460 mt in 1968 and have generally 

decreased since then (Figure 5). 

2,300 mt in 1969 and 1970. There was a steady rising trend before those 

years and an irregularly declining trend after (Figure 6). The trend of 

sailfish catches was up before 1967, when 1,972 mt were caught, then 

decl ined to present 1 eve1 s (Figure 7 1. 

Black marlin 

Swordfish catches amounted to almost 

I.C. Value of Catch 

Most of the Indian Ocean billfish catch is presumed to have been 

sold in Japan. The average monthly ex-vessel prices at Yaizu, Japan, for 

blue, striped, and black marlins, and swordfish, from January 1978 to May 

1979 ([U .S.] National Marine Fisheries Service 1978-1979) , are presented i

Table 3. During that period, striped marlin, the most valuable of the 

billfish species, sold for $2,316 a short ton to $4,345 a short ton. 

Swordfish prices were usually better than blue marlin prices which, in 

turn, were usually better than black marlin prices. Swordfish prices 

ranged from $2,129 a short ton to $2,833 a short ton; blue marlin, $1,933- 

$3,156 a short ton; and black marlin, $1,638-$2,744 a short ton. 

I.D. Current Management of the Fishery 

None of the billfishes in the Indian Ocean are currenty under 

management. 

11. NATURE AND SIGNIFICANCE OF U.S. AND 

FOREIGN PARTICIPATION IN THE FISHERY 

The U.S. is interested in the billfishes of the Indian Ocean as a 

resource, but is not actively involved in fishing for them. 

111. STATUS OF THE STOCKS 

1II.A. Stock Structure 

The extant data on the spawning areas and the geographical 

variation in catch rates suggest a single stock of blue marlin in the 
-1 27- 

n TOTAL CATCH 

ABUNDANCE INDEX I 

YEARS 

- 

Y m 

0 

0 

P 

0 

\ 

r Iz 

X W

0 

W O 

z 

z 

3 

- 

1 

3 

a m 

xx) 

250 

m 

mz 

B 

H - 

I

150 5 

L

L

W

W 

IO 

LW

z 

loo e 

50 

0 

Figure 3.--Estimated total catch (lo3 MT), relative abundance (kg/100 

hooks), and effective effort (lo6 hooks) for Indian Ocean blue marlin. 

(From Wetherall et a1 . see text footnote 1 .) 
-1 28- 

5 

u) 

i3 

1P 0 

e 

\ 

r D - 3 

n 

z 

z 

2; 13 

m 

a 

I 

0 

STRIPED MARLIN 

4- 

3- 

2- 

400 

- 360 

- 320 

~ 280 ? 

-240 

-200 

-160 

I20 

-80 

-40 

-0 

YEARS 

Figure 4.--Estimated total catch (lo3 MT) , relative abundance (kg/lOO 

hooks), and effective effort (lo6 hooks) for Indian Ocean striped marli

(From Wetherall et al. see text footnote 1 .) 
-1 29- 

3.0 I I I I I I l l l I I I I I 

ABUNDANCE INDEX (EAST 1 

n 

2.0 - 

0 

ABUNDANCE INDEX (WEST 1 

1960 1965 1970 I975 

YEARS 

80 

70 

60 

w

40 

30 

20 

10 

0 

Figure 5.--Estimated total catch (lo3 MT), relative abundance (kg/100 

hooks), and effective effort (lo6 hooks) for Indian Ocean black marlin

(From Wetherall et al. see text footnote 1.) 
-1 30- 

SWORDFISH 

25 - -25 

Figure 6.--Estimated total catch (lo3 MT) and relative abundance (kg/10

hooks) for Indian Ocean swordfish. 

index areas. (From Wetherall et a1 . see text footnote 1 .) 

Abundance indices are given for two 
-1 31 - 

lllll 

SAILFISH 

111ll111111111~1~1

1955 ' 1960 1965 I970 1975 

YEARS 

Figure 7.--Estimated total catch (lo3 MT) and relative abundance (kg/10

hooks) for Indian Ocean sailfish. 

index areas. (From Wetherall et al. see text footnote 1 .) 

Abundance indices are given for two 
-1 32- 

Table 3.--Monthly average ex-vessel prices of billfishes (U.S. dollars 

per short ton) at Yaizu fish market, January 1978-May 1979. 

[U.S.] National Marine Fisheries Service 

(From 

1978-1979.) 

~~ 

Month Striped marlin Blue marlin Black marlin Swordfish 

1978 

January 

February 

March 

Apri 1 

May 

June 

July 

August 

September 

October 

November 

December 

3,482 

2,823 

3,452 

2 , 722 

2,614 

2,462 

4,345 

2,507 

2,903 

2,856 

3,981 

2,698 

2,009 

2,326 

2,299 

2,515 

2,112 

1,991 

2,122 

2,275 

2,039 

2,412 

3,165 

2,323 

2 , 605 

2.070 

2 io25 

2,082 

1,929 

2,090 

2,272 

1,638 

1,943 

2,055 

2,202 

1,934 

2,423 

2,503 

2,647 

2,833 

2,343 

2,263 

2 , 658 

2,826 

2 , 769 

2,793 

2,590 

2,703 

1979 

January 

February 

March 

Apri 1 

May 

4,141 

4,046 

4,095 

2,316 

2,489 

1,933 

2,027 

2,510 

2,658 

2,626 

2 , 744 

2,059 

1,871 

1,730 

1,818 

2,455 

2,440 

2,580 

2,232 

2,129 
-1 33- 

c 

Indian Ocean. 

mu1 tip1 e stock hypothesis, but s i m i l a r types of data suggest the 

possibility of multiple stocks for striped marlin, black marlin, swordfis

and sailfish in this area. 

There are few definitive data to support either a single o

I I1 .B. Stock Assessment and Fishery Eva1 uation 

I I I. B .l. Trends in Catch-per-Un i t-Effort 

There was a decline in the catch-per-unit-effort over t

1952 to 1976 period in the Japanese longline fishery for blue marlin 

(Figure 31, striped marlin (Figure 61, and black marlin (Figure 5). 

rates for swordfish have not declined significantly (Figure 61, and catch 

rates for sail fish (incl uding small amounts of shortbill spearfish) have 

been quite variable although a general increase over the 1952 to 1976 

period is evident (Figure 7). 

Catc

III.B.2. Results of Production Model Analvsis 

The following production model analyses were applied to 

available data for Indian Ocean billfishes to obtain a better indication 

the status of the stocks (FAO, in press): 

The production model analysis for blue marl in suggeste

a MSY (maximum sustainable yield) of 3,400-3,600 mt achievable with 

substantially less effort than has recently been expended (Table 4 1. 

However, the curve fits the data points poorly (Figure 81, suggesting tha

there may be significant errors in the total catch estimates. 

For striped marlin, assuming a single stock, the MSY 

from the production model analysis is 3,500 mt at a level of effort 

considerably more than the highest effort expended to date (Table 4). 

Annual catches at effort levels of 150 to 300 million hooks are widely 

variable about the equilibrium yield curve (Figure 9). 

The estimated MSY for black marlin is 1,400 to 1,500 m

(Table 4). 

yield-effort curve (Figure 10) is quite flat. Effort levels of 40 to 60 

mill ion hooks have resulted in catches with considerable variation about 

the equilibrium yield curve. The catch data points for 1972 to 1976 are 

below the curve, whereas the points for 1968 to 1971 are all above the 

curve, suggesting the possibility of some systematic bias in the above 

estimates. 

Optimum effort is less than those of recent levels but the 

The data for swordfish suggest that longlining has ha

no significant impact on the swordfish population, so no production mode

analysis was attempted. 
-1 34- 

CaJ 

Lo 

roo 

ES a0 

OaJ 

a, cm 

ra .- . u- Ero 

H 

c, LaJ 

0 

Y 

0 

GO 

a= 

U 

<w ID 

0 

Y 

0 +Jo 

0 

nc 

a <w u) -I 0 

c- I- 

-700 

0000 

0000 

0000 

.... 

-7-7 

.... 

0000 

dNrnaJ 

hCONO 

hNOO moo0 .... ol--cmNmN 

OLDDu3V) 

0000 

.... 

m--hCO 

Nhhh 

N 

O*Oh 

-NO0 

0000 

.... 
-1 35- 

c 

058 

059 

072067 068 

690 5Y=c:\e 066 071 

70 4 

055 / 063 074 =\ 

061 

76d75 

BLUE MARLIN 

I I I I I I 

25 50 75 100 125 150 175 

EFFECTIVE EFFORT ( IO' HOOKS ) 

Figure 8.--Predicted relationship between equilibrium yield (lo3 MT) a

effective effort (lo6 hooks) for Indian Ocean blue marlin, based on 

production model analysis. (From Wetherall et al. see text footnote 1 
-1 36- 

I I I I I , 

STRIPED MARLIN e68 69 

e67 

66ee76 

7( 

e73 

e72 

d54 I I I I I I 

50 100 153 2M) 253 300 I 

U 

EFFECTIVE EFFORT ( IO’ HOOKS) 

Figure 9.--Predicted relationship between equilibrium yield (lo3 MT) and 

effective effort (lo6 hooks) for Indian Ocean striped marlin, based on 

production model analysis. (From Wetherall et al. see text footnote 1.
-1 37- 

2.5- 

2.0 

I5 1.5- n 

0 

a 

w 

- 

1 

> 

9 1.0- 

n 

m 

i 

3 

w 0 

.!i 

BLACK MARLIN 

-- 

e 69 

68 

73. 

e76 

e 75 e 74 

e72 

I I I I I 

EFFECTIVE EFFORT ( IO' HOOKS) 

IO 20 30 40 50 60 I1 

OO 

,- 

Figure 10.--Predicted relationship between equilibrium yield (lo3 MT) 

effective effort (106 hooks) for Indian Ocean black marlin, based on 

production model analysis. (From Wetherall et a1 . see text footnote 
-1 38- 

fish data, like tile swordfish data, indicate the 

stock has not been affected by fishing. The potential yield for sailfish 

is probably much higher than the maximum annual catch taken thus far. 

III.B.3. 

I I1 .B.4. 

The sai 

Resul ts of Yi el d-per-Recrui t Analysis 

None avail ab1 e. 

Resul ts of SDawner/Recrui tment Anal vsi s 

III.B.5. 

None available. 

Resul ts of Other Anal vses/Simul ations 

None avail ab1 e. 

1II.C. Current Evaluation of Stocks and the Fishery 

Because of deficiencies in estimates of total catch for Indian 

Ocean billfishes, the results of the production model analyses given above 

per-unit-effort for blue marl in and black marl in since the inception of the 

longline fishery suggests that no significant increases in total yield can 

be expected for these stocks. The potential for increased striped marlin 

yields appears to be somewhat greater; the stocks of swordfish and sailfish 

do not appear to have been appreciably affected by the effort expended to 

date. 

should be considered tentative. However, the substantial decline in catch- 

IV. STATUS OF CURRENT RESEARCH NEEDS AND EFFORTS 

1V.A. Major Research Problems 

Better assessments of the status of Indian Ocean billfishes are 

needed which will require considerable improvements in fishery statistics. 

Steps should be taken to correct deficiencies in species identification and 

to provide for the acquisition of catch data by species. 
-1 39- 

1V.B. Current Research Efforts 

Compared to the study of other species, research on billfishes 

the Indian Ocean has been considered of low priority and there are few 

published papers on the subject in the literature. Based on the result

longline fishing, a study of the distribution and biology of striped m

in the Indian Oce n was published in 1978 (Pillai and Ueyanagi 1978). 

background papers's2 on the assessment of Indian Ocean bill fishes were 

presented at the Work.shop on the Assessment of Selected Tuna and Billfi

Stocks in the Pacific and Indian Oceans held in Shimizu, Japan, in June 

1979 (FAO, in press). 

Current research efforts on Indian Ocean bill fishes include 

studies on their general biology at the Central Marine Fisheries Resea

Institute, India, and studies on their biology and population dynamics 

the Far Seas Fisheries Research Laboratory Shimizu, Japan. 

1V.C. Future Research Needs 

1) Because research on Indian Ocean billfishes has been conside

of low priority, these species have been the subject of comparatively 

1 i ttl e research. 

recruitment for Indian Ocean bill fishes are needed. 

Est.imates of growth rates , mortal i ty rates , and 

2) One of the first attempts at assessing the status of Indian 

Ocean billfishes was made at the Shimizu Workshop (FAO, in press). It 

pointed out that deficiencies in estimates of total catch for Indian Oc

bill fishes made the re1 iable assessment of potential yield and optimum 

fishing effort difficult. Re1 iable assessment of the status of Indian 

Ocean bill fishes requires considerable improvements in the fishery 

statistics. In particular, steps are needed to improve basic requireme

such as correctly identifying species and allowing for separate recordi

of the catch of each species in longline logbooks. 

I.V.C.l. - Suggested Approach and Methods 

First priority should be given to collecting statisti

of total catch. Data on fishing effort, size composition, and detailed 

local ity of capture are a1 so essential for stock and fishery assessment

Participants at the Shimizu Workshop strongly recommended that countrie

1 anding large quantities of tuna (but collecting inadequate fishery 

*Honma, M., and S. Ueyanagi. 1979. Stock assessment of billfishes i

the Indian Ocean. 

Tunas and Billfish Stocks in the Indian and Pacific Oceans. Shimizu, 

Japan, 13-22 June 1979. 

Prepared for the Workshop on the Assessment of Sele
-1 40- 

statistics) take action to 

billfishes. In addition to 

statistics cannot be effect 

until regional institutions 

1V.D. Status of SWFC Data 

mprove their data. The same holds true for t

national data collection efforts, the 

vely organized, disseminated, and evaluated 

are organized to accomplish these tasks. 

Base 

Pub1 ished bill fish fishery statistics from Japan and Taiwan are i

Attempts should b

the data base maintained at the Honolulu Laboratory, which a1 so contains 

data obtained through contacts with scientists in Japan and Taiwan. 

from Korean longline operations, however, are lacking. 

made to obtain these missing data and to improve the accuracy of data 

coll ected. 

Data 

LITERATURE CITED 

Food and Agriculture Organization of the United Nations. 

1977. Catches and landings, 1976. FA0 Yearbook Fish. Stat. 42, 

323 p. 

In press. Summary report of the Workshop on the Assessment of 

Selected Tuna and Billfish Stocks in the Pacific and Indian Oceans, 

Shimizu, Japan, 13-22 June 1979. FA0 Fish. Rep. 

Honma, M., and Z. Suzuki. 

1972. Stock assessment of yellowfin tuna exploited by longline 

fishery in the Indian Ocean, 1959-1969. 

Bull. Far Seas Fish. Res. Lab. (Shimizu) 7: 1-25. 

[In Jpn., Engl. Abstr.] 

Kikawa, S., T. Koto, C. Shingu, and Y. Nishikawa. 

Seas Fish. Res. Lab., S. Serv. 2, 28 p. 

1969. Status of tuna fisheries in the Indian Ocean as of 1968. Far 

Pillai, P. P., and S. Ueyanagi. 

1978. Di stribution and biology of the striped marl in, Tetrapturus 

audax (Philippi), taken by the longline fishery in the Indian 

Ocean. Bull. Far Seas Fish. Res. Lab. (Shimizu) 16: 9-32. 

Shomura, R. S. (editor). 

1980. Summary report of the Bill fish Stock Assessment Workshop, 

Pacific resources. NOAA Tech. Memo. NMFS-SWFC-5, 58 p. 

Ueyanagi, S. 

1974. A review of the world commercial fisheries for billfishes. 

- In R. S. Shomura and F. Williams (editors), Proceedings of the 

International Billfish Symposium, Kailua-Kona, Hawaii, 9-12 August 
-1 41 - 

.- 1972, Part 2. Review and Contributed Papers, p. 1-11. U.S. Dep. 

Commer., NOAA Tech. Rep., NMFS SSRF-675. 

[U .S.l National Marine Fisheries Service. 

1978-1979. Foreign fishery information re1 ease. Supplement to 

Marketing News Report. 
-1 43- 

STATUS REPORT: EASTERN TROPICAL PACIFIC YELLOWFIN TUNA 

by 

Samuel F. Herrick, Jr. 

Southwest Fi sheries Center 

Oceanic Fi sheries Resources Division 

La Jolla, California 

ABSTRACT 

The status of eastern Pacific yellowfin tuna has been evaluated us

general production models and age-structured model s. 

production model analyses indicate that the eastern Pacific ye1 lowfin 

fishery is currently operating at levels above maximum sustainable yiel

The age-structured analyses raise concerns over the increased dependenc

the fishery on age-1 fish. Recent increases in age-1 catches could lea

a decrease in yield-per-recruit and a diminished potential yield. 

fishing on a succession of poor recruit classes could reduce the adult 

population such that recruitment failure occurs. 

trends in the near future are complicated by a failure to reach agreem

on a mechanism for implementing an eastern Pacific yellowfin conservat

program in 1980. 

Resul ts of the 

Heav

Efforts to reverse th

c 
-1 44- 

I. DESCRIPTION OF THE FISHERY 

The eastern Pacific Ocean yellowfin tuna fishery is primarily 

conducted within an area known as the eastern tropical Pacific (ETP), whic

is bounded by 40" N latitude, 30" S latitude, 150" W longitude, and the 

west coasts of North, Central, and South America. For management purposes

the Inter-American Tropical Tuna Commission (IATTC) divides the ETP into 

two subregions: 1)the Commission Yellowfin Regulatory Area (CYRA), and 2) 

the remaining area outside the CYRA (Figure 1). Longline and surface gear

(baitboats, purse seiners, and bolicheras) are used to catch skipjack, 

bigeye, bluefin, and albacore tunas in the ETP, as well as yellowfin tuna. 

Jig boats or trollers also fish in the ETP for tuna but tend to 

concentrate their fishing effort in the northern fringe of the CYRA. Jig 

boat catches of yellowfin tuna are usually incidental to those of albacore

the target species, and therefore make only a minor contribution to the ET

yellowfin catch. 

I.A. History of the Fishery 

Catches of ye1 1 owfin tuna were reported by U.S. bai tboats fishing 

inshore areas off southern California as early as 1919. 

dominated the fishery until the 1 ate 1950's, when major technological 

advancements in gear precipitated a 1 arge scale conversion to purse 

seining. Between 1958 and 1960 the purse seine component of the eastern 

Pacific tuna fleet soared from 13% to 54X, and by the end of 1960 the purs

seine fleet was operating throughout its present north-south range, from 

California to Peru. As the fishery extended southward, many Latin America

nations, attracted by the performance of the U.S. purse seiners, started 

developing their own tuna fleets. Since then the fishery has grown fairl

steadily, and by 1979 vessels from 18 countries were participating in the 

fishery. In terms of numbers, the 1979 ETP combined surface fleet 

consisted of 81% purse seiners, 14% baitboats, 4% bolicheras (small purse 

seiners of less than 45 mt carrying capacity) and 1% jig boats. 

seiners accounted for 98% of the ETP carrying capacity, with baitboats, 

bo1 icheras, and jig boats contributing the remaining 2%. 

Baitboats 

The purse 

Fishing for yellowfin tuna in the ETP west of the CYRA and east o

150" W 1 ongi tbde devel oped foll owing World War I I, when Japanese 1 ongl iner

expanded their range of operations eastward from the western Pacific. 

Japanese longliners began fishing in the ETP in the late 1950's, and 

longliners from Taiwan and South Korea entered the fishery in 1962 and 

1965, respectively. Until the late 1960's, fishing in the "outside" area 

was conducted solely by longliners. Large purse seiners began to fish in 

the outside area in 1968-1969, two years after the yellowfin quota system 

was established for the CYRA. 
-1 45- 

150. 140' 120' I100 100' 80' 70' 

Figure 1. The eastern tropical Pacific Ocean showing the historical area 

of the fishery for yellowfin tuna, the more recently fished 

area within the Commission's Yellowfin Regulatory Area (CYRA), and the area outside the CYRA. 
-1 46- 

In recent years, the U.S., Japan, Korea, Taiwan, and Costa Rica 

have participated in the outside fishery, with the U.S. responsible for 

more than 95% of this area's yellowfin catch. The surface catches of 

yellowfin from the outside area have ranged from a low of 1,100 mt in 1968 

to a high of 46,000 mt in 1976. 

outside area has decreased dramatically (13,000 mt in 1979). 

Since 1976, the yellowfin catch from the 

In 1979, the U.S. was the leading participant in the overall ETP 

yellowfin fishery with 61% of the catch, followed by Mexico (13%), and 

Ecuador (5.5%) (Figure 2). 

ETP yellowfin catch included Bermuda, Canada, Colombia, Congo, Costa Rica, 

Japan, Korea, Netherlands, New Zealand, Nicaragua, Panama, Peru, Senegal, 

Spain , and Venezuel a. 

Other countries that contributed to the 1979 

I.B. Trends in Catch and Effort 

Catches of yellowfin tuna from the ETP have been reported as far 

back as 1919, when approximately 300 mt were landed in California. 

increased steadily thereafter (except for a decrease during World War 11) 

to approximately 102,000 mt in 1950. Catches declined in the 1950's to a 

low of 63,000 mt in 1954 but rebounded sharply, with the introduction of 

the modern purse seine technology, to 109,000 mt in 1961. 

1979 an annual quota was placed upon yellowfin caught within the CYRA and 

CYRA in 1966 to a preliminary catch of 177,000 mt in 1979 (Figure 3). 

Catche

From 1966 to 

the catch trend during that period reflected the quota: 83,000 mt from th

Because the ETP tuna fishery exploits both yellowfin and skipjack 

tunas over much of the areas fished, it is difficult to distinguish fishin

effort by species. However, estimates based upon yellowfin catch and 

yellowfin catch-per-standard-days-fishing in C1 ass-3 (92 to 182 mt carrying 

capacity) purse seine units show effort increasing from approximately 

18,000 standard days in 1967 to approximately 78,000 standard days in 1979

Estimates using yellowfin catch from the outside area and catch-per-dayfishing in Class-6 (greater than 365 mt carrying capacity) purse seine 

units indicate that effort increased from approximately 900 days in 1969 t

approximately 4,000 days in 1974, then declined to 1,800 days in 1979. 

I .c. Value of Catch 

Of the major ETP fishing nations, ex-vessel yellowfin prices are 

available only for the U.S. United States ex-vessel prices for yellowfin 

tuna in 1979 were $1,044/mt for yellowfin greater than seven (7) pounds, and $890/mt for yellowfin less than seven (7) pounds. Based upon an 

average U.S. ex-vessel price of $967/mt, the 1979 yellowfin catch of 

177,000 mt from within the CYRA generated approximately $171 million in 

'landings revenue. The yellowfin catch from outside the CYRA (13,000 mt) 

generated approximately $13 million. The ex-vessel revenue generated by 

the combined 1979 yellowfin catch inside and outside the CYRA was 

approximately $184 million. 
-1 47- 

OTHER 20% 

ECUADOR 6% 

MEXICO 13% 

,USA 61% 

Figure 2. rlajor participants in the eastern tropical Pacific 

Ocean yellowfin tuna fishery based upon percent of 

total catch in 1979. 

200, 

m 

0 

X 

I5 

I 

V 

lV 

c 

v 

a 

501 

O! / 

I 

/ 

I 1 I I I I I 

1961 63 65 67 69 71 73 75 77 

YEAR 

3 

Figure 3. Catches of yellowfin tuna from inside the CYRA and outside 

the CYRA in the eastern tropical Pacific Ocean. 
-1 48- 

I.D. Current Management of the Fishery 

In 1950 the Inter-American Tropical Tuna Commission (IATTC) was 

formed through a Convention between the Republic of Costa Rica and the 

United States. 

fish for tropical tunas in the ETP with the unanimous consent of the 

present members. Current members include the United States, Panama, 

Canada, Japan, France, and Nicaragua (Ecuador, Mexico, and Costa Rica have 

withdrawn from the Commission). 

The convention is open to other governments whose nationa

The principal duties of the Commission under the Convention are t

1) study the biology, ecology, and population dynamics of the tunas and 

related species of the eastern Pacific Ocean with a view toward determinin

the effect of fishing and natural factors on their abundance; and 2) 

recommend, when appropriate, conservation measures that will maintain the 

fish stocks at levels which will afford maximum sustainable catches. 

The first conservation measure proposed by the Commission was a 

quota limiting the annual catch of yellowfin tuna from the ETP for 1962. 

But the first CYRA yellowfin quota was not implemented until 1966. Since 

then yellowfin catch quotas have been imposed or recommended annually. 

(Since 1971 these quotas have been expressed as base numbers plus the 

possibility of one or two increments to be added at the discretion of the 

Director of Investigations. The increments are part of an over-fishing 

experiment designed to estimate empirically the re ationship between catch 

and effort.) 

The closure date for unrestricted ye1 1 owf 

CYRA is establ ished when 

n fishing inside the 

current catch + expected catch of yellowfin by vessels at sea 

engaged in unrestricted fishing and by vessels 

expected to depart on unrestricted trips within 

the specified grace period 

= the quota - that portion of the quota reserved for the 

incidental catch of yellowfin after the closure 

of the CYRA 

+ any special CYRA ye1 1 owfin a1 1 ocations granted 

during the year. (There are special allocations 

for "smal 1 " vessel s, newly-constructed vessel s of 

developing nations, and vessel s engaged in 

Commission-designated research programs.) 

Further safeguards call for the immediate curtailment of yellowfin 

fishing if, at any time, the yellowfin catch-per-standard-days-fishing 

within the CYRA falls below 2.7 mt. 
-1 49- 

In 1979 the CYRA quota was 159,000 mt with increments of 18,000 

and 14,000 mt. 

of 150,000 mt with provisions for incremental increases to 191,000 mt. 

For 1980 the Commission recommended a CYRA yellowfin qu

11. NATURE AND SIGNIFICANCE OF U.S. AND FOREIGN 

PARTICIPATION IN THE FISHERY 

Virtually all of the U.S. yellowfin catch from the ETP is landed an

consumed domestically. In 1979, domestic 1 andings of a1 1 tuna species 

totalled 213,000 mt; of these, 126,000 mt, or 55%, were yellowfin. Of a

1979 domestic ye1 lowfin 1 andings, approximately 120,000 mt were taken fr

the ETP. This represents 95% of all domestic yellowfin landings and 52% 

all domestic tuna landings for 1979. The domestic yellowfin catch from 

ETP contributed approximately 20% of the 595,000 mt of tuna (all species

used in the 1979 U.S. cannery supply of fresh and frozen tuna (domestic 

1 andings and foreign imports). 

During 1979 the U.S. tuna fleet operating in the ETP consisted of 1

purse seiners (81%), 28 baitboats (17%), and 3 jig boats (2%). 

U.S. fleet carrying capacity, purse seiners contributed approximately 

90,000 mt, baitboats 2,300 mt, and jig boats 27 mt. The domestic ETP 

yellowfin catch in 1979 generated approximately $116 mill ion in landings 

revenue, based upon 1979 U.S. ex-vessel prices. 

In terms 

Besides being the cornerstone of the U.S. tuna fleet operations, th

ETP yellowfin fishery contributes significantly to employment in U.S. 

canneries located in California and Puerto Rica. Tuna canneries in 

Cal ifornia employed an average of 6,215 people during 1978, while canne

in Puerto Rico employed an average of 6,834 people. While these canner

process other species on occasion (e.g. bonito, black skipjack, anchovie

and mackerel), tuna is the mainstay of cannery operations and without tu

these canneries would probably cease to exist. 

last decade. 

catch increased from 18% to 37%, reaching 43% in 1978. While U.S. flee

carrying capacity in the eastern Pacific has declined by about 8% since 

1976, foreign capacity has grown by over 30%. From 1976 through August 

1980 the number of foreign purse seiners fishing in the eastern Pacific 

rose from 94 to 125 (Table 11, representing a 33% decrease in the numbe

U.S. purse seiners. However, since 1978 the combined carrying capacity 

the U.S. and foreign purse seine fleets-has remained almost constant. 

Foreign tuna fishing activity in the ETP has shown an upsurge over 

From 1970 to 1979 the foreign portion of the CYRA yellowf

Most of the growth‘in foreign purse seine numbers since 1977 can be 

attributed to vessel flag transfers. Transfers of U.S. purse seiners to 

foreign flags fishing in the eastern Pacific from 1977 through Septembe

1980 numbered 14, with a total carrying capacity of 12,419 mt (Table 2). 

In addition, seven new vessels destined for foreign fleets operating in 

eastern Pacific were completed during this period, or are currently und

construction in U.S. shipyards. All of these new vessels have a 1,092 m

carryi ng capaci ty . 
-1 50- 

E 

tT, 

.r 

Q, 

L 

0 

cc 

-0 

E 

lu 

m 

L 

0 

cc 

n 

v) 

E 

0 

c, 

.C 

M 

cn 

.=r 

W 

rl 

. 

N 

m 

d 

In 

In 

. 

-3 

0 

rl 

N 

In 

LD 

m 

0 

d 

. 

N 

r( 

r 

P 

rr\ 

r-i 
-1 51 - 

Table 2. U.S. tuna purse seine flag transfers, 1977 to 1980. 

~~~~ ~ - 

Carrying 

Ccvntr*{ tc :ilhich Capacj ty 

Transferrer! (r”ctr ic Tors) Year Built 

1377-1978 

AI et hF r la nd s 

;:e t he r la nd s 

Panana 

Panama 

Costa Rica 

Costa Rica 

Costa Rica 

Net her 1 a nds 

tketherlands 

tl n t i 1 1 e s 1,000 

Antilles 1,oclo 

71 o 

71 o 

71 11 

Antilles 1,090 

Antilles 1,0:3r) 

1,000 

a4 5 

1972 

1973 

1963 

1052 

1969 

1967 

1970 

1973 

1972 

1979 

Cayman Islands (British) 4 90 1365 

1930 (through September) 

Venezuela 

CayFan Islands 

Yexico 

’illcxico 

Total Canacity 

1,273 

1,099 

591 

1,000 

12,413 

1972 

1974 

1967 

1971 
-1 52- 

A major factor influencing the role of U.S. tuna fishing in the ETP is 

that a CYRA yellowfin conservation program was not adopted for 1980. 

situation stemmed primarily from the inability of Mexico, Costa Rica, and 

the United States to reach agreement on new management and access 

arrangements for tuna resources in the eastern Pacific. Until an eastern 

Pacific tuna management regime acceptable to Mexico and Costa Rica can be 

enacted by the member countries of the IATTC, the U.S. may be forced to 

concentrate its fishing effort in the areas outside the ZOO-mile zones of 

the countries bordering on the ETP. If such becomes the case, the U.S. 

would lose access to areas from which 65% of its historical catches of ETP 

yellowfin and skipjack tuna have been taken. 

the yellowfin tuna caught in the outside areas of the ETP (areas A2 and A3, 

Figure 1) associate with porpoise, porpoise quotas are likely to be reached 

earlier in the year, which would severely limit the ability of the U.S. 

fleet to catch yellowfin in the ETP. 

This 

Furthermore, since most of 

With exclusive access to highly productive fishing areas in the ETP, 

the fleets of the coastal nations adjacent to the resource can be expected 

to continue growing. Much of this growth may be through flag transfers of 

U.S. vessels otherwise denied access to these areas. 

111. STATUS OF THE STOCKS 

Research on the population dynamics of ETP yellowfin tuna is conducted 

by the scientific staff of the IATTC. 

staff undertook investigations in the following areas: 1) population 

structure and migration; 2) abundance estimates and their re1 ation to 

fishing success; 3) size composition and distribution of tunas by time and 

area; 4) feeding habits; 5) growth studies; 6) tuna/porpoise relationships; 

and 7 ) oceanography and tuna ecology. 

During 1979 the IATTC scientific 

e 

I I1 .A. Stock Structure 

During 1979 the IATTC scientific staff continued its studies on the 

rates of mixing of individual tuna from different geographic areas of the 

Pacific. Results of these studies to date are inconclusive. However, 

tagging experiments indicate that the rate of mixing for yellowfin between 

the area inside the CYRA and outside the CYRA is low. Therefore, the 

production model analyses which have been done assume yellowfin tuna in 

these two areas to be two separate stocks. 
-1 53- 

.- 

I I1 .B. Stock Assessment and Fishery Eva1 uation 

c. 

I I I. B. 1. Trends i n Catch- per- Un i t-E f fort 

The catch-per-standard-days-fi shing (CPSDF) is used 

the Commission as an index of relative apparent abundance of yellowfin 

well as an index of relative fishing success. Annual CPSDF in Class-3 

purse seine units and catch-per-day-fishing (CPDF) in C1 ass-6 purse se

units for unregulated yellowfin fishing in the CYRA during the period 

to 1979 is shown in Figure 4. 

1970 and started to decline (with the exception of 1972) at a fairly s

rate thereafter. The preliminary data for 1980 show a continuation of 

downward trend. 

It can be seen that CPSDF was highest i

III.B.2. Results of Production Model Analysis 

Two production model analyses were employed in 1979 to 

determine the status of the yellowfin stock inside the CYRA. 

used the 1 ogistic model but incorporated different time periods and 

employed different purse seine classes to standardize effort. 

cases, average maximum sustainable yield (AMSY) was estimated to be ab

159,000 mt (Figures 5A and B). In each case, the 1976 to 1979 points 

to the right of the peak of the curve, indicating that the effort has 

apparently exceeded the level necessary to achieve AMSY. 

at the 1976 to 1979 level over the next few years, one of two situation

would be likely to occur. First, the catch could decrease, which would 

indicate that the stock of yellowfin probably changes in response to 

fishing as predicted by the production model. 

remain approximately constant or even increase. If the latter occurs, 

could indicate that the model may not be appropriate. 

determined only by continuation of the Commission's experimental 

overfishing program. 

Both met

In both 

If effort is 

Second, the catch could 

This can be 

Tagging experiments have indicated that the rate of 

mixing of yellowfin between the CYRA and outside area is low, so that 

date, yellowfin of the outside area have been considered separately fro

those of the CYRA. 

indicate that catch has remained proportional to effort. No productio

models, however, have been f i t t e d t o these data. If the logistic mode

applicable, the data would appear to indicate that the fishery is oper

on the left-hand or underfishing side of the equilibrium production cu

This suggests that there is no biological reason for imposing limits o

yellowfin catch or the intensity of fishing outside the CYRA. 

Catch-and-effort data from outside the CYRA (Figur

III.B.3. Results of Yield-per-Recruit Analysis 

Estimated relationships among size at entry, fishing 

effort, and yield-per-recruit are shown in Figures 7A, B and C. Resu

the yield-per-recruit analysis suggest that with the given fishing pat

(mu1 tip1 ier = 1.01, increasing size-at-entry would increase yield-per- 
-1 54- 

cn 

Z 

0 

c 

v) 

z 

e 

6 

4 

2 

20 

IO 

1.0 

I I I I I 

CPSDF - CLASS 3 

I I I I I I I I I I 

70 72 74 76 78 

YEAR 

Figure 4. Annual catch-per-standard-days-fishing in Class-3 and 

catch-per-days-fishing in Class-6 purse seine units 

for unregulated fishing in the CYRA, 1970 to 1979. 
-1 55- 

I I I 1 I I I 

76 0 77 - e 79 

74 

73 75 70 0 

A 

A 

- 

- 

I 

IO x) 30 40 50 60 70 

200 

1 I I I I I 1 

760 77 

74 0 

0 

70 0 79 0 75 73 

200 - B 

a 

I50 - 

100 - 

1 I I 

0 5 10 15 20 25 30 35 

I50 

IO0 

cn 

50 

0 

k 

LL 

0 

mo 

n 

z 

U 

m 

14 

A 

_. 

3 

0 

I 

b 

I: 

0 

I0 

a 

# 

EFFORT IN THOUSANDS OF DAYS STANDARDIZED TO CLASS 6 

Figure 5. a) Equilibrium catch curve for the yellowfin tuna fishery 

inside the CYRA, 1967 to 1979. Effort in days fishing 

is standardized to Class 3 purse seiners. 

b) Equilibrium catch curve for the yellowfin tuna fishery 

inside the CYRA, 1968 to 1979. Effort in days fishing 

is standardized to Class-6 purse seiners. 
-1 56- 

50 

v) 

z 

0 

ILL 40 

0 

v) 

0 

z 

a 2 30 

0 

I 

I- 

- z 

X 20 

0 

la 

0 

IO 

0 

0 

I 1 1 I 

e 71 

e 69 77 

a. 0 79 

78 

76 

e 75 

e 

73 

0 

72 

.74 

e 70 

I 2 3 4 

THOUSANDS OF DAYS OF EFFORT, CLASS-6 VESSELS 

Figure 6. Relationship between catch and effort for yellowfin tuna 

in the area outside the CYRA, 1969 to 1979. 
-1 57- 

1 I I 

62 

40 

24 

13 

7 

3 

v) 

z 

3 

0 62 

a 

n 

z 

40 

24 

> 

CL 

c 

W 

z 13 

7 kU 

3 

W 

N 

I I I I I I 1 I ~7 

I I 1 1 I 1 I I I 

n 1 

62 

40 

24 

13 

7 

3 

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 

MULTl PLI E R 

Figure 7. Yield-per-recruit isopleths for yellowfin tuna inside the CYRA; a) based on 

the age structure of the catch during 

the period 1968 to 1972 and natural mortality rate M=0.8, b) based on the age 

structure during the period 1973 to 

1978 and M=0.8, c) based on the age 

structure during the period 1968 to 

1972 and M=0.6. 
-1 58- 

recruit. Given a 3-1 b size-at-entry, increasing effort would not 

substantially increase yield-per-recrui t in each of the cases presented. 

I I I .B.4. Resul ts of Spawner/Recrui tment Analysis 

Large catches of 1 year-old yellowfin were taken from the 

CYRA in 1978 and 1979. 

relatively greater catches of young fish were due to increased 

recruitment, increased vulnerability of small fish resulting from average 

recruitment, a shift of effort to areas where small fish are more abundant, 

a shift in the population structure away from large fish, or some 

combination of these. If the first case is true, large catches could be 

expected in subsequent years when the fish from the large recruitment 

become available as medium- and large-sized fish. However, in the second 

and third cases, the opposite would be true due to a scarcity of mediumand large-sized fish after the small ones had been heavily exploited. In 

1979 the fish recruited in 1978 appear to have contributed heavily to the 

fishery as 2 year-olds, suggesting above-average recruitment in 1978. In 

general, the data suggest that there has been an increased dependency of 

the fishery upon 1 year-old fish in recent years. 

This raises questions as to whether these 

III.B.5. Results of Other Analyses/Simul ations 

Cohort analysis was used to estimate the numbers and 

weights of fish of various cohorts at the time of recruitment and at 

various intervals thereafter. 

During 1968 to 1971 the total CYRA yellowfin biomass 

averaged about 319,000 mt and was comprised of a large proportion of older 

fish; this resulted from above-average 1966 and 1967 recruitments which 

were 1 ightly exploited as juveniles (Figure 8). Bel ow-average recruitment, 

together with increasing rates of exploitation during 1969 to 1972, led to 

a decline in the biomass of both young and old fish during 1972 and 1973. 

The lower biomass of older fish persisted through 1974, while the abundance 

of smaller fish began to increase due to an extremely large 1974 yearclass. The 1974 year-class accounted for most of the increase in biomass 

of large fish late in 1975, during 1976, and into early 1977. The largest 

catch of yellowfin in the history of the eastern Pacific fishery was made 

during 1976. However, poor recruitment in 1976 and 1977, coupled with 

heavy exploitation of young fish since 1973, has resulted in the biomass of 

both young and old fish decreasing to the lowest level yet observed in the 

fishery. Although recruitment in 1978 was high (exceeded only by that of 

19741, the 1978 year-class is not expected to contribute significantly to 

the fishery in 1980 and 1981 because so many individuals were captured as 1 

and 2 year-olds. Preliminary estimates of the 1979 recruitment appear to 

be sl ightly 1 ower than average. 
s 

-1 59- 

1966 

40 

20 

UJ 

z 

0 

c 

LL 

0 

v) 

3 

0 

I 

c 

cz 

z 

0 

c 

1971 

1972 

120 - 100 - 

60 - 

40 - - 20 - 

- 

- 

1968 80.- - 

- 

- 

1 

140 

120 - 

80 - - 

60 

40 

20 

100 - 

- - - 

- 

1969 loo 

- - 

- 

- 

- 

- 

I 

- 

I- 80- 1970 a 60- 1 - 

- 

40 - - 

100 

80 - 

60 - 

40 - 

20- - 

- - 

- 

- 

- 

IIIIIII 

80 n 

1973 ifii-5J ::w 20 

I974 

1975 

I976 

1977 

1978 

LL 

0 

Iroot -I 

20 

g 100 

80 - 60 

40 

20 

‘979 ?Ld 20 

012345+ 01 2345t 

AGE IN YEARS 

Figure 8. Annual biomass estimates of yellowfin in the 

CYRA by age groups, 1965 to 1979. 
-1 60- 

1II.C. Current Evaluation of Stocks and the Fishery 

Based upon the production model analyses, it does not appear that 

increasing the effort on yellowfin within the CYRA will result in an 

increased yield. Depending upon the shape of the right hand side of the 

production curve, the catch can remain constant as effort increases or it 

can decl ine. 

If CPSDF indices accurately reflect trends in yellowfin abundance

the population is currently at its lowest known level. 

that caution should be exercised in increasing the catch beyond the curren

best estimate of AMSY (159,000 mt). 

It appears then 

In 1978 concern was expressed over the changing size composition 

of the CYRA yellowfin catch. 

yellowfin is variable and that this variability, coupled with a shift of 

fishing mortality to the younger age groups, could lead to reduced catches 

of yellowfin in years of below-average recruitment. 

It was noted that the recruitment of 

If the number of larger fish in the ETP yellowfin population is t

be increased, the fishery should be less dependent upon 1 year-old fish. 

As pointed out in the 1978 IATTC Annual Report, however, while protecting 

the young yellowfin would eventually bring substantial benefits to the 

fishery, this reduction in catch would be difficult to accomplish. 

IV. STATUS OF CURRENT RESEARCH NEEDS AND EFFORTS 

1V.A. Major Research Problems 

The immediate biological problem facing the ETP yellowfin fishery 

concerns its growing dependence on 1 year-old f.ish. 

year-old catches and concurrent decreases in yield-per-recruit results in 

diminished potential yield and dependence of fishing success on recruit 

class strength. In addition, heavy fishing on a succession of poor recru

classes could reduce the adult population to a level such that recruitment 

failure may occur. Analyses of management measures designed to reverse 

this trend, such as time/area/gear closures, could be undertaken to assess 

not only the biological impact on the resource itself, but also the socioeconomic impacts on the resource constituency. 

The increase in 1 

The failure to implement a yellowfin conservation program in the 

ETP for 1980 strongly suggests that the biological condition of the fisher

cannot be managed unless there is some acceptable mechanism for resolving 

confl icts related to the distribution of resource-related benefits among 

active and potential participants in the fishery. Evaluation of potential 

resource strengths, fishery interests, and national p r i o r i t i e s of those 

affected by such actions. 

management actions should therefore be made with regard to the diversity i
-161- 

1V.B. Current Research Efforts 

There are currently no U.S. research efforts directed specific

toward the conservation and/or exploitation of ye1 lowfin tuna resources 

the ETP per se. 

tuna/porpoi se-re1 ated issues. 

What research there is concerns itself mainly with 

The IATTC is the organization primarily responsible for condu

research on the yellowfin tuna industry. Its studies on the ETP yellow

fishery and resource required a scientific and support staff of 50 in 1

The U.S. contributed $1,607,200 of the IATTC's $2,746,339 operating bud

1V.C. Future Research Needs 

1) Effort standardization needs to be investigated in the 

multispecies U.S. tuna fishery. 

2) An ETP tuna fishery economic data base needs to be 

established. 

IV.C.l. Suggested Approach and Methods 

1) The Southwest Fi sheries Center (SWFC) currently 

conducts no research on ETP yellowfin tuna, but it might be able to ut

data contained in its tuna/porpoise data base to confirm results of ce

IATTC analyses. These data could also be used to investigate effort 

standardization in the U.S. tuna fishery. 

2) 

established on an individual fleet basis in order to analyze the econom

impacts of proposed management pol icies. To supplement the economic da

it will be necessary to acquire some extensive information on vessel/fl

operations in the ETP (i.e., days at sea, days fished, species catch 

compositions, areas exploited, and fishing techniques) from the 

vessel s/fleets for which economic data are obtained. Other considerat

which will help complete the economic picture include disposition of 

catches, costs of processing, inventory-holding and distribution of fin

products, economic feasibil i ty of plant re1 ocations, consumer demand 

characteristics, and international trade in ETP tuna and tuna products

An ETP tuna fishery economic data base could be 
-1 62- 

1V.D. Status of SWFC Data Base 

The SWFC does not collect data on the ETP yellowfin fishery exce

those pertaining to the U.S. tuna/porpoise observer program. Eastern 

tropical Pacific yellowfin tuna effort and biological data are collected 

and archived by the IATTC. 
-1 63- 

STATUS REPORT: EASTERN TROPICAL PACIFIC SKIPJACK TUNA 

Ronald G. Rinaldo 

Southwest Fi sheries Center 

Oceanic Fisheries Resources Division 

La Joll a, Cal ifornia 

ABSTRACT 

The stock structure of skipjack tuna in the Pacific Ocean is po

understood. In the eastern Pacific fishery for skipjack tuna, there 

appears to be no significant relationship between effort and apparen

abundance. Yield-per-recrui t analysis on a partial stock indicates 

maximum yiel d-per-recrui t could be obtained at a greater fishing eff

than is currently applied. 

skipjack tuna in the eastern Pacific does not appear to affect stock 

abundance, and there is no need to restrict the catch. 

According to the IATTC, the fishery for 
-1 64- 

I. DESCRIPTION OF THE FISHERY 

More skipjack tuna are harvested on a world basis than any other tuna 

species; most of these are taken from the Pacific Ocean. The estimated 

annual average catch in the western Pacific Ocean from 1965 to 1972 was 

220,000 metric tons (rnt); 80,000 mt was the average for the eastern 

Pacific. Estimates from 1973 to 1978 indicate that catches for the wester

Pacific (420,000 mt) and the eastern Pacific (108,000 mt) had increased 

great1 y . 

The skipjack tuna fishery in the eastern Pacific is an outgrowth of 

the California a1 bacore fishery. 

yellowfin and skipjack tuna comprise the major species harvested. 

It is a mu1 tispecies fishery where 

I.A. History of the Fishery 

The industry originated in California near the turn of the century

the initial target was albacore, which was first successfully canned in 

1903. 

California albacore fishery could not satisfy the demands of the tuna 

and skipjack tunas were found in the warmer waters of the eastern Pacific; 

by 1930 the fishery had expanded south to the Central American coast and 

outlying islands. 

latitude and from the North and South American coast to 150" W. longitude. 

Substantial fisheries occur in the northeastern Pacific Ocean near Baja 

California, the Revillagigedo Islands, and C1 ipperton Island, and in the 

southeastern Pacific Ocean near Central America, northern South America, 

Cocos Is1 and-Bri to Bank , and the Gal apagos Is1 ands. 

The fishery for yellowfin and skipjack tunas developed when the 

canners. The high-seas tuna fishery expanded rapidly as abundant yellowfi

In 1979 the fishery extended from about 33" N to 19" S 

In the eastern Pacific Ocean, about 80% to 95% of the catch is 

taken by purse seiners. 

most of the remaining 5% to 20%. 

by longliners, as incidental catch. 

A few baitboats remain in the fishery, catching 

Only small amounts of skipjack are caugh

In 1979 vessels from Bermuda, Canada, Colombia, Congo, Cost Rica, 

Ecuador, Japan, Korea, Mexico, Netherlands, New Zealand, Nicaragua, Panama

Peru, Senegal , Spain, United States, and Venezuela engaged in the eastern 

Pacific tuna fishery (Table 1). Ten of the 18 countries made significant 

catches of skipjack tuna in the Inter-American Tropical Tuna Commission 

(IATTC) Ye1 lowfin Regill atory Area (CYRA). The vessel s of three countries 

caught over 70% of the skipjack: United States, 53.8%; Ecuador, 13.2%; and 

Netherlands, 6.9% (Figure 1). 
-1 65- 

Tab le 1. Catches of skipjack by flag of vessel in the Inter-American Tropical Tuna 

Commission's Yellowfin Regulatory Area (CYRA) by vessels of all flags west 

of the CYRA and east of 150' W, and total catches for the eastern Pacific 

east of 150" W (in thousands of metric tons). The 1979 data are preliminary. 

CYRA West of CYRA Total 

w_ year . U.S.A. Ecuador Panama bkxico Peru Others& -Total' east .of 150"11 eastern P

1961 51.3 

1962 55.7 

1903 73.8 

1964 41.8 

1365 58.7 

196G 44.1 

1967 93.6 

1969 34.2 

1970 33.4 

1971 76.4 

1972 21.0 

1313 26.0 

1374 (16.0 

1975 64.3 

1376 86.7 

7977 48.6 

?9?3 97.7 

1979 69.8 

*"4 1968 50.8 

11 .6 

10.2 

12.6 

9.3 

14.9 

10.5 

17.3 

12.9 

15.6 

8.8 

11.9 

4.5 

4.4 

7.8 

17.0 

6.2 

10.0 

11 -8 

17.4 

0.0 1.0 

1 .o 1 -0 

2.8 1.3 

0.4 1.4 

0.0 1.6 

0.2 1.4 

0.4 3.9 

1 eo 2.5 

3.4 1.6 

2.1 3.4 

4.3 4.1 

0.8 2.4 

2.3 2.3 

3.9 4.5 

72.8 6.6 

4-5 7.1 

5.1 3.8 

5-6 4.9 

8.2 4.7 

4.4 0.1 

2.7 0.3 

1.5 0.2 

0.9 1.2 

0.2 4.8 

0.0 3.7 

0.0 3.4 

0.6 1.8 

0.2 7.0 

0.2 3.3 

1.9 5.7 

1.2 12.8 

3.2 18.9 

2.8 19.5 

2.6 14.0 

3.1 42.0 

1.0 30.3 

4b4 0.5 

0.1 2.3 

68.4 

70.9 

95.4 

54.6 

76.7 

58.6 

120.2 

70.9 

58.2 

50-7 

103.9 

32.2 

42.6 

76.2 

122.8 

126.8 

84.1 

167.5 

129.0 

ob0 

0.0 

0.0 

0.0 

0.0 

0.0 

0.0 

0.0 

0.9 

5.9 

0.9 

1 .l 

1.3 

2.5 

1.9 

1.0 

2.6 

2.8 

2.8 

68-4 

70.9 

95.4 

54.6 

76.7 

58.6 

120.2 

70.9 

39.1 

56.0 

704.8 

33.3 

43.9 

78.7 

724.7 

127.8 

86.7 

370.3 

137.8 

a - The catches of vessels that belonged to only one fishing company in orte or more 

years hzve been grouped to preserve the confidentiality of the records. 

include t,he catches of vessels of Bermuda, Canada, Chile, Colombia, Congo, Costa 

Rica, .France, Korea, Netherlands, New Zealand, Nicaragua, Senegal 

Venezue'l a. 

These 

Spain, and 
-1 66- 

NETHERLANDS 6.9 To 

/ CANADA 1.0% 

BERMUDA 3.0 O/o 

- +PERU 0.8% 

COSTA RlCA 3.9% 

MEXICO 3.8 Oh 

.ECUADOR 13.6 v0 

Figure 1. 1979 skipjack tuna catch (129,400 mt), by country, in 

the CYRA. 
-1 67- 

I.B. Trends in Catch and Effort 

#-=- 

Annual catches of skipjack by the eastern Pacific tuna fleet 

fluctuate greatly, and there are no obvious trends. During the 1961 to 

1979 period, the catches ranged from 33,300 mt in 1972 to 170,300 mt in 

1978 (Table 1). 

129,200 mt: an increase of 76% over the mean catch for the previous 12 

years. 

The mean annual catch during the 1976 to 1979 period w

The size composition of skipjack tuna samples taken in the IATT

yellowfin regulatory area during 1967 through 1980 is shown in Figure 2. 

Differences among years are apparent; the incidence of fish larger than 

cm was highest in 1971-73 and lowest in 1978-79. 

In the eastern Pacific most of the skipjack is caught within 60

nautical miles of land, off the coasts of Central America and northern 

South America (Figure 3). 

caught in waters off Baja California and Ecuador, and in the Gulf of 

Guayaquil; in the 1970's the largest catches were usually made offshore 

between 5" and 15" N latitude and in the Panama Bight. 

years, however, the center of abundance in the southern area seems to h

shifted to waters off Colombia and Central America. 

an average of 73% of the skipjack caught east of 150" W longitude were 

taken within 200 nautical miles of land. Most of the catch comes from t

area south of 15" N latitude (Figure 4). 

During the 1960's much of the skipjack was 

During the past 

During 1975 to 1979

In general there is a little seasonal variation in the skipjac

fisheries in the equatorial areas. 

equator, the more the catches peak in the summer months. In the Panama 

Bight skipjack catches are low from August to March and peak from April 

July. 

from May to July and a minor one in October and November. 

The greater the distance from the 

Near Ecuador they are low from January to April , with a major pe

The numbers of vessels fishing for tropical tunas in the easte

Pacific since 1961 and their total carrrying capacity are given in Table 

The number of larger purse seiners (> 401 short tons of carrying capaci

increased gradually from 9 in 1961 to 24 in 1967; it then increased 

rapidly, reaching 158 in 1976, and remained near this level through 197

The number of baitboats remained fairly constant, between 91 and 116, fr

1961 to 1976, but decreased rapidly to 45 by 1979. The total carrying 

capacity of all gears in the fleet increased from 36,600 mt in 1961 to 

169,000 mt in 1979. 

baitboats, 0.2% bolicheras (small purse seiners with < 50 short tons o

carrying capacity) , and less than 0.1% jigboats in terms of capacity; i

terms of numbers, 80.7% were purse seiners, 14.0% baitboats, 4.4% 

bo1 icheras, and 0.9% jigboats. 

The 1979 fleet consisted of 97.7% purse seiners, 2

In the eastern Pacific the logged effort by purse seiners rema

fairly constant between 1961 and 1969, ranging from 14,800 to 19,700 da

of fishing, standardized to Class-3 vessels (101-200 short tons of carry
-1 68- 

4- 

8- 

4- 

12 

,2 1 1967 ' 

8 

AVERAGE WEIGHT = 6.68 

- - 

- - 

- - 1968 A.W. = 8.13 - 

- - 

- - 

- - 1969 A.W. = 6.19 - 

A.W. = 6.17 

LENGTH IN CENTIMETERS 

I I 2 3 4 5 67890 12 15 20 

WEIGHT IN POUNDS 

Figure 2. Length frequencies of skipjack 

caught in the CYRA, 1967 to 

1979. 
-1 69- 

Figure 3. Catches of skipjack in the eastern Pacific Ocean in 1979 

by 1" areas for all trips for which usable logbook data 

were obtained. 
-1 70- 

Figure 4. Estimated CYRA catches of skipjack north and south of 15" N, 

1961 -1 978. 
-1 71 - 

Li 
-1 72- 

capacity). The logged effort began increasing in 1970, reaching 41,400 

days in 1976 and 41,200 days in 1978, then declined to 39,200 days in 1979. 

The actual effort is considerably greater than the logged effort. 

the past 10 years the actual skipjack effort has been estimated to average 

90% greater than the logged effort. No trend is apparent in the logged 

effort. 

During 

I.C. Value of Catch 

Ex-vessel values for major fishing countries other than the U.S. in 

the ETP are unavailable. U.S. ex-vessel prices paid for skipjack tuna in 

1979 were approximately $l,OOO/short ton for skipjack tuna weighing less 

than 4 pounds and $1,10O/short ton for skipjack tuna greater than 4 pounds. 

Based on the 1979 catch of skipjack tuna in the CYRA of 142,600 short 

tons, the value of the 1979 skipjack tuna catch in the CYRA was 

approximately $149,730,000. 

outside the CYRA and the average 1979 U.S. ex-vessel price, the value of 

the skipjack tuna catch from outside the CYRA (3,000 short tons) was 

approximately $3,150,000. The total 1979 eastern Pacific catch of skipjack 

tuna was worth approximately $152,880,000. 

Based on the 1979 catch of skipjack tuna from 

I.D. Current Management of the Fishery 

There are currently no regulations for skipjack in the Pacific 

Ocean. The State of California had required a minimum weight of 4 pounds 

(1.8 kg) since 1939, but this was repealed in 1975. 

11. NATURE AND SIGNIFICANCE OF U.S. AND FOREIGN 

PARTICIPATION IN THE FISHERY 

The fishery for tropical tunas in the eastern tropical Pacific was 

Areas of particular interest 

started by American fishermen, and the skipjack and yellowfin tuna 

resources continue to be a U.S. concern. 

include: 

and consumption in the United States. 

the catch of the domestic fleet, imported catch, and processing 

United States tuna cannery receipts for tunas during 1978 were 581,418 

In 

Imports 

short tons, whole weight. Approximately 35% of the raw cannery product 

(catch plus imports) was skipjack tuna which originated in the Pacific. 

addition, the Pacific skipjack tuna catch comprised 42% of the total 1978 

U.S. tuna catch available on the imports from the eastern Pacific. 

for 1978 were dominated by skipjack tuna (56%) and yellowfin tuna (22%). 

In 1979, American flag vessels caught 76,707 mt or 53.8% of the total 

catch of skipjack tuna in the eastern Pacific. The carrying capacity of 
-1 73- 

.- 

American flag vessels fishing in the eastern Pacific in 1979 totaled 

110,919 mt (61% of total carrying capacity of all flag vessels), made up 

approximately 98% seiners, 2% baitboats, and < 1% jigboats by capacity. 

number, the fleet was composed of 138 purse seiners, 28 baitboats and 3 

j igboats. 

The U.S. fleet usually fishes the CYRA for yellowfin and skipjack 

tunas from January to the closure of the CYRA. When the CYRA closes to 

yellowfin fishing, the majority of the larger purse seiners move either t

areas outside the CYRA or to the Atantic Ocean. Smaller purse seiners, 

baitboats, and jigboats continue to fish the CYRA for skipjack tuna and 

species of tuna (bluefin or albacore) other than yellowfin. 

The U.S. commitment to the conservation of skipjack and yellowfin tu

stocks in the eastern Pacific is indicated by its membership in the IATTC

The monetary commitment of the U.S to the IATTC was $1,607,000 in 1979, o

approximately 93% of the 1979 IATTC contributions ($1.7 million) from 

member countries. 

111. 

1II.A. Stock Structure 

STATUS OF STOCKS 

Skipjack tuna are distributed across the Pacific in tropical and 

sub-tropical latitudes, usually in waters exceeding 20" C at the surface. 

They occur commonly from about 40" N to 40" S latitude in the western 

Pacific, and from about 30" N to 30" S in the eastern Pacific. Their 

distribution is probably influenced by the temperature of the prevailing 

currents, which are warm and poleward-flowing in the west, and cold and 

equator-ward in the east. 

The population structure of skipjack in the Pacific Ocean is not 

well understood. One hypothesis proposes that all skipjack in the Pacifi

belong to one population that is spawned in the equatorial regions west o

140" W longitude, that the young fish migrate poleward into the fishing 

areas, and that the older fish return to the equatorial regions to spawn. 

Another more recent hypothesis suggests that there may be at least two 

subpopulations of skipjack in the Pacific Ocean: 

subpopulation, and the central and eastern Pacific suhpopul ation. Recent 

tagging studies conducted by the South Pacific Commission have shown 

extensive migrations of skipjack in the south and equatorial Pacific Ocea

When the analyses of these data are complete, the population structure of 

this species will probably be more clearly understood. 

the western Pacific 

There appear to be two main groups of skipjack in the eastern 

Pacific: a northern group off the west coast of Baja California, in the 

Gulf of California, and around the Revillagigedo Islands; and a southern 

group from off Central America to off northern Chile. 

skipjack are excluded from the southern coast of Mexico by a cell of warm 

In most years 
-1 74- 

water in that area. 

northern and southern areas, but considerable mixing of fish within the 

areas. Studies of the distribution of fish larvae, however, have shown 

that there is virtually no spawning of skipjack in the eastern Pacific 

(east of 130" W longitude). Skipjack apparently arrive in the eastern 

Pacific when they are about 1 to 1-1/2 years old and return to the central 

and central-western Pacific when they are about 2 to 2-1/2 years old. 

Evidence for the latter is provided by the fact that 25 skipjack tagged in 

the eastern Pacific have been recaptured near the Hawaiian and Line Islands 

and one other has been recaptured between the Marshall and Mariana Islands. 

There is little interchange of fish between the 

I I1 .B. Stock Assessment and Fishery Eva1 uation 

I I I. B . 1 . Trends i n Catch- Der- Un i t-E f fort 

The first measure of apparent abundance for the skipjack 

fishery of the eastern Pacific was developed in 1956. The catches-per-day 

of fishing by baitboats of different carrying capacities were compared to 

obtain standardization factors among vessel size classes, and these were 

used to standardize the effort to that of a single size class. 

method, modified for purse seiners, is still in use today: it is the logged 

catch divided by the logged effort standardized to Class-3 seiners (vessels 

of 101-200 short tons of carrying capacity). 

This 

index of abundance for the 1960 to 1979 period reveals no apparent trend 

( Figure 5 ) . 

This 

It is biased in that it 

includes effort on a combined resource which also includes yellowfin. 

A method of eliminating some of the effort on yellowfin 

to obtain an index of abundance for skipjack in the eastern Pacific was 

described in IATTC's 1976 annual report. Twenty-two 5" areas where most of 

the skipjack have been caught were selected, but only data from areaquarter strata having > 100 standardized days of logged effort and > 200 

short tons of logged skipjack caught were used. This eliminated an average 

of 43% of the effort while retaining 89% of the skipjack catch for purse 

seiners during the 1961 to 1979 period. The catch-per-unit-effort by purse 

seiners shows a downward trend in the area south of 5" N latitude, but no 

clear trends are apparent for the northern areas. 

III.B.2. Results of Production Model Analysis 

Attempts to fit the production model to eastern Pacific 

skipjack data have been unsuccessful. 

in the CYRA, standardized to Class-3 units (vessels of 101 to 200 ton 

carrying capacity) , are shown in Figures 6 and 7. 

areas of the CYRA, while Figure 7 includes only selected 5" areas where 

significant amounts of skipjack are caught. 

Plots of purse seine CPUE and effort 

Figure 6 includes all 5" 

The IATTC has suggested some possible reasons for the 

model not fitting. Tagging studies and larval surveys indicate the fishery 
-1 75- 
-1 76- 

0 4- $;; 

n2 5- 

Lg 

E? 

L? 

&fJ 

$2 

2- 

b-> 

O+ 

I I I I 

67 NORTH OF 15ON. - 

71 70 

0 0- 

68 63, 76 78 

0 0 75 

72 690 @ 0 0 @64 

0 

61 660 73 Q0 65 

74 77 62 0 0 

1 I 1 I 

0 

67 

0- 

I 

SOUTH OF 15" N. 

- 

28. 

a. 

a 

z 

u 

0 

1 I 1 I I I 

64 0 

63 

68 0 

0 

71 

0 

6S 

70 

0 

75 fi 

Figure 6. Relationships between CPUE and effort (unregulated and 

regulated) for skipjack in the CYRA north and south of 

15" N, using data for all 5' areas, 1961 to 1978. 
-1 77- 

8 

6- 

4, 

2- 

0 

a 

I 1 1 1 I 1 I 

67 - 

0 

- NORTH OF 15O N. 

- 

c - 

72 73 63 

a@ 71 - 

70 0 0 

- 64 76 0 680 

- 

78 66 62 ,6'@69 Q) 

61 8 

- 

Q Q 

0 Q 77 

- 74 75 - 

I 1 1 I I I I A 

E 14- 

Q 

n 

n 

a 

a 12 

n 

a 

a IOa 

2 

trn 

W 

I 

0 

u 

+- 8- 

a 

6- 

4- 

2- 

arr 

- 

- 

- 

- 

- 

- 

- 

SOUTH OF 15.N. 

o 

67 

71 

64 63 ' 

Q 

68 0 

Q 

065 

66 

0 75 Q h 

69 0 --( 62 

61 0 

VJ 76 70 0 

Io 78 

0 1 1 I I I 1 

0 5 10 15 20 25 30 

STANDARD DAYS FISHING (PS3) x 1000 

Figure 7. Relationships between CPUE and effort (unregulated and 

regulated) for skipjack in the CYRA north and south of 

15" N, using only data for selected 5" areas, 1961 to 

1978. 
-1 78- 

is not on a unit stock. In addition, environmental studies indicate that 

perturbations caused by environmental fluctuations may mask changes in 

apparent abundance caused by fishing effort. 

increased in recent years, due to increases in the size of the fleet. This 

has apparently not depleted the resource because some of the greatest total 

catches have been made during the last few years. 

there is still no apparent relationship between skipjack tuna stock 

abmdance and fishing effort. 

The fishing effort has 

This indicates that 

III.B.3. Results of Yield-per-Recruit Analysis 

The estimated re1 ationships among size-at-entry, fishing 

effort, and yield-per-recruit are shown in Figure 8. The top panel is 

based upon age-specific fishing mortality rates estimated from lengthfrequency data obtained during 1967 to 1969, the middle panel is based upon 

rates estimated from data obtained during 1971 to 1973, and the lower panel 

is based upon rates estimated from data obtained during 1975 to 1977. 

Increasing the size-at-entry would not appreciably 

change the yield-per-recruit at fishing effort levels observed during the 

years in auestion (F mu1 tip1 ier = 1.0). 

between 0.75 and 1.00 pounds for the 1975 to 1977 period. 

fish: ng mortal i ty 1 eve1 s , an increase in size-at-entry wotil d decrease the 

yield-per-recruit. 

The yield-per-recruit remains 

At higher 

Increasing effort at current size-at-entry would 

increase the yield-per-recruit to the fishery. 

would double the instantaneous fishing mortality would result in an 

increase in yield-per-recrui t of approximately 25%. 

result in an increased yield-per-recruit even at higher sizes-at-entry for 

both the 1971 to 1973 and 1975 to 1977 periods. 

An increase in effort which 

Increased effort would 

In general, the yields are highest with a size-at-entry 

of about 35 cm (about 1.7 pounds) and with fishing effort considerably 

greater than has so far been the case in the eastern Pacific Ocean. This 

is because the losses to the total weight of a cohort of fish by natural 

mortality and emigration exceed the gains to it by growth, even when the 

fish are only 35 cm long and are presumably growing rapidly. 

111.6.4. Results of Spawner/Recruitment Analysis 

No spawner/recruitment analyses are avail able for central 

and eastern Pacific skipjack tuna. 

Possible environmental effects on year-class recruitment 

of skipjack caught in the eastern Pacific have been investigated by the 

IATTC in an attempt to explain some of the variation in the catches. 

Significant correlations have been found between indices of skipjack 

abundance in the eastern Pacific and sea-surface temperatures in the 

spawning areas of the central tropical Pacific (180" to 130" W longitude) 
-1 79- 

55- 0.50 0.75 I .oo 1.10 

50- 

45 - 

40- 

35 I I I I I 1 I 1 

0.5 I .o 1.5 20 2.5 3.0 3.5 4.0 

MULTIPLIER OF F 

Figure 8. Relationships among size at entry, fishing effort, 

and yield-per-recruit for skipjack. 
-1 80- 

approximately 1-1/2 years earl ier; re1 ated meteorological variables such as 

barometric pressure differences and wind speeds are a1 so important factors. 

These investigations indicate that approximately 47% of the variation in 

the annual catch rate (numbers of fish per standardized day's fishing) of 

12- and 24-month old skipjack in the eastern Pacific may be explained by 

the wind-mixing index in the spawning areas of the central Pacific 

approximately 1-1/2 years earl ier. 

III.B.5. Results of Other Analyses/Simulations 

Estimates of the general magnitude of the potential yield 

of skipjack in the Pacific are available. These estimates follow less 

rigorous techniques and give widely different results. 

method of Beverton and Holt, Rothschild estimated the potential yield of 

skipjack from the central Pacific. 

state yield in the eastern Pacific and assuming a sojourn time of 2 months 

in the fishing areas of the eastern Pacific, he estimated the potential 

yield in the central Pacific to be 5 to 17 times greater than the yield in 

the central Pacific, or 350,000 mt to 1,190,000 mt. Assuming a sojourn 

time of 6 months, he estimated the yield to be 140,000 mt to 420,000 mt. 

However , Si1 1 iman , using a popul ation simulation method, estimated a 

potential yield of 180,000 to 275,000 mt for the eastern Pacific fishery 

and the unexploited areas of the central and eastern Pacific. 

Following the 

Using 70,000 mt as an average steadyThe Fisheries Agency of Japan has estimated the 

potential yield for the entire Pacific to be from 800,000 to over 1,000,000 

mt. They assumed the skipjack spawning stock was about twice that of other 

tunas, based on a 1.7 to 1.8 ratio of skipjack larvae to other larvae 

collected. They then extrapolated the catch of other tunas at that time to 

obtain estimates of the potential skipjack tuna yield from the entire 

Pacific Ocean. 

II1.C. Current Evaluation of Stocks and the Fishery 

A relationship between stock abundance and total effort could not 

be detected, and the potential production of skipjack tuna stocks in the 

eastern Pacific has not been satisfactorily established. In the eastern 

Pacific skipjack fishery, the yields per recruit generally are highest with 

a size-at-entry of 35 cm (about 1.7 pounds) and at fishing effort levels 

considerably greater than has so far been the case. This is because the 

losses to the total weight of a cohort of fish by natural mortality and 

emigration exceed the gains to it by growth. The IATTC indicates that 

neither the general 

examined so far indicate any need for the management of skipjack. 

production models nor the age-structured models 
-181- 

IV. STATUS OF CURRENT RESEARCH NEEDS AND EFFORTS 

1V.A. Major Research Problems 

Management should be directed toward all parts of a single stock, 

rather than a part of a stock, a mixture of several stocks, or a mixture o

parts of several stocks. 

the stocks or subpopulations of skipjack in the Pacific Ocean. 

Therefore, it is of prime importance to define 

1V.B. Current Research Efforts 

There is no current U.S. research effort on the eastern Pacific 

skipjack tuna fishery; all research is being conducted by the InterAmerican Tropical Tuna Commission. The IATTC has recently increased its 

tagging of skipjack in the eastern Pacific Ocean and conducted tagging 

experiments in French Polynesia. 

tagging skipjack in large numbers in the western and central Pacific Ocean 

in recent years. 

subpopulation identification is being carried out in the western and 

central Pacific. 

an operating budget of $2,746,000. 

The South Pacific Commission has been 

In addition, collection of blood samples for 

In 1979 the IATTC employed approximately 50 people with 

Various other organizations, particularly the Food and Agricul tur

Organization of the United Nations, are also striving to obtain better 

catch and effort data for skipjack in the western and central Pacific. 

When these studies produce results, it will be possible to better ascertai

the status of the Pacific Ocean skipjack tuna subpopulations with regard t

f i shi ng. 

1V.C. Future Research Needs 

The stock structure of skipjack tuna in the Pacific Ocean, 

particularly the eastern Pacific, is poorly understood. It has been 

suggested that this is due to the fact that most studies on skipjack tuna 

have been based on populations occurring in relatively small areas whereas 

studies on an oceanwide basis are needed. 

1V.D. Status of SWFC Data Base 

Skipjack tuna catch and related data for the fishery in the CYRA 

Data are generally not available through the SWFC except for those 

and adjacent areas in the eastern tropical Pacific are in the files of 

IATTC. 

a1 ready pub1 ished by IATTC. 
-1 82- 

STATUS REPORT: WESTERN PACIFIC SKIPJACK TUNA 

Howard 0. Yoshida 

Southwest Fi sheries Center 

Honol ul u , Hawaii 

ABSTRACT 

The major fisheries for skipjack tuna are located adjacent to 

continents and islands. In the western Pacific, the Japanese pole-andline, live-bait fishery is the largest and the oldest established fishery. 

The stock structure of skipjack tuna in the Pacific is not very well known. 

A1 though no production model analyses or other analyses and simul ations 

have been attempted for western Pacific skipjack tuna, all available 

information suggests that the resource is still underexploited. 

important research needs for skipjack tuna in the Pacific is the 

el ucidation of the population structure of the resource. 

One of the 
-1 83- 

1. DESCRIPTION OF THE FISHERY 

I.A. History of the Fishery 

c 

Skipjack tuna (Katsuwonus pelamis) are widely distributed in the 

Pacific Ocean (Figure 1). 

continents and islands where oceanographic features such as upwelling 

concentrate large numbers of fish near the surface. 

fisheries, the Japanese pole-and-1 ine, live-bait fishery in the western 

Pacific is by far of greatest antiquity. The origin of the Japanese 

fishery is obscure; however, skipjack tuna fishing is mentioned in the 

oldest (semilegendary) account of Japanese history. Keen (1965) stated 

that the Japanese pole-and-line fishery for skipjack tuna dates from at 

least the early part of the Tokugawa Period (1603-1868). 

The majmeries are located adjacent to 

Of the major Pacific 

The Japanese skipjack tuna fishery, which was earlier limited to 

coastal waters of Japan, has expanded eastward and southward into 

subtropical and tropical waters. The expansion of the fishery into these 

waters involved not only pole-and-line vessels but purse seiners as well. 

Skipjack tuna fisheries are also well developed or developing in 

Hawaii and many island areas in the western Pacific. Uchida (1975) 

reviewed the recent development of skipjack tuna fisheries in the central 

and western Pacific, including those of French Polynesia, Hawaii , Samoa, 

Tonga, Australia, Fiji , Tuvalu (Ell ice Islands) , Indonesia, Korea, New 

Hebrides, New Caledonia, New Zealand, Papua New Guinea, Philippines, 

Solomon Islands, and the Trust Territory of the Pacific Islands. Kiribat

and Singapore also show landings of skipjack tuna (Food and Agricultural 

Organization of the United Nations 1979). Japan is the major producer of 

skipjack in the western Pacific, and also is involved in the fisheries of 

some of these countries or political entities through joint venture 

arrangements. 

landings of skipjack tuna in Taiwan, there apparently is a troll fishery 

unknown magnitude there. 

The U.S. (Hawaii) has a small surface fishery in the western 

Pacific and American tuna seiners have been making western Pacific 

exploratory fishing cruises. 

Although the FA0 yearbooks of fishery statistics show no 

I.B. Trends in Catch and Effort 

The catch of skipjack tuna in the western Pacific increased from 

224,400 to 532,296 metric tons (mt) during 1970-1978 (Figure 2). The cat

in the Japanese pole-and-1 ine fishery between 50"N and 30"s 1 ati tude and 

1lO"E and 150"W longitude ranged from 119,643 to 245,611 mt, and showed a

increasing trend between 1970 and 1977 (Figure 3). 
-1 84- 

Figure 1 .--Skipjack tuna distribution and fisheries in the Pacific Ocean. 

(Adapted from Joseph et al. 1979.) 
-1 85- 

YEAR 

Figure 2.--Annual catch of skipjack tuna in the western 

Pacific, 1970-78. (Source: FA0 1976, 1977, 1979.) 
-1 86- 

"i 

O' 1970 19171 1972 LSD 1974 1975 1976 1977 

YEAR 

Figure 3.--Skipjack tuna catch in the Japanese pole-and-line 

fishery in the Pacific between lat. 50"N and 30"S, long. 

1lO"E and 150°W, 1970-77. 
-1 87- 

.- 

Fishing effort in the Japanese pole-and-1 ine fishery between 50"N 

and 30"s latitude and 1lO"E and 150"W longitude increased from 37,761 day

fished in 1970 to 76,007 days fished in 1977 (Figure 4). 

I.C. Value of Catch 

From 1969 to 1978, the mean annual ex-vessel price of skipjack tu

at Yaizu, one of the important tuna landing ports in Japan, ranged from 

$291 to $797 per short ton; the ex-vessel value of skip'ack tuna in Hawa

Except for slight setbacks in 1972 and 1978, the ex-vessel prices at Yaiz

have been on a continuous upward trend. Based on the average ex-vessel 

price of $797 per short ton at Yaizu, the western Pacific catch of skipja

tuna (532,296) in 1978 was valued at $467,639,750. 

during 1968-1977 ranged from $330 to $957 per short ton f (Figure 5). 

I .D. Current Management of the Fishery 

The western Pacific skipjack tuna stock is not currently under 

management . 

11. NATURE AND SIGNIFICANCE OF U.S. AND FOREIGN 

PARTICIPATION IN THE FISHERY 

Th U.S. imported 61,046 mt of skipjack tuna for "consumption d 

general imports"' in 1976 from western Pacific countries and i'sl and states 

(U.S. Bureau of the Census 1977). 

transshipping facil i ties at Pal au and Tahiti and conduct exploratory 

cruises to the western Pacific in search of new sources of tuna. 

U.S. tuna interests operate freezing a

'Hawaii Division of Fish and Game. Commercial fish catch by species, 

State of Hawaii. (Issued monthly; a1 so annual summaries.) 
-1 88- 

1970 1971 1972 I973 1974 1975 1976 1977 

YEAR 

Figure 4.--Fishing effort in the Japanese pole-and-line 

fishery in the Pacific between lat. 50"N and 30"s and 

long. 1lO"E and 150"W, 1970-77. 
-1 89- 

100 

a 

P w 

- 

I I I I I I I I I 1 

I , I I I I I I loo0 

500 

400 

300 0 m 

Figure 5.--Ex-vessel value of skipjack tuna landed in Yaizu, 

Japan, 1969-78, and in Hawaii, 1968-77. 

National Marine Fisheries Service 1969-1978 and Hawaii Division of Fish and Game see text footnote 1.) 

(Data from [U.S.] 
-1 90- 

111. STATUS OF THE STOCKS 

1II.A. Stock Structure 

The stock structure of skipjack tuna in the Pacific is unclear. It 

has been hypothesized that two subpopulations exist in the Pacific, one in 

the western Pacific and the other in th eastern and central Pacific 

(Fujino 1970). However, recent studies indicate that a1 though the 

possibility of genetically isolated skipjack tuna populations in the 

Pacific cannot be ruled out, the available data do not indicate stable 

geographical boundaries between genetically isolated sub-popul ations, as 

advanced by Fujino (1970, 1976). 

skipjack tuna blood genetics sponsored by the Skipjack Survey and 

Assessment Programme of the South Pacific Commission in September 1980, 

indicated that "the apparent esterase cl ine constitutes evidence that 

Pacific Ocean skipjack do not comprise a panmictic population, in which 

complete mixing would occur across the extremes of the popul ation range, 

within a single generation." There apparently is some *'resistance'' to 

complete mixing of skipjack tuna across the Pacific but the nature and 

magnitude of the 'Iresi stance'' could not be ascertained from the avail able 

genetics data. 

5 

Data presented at the second workshop on 

I I1 .B. Stock Assessment and Fishery Eva1 uation 

III.B.l. Trends in Catch-per-Uni t-Effort 

An analysis of the Japanese coastal and distant water 

skipjack tuna fisheries for the period 1957-1973 (Ishida 1975) showed 

neither an upward nor downward trend in the catch rate (Figure 6). Updated 

analyses on changes in catch, effort, population index, density index, and 

efficiency of effort, indicated a possible decreasing trend in the catchper-unit of effort north of 10"N latitude and in the area north and west of 

Papua New Guinea. However, density indices in equatorial regions 

2Skipjack Survey and Assessment Programme. 1980. Progress review of 

genetic analysis of skipjack blood samples by the Skipjack Survey and 

Assessment Programme. Presented at the Twelfth South Pacific Commission 

Regional Technical Meeting on Fisheries, Noumea, New Caldonia, 17-21 

November 1980. 
-1 97- 

80- 

60 

- I ~''''',I,I, I 

- 

02 5 ~~ 

- 

Figure 6.--Catch per day's fishing by vessel size classes 

in the Japanese skipjack tuna pole-and-line fishery. 

(From Ishida 1975.) 
-1 92- 

fluctuated considerably and showed no consistent t ends (Kasahara 19783; 

Tohoku Regional Fisheries Research Laboratory 1978 1. If 

III.B.2 Results of Production Model Analysis 

None available. 

111.6.3 Results of Yield-per-Recruit Analysis 

None avail ab1 e. 

III.B.4 Results of Spawner/Recruitment Analysis 

None avail ab1 e. 

I I1 .B.5 Resul ts of Other Analyses/Simul ations 

None avail ab1 e. 

1II.C. Current Evaluation of Stocks and the Fishery 

A1 1 available evidence suggests that the western Pacific skipjack 

tuna resources are still underexpl oi ted (Kearney 1979). 

3Kasahara, K. 1978. Assessment of skipjack stocks in the Japanese 

baitboat fishery. Tohoku Regional Fisheries Research Laboratory, Shiogama, 

Japan. 

of Experts on Central and Western Pacific Skipjack, Mainla, Philippines, 

1-2 March 1978. 

Paper submitted to the First Session of the IPFC Working Party 

4Tohoku Regional Fisheries Research Laboratory. 1978. Atlas of catch 

and CPUE of skipjack tuna in the Japanese baitboat fishery, 1972-76. 

Paper submitted to the First Session of the IPFC Working Party of 

Experts on Central and Western Pacific Skipjack, Manila, Philippines, 

1-2 March 1978. 
-1 93- 

IV. STATUS OF CURRENT RESEARCH NEEDS AND EFFORTS 

R” 

1V.A. Major Research Problems 

Skipjack tuna are widely distributed in the Pacific Ocean and are 

believed to constitute a large resource. All the evidence available to 

date indicates that the resource is still underexploited. It has been 

stated that conservation of the skipjack tuna resource would not be a 

significant issue in the future development of fisheries in the western 

equatorial Pacific and that development and management strategies will 

likely be directed at maximizing yields and optimizing socioeconomic 

returns (Kearney 1979). 

1V.B. Current Research Efforts 

The South Pacific Commission (SPC) headquartered at Noumea, New 

Caledonia, recently initiated a skipjack tuna assessment program in the S

area of interest. The SPC research effort includes tagging, study of blo

genetics, exploratory fishing for tuna and bait, and analyzing basic 

biological data (length, weight, sex, maturity, and stomach contents). 

The Tohoku Regional Fisheries Research Laboratory (presumably the 

major agency for skipjack tuna research in Japan) prepares an atlas of 

Japanese skipjack tuna fishing operations in the southern fishing grounds

which includes data on monthly catch rates and length-frequency 

distributions. Research on skipjack tuna has also been conducted in Taiwa

including studies on age and growth, larvae, sexual maturity and fecundit

and morphometrics. 

1V.C. Future Research Needs 

Results of recent studies on blood genetics suggest a complex 

population structure for skipjack tuna in the Pacific Ocean. 

evidence indicates that the skipjack tuna resource is still underutilized

it is important to determine the population structure of Pacific skipjack 

tuna clearly. 

Although a

IV.C.l. Suaaested ADDrOaCh and Methods 

The Skipjack Survey and Assessment Programme of the Sou

The Programme is a1 so conducting skipjack tuna blood 

Pacific Commission recently completed the field work for a skipjack tuna 

tagging program. 

genetics studies and other ancillary studies to investigate the stock 

structure of Pacific skipjack tuna. It is expected that much will be 
-1 94- 

learned from the results of these studies. However, it is anticipated that 

there will continue to be gaps in the knowledge of skipjack tuna stock 

structure and ecology. These approaches and methods should be continued in 

the study of the population structure of Pacific skipjack tuna. 

1V.D. Status of SWFC Data Base 

Data from Japanese baitboat operations pub1 ished in annual 

statistical digests are included in the data base maintained at the 

Honolulu Laboratory. 

the western Pacific and data from the Hawaiian pole-and-1 ine fishery, 

including size data, are also included in the data base. 

Landing statistics from a few of the island states in 

LITERATURE CITED 

Food and Agriculture Organization of the United Nations. 

1976. Catches and landings, 1975. FA0 Yearbook Fish. Stat. 40, 

417 p. 

1977. Catches and landings, 1976. FA0 Yearbook Fish. Stat. 42, 

323 p. 

1979. Catches and landings, 1978. FA0 Yearbook Fish. Stat. 46, 

372 p. 

Fujino, K. 

1970. Immunological and biochemical genetics of tunas. Trans. 

Pm. Fi Sh. SOC. 99: 152-178. 

1976. Subpopulation identification of skipjack tuna specimens from 

the southwestern Pacific Ocean. Bull. Japan SOC. Sci. Fish. 

42: 1229-1235. 

Ishida, R. 

1975. Skipjack tuna fishery and fishing grounds (Katsuo gyogyo to 

gyojyo). 

of solid rxactive wastes on living marine resources (Hoshasei 

kotai haiki butsu no kaiyo shobun ni tomonau kaisan seibutsu to 

ni kansuru chosa hokokusho). Jpn. Fish. Agency, Tokai Reg. 

Fish. Res. Lab., Tohoku Reg. Fish. Res. Lab., and Far Seas Fish. 

Res. Lab., p. 88-92. July 1975. (Engl. transl. by T. Otsu, 

1975, 1 p., Transl. No. 12; available Southwest Fish. Cent., 

Natl. Mar. Fish. Serv., NOAA, Honolulu, HI 96812. 

From Reports pertaining to effects of ocean disposal 
-1 95- 

Joseph, J., W. Klawe, and P. Murphy. 

1979. Tuna and billfish--fish without a country. Inter-Am. Trop. 

Tuna Comm., La Jolla, Calif. 46 p. 

Kearney, R. E. 

1979. An overview of recent changes in the fisheries for highly 

migratory species in the western Pacific Ocean and projections 

for future developments. South Pac. Bur. Econ. Coop., Suva, 

Fiji, SPEC(79)17, 96 p. 

1980. Skipjack Survey and Assessment Programme. Annual report for 

the year ending 31 December 1979. South Pac. Comm., Noumea, 

New Caledonia, 14 p. 

Keen, E. A. 

1965. Some aspects of the economic geography of the Japanese 

skipjack tuna fishery. 

195 p. 

Ph.D. Thesis, Univ. Washington, Seattle, 

Uchida, R. N. 

1975. Recent development in fisheries for skipjack tuna, 

Katsuwonus pelamis, in the central and western Pacific and the 

Indian Ocean. In Studies on skipjack in the Pacific, p. 1-57. 

FA0 Fish. Tech.Pap. 144. 

U.S. Bureau of the Census. 

1977. U.S. imports for consumption and general imports. Report 

FT 246, annual 1976. U.S. Gov. Print. Off., Wash., D.C., 

442 p. 

[U.S.] National Marine Fisheries Service. 

1968-1978. Foreign fishery information re1 ease. Suppl ement to 

Market News Report. 
-1 96- 

STATUS REPORT: WESTERN PACIFIC YELLOWFIN TUNA 

Howard 0. Yoshida 

Southwest Fisheries Center 

Honol ul u , Hawaii 

ABSTRACT 

Yellowfin tuna are primarily caught by longline gear in the western 

Pacific. Although the stock structure of yellowfin tuna is not well known, 

it has been hypothesized that there are two separate stocks in the Pacific, 

one in the eastern Pacific and the other in the western Pacific, which are 

separated by a less clearly defined stock in the central Pacific. A stock 

production model based on longline catches of yellowfin tuna in the entire 

Pacific indicated that the stock is capable of sustaining the current level 

of catches. 

Pacific is to determine the relation and the extent of mixing of fish that 

are available to surface gear and longline gear. 

An important research need for yellowfin tuna in the western 
-1 97- 

I. DESCRIPTION OF THE FISHERY 

I.A. History of the Fishery 

Yellowfin tuna (Thunnus albacares) in the western Pacific Ocean 

(west of ca. 150" W longmis caught primarily by longline gear; 

smaller amounts are taken by pole-and-line, purse seine, and other surfac

fishing gear. 

Pacific Ocean between approximately 45" N and 45" S latitude is an 

outgrowth of the Japanese longline fishery, which was generally confined 

the western Pacific before World War 11. 

quickly expanded eastward after the war and reached the American continen

in 1964 (Figure 1). 

1962 and those from South Korea, in 1965 (Suzuki et al. 1978). Because th

1 ongl ine fishery extends completely across the Pacific Ocean , for the 

purpose of this report yellowfin tuna are considered for the entire Pacif

Ocean insofar as they relate to the longline fishery. 

The longline fishery that now extends completely across th

The Japanese longline fishery 

Longline vessels from Taiwan joined the fishery in 

Japan, Taiwan, and the Philippines have surface fisheries for 

yellowfin tuna in the western Pacific. Australia, Fiji, Gilbert Islands, 

Papua New Guinea, New Zealand, and French Polynesia also show landings of 

yellowfin tuna (Food and Agriculture Organization of the United Nations 

[FAO] 1977, 1978). 

The U.S. (Hawaii) has a small longline fishery and also a surfac

fishery for yellowfin tuna in the western Pacific. 

I.B. Trends in Catch and Effort 

The total annual catch of yellowfin tuna (all gear combined) rang

from 28,586 to 193,518 mt from 1952 to 1977 in the western Pacific (Table 

1). The catches made in the various Japanese fisheries (which totaled 

28,118 to 101,480 mt from 1952 to 1977) contributed the largest amount to 

the western Pacific annual total (Table 2). The bulk of the Japanese tot

annual catch is taken by longline vessels over 20 gross tons. Table 2 al

shows the catch by gear, for other countries fishing yellowfin tuna in th

western Pacific 

The total western Pacific catch of yellowfin tuna peaked in the 

mid-1960's (with a high of 110,458 mt in 19661, declined slowly to 76,121 

mt in 1971, then increased rapidly to levels higher than that in the 

1960'~~ reaching 193,518 mt in 1977 (Figure 2). 

Philippines since 1974 (Table 2) account for the increase in the total 

recorded catch of yellowfin tuna in recent years (FAO, in press). 

Reported catches from th

The total (Japan, Korea, Taiwan) fishing effort for yellowfin tu

in the Pacific generally showed an increasing trend from 75 million 
-1 98- 

Figure 1.--Expansion of the Japanese longline fishery in the Pacific Ocean. 

(From Kume 1972.) 
-1 99- 

"m.. 

Table 1.--Catch of yellowfin tuna in the western Pacific (all gear) in metric tons. (Data from Honma and Suzuki see text footnote 2.) 

Grand 

Year Japan Korea Taiwan Philippines Others Total 

1952 

1953 

1954 

1955 

1956 

1957 

1958 

1959 

1960 

1961 

1962 

1963 

1964 

1965 

1966 

1967 

1968 

1969 

1970 

1971 

1972 

1973 

1974 

1975 

1976 

1977 

28,586 

40,164 

43,450 

36,903 

28,118 

69,865 

74,929 

72,189 

77,485 

98,363 

100,426 

101,480 

89,440 

82,265 

96,137 

68,867 

73,116 

73,520 

71,645 

56,317 

75,053 

77,468 

81,359 

72,674 

94,818 

93,638 

500 

2,000 

3,000 

1,900 

5,300 

3,500 

2,000 

5,300 

11,800 

12,000 

15,104 

10,366 

15,613 

16,580 

1,192 

2,724 

2,377 

2,109 

1,753 

1,568 

1,301 

2,606 

5,513 

5,149 

5,795 

7,890 

11,221 

6,629 

11,452 

10,598 

10,502 

14,404 

13,368 

19,226 

3 00 

100 

100 

100 

100 

100 

100 

100 

100 

14,900 1.620 

28,586 

40,164 

44,642 

39,627 

30,495 

71,974 

76,682 

73,757 

78,786 

100,969 

105,939 

106,629 

96,035 

92,255 

110,458 

77,496 

89,968 

87,718 

84,247 

?6,121 

100,321 

125.214 

12,706 51,732 1;511 162;412 

16,867 52,793 1,823 154,523 

17,235 44,478 8,852 180,996 

20,042 59,263 3,995 193,518 
-200- 

h 

h 

I 

N 

m 

cn 

e 

m 

t 

m 

aJ 

V 

0 

e 

q 

-0 

ox 

-E 

mo 

SL 

0% 

c, 

rd 

V 

-0 

aJ 

c, 

v) 

W 

I 

I 

N 

W 

F 

n 

rd 

IIm 

m 

L 

W 

c 

w 

0 

I .C .- 

c in mn 

3 

rd 

t- m 

L 

-r 

aJ 

-c 

c, 

0 

5 

W 

L 

0 

Y 

I maJ 

.r 5 mo 

an 

IN 

OaJ 

CC 

0 .- AL 

rd 

aJ 

-0 

r= 

5 

I n 

-0 

c 

Iu 

5 

W 

N 

v 

m 

c 1 

5 

W 

5 

3 

n 

a 

a 

h 

0 

7 

2- 
-201 - 

c200 

I80 

YELLOWFIN TUNA 

160 

140 

- 

mg 120 

0 

0 100 

- 

I 

5 

g 80 

-1 

I60 

40 

20 

1955 I960 1965 I970 I975 

YEARS 

0 

Figure 2.--Yellowfin tuna annual catch trends in the western Pacific 

Ocean. (Data from Honma and Suzuki see text footnote 2.) 
-202- 

effective hooks in 1953 to 547 million effective hooks in 1977 (Table 3). 

Most of the longline fishing effort in the early years was expended by 

Japan, and although Korea and Taiwan have increased their longline effort 

in recent years, Japanese longliners still account for a large part of the 

total effort. 

I.C. Value of Catch 

The mean annual ex-vessel price of yellowfin tuna at Yaizu, Japan, 

ranged from $511 to $1,873 per short ton from 1969 to 1978 ([U.S.] National 

Marine Fisheries Service, 1969 to 1978; Federation of Japan Tuna Fisheries 

Cooperative Association and Japan Tuna Fisheries Federation [1976?1); the 

ex-vessel price ranged from $985 to $1,984 per short ton from 1968 to 1977 

in Hawaii' (Figure 3). 

short ton in 1978 at Yaizu, Japan, the value of the western Pacific 

yellowfin tuna catch in 1978 was $387,166,528. 

Based on the mean ex-vessel price of $1,815 per 

I .D. Current Management of the Fishery 

The western Pacific yellowfin tuna is not currently under 

management 

11. NATURE AND SIGNIFICANCE OF U.S. AND FOREIGN 

PARTICIPATION IN THE FISHERY 

The yellowfin tuna is one of the important species caught in the 

Hawaiian longline fishery. 

recreational fishery in Hawaii. 

It is also an important species in the 

Yellowfin tuna are landed at American Samoa, Tahiti, and other island 

areas where U.S. interests operate canneries or transshipment facilities. 

American purse seiners have a1 so been making exploratory fi shing voyages in 

the western Pacific. 

'Hawaii Division of Fish and Game. Commercial fish catch by species, 

State of Hawaii. (Issued monthly; also annual summaries.) 
-203- 

Table 3.--Catch (metric tons) and effective effort (x lo3 hooks) for 

yellowfin tuna in the Pacific Ocean, 1951-77. (Adapted from FA0 in press.) 

Japanese longline Total (Japan, Korea, Taiwan) 

fisheries 1 ongl ine fisheries 

Year Catch Effort Catch Effort - 

1952 

1953 

1954 

1955 

1956 

1957 

1958 

1959 

1960 

1961 

1962 

1963 

1964 

1965 

1966 

1967 

1968 

1969 

1970 

1971 

1972 

1973 

1974 

1975 

1976 

- 

1977 

22,477 

33,288 

34,174 

28,794 

'22,717 

60,976 

60,608 

55,146 

68,438 

84,527 

79,632 

88,050 

71,508 

66,809 

77,469 

47,982 

52,265 

56,110 

50 ,940 

40,930 

53,345 

47,973 

44,316 

45,996 

55,497 

57,300 

74,252 

85,475 

81 .382 

133 ; 412 

113,524 

163,402 

167,694 

164,967 

190,837 

269 , 104 

322,379 

333.814 

276 ; 504 

281 ,309 

313,521 

232,519 

239,155 

238,602 

197 , 668 

222,433 

266,719 

274,479 

287,845 

260,001 

306,615 

311,091 

22,799 

33,288 

35,621 

31,672 

25,094 

63,438 

62,538 

57,041 

69,993 

87,428 

85,436 

93,466 

77,953 

76,894 

92,607 

58,050 

69,549 

72,474 

67,392 

63,396 

81,985 

81,343 

74,2 97 

78,063 

94,113 

100,924 

75,316 

85,475 

84,828 

146,747 

125,403 

170,000 

173,034 

169,602 

195,173 

278,339 

345,876 

354,347 

301,425 

323,773 

374,785 

281,308 

318,243 

308,188 

261,508 

344,525 

409,916 

465,402 

482,580 

441,265 

51 9 , 965 

547,932 

lprovisional estimate. 
-204- 

I I I I I I I I 

--A 

0 I I I I 1 I I I 

1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 

YEARS 

Figure 3.--Mean annual ex-vessel value of yellowfin tuna landed in Yaizu, 

Japan, 1968-78 and in Hawaii, 1968-77. (Data from [U.S.] National Marine 

Fisheries Service 1969-1978; Federation of Japan Tuna Fisheries Cooperative Association and Japan Tuna Fisheries Federation [1976?]; Hawaii 

Division of Fish and Game see text footnote 1.) 
-205- 

111. STATUS OF STOCKS 

1II.A. Stock Structure 

The stock structure of yellowfin tuna in the Pacific Ocean is no

perfectly clear but a hypothesis has been advanced that there are two 

distinct stocks, one in the eastern Pacific and the other in the western 

Pacific, separated by a less clearly defined stock in the central Pacific 

(Suzuki et a1 . 1978). 

I I1 .B. Stock Assessment and Fishery Eva1 uation 

I I I. B .l. Trends in Catch- Der-Un i t-Effort 

In a study to examine the changes in catch-per-uniteffort in the Japanese longline fishery, the Pacific Ocean was divided in

nine areas (Figure 4). 

per-unit-effort fell sharply in most areas, then showed a relatively stea

and gradual decline as nominal effort increased (Figure 5). 

After the first few years of fishing, the catchIII.B.2. Results of Production Model Analysis 

A1 though a production model analysis was not possible 

the combined surface and longline fishries for yellowfin tuna in the 

western Pacific, an analysis (Honma and Suzuku') was possible for the 

entire Pacific longl ine fishery, which probably reflects the situation i

the western Pacific longl ine fishery (Figure 6). 

that the total effort is at or approaching the level producing MSY (maxim

sustainable yield), which is estimated at around 80,000 to 90,000 mt. 

This analysis suggests 

III.B.3. Results of Yield-per-Recruit Analysis 

None avail ab1 e. 

III.B.4. Results of Spawner/Recruitment Analysis 

None available. 

'Honma, M., and Z. Suzuki. 1979. Stock assessment of Pacific yellowf

tuna exploited by the tuna longline fihsery together with surface and 

other fisheries in the western and central Pacific. Prepared for the 

Workshop on the Assessment of Selected Tuna and Billfish Stocks in the 

Indian and Pacific Oceans, Shimizu, Japan, 13-22 June 1979. 
-206- 

50' 

40' 

20C 

O0 

2oc 

40' 

.- 

Figure 4.--Subareas in the longline fishery for yellowfin tuna in the 

Pacific. (From FA0 in press.) 
-207- 

- 

u) Y 

I 

8 

z 

2 ,, , ,,/,,,,,,,,,,/,,,,/,I, 

IM SUB-AREA I 

SUB-AREA 3 

~ 

IPACIFIC 

Figure 5.--Catch rate for yellowfin tuna in the Japanese longline fishery 

by subareas. (Adapted from FA0 in press.) 
-208- 

ITC 1 

5 

1 1 1 , 100 200 300 400 500 600 700 

FISHING EFFORT ( IO6 EFFECTIVE HOOKS) 

Figure 6.--Catch and effort plots with curves fitted to the model for 

m = 0, 1, and 2 (k = 3), respectively, for yellowfin tuna caught in the 

Pacific-wide longline fishery, 1952-77. (From FA0 in press.) 
-209- 

a 

III.B.5. Results of Other Analyses/Simulations 

None avail able. 

1II.C. Current Evaluation of Stocks and the Fishery 

Although the condition of the western Pacific yellowfin tuna 

stock(s) is not certain, it appears that the stock is capable of sustaining 

the current level of fishing, or perhaps more. It was estimated that the 

MSY for the Pacific longline fishery for yellowfin tuna was around 80,000 

to 90,000 mt and that increased longline fishing effort was unlikely to 

result in a significant increase in sustained catch. 

IV. STATUS OF CURRENT RESEARCH NEEDS AND EFFORTS 

1V.A. Major Research Problems 

The following factors need to be determined: 

1) Growth parameters of western Pacific yellowfin tuna. 

2) The relation and the extent of mixing of fish available to 

surface gear and longline gear. 

3) Yield-per-recruit estimates: It has been pointed out that the 

surface fisheries in the Philippines may be making substantial catches of 

small yellowfin tuna, which is not good from a yield-per-recruit 

standpoint. 

In addition, production model analysis incorporting surface catch 

and effort data should be undertaken. 

1V.B. Current Research Efforts 

A background paper on a preliminary assessment of western Pacific 

Since that time there has 

yellowfin tuna exploited by the long1 ine fishery (Honma and Suzuki , see 

footnote 2) was presented at the tuna and billfish stock assessment 

workshop held at Shimizu, Japan, in June 1979. 

been no concerted effort to continue these studies. 
-21 0- 

1V.C. Future Research Needs 

Some of the research needs for the western Pacific yellowfin tuna 

include necessary data for stock assessment purposes: 

1) The magnitude and size composition of the large Philippine 

surface catch of yellowfin in recent years should be accurately estimated 

and historical catches documented. 

2) The problem of double reporting of catches should be resolved. 

3) Estimates of misidentified or unidentified yellowfin tuna in 

the catches are needed. 

4) Size-composition data are needed from all the fisheries, 

particularly the surface fisheries. 

5 Yi el d/recrui t estimates are rleeded for stock assessment and 

for production model analyses (which inci de surface catch and effort 

data). 

6) Effects of competition between surface and 1 ongl ine fisheries 

should be further examined. 

7) The extent of mixing between fish available to surface and 

longline gears should be examined. 

8) Additional estimates of the growt!: of yellowfin tuna Sn the 

western Pacific are needed. 

IV.C.l. Suggested Approach and Methods 

1) 

countries for the collection of yellowfin tuna fishery statistics, 

particularly those from the Phil1 ippines. 

Cooperative arrangements should be made with foreign 

2) The extent of mixing between fish available to 

surface and longline gears could be assessed by means of tagging 

experiments. 

1V.D. Status of SWFC Data Base 

The data on catch, catch-per-effort, and length frequencies needed 

for assessment studies on yellowfin in the Pacific are either inadequate or 

8'8 lacking and should therefore be secured. In particular, the large 
-21 1- 

surface catch of yellowfin in the Philippines in recent years should be 

documented, and longer historical catch data obtained. Problems on double 

reporting of catches, and misidentified or unidentified yellowfin tuna 

catches, must a1 so be corrected. 

LITERATURE CITED 

Federation of Japan Tuna Fisheries Cooperative Association 

and Japan Tuna Fisheries Federation. 

[1976?1 Katsuo to maguro (skipjack and tunas). Statistics of 

Japanese tuna fishery, 1975, 25 p. 

Food and Agriculture Organization of the United Nations. 

1977. Catches and landings, 1976. FA0 Yearbook Fish. Stat, 42, 

323 p. 

1978. Catches and landings, 1977. FA0 Yearbook Fish. Stat. 44, 

343 p. 

In press. Summary report of the Workshop on the Assessment of 

selected Tuna and Billfish Stocks in the Pacific and Indian Oceans, 

Shimizu, Japan, 13-22 June 1979. 

Kume, S. 

1972. Tuna fisheries and their resources in the Pacific Ocean. 

Indo-Pac, Fish. Counc. Proc., 15th Sess., Sect. 3: 390-423. 

Suzuki, Z., P. K. Tomlinson, and M. Honma. 

1978. Population structure of Pacific yellowfin tuna [In Engl. and 

Span.] Inter-Am. Trop Tuna Comm. Bull. 17: 277-441. 

[U.S.] National Marine Fisheries Service. 

1969-1978. Foreign fishery information release. Supplement to 

Market News Report. 
-21 2- 

STATUS REPORT: SOUTH PACIFIC ALBACORE 

by 

Jerry A. Wetherall 

Southwest Fi sheries Center 

Honol ul u, Hawaii 

ABSTRACT 

The South Pacific albacore stock has been fished since 1952. Most of 

the catch is taken by longline vessels from Japan, the Republic of Korea, 

and Taiwan. Long1 ine catch-per-unit-effort decl ined considerably between 

1962 and 1974 as effort and catch increased. 

recently in spite of lowered effort. 

longliners i s i n the neighborhood of the estimated MSY for this fishery, 

35,000 mt, and no sustained increase in longline catch can be expected. 

Potentials for expanding the surface catch of relatively small albacore are 

unknown. 

However, catch rates 

increased in recent years so that average annual catch has increased 

Present average annual catch by 
-21 3- 

I. DESCRIPTION OF THE FISHERY 

I.A. History of the Fishery 

"- 

A1 bacore, Thunnus alalunga, is one of the most important species 

taken in the Southmc tuna longline fishery by vessels from Taiwan, 

the Republic of Korea, and Japan. Small amounts of South Pacific albacore 

are taken by surface trollers of Chile and New Zealand. 

As part of the general eastward expansion of the Japanese longline 

fishery after World War 11, Japanese longliners began fishing in the 

western South Pacific in 1952, principally for yellowfin tuna. In 1954, a 

small fleet of Japanese longliners based at American Samoa began fishing 

for tunas to supply an American tuna cannery in Pago Pago. The Japanese 

also established a base in 1958 at Espiritu Santo, New Hebrides, and in 

1963 at Fiji. 

Tahiti. 

based on Japanese longline fishing operations from 1952 to 1976, extends 

from the equator to approximately 45"s latitude between 135"E and 80"W 

1 ongi tude (Figure 1 . 

A base for foreign longliners has also been established at 

The geographical boundaries of the fishery in the South Pacific, 

I.B. Trends in Catch and Effort 

The estimated total annual catch of South Pacific albacore from 

1952 to 1978 ranged between 210 and 49,275 mt (metric tons) (Table 1). 

catch rose rapidly from 210 mt in 1952 to 39,479 mt in 1962, and has since 

fluctuated, reaching a low of 24,975 mt in 1963 and a high of 48,691 mt in 

1973 (Figure 2). However, longline catch data are often available only in 

number of fish caught, or may be incomplete in other ways; therefore, the 

total atch in weight for Japan, Korea, and Taiwan is estimated (Wetherall 

The 

et al. € 1. 

The total number of longliners based at Pago Pago increased from 

18 in 1954 to 344 in 1973, with Korean and Taiwanese boats gradually 

rep1 acing Japanese vessel s during this period (Table 2). Since 1973 the 

total number of vessels has declined to the present level of about 200. 

Total fishing days by Taiwanese vessels reached a peak of 22,028 in 1973, 

but has declined to less than 10,000 in recent years (Table 3). 

values for Korean longliners are 27,111 and 16,000 fishing days, 

Comparable 

*- 

'Wetherall, J. A., F. V. Riggs, and M. Y. Y. Yong. 1979. Assessment 

of the South Pacific albacore stock. SWFC Admin. Rep. H-79-6, Natl. 

Mar. Fish. Serv. , NOAA, Honolulu, Hawaii, 41 p. Prepared for the Workshop on the Assessment of Selected Tunas and Billfish Stocks in the 

Indian and Pacific Oceans, Shimizu, Japan, 13-22 June 1979. 
-21 4- 

Figure 1.--The geographical boundaries of the South Pacific longline 

fishery for albacore. 

footnote 1 .) 

(Adapted from Wetherall et al. see text 
-21 5- 

Table 1.--Estimated total catches in metric tons of South Pacific 

albacore, 1952-78. The 1978 estimates are preliminary. 

~~~~~ ~ ~~ 

Column 1 2 3 4 5 6 7 

Japan 

and 

Year Japan Taiwan Taiwan R Korea Other Total 

1952 210 

1953 1,091 

1954 10,200 

1955 8,420 

1956 6,220 

1957 9,764 

1959 19,344 

1960 23,756 

1961 25,628 

1962 38,880 

1963 33,500 

1964 21,435 

1965 19,305 

1966 23,401 

1967 16,640 

1968 7,707 

1969 5,559 

1970 6,560 

1971 4,339 

1972 2,796 

1973 2,381 

1974 1,847 

1975 1,045 

1976 1,906 

1977 2,240 

1978 -- 

1958 21,558 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

0 

608 

62 9 

1,640 

6 , 669 

14,910 

14,496 

9,883 

12,463 

21 , 584 

23 , 050 

28,858 

19,980 

15,092 

19,954 

21 , 345 

-- 

210 

1,091 

10,200 

8 , 420 

6 , 220 

9 , 764 

21,558 

19,344 

23 , 756 

38 , 880 

34,108 

22 , 064 

20,945 

30,070 

31,550 

22 , 203 

15,442 

19,023 

25 , 923 

31,239 

21,827 

16,137 

21,860 

23 , 585 

25,628 

25,846 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

0.0154 

0.0400 

0.1319 

0.3058 

0.3597 

0.4347 

0.4566 

0.6451 

0.6097 

0.5586 

0.5586 

0.5586 

0.5586 

0.5586 

0.5586 

0.5586 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

146 

456 

610 

3 30 

599 

1,367 

2,911 

6,405 

10,817 

13,717 

10,138 

9,963 

11,599 

14,482 

14,439 

17,452 

12,194 

9,015 

12,212 

13,176 

-- 

210 

1,091 

10,200 

8,420 

6,220 

9,764 

21 , 704 

19,800 

24,366 

25 , 958 

39,479 

35,475 

24,975 

27,450 

41 , 387 

45 , 371 

32,355 

25,405 

30 , 672 

40 , 605 

40 , 753 

49 , 275 

34,911 

25 , 798 

34 , 097 

37 , 381 

40 500 

Cments: 

Colunn 1 - Japanese longline catch fn metric tons, courtesy of 5. 

Colunn 2 - Catch by Taiwan's high-seas longliners (>50 GT) based at 

Ueyanagi. Far Seas Fisheries Research Laboratory. 

foreign ports, estimated fron published Taiwan catch 

statistics and average weights of albacore landed at Pngo 

Pago. 

Colunn 3 - Colunn 1 plus colunn 2. 

Colunn 4 - R Is ratio of Korean catch of South Pacific albacore to 

total catch of this species by dapan and Taiwan, estimated 

fron data in Skillman (1975). 

Colunn 5 - Colunn 3 x colunn 4, except fqr 1958-61, which are fron 

Pmerlcan Samoa cannery records. 

Colunn 6 - Includes catch by Chile ana New Zealand. 
-21 6- 

50 

40 

30- 

20 

10 

A L 0 ACO RE 

~ 

- 

~ 

0- 1955 1960 1965 1970 1975 

YEARS 

Figure 2.--Total catch of albacore in the South Pacific longline 

fishery, 1952-78. (Data from Wetherall et al. see text footnote 1.) 
-21 7- 

rrr 

Table Z.--Number of longline vessels based at Pago Pago, PFnerican 

Samoa, by national i ty, 1954-80. 

Number of vessel s -~ 

Year Japan Taiwan Korea Undetermined Total 

1954 17 -- -- 1 18 

-- -- -- 50 

-- -- -- 56 

1955 50 

1956 56 

1957 61 -- -- 1 62 

76 -- 2 1 79 

1959 64 -- 4 1 69 

1958 

1960 60 -- 3 1 64 

55 -- 2 1 58 

1962 79 -- 5 1 85 

1961 

1963 117 -- 10 1 128 

16 -- 121 

-- 157 

1964 94 11 

1965 101 23 33 

79 76 55 -- 210 

-- 2 59 

1966 

69 

-- 2 34 

1967 62 128 

1968 39 110 85 

71 76 -- 165 

-- 205 

1969 18 

81 

-- 218 

1970 9 115 

124 90 

-- 2 32 

1971 4 

95 

-- 344 

1972 2 135 

172 

-- 320 

-- 172 

-- 149 171 

1973 

-- 77 135 -- 212 

1974 

-- 93 119 -- 212 

1975 

-- 88 114 -- 2 02 

1976 

1978 -- 85 113 -- 198 

1977 

1979 -200 

1980 -. 200 
-21 8- 

Table 3.--Estimated number of vessel trips, fishing days per trip, and 

total fishing days for longliners based at American Samoa, 1954-78. 

Japan Ta i wan Korea 

Days/ Days/ Days/ Year trip Trips Days trip Trips Days trip Trips Days 

1954 

1955 

1956 

1957 

1958 

1959 

1960 

1961 

1962 

1963 

1964 

1965 

1966 

1967 

1968 

1969 

1970 

1971 

1972 

1973 

1974 

1975 

1976 

1977 

1978 

-- 

17.4 

21.1 

24.4 

23.3 

21.5 

22.0 

24.6 

27.5 

30.7 

32.1 

35.7 

39.6 

38.7 

37.9 

40.2 

29.8 

58 

142 

2 62 

263 

330 

287 

283 

2 60 

339 

423 

277 

275 

229 

2 02 

100 

47 

26 

13 

4 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

4,576 

6,963 

7,003 

6,594 

5,590 

7,678 

10,406 

7,618 

8,442 

7,351 

7,211 

3,960 

1,819 

98 5 

523 

119 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

23.2 

27.6 

27.5 

33.0 

40.3 

38.9 

40.4 

45.3 

46.8 

52.2 

55.4 

62.5 

59.2 

39.6 

36.3 

-- -- 

27 626 

97 2,677 

295 8,112 

355 11,715 

267 10.760 

213 -81286 

326 13,170 

328 14,858 

350 16,128 

422 22,028 

327 18,116 

134 8,375 

152 8,998 

231 9,152 

136 4,932 

-- 

-- 

-- 

22.6 

26.7 

23.0 

25.0 

24.9 

30.9 

27.4 

34.2 

41.6 

44.3 

47.5 

47.3 

46.7 

54.5 

54.4 

56.6 

47.6 

55.8 

57.6 

47.2 

38.0 

-- 

-- 

7 

14 

44 

8 

40 

69 

69 

165 

246 

241 

214 

289 

2 99 

282 

349 

479 

422 

2 62 

276 

258 

2 92 

-- 

-- 

-- 

-- 

158 

3 74 

1,012 

2 00 

996 

2,132 

1,891 

5,643 

10,234 

10,676 

10,165 

13,670 

13,496 

15,369 

18,986 

27,111 

20,087 

14,620 

15,898 

12,174 

11,122 
-21 9- 

.- respectively. Korean effort is centered in the lower latitudes of the 

South Pacific and in the equatorial region where a substantial part of the 

catch is bigeye tuna and yellowfin tuna, whereas the Taiwanese vessels 

concentrate on albacore grounds further south. 

I.C. Value of Catch 

Except for a decline in 1975, the mean annual ex-vessel value of 

albacore landings in the American Samoa longline fishery rose from a low of 

$426 per short ton in 1969 to $1,358 per short ton in 1978 (Figure 3). 

I .D. Current Management of the Fishery 

11. NATURE AND SIGNIFICANCE OF U.S. AND FOREIGN 

PARTICIPATION IN THE FISHERY 

In 1953, a California seafood company obtained a lease from the 

Department of the Interior for a small tuna cannery in Pago Pago and began 

taking deliveries of tuna from Japanese long1 iners under contract. This 

marked the beginning of the tuna longline fishery in the South Pacific 

(Otsu 1966). In 1963 a second U.S. firm began operating a tuna canning 

plant in American Samoa. 

venture with French companies in operating a tuna transshipping base at 

Tahiti. 

6--. 

Pmerican interests are also involved in a joint 

Albacore landed at American Samoa represented an estimated 78% of the 

catch of this species in the South Pacific in 1970, but normally vessels 

based at Pago Pago account for only 30 to 60% of the harvest (Figure 4). 

111. STATUS OF THE STOCKS 

1II.A. Stock Structure 

South Pacific albacore are considered to be a distinct 

subpopulation confined to the current systems of the Southern Hemisphere. 

There is no evidence of intermingling with North Pacific albacore stock(s), 

and no evidence of mu1 tiple subpopulations within the South Pacific. 
-220- 

0 1 I 1 I 1 I f I970 1972 I974 1976 1978 

YEARS 

Figure 3.--Ex-vessel value of albacore in the American Samoa longline 

fishery. 

1978.) 

(Data from [U.S.] National Marine Fisheries Service 1969- 
-221 - 

11" I"I'1' 

.c 

, Ill 11,111 I I,l 

1960 1965 I970 1975 1955 

YEARS 

Figure 4.--Fraction of the estimated total South Pacific longline catch 

of albacore landed at American Samoa, 1954-76. (Data from Wetherall et 

al. see text footnote 1.) 
-222- 

I I1 .B. Stock Assessment and Fishery Eva1 uation 

III.B.l. Trends in Catch-per-Uni t-Effort 

Annual indices of abundance based on catch per 1,000 

hooks by longliners based at Pago Pago and adjusted for changes in spatial 

distribution of nominal fishing effort (Wetherall et al. 1979; see footnote 

1) show a fairly steady decline in catch-per-unit-effort from the beginning 

of the index period in 1962 to 1974 (Table 4). 

uni t-effort has steadily increased. 

Since 1975 the catch-perI11 .B.2. Results of Production Model Analysis 

The most recent production model analysis of the South 

Pacific albacore fishery was based on the abundance index and effective 

effort statistics displayed in Table 4 (Wetherall et al. 1979; see footnote 

1). 

The results, shown in Figure 5, suggest that further expansion of the 

longline fishery would be unproductive. 

reduce effort substantially with little reduction in catch. The MSY 

(maximum sustainable yield) of the longline fishery was estimated to be 

about 35,000 mt. 

The Gul land procedure for approximating equil ibrium effort was used. 

Indeed, it may be possible to 

I I I. B .3. Resul ts of Yi el d-per-Recrui t Analysi s 

No cohort analyses have been attempted with South Pacific 

albacore due to the extreme difficulty of separating year-classes in the 

1 ongl ine catch. Furthermore, no yield-per-recruit analysis has been done, 

in the usual sense, but a simulation model linking a yield-per-recruit 

model with a1 ternative stock-recrui tment hypotheses has been explored (see 

Section III.B.5). 

111.6.4. Results of SDawner/Recruitment Analyses 

No analysis of the spawner-recruit process has been done, 

nor are data available which would permit such a study. Wetherall et a1 . (see footnote 1) estimated the average recruitment of 2 year-old a1 bacore 

to be 8.4 million fish. Average spawning stock (fish over 5 years old) 

corresponding to this average recruitment, in the absence of fishing and 

with growth and natural mortality rates as given by Wetherall et a1 . , is 

about 130,000 mt (see Section III.B.5). 

I I1 .B.5. Resul ts of Other Analyses/Simul ations 

An age-structured simulation model was constructed by 

Wetherall et a1 . to study the response of maximum sustainable yield of the 
-223- 

Table 4.--Index of a undance (kg/100 hooks), and estimated total effective effort (10 k hooks) for the South Pacific albacore fishery. 

Effect ‘ve effort b Abundance index 

Year (kg/100 hooks) (10 hooks) 

1962 146.00 27 

1963 85.76 41 

1965 72.02 38 

1966 63.66 65 

1967 42.56 107 

1968 33.76 96 

1969 41.03 62 

1970 35.42 87 

1971 29.90 136 

1973 20.19 2 44 

1974 13.86 252 

1975 13.64 198 

1976 18.00 203 

1964 75.39 33 

1972 21.45 190 

1977 21.71 191 
-224- 

I I I I 

*77 e73 

e76 

a 

m $ 15 

8 

51 

I I I 

50 100 150 200 

EFFECTIVE EFFORT ( IO' HOOKS) 

Figure 5.--Projected relationship between equilibrium yield and effective 

effort for South Pacific albacore, based on production model with 3-yr 

effort averaging. (From Wetherall et a1 . see text footnote 1 .) 
-225- 

c 

albacore stock to changes in age at-first-capture under a variety of stock 

recruitment hypotheses. Under constant recruitment, MSY was judged to be 

about 38,000 mt at an age-of-first-capture of 4 years, but MSY at 3-year o

5-year minimum age limits was only slightly less. Under more conservative 

stock-recrui tment hypotheses, 1 ower MSY' s were computed and were achieved 

at progressively higher ages-at-first-capture. The results of the 

simulation analysis are considered to be preliminary. 

1II.C. Current Evaluation of Stocks and the Fishery 

The South Pacific albacore stock is considered to be in a healthy 

condition. 

considerably to perhaps 20% of its initial level, but unless recruitment is 

strongly dependent on size of spawning stock, such a reduction can be 

sustained. There is no indication of recruitment failure. Following its 

peak in 1973 the nominal effort has been reduced. Catch rates have 

increased; therefore, average annual catch has increased in spite of lower 

effort. 

Catch-per-unit-effort in the long1 ine fishery has been reduced 

Further reduction in longlining effort should be beneficial. 

Expansion of surface fisheries may be feasible. 

baitboats are known to be considering exploratory a1 bacore fishing 

expeditions in the region of the subtropical convergence east of New 

Zeal and (Shiohama 1979). 

Indeed, Japanese 

IV. STATUS OF CURRENT RESEARCH NEEDS AND EFFORTS 

1V.A. Major Research Problems 

Eva1 uation of potential s for expanding surface fisheries on South 

Pacific albacore is an important area for research. 

theoretical studies of stock productivity using age-structured simulation 

models, 2) possible tagging of 2- and 3-year old albacore available to 

development of the surface gear, 3) evaluation of recapture rates in the 

1 ongl ine fishery, and 4 

using the wealth of observations on the subsurface longline operations. 

This would require 1) 

methodol ogy to predict surface fi shery potential s 

1V.B. Current Research Efforts 

Current work on South Pacific albacore by the SWFC includes: 

1) 

general upgrading of the American Samoa catch-per-uni t-effort and 

landings statistics. 

Improving the data base for South Pacific albacore through a 
-226- 

2) Development of a fishery monitoring and information system 

for South Pacific a1 bacore. 

3) Eva1 uation of procedures to estimate surface fishery poten- tial s using the age-structured simulation model and production model 

analyses based on selected segments of the popul ation. 

was done in April and May of 1980 and will be continued in FY 1981. 

Prel iminary work 

1V.C. Future Research Needs 

None proposed at this time. 

1V.D. Status of SWFC Data Base 

The Far Seas Fisheries Research Laboratory has maintained albacore 

catch statistics of Japanese longliners fishing in the South Pacific since 

1952. 

respective flag vessels fishing in the South Pacific. Some of these data, 

and data from the fishery based at Pmerican Samoa, are available on tapes 

in the files of the Honolulu Laboratory. 

available from FA0 and the New Zealand Government. 

The governments of Taiwan and Korea also compile data on their 

Data on surface catches are 

Logbook systems maintained by Japan, Korea, and Taiwan provide 

data on catch I“n number of fish, effort in number of hooks fished, and 

locality fished for each day of fishing. 

also collects logbook data providing the same kinds of data from vessels 

based at Pago Pago. collected by the governments of Japan, Taiwan, and American Samoa. 

addition, “,he Honolulu Laboratory maintains files of landings statistics 

provided by the two canneries in American Samoa. 

The government of American Samoa 

Data on the size composition of the catches are 

In 

The qual i ty of logbook data is probably adequate for production 

model analyses. The quality of the size-composition data is inadequate, 

since time and location of capture cannot be accurately determined. 

to changes in unloading procedures at the tuna canneries, sex and weight 

determinations were discontinued in 1970, but length-frequency data are 

still being collected in American Samoa. 

Owing 

LITERATURE CITED 

Otsu, T. 

1966. The South Pacific long-line fishery for albacore tuna, 

1954-64. Commer. Fish. Rev. 28(7): 9-12. 
-227- 

Shiohama, T. 

1979. Considerations on the pole fishing in the longline filleted 

skipjack ground of albacore. [In Jpn.] Bull. Jpn. SOC. Fish. 

Oceanogr. 34: 170-173. 

Skillman, R. A. 

1975. An assessment of the South Pacific albacore, Thunnus 

alalunga, fishery, 1953-72. U.S. Natl. Mar. Fish. Serv., Mar. 

Fish. Rev. 37(3): 9-17. 

[U .S.] National Marine Fisheries Service. 

1969-1978. Foreign fishery information release. Supplement to 

Market News Report. 

c 
-228- 

STATUS REPORT: NORTH PACIFIC ALBACORE 

Earl Weber 

Southwest Fi sheries Center 

Oceanic Fisheries Resources Division 

La Jolla, California 

ABSTRACT 

The North Pacific albacore stock is harvested primarily by the 

Japanese surface and longline, and North American surface fleets. 

of these fleets have been in the vicinity of 100,000 mt in recent years, 

with a record catch of nearly 124,000 mt in 1976. The North American 

surface fi shery , comprised primarily of U .S. troll vessel s , 1 anded an 

annual average catch of approximately 20,000 mt during the period of 1969 

through 1978 but landed less than 5,000 mt in 1979. The U.S. imports an 

additional 80,000 to 90,000 mt of albacore to meet domestic demand and a 

substantial part of this originates from the North Pacific stock. 

Catches 

A1 though heavily harvested, the stock is considered heal thy. Effort 

levels in recent years have been below those required to produce maximum 

average sustainable yields (MASY) . indicated a decrease in Y/R following the expansion of the Japanese surface 

fishery. Slight gains in Y/R are possible through increased effort on 

larger fish but substantial gains are unlikely with the fishery i n i t s 

present configuration. Catch rates for all three major fleets have shown 

gradual decreasing trends. 

Yield-per-recruit (Y/R) analyses 
-229- 

I. DESCRIPTION OF THE FISHERY 

I.A. History of Fishery 

Albacore (Thunnus alalunga) is a single species found world-wide in 

most temperate ocean areas. In the Pacific Ocean, north and south stocks, 

separated near the equator, are thought to exist. 

The North Pacific stock is fished by three major fleets: the 

Japanese surface fleet, the predominantly Japanese longline fleet, and the 

North Pmerican surface fleet. The Japanese skipjack pole-and-1 ine fleet, 

which has been operating during the spring months since the 192O's, began 

expanding its operations offshore along the Kuroshio front in the early 

1970's. As a result, it has substantially increased its catches, 

particularly of two-and three-year-old a1 bacore. The 1 ongl ine fishery, 

comprised primarily of Japanese vessels with some from Taiwan and Korea, 

has been operating in the mid-to western north Pacific during the winter 

months since the early 1950's. The North American surface fleet consists 

primarily of U.S. vessels with some Canadian vessels. This fleet, mostly 

jigboats or trollers with some baitboats, has been fishing off the coast of 

North America since about 1900. 

I.B. Trends in Catch and Effort 

Yearly catches, by country and gear type, are shown in Table 1 for 

Data are missing for some countries prior to 1961, but the 

Catches 

1940-1978. 

remainder of the series is considered to be essentially complete. 

for the Japanese surface, Japanese longl ine, and North American surface 

fleets, and the combined total catches, are shown in Figure 1 for 1961- 

1978. During 1961-1974, the total catch increased, particularly in the 

early 1970's, with a record catch of 114,858 mt in 1974. 

declined to 86,327 mt in 1975 but rose to a new record of almost 124,000 m

in 1976. Total catches have decreased since 1976. The trends in the total 

catch in the 1970's reflect changes in the Japanese surface fishery, which 

became the major producer during this period. 

fishery catches decreased from 1967 through 1975, and have increased only 

slightly since then. The North American fishery catches, characterized by 

periodic increasing and decreasing trends, have been declining since 1972. 

Preliminary data indicate a 1979 catch of 4,938 mt, one of the poorest 

years on record. 

The catch 

The Japanese longl ine 
-230- 

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-231 - 

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I- 70- 

60- 

150- 

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TOTAL 

North America 

- 

- Japanese surface 

---- Japanese long I he 

01 1 I 1 1 I 1 I I I I I I I I I I I J 

61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 70 

YEAR 

Figure 1. Yearly catches of North Pacific albacore, by weight, by 

the Japanese surface, Japanese longline, North American 

surface fishery and the total catches for years 1961 to 

1978. 
-232- 

Yearly effort for the Japanese surface, Japanese longline, and 

U.S. surface fisheries are shown in Figure 2. Units o f e f f o r t among 

fisheries cannot be compared because effort has not been successfully 

standardized; therefore, no attempt is made here to describe trends in 

total effort. 

Effort in the Japanese pole-and-1 ine fishery, currently the 

major producer, increased substantially in the 1970's. Effective effort in 

the Japanese long1 ine fishery decreased dramatically from 1967 through 

1975, then increased slightly in years 1976 through 1978. Effort in the 

U.S. fishery was reasonably constant throughout the 1960's but more than 

tripled between 1970 and 1972. This apparent change may be partially an 

artifact of changes in the statistical reporting system. 

through 1977 appears to be stable at a level well below that reported for 

1972, but above that for the 1960's. 

Effort from 1973 

I.C. Value of the Catch 

The U.S. fleet landed an annual average of 20,400 mt of albacore 

between 1969 and 1978. 

annual catch was worth $37 million. 

At current ex-vessel prices ($1800/mt), the average 

I.D. Current Management of the Fishery 

There is currently no organization responsible for the management 

of fisheries for North Pacific albacore. 

11. NATURE AND SIGNIFICANCE OF U.S. AND FOREIGN 

PARTICIPATION IN THE FISHERY 

Albacore, which is generally canned in water and marketed as white 

meat tuna, is a popular product in the U.S. The U.S. surface fishery 

currently consists of more than 900 vessels; from 1969 to 1978, these 

vessels landed an annual average of 20,440 mt worth an average of $37 

mill ion (ex-vessel Because demand exceeds supply, 80% 

of the total U.S. demand is typically imported from as many as 40 

countries; an estimated 40% to 45% of the imports originate from the 

Pacific, historically the most heavily harvested ocean (Figure 3). 

Although the exact proportions of the Pacific imports that originate in the 

North Pacific are not known, they may be as high as 75% in some years. 

In recent years some U.S. fishermen have begun fishing in the 

vicinity of Midway Island, where they have experienced high catch rates. 

Foreign participation has a1 so increased. 

became the major producer of North Pacific albacore in the early 1970'~~ 

at current prices. 

The Japanese surface fishery 
-233- 

m- 0 201 

- I 

Y 

O Llot /- "I 

I I I I I I I I I 

h 

(D 

o 500. 

JAPANESE LONGLINE FISHERY 

100 - 

OL I I I I I I I I 

- 

60- NORTH AMERICAN 

- SURFACE FISHERY 

40 - 

20 - 

- 

0. 

1961 1963 1965 1967 1969 1971 1973 1975 1977 

I I I I 1 I I I 

Figure 2. Yearly effort in the Japanese surface, Japanese longline, 

and North American surface fishery for years 1961 to 1978. 
-234- 

AM 

% 

Figure 3. Percentages, by weight, of albacore caught by ocean in 1977. 
-235- 

_*A when it expanded its pol e-and-1 ine operations offshore a1 ong the Kuroshio 

front. The developing Japanese coastal gill net fishery has also begun 

reporting catches of North Pacific albacore, as have the longline fleets of 

Taiwan and Korea which have recently begun fishing in the North Pacific. 

111. STATUS OF THE STOCKS 

The status of North Pacific albacore was assessed by participants 

attending the Fifth North Pacific Albacore Workshop held in June and July 

1980. 

1II.A. Stock Structure 

The Pacific albacore population is assumed to be composed of north 

and south stocks separated near the equator. The complex migratory 

patterns of juveniles within the north stock have led some scientists to 

hypothesize that more than one stock exists in the North Pacific, but not 

enough is currently known about the migration of adults to substantiate 

this hypothesis; therefore, a single north stock is assumed. 

- 111.6. Stock Assessment and Fishery Evaluation 

I I I. B . 1 . Trends i n Catch- per- Un i t-E f fort 

Because of difficulties associated with standardizing 

effort among the different gears, an overall index of abundance for the 

entire fishery is not available. However, catch-per-unit-effort (CPUE) for 

the Japanese surface, Japanese longline, and U.S. surface fisheries (Figure 

4) have all shown decreasing trends in recent years. 

111.6.2. Results of Production Model Analysis 

Production model analysis is also problematic due to the 

effort standardization problem. 

workshop (Figure 5) predicted a maximum sustainable average yield (MSAY) of 

between 104,000 and 236,000 mt. 

"best" value, the midpoint of 170,000 mt may be reasonable. 

An analysis prepared for the a1 bacore 

Although it is impossible to select a 

111.6.3. Results of Yield-per-Recruit Analysis 

Yield-per-recruit (Y/R) analyses indicate that the 

expansion of the Japanese surface fishery in the early 1970's decreased the 

c" Y/R for the entire fishery (Figure 6). While the Y/R for the Japanese 
-236- 

0.8 

0.6 

h 

- 

- 

JAPANESE LONGLINE FISHERY 

6 

U 

\ 

I2 

Y 

0 

CD 

0 

;1: 

2 

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a4- 

2- 

0 

JAPANESE SURFACE FISHERY 

I I I I 1 I I 1 - 

0.0 ' 1 I I 1 I I 1 I I 

- 

40 - NORTH AMERICAN 

- SURFACE FISHERY 

0 

1961 1963 1965 1967 1969 1971 1973 1975 1977 

I I I I I I i I 

Figure 4. Yearly catch rates of North Pacific albacore in the 

Japanese surface, Japanese longline and North American 

surface fishery for years 1961 to 1978. 
-237- 

"- 

15 

IO 

5 

0 

74 - 76 . / 

73 / 

73. 

7 

/ 

M=1.001 

M =2 

I 11111111111111111111lllllll 

0 5 IO 15 20 25 30 

STANDARD FISHING EFFORT IN lo4 UNITS 

Figure 5. Equilibrium yield curves and observed data for North 

Pacific albacore, years 1961 to 1978. 
-238- 

120- 

110- 

100 

90 

80 

70 

E 60- 0 

v- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

I- 50- 

kzW 

2 40- 

3 

Figure 6. Estimated yield-per-recruit, as functions of age at recruitment and fishing mortality vector multiplier, of North Pacific 

albacore taken before and after 1971 by all gears combined. 

I I I I I I 1 I I I I I I I I I I 
-239- 

surface fishery increased, the gains were not enough to offset the 

decreases in Y/R for the longline and North American surface fisheries. 

The analyses predicted that gains in Y/R were possible through increased 

effort on larger fish. Y/R isopleths for the Japanese surface, Japanese 

longline, and North American surface fishery are shown in Figures 7, 8, and 

9, respectively. 

III.B.4. Results of Spawner/Recruitment Analysis 

No satisfactory spawner/recrui t re1 ationship has been 

establ ished. 

of spawner and recruit abundance. 

Previous analyses have failed to develop appropriate indices 

III.B.5. Results of Other Analyses/Simulations 

Additional analyses have shown very poor correlation 

between indices of abundance among the three major fisheries, even when 

annual age specific catch rates were used. 

1II.C. Current Evaluation of Stocks and the Fishery 

At present North Pacific albacore are being fished at effort levels 

below those that permit harvest at MSAY. 

through increased effort on older fish, but substantial increases are 

unlikely given the present patterns of fishing. There is currently no 

evidence to indicate a depletion of the adult (spawner) stock. 

Modest gains in Y/R are possible 

IV. STATUS OF CURRENT RESEARCH NEEDS AND EFFORT 

1V.A. Major Research Problems 

The most immediate research needs include: 1) Development of noneffort based assessment methods to augment the existing analytical models; 

2) validation of currently accepted growth rate of North Pacific albacore, 

which are determined from daily otolith increments using a newly developed 

fin ray technique; 3) re-examination of the population dynamics of the 

stock in the light of recent and future improvements in parameter 

estimation; 4) investigation of stock structure through differences in 

bio-chemical information among fish from different areas, through the study 

of oceanic phenomena that might explain stock separation and through the 

development of a model to test various stock structure hypotheses; and 5) 

the identification and quantification of environmental variables for input 

catch levels and catch rates, among and within the major fisheries. 

- into an environmental simulation model designed to explain variability in 
-240- 

I- 50- 

kzW 

40- 

3 

BAITBOAT - BEFORE 1971 

I I I I I I I I I I I I I I I I I 

Figure 7. Estimated yield-per-recruit, as functions of age at recruitment and fishing mortality vector multiplier, of North Pacifi

albacore taken before and after 1971 by the Japanese surface 

fishery . 
-241 - 

120r 

- 

110 - 

- 

100 - 

- 

90 - 

- 

80 - 

- 

70 - 

LONGLINE - BEFORE 1971 

I1 0 

$ 120. 

E 110 

(3 

z 

w 100 -J 

90 

80 

IO3 07 

- LONGLINE - AFTER 1971 

O50 

40 

0 45 

I I I I I I I I I I I I I I I I I 1 I 

02 04 0.6 0.8 IO 12 14 1.6 1.8 2.0 

MULTIPLIER OF EFFORT 

Figure 8. Estimated yield-per-recruit, as functions of age at recruitment and fishing mortality vector multiplier, of North 

Pacific albacore taken before and after 1971 by the 

Japanese 1 ongl i ne fishery . 
-242- 

JIGBOAT - BEFORE 1971 

I I I I I I I I I I I I I I I I I I I 

02 0.4 06 0.8 IO I .2 14 16 I .8 2.0 W 

(L 

JIGBOAT - AFTER 1971 

50 

40 

c -2 0 

.c 20 

I I I I 1 I I I I I I I I I I I I I 

0.2 0.4 0.6 0.8 1.0 1.2 I .4 1.6 18 2 .o 

MULTIPLIER OF EFFORT 

Figure 9. Estimated yield-per-recruit, as functions of age at recruitment and fishing mortality vector multiplier, of North Pacific 

albacore taken before and after 1971 by the North American 

surface fishery. 
-243- 

1V.B. Current Research Efforts 

IV.B.l. Research Conducted by SWFC 

Research efforts in 1980 were directed toward: 1) 

assessment of the stock using conventional techniques such as cohort, 

yield-per-recrui t, and spawner/recruitment analyses, and 2) development of 

a fi shery/environment simulation model intended to describe mathematically 

the fish-fishery interaction and test hypotheses on the effects of 

management actions on the stock. This model is also intended to guide 

future research. Additional research efforts are being conducted by the 

A1 bacore Fisheries Investigation in the Coastal Fisheries Resources 

Division of the SWFC, La Jolla. 

A1 bacore Oceanography Research --This research is 

designed to gain understanding of the environmental effects on albacore 

distribution, availability, migration, vulnerability, and possible 

abundance. 

key environmental processes that may be used in fi sh/fi shery/environment 

models for use in providing advice for eventual international management o

the North Pacific albacore resource. Specific studies include 1) the 

influence of North Pacific Transition Zone frontal structure on a1 bacore 

migration, distribution, and availability, with studies being conducted 

using data from research cruises, cooperating fishing vessels through joint 

studies with AFRF and others, and historical data files; 2) acoustic 

tracking studies to determine albacore depth distribution and optimal ocean 

temperature re1 ationships that may affect avail abil i ty and vu1 nerabil i ty; 

3) the influence of coastal upwell ing on avail abil i ty and vu1 nerabil i ty , using fishery data from logbooks and upwelling indices from PEG; 

sate1 1 i te-oceanography studies to evaluate the use of ocean measurements 

made from space to monitor key oceanographic conditions that infl uence 

albacore distribution, migration, and availability; and 5) the development 

of indices of environmental conditions affecting albacore for use in 

fish/fishery/environment models, using historical data bases and data from 

research vessel s and cooperating fishery vessel s. 

The goal of the research is to develop quantifiable indices of 

4) 

A1 bacore Biology Research --The objective of this 

research is to gain knowledge and understanding of selected areas of 

a1 bacore biology for use in a1 bacore oceanography research and popul ation 

assessment studies. Specific research areas include: 

1) Age and Growth Studies--These are being conducted using 

albacore tag release and recovery data from the cooperative NMFS/AFRF albacore tagging program, and the otolith 

daily ring increment method of ageing fish. The latter, 

which is part of the tagging program, involves a field/ 

laboratory study to evaluate the rate of otolith ring formation in albacore, using injection of tetracycline to 

''mark'r otoliths at time of release of tagged albacore. In 

addition, a study is being conducted in -3Qperation with 
-244- 

Canadian fishery scientists, as recommended at the Fourth 

North Pacific A1 bacore Workshop (NPAWS), to intercal ibrate 

and evaluate the otolith daily ring increment and fin 

ray circular methods for ageing albacore. 

2) Stock Structure Studies--These studies are being conducted 

to determine if the North Pacific albacore population is 

composed of more than one substock, as has been indicated 

by results from the cooperative NMFS/AFRF tagging program. 

The studies are being conducted using data on tag release 

and recovery, and size composition. In addition, samples 

have been coll ected for biochemical investigation (to be 

done at Scripps Institution of Oceanography) as recommended at the Fourth North Pacific Albacore Workshop. 

Migration Studies--These studies are designed to examine 

albacore migration on trans-oceanic macroscales and within region mesoscales. They are related to 1) the investigation of stock structure and 

the distribution of proposed substocks of North Pacific albacore, and 2) 

a1 bacore oceanography studies which investigate the role of environmental 

factors and conditions that influence the timing and rate of albacore 

migrations. 

size composition data, fi shery-oceanography data gathered from cooperating 

f i shi ng vessel s and research crui ses, and resul ts from acoustic tracking 

experiments. 

These studies are conducted using data on tagging and release, 

Environmental Physiology Studies--These studies are 

designed to gain understanding of a1 bacore physiol ogical/biochemical 

processes, with an emphasis on thermoregulation and the role that it may 

pl ay in understanding causal factors operating in f i sh-ocean re1 ationships. The studies are carried on cooperatively with fishery 

physiologists and medical research scientists from universities and private 

research foundations. Experiments are carried on aboard ship with live 

albacore; in some cases, albacore specimens and samples are collected at 

sea and analyzed in the laboratory. 

transport live albacore to shoreside facilities and hold them in 

captivity. 

NMFS; major equipment and supplies are provided by the individual 

cooperating scientists. 

There have also been attempts to 

Shiptime, 1 imited equipment, and some supplies are provided by 

Foreign scientists from Japan, Canada and Taiwan are 

a1 so engaged in r e 1 a t e d research activities. 

areas as population dynamics, migration patterns, oceanography, and growth 

rates. 

These include such research 
-245- 

IV.B.2. A1 bacore Fishery Advisory Service 

The overall goal of the fishery advisory service is to 

develop a real-time fishery management system whereby fishery information 

required for proper management can be exchanged between fishery/ 

managers/scientists and the fishing industry. Only the rudiments of such a 

system are in operation at the La Jolla Laboratory, including: 1) seasonal 

forecast of the timing and distribution of the fishery issued prior to the 

start of the season; 

fishing season by mail to fishermen, processors, fish buyers, and moorages; 

3) daily albacore fishing broadcasts transmitted during the fishing season 

by radio station WWD, Point Reyes Coast Guard, and four commercial radio 

stations along the Pacific west coast; 4) contacts with albacore fishing 

industry and sportfishermen in the form of oral presentations at meetings 

and workshops, and answering several hundred telephone and mail inquiries 

for information concerning a broad range of topics about albacore received 

from fishermen and others in the fishing industry, scientists, students, 

recreational fishermen, and interested pub1 ic. 

2) bi-weekly fish bulletins distributed during 

1V.C. Future Research Needs 

1) Hypotheses need to be formulated which are concerned with stock 

structure, migration, mortality, availability, and the role of environment 

in affecting the abundance of North Pacific albacore. 

environmental indices necessary for hypothesis testing must be identified 

and quantified for use in a fishery model currently under development. 

This model will provide a focal point for many of the albacore research 

projects, serving as a means of analyzing various data fields and testing 

f i shery hypotheses. 

YFishery and 

2) Studies of age and growth are proposed, which will improve the 

age-specific fishery data that are the basis of fishery assessment work. 

1V.D. Status of SWFC Data Base 

North Pacific albacore data are stored on magnetic tape at the 

Southwest Fisheries Center. These data are adequate for non-effort based 

assessment work and are, with few exceptions, complete. Needed are 

historical data from the Korean longline fishery, and data from the 

Japanese high seas drift gill net squid fishery which is taking incidental 

catches of small (approximately 20 cm) albacore and discarding them dead. 

Recently emphasis has been placed on obtaining catch, effort, and size 

frequency data from individual catcher vessels of the U.S. fleet. These 

data will provide for more precise parameter estimation. 
-246- 

STATUS REPORT: NORTH PACIFIC BLUEFIN TUNA 

Doyle A. Hanan 

California Department of Fish and Game* 

ABSTRACT 

Northern Pacific bluefin tuna are fished by surface gear including 

purse seine, xrolling, bait, gill net, trap, and harpoon in the eastern and 

western Pacific. 

Pacific and, to a lesser extent, in the central and eastern Pacific and the 

east Indian Ocean. 

Bluefin are also caught by longline in the western 

The resource appears to be composed of a single stock; the western 

Pacific catch is composed of juveniles and mature adults while the eastern 

Pacific catch consists mainly of 1-, 2-, and 3-year old fish. Presence of 

a second stock off New Zealand is not confirmed by studies. 

*At the Southwest Fi sheries Center , La Joll a , Cal ifornia , under 

Cooperative Agreement 81-ABH-0040. 
-247- 

I. DESCRIPTION OF THE FISHERY 

I.A. History of the Fishery 

c" 

c 

A surface sport fishery for bluefin existed in the California Bigh

Bluefin hav

as early as 1898, but commercial fishing did not begin until seines were 

tried about 1914; the first large catch was reported in 1918. 

historically been fished opportunistically by the San Pedro purse seine 

fleet in the California Bight. When larger tuna baitboats converted to 

seining in the late ~O'S, the effective fishing range was extended to 

include the area from Cab0 San Lucas to Point Conception, and occasionally 

as far north as British Columbia. 

In the western Pacific, traps were first used to catch bluefin; 

purse seining began about 1950, with the first important catches about 

1958. Trolling gear, baitboats, gill nets, and harpoons are used near 

Japan. A multispecies longline fishery, with smaller boats (less than 50 

tons) operating near Japan and larger boats ranging throughout much of the 

Pacific (Figure 21, also takes bluefin tuna. 

A bluefin fishery in the eastern Pacific consists of the local 

purse seine fleet out of San Pedro, California, and the "high seas" tuna 

fleet based in San Diego, California. Since 1975, Mexico has entered the 

fishery with an expanding purse seine fleet out of Ensenada, Mexico. 

The western and central Pacific fishery is dominated by Japan; 

however, Taiwan and Korea are also operating longline fisheries in that 

area. 

1,B. Trends in Catch and Effort 

In recent years, North Pacific bluefin contributed about 1% to the 

world tuna catch. From 1918 to 1958, the North Pacific bluefin catch 

averaged 5,066 metric tons (mt) per year (Table 1). After the "high seas'' 

baitboats converted to seining in the late ~O'S, the fishery expanded to 

the waters off Baja Califoria, and the average yearly catch in the eastern 

Pacific climbed to 9,076 mt. A running 10-year average of the bluefin 

catch in the eastern Pacific reveals an overall decline since 1961, 

underscored by a projected 1980 catch of 3,000 mt (Figure 1). Further 

emphasizing a decline in the bluefin catch is the eastern Pacific sport 

catch, which averaged 7,532 fish per year during 1936 to 1957, but decline

to 1,835 fish per year during 1958 to 1979 (Table 1). 

The commercial fishery in the western Pacific (which began about 

1958) has a mean annual catch for 1964 to 1978 of 14,700 mt, with a range 

from 4.8 to 30 thousand mt (Table 1). 

to levels comparable to the eastern Pacific catch. 

data for the western Pacific is not available at this time. 

It also shows a significant decline 

A summary of effort, 
-248- 

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-250- 

Figure 2. Average annual distribution of northern bluefin caught by 

Japanese longliners during 1972 to 1976 (after Wm. Bayliff, 

1979, Inter-American Tropical Tuna Commission, Annual Report). 
-251 - 

I.C. Value of Catch 

Ex-vessel prices for bluefin at Cal ifornia canneries have 

historically been set just below yellowfin prices, but above those for 

skipjack. In 1979, 6,743 mt at an ex-vessel price of $1,023/mt were caugh

in the eastern Pacific, for an ex-vessel value of $6.9 million. Although 

the price increased to $1,298/mt in 1980, only about 3,000 mt have been 

caught for an ex-vessel value of $3.9 million. In 1980 about 130 mt of 

bluefin were delivered to the Los Angeles fresh fish markets at prices nea

$2,20O/mt, for a value of about $300,000. 

Ex-vessel prices of northern Pacific bluefin at Yaizu, Japan, 

fluctuated between $4,400 and $13,97O/mt in 1979. In all, 454 mt were 

landed for a value of $2.5 million. During 1980, the price has fluctuated 

between $2,310 and $15,95O/mt; through September, 1,179 mt were landed for 

an ex-vessel value of $5.1 million. 

The total value of combined eastern and western Pacific ex-vessel 

price data for northern Pacific bluefin for 1980 was about $9 million. 

I.D. Current Management of the Fishery 

The only regulation of eastern Pacific bluefin is a 7.5-lb size 

limit in California, but the limit is superfluous since bluefin of that 

size are rare in the eastern Pacific. In the western Pacific, there are 

some regulations on the number of vessel s fishing for particular species, 

but this is not restricted to bluefin. 

11. NATURE AND SIGNIFICANCE OF U.S. AND FOREIGN 

PARTICIPATION IN THE FISHERY 

The U.S. commercial fleet currently fishes bluefin incidentally, as 

most of the tuna effort is directed towards yellowfin and skipjack. Since 

the ex-vessel price of bluefin is only $20/short ton less than that for 

yellowfin, skippers will set on bluefin, if a school of sufficient size is 

located, or will "top off" the load with bluefin on the return to port. 

Since most of the U.S. catch is taken within ZOO miles of the shore 

off Baja California, the negotiations concerning Mexico's ZOO-mile 1 imit 

will have significant bearing on future U.S. catch of bluefin. 

of U.S. fishing from current bluefin areas could shift the U.S. fishing 

effort beyond the Mexican 200-mile limit, or return it to the California 

Bight. 

Exclusion 
-252- 

111. STATUS OF THE STOCKS 

1II.A. Stock structure 

North Pacific bquefin spawn near the surface from April to July in 

the Philippine Sea. 

gear until their first or second winter, when some migrate to the eastern 

Pacific to enter the fishery during May to October. Data based on 11 

transpacific tag returns show that the fish may remain in the eastern 

Pacific 1 to 3 years before making the 2-year migration back to thespawning grounds. 

Northern Pacific bluefin are a1 so reported in the Austral ia-New Zealand 

area, but the origin of these fish is unclear (Figure 3). 

Young fish remain near Japan and are fished by surface 

Longliners probably exploit this returning migration. 

1II.B. Stock Assessment and Fishery Evaluation 

I I I . B . 1 . Trends i n Catch- per-Un i t-E f fort 

This preliminary analysis is based on the summary data 

for 1957 to 1966 from a recent California Department of Fish and 

Game/National Marine Fisheries Service study, plus adjusted Inter-American 

Tropical Tuna Commission (IATTC) figures for 1966 to 1979; both are 

expanded to represent the eastern Pacific catch (Table 1). 

complete time series, the catch-per-uni t-effort (CPUE) index decl ines 

s l i g h t l y (b = -0.123 per year) , with a mean vaue of 2.45 mt per day (SD = 

1.4). The mean CPUE for the most recent 12 years (x = 1.8, SD = 0.49) is 

about half that of the previous 10 years (x = 3.28, SD = 1.721, while 

nominal effort during this 22-year series has not significantly increased 

(b = 0.07 per year). 

Over the 

III.B.2. Results of Production Model Analysis 

None avail ab1 e. 

III.B.3. Results of Yield-per-Recruit Analysis 

None available. 

III.B.4. Results of Spawner/Recruitment Analysis 

None avail ab1 e. 
-253- 

Figure 3. A model for northern bluefin migration in the Pacific Ocean 

(after Wm. Bayliff, 1979, Inter-American Tropical Tuna 

Commission, Annual Report). 
-254- 

III.B.5. Results of Other AnalvseslSimulations 

None available. 

1II.C. Current Evaluation of Stocks and the Fishery 

The decline in bluefin catches in recent years cannot at this time 

be attributed to a particular cause because none of the necessary analyses 

have been done. 

IV. STATUS OF CURRENT RESEARCH NEEDS AND EFFORTS 

1V.A. Major Research Problems 

Basic fishery models are needed for this resource, which is not 

currently being managed. 

trans-Pacific, mu1 ti-national nature of the fishery. Better data are 

particularly needed for the western Pacific, as there is difficulty in 

separating northern from southern bluefin in the Japanese data. 

A major problem in developing the models is the 

1V.B. Current Research Efforts 

Two research programs are currently underway on bluefin tuna. The 

Inter-American Tropical Tuna Commission (IATTC) has three biologists at 

SWFC who are 1) assembling logbook information from IATTC files, 2) writing 

a synopsis of biological data, 3) tagging bluefin in season, and 4) 

starting growth studies using tags and scale reading. IATTC also has a 

biologist doing tagging studies of juvenile bluefin near Japan. In 

addition, NMFS and CF&G have a joint project at SWFC: one biologist is 

evaluating existing bluefin data and will attempt to develop any fisheries 

models that are appropriate. 

1V.C. Future Research Needs 

1) An attempt should be made to merge western and eastern 

Pacific fishery data since evidence points to a single stock. 

2) 

both west and east. 

Indices of abundance need to be developed and refined for 
-255- 

3) Exploitation rates need to be developed. 

4) Management model s such as yield-per-recrui t and surplus 

production need devel opment. 

5) Factors relating to management, such as time-area patterns 

of occurrence, need evaluation. 

IV.C.l. Suaaested ADDrOaCh and Methods 

In addition to current work being done at SWFC, the 

foll owing projects might be considered: 

1) Exploitation rates could be developed for the 

eastern Pacific uti1 izing information obtained from tagging, cohort 

analysis, mortality, and emigration analyses yet to be done. 

2) Aerial spotter information might be used to develop 

indices of abundance. 

1V.D. Status of SWFC Data Base 

The data base, which has been established this year via the NMFSCF&G project, consists of eastern Pacific tuna logbook data, 1957 to 1970, 

1974; length-frequency data, 1923 to 1925, 1951 to 1966; 1 ength-weight-age 

data, 1963 to 1971; length-weight data, 1960 to 1965, 1971 to 1974; monthly 

California landings, 1926 to 1976; tag return data, 1953 to 1969; and a 

vessel ' 1 ist, 1957 to 1978. 

The data base for the western Pacific is the Japanese longline 

information, 1962 to 1980; the Japanese baitboat information, 1970 to 1976; 

and the Taiwanese deep sea longline information, 1967 to 1975. 

.- 
-256- 

STATUS REPORT: PACIFIC SWORDFISH 

by 

James L. Squire, Jr. 

Southwest Fisheries Center 

Oceanic Fisheries Resources Division 

La Joll a, Cal ifornia 

ABSTRACT 

The stock structure of swordfish populations in the Pacific is not 

clear. Information and data evaluated at the Billfish Stock Assessment 

Workshop suggest the population consists of either a single Pacific-wide 

stock, or northwestern, southwestern, and eastern Pacific stocks. For the 

1952-1963 data series, a production model analysis gave a Pacific-wide MSY 

estimate of 20,000 mt with an effort level of 2.2 million hooks/5" area. 

The average (1966-1975) catch of 14,000 mt produced by 1.8 million hooks/5" 

area indicates that the fishery does not appear to be overexploiting the 

stock, and that the stock is in good condition. 

Recent catches (1978) indicate levels of total catch equalling about 

18,000 mt, approximately 2,000 mt less than MSY. High demands world-wide 

may drive the catch figure to the level of current MSY estimates or above 

within a short period of time. 
-257- 

I. DESCRIPTION OF THE FISHERY 

I .A. Hi story of the Fi shery 

Swordfish (Xi phias gladius) is distributed throughout the tropical 

and temperate watersemc, Atlantic, and Indian Oceans. 

more abundant in coastal waters but is also found in continous patches in 

tropical and subtropical open ocean areas, as evidenced by longline catch 

rate data (Figure 1). In the Pacific, swordfish are taken commercially off 

the western coasts of the United States, Mexico, Ecuador, and Peru; near 

New Zealand and Australia; off the eastern coasts of Japan and Taiwan; and 

off the southeast coast of Asia. The limits of commercial distribution are 

approximately 50"N to 35"s latitude. Swordfish are caught by a variety of 

gear, including longl ines, handlines, harpoons, gill nets, rod-and-reel , and purse seine. However, the majority of swordfish are caught by longline 

gear designed for capturing tunas. This gear, when properly modified and 

used specifically for catching swordfish, has the capability of catching 

large quantities. The longline fleets of Japan, Korea, and Taiwan catch 

substantial amounts of swordfish in the Pacific (Table 1). U.S. domestic 

longline vessels take a small amount (c. 4.4 mt/yr) of swordfish near the 

Hawaiian Islands. Mexico, Costa Rica, Ecuador, and Peru are currently 

developing longl ine fisheries through joint ventures with western Pacific 

countries. 

It is 

c 

The next most common methods for capturing swordfish include 

harpoon and drift and set gill nets. The Japanese are increasingly using 

drift gill nets to catch tunas and swordfish; more than 10% of the Japanese 

swordfish catch is currently made using this method (Figure 2) and this 

percentage is increasing. 

The Japanese harpoon and d r i f t g i l l net fishery lands about 3,000 

tons of bill fish (striped marl in/swordfi sh) from coastal waters about 

Sanriku (northeastern Honshu) , around Izu Island, and in the east China 

Sea. Taiwan also has a harpoon fishery for swordfish, and Mexico is 

developing a drift gill net fishery. 

In the waters off the west coast of the United States, there exists 

a commercial harpoon and drift gill net fishery. The use of drift gill 

nets for the capture of swordfish and oceanic sharks is a rapidly growing 

fishery off California: it is estimated that 37% of the swordfish landed 

in California in 1979 were caught with drift gill nets. A minor rod-andreel fishery for swordfish also exists here. Southern California has the 

largest domestic catch of swordfish of any U.S. area in the Pacific; 

California catches normally range between 2-3% of the total Pacific Ocean 

catch, but in 1978 it equalled 12% of the total Pacific catch. 

c- Rod-and-reel sport fishing for swordfish in the Pacific is on the 

increase. Participating countries include the United States (near 

-259- 

Table 1. Total Pacific swordfish catch 

(metric tons) , 1952 to 1976. 

-- 

Year 

1952 

1953 

1954 

1955 

1956 

1957 

1958 

1959 

1960 

1961 

1962 

1963 

1964 

1965 

1966 

1967 

1968 

1969 

1970 

1971 

1972 

1973 

1974 

1975 

1976 

1977 

1978 

MT 

11,339 

11,689 

13,392 

16,485 

12,584 

16,243 

21., 341 

19,663 

23,409 

24,286 

14,604 

14,133 

10,112 

12,949 

14,601 

15,649 

15,230 

18,934 

16,727 

1 i ,037 

11,029 

13,791 

11,664 

16,409 

19,309 

18,312 

18,265 

Average (4 year) 1975-1 978 , 18,198 mt. 
-260- 

UNITE 

JAPAN 

TAIWAN 

Figure 2. Relative swordfish catch by country for the Pacific 

Ocean. Current total Pacific catch is about 18,000 

mt. U.S. catch averages about 409 mt or 2% of total 

Pacific catch. 
-261- 

I 

CPI 

California), Japan, and Mexico, Peru, Ecuador, and Costa Rica. 

1 atter four countries a1 so have coastal hand1 ine fisheries for swordfish. 

In addition, incidental catches are sometimes made with purse seines, and 

by gill nets which are being fished for other species. 

These 

I.B. Trends in Catch and Effort 

The total annual catch of swordfish in the Pacific Ocean increased 

from 11,300 mt in 1952 to a high of 24,300 mt in 1961 (Table 1); since 196

the catch has fluctuated between 10,000 and 19,000 mt. 

decreased in 1971, the year that the Food and Drug Administration began to 

enforce guidelines on mercury contamination in fish in the U.S. and Canada

However, even without the U.S. and Canadian market for imported swordfish, 

the total Pacific catches have increased in recent years, peaking at 19,300 

mt in 1976. The FDA 1 imits were relaxed in 1979. 

Catch rates 

In 1976, Japan produced over 90% of the total Pacific swordfish 

catch. Taiwan, Korea, Peru, and the U.S. (in that order) produced the 

remaining 10%. The total Pacific swordfish catch by country is given in 

Table 2. Annual catch has ranged from 11,000 to 24,300 mt, with current 

catches averaging about 17,500 mt. 

Within the U.S. Fishery Enforcement Zone (waters to 200 nm), a 

commercial and sport fishery exists for swordfish by U.S., Japanese, and 

other foreign nationals. 

swordfish catch, by location, within this zone. The harpoon and drift gil

net fishery off Cal ifornia accounts for approximatley 95% of the domestic 

swordfish production in the Pacific. 

increased its catch during the 1970's; Figure 3 shows the California catch 

(1918-1978) in mt. 

equalling 12.4% of the 1971-1976 Pacific-wide annual average. 

the harpoon was the major gear type; in 1979, however, it was estimated 

that 37% of the catch (324 mt) was made with d r i f t g i l l nets. 

Table 3 gives a summary of the estimated 

The harpoon fishery substantially 

The largest catch was recorded in 1978 (1,609 mt), 

Up to 1979 

The amount of foreign longline effort being targeted upon swordfish 

is unknown. The known effective fishing effort for Pacific swordfish has 

fluctuated between 270 million and 550 million hooks (Figures 4 and 5). 

The level in 1975 was about 300 million hooks. 

gill net effort for billfishes and other species appears to be increasing 

rapidly. 

Foreign and domestic drift 

I.C. Value of Catch 

In the United States, the ex-vessel price of swordfish on the fresh 

market ranges from $1.75 to $3.50/lb. In the California fishery, the 

average ex-vessel price in 1980 was about $2.50/7b. Ex-vessel (dressed) 

prices of $2.50-$3.00/1b. would bring $5,000-$6,000 per short ton, or 

$5,500-$6,600/mt. Assuming a price of $2.00/lb., the catch in 1978 was 
-262- 

Table 2. Swordfish catches (metric tons) by couritries for the Pacific Oc

Year 

1552 

1953 

1954 

1955 

1956 

1557 

1958 

1959 

1960 

1961 

1962 

-1 963 

1964 

1965 

1966 

1967 

1968 

1969 

1970 

1971 

1972 

1973 

1974 

1975 

1976 

1977 

1976 

1979 

Japan 

11,182 

11,604 

13,301 

16,220 

12,167 

15,771 

20,815 

19,136 

22,944 

23,636 

14,037 

13,775 

9,703 

11,955 

13,283 

13,083 

12,983 

15,612 

11,301 

9,182 

8,845 

9,644 

9,517 

11,274 

15,682 

13,867 

---- 

---- 

-- 

Ta i kia n 

77 

185 

254 

250 

24 7 

262 

273 

432 

544 

3 00 

300 

300 

600 

838 

974 

1,023 

1,053 

1,149 

1,111 

1,269 

1,157 

1,099 

1,290 

---- 

---- 

---- 

-- 

Korea 

41 

47 

55 

89 

115 

115 

115 

115 

115 

115 

444 

301 

--- 

--- 

I__- 

Un i tcd 

States 

157 

85 

14 

80 

163 

222 

279 

265 

192 

21 8 

23 

58 

109 

194 

277 

181 

118 

61 0 

558 

91 

157 

363 

384 

51 2 

53 

289 

7,609 229 

- 

Chile 

200 

200 

200 

200 

300 

200 

200 

100 

400 

21 8 

137 

13 

30 

--- 

Peru 

-- 

300 

200 

1,300 

800 

1,200 

2,400 

200 

600 

1,900 

270 

158 

294 

41 5 

---- 

Others 

100 

100 

100 

100 

100 

100 

3 

3 

31 3,156 

--- 

Total 

11,339 

11,689 

13,392 

16,485 

12,584 

16,243 

21,341 

19,663 

23,409 

24 , 286 

14,604 

14,133 

10,112 

12,949 

14,601 

15,649 

15,230 

18,934 

15,727 

11,0;7 

11,029 

13,791 

11,664 

13,376 

17,190 

18,060 

---- 

Incl udes Taiwan. 
-263- 

Table 3. Estimated average catch of swordfish 

by portion of the U.S. Flskery Conservation Zone in metric tons. 

Location 

Hawaii (including Midway) 

West Coast (off Cal i*fornia) 

Guam & northern Marianas 

American Samoa 

Possessions 

AVERAGE 

TOTAL AVERAGE 

Donies t i c/ Fore i gn 

4.4m1.3 MT 

225.4/ - 

2/7.2 

43.3 

-/28.1 

230/149.9 NT 

380 MT 
-264- 

a 

I ,60C 

I ,40C 

1,20c 

0 

a - 1,ooc 

ILhJ 

80C 

7 

v) 

(3 

c3 

7 

J 

v) 

7 

- 

600 

400 

200 

0 

i 

SWORDFISH - 

CALI FO R N I A COM M E RC I AL CATCH 

- 

- 

II 

YEAR 

Figure 3. California commercial landings, 1918-1980, in metric 

tons, adjusted to round weight. Recreational catch 

average about 29 swordfish per year (2.7 mt) . 
-265- 

.c 

c 

12 

IC c 

He 

2- 

E 

8 

\ 

0 

z 

W 

Y 

B 4 

a 

I 

E 

6 

0 

C 

,EFFECTIVE EFFORT SWORDFISH .? 

1111111111111 I1 111 1111 11 

1955 1960 1965 1970 197 

YEAR 

Figure 4. Pacific-wide catch rate and effective fishing effort 

for swordfish, 1952 to 1975. 
-266- 

- 

- 

- 

- 

2E! 

24 

20 

16 

12 

8 

4 

0 

240 

200 

160 

120 

80 

AREA I 

8 ,1111,111111,,,[, 

4- 

AREA 3 

8- 

YEAR 

Figure 5. Catch rates and effective fishing effort for 

swordfish in the Pacific Ocean. 
-267- 

worth $7.0 million. 

based upon an ex-vessel price of $1.19 (U.S.) in July 1979, was $2,622/mtY 

for a total of $36 mill ion (U.S.). 

The value of the Japanese Pacific swordfish catch, 

I.D. Current Management of the Fishery 

I .D.1. International Management 

Swordfish in the Pacific Ocean are under no international 

management scheme at present. 

Billfishes, which sets optimum yields for all the species of billfishes in 

the U.S. Fishery Conservation Zone around Hawaii, American Samoa, Guam, and 

California, is now in force. 

A preliminary Management P1 an for Pacific 

I .D.2. Domestic Fishery Management 

Cal ifornia Regulations 

Swordfish fishing in territorial waters, and by 

California citizens in territorial and international waters, is regulated 

by the State of California; no other west coast or central Pacific states 

have restrictions on their fisheries. California has restrictions on 

commercial and recreational fishing aside from the normal 1 icense and 

permits. Recreational fishing regulations prescribe gear as trolled or 

cast lures, or bait only, and a daily catch not to exceed two (2) fish per 

day per angler. Commercial regulations prescribe either the harpoon or 

gill net only, with no seasonal or catch limits. 

Federal Regul ations 

No federal regulations currently pertain to the taking of 

swordfish by domestic fishermen off the west coast Fishery Conservation 

Zone (FCZ) or in other FCZ areas of the Pacific. A Federal Fishery 

Management Plan (FMP) f o r b i l l f i s h and oceanic sharks is being prepared 

under authorization of the FCMA of 1976 for the central and western Pacific 

FCZ by the Western Pacific Fishery Management Council, and for the U.S. 

west coast FCZ by the Pacific Fishery Management Council. These Plans will 

deal with both foreign and domestic bill fish and oceanic shark fisheries 

within the FCZ and, when authorized, will supersede any State regulation 

currently in force for the management of swordfish fishing. 

11. NATURE AND SIGNIFICANCE OF U.S. AND FOREIGN 

PARTICIPATION IN THE FISHERY 

The public demand for swordfish exceeds the United States supply even 

in years of high catch. 

small-boat commercial fleet in southern California. In 1979, 1,206 

The swordfish fishery supports a substantial 
-268- 

swordfish permits were issued by California Fish and Game to commercial 

fishing license holders. The number of boats involved in the California 

fishery is about 400: data from logbooks indicate about half the commercial 

permit holders will actually fish. To this must be added the commercial 

fish processing, wholesale, and retail segment of the fishery. The exact 

amount of its value in employment and income is unknown. 

There is considerable interest in fishing off southern California for 

swordfish by rod-and-reel recreational fishery. However, the major effort 

is targeted on striped marlin with swordfish as an incidental catch. 

Hawaii, where the domestic commercial longline industry is small, the catch 

of swordfish is also incidental to the catch of tunas and other species of 

bill fish. While some progress in increasing the efficiency of the rod-andreel angler has taken place, the catch remains very low (average = 29 

f i sh/year) . 

In 

The California d r i f t g i l l net fishery is growing, having increased 

several-fold in 1980, and the number of units now totals about 100. 

Although the catch of swordfish amounts to only 4-5% of the total catch (by 

numbers), its value contributes about 50% of the income to the d r i f t g i l l 

net unit (Figure 6). Traditionally the drift gill netter targeted 

throughout the year on sharks (thresher/mako) and caught some swordfish 

during the summer and fall season, but the drift gill net units currently 

entering the fishery (a limited entry fishery by C.F.&G.) are targeting on 

sharks and swordfish. It is expected that the gill net fishery will grow, 

due to its ability to catch swordfish and thresher shark, and because of 

its fuel efficiency. Production from the harpoon fishery has the potential 

to increase if the current restrictions on use of airplanes for searching 

are removed. 

In 1976 the Government of Mexico declared a 200-nm economic zone 

and began enforcement of this zone in early 1977. Within the economic zone 

is a high catch rate area for swordfish (off the northwest t i p o f Baja) and 

the highest catch rate area in the Pacific for striped marlin (about the 

tip, and southwest of Baja). Historically, U.S. commercial fishermen have 

sometimes operated off the northwest coast of Baja California, but U.S. 

fishermen are currently restricted from fishing in Mexican waters. The 

Mexican Government is encouraging the commercial exploitation of swordfish 

and striped marlin through joint ventures with the Japanese and by special 

licenses granted to U.S. vessels capable of using drift gill nets, 

harpoons, and longline gear. The Japanese joint venture is for the purpose 

of catching striped marlin for export to Japan; tuna and shark are also 

landed in Mexico. As of December 1980, nine of these longliners were 

operating out of Ensenada. The arrangements with U.S. fishermen fishing in 

Mexican waters have targeted on catches of swordfish for export to the U.S. 
-269- 

.- 

STRIPED MAR 

THRESHER §HARK 

IN 0.2% NUMBERS 

SWORDFISH 3.8% 

SOUPFIN SHARK 1.6% BLUE SHARK 

MAKO §HARK 

THRESHER §HARK 

IN 0.2% NUMBERS 

SWORDFISH 3.8% 

SOUPFIN SHARK 1.6% BLUE SHARK 

MAKO §HARK 

THRESHER SHARK 72.6% 

STRIPED MARLIN 0.2% . 

SWORDFISH 7.3% 

SOUPFIN §HARK 0.3% 

MAKO SHARK 1. 

WEIGHT 

Figure 6. Catch composition of drift gill net boats from fishing logs 

for 486 nights of gill netting in 1979. Catch equalled 

10,590 fish or an estimated 1,128,131 lbs. 
-270- 

111. STATUS OF THE STOCKS 

1II.A. Stock Structure 

The stock structure of the swordfish population of the Pacific 

Ocean has not been clearly defined. Available data on distribution of 

larvae and on longline catch rates suggest that the population consists of 

either 1) a single, Pacific-wide stock, or 2) three separate stocks with 

centers of concentration in the northwestern (Area 1) , southwestern (Area 

2), and eastern (Area 3) regions of the Pacific Ocean (Figure 1). 

111.6. Stock Assessment and Fishery Evaluation 

I I I. 6.1. Trends in Catch-per-Un i t-Ef fort 

The trends in swordfish catch rate and effort for the 

Pacific Ocean are shown in Figures 4, 5, and 7. The longest available time 

series of catch rates is for the Japanese longline fleet. 

catch rates for this fleet reached a peak of about 10 fish/10,000 hooks in 

1958, then declined to a low of 4 fish/10,000 hooks in 1967; rates have 

since stabilized at about 5 fish/10,000 hooks. 

Total Pacific 

111.6.2. Results of Production Model Analysis 

The condition of the swordfish stocks of the Pacific was 

evaluated, based on different hypotheses about the stock structure of the 

population: hypothesis 1 assumed a single Pacific-wide stock, and 

hypothesis 2, three separate stocks. 

Single Pacific-wide Stock--The relation of catch and 

effective fishing effort (a projection of effort for catches where no 

effort data are available), assuming a single Pacific-wide stock, is shown 

in Figure 7. The data points fall into two clusters, separated by a sharp 

break between 1963 and 1964, which corresponds approximately to the period 

when the operational methods in the productive northwestern fishing area 

changed from longline night fishing, which is directed at swordfish, to a 

day operation which targets on tunas. 

The production model does not appear to fit the data 

well, because the points offer no solution for the 1964-1975 data series 

and give a maximum sustainable yield (MSY) estirnte of 20,000 mt per year 

with 2.2 mill ion hooks/5" area for the 1952-1963 series. Presumably during 

the 1952-1963 period the fishery was more efficient in catching swordfish 

than during the 1964-1975 period. 

of about 14,100 mt produced by 1.8 million hooks/5" area) indicates that 

the fishery does not appear to be overexploiting the stock and that the 

stock is in good condition. 

The current (average for 1966-75) catch 
-271 - 

,414 

25 I I I f 1 I 1 1 I I I 

24 c SWORDFISH 

m= 2.0 

-- bud/ /’ k=l 

22 t 50 // / 

I I I I I I I I I I I 

II 12 13 14 15 16 17 18 19 20 21 

IO5 HOOKS/ 5O SQUARE 

Figure 7. Relationship of catch of swordfish and effective fishing 

effort. 

model) is shown for data for 1952 to 1963 only. 

The equilibrium yield curve (Schaefer production 
-272- 

Three separate stocks--Compl ete data for production 

model analvsis. assuminq three stocks in the Pacific were not available for 

examination. 

based on estimates of apparent abundance from Japanese longline data for 

An appraisal of the condition of the stocks was therefore 

1952-1975. 

For this paper, an analysis of only the eastern Pacific 

Longline catches in the eastern Pacific (Area 3 of Figure 

stock is given. 

1) showed an increasing trend after 1960, following a period of small 

catches from 1952 to 1960 (Figure 8); the catch rates gradually increased 

from about 2 fish/10,000 hooks in 1954 to 6 fish/10,000 hooks in I968 

(Figure 5). In 1969 and 1970, the catch rates increased sharply to a 

record high of about 11 fish/10,000 hooks, before declining to a level of 

about 6 fish/10,000 hooks in 1971-1975. 

111.6.3. 

I I I .B.4. 

111.6.5. 

Results of Yield-per-Recruit Analysis 

None avail ab1 e. 

Resul ts of Spawner/Recruitment Analysis 

None avail ab1 e. 

Results of Other Analyses/Simul ations 

None avail ab1 e. 

1II.C. Current Evaluation of Stocks and the Fishery 

The swordfish stocks of the Pacific Ocean appear to be healthy and 

capable of sustaining increased yields with increased effort. However, 

should the longline fishery resort to night fishing as was the standard 

method of fishing in some areas prior to the mid-1960'~~ then the greater 

efficiency of the gear could result in the catch exceeding the MSY when the 

current level of fishing effort is increased about 25%. 

Avail able techniques for stock identification are expensive to 

apply and not entirely re1 iable in producing clear results. Different 

stock structure hypotheses should be tested with existing fisheries data to 

determine their impact on assessments before any major program for stock 

identification of swordfish is considered. The key to more precise stock 

assessments for swordfish is more re1 iable information on stock densities 

and better estimates of population dynamics parameters. 
-273- 

c 

20 I 

111111III Illlllllllllllll 

iI1IIII 

AREA 2 

10 

5 

0 

25 

20 PACIFIC -WIDE 

I5 

IO 

5 

0 

1955 1960 1965 1970 197! 

YEAR 

c Figure 8. Swordfish catch in the Pacific Ocean, 1952 to 1975. 
-274- 

The Cal ifornia commercial swordfish fishery has socio-economic 

problems whereby limited techniques of fishing are leading to an 

inefficient fleet and lower production. The fishery is overcapitalized and 

the average vessel in the fleet experienced a loss of over $4,000 per year. 

This fishery could be managed to increase production substantially. 

example, use of aircraft can increase the efficiency of the harpoon fleet 

by 2.6:l. 

For 

IV. STATUS OF CURRENT RESEARCH NEEDS AND EFFORTS 

1V.A. Major Research Problems 

The major research problems concerning the swordfish in the eastern 

Pacific Ocean centers on whether the stock is Pacific-wide or composed of 

the three separate substocks. To better define the stock structure, 

studies to determine the range and magnitude of migration of swordfish are 

required. A full range of stock identification techniques should be 

employed such as genetic studies, time/area catch analysis, and tagging to 

determine the degree of intermingling. 

c;l iected from all fisheries, and catch-and-effort data from the surface 

fisheries. Seasonal target areas for the different species also need to be 

defined relative to production in numbers and the value of the catch in 

Size and sex data should be 

relation to tuna when it is the target species. 

1V.B. Current Research Efforts 

No major research programs on swordfish are known for the 

northwestern coast of South America, Central America and Mexico, or at 

other locations in the Pacific. A small amount of stock assessment work is 

being conducted in Japan (Far Seas Research Laboratory, Shimizu, Japan) 

relative to stocks of swordfish in the world oceans. At the present time, 

only a very limited amount of effort is being given to biological research 

and stock assessment of swordfish in the U.S.: 

1) The National Marine Fisheries Service, in cooperation with the 

Pacific Marine Fisheries Commission and the California Department of Fish 

and Game, sampled swordfish catches at sea in 1978 and 1979. 

2) The NMFS is cooperating with the Western Pacific and Pacific 

(west coast) Fishery Management Councils in the development of the Fishery 

Management P1 an. 

3) The NMFS sponsored the Cooperative Marine Game Fish Tagging 

Program, which has encouraged the tagging of swordfish and striped marlin 

off southern California. 

interest to the Pacific Councils' FMP. 

Swordfish (and striped marl in) are of particular 
-275- 

4) The California Department of Fish and Game is analyzing data 

on the California drift gill net fishery for swordfish. 

1V.C. Future Research Needs 

Research relative to the needs of management for the total oceanic 

resource of swordfish is needed for: 1) definition of areas and seasons of 

spawning in the eastern Pacific, 3) determination of catch composition, 4) relation of sub-surface and surface 

distribution to the physical and biological environment, and 5) analysis 

of CPUE data shifts to determine migratory trends. 

California swordfish fishery and resource, the following research is rleeded 

for further development of management advice: 

1) Sampling program for both the commercial and recreational 

2) age and growth rates, 

For the southern 

* 

billfish fishery. 

2) Survey of effective effort and economic significance of the 

southern Cal ifornia recreational and commercial fleet. 

3) Determination of near surface and subsurface abundance and 

size distribution of swordfish off southern California. *- 

4) Determination of migratory patterns and exploitation rates 

(southern California fishery) using both long-term and short-term (diel ) 

studies. 

1V.D. Status of SWFC Data Base 

Swordfish logbook data for 1979 are being placed into the CoastSwordfish tagging data will also be placed 

wide Data System at SWFC through a cooperative program with the California 

Department of Fish and Game. 

into the system, which will update the 1963-1980 data base. 

More detailed basic catch and effort data are needed to make more 

precise stock assessments. Data presented in closer grid spacing (less 

than 5" area) would be desirable for determining stock movements within 

areas of high CPUE. 

The U.S. fishing industry supplies good to excellent effort data 

from the California logbook system for commercial catches; California and 

Hawaii both supply a fair coverage of catch data for the commercial 

*A cooperative effort with the California Department of Fish and Game. 
-276- 

longline and recreational catches. Japan also supplies good to excellent 

data on both catch and effort in its longline fishery, but the data 

obtained from Korea and Taiwan range from poor to barely adequate. 
-277- 

--.- 

STATUS REPORT: PACIFIC STRIPED, BLUE, AND BLACK MARLINS 

Howard 0. Yoshida 

Southwest Fisheries Center 

Honol ul u, Hawaii 

ABSTRACT 

The blue marlin, striped marlin, and black marlin are primarily caugh

by longline gear in the Pacific. The available evidence suggests that blue 

marl in comprise a single equatorially-centered stock in the Pacific. 

hypotheses have been advanced for striped marlin stocks in the Pacific: 

(1) a single-unit stock and (2) a two-stock structure where a North 

Pacific stock and a South Pacific stock are separated roughly at the 

equator, with some intermixing in the eastern Pacific. 

evidence suggests the possibility of a multiple (two or three) stock 

structure for black marlin in the Pacific: one in the eastern Pacific and 

two in the western Pacific. The production model analysis, together with 

the declining catch rate, suggests that the Pacific blue marlin stock is 

being overfished. 

appears to be in good condition. 

for the Pacific black marlin. 

stock structure of marlins in the Pacific. 

Two 

The available 

On a Pacific-wide basis, the striped marlin stock 

No production model analysis is available 

A high priority task is to better define the 
-278- 

I. DESCRIPTION OF THE FISHERY 

I.A. History of the Fishery 

The blue marl in (Makaira niaricans). striDed marl in (TetraDturus 

audax) , and black marl in (micar are widely distributed in the' Pacific 

Ocean (Figures 1-3). The major fisheries for these three species are the 

longline and harpoon fisheries of Japan, Taiwan, and Korea.' The first 

major exploitation of the marlin resources began with the advent of the 

high-seas longline operations of Japan following World War 11. A1 though 

the quest was for large tuna species, the gear caught all large fish, of 

which the marlins were a significant component. Beginning in the western 

Pacific, the advancing front of longline operations (Figure 4) reached 

130"W longitude by 1944 and the American Continents by 1965. Thereafter 

the fishery expanded southward (Ueyanagi 1974). 

Longline boats of Taiwan and Korea later followed the Japanese in 

fishing the high seas. The longline fleet of Taiwan, after 40 years of 

coastal operations, began its high-seas venture in 1954. The longline 

fleet was composed of 42 boats in 1962, increasing rapidly to 457 boats in 

1971 (Huang 1974). The major part of the effort, however, has shifted from 

the Pacific Ocean to the Indian and Atlantic Oceans since 1968 (Table 1). 

Historic accounts of longline activities of Korea are sketchy but beginning 

around 1958, Korean longline vessels joined the longline fishing fleet 

based at American Samoa (Otsu and Sumida 1968). The longline efforts of 

Taiwan and Korea in the Pacific have been almost entirely in the South 

Pacific where almost all of their tuna are sold to two American canneries 

in American Samoa. 

There are other fisheries which catch marlin but these are riot farranging and their catches are relatively small. A Hawaiian longline 

fishery, which was started in 1917 (June 9501, reached a peak of 76 boats 

in 1950 and declined to 18 boats in 1977.i The marlin catch in this 

fishery is primarily striped marlin and secondarily blue marlin. 

black marl in are a1 so caught. 

A few 

A harpoon fishery for striped marlin has existed in Japan since 

ancient times (Ueyanagi 1974). 

techniques to Taiwan in 1913 (Huang 1974). Sport trolling for marlins in 

the Pacific had its beginnings in the early years of this century. 

California. Australia, and New Zealand were centers at that time. In the 

The Japanese introduced the harpoon 

past 30 years, sport fishing for marlins 

'Fishery management pl an for bill fish and 

Pacific Fishery Management Council , Hono 

draft. 

)as experienced a spurt in 

associated species. Western 

ulu, Hawaii. September 1980 
-279- 
-280- 
-281 - 
-282- 

Figure 4.--Expansion of Japanese longline fishing in the Pacific Ocean. 

(From Kume 1972.) 
-283- 

Table 1.--Distribution of fishing efforts of Taiwan deep-sea 

longline fleet, 1967-71. (From Huang 1974.) 

Fi shi ng trips 

Number of 

Year vessel s Total Pacific Indian At1 antic 

1967 2 54 570 380 169 21 

1968 333 1,007 3 59 467 181 

1969 3 96 1,158 2 98 576 2 84 

1970 418 1,258 435 539 2 84 

1971 457 ‘1,182 4 95 409 2 78 ~~ ~ 

‘Estimated. 

Table 2.--Total Pacific catch (metric tons) of marlin b species, 

1952-76. (Data for 1952-75 from Shomura 1980. 7 

Year Striped marl in Blue marlin Black marlin 

1952 

1953 

1954 

1955 

1956 

1957 

1958 

1959 

1960 

1961 

1962 

1963 

1964 

1965 

1966 

1967 

1968 

1969 

1970 

1971 

1972 

1973 

1974 

1975 

1976 

4,994 

3,789 

7,256 

7,075 

7,724 

7,150 

8,999 

8,986 

7,362 

10,084 

13,685 

16,944 

23,480 

24,017 

20.967 

22;050 

27.143 

21 706 

24,221 

24,264 

14,541 

15,407 

14,669 

16,279 

17,032 

15,525 

17,250 

10,519 

24,190 

18,770 

23,500 

22,106 

20,275 

18,155 

26,581 

30,743 

31,344 

23,233 

18,585 

18,588 

17,233 

15,283 

17,427 

20,115 

13,342 

15,300 

17,285 

15,594 

12,546 

14,813 

1,806 

3,188 

5,370 

5,379 

6,466 

6,376 

4,548 

3,081 

2,721 

3,170 

4,066 

3,180 

2,805 

4,039 

3,729 

2,836 

3,547 

2,546 

2,207 

2,674 

3,424 

3,720 

3,048 

2,796 

3,132 
-284- 

technology as well as popularity. 

species include Mexico, New Zealand, and California for striped marl in; 

Hawaii, Tahiti, and Guam for blue marl in; and Australia and Chile for black 

marlin. In addition, the number of marlin anglers is increasing in Fiji, 

Papua New Guinea, and Japan. 

fishermen from all over the world. 

Centers of activity for the various 

Marlin fishing in the Pacific attracts sport 

I.B. Trends in Catch and Effort 

Blue marlin--Catches increased from 15,525 metric tons (mt) in 1952 

to a peak of 31,344 mt in 1963 (Figure 5 and Table 2). 

have fluctuated, generally declining to 14,813 mt in 1976. Effective 

fishinq effort increased from 50 million hooks in 1952 to about 269 million 

hooks in 1963 and fluctuated around 200 million hooks from 1964 to 1975 

(Figure 6 ) . 

Since then catches 

Striped marlin--From 4,994 mt in 1952, catches reached a high of 

27,143 mt in 1968 (Figure 7). 

abruptly to 14,541 mt and has hovered about 15,000 mt since. 

effective fishing effort (Figure 8) showed an increasing trend from 1952 

through 1964. 

mil 1 ion hooks. 

In 1972 the striped marlin catch dropped 

Since then fishing effort has fluctuated between 100 and 200 

Total 

Black marlin--The catch rose from 1,806 mt in 1952 to a hiqh of 

6,466 mt in 1956 ( Figure 9). It then fluctuated between 2,207 and 4,066 mt 

from 1959 to 1976. Effort data were summarized for four Pacific areas: 

northwestern (Area 11, southwestern (Area 21, eastern (Area 3), and western 

(Area 4, a combination of Area 1 and 2) (see Figure 3). Effective fishing 

effort from 1952 to 1975 has been erratic and does not show any discernible 

trend in Areas 1, 2, and 4 (Figure 10). In the eastern Pacific (Area 31, 

where the Japanese tuna fishery commenced in 1956, effort has been on a 

generally increasing trend. 

I.C. Value of Catch 

The ex-vessel prices of marlin from January 1978 to Flay 1979 at 

During that period, striped marlin prices ranged from 

Yaizu, Japan, show striped marlin to be the most valuable of the three 

species (Table 3). 

$2,316 to $4,345 a short ton. 

than black marlin, selling for $1,933 to $3,165 a short ton. Black marlin 

prices fluctuated between $1,638 and $2,744 a short ton. 

Blue marlin usually commanded a better price 

I .D. Current Management of the Fishery 

The marlins are under no management scheme at present. 

Preliminary Management Pl an for Pacific Billfishes, which sets optimum 

A 
-285- 

35 

3c 

h 

V, 25 

z 

e 

0 

W 

r 

0 

0 

0- 15 

I 

2c 

- 

v 

e 4 IO 

5 

0 

Figure 5.--Pacific catch of blue marlin, 1952-76. (Data from Table 2.) 
-286- 

BLUE MARLIN 

CATCH RATE 

-0 / 

.O \ ,EFFECTIVE EFFORT 

- 300 

- 200 

- 100 

Illllllllllllllllll Illlllo 

1955 I960 1965 I970 I975 

YEAR 

h 

cn 

5 

P 

G 

z 

-J 

0 

Y 

k 

e 

LL 

W 

W 

> 

Io 

W 

LL 

LL 

W 

- 

Figure 6.--Catch rate and effective fishing effort for blue marlin in 

the Pacific Ocean. (From Shomura 1980.) 
-287- 

1 

3c 

25 

- 

0 

z 

20 

0 

0: 

Iw 

0 

0 

0 

I IO 

15 

- .. 

Y 

5 

0 

5 

0 IIllIl1111111111111IlIII I 

1955 1960 1965 1970 1975 

YEARS 

Figure 7.--Pacific catch of striped marlin, 1952-76. (Data from Table 2.) 

a 
-288- 

c I 

cn 

8 

P 

0 

0 

0 

- 

\ 

0 

2 

W 

a 

I 

v 

G 

E 

o 

4 1 pAclFlc 

STRIPED MARLIN 

1200 

YEAR 

0 

I 

I 

I 

I 

I 

cn 

Y 

0 

0 

I 

z 

-I 

-I 

0 

A 

E! 

5 

a 

8 

v 

tLL 

W 

0 

I 

LL 

W 

> 

Io 

W 

LL 

LL 

W 

z 

<" 

- 

Figure 8.--Catch rates and effective fishing effort for striped marlin 

in the Pacific Ocean, 1952-75. (From Shomura 1980.) 
-289- 

7 

6 

-5 

cn 

z 

e 

0 

a4 

tW 

z 

8” - 

Y 

I 

0 

t0 

a2 

I 

0 1111111111111111111IIIIII 

I955 I960 I965 I 970 I975 

YEARS 

Figure 9.--Pacific catch of black marlin, 1952-76. (Data from Table 2.) 
-290- 

t 

I 

I 

I 

I 

I 

cn 

c5 

25 

P 

2- 

P 

8 

\ 

Y 

W 

U 

I 

0 

u 

G 

G 

6- 60 

4- 40 

- 

- 

2- 20 - 

0 I 0 Ill 

YEAR 

z 

IU 

LL 

W 

W 

ILL 

LL 

W 

Y 

e 

I 

z: 

Figure 10.--Catch rates and effective fishing effort for black marlin 

in the Pacific Ocean, 1952-75. (From Shomura 1980.) 
-291 - 

,- 

Table 3.--Ex-vessel marlin prices (U.S. dollars per short ton) in Japan, 

January 1978-May 1979. (From [U.S.] National Marine Fisheries Service 

1978-1 979. ) 

Striped marl in B1 ue marl in B1 ack marl in 

1978 

3 anuary 

February 

March 

Apri 1 

M aY 

June 

July 

August 

September 

October 

November 

D ec em be r 

1979 

January 

February 

March 

April 

May 

3,482 

2,823 

3,452 

2,722 

2,614 

2,462 

4,345 

2,507 

2,903 

2,856 

3,981 

2,698 

4,141 

4,046 

4,095 

2,316 

2,489 

2,009 

2,326 

2,299 

2 515 

2,112 

1,991 

2,122 

2,275 

2,039 

2,412 

3,165 

2,323 

1,933 

2,027 

2,510 

2,658 

2,626 

2,605 

2,070 

2,025 

2,082 

1,929 

2,090 

2,272 

1,638 

1,943 

2,055 

2,202 

1,934 

2,744 

2,059 

1,871 

1,730 

1,818 
-292- 

yields for all the species of billfishes in the U.S. Fishery Conservation 

Zone around Hawaii, American Samoa, Guam, and California, is now in force. 

11. NATURE AND SIGNIFICA.NCE OF U.S. AND FOREIGN 

PARTICIPATION IN THE FISHERY 

The marlins are prized game fishes. 

marlins is primarily of a recreational nature, the commercial aspects of 

the marlin fishery are not to be ignored. 

blue, and lack marlins brought about $332,000 in revenue to the fishermen 

Although the U.S. interest in 

In 1976 the sale of striped, 

in Hawaii. P 

I11 

mar 

111. STATUS OF THE STOCKS 

A. Stock Structure 

B1 ue marl in--Availabl e evidence seems to indicate that the blue 

in comprise a single equatorially-centered stock in the Pacific. 

Concentrations of blue marl in occur a1 ternately at locations on both sides 

of the eauator during the respective sullrmer seasons. The large, apparently 

single area of blue marlin spawning in the western Pacific, which includes 

areas of high spawning densities in the west and declining densities to the 

east, has been suggested as evidence for the unit stock assumption. 

Confirmation of the unit stock of blue marlin stock struct.ure hypothesis is 

needed. 

Striped marlin--Although the stock structure of the striped marlin 

in the Pacific is not clear, two likely hypotheses have been advanced: 1) 

a single-unit stock suggested by the continuous, horseshoe pattern of 

striped marlin distribution in the Pacific, and 2) a two-stock structure, 

where a North Pacific stock and a South Pacific stock are separated roughly 

at the eauator, with some intermixing in the eastern Pacific (Figure 2). 

Black marlin--The stock structure of black marlin in the Pacific is 

unclear, but their restricted coastal distribution and the occurrence of 

isolated high catch-rate areas suggest the possibil i ty of more than one 

stock. It has been suggested that two or three stc<cks exist: one in the 

eastern Pacific and two in the western Pacific (Figure 3). The situation 

is complicated by the strong possibility that black marlin from the Indian 

Ocean mix with fish from the western Pacific. 
-293- 

.- 

1II.B. Stock Assessment and Fishery Evaluation 

u 

I I I . R . 1 . Trends i n Catch- per- Un i t-E f fort 

B1 ue marl in--The catch-per-uni t-effort steadily decl ined 

from 3.0 fish/1,@00 hooks in 1952 to about 0.5 fish/1,00@ hooks in 1975 

(Fiaure 6). 

Striped marl in--The catch rate for the entire Pacific 

showed a slow, long-term decline from 1952 to 1975. The catch rate in the 

North and South Pacific showed long-term declines since the 1950's (Figure 

8). 

B1 ack marl in--The catch rate in the northwestern Pacific 

(Area 1) reached a peak in 1954 and declined to its lowest in 1975 (Figure 

10). 

declined to less than 4 fish/10,000 hooks in 1957, then fluctuated between 

1 and 3 fish/10,@00 from 1958 to 1975. 

reached a peak in 1957 and declined thereafter. The western Pacific (Area 

4) catch rate reflected the same trends as its constituent areas (Areas 1 

and 2). 

In the southwest (Area 2), the catch rate reached a peak in 1955, 

The catch rate in the east (Area 3) 

III.E.2. ReStJl ts of Production Yodel Analysis 

The following discussion of production model analyses on 

the stocks of blue marlin, striped marlin, and black marlin is based on the 

results of the Billfish Stock Assessment !nlorkshop held at the Honolulu 

Laboratory from 5 to 14 December 1977 (Shomura 1980). 

Blue marlin--Based on the assumption that the blue 

marlin in the Pacific comprises a single oceanwide stock, production model 

analysis gives a MSY estimate of 22,000 mt, which is associated with an 

effective fishing effort equal to about 50% of the 1975 total effective 

effort (Figure 11). This result, combined with the steadily decreasing 

catch-per-unit-effort in spite of increased fishing effort, indicates the 

stock is overfished (Shomura 1980). 

Striped marlin--Assuming a single, oceanwide stock, the 

MSY estimate is 24,000 mt at an optimum effective effort of 3.4 million 

hooks/5" sauare (Figure 12). 

to 27,100 mt at an average effective effort of 1.5 to 2.25 million hook,s/5" 

square, the MSY estimate infers a striped marlin population that is not 

being overexpl oi ted. 

Considering the 1964-1975 catches of 14,500 

Assuming a two-stock population structure, a North 

Pacific stock and a South Pacific stock, the results of the production 

model analysis indicate a perplexing picture for the North Pacific stock 

and a South Pacific stock that is being fished at about optimum level 

(Figure 12). The catches in the South Pacific for 1973-75, however, were 
-294- 

32 

28 

24 

20 

16 

12 

a4- 

36 I I I 1 I 1 I I I I I I 

- BLUE MARLIN 62 63 - 

m = 1.87 

- k=5 - 

- - 

- - 

- - 

- - 

/ 54 \ 

/ \ 

/ \ 

\ - 

\ 

/ 

/ 

/ \ - \ 

\ 

/ 

/ 

I I I I I I I I I I \ 

Figure 11.--Relation between catch of blue marlin and effective fishing 

effort. 

( From Shomura 1980. ) 

The equilibrium yield curve is based on the production model. 
-295- 

c 

v) 

z 

0 Io 

c 

IW 

z 

0 

0 

0" 

k 

- 

Y 

I 

0 

0 

24u 24 \ 

SOUTH PACIFIC 

16 

R" 

02 - 

I I I I I I I 

HUNDRED THOUSAND HOOKS PER 5O SQUARE 

Figure 12.--Production models for hypothesized striped marlin stocks 

in the Pacific Ocean. (From Shomura 1980.) 
-296- 

I I 1 I I I 24 I I I I 1 1 - - 

20- 

61 

12 - - 

72 

8- - 

4- - 

AREA 2 

52 

1 I I I I I 

0 4 8 12 16 20 24 

567 

5 I I 1 1 I I 

73 

4- 

3- 

2- 

IAREA 3 

60 m55 f----157 754 

d60 

0; b 

100,000 HOOKS / 5O SQUARE 

Figure 13.--Relation between catch and effective effort for black 

marlin in four areas in the Pacific Ocean. (From Shomura 19SO.\ 
-297- 

far below the equilibrium yield curve. 

determine the reason for the low catches before an accurate interpretation 

of the results can be made. For the North Pacific stock, the MSY estimate 

was 70,000 mt at an optimum effective effort of 13.2 million hooks/5" 

square. 

mill ion hooks/5" square fished through 1975. 

Further research is needed to 

This effort seems unreasonably high in l i g h t o f the maximum of 1.5 

Black marlin--Because of uncertainties in the data on 

total catch and the stock structure of black marlin in the Pacific, no 

attempt was made to fit production models or to estimate WSY for black 

marlin in any area of the Pacific. 

and effort (Figure 13) indicated that a reliable production model analysis 

will require a better accounting of the catches. 

The relation between estimated catch 

I II.B.3. 

I11 .B.4. 

111.8.5. 

Results of Yield-per-Recruit Analysis 

None avail ab1 e. 

Pesul ts of SDawner/Recrui tment Anal vsi s 

None avail ab1 e. 

Results of Other Anal vses/Simul ations 

None avail able. .- 

1II.C. Current Evaluation of Stocks and the Fishery 

B1 ue marl in--The decl ining catch-per-uni t-effort and the resul ts o

the production model analysis suggest that the Pacific blue marlin stock i

being overfished. 

Striped marl in--On a Pacific-wide basis, the striped marl in stock 

appears to be in good condition and may be capable of producing increased 

yields with a modest increase in fishing effort. 

yields is better for the North Pacific fishery than for the fishery in the 

South Pacific, which may be operating at or beyond the level of MSY. 

The outlook for increase

Black marlin--While no attempt was made to fit production models o

estimate MSY for black marlin stock(s) in the Pacific, the substantial 

decline in catch rates during the period from the early 1950's to 1975 

suggests that a very large increase in total catch over levels in the earl

1970's is probably not sustainable. 
-298- 

IV. STATUS OF CURRENT RESEARCH NEEDS AND EFFORTS 

1V.A. Major Research Problems 

Population assessments for all three species were based on 

incomplete catch and effort data. 

particularly of the black marl in. 

would contribute more definitive assessments of the populations. 

analyses, size-at-age relat.ionships need to be confirmed for blue and 

striped marlins and need to be obtained for black marlin. 

estimates of population parameters, e.g. , natural and fishing mortality 

rates, recruitment rates, etc. 

Better sssessments are needed, 

Yield-per-recruit and cohort analyses 

For these 

A1 so needed are 

Another problem related to population assessment is the lack of 

knowledge of the stock structures of these species, although it may be 

possible to circumvent the need for precise stock identification. The 

Billfish Stock Assessment Workshop (Shornura 1980) recommended the use of 

simul ation studies to evaluate the sensitivity of stock assessments to 

various stock structure hypotheses on the striped warlin so that the need 

for a stock identification program might be determined. Should such 

studies prove to be effective for striped marlin, they should be considered 

for the blue marl in and black marlin as well. 

1V.B 

marl 

Current Research Efforts 

The first attempts to assess the status of blue marlin, striped 

n, and black marlin stocks were described in background papers 

submitted to the Billfish Stock Assessment Workshop (Shomura 1980). The 

need for further research on the billfishes was stressed at the workshop 

but, aside from routine data collecting efforts, no real effort is being 

expended to update the stock production analyses or carry out other 

analyses suggested at the workshop. 

1V.C. Future Research Needs 

Detailed data on growth, mortality, reproductive rates, and other 

vital determinants of population dynamics which are required for a complete 

understanding of the effects of fishina on stock productivity and catch, 

are not available for Pacific billfishes such as tbe blue marlin, black 

marlin and striped marlin. Limited data on size composition and growth 

rates are available, as well as some statistics on nominal fishing effort 

and catch. These permit only tentative assessment of the stocks. Effort 

is therefore needed to upgrade these assessments and to define better the 

stock structure of the marlin species in the Pacific. 
-299- 

IV.C.l. Suaaested Amroach and Methods 

1) The assessment of the billfish stocks was based on 

various assumed stock structures and computed measures of effective fishing 

effort, a statistic which is assumed to be proportional to fishing 

mortality. These assumptions are difficult to test and verify. Computer 

silnul ations to examine the sensitivity of stock assessment conclusions to 

changes in assumptions should be carried out. 

2) While tagging experiments provide some of the 

necessary information on stock structure, the low catch rates of marlins in 

commercial and recreational fisheries suggest that other techniques are 

probably more suitable, e.g., immunogenetic methods. 

1V.D. Status of SWFC Data Base 

The data base maintained at the Honolulu Laboratory includes 

billfish catch and effort data from the Japanese and Taiwan longline 

fisheries in the Pacific. The longline operations of Korea, however, are 

poorly documented. 

All nations with billfish fisheries should be urged to update or 

I establ ish sampl ing programs to insure the collection of adequate 

statistics, including 1) total catch by species, gear, type of fishing 

operation, and ocean region; 2) total nominal effort by gear, type of 

fi shin? operation, and ocean region; 

small area-time strata, gear, and type of fishing operations; and 4) size 

and sex composition of the catches by species and by small area-time 

strata. 

3) catch-per-uni t-effort by effort, 

LITERATURE CITED 

Huang, H. C. 

1974. Billfish fishery of Taiwan. In R. S., Shomura and 

F. William (editors) , Proceedings of %e International Billfish 

Symposium, Kailua-Kona, Hawaii, 9-12 August 1972, Part 2. Review and 

Contributed papers, p. 332-335. U.S. Commer., ElCAA Tech. Rep. 

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1968. Distribution, apparent abundance, and size composition of 

a1 bacore (Thunnus a1 a1 unga) taken in the 1 ongl ine fishery based 

in Pmerican Samoa, 1954-65. U.S. Fish. Wildl. Serv. , Fish. Bull. 

67:47-69. 

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Pacific resources. NOAA Tech. Memo. NMFS-SWFC-5, 58 p. 

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APPEND I X 
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.- 

LIST OF ATTENDEES 

SOUTHWEST FISHERIES CENTER 

TUNA RESEARCH WORKSHOP 

December 15-17 , 1980 

San C1 emente, California 

OFFICE OF INTERNATIONAL FISHERIES AFFAIRS 

Carmen J. Blondin 

Barbara K. Rothschild 

SOUTHWEST REGIONAL OFFICE 

John Davies 

CALIFORNIA DEPARTMENT OF FISH GAME 

Doyle Hanan 

SOUTHWEST FISHERIES CENTER 

Center Director's Office 

Izadore Barrett 

John F. Carr 

David J. Flackett 

Honol ul u Laboratorv 

Roy Mendel ssohn 

Fletcher V. Riggs 

Richard S. Shomura 

Robert A. Skillman 

Jerry A. Uetherall 

Howard 0. Yoshida 

La Jolla Laboratorv 

Coastal Fisheries Resources Division 

R. Michael Laurs 
-302- 

Oceanic Fi sheries Resources Division 

Norman W. Bartoo 

Atilio L. Coan, Jr. 

Richard H. Evans 

Samuel F. Herrick 

Anthony P. Majors 

Wesley W. Parks 

Ronald G. Rinaldo 

Gary T. Sakagawa 

James L. Sauire, Jr. 

Earl C. Weber 

Pacific Environmental GrOUD. Monterev 

Richard H. Parrish 

Paul H. Sund