NOAA Technical Report NMFS 104 December 1991

Incidental Catch of Marine

Mammals by Foreign and

Joint Venture Trawl Vessels in the

U.8. EEZ of the North Pacific,

1973-88

Michael A. Perez

Thomas R. Loughlin

u.s. Department of Commerce
NOAA Technical Report NMFS

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the &heries, edited by Harold L. Pratt Jr., Samuel

H. Gruber, and Toru Taniuchi. July 1990,518 p.

91. MariDe flora aad fauaa ofthe _rtlae..tera Uaited

Stat_EcbiaoclerJData: CriDoidea, by Charles G.

Messing and John H. Dearborn. August 1990, 30 p.

92. Geaeac. iD aqaac:ultare: proceediap of the _-

teeDth U.S.-JapaD _eetiDS OD aquacultureI

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edited by Ralph S. Svrjcek. November 1990, 81 p.

93. DWtn"butioa aad abuaUace ofjuveaile .alD1oaiet.

off OrepD aad W..laiapoa, 1981-1985, by William

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94. AD eeoDOD1la saiele to a11ocatiOD of&h .toc:b betweeD eoaunerdal aad recreatioaal &heries, by

Steven F. Edwards. November 1990, 29 p.

95. Larval fUh recraitIDeDt aDel re.earch iD the

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larval &h eoaf'ereaeel Merin, Mesieo, 21-26 May

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96. Mariae flora aDel t'auaa of the E..tera Uaited

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98. Mariae mammal .traadiap ia the Uaited States;

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and PeterJ. Hayward. February 1991, 4-8 p.

100. Mariae flora IIIIcl fluma oldie Eutera Uaited State.:

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19 p.
NOAA Technical Report NMFS 104

Incidental Catch of Marine Mammals

by Foreign and Joint Venture Trawl

Vessels in the U .8. EEZ of the

North Pacific, 1973-88

Michael A. Perez

Thomas R. Loughlin

December 1991

U.S. DEPARTMENT OF COMMERCE

Robert Mosbacher, Secretary

National Oceanic and Atmospheric Administration

John A. Knauss, Under Secretary for Oceans and Atmosphere

National Marine Fisheries Service

William W. Fox Jr., Assistant Administrator for Fisheries
The National Marine Fisheries Service (NMFS) does not approve,

recommend or endorse any proprietary product or proprietary

material mentioned in this publication. No reference shall be made

to NMFS, or to this publication furnished by NMFS, in any advertising or sales promotion which would indicate or imply that NMFS

approves, recommendsor endorses any proprietary product or proprietary material mentioned herein, or which has as its purpose

an intent to cause directly or indirectly the advertised product to

be used or purchased because of this NMFS publication.

11
CONTENTS

Abstract

Introduction

Methods

Observer Data

Estimated Catch

Results

Observed Incidental Take

Northern Sea Lions in Alaska

Incidental Catch Rates

Estimated Take

Incidental Take by Month and Time of Day

Age and Size

Other Marine Mammal Species in Alaska

Marine Mammal Species in

Washington, Oregon, and California

Discussion

Summary

Acknowledgments

Citations

Appendix 1

Appendix 2

111

1

1

2

3

4

6

6

25

25

31

34

35

41

42

43

51

53

53

54

56
IV
Incidental Catch of Marine Mammals

by Foreign and Joint Venture Trawl Vessels

in the U.S. EEZ of the North Pacific, 1973-88

MICHAEL A. PEREZ and THOMAS R. LOUGHLIN

National Marine Mammal Laboratory

Alaska Fisheries Science Center

National Marine Fisheries Service, NOAA

7600 Sand Point Way N.£.

Seattle, WA 98115-0070

ABSTRACT

During 1973-88, 3,661 marine mammals of 17 species were reported as incidental

catch by U.S. fishery observers aboard foreign and joint venture trawl vessels in the U.S.

Exclusive Economic Zone in the North Pacific Ocean and the Bering Sea. Northern sea

lions (Eumetopias jubatus) accounted for 90% of the reported incidental mortality in the

Gulf of Alaska and eastern Bering Sea. Nearly half of these sea lions were taken in trawl

nets in the Shelikof Strait, Alaska, joint venture fishery during 1982-84. However, high

incidental mortality rates (>25 sea lions per 10,000 metric tons of groundfish catch) also

occurred in the foreign fisheries near Kodiak Island and in the Aleutian Islands area in

earlier years. Estimated annual mortality of incidentally caught northern sea lions in

Alaska declined from 1,000 to 2,000 animals per year during the early 1970s and 1982 to

fewer than 100 animals in 1988. In the Bering Sea most sea lions incidentally caught were

males, while in the Gulf of Alaska females were more frequently caught. Females may also

have been dominant in the incidental catch of sea lions in the Aleutian Islands area, but

age and sex composition data are limited. Incidental mortality of adult female sea lions

by foreign trawl fisheries in these areas could have partially contributed to the reported

declines in northern sea lion populations in Alaska during the 1970s, but it cannot alone

account for the present decline in population size.

Introduction _

Foreign trawl fishing was first introduced as a method

of harvesting Pacific Ocean perch (POP: Sebastes

alutus), walleye pollock (Theragra chalcogramma), and

yellowfin sole (Limanda aspera) by the Japanese in the

northeast Pacific Ocean as an exploratory fishery in

1929 and 1933-37 (Natural Resources Consultants

1984). AJapanese mothership with 9-12 catchervessels fished the Bering Sea during 1940; the fishery

terminated during the war, then started again in 1954

with the return of two Japanese motherships and

nine catcher boats (Natural Resources Consultants

1984). Soviet exploratory fishing operations in the

Bering Sea began in the early 1930s, but commercial

operations did not begin until 1959 (Natural Resources Consultan ts 1984). During the late 1950s and

early 1960s Soviet and Japanese trawlers concentrated on POP and yellowfin sole until catches of

both began to decline in the late 1960s. Since then

walleye pollock has dominated foreign trawl catches,

accounting for 60-75% of the total harvest (Natural

Resources Consultants 1984).

Northern sea lions (Eumetopias jubatus) and other

marine mammals have been caught incidentally in foreign trawl fisheries in the Bering Sea and Gulf of

Alaska since the onset of these fisheries. Data on the

incidental catch of marine mammals and other species

were recorded for several years by U.S. observers on a

few foreign ships beginning in 1973. However, passage

of the Magnuson Fishery Conservation and Management Act of 1976 (FCMA) required foreign vessels to

accept observers, and, as amended in 1983, established the U.S. Exclusive Economic Zone (EEZ). A

standardized reporting system for the collection of

data on the incidental take of marine mammals in the

U.S. EEZ was developed in mid-1977, resulting in the

routine collection of data by all observers since 1978.
2 NOAA Technical Report NMFS 104

500

1-540 30.\-

Charlotte'.

-47°30'

Columbia

-43°00

Eureka -40°30'

Monterey

-35°30'

Conception -32°30'

1400 1300 1200

Yakutat

Northeast

Pacific Ocean

Area-III

I

Area-II :

I

I

I

I

Bering Sea

I

I

I

I

I : r? "I '#1 I : &?J" ' : '9.~ 1v ChirikOfl

I ". • . ..",' ' Shumagin 0' ol! : Area-Iv ".

,--------------------- R

I

Figure 1

U,S, statistical fishing areas in the Bering Sea and nOl theast Pacific Ocean used to summarize catch

and effort data,

Northern sea lions are the predominant marine

mammal species incidentally caught in commercial

groundfish fisheries in the North Pacific (Loughlin et

aL 1983: Loughlin and Nelson 1986). Many sea lions

incidentally caught during fishing operations are

alive when brought aboard vessels (up to 34% in

1979); however, mortality of sea lions caught in joint

venture UV) fisheries composed of U.S. trawlers delivering fish to foreign processors was nearly 100%

(Loughlin and Nelson 1986),

The trend in the number of adult and juvenile

northern sea lions counted on land in most of western Alaska has been declining over the past 30 years

at an annual rate of about 4.5%, from about 140,000

animals in 1956-60 to about 25,000 in 1989 (Merrick

et aL 1987; Loughlin et aL 1990), In some areas the

decline has been even more dramatic. For instance,

in the eastern Aleutian Islands the count has declined by 93% (from about 41,220 in 1960 to less

than 3,000 in 1989) and in the western Gulf of Alaska

levels have dropped by 82% (from about 24,000 in

1956 to about 4,400 in 1989), Numbers of pups

counted at western Alaskan rookeries have also declined (Merrick et aL 1987; Loughlin et aL 1990).

The reasons for the decline are unknown but may be

related to disease, environmental perturbations, decreased food supplies, or direct interactions with foreign and domestic commercial trawl fisheries or

other types of fishing activities (Loughlin and

Merrick 1989). The possible role that incidental

catch had in contributing to the sea lion decline is

the subject of this paper,

We present a reanalysis, by area and vessel class, of

the incidental catch data for the years 1978-81, and

our analysis of the comhined incidental catch data

for the years 1973-88, We also discuss changes in

mean length arid age of incidentally (aught sea lions,

and the relationship of these changes and the estimated level of incidental catch to recent declines in

sea lion population abundance,

Methods _

This paper discusses the incidental take of marinf'

mammals in the foreign and]V groundfish fisheries

occurring on independent stern trawlers and

mothership-based trawl fleets. Data from longline or

snail-pot fisheries were not included because the reported marine mammal incidental take is either extremely low (longline) or zero (snail-pot), Also, we

do not address the issue of incidental take of marine

mammals in U.S. domestic fisheries because of the

paucity of incidental catch data for those fisheries

through 1989,

We report marine mammal incidental take data by

year, fishery (country and vessel class), and U.S,

statistical reporting areas (Fig, 1). Data from ]V

fisheries are presented only for the total fishery, not

by the country-specific ventures with the domestic
Perez and Loughlin: Incidental Catch of Marine Mammals 3

U.S. catcher boats. Data are summarized for three

geographical regions: Bering Sea and Aleutian

Islands; Gulf of Alaska; and Washington, Oregon,

and California.

Observer Data

During the period 1973-77, U.S. observers aboard

foreign vessels infrequently reported the occurrence

of marine mammals in fishing trawl nets. During that

period, incidental take data were recorded in an inconsistent manner. The current U.S. observer data

reporting system which was developed in 1977, assigned the duty of recording standardized data on

incidental take of marine mammals to all observers

(Loughlin et al. 1983). However, the collection and

recording of fishery-related data remained the

observer's primary responsibility; marine mammal incidental catch data were secondary in nature and recording was not to interfere with the collection of

fishery catch data. Data forms for recording marine

mammal incidental take were not available to all observers un til late 1977. Therefore, only data since

1978 have been uniformly recorded using a standardized system.

U.S. observers recorded either data on 1) hauls

actually observed or sampled, or 2) all hauls, including those not observed or sampled, using information supplied by the crew. It should be noted, however, that in many cases the observer did see (and

measure) the incidentally caught marine mammal

from an unsampled haul (the crew reported the animal to the observer). Therefore, this paper includes

incidental catch data in which the total observed fish

catch (metric tons, t) includes both sampled and

unsampled hauls. We were not able to exclude marine mammal data from unsampled hauls for every

cruise. However, in all cases we included the fish

catch for each haul with reported incidental take of

marine mammals in the total catch monitored by observers. We have not included 1) reported o.:currences of isolated marine mammal parts (decomposed skulls or bones, usually from large whales), 2)

mammals caught in trawls on vessels without observers but cited on data forms when observers were informed by radio conversation of such occurrences, 3)

mammals caught by vessels where observers were

merely passengers awaiting transfer to another vessel,

or 4) mammals reported caught in waters outside the

U.S. EEL on vessels with U.S. observers aboard.

Many observers did not have previous experience

with marine mammal biology, and observer training

on biological data collection from marine mammals

was limited during most years, especially prior to

1982; collection of such data was a low priority. When

observers did obtain biological data and specimens

from the incidentally caught marine mammals, they

did not always collect length measurements. The type

of measurement, standard or curvilinear length

(American Society of Mammalogists 1967), was often

not recorded. Canine teeth (used for ageing by

counting dentine lines of sectioned teeth) were seldom collected; most of the tooth specimens were obtained by observers in the Shelikof Strait]V fishery

during 1982-84. Therefore, sample sizes for aged

and sized animals differ. Although observers occasionally recorded information on the sex of incidentally caught northern sea lions, these data were unreliable. In many instances tooth specimens (which

provide a better guide to the animal's sex) disagreed

with the observer's recorded data. Therefore, analyses in this report using information on sex or age

have been based only on data from teeth collections.

Ageing of teeth was done by National Marine Mammal Laboratory (NMML) personnel; the age estimates by 3 or 4 persons were averaged. Data from

canine tooth specimens were only available for 1977-

87; teeth collected during 1988 have not been

processed.

Data on location and fishing times, including times

of net retrieval (from the bottom) and trawl duration, were available for most catches observed by U.S.

observers aboard foreign independent trawlers (not

mothership-based fleets) from 1980 to 1988, except

during 1984. With few exceptions, location and

fishing times of hauls in the]V fisheries were unavailable prior to 1985. Locations for foreign mothership

catches in all years, and]V catches during 1978-84,

were based on the noon position of the processor

vessel.

Times of start and end of net retrieval were recorded by observers in GMT and were later converted to local time. Incidental take was summarized

for daytime and nighttime periods. Sunrise and sunset times were not recorded by observers. They were

estimated for this paper using the standard calculation formulae in the astronomical ephemeris and

nautical almanac (without correction for refraction,

changes in right ascension, or declination of the sun

during the day).

In order to describe an average diel pattern of incidental take throughout the year, local clock times

were converted to relative proportions of the day

with respect to dawn or dusk. These proportions

(percentages) were grouped into 24 equal divisions

(hours) to represent a standardized fishing day for all

years, months, and areas. This procedure was necessary because the length of the day varies by latitude

and season. For each haul, the total number of daylight or night hours in the 24-hour period on that

date was calculated. The percentage of the day or
4 NOAA Technical Report NMFS 104

night at which the haul occurred was calculated as

the ratio of the time of net retrieval relative to the

respective length (hours) of day or night.

Estimated Catch

Estimates of the total incidental take of marine mammals were calculated on the basis of the number of

observed marine mammals incidentally caught per

observed tonnage of groundfish. Groundfish catch

(tonnage) is the only statistic for the magnitude of

the fishery that is available for all trawl fisheries and

years; effort data on total number of hauls are not

available. Groundfish catches by all trawl gear, i.e.

stern (one boat fishing separately with one net) and

pair (two boats fishing together at the same speed

with one net between them), were included in making estimates. We included marine mammals caught

but not seen by the observer to avoid underestimating the total incidental take in the fishery when total

daily tonnage was used as an indicator of the observed fish catch.

Data for the total fish catch by the foreign fisheries

prior to 1978 were obtained from Murai et al. (1981)

and Berger et al. (1986); data for groundfish catch by

vessel class, gear type, and INPFC statistical area

came from Sueto Murai (Alaska Fisheries Science

Center, NMFS, NOAA, 7600 Sand Point Way .E.,

Seattle, WA 98115, unpubl. data). Data on location

and total daily fish catch for cruises with observers

during 1973-77 were obtained from original master

data files of the Foreign Fisheries Observer Program

and the groundfish fisheries database of the Alaska

Fisheries Science Center (Resource Ecology and Fisheries Management Division, Alaska Fisheries Science

Center, NMFS, NOAA, 7600 Sand Point Way N.E.,

Seattle, WA 98115). Data for location, fishing time,

and total fish catch monitored by observers during

1978-88 were obtained from marine mammal incidental take records and fish catch forms provided by

observers. Data sources on observer coverage, number of fishing days, and the total fishery catch by

country, statistical reporting area, vessel type, month,

and year during 1978-88 are listed in Appendix 1.

The total observed tonnage of groundfish in this

paper will differ somewhat from values given in the

Foreign Fisheries Observer Program reports (see Appendix 1) which usually include only hauls sampled

for catch composition. Also, observers reported only

a summary of the total daily catch (all hauls combined) and not the catch in each haul for all foreign

sessels during 1973-77, foreign mothership vessels

during 1978-86, and]V vessels during 1978-84.

Rates of incidental take for the years 1978-88 were

calculated by the following subgroups: species, statistical area, fishery, country, vessel type, and year. Average rates of incidental take were calculated by region

and country for the period 1973-77. The rates were

calculated as ratio estimates (l'R) from the sum of the

dead marine mammals reported in the catch divided

by the sum of the observed tonnage of fish catch for

each subgroup. Standard errors and variance of the

ratio estimate were calculated by the simple random

sampling ratio estimate method discussed by

Cochran (1977). The fraction of hauls (or fishing

days) observed in the total fishery is unknown; instead, the percentage of total tonnage sampled was

used as an estimate of the fraction of total effort observed. The normal approximation was assumed to

be appropriate because the sample size (number of

hauls sampled) was nearly always large (>50). The

resulting values are reported as multiples of 10,000 t

of fish catch. The formulae used to calculate catch

rates and ratio estimates are listed in Appendix 2.

Total estimated incidental take of marine mammals

for each subgroup was calculated by multiplying the

observed rates of inciden tal take (per 104 t of fish

catch) by the total tonnage caught by the entire

fishery in that subgroup. The resulting estimated totals (ratio estimates) were summed over all subgroups to provide regional totals for all fisheries combined in each year. The variance of the total for all

combined strata (subgroups) was calculated as the

sum of the product of the variar.ce of each stratum

times the square of the respective total fishery catch

(tonnage) in each stratum.

If the percentage of groundfish catch observed in

any subgroup was less than 5% of the total fishery

catch (as stated previously, tonnage was used as an

estimate of total effort because the total number of

trawls in the fishery is unknown), then the calculated

rate of incidental take was not used. This method was

used to avoid high estimates based only on one observed mammal; 5% was arbitrarily chosen on the

basis of an examination of the shape of the curve of

calculations with only one observed animal. Instead,

one of four rates, in the following order, was used as

a replacement when the percentage (tonnage basis)

of the fish catch monitored by observers was equal to

or greater than 5% for the replacement group: 1) the

average rate for all fisheries, trawlers combined, of

the same country in the same year and statistical

area; 2) the average rate for all fisheries, trawlers and

countries combined, in the same year and statistical

area; 3) the average rate for all fisheries, trawlers

combined, of the same country and statistical area

for the five-year period the year under analysis belongs to (i.e., 1978 to 1982); or 4) the average rate

for all foreign fisheries combined of the statistical

area for the five-year period the year under analysis

belongs to. This procedure was not needed for analy-
Perez and Loughlin: Incidental Catch of Marine Mammals 5

Table I

Summary by region of incidentally taken marine mammals reported by U.S. observers on foreign and joint venture (]V)

trawl vessels in the Exclusive Economic Zone (EEZ) in the North Pacific Ocean and eastern Bering Sea, 1973-88. a For

each fishery, total observer coverage (percent) and the total groundfish catch (percent of total catch by both fisheries

combined) in the EEZ during all years are listed. Decomp. = decomposed animals.

Bering Sea and Washington, Oregon,

Aleutian Islands Gulf of Alaska and California

Species Dead Alive Decomp. Dead Alive Decomp. Dead Alive Decomp.

Northern sea lion,

Eumetopias jubatus 1,053 264 102 1,603 150 10 6

California sea lion,

Zalophus californianus

Northern fur seal,

Callorhinus ursinus 41 13 6

Northern elephant seal,

Mirounga angustirostris 3

Harbor seal,

Phoca vitulina 28 9 3 5

Spotted seal,

Phoca largha 3 2

Ringed seal,

Phoca hispida 2

Ribbon seal,

Phoca fasciata 17

Bearded seal,

Erignathus barbatus 4

Walrus,

Odobenus rosmarus 76 1 68

Unidentified pinnipeds 42 2 38 2

Sea otter,

Enhydra lutris 3

Minke whale,

Balaenoptera acutorostrata 2

Risso's dolphin,

Grampus griseus

Pacific white-sided dolphin,

Lagenorhynchus obliquidens 3

Killer whale,

Orcinus orca 2

Harbor.porpoise,

Phocoena phocoena 3

Dall's porpoise,

Phocoenoides dalli 11 2 1 8

Unidentified cetaceans 7 18 2 9

Unidentified marine mammals 2 8 11

Total 1,290 268 272 1,632 151 11 33 3

Bering Sea and Washington, Oregon,

Aleutian Islands Gulf of Alaska and California

Foreign ]V Total Foreign ]V Total Foreign ]V Total

Observer coverage (percent)b 32.1 56.8 37.9 13.1 69.6 30.0 17.2 74.6 34.6

Groundfish catch (percent) C 83.3 78.1 82.0 9.2 12.0 9.9 7.5 9.9 8.1

a Data reporting by Foreign Vessel Observer Program observers was consistent only for the years 1978-88.

b Percent of total fish catch in trawl nets of each fishery monitored by Foreign Vessel Observer Program observers during 1973-88

(years combined).

C Percent of total groundfish catch caught by each trawl fishery during all years (1973-88).
6 NOAA Technical Report NMFS 104

ses of data from 1983 to 1988 because the percentage

of catch monitored by U.S. observers exceeded 5%

for all statistical areas, vessel classes, and years.

Observed incidental catch rates for motherships of

foreign fisheries were not used in obtaining regional

totals of estimated incidental take by year. An alternative method was necessary because the total daily

groundfish catch for motherships includes groundfish catch from unobserved hauls which will bias ratio

estimates of incidental take downward. Thus, the observed rates for motherships were presumably low

owing to the different method used to report the

observer monitored fish catch (observers recorded

total daily catch for motherships and individual haul

catch for stern trawlers). Instead, the average rate of

incidental take by independent foreign trawlers (all

countries combined) in the same year and statistical

area was used to estimate incidental take by

mothership fleet trawlers.

The observed incidental take rates on ]V vessels

were always used to obtain regional totals of estimated incidental take of marine mammals by ]V

fisheries. Because the percentage of groundfish catch

monitored by observers was always reported as ;:'5%,

no replacement rate method (an alternative method

discussed previously which was necessary for stern

trawlers to avoid high estimates based on one observed animal) was used for]V fisheries. In addition,

although observers recorded total daily catch for ]V

fisheries prior to 1985, the approach used for foreign

motherships to estimate regional totals of estimated

incidental take was not used for]V fisheries.

For fishery subgroups with no observer coverage

(the percentage of the total foreign vessel days on

fishing grounds sampled by observers), the average

rate of incidental take of marine mammals (i.e., only

the marine mammal species for which rates were calculated) for all trawlers, countries, and years (1978-

88) combined in the same statistical area was used to

estimate the regional totals of incidental take. This

average rate was also used for the unmonitored portion (tonnage for hauls and vessels not sampled by

observers for incidental catch) of the fish catch in

subgroups where no marine mammals were reported

in the catch. A similar approach was used for ]V

fisheries using data only from]V fisheries.

Total mortality of northern sea lions in the trawl

fisheries for years prior to 1978 was estimated using

<the average observed rate (and 95% confidence limits) of incid~ntal catch of dead sea lions by foreign

trawlers (mothership fleets excluded) during 1973-

77. We did not estimate total mortality of other marine mammal species in the trawl fisheries for years

prior to 1978.

Results _

Observed Incidental Take

Seventeen marine mammal species were caught incidental to fishing operations by foreign and JV

1500

Bering Sea

" . ·,·4 "'~l .::t.' "t-J"'. • ".

Figure 2

Locations in the Bering Sea and northeast Pacific Ocean where northern sea lions were incidentally caught during

fishing operations, 1973-88. Decomposed animals were not included.
Perez and Loughlin: Incidental Catch of Marine Mammals 7

, IiJ • 600 " N '"C'h '" 4' '0

"""'~ 0.,.

~6~~ Gulf of Alaska

Bering Sea 0

'" ' ",0

"' .. 0

6t:. I':> 0

550

.... ~"6'~

'" 500

NE

Pacific

Ocean

45'

450

NE Pacific Ocean

40'

1280W 1180

400

175°E 1800 175°W 1700 1650 1600 1550 1500 1450 1400 1350 1300 1250

Figure 3

Locations in the Bering Sea and northeast Pacific Ocean where pinnipeds, except northern sea lions,

were incidentally caught during fishing operations, 1973-88. Locations off the coast of Washington,

Oregon, and northern California are shown in the inset. Decomposed animals were not included. Key to

symbols: 6 = northern fur seal; + = harbor seal or spotted seal; <) = ribbon seal; 0 =walrus; and * = other

pinniped species.

600N

0 0

Bering Sea

'b Gulf 0/ Alaska

0 0

550

""6' .J500

NE

Pacific

Ocean

45'

N. E. Pacific Ocean

450

40"

12S"W 123' l1S" 400

175°E 1800 175°W 1700 1650 1600 1550 1500 1450 1400 1350 1300 1250

Figure 4

Locations in the Bering Sea and northeast Pacific Ocean where cetaceans were incidentally caught during

fishing operations, 1973-88. Locations off the coast of Washington, Oregon, and northern California are

shown in the inset. Decomposed animals were not included. Key to symbols: 6 = Pacific white-sided

dolphin; <) = killer whale; + = harbor porpoise; 0 = Dall's porpoise; and * = other cetacean species.
8 NOAA Technical Report NMFS 104

Table 2

Summary by year of incidentally taken marine mammals reported by U.S. observers on foreign and joint venture (IV)

trawl vessels in the Exclusive Economic Zone (EEZ) in the North Pacific Ocean and eastern Bering Sea, 1973-88. a

Totals include animals found dead in catch (excluding decomposed); numbers in parentheses refer to an additional

number of animals caught and released alive. For each year total observer coverage (percent) and the total groundfish

catch (percent of total catch by both fisheries combined) in the EEZ are listed.

Species

Northern sea lion,

Eumetopias jubatus

California sea lion,

Zalophus californianus

orthern fur seal,

Callorhinus ursinus

Northern elephant seal,

Mirounga angustirostris

Harbor seal,

Phoca vitulina

Spotted seal,

Phoca largha

Ringed seal,

Phoca hispida

Ribbon seal,

Phoca fasciata

Bearded seal,

Erignathus barbatus

Walrus,

Odobenus rosmarus

Unidentified pinnipeds

Pacific white-sided dolphin,

Lagenorhynchus obliquidens

Killer whale,

Orcinus orca

Harbor porpoise,

Phocoena phocoena

Dall's porpoise,

Phocoenoides dalli

Unidentified cetaceans

Unidentified marine mammals

Total

Observer coverage (percent) b

Groundfish catch (percent) C

1973

13(4)

25

38(4)

7.3

7.7

1974

73(10)

74(10)

7.1

7.9

1975

24(5)

25(5)

5.6

6.8

1976

27(11)

2

30(11 )

6.4

6.8

1977

53(12)

2(1)

57(13)

34.3

5.0

1978

72(41)

-(1)

-(1)

74(43)

34.0

5.7

1979

68(39)

2

4

9

85(39)

37.2

5.4

1980

52(7)

4

-(1)

57(8)

16.5

5.4

1981

45(14)

2

2

53(14)

23.6

5.8

Species

Northern sea lion,

Eumetopias jubatus

California sea lion,

Zalophus californianus

orthern fur seal,

Callorhinus ursinus

Northern elephant seal,

Mirounga angustirostris

Harbor seal,

Phoca vitulina

1982

725(146)

4

2

1983

425(79)

4

6

1984

560(26)

17

4

1985 1986

286(14) 163(4)

5 4

9 6

1987

44(3)

3

5

1988

32

2

2

Total

2,662(415)

48

3

36
Perez and Loughlin: Incidental Catch of Marine Mammals 9

Table 2 (continued)

Species

Spotted seal,

Phoca largha

Ringed seal,

Phoca hispida

Ribbon seal,

Phoca fasciata

Bearded seal,

Erignathus barbatus

Walrus,

Odobenus rosmarus

Unidentified pinnipeds

Pacific white-sided dolphin,

Lagenorhynchus obliquidens

Killer whale,

Orcinus orca

1982

2

1983

5

3

3

1984

7

2

3

1(1)

1985

20

4

1986

2

11

3(1)

1987

20(1)

3

1988

16

2

3

Total

3

2

17

4

76(1)

44(2)

3

2(1)

Harbor porpoise,

Phocoena phocoena

Dall's porpoise,

Phocoenoides dalli

Unidentified cetaceans

Unidentified marine mammals

Total

Observer coverage (percent) b

Groundfish catch (percent) c

2 4 2

2 2 3

12

736(146) 452(79) 601 (27) 343(14) 192(5) 76(4) 62

52.7 60.7 76.3 63.7 63.0 54.9 58.5

5.5 5.9 7.1 7.4 6.6 5.7 5.3

3

20(2)

18(1)

13

2,955(422)

36.9

100.0

a Data reporting by Foreign Vessel Observer Program observers was consistent only for the years 1978-88.

b Percent of total fish catch of all trawl fisheries monitored by Foreign Vessel Observer Program observers for incidental catch during

1973-88.

c Percent of total fish catch (all foreign and]V fisheries combined) during all years (1973-88) combined.

groundfish trawl vessels during the period 1973-88 in

the U.S. EEZ of the North Pacific Ocean and Bering

Sea (Table 1). Most of the 3,661 mammals caught

died in the nets, but some (422) were released alive.

Decomposed animals represented 20-50% of the incidental take of most marine mammal species caught

in the nets (Table 1). Three (sea otter, Enhydra lutris;

minke whale, Balaenoptera acutorostrata; and Risso's

dolphin, Grampus griseus) species were represented

only by decomposed animals.

Northern sea lions represented 87% of the total

marine mammal incidental take reported by U.S. obs~rvers during 1973-88. Only 4% of the 3,189 sea

lions caught were decomposed animals (Table 1). Excluding decomposed animals, 42.8% of the northern

sea lions incidentally taken during this period were

caught in the Bering Sea; 57.0% were caught in the

Gulf of Alaska; and 0.2% were caught off Washington, Oregon and California (Table 1; Fig. 2).

Other pinniped species (excluding decomposed

animals) incidentally caught during 1973-88 were 48

northern fur seals (Callorhinus ursinus) ; 1 California

sea lion (Zalophus californianus) ; 36 harbor seals

(Phoca vitulina); 17 ribbon seals (Phoca fasciata); 12

phocid seals of other species; 77 walruses (Odobenus

rosmarus); and 46 unidentified pinnipeds. Most of the

total catch of these species occurred in the Bering

Sea (Fig. 3).

Cetaceans represented 1.5% of the total incidental

take during 1973-88 (Table 1). Dall's porpoise

(Phocoenoides dalli; 0.7%) was the most commonly

caught cetacean. Most cetaceans were caught in the

Bering Sea or off Washington, Oregon, and California (Table 1; Fig. 4).

Except for northern sea lions, observed incidental

takes for marine mammals were low, averaging less

than five animals per species per year (Table 2). The

observed take of walruses per year has exceeded this

average since 1985, because of increased ]V fishing

effort in Bristol Bay where walruses are frequently

found.

Northern sea lions were observed caught in greater

numbers by]V fisheries (66% of all sea lions taken,

Table 3) than by foreign fisheries during 1978-88,
10 NOAA Technical Report NMFS 104

Table 3

Summary by country of incidentally taken marine mammals reported by U.S. observers on foreign and joint venture

(IV) trawl vessels in the Exclusive Economic Zone (EEZ) in the North Pacific Ocean and eastern Bering Sea, 1973-88.a

For each country total observer coverage (percent) and the total groundfish catch (percent of total catch by all

countries combined) in the EEZ during all years al-e listed.

Species

Northern sea lion,

Eumetopias jubatus

California sea lion,

Zalophus californianus

Northern fur seal,

Callorhinus ursinus

Northern elephant seal,

Miraunga angustirostris

Harbor seal,

Phoca vitulina

Spotted seal,

Phoca largha

Ringed seal,

Phoca hispida

Ribbon seal,

Phoca fasciata

Bearded seal,

Erignathus barbatus

Walrus,

Odobenus rosmaTUS

Unidentified pinnipeds

Pacific white-sided dolphin,

Lagenorhynchus obliquidens

Killer whale,

Orcinus orca

Bulgaria

People's

Republic of

China

West

Germany

13

Japan

512(301)

26

3

14

17

19

33

1(1)

Republic

of

Korea

63(22)

3

4

3

Mexico

2

Harbor porpoise,

Phocoena phocoena

Dall's porpoise,

Phocoenoides dalU

Unidentified cetaceans

Unidentified marine mammals

Total

Groundfish catch (t)

Percent of all-nation

combined groundfish catch'

Observer coverage (percent)d

Species

Northern sea lion,

Eumetopias jubatus

California sea lion,

Zalophus californianus

Northern fur seal,

Callorhinus ursinus

2 0

38,566 2,007

0.1 <0.1

21.6 70.5

Poland Portugal

22

13

110,731

0.4

37.6

Taiwan

2(2)

7

8

1

643 (302)

14,163,598

51.7

34.0

U.S.S.R.

97(11 )

74 (22)

2,095,920

7.6

30.5

Total

foreign b

713(336)

30

2

10,632

<0.1

12.0

JV

1,949(79)

18
Perez and Loughlin: Incidental Catch of Marine Mammals II

Table 3 (continued)

Total

Species Poland Portugal Taiwan U.S.S.R. foreign b JV

Northern elephant seal,

Mirounga angustirostris 3

Harbor seal,

Phoca vitulina 20 16

Spotted seal,

Phoca largha 2

Ringed seal,

Phoca hispida 2

Ribbon seal,

Phoca fasciata 17

Bearded seal,

Erignathus barbatus 3

Walrus,

Odobenus rosmarus 22 54(1)

Unidentified pinnipeds -(1) 33(1) 11 (1)

Pacific white-sided dolphin,

Lagenorhynchus obliquidens 3 3

Killer whale,

Orcinus orca 1(1)

Harbor porpoise,

Phocoena phocoena 2

Dall's porpoise,

Phocoenoides dalli 2(1) 4(1) 14(2) 6

Unidentified cetaceans 1 9(1) 18(1)

Unidentified marine mammals 1 2 11

Total 31 (2) 0 2(2) 111(13) 880(341) 2,075(81)

Groundfish catch (t) 794,886 182 25,118 3,443,646 20,685,285 6,706,260

Percent of all-nation

combined groundfish catch C 2.9 <0.1 0.1 12.6 75.5 24.5

Observer coverage (percent)d 34.3 75.3 4.4 3.8 28.9 60.1

a Totals include animals found dead in catch (no decomposed); numbers in parentheses refer to an additional number of animals

caught and released alive.

b Includes animals for which data on country-specific fishery were not recorded.

C Percent of total groundfish catch (all foreign andJV fisheries combined) during all years (1973-88) combined.

d Percent of total fish catch of that country-specific fishery monitored by Foreign Vessel Observer Program observers during 1973--88

(years combined).

particularly during 1982-84 in Shelikof Strait in the

northwestern Gulf of Alaska. Walruses were also incidentally caught more often (70%) by]V fisheries in

the Bering Sea, but 66% of the other marine mammal species were caught more frequently by foreign

fisheries (Table 3). Japanese vessels accounted for

most (77%) of the incidentally caught marine mammals in the foreign fisheries, as well as 52% of the

total fish catch during 1973-88 by all fisheries combined (Table 3). Although]V fisheries caugh t most of

the observed take of northern sea lions, they caught

only 24% of the total fish catch during 1973-88

(Table 3).

Fishery trends by year, region, and country must be

considered when comparing the reported in,cidental

takes of marine mammals in Tables 1-3. The effort of

the foreign fishing fleets was reduced annually with

the rise of the]V and domestic fisheries. The foreign

trawl fisheries ceased fishing in the U.S. EEZ in

Alaska in 1988.Joint venture fisheries in the U.S. EEZ

of the North Pacific Ocean first began in 1978 with

low fishing effort. The total fish catch by]V fisheries

has increased each year, exceeding the catch of foreign fleets off Washington, Oregon, and California in

1982 (Fig. 5A); in the Gulf of Alaska by 1983

(Fig. 5B); and in the Bering Sea by 1986 (Fig. 5C).
12 NOAA Technical Report NMFS 104

Foreign and ]V fisheries varied by region during

1973-88 when 82% of the total fish catch was taken

in the Bering Sea, 10% in the Gulf of Alaska, and 8%

off Washington, Oregon and California (Table 1).

Foreign fisheries accounted for 78.8% of the total

340,170 trawl vessel fishing days from 1978 to 1988

and]V fisheries account for the difference. During

this period, foreign trawl vessels operated a total of

14,859 days (5%) fishing in the U.S. EEZ off Washington, Oregon, and California (Fig. 6A); 31,342 days

(12%) fishing in the U.S. EEZ in the Gulf of Alaska

(Fig. 6B); and 221,836 (83%) days fishing in the U.S.

EEZ in the Bering Sea (Fig. 6C). Joint venture vessels

operated a total of 14,338 days (20%) fishing in the

U.S. EEZ off Washington, Oregon and California

(Fig. 6A); 8,464 days (12%) fishing in the U.S. EEZ in

the Gulf of Alaska (Fig. 6B); and 49,331 days (68%)

fishing in the U.S. EEZ in the Bering Sea (Fig. 6C).

Observer coverage on foreign vessels increased

from 10-35% during 1978 to 90-100% during 1988

(Fig. 7, A through C) (observer coverage of JV

fisheries during 1978 was near 100% because the

fishery began late in the year with a few vessels). Coverage was similar among regions, but higher for the

1,400 Gulf of Alaska 40,000

1,200

Gulf of Alaska

III

>0-

1,000 III 30,000

B "C

800 8i

III

Gl 20,000 600 >

400

Washington, Oregon and California

Washington, Oregon and California

o~--~"""""""""'~IfZUIIIf-'l~.l.......;F-""--r197879 80 81 82 83 84 85 86 87 88

o~---'P-''''F'~''--tf-L-.p..~~~F-U~-14

197879 80 81 82 83 84 85 86 87 88

10,000

20,000

40,000

10,000

30,000

A

200

o .- 197879 80 81 82 83 84 85 86 87 88

1,400

1,200

1,000

800

600

400

200

O~----~IIIII='.JIIIZ~fA-¥~~~fA-I~~

197879 80 81 82 83 84 85 86 87 88

Vi

c:

u

't:

4i

E

'0

Ul

B "C

c:

lIS

Ul

:::J

0

u

3

Ul

u::

A

E:'JJoint venture

Bering Sea and Aleutian Islands

• Foreign

40,000

O~---'l-''''F'-"'''f'......,~'t''"'''''''UIIIf.Llllllf'J-"''I-''--¥ 197879 80 81 82 83 84 85 86 87 88

Year

10,000

C 30,000

20,000

Bering Sea and Aleutian Islands

P1 o I

197879 80 81 82 83 84 85 86 87 88 I

Year

• Foreign E:'J Joint venture] ! '-----------__J

1,400

1,200

1,000

C 800

600

400

200

Figure 5

Total metric tons of fish caught by foreign and joint venture fishing vessels in the U.S. Exclusive Economic Zone,

1978-88: (A) off the coast of Washington, Oregon, and

California; (B) in the Gulf of Alaska; and (C) in the Bering

Sea and Aleutian Islands region.

Figure 6

Total number of vessel days with fishing operations for foreign and joint venture fisheries in the U.S. Exclusive Economic Zone, 1978-88: (A) off the coast of Washington, Oregon, and California; (B) in the Gulf of Alaska; and (C) in

the Bering Sea and Aleutian Islands region.
Perez and Loughlin: Incidental Catch of Marine Mammals 13

Table 4

Number of northern sea lions reported by U.S. fishery observers incidentally' caught by subgroup (area, vessel class,

nation, and year) in the U.S. Exclusive Economic Zone in the Bering Sea, 1978-88, and an estimation of the total

incidental take of northern sea lions in the fishery. Catch rates are the ratio (R) ± twice the standard error (s(R» of

observed incidental take of only dead animals to observed groundfish catch (per 10,000 metric tons [t] basis). Estimated

takes of only dead sea lions are the ratio estimate (}7R) ± the 95% confidence limits (L95%). Refer to Figure 1 for the

locations of the areas in the left column. * = the estimated lower 95% confidence level was less than the number of

animals reported by U.S. observers; ** = the estimated lower 95% confidence level was less than zero.

Groundfish Northern sea lions

Number Number

Vessel Total Observed Percent of hauls dead (alive)

nation catch catchb of catch observedc reported R± 2 s(R)

yeara (t) (t) observed (n) in catchd (X 10-4) YR ± L95%

Area-I

Small stern trawler

Japan

1978 21,482.6 1,246.8 5.8 908 0 (2) 0

1979 28,287.1 1,069.5 3.8 467 I (5) 9.35 ± 18.34 26 ±51 ** 1980 42,177.0 1,318.3 3.1 373 0 0

1981 38,809.1 487.5 1.3 155 0 0

1982 34,003.1 8,018.7 23.6 2,087 I (13) 1.25 ± 2.18 4±8 ** 1983 37,375.4 14,316.8 38.3 4,855 6 (10) 4.19 ± 2.69 16 ± 9

1984 54,283.0 35,434.5 65.3 5,386 19 (7) 5.36 ± 1.66 28 ±9

1985 36,132.2 27,681.8 76.6 3,728 17 6.14 ± 1.52 22 ±5

1986 22,871.9 16,544.9 72.3 1,361 3 1.81 ± 1.l0 4±3 * 1987 2,272.3 1,686.5 74.2 174 0 0

Republic of Korea

1981 9,052.0 321.0 3.6 13 0 0

1982 13,567.9 4,053.0 29.9 241 I 2.47 ± 4.15 3±5 ** 1983 10,922.7 3,701.7 33.9 169 0 0

1984 12,401.2 7,101.4 57.3 291 0 0

1985 14,404.6 9,217.9 64.0 367 0 0

1986 8,738.4 6,320.2 ~72.3 265 0 0

Portugal

1984 182.0 137.1 75.3 58 0 0

Taiwan

1978 882.6

1979 160.3

1980 53.4

1981 1,730.6

1982 4,189.7 636.1 15.2 149 0 (2) 0

Large surimi trawler

Japan

1978e 142,044.2 27,683.2 19.5 1,124 19 (5) 6.86 ± 3.48 97 ±49

197ge 159,280.5 30,836.2 19.4 1,555 5 (2) 1.62 ±'I.30 26±20

1980 163,050.4 9,986.8 6.1 495 5 5.01 ± 5.12 82 ±82 * 1981 164,053.8 19,271.1 Il.8 1,012 I (2) 0.52 ± 0.98 9 ± 15 ** 1982 129,264.5 51,405.2 39.8 2,267 8 (6) 1.56 ± 0.85 20 ± II

1983 64,329.1 35,832.4 55.7 1,517 I (2) 0.28 ± 0.37 2±3 ** 1984 47,362.2 28,182.1 59.5 1,051 2 (5) 0.71 ± 0.64 3±3 * 1985 81,514.7 49,536.8 60.8 1,453 13 (2) 2.62 ± 0.98 21 ± 8

1986 6,576.8 4,442.7 67.6 III 0 0

Republic of Korea

1986 23,435.9 16,572.2 70.7 359 0 0

1987 501.7 327.1 65.2 18 0 0
14 NOAA Technical Report NMFS 104

Table 4 (continued)

Groundfish Northern sea lions

Number Number

Vessel Total Observed Percent of hauls dead (alive)

nation catch catchb of catch observed c reported R±2 s(R)

yeara (t) (t) observed (n) in catch d (XI0-4 )

,

YR ± 45%

Large freezer trawler

People's Republic of China

1986 1,550.9 1,010.1 65.1 84 0 0

Japan

1980 11,888.4 636.6 5.4 49 0 0

1981 12,897.7 588.8 4.6 106 0 0

1982 14,257.7 4,253.7 29.8 453 0 0

1983 20,707.6 8,851.0 42.7 860 1 1.13 ± 1.71 2±3 **

1984 20,587.5 9,970.3 48.4 934 0 0

1985 16,623.1 8,069.4 48.5 681 2 2.48 ± 2.52 4±4 *

1986 6,443.7 4,265.7 66.2 270 10 23.44 ± 9.24 15 ± 6 *

West Germany

1980 6,658.3 867.0 13.0 51 0 0

1981 8,727.1 1,062.2 12.2 52 0 0

1982 1,183.9 555.9 47.0 22 2 35.98 ± 53.01 4±6 **

1983 10,161.3 6,370.8 62.7 157 0 0

1984 7,402.3 4,104.5 55.4 104 I 2.44 ± 3.25 2±3 **

Republic of Korea

1978 51,576.1 5,292.6 10.3 199 1 (4) 1.89 ± 3.57 10 ± 18 **

1979 52,459.9 5,893.0 11.2 267 0 (2) 0

1980 85,178.2 6,816.2 8.0 281 2 2.93 ± 3.99 25 ±33 **

1981 90,493.7 15,974.8 17.6 592 0 0

1982 124,811.1 46,285.4 37.1 1,538 9 (5) 1.94 ± 1.14 24 ± 14

1983 185,897.6 82,249.8 44.2 2,557 4 0.49 ± 0.36 9±7 *

1984 177,121.8 110,900.4 62.6 3,199 9 (2) 0.81 ± 0.33 14 ± 5

1985 173,564.7 114,031.5 65.7 2,998 17 (2) 1.49 ± 0.45 26 ±8

1986 54,744.3 40,266.1 73.6 1,248 1 0.25 ± 0.26 I ± 1 *

1987 1,116.7 647.1 58.0 40 0 0

Poland

1979 12,114.7 1,042.1 8.6 122 0 0

1980 26,168.4 2,036.0 7.8 196 0 0

1981 32,184.9 5,658.7 17.6 402 3 5.30 ± 9.62 17 ± 30 **

1984 46,728.7 30,858.5 66.0 1,582 4 1.30 ± 0.75 6±4 *

1985 20,399.0 14,540.2 71.3 732 2 1.38 ± 1.04 3±2 *

1986 3,633.3 2,341.6 64.4 148 0 0

Taiwan

1978 805.2

1980 742.1

1981 1,578.7

1982 1,510.0 460.9 30.5 76 2 43.39 ± 51.94 7±8 **

U.S.S.R.

1978 94,820.9 6,210.7 6.5 700 1 (1) 1.61 ± 3.11 15 ± 29 **

1979 62,928.2 5,028.8 8.0 474 0 0

1980 4.0

1984 22,812.6 12,272.0 53.8 722 0 0

1985 10,652.3 6,263.1 58.8 405 1 1.60 ± 2.05 2±2 *

Surimi mothershipf

Japan

1978g 235,210.0 186,197.3 79.2 293 6 (2) 0.32:f: 0.14 8±4 **

1979g 207,610.0 156,732.6 75.5 293 0 0

1980 176,450.0 42,612.0 24.2 70 0 0

1981 357,340.0 153,844.4 43.1 253 0 0
Perez and Loughlin: Incidental Catch of Marine Mammals 15

Table 4 (continued)

Groundfish Northern sea lions

Number Number

Vessel Total Observed Percent of hauls dead (alive)

nation catch catch b of catch observed c reported R±2 s(R)

yeara observed in catchd (XI0-4) A

(t) (t) (n) YR ± 45%

1982 366,490.0 332,381.3 90.7 554 0 0

1983 269,380.0 246,501.1 91.5 452 0 0

1984 2,880.0 2,410.0 83.7 7 0 0

1985 25.3

Freezer mothership

Japan

1980 38,515.5 35,381.3 91.9 1I5 0 0

1981 41,129.9 40,000.5 97.2 129 0 0

1982 40,597.7 38,032.5 93.7 130 0 0

1983 39,717.3 39,717.3 100.0 144 0 0

1984 39,829.6 39,240.7 98.5 136 0 0

1985 33,898.2 33,898.2 100.0 124 0 0

1986 33,048.3 31,142.4 94.2 109 0 0

Joint venture mothership (countries combined)

1980 32,126.2 8,863.1 27.6 203 I l.l3 ± 1.94 4±6 **

1981 74,122.0 28,625.3 38.6 264 I 0.35 ±0.62 3±4 **

1982 89,270.3 61,525.6 68.9 695 3 0.49 ±0.37 4±4 *

1983 192,598.8 107,811.2 56.0 779 21 1.95 ± 0.88 38 ± 17

1984 261,128.0 220,343.2 84.4 1,831 21 0.88 ±0.25 25 ±6 *

1985h 574,785.0 246,974.0 43.0 1I,949 29 l.l0 ± 0.33 65 ± 19

1986h 780,652.6 412,128.0 52.8 16,294 42 0.94 ± 0.25 78± 19

1987h 944,213.2 507,665.0 53.8 14,996 8 0.16 ± 0.08 15 ± 7

1988h 971,629.0 577,946.4 59.5 19,692 23 0.40 ± 0.1I 39 ± II

Area-II

Small stern trawler

Japan

1978 103,332.3 4,079.7 4.0 2,399 0 (4) 0

1979 69,976.6 4,221.0 6.0 1,562 0 (5) 0

1980 65,432.7 1,728.3 2.6 619 2 11.57 ± 15.76 76 ± 103**

1981 69,308.4 4,745.2 6.8 1,394 8 (6) 16.86 ± 11.50 1I7 ± 78

1982 53,055.9 1I,366.8 21.4 5,478 I (36) 0.88 ± 1.56 5±8 **

1983 52,010.9 21,638.8 41.6 10,297 10 (15) 4.62 ± 2.23 24 ± II

1984 52,626.2 38,560.3 73.3 7,729 6 1.56 ±0.66 8±4 *

1985 35,050.1 28,947.2 82.6 3,980 2 (4) 0.69 ± 0.41 2±2 *

1986 17,778.1 13,709.6 77.1 1,758 0 (1) 0

1987 13,609.1 8,697.7 63.9 1,312 0 0

Republic of Korea

1981 2,052.1

1982 3,456.3 225.6 6.5 39 0 0

1983 1,356.6

1984 2,010.7 917.1 45.6 38 1 10.90 ± 16.47 2±4 **

1985 936.8 814.3 86.9 18 0 0

1986 9.9

Taiwan

1978 1,027.5

1979 1,123.0

1980 3,069.0

1981 774.0

1982 350.8
16 NOAA Technical Report NMFS 104

Table 4 (continued)

Groundfish Northern sea lions

Number umber

Vessel Total Observed Percent of hauls dead (alive)

nation catch catch b of catch observedc reported R±2 s(R)

yeara (t) (t) observed (n) in catch d (X 10-4) ,

YR ± 45%

Large surimi trawler

Japan

1978' 203,135.8 28,466.5 14.0 937 2 (I) 0.70 ± 0.92 14 ± 19 ** 1979' 149,818.9 31,011.0 20.7 1,144 4 (2) 1.29 ± 1.15 19 ± 17 * 1980 125,926.9 11,919.6 9.5 569 0 0

1981 128,479.8 10,435.5 8.1 594 0 0

1982 164,072.0 35,633.5 21.7 1,425 1 (2) 0.28 ± 0.50 5±8 ** 1983 181,242.2 76,654.2 42.3 3,060 4 (3) 0.52 ± 0.49 9±8 * 1984 176,734.5 103,524.4 58.6 3,683 8 0.77 ± 0.39 14 ± 6

1985 112,880.3 72,435.0 64.2 2,330 1 0.14±0.17 2±1

1986 29,332.8 14,638.6 49.9 279 0 0

Republic of Korea

1986 2,221.5 2,027.2 91.3 35 0 0

Large freezer trawler

People's Republic of China

1986 51.2 7.3 14.3 4 0 0

West Germany

1980 32.4

1981 2,400.4 157.4 6.6 11 0 0

1982 696.6

1984 1,003.0 805.7 80.3 34 0 0

Japan

1980 1,429.0 93.6 6.6 17 0 0

1981 421.3

1982 207.6

1983 608.0 583.5 96.0 29 0 0

1984 4,605.9 1,397.7 30.4 137 0 0

1985 364.4 201.2 55.2 20 0 0

1986 1,137.7 573.0 50.4 30 0 0

Republic of Korea

1978 15,691.4 621.9 4.0 66 0 0

1979 44,466.7 6,149.3 13.8 418 0 0

1980 71,986.4 5,374.0 7.5 223 0 0

1981 40,507.4 3,930.0 9.7 224 0 0

1982 34,713.9 6,442.1 18.6 216 0 0

1983 15,088.0 1,168.2. 7.7 30 0 0

1984 31,915.1 17,370.5 54.4 570 0 0

1985 21,931.4 14,443.1 65.9 380 0 0

1986 2,917.0 2,440.7 83.7 52 0 0

Poland

1979 6,169.0 2,212.5 35.9 203 0 0

1980 16,007.5 905.6 5.7 95 0 0

1981 17,242.6 3,462.3 20.1 310 0 0

1984 363.0 80.0 22.0 6 0 0

1985 2,440.8 2,440.8 100.0 163 1 4.10

Taiwan

1978 510.8

1979 729.1

1980 1,616.0

1981 1,895.5

1982 791.6
Perez and Loughlin: Incidental Catch of Marine Mammals 17

Table 4 (continued)

Groundfish Northern sea lions

Number Number

Vessel Total Observed Percent of hauls dead (alive)

catch b observed c A A

nation catch of catch reported R±2 s(R)

yeara in catch d (xlO-4 )

A

(t) (t) observed (n) YR ± L95%

U.S.S.R.

1978 101,789.1 1,978.2 1.9 122 I 5.06 ± 9.97 51±101**

1979 64,402.3 6,506.5 10.1 609 5 7.68 ± 8.76 49 ±56 **

1980 2,592.6

1984 24.1

Surimi mothershipf

Japan

1978g 248,880.0 214,052.9 86.0 282 2 0.09 ± 0.08 2±2 .*

1979g 251,620.0 239,990.1 95.4 338 0 0

1980 246,870.0 73,504.2 29.8 155 0 0

1981 52,240.0 30,228.4 57.9 62 0 0

1982 32,040.0 16,511.6 51.5 41 0 0

1983 88,620.0 57,652.7 65.1 98 0 0

1984 330,260.0 268,620.2 81.3 499 0 0

1985 379,571.4 328,385.8 86.5 539 0 0

1986 212,430.8 186,338.3 87.7 264 0 0

Freezer mothership

Japan

1980 74.0

Joint venture mothership (countries combined)

1980 169.4 141.7 83.6 4 0 0

1981 398.1

1982 75.1 75.1 100.0 0 0

1983 63.7

1984 44,808.5 44,226.3 98.7 155 0 0

1985h 11,062.1 4,973.3 45.0 154 0 0

1986h 298,939.1 155,621.0 52.1 3,537 0 0

1987h 339,633.6 160,640.5 47.3 3,775 5 0.31 ± 0.24 6±4 *

1988h 263,278.0 129,751.7 49.3 2,811 0 0

Area-III

Small stern trawler

Japan

1978 205.5

1979 163.8

1980 197.9

1981 4.6

1982 218.3

1983 5.5

Republic of Korea

1984 88.0 84.0 95.4 4 0 0

Large freezer trawler

Japan

1984 27.0

Republic of Korea

1978 35.0

1982 5.2

1984 160.5 160.5 100.0 18 0 0 0

Poland

1984 72.4
18 NOAA Technical Report NMFS 104

Table 4 (continued)

Groundfish Northern sea lions

Number Number

Vessel Total Observed Percent of hauls dead (alive)

nation catch catch b of catch observed c reported 8.± 25(8.)

yeara (t) (t) obsened (n) in catchd (xl0-') YR ± 45%

Joint venture motbership (countries combined)

1980 185.0

1987 690.9

Area-IV

Small stern trawler

Japan

1978 36,331.5 2,336.7 6.4 1,210 0 (2) 0

1979 56,383.7 2,279.8 4.0 1,180 3 (12) 13.16 ± 14.89 74 ±82 **

1980 74,142.6 1,032.8 1.4 263 19 (1) 183.97 ± 135.61 1,364 ±990

1981 58,364.2 1,265.7 2.2 331 1 7.90 ± 15.68 46±90 **

1982 46,691.5 4,331.5 9.3 1,648 3 (7) 6.93 ± 7.63 32 ±35 **

1983 38,159.6 8,591.8 22.5 1,300 18 (23) 20.95 ± 9.63 80±36

1984 37,794.0 24,801.5 65.6 1,865 3 (1) 1.21 ± 0.82 5±3 *

1985 30,986.2 26,291.2 84.8 496 2 (1) 0.76±0.59 2±2 *

1986 6,387.1 5,247.6 82.2 126 0 0

Republic of Korea

1981 2,017.4 49.7 2.5 2 0 0

1982 1,358.4 206.6 15.2 18 0 0

1983 1,261.3

1984 1,402.8 356.1 25.4 14 0 0

1985 445.8 211.0 47.3 6 0 0

1986 575.8 539.0 93.6 15 0 0

Large surimi trawler

Japan

1978e 1,223.4

197ge 2,487.1 80.3 3.2 48 0 0

1980 6,741.8

1981 3,342.5

1982 3,037.8

1983 4,411.6

1984 4,464.7 1,959.7 43.9 67 6 30.62 ± 25.79 14 ± 11 **

1985 3,859.3 3,405.7 88.2 51 1 2.94 ± 2.01 1 ± 1 *

Republic of Korea

1986 2,082.0 1,158.1 55.6 13 0 0

Large freezer trawler

People's Republic of China

1986 399.9 394.0 98.5 23 0 0

West Germany

1980 38.8

1981 745.3 140.3 18.8 13 10 712.76±895.19 53 ±73 **

1982 14,550.7 8,120.1 55.8 283 0 0

1983 13,641.2 6,348.2 465 177 0 0

1984 15,489.3 13,137.1 84.8 377 0 0

Japan

1980 2,051.8 44.3 2.2 15 0 0 I

1981 3,946.8 189.7 4.8 72 0 0

1982 2,933.7 863.7 29.4 60 0 0

1983 1,396.0 984.2 70.!> 50 0 0

1984 1,004.3 860.6 85.7 57 0 0

1985 779.9 55.1 7.1 5 0 0
Perez and Loughlin: Incidental Catch of Marine Mammals 19

Table 4 (continued)

Groundfish Northern sea lions

Vessel

nation

yeara

Total

catch

(t)

Number Number

Observed Percent of hauls dead (alive)

catchb of catch observedc reported

(t) observed (n) in catchd

253.4 1.2 10 0 0

2,631.8 11.4 85 0 0

2,820.9 19.3 194 2 7.09 ±9.08

874.0 6.1 63 0 0

2,357.2 22.7 77 0 0

2,669.2 49.2 64 0 0

1,506.2 56.6 25 0 0

371.2 6.3 64 1 26.94 ± 53.10

436.2 7.8 34 0 0

4,057.0 79.4 212 0 0

7,320.4 78.0 393 0 0

2,315.1 71.8 157 0 0

Republic of Korea

1978 1,11 0.6

1979 905.7

1980 20,251.0

1981 23,184.4

1982 14,591.6

1983 14,285.1

1984 10,385.7

1985 5,426.1

1986 2,661.4

Poland

1980 5,917.6

1981 5,597.1

1984 5,108.3

1985 9,379.5

1986 3,222.2

Taiwan

1980 27.5

U.S.S.R.

1978 24,375.1

1979 23,445.2

1980 960.1

3,709.1

2,734.5

120.9

15.2

11.7

12.6

541

256

9

o (1)

18 (3)

7

o

65.83 ± 40.29

578.99 ± 1,193.22

1O±13 **

16±31 **

154 ± 93

56 ± 132**

Joint venture mothership (countries combined)

1980 91.2

1981 4,014.9

1982 19,382.0 12,883.1 66.5 113 8 (2) 6.21 ± 3.00 12 ±6 *

1983 18,492.3 14,741.8 79.7 95 64 (3) 43.41 ± 12.28 80 ± 23 *

1984 51,605.9 47,097.9 91.3 511 122 (4) 25.90 ± 8.14 134 ± 41 *

1985h 53,574.4 34,031.7 63.5 1,617 79 (1) 23.21 ± 7.14 124 ± 38

1986h 70,621.5 43,645.1 61.8 1,647 49 11.23 ± 2.89 79±20

1987h 71,363.5 47,241.0 66.2 1,847 13 (2) 2.75 ± 0.89 20± 7

1988h 66,509.0 38,284.7 57.6 1,188 2 0.52 ± 0.48 3±3 *

a Small stern trawler: trawl vessel <1,500 gross tons; large surimi trawler: trawl vessel >1,500 gross tons targeting on pollock to produce

surimi, a minced meat product; large freezer trawler: trawl vessel >1,500 gross tons which produces frozen whole fish and fillet

products; surimi mothership: vessel with a fleet of catcher boats targeting on pollock to produce a minced meat product; freezer

mothership: vessel with a fleet of catcher boats which produces frozen whole fish or frozen products; joint venture mothership:

processing vessel of the joint venture fisheries which receives catches from U.S. fishing vessels.

b Observed tonnage listed for motherships (all years) and joint venture vessels (1978-84) are total daily catch, and include hauls not

sampled for fish composition nor monitored for presence of marine mammals.

C Data are fishing days with observer coverage for motherships (all years) andjoint venture vessels during 1978-84.

dTotals include only dead animals (excludes "decomposed in catch"); numbers in parentheses are additional animals caught and

released back to sea still alive.

e During 1977-79 Japan reported total tonnage in the fishery only by large trawler classes (not distinguished between surimi or freezer

vessels). These categories have been lumped.

J Excludes Danish seine catches.

gDuring 1977-79 Japan reported total tonnage in the fishery only by motherships (not distinguished between surimi or freezer

vessels). These categories have been lumped.

h Observer data were based on hauls observed for joint venture vessels during 1985-88.
20 NOAA Technical Report NMFS 104

Table 5

Number of northern sea lions reported by U.S. fishery observers incidentally caught by subgroup (area, vessel class,

nation, and year) in the U.S. Exclusive Economic Zone in the Gulf of Alaska, 1978-88, and an estimation of the total

incidental take of northern sea lions in the fishery. Catch rates are the ratio (R) ± twice the standard error (s(R» of

observed incidental take of only dead animals to observed groundfish catch (per 10,000 metric tons [t] basis). Estimated

takes of only dead sea lions are the ratio estimate (YR ) ± the 95% confidence limits (L95%). Refer to Figure 1 for the

locations of the areas in the left column. * = the estimated lower 95% confidence level was less than the number of

animals reported by U. S. observers; ** = the estimated lower 95% confidence level was less than zero.

Groundfish Northern sea lions

Number Number

Vessel Total Observed Perce~lt of hauls dead (alive)

nation catch catch b of catch observedc reported R±2 s(f~)

yeara (t) (t) observed (n) in catchd (X 10-4 ) YR ± L95%

Shumagin

Small stern trawler

Japan

1978 2,262.1 267.4 11.8 200 0 (7) 0

1979 1,990.7 74.8 3.8 41 0 0

1980 1,209.8 2.6 0.2 1 0 0

1981 5,116.8 734.0 14.3 154 0 0

1982 8,782.0 4,203.6 47.9 1,142 0 (2) 0

1983 6,175.1 3,014.9 48.8 867 1 (1) 3.32 ± 4.73 2±3 ** 1984 4,080.6 2,634.5 64.6 173 8 30.37 ± 24.15 12 ± 10 * 1985 6.0 0.2 3.3 1 0 0

Republic of Korea

1981 3,863.1 130.2 3.4 16 0 0

1982 1,230.1 234.9 19.1 18 0 0

1983 2,602.8 1,013.2 38.9 28 1 9.87 ± 15.97 3±4 ** 1984 1,719.3 1,502.7 87.4 49 0 0

1985 552.8 379.8 68.7 13 0 0

Mexico

1979 3,528.4 70.5 2.0 16 0 0

Large surimi trawler

Japan

1978d 4,904.0 91.0 1.9 24 0 0

1979d 2,944.8 214.5 7.3 44 0 0

1980 10.2

1981 9,864.7 1,969.4 20.0 85 0 0

1982 12,901.6 4,784.9 37.1 237 0 0

1983 11,527.6 4,352.9 37.E 251 0 (2) 0

1984 16,041.8 7,704.7 48.0 244 25 32.45 ± 20.45 52 ± 32 * 1985 16,027.2 8,553.1 53.4 260 1 (1) 1.17 ± 1.60 2±3 **

Large freezer trawler

Japan

1980 334.9 38.7 11.6 19 0 0

1981 2,559.6 767.4 30.0 95 0 0

1982 5,171.5 1,594.2 30.8 241 0 0

1983 3,362.3 850.2 25.3 156 0 0

1984 657.5 243.3 37.0 64 0 0

Republic of Korea

1978 33,402.4 2,478.0 7.4 122 1 4.04 ± 7.83 13 ± 26 ** 1979 25,489.8 2,340.1 9.2 107 0 0

1980 31,194.2 4,966.9 15.9 134 0 0

1981 25,960.3 2,109.6 8.1 72 0 0

1982 20,897.7 4,604.1 22.0 200 0 0
Perez and Loughlin: Incidental Catch of Marine Mammals 21

Table 5 (continued)

Groundfish Northern sea lions

Number Number

Vessel Total Observed Percent of hauls dead (alive)

nation catch catch b of catch observedc reported fa 2 s(fl)

yeara in catchd (xl0-4 )

A

(t) (t) observed (n) Y. ± 4,5%

Republic of Korea (continued)

1983 23,412.8 8,374.4 35.8 241 0 0

1984 21,199.4 15,016.1 70.8 306 0 0

1985 7,396.6 5,341.9 72.2 84 0 0

Mexico

1979 1,847.9

Poland

1979 283.9

1980 5,970.8 89.2 1.5 10 0 0

1981 16,817.2 1,712.4 10.2 89 0 0

U.S.S.R.

1978 1,955.9 0.6 0.03 3 0 0

1979 248.1 56.1 22.6 15 0 0

1980 18,404.7 1,363.8 7.4 189 1 7.33 ± 14.19 13 ± 26 **

Joint venture motbership (countries combined)

1978 48.0 48.0 100.0 4 0 0

1979 37.6 37.6 100.0 3 0 0

1980 135.9 65.0 47.8 3 0 0

1981 21.2 15.6 73.6 1 0 0

1982 182.7 182.7 100.0 5 0 0

1983 4,321.8 3,018.6 69.8 83 0 0

1984 11,470.6 10,274.4 89.6 176 I 0.97 ± 0.81 1 ± 1 *

1985e 15,247.3 10,621.5 69.7 415 1 0.94 ± 1.04 1±2 **

1986e 7,448.5 6,771.0 90.9 206 1 1.48 ± 0.89 1 ± 1 *

1987e 25,653.0 11,786.5 46.0 332 1 0.85 ± 1.25 2±3 **

1988e 7.0 6.5 92.9 1 0 0

Chirikof

Small stern trawler

Japan

1978 617.1 56.8 9.2 32 0 0

1979 1,233.3 4.5 0.4 1 0 0

1980 2,917.5 468.5 16.1 72 0 0

1981 3,765.1 996.2 26.5 215 0 (1) 0

1982 5,849.6 3,424.8 58.6 541 1 (2) 2.92 ± 3.75 2±2 *

1983 5,068.5 2,966.3 58.5 644 1 (2) 3.37 ± 4.35 2±2 *

1984 3,452.5 2,604.3 75.4 323 0 (1) 0

Republic of Korea

1981 5,461.9 147.9 2.7 12 0 0

1982 3,100.8 1,619.1 52.2 113 0 0

1983 2,522.5 375.4 14.9 11 0 0

1984 642.5 538.0 83.7 13 0 0

Mexico

1979 812.1 169.3 20.8 36 2 118.13 ± 141.02 10 ± 11 **

Large surimi trawler

Japan

1978d 8,968.3 1,294.2 14.4 152 5 (2) 38.63 ± 51.42 35 ±45 **

1979d 3,316.6 781.2 23.6 80 0 0

1980 6,756.6 48.1 0.7 6 0 0

1981 19,832.0 1,162.0 5.9 39 1 8.61 ± 16.86 17 ± 34 **

1982 20,092.3 9,487.0 47.2 347 0 (2) 0

1983 18,070.8 7,742.4 42.8 309 11 14.21 ± 8.95 26 ± 16 *
22 NOAA Technical Report NMFS 104

Table 5 (continued)

Groundfish Northern sea lions

Number Number

Vessel Total Observed Percent of hauls dead (alive)

nation catch catch b of catch obscrvedc reported R± 2 s(R)

yeara (t) observed In) in catch d (X 10-4 )

A

(t) Y. ± L95%

Japan (continued)

1984 19,370.3 10,525.0 54.3 362 16 (1) 15.20 ± 7.49 29 ± 15 *

1985 206.3 131.3 63.6 16 0 0

Large freezer trawler

Japan

1980 2,328.9 90.7 3.9 17 1 110.25 ± 218.82 26 ±54 **

1981 6,729.5 2,083.8 31.0 145 2 9.60 ± 11.39 6±8 **

1982 5,775.7 1,778.5 30.8 300 1 5.62 ±9.39 3±6 **

1983 8,393.6 2,781.7 33.1 428 1 3.60 ± 5.88 3±5 **

1984 2,019.7 875.1 43.3 303 0 0

1985 869.1 756.3 87.0 16' 0 0

Republic of Korea

1978 875.8 189.9 21.7 11 0 0

1981 31,658.0 1,628.8 5.1 69 0 0

1982 23,444.4 3,747.7 16.0 179 5 (1) 13.34±20.19 31 ± 47 **

1983 19,733.4 6,702.9 34.0 173 0 0

1984 16,145.8 11,258.2 69.7 282 0 0

1985 869.1 756.3 87.0 16 0 0

Mexico

1979 17.5

Poland

1979 18,673.7 204.0 1.1 20 0 0

1980 7,303.6

1981 24,237.5 570.6 2.4 45 4 70.10 ± 106.23 170 ± 259**

1984 665.3 399.1 60.0 30 2 50.11 ± 65.06 3±5 **

U.S.S.R.

1978 56,323.1 2,110.3 3.8 210 10 (1) 47.39 ± 32.42 267 ± 180

1979 8,156.8 367.7 4.5 58 0 0

1980 19,565.9 492.9 2.5 47 0 0

Joint venture mothership (countries combined)

1979 61.5 61.5 100.0 4 0 0

1980 876.7

1981 16,944.3 4,439.0 26.2 23 13 29.29 ± 29.24 50 ± 51 **

1982 71,126.9 32,159.7 45.2 231 651 (5) 202.43 ± 105.80 1,440 ± 742

1983 125,127.5 110,034.3 87.9 549 255 (1) 23.17 ± 5.66 290 ± 70 *

1984 178,062.8 165,400.2 92.9 875 211 (1) 12.76 ± 1.72 227 ± 30 *

1985' 214,376.7 113,265.7 52.8 2,993 52 (2) 4.59 ± 1.53 98 ±32

1986' 42,654.7 22,886.8 53.7 596 38 (1) 16.60 ± 8.40 71 ± 35 *

1987' 1,626.9 1,376.6 84.6 84 0 0

1988' 1,136.0 1,034.9 9L 57 0 0

Kodiak

Small stern trawler

Japan

1978 5,344.6 1,146.2 21.4 543 10 (2) 87.24 ± 57.30 47 ±30

1979 5,399.5 975.2 18.1 401 1 10.25 ± 18.60 6±9 **

1980 9,581.5 571.3 6.0 179 0 (1) 0

1981 7,157.7 342.4 4.8 126 0 (3) 0

1982 5,853.7 1,723.5 29.4 766 0 (1) 0

1983 5,359.6 2,027.1 37.8 1,105 2 (13) 9.87 ± 11.01 5±5 *

1984 6,515.0 4,366.5 67.0 589 1 (1) 2.29 ± 2.64 1 ± I *

1985 8.6 1.8 20.9 3 0 0
Perez and Loughlin: Incidental Catch of Marine Mammals 23

Table 5 (continued)

Groundfish Northern sea lions

Number Number

Vessel Total Observed Percent of hauls dead (alive)

nation catch catch b of catch observedc reported R±2 s(R)

yeara (t) (t) observed (n) in catch d (X 10-4 ) y. ± 45%

Republic of Korea

1981 163.3 4.7 2.9 4 0 0

1982 2.1 0.3 14.3 I 0 0

Mexico

1979 4,143.4 804.3 19.4 86 0 0

Large surimi trawler

Japan

1978d 15,522.4 3,972.4 25.6 691 II (2) 27.69 ± 22.56 43 ± 34 *

1979d 25,059.6 5,020.4 20.0 379 15 (4) 29.88 ± 23.86 75 ±59

1980 16,949.6 616.0 3.6 50 0 0

1981 4,037.7

1982 2,119.5 673.0 31.8 21 0 0

1983 2,806.9 1,179.6 42.0 62 0 0

1984 10,488.2 6,356.6 60.6 225 4 6.29 ± 4.85 7±5 *

1985 6,762.4 3,088.8 45.7 115 0 0

Large freezer trawler

Japan

1980 9,233.2 181.5 2.0 41 0 0

1981 4,646.3 472.7 10.2 96 I 21.16 ± 40.46 10 ± 18 **

1982 8,580.9 2,569.9 30.0 761 I (3) 3.89 ± 6.51 3±6 **

1983 5,446.1 1,266.3 23.2 504 I 7.90 ± 13.86 4±8 **

1984 1,827.2 706.8 38.7 278 0 0

Republic of Korea

1981 95.5 0.6 0.6 2 0 0

1982 938.7 740.6 78.9 34 0 0

Poland

1978 1,266.0

1980 786.9

1984 2,246.8 1,321.8 58.8 95 0 0

U.S.S.R.

1978 4,342.0 165.1 3.8 54 0 0

1979 22,577.9 3,156.2 14.0 467 5 15.84 ± 13.10 36 ± 29

1980 16,632.4 775.7 4.7 161 5 (I) 64.46 ± 65.77 107 ± 108**

Freezer mothership

Mexico

1979 234.3 234.3 100.0 9 0 0

Joint venture mothership (countries combined)

1979 1,332.3 205.5 15.4 15 0 0

1980 898.1

1982 3,140.4 1,428.8 45.5 14 10 69.99 ± 51.09 22 ± 17 *

1983 13,534.9 11,302.0 83.5 245 13 (1) 11.50 ± 8.79 16 ± II *

1984 30,091.7 28,283.1 94.0 801 7I (3) 25.10 ± 6.02 76 ± 17 *

1985' 17,580.7 12,160.1 69.2 609 2 1.64 ± 1.29 3±2 *

1986' 15,183.8 7,998.5 52.7 317 4 5.00 ± 3.44 8±5 *

1987' 5,245.7 4,437.4 84.6 330 0 0

1988' 2,628.0 1,697.5 64.6 101 0 0
24 NOAA Technical Report NMFS 104

Table 5 (continued)

Groundfish Northern sea lions

Number Number

Vessel Total Observed Percent of hauls dead (alive)

nation catch catch b of catch observed c reported R±2 s(R)

yeara (t) (t) observed (n) in catch d (XI0-') A

Y. ± L95%

Yakutat

Small stern trawler

Japan

1978 5,644.8 498.1 8.8 330 3 (2) 60.23 ± 66.42 34 ±37 ** 1979 4,024.6 316.9 7.9 108 I 31.56 ± 60.82 13 ± 24 ** 1980 6,705.5 406.7 6.1 161 0 (I) 0

1981 7,201.3 93.9 1.3 57 0 0

1982 9.6 5.6 58.3 II 0 0

1983 20.2

Republic of Korea

1981 630.7

Mexico

1979 48.2

Large surirni trawler

Japan

1978d 2,321.6 351.2 15.1 106 0 (I) 0

1979d 4,330.6 624.7 14.4 104 0 0

1980 497.4 1.0 0.2 1 0 0

1981 188.3

Large freezer trawler

Japan

1980 8,495.2 238.6 2.8 58 0 (1) 0

1981 4,736.0 223.0 4.7 60 0 0

Republic of Korea

1979 3,243.5

1980 210.2 62.6 29.8 II 1 159.74 ± 303.85 3±7 ** 1981 6,847.1 29.9 0.4 1 0 0

Poland

1981 27.8

U.S.S.R.

1978 7.0

1979 63.6 19.6 30.8 17 0 0

Joint venture mothership (countries combined)

1979 47.8 37.0 77.4 6 0 0

Southeastern

Small stern trawler

Japan

1978 59.0

1979 1,224.9 139.3 I }.L, 96 0 0

1980 557.1 101.9 18.3 43 0 0

1981 594.4 63.8 10.7 22 0 0

Large surirni trawler

J<lpan

1978d 5,252.2 195.0 3.7 31 0 0

1979d 6,583.1 1,756.5 26.7 485 0 (3) 0

1980 9.9
Perez and Loughlin: Incidental Catch of Marine Mammals 25

Table 5 (continued)

Vessel

nation

yeara

Total

catch

(t)

Groundfish

Number Number

Observed Percent of hauls dead (alive)

catch b of catch observed c reported

(t) observed (n) in catchd

Northern sea lions

R±2 s(R)

(X 10-')

6,144.9

6,049.9

Large freezer trawler

Japan

1980

1981

Republic of Korea

1978 3.3

1979 412.2

U.S.S.R.

1978 8.0

529.6

41.8

8.6

0.7

180

14

o

o

o

o

Joint venture mothership (countries combined)

1979 11.5 8.6 74.8 2 o o

a Small stern trawler: trawl vessel <1,500 gross tons; large surimi trawler: trawl vessel >1,500 gross tons targeting on pollock to produce

surimi, a minced meat product; large freezer trawler: trawl vessel >1,500 gross tons which produces frozen whole fish and fillet

products; surimi mothership: vessel with a fleet of catcher boats targeting on pollock to produce a minced meat product; freezer

mothership: vessel with a fleet of catcher boats which produces frozen whole fish or frozen products; joint venture mothership:

processing vessel of the joint venture fisheries which receives catches from U.S. fishing vessels.

b Observed tonnage listed for motherships (all years) and joint venture vessels (1978-84) are total daily catch, and include hauls not

sampled for fish composition nor monitored for presence of marine mammals.

C Data are fishing days with observer coverage for motherships (all years) and joint venture vessels during 1978-84.

dTotals include only dead animals (excludes "decomposed in catch"); numbers in parentheses are additional animals caught and

released back to sea still alive.

e During 1977-79 Japan reported total tonnage in the fishery only by large trawler classes (not distinguished between surimi or freezer

vessels). These categories have been lumped.

f Observer data were based on hauls observed for joint venture vessels during 1985-88.

relatively smaller fisheries off Washington, Oregon,

and California (Fig. 7A) and in the Gulf of Alaska

(Fig. 7B) than for the large fisheries in the Bering

Sea (Fig. 7C). The percentage of the total fish catch

sampled by U.S. observers by region was likewise

similar; about 35% of the total fish catch during

1973-88 was monitored for incidental take of marine

mammals and the amount of observer coverage increased each year to about 60% by 1988 (Tables 1

and 2). However, fish catch sampling by observers by

year averaged less than 50% of the total fish catch

prior to 1982 (Table 2) and less than 10% during

) 973-76. The combined foreign and]V fisheries have

been at a similar level of groundfish catch each year

since 1977, and foreign fisheries were slightly higher

(7-8%) during 1973-76 (Table 2). Thus, numbers of

incidentally caught mammals reported by observers

during 1973-81 on a regional or country-specific

fishery basis were probably less than the true level of

incidental take (on vessels with observers aboard) at

that time because observers had less opportunity to

see marine mammals in the catch.

Northern Sea Lions in Alaska

Incidental Catch Rates-Most northern sea lions

caught died during fishing operations (Tables 1, 4,

and 5). From 1978 to 1988, 14% of the incidental

catch of northern sea lions were alive when the haul

was retrieved, and these were released (Table I). It

was more common to observe live sea lions caught in

trawl gear in the 1970s and early 1980s in the foreign

fisheries than in recent years in the]V fisheries which

had a predominance of dead sea lions in the catch

(Fig. 8).

Incidental take of northern sea lions, both reported and estimated, during 1978-88 is listed by

country, vessel class, and statistical fishing area in

Table 4 for the Bering Sea and Table 5 for the Gulf of

Alaska. Catch rates ranged from zero to 713 sea lions

taken incidentally per 10,000 t of fish caught in the

Bering Sea. The highest observed catch rates for the

Bering Sea occurred in Area-IV during 1980-81 in

the large freezer trawler (vessels >1,500 gross tons

producing frozen whole fish and fillet products)
26 NOAA Technical Report NMFS 104

Washington, Oregon and California regional basis, the average observed rates of incidental take of dead northern sea lions during 1978-88

were higher for statistical areas in the Gulf of Alaska

region than for those in the Bering Sea (Table 6).

These average rates are values expressed on a

10,000 t basis. They do not reflect estimates of total

incidental take in the fishery, which were often substantially less than the observed rate for a specific

fishery, area, and time period (Tables 4 and 5). The

percentage of the total groundfish take monitored

for the presence of incidentally caught marine mammals ranged from 0.03% to 100% on foreign trawlers,

and from 15.4% to 100% on foreign and]V processors (mothership vessels). Also, the calculated incidental catch rates in Tables 4 and 5 may, in some

cases, be underestimated for foreign processors because observers had less opportunity to observe inci-

.dentally caught marine mammals in the mothershipbased foreign fisheries (and incidental catch rates

were calculated on the basis of total daily groundfish

catch, rather than observed hauls).

Calculated standard errors of incidental catch rates

(from the ratio of observed marine mammal mortality to groundfish catch) were often high, almost

equal to the value of the calculated catch rate. Thus,

calculated 95% confidence limits for these rates often yielded lower limit estimates of total take that

were less than the actual take seen by U.S. fishery

observers, and sometimes even less than zero (Tables

1978 79 80 81 82 83 84 85 86 87 88

20

o--,-.........."V"'-.

40

o

60

80

20

40

60

80

100 Bering Sea and Aleutian Islands

100 Gulf of Alaska

CIl

Cl

e

CIl 80 >

0

...

lii 60

8 III

.a

0 40

E

20 CIl

l1.

0

1978 79 80 81 82 83 84 85 86 87 88

c

A

100

1978 79 80 81 82 83 84 85 86 87 88

Year

• Foreign EJ Joint-venture

Figure 7

Percent observer coverage of the total number of fishing

days by foreign and joint venture (IV) vessels in the U.S.

Exclusive Economic Zone, 1978-88: (A) off the coast of

Washington, Oregon, and California; (B) in the Gulf of

Alaska; and (C) in the Bering Sea and Aleutian Islands

region. Observer coverage of]V fisheries during 1978 (first

year of the ]V fisheries) was near 100% because total

fishing effort that year was very low, occurring on a few

boats all of which had observers aboard.

1,000

!:!

fl 800 .~.,

c:

,g

as 600 III

'0

.a 400 E

:>

c:

..,

CIl

200 III

.a

0

o

1mn M 83 M M

Year

Figure 8

Total number of northern sea lions reported by U.S.

fishery observers seen in the groundfish catch on foreign

and joint venture vessels in the U.S. Exclusive Economic

Zone in Alaska during 1978-88. Decomposed animals were

not included.

fisheries of the U.S.S.R. (579 sea lions per 104 t;

1980) and West Germany (713 sea lions per 104 t;

1981) (Table 4). In the Gulf of Alaska incidental

catch rates of northern sea lions ranged from zero to

202 animals per 104 t of fish caught. The highest observed catch rate of northern sea lions in the Gulf of

Alaska occurred in the Chirikof area during 1982 in

the ]V fisheries in Shelikof Strait (Table 5). On a

_Dead o Released alive
Perez and Loughlin: Incidental Catch of Marine Mammals 27

Table 6

Observed incidental mortality rate of northern sea lions per 104 metric tons of groundfish caught by region, area,

fishery, and year (1978-88) in the .S. Exclusive Economic Zone in Alaska. a Catch rates are the ratio ± twice the

standard error of observed incidental take to observed ground fish catch. The sample size is shown in parentheses below

each rate. b Refer to Figure 1 for the locations of the areas in the left column. ]V = joint venture fishery; NF = no fishery.

Region

area

fishery 1978 1979 1980 198! 1982 1983

Bering Sea and Aleutian Islands

Foreign 2.94 ± 1.35 3.63 ± 1.41 8.27 ± 4.73 3.25 ± 2.35 1.62 ± 0.53 1.64 ± 0.41

(8,206) (8,305) (3,329) (5,402) (16,194) (25,121)

JV NF NF l.ll ± 1.93 0.35 ± 0.63 1.48 ± 0.63 6.95 ± 2.22

(207) (264) (809) (874)

Area-I

Foreign 5.19 ± 2.56 1.37 ± 1.04 3.23 ± 2.67 0.92 ± 1.37 1.99 ± 0.72 0.79 ± 0.34

(2,931) (2,885) (1,445) (2,332) (6,833) (10,115)

JV NF NF 1.13 ± 1.94 0.35 ± 0.62 0.49 ± 0.37 1.95 ± 0.88

(203) (264) (695) (779)

Area-II

Foreign 0.85 ± 0.94 1.80 ± 1.33 1.00 ± 1.36 3.52 ± 2.39 0.37 ± 0.47 1.40 ± 0.62

(3,524) (3,936) (1,523) (2,533) (7,158) (13,416)

JV NF NF 0 0

(4) (0) (1) (0)

Area-III

Foreign

(0) (0) (0) (0) (0) (0)

JV J F NF NF NF NF

(0)

Area-IV

Foreign 0 41.22 ± 23.05 148.14 ± 109.92 23.34 ± 31.80 3.06 ± 2.46 10.72 ± 4.94

(1,751) (1,484) (361) (537) (2,203) (1,590)

JV F NF 6.21 ± 3.00 43.41 ± 12.28

(0) (0) (1l3) (95)

Gulf of Alaska

Foreign 31.21 ± 12.51 14.04 ± 8.06 7.24 ± 5.57 5.23 ± 4.70 1.94 ± 1.78 4.22 ± 1.97

(2,509) (2,561) (1,380) (1,518) (4,912) (4,779)

JV 0 0 0 29.18 ± 29.02 195.73 ± 100.45 21.55 ± 5.49

(4) (30) (3) (24) (250) (877)

Shumagin

Foreign 3.52 ± 6.84 0 1.55 ± 2.93 0 0 1.14 ± 1.27

(349) (223) (353) (511) (1,838) (1,543)

JV 0 0 0 0 0 0

(4) (3) (3) (I) (5) (83)

Chirikof

Foreign 41.08 ± 26.65 13.10 ± 18.16 9.09 ± 18.OJ 10.62 ± 10.54 3.49 ± 3.52 6.32 ± 3.67

(405) (195) (142) (625) (1,480) (1,565)

JV NF 0 29.29 ± 29.24 202.43 ± 105.80 23.17 ± 5.66

(4) (0) (23) (231) (549)

Kodiak

Foreign 39.74 ± 21.70 21.09 ± 13.00 23.32 ± 24.16 12.19±23.83 1.75 ± 2.88 6.71 ± 6.36

(1,288) (1,333) (431) (228) (1,583) (1,671)

JV NF 0 NF 69.99 ± 51.09 11.50 ± 8.79

(15) (0) (14) (245)

Yakutat

Foreign 35.32 ± 38.71 10.40 ± 20.12 14.11 ± 27.72 0 0

(436) (229) (231) (118) (11) (0)

JV F 0 NF NF F NF

(6)

Southeastern

Foreign 0 0 0 0 NF NF

(31) (581) (223) (36)

JV NF 0 NF NF NF NF

(2)
28 NOAA Technical Report NMFS 104

Table 6 (continued)

Region

area

fishery 1984 1985 1986 1987 1988

Bering Sea and Aleutian Islands

Foreign 1.31 ± 0.24 1.52 ± 0.~4 ] .03 ± 0.33 0 NF

(28,215) (18,270) (6,363) (1,544)

JV 4.34 ± 1.13 3.58 ± ].0] 1.41 ±0.27 0.36 ± 0.10 0.34 ± 0.09

(2,497) (13,720) (2] ,478) (20,618) (23,691)

Area-l

Foreign 1.46 ± 0.33 2.27 ± 0.39 1.53 ± 0.46 0 F

( 13,327) (10,364) (3,846) (232)

JV 0.88 ± 0.25 UO ± 0.33 0.94 ± 0.25 0.16 ± 0.08 0.40 ± 0.11

(] ,83]) (11,949) (16,294) (14,996) (19,692)

Area-Il

Foreign 0.92 ± 0.32 0.34 ± 0.19 0 0 NF

(12,197) (6,891) (2,158) (1,312)

JV 0 0 0 0.31 ± 0.24 0

(155) (154) (3,537) (3,775) (2,811)

Area-Ill

Foreign 0 NF NF f F

(22)

]V t F NF NF NF

(0)

Area-IV

Foreign ].89 ± 0.99 0.75 ± 0.52 0 NF F

(2,669) (1,015; (359)

JV 25.90 ± 8.14 23.21 ± 7.14 1l.23 ± 2.89 2.75 ± 0.89 0.52 ± 0.48

(511) (1,617) (1,647) (1,847) (1,188)

Gulf of Alaska

Foreign 8.48 ± 2.60 0.55 ± 0.72 'F NF NF

(3,336) (508)

JV 13.88 ± 1.73 4.04 ± 1.26 J1.42 ± 4.94 0.57 ± 0.77 0

(1,852) (4,017) (1,119) (746) (159)

Shumagin

Foreign 12.18 ± 5.53 0.70 ± 0.89 NF 1 F NF

(836) (358)

JV 0.97 ± 0.81 0.94 ± 1.04 1.48 ± 0.89 0.85 ± 1.25 0

(176) (415) (206) (332) (1)

Chirikof

Foreign 6.87 ± 2.91 0 NF NF NF

(1,313) (32)

JV 12.76 ± 1.72 4.59 ± 1.53 16.60±8.40 0 0

(875) (~,993) (596) (84) (57)

Kodiak

Foreign 3.92 ± 2.61 0 F F F

(1,187) (118)

]V 25.10 ± 6.02 1.64 ± 1.29 5.00 ± 3.44 0 0

(801) (609) (317) (330) (101 )

Yakutat

Foreign NF NF NF NF NF

JV NF F NF NF NF

Southeastern

Foreign NF NF NF NF NF

JV NF NF NF NF NF

a Incidental take rates in the table refer only to dead sea lions caught (no decomposed animals nor animals caught and released alive).

Dashes indicate that no northern sea lions were observed in the catch, but since observer coverage was rarely near 100%, the true

rate was not necessarily zero. Rates for the foreign fishery were based only on reponed takes and fish catch which occurred on

independen t stern trawlers.

b The sample size is the number of hauls observed for presence of marine mammals, except for joint venture vessels during 1978-84

for which the number of fishing days was used as the sample size.
Perez and Loughlin: Incidental Catch of Marine Mammals 29

4 and 5). Neither of these cases are realistic, and

either zero or the actual reported take, whichever

was higher, was used as the minimum estimate in

such cases in summing incidental takes for specific

fisheries and areas to get totals by region and year.

The calculated negative lower confidence limits suggest that either the underlying distribution of the

data may not be normal or the sample size is too

small, or both. These confidence intervals have been

reported (Tables 4 and 5) to show the status and

variability of the data. In many cases bootstrapped

variances will yield more realistic confidence interval

values. However, this procedure was not used, nor

were the data transformed, because of the small numTable 7

Observed incidental mortality rates of northern sea lions taken by vessel class (countries combined) and area in the

foreign trawl fishery (motherships excluded) in the U.S. Exclusive Economic Zone off Alaska, 1978-87. The number

of hauls observed, average groundfish catch (metrjc tons, t) per observed haul, agd percent of the total fishery by

area are also shown. Mortality rates are the ratio !fl.) ± twice the standard error (s!fl.» of observed incidental take to

observed fish catch (per 10,000 t). Refer to Figure 1 for the locations of the areas in the left column.

Number Average

Percent of observed

of hauls fish catch 1\ 1\

Area total observed per haul R± 2 s(R)

vessela fisheryb (n)C (t) (X 10-4)

Area-I

Small stern trawler 13.8 21,047 (35) 6.6 3.45 ± 0.86

Large surimi trawler 33.9 10,532 (28) 25.7 1.88 ± 0.50

Large freezer trawler 52.3 22,731 (38) 25.0 1.32 ± 0.26

Area-II

Small stern trawler 23.5 36,623 (25) 3.8 2.15 ± 0.68

Large surimi trawler 54.3 14,051 (31) 27.5 0.52 ± 0.21

Large freezer trawler 22.2 3,974 (15) 20.2 0.88 ± 0.77

Area-IV

Small stern trawler 60.2 8,474 (20) 9.2 6.32 ± 2.17

Large surimi trawler 4.3 131 (23) 49.8 10.73 ± 9.66

Large freezer trawler 35.5 3,364 (28) 19.4 5.81 ± 3.11

Shumagin

Small stern trawler 11.8 2,719 (33) 5.2 7.01 ± 6.28

Large surimi trawler 18.2 1,094 (41) 25.1 9.47±6.15

Large freezer trawler 69.9 2,198 (21) 23.7 0.38 ± 0.48

Chirikof

Small stern trawler 9.2 2,013 (38) 6.6 2.99 ± 2.36

Large surimi trawler 21.9 1,165 (36) 25.9 10.95 ± 4.48

Large freezer trawler 68.9 2,579 (14) 14.4 7.01 ± 3.47

Kodiak

Small stern trawler 23.4 3,803 (24) 3.1 11.70 ± 6.20

Large surimi trawler 20.4 801 (40) 21.5 13.34 ± 8.23

Large freezer trawler 56.3 3,235 (13) 4.6 13.31 ± 6.21

Yakutat

Small stern trawler 44.0 667 (5) 2.0 3 0.28 ± 29.48

Large surimi trawler 1.2 10 (35) 24.3 0

Large freezer trawler 54.8 348 (4) 3.8 7.65 ± 15.00

a Small stern trawler: trawl vessel <.1,500 gross tons; large surimi trawler: trawl vessel >1,500 gross tons targeting on pollock to produce

surimi, a minced meat product; large freezer trawler: trawl vessel >1,500 gross tons which produces frozen whole fish and fillet

products.

b The percent of the total fishery of the three vessel classes in each area. During 1977-79 Japan reported total tonnage in the fishery

only by large trawler classes (not distinguished between surimi or freezer vessels). Estimates of the total fish catch for Japan by each

large trawler class during 1977-79 were based on the relative proportion of the total fish catch by each of the two Japanese large

trawler classes during 1980-88.

C The numbers in parentheses are the percent of observer coverage of the total fish catch by the vessel class fishery in the respective

area.
30 NOAA Technical Report NMFS 104

ber of hauls with incidentally caught marine mammals. Even if such efforts were undertaken, they

would not help in understanding the data any better.

The observed average incidental take rates ranged

from 0.35 to 8.28 dead northern sea lions per 104 t of

total fish catch each year in the Bering Sea during

1978-88 in the foreign and]V fisheries (Table 6).

Except for the years 1978 and 1980 for Area-I and

1981 for Area-II, incidental take rates of dead sea

lions occurring in fishing trawls were equivalent or

lower than two animals per 104 t (Table 6). Northern

sea lions were not observed caught in the U.S. EEZ in

Area-III. However, fishing effort was low during

1978-88 in Area-III and the size of the U.S. EEZ in

Area-III is also very small (Fig. 1). Although the rate

of sea lions taken incidentally in the U.S. waters of

Area-III may be zero, the catch rate for international

waters of Area-III cannot be ascertained (but observers aboard foreign vessels passing through international waters have reported some sea lions incidentally caught there). The likelihood of northern sea

lions being incidentally caught in trawls in the Bering

Sea was greatest in Area-IV where catch rates ranged

from 0.52 to 143.80 dead sea lions per 104 t of fish

catch in the foreign and]V fisheries during 1978-88

(Table 6). Higher incidental take rates for Area-IV

should be expected because Area-IV encompasses a

large part of the Aleutian Islands where several

northern sea lion rookeries are located (Loughlin et

al. 1984).

In the Gulf of Alaska average incidental catch rates

ranged up to 31 dead sea lions per 104 t of fish catch

in trawls of the foreign fishery and up to 196 dead

sea lions per 104 t in trawls of the ]V fishery by year

during 1978-88 (Table 6). These were based primarily on observed incidental catch in the Chirikof,

Kodiak and Yakutat statistical fishing areas where sea

lions are most numerous in the Gulf of Alaska

~Loughlin et al. 1984). Dead sea lions were not observed in the Southeastern fishing area where fishing

effort was low (Table 5). Except for 1984, dead sea

lions occurred in fishing trawls in the Shumagin area

Table 8

Estimated incidental mortality of northern sea lions in the foreign and joint venture groundfish trawl fisheries (all

countries combined) in the U.S. Exclusive Economic Zone of the Bering Sea and Aleutian Islands during 1978-88.

Estimates of the number of dead northern sea lions are the ratio estimate (YR,Ja and the lower (L1) and upper (L2) 95%

confidence limits. b * = the estimated lower 95% confidence level was less than the number of animals reported by U.S.

observers (the latter was used as the minimum estimate); ** = the estimated lower 95% confidence level was less than

zero (the number of animals reported caught by U.S. observers was used as the minimum estimate).

Foreign fisheries Joint venture fisheries

Estimated number Estimated number

Percent of dead sea lionse Percent of dead sea lions

Total fish Total fish

groundfish catch groundfish catch

Year catch (t)C observedd YR, L1 L. catch (t) C observed!' YRs L, L2

1978 1,284,470 10.2 335 249 421 no fishery

1979 1,194,532 13.5 465 340 590 no fishery

1980 1,196,256 5.9 472 304 640 32,572 27.6 4 1 ** 10

1981 1,170,521 9.8 422 295 549 78,535 36.4 9 4 14

1982 1,102,650 28.0 210 158 262 108,727 68.5 16 11 * 23

1983 1,050,960 41.1 198 156 240 211,155 57.9 118 90 146

1984 1,107,131 61.2 147 126 168 357,542 92.2 157 143 * 199

1985 991,368 67.3 112 97 127 639,422 47.2 187 145 229

1986 442,253 69.3 31 24 38 1,150,213 56.0 154 126 182

1987 17,500 64.9 0 0 0 1,355,901 53.0 46 34 58

1988 no fishery 1,301,416 57.3 43 32 54

Total 9,557,639 29.8 2,392 2,122 2,662 5,235,483 56.8 734 660 808

a The sum of estimates for the subgroups (area, vessel class, country, and year) used in Table 4.

b Sample size (number of hauls observed, or observed fishing days for joint venture fisheries during 1980-84) can be summed from

the data by area, vessel class, country, and year in Table 4.

C Trawl catches only during 1978-88. Danish seine catches by Japanese mothership-based fisheries were excluded for foreign fisheries.

d Values in this column were based on independent stern trawler data only; no mothership-based fishery data.

e The estimated number of dead northern sea lions includes estimates for the Japanese mothership-based trawl fisheries using

observed mortality rates from independent foreign (all countries combined) stern trawlers as an estimate.

f Values for the percent of fish catch observed during 1980-84 listed in this column are higher than true values (unknown) since joint

venture data for those years were based on total daily fish catch rather than hauls observed.
Perez and Loughlin: Incidental Catch of Marine Mammals 31

Table 9

Estimated incidental mortality of northern sea lions in the foreign and joint venture groundfish trawl fisheries (all

countries combined) in the U.S. Exclusive Economic Zone of the Gulf of Alaska during 1978-88. Estimates of the

number of dead northern sea lions are the ratio estimate ()~'Rs) a and the lower (L,) and upper (L2 ) 95% confidence

limitsb. * = the estimated lower 95% confidence level was less than the number of animals reported by U.S. observers

(the latter was used as the minimum estimate); ** = the estimated lower 95% confidence level was less than zero (the

number of animals reported caught by U.S. observers was used as the minimum estimate).

Foreign fisheries Joint venture fisheries

Estimated number Estimated number

Percent of dead sea lions Percent of dead sea lions

Total fish Total fish

groundfish catch groundfish catch

Year catch (t) C observed YRs L, L2 catch (t) C observedd YRs L, L.

1978 149,080 8.6 247 164 330 48 100.0 0 0 0

1979 145,655 11.7 197 125 269 1,491 23.5 2 2 2

1980 171,801 6.4 240 128 352 1,911 3.4 3 2 4

1981 198,242 7.7 159 109 209 16,966 26.3 50 13 ** 101

1982 124,750 33.0 68 21 115 74,450 45.4 1,462 721 2,203

1983 114,502 37.2 69 49 89 142,984 87.0 306 268 * 376

1984 107,072 61.7 115 78 152 219,625 92.9 304 283 * 339

1985 31,829 57.4 8 5 11 247,205 55.0 102 70 134

1986 no fishery 65,287 57.7 80 44 116

1987 no fishery 32,526 54.1 4 1 7

1988 no fishery 3,771 72.6 1 1 1

Total 1,042,930 21.5 1,103 926 1,280 806,263 69.6 2,314 1,569 3,059

a The sum of estimates for the strata (area, vessel class, country, and year) in Table 5.

b Sample size (number of hauls observed, or observed fishing days for joint venture fisheries during 1978-84) can be summed from

the data by area, vessel class, country, and year in Table 5.

C Trawl catches only during 1978-88.

d Values for the percent of fish catch observed during 1978-84 listed in this column are higher than true values (unknown) since joint

venture data for those years were based on total daily fish catch rather than hauls observed.

at rates similar to those for the adjacent Area-I of the

Bering Sea.

Catch rates were generally highest (>10 dead sea

lions per 104 t of fish catch) for large surimi trawlers

(vessels >1,500 gross tons targeting on pollock to produce surimi, a minced meat product) in areas of high

sea lion abundance (Area-IV, Chirikof and Kodiak;

Table 7). Rates for small stern trawlers (vessels <l,500

gross tons) were higher than for large trawlers in

Area-I and Area-II of the Bering Sea (Table 7). However, rates for small stern trawlers were less than

those of large freezer trawlers in all other areas of

Alaska except Yakutat where observer coverage for

small stern trawlers was very low (5%).

The declines in incidental catch rates seen in recent years by foreign fisheries is principally a function of decreasing fishing effort. ]V fisheries, which

reported the highest incidental take of northern sea

lions during 1978-88 and had the lower fishing effort, caught a higher average number of mammals

per day or haul than foreign fisheries.

Estimated Take-A total estimate of 6,543 (lower

95% confidence limit, L] = 5,728; upper 95% confidence limit, L2 = 7,358) northern sea lions were incidentally caught and died in trawls of both the foreign

and ]V fisheries throughout Alaska during 1978-88

based on U.S. observer data of dead animals (Tables

8 and 9). However, there has been a declining trend

in total estimates of northern sea lions caught by foreign and]V groundfish fisheries in Alaska during the

1980s (Fig. 9). For example, an estimated 335 sea

lions were incidentally taken by these fisheries in the

Bering Sea during 1978, but only 43 were taken in

1988 (Table 8). Likewise, 247 were estimated to have

died during fishing operations in 1978 in the Gulf of

Alaska, but only one sea lion was estimated to have

been killed during 1988 (Table 9). With the exception of the 1982 Shelikof Strait]V fishery (estimated

total incidental catch of 1,440 ± 742 dead sea lions in

the Chirikof area based on an average observed mortality rate of 202.4 ± 52.9 dead sea lions per 104 of

fish catch; Table 5), ]V fisheries throughout Alaska

were estimated to have an average incidental mortality in the catch of less than 500 sea lions per year

(Fig. 9). Foreign fisheries were estimated to have

caught more than 500 sea lions each year prior to

1982 (Fig. 9).
32 NOAA Technical Report NMFS 104

1.500

,g

1978 79 80 81 82 B3

Year

84 85 86 87 88

Figure 9

Estimated number of incidentally taken northern sea lions which died during trawl fishing

operations of foreign and joint venture vessels

in the U.S. Exclusive Economic Zone in Alaska

during each year, 1978-88.

Area-I Area·1I Area·11I Area-IV Shumagin Chirikof Kodiak Yakutat Southeast

60

50

'iii'

III 40 eIII

:s- 30

E

Gl 20 Gl

tI.

10

0

• Foreign

o Groundllsh catch

• sea lion catch rate

ILl Joint venture

Estimated number of dead sea lions

Figure 10

Percent of total for the amount of metric tons

of groundfish caught in the fishery, incidental

catch rate (ratio of observed number of dead

(no decomposed) sea lions per 104 metric tons

of groundfish catch), and the total estimated

number of incidentally taken northern sea lions which died during trawl fishing operations

of foreign (motherships excluded) and joint

venture vessels in the U.S. Exclusive Economic

zone in the seven statistical areas of Alaska during 1978-88.

Table 10

Number of northern sea lions incidentally caught as repurted by U.S. fishery observers by region, vessel class, and

nation in the U.S. Exclusive Economic Zone in the Bering 'Sea and Gulf of Alaska, 1973-77. a Catch rates are the ratio

(R) ::': twice the standard error (s(R» of observed inciden tal take of only dead animals to observed groundfish catch

(per 10,000 metric tons (t) basis).

Groundfish Northern sea lions

Number Number

Vessel Observed of dead (alive)

nation catch C observer reported R ±2 s(R)

yearb (t) days (n) in catch d (X 10-4)'

Bering Sea and Aleutian Islands

Small stern trawler

Japan

1976 9.6 1 0 0

1977 2,048.7 252 0 (1) 0

Large surimi trawler

Japan

1973 28,480.7 191 28 (2)1 9.83 ± 3.24

1974 24,497.1 201 52 (9) 21.23 ± 11.14

1975 20,236.0 182 14 (1) 6.92 ± 3.93

1976 23,612.1 204 2 (3) 0.85 ± 1.20

1977 28,105.0 297 13 (1) 4.63 ± 3.54
Perez and Loughlin: Incidental Catch of Marine Mammals 33

Table 10 (continued)

Groundfish Northern sea lions

Number Number

Vessel Observed of dead (alive)

nation catch C observer reported R ±2 s(R)

yearb (t) days (n) in catchd (X 10....)'

Large freezer trawler

Korea

1977 8,081.0 93 5 (2) 6.19 ± 5.45

U.S.S.R.

1975 1,176.2 26 I 8.50 ± 16.92

1976 1,933.1 31 0 0

1977 II,223.9 269 9 (9) 8.02 ± 6.68

Surimi mothership

Japan

1973 110,800.0 145 4 0.36 ± 0.36

1974 112,556.0 177 14 (1) 1.24 ± 0.64

1975 68,821.0 86 3 0.44 ± 0.50

1976 62,885.3 II2 9 (1) 1.43 ± 1.22

1977 337,449.2 453 6 0.18 ± 0.08

Freezer mothership

Japan

1973 12,730.0 27 7 (2) 5.50 ± 3.20

1974 14,876.5 49 3 2.02 ± 2.98

1975 9,470.0 23 2 2.11 ± 2.96

1976 13,173.0 41 2 (2) 1.52 ± 2.07

1977 35,439.0 111 2 0.56 ± 0.79

Gulf of Alaska

Small stern trawler

Japan

1975 347.2 46 0 0

1976 1,790.9 II7 7 (5) 39.09 ± 39.63

1977 2,097.8 230 I (1) 4.77 ± 9.51

Large surimi trawler

Japan

1975 1,775.9 65 0 (2) 0

Large freezer trawler

Japan

1975 711.0 15 2 (1) 28.13 ± 37.84

1976 1,170.0 46 0 0

1977 6,748.2 197 4 (6) 5.93 ± 5.82

U.S.S.R.

1974 432.5 10 4 92.49 ± II8.76

1975 468.0 22 2 (1) 42.74 ± 52.02

1976 1,054.2 46 5 47.43 ± 67.88

1977 4,824.4 184 11 (1) 22.80 ± 17.95

a Only fisheries with observer coverage during 1973-77 are listed.

b Small stern trawler: tra,,1 vessel <l ,fiOO gross tons; large surimi trawler: trawl vessel >1,500 gross tons targeting on pollock to produce

surimi, a minced meat product; large freezer trawler: trawl vessel >1,'100 gross tons which produces frozen ",')Ole fish and fillet

products; surimi mothership: vessel ,-'ith a fleet of catcher boats targeting on pollock to produce a minced meat pf0du~[; freezer

mothership: vessel with a fleet of <;archer boats which produces frozen whole fish or frozen products.

C Total daily catch; includes hauls not monitored by observers for fish composition or presence of marine mammals.

d Does not include decomposed sea lions. The Qumbers in parentheses refer to the number of additional sea lions which were caught

alive and released back to sea.

, The observed sampling fraction of the total fishery is not known by vessel class from 1973 to 1977, but was assumed to be low at that

time. This parameter was ignored in the calculation of standard errers of incidental take rates for this time period. The effect of

ignoring the correction for the observed sampling fraction is to overestimate the standard error of the ratio estimate (Cochran

1977).

f Includes unidentified pinnipeds from the earliest observer cruises in 1973. These animals were most likely northern sea lions based

011 cruise reports.
34 NOAA Technical Report NMFS 104

Figure 11

Incidental mortality of northern sea lions (per 104

metric tons of groundfish) by foreign (motherships

excluded) and joint venture fisheries in the U.S. Exclusive Economic Zone during four time periods

(1973-77, 1978-81, 1982-84, and 1985-88) in (A)

the Bering Sea and Aleutian Islands region and (B)

the Gulf of Alaska.

1985-88

Gulf of Alaska

1982-84 1985-88

Bering Sea and Aleutian Islands

1978-81

1978-81 1982-84

Years

30

25

A 20 .c

III

;: 15 '5

-0 10

8

0 5 ...

i 0 III 1973-77 c

,g

! 30

'l:I 25

B III

'l:I

'5 20

! 15

E

::J

z 10

5

0

1973-77

Within Alaska, 79% of the total estimated mortality

of northern sea lions occurred in three statistical

fishing areas: 19% in Area-I of the Bering Sea, 21 % in

Area-IV of the Bering Sea, and 39% in the Chirikof

area in the Gulf of Alaska (Fig. 10). About 89% of the

total groundfish catch in the fishery occurred in

these three areas, but not in the same proportions as

the estimated incidental catch of marine mammals.

The observed rate of incidental mortality of northern

sea lions was 25 times higher for Chirikof than for

Area-I where the total groundfish catch was over

eight times greater (Fig. 10). However, because of

greater fishing effort in the Bering Sea, the total estimated take of northern sea lions in trawls in Area-I

was half what it was in Chirikof during 1978-88

(Fig. 10).

The 1973-77 catch rates of northern sea lions, by

year and vessel class, were generally higher than

those during 1978-88 (Table 10, Fig. 11). During

1973-77 the average rates of dead sea lions per 104 t

of fish catch in the Bering Sea and in the Gulf of

Alaska were 8 and 16, respectively. These data suggest

a declining trend in incidental take during 1973-77,

similar to 1978-88 (Tables 4 and 5). The decline in

catch rates of dead sea lions in the foreign fisheries

from 1973 to 1988 is also il1ustrated by Figure 11.

There was a 50% reduction in the incidental mortality rate in the Bering Sea from 1973-77 to 1978-81

(but observer coverage was low at that time). There

was also a nearly 50% reduction in catch rates by

successive, approximate four-year periods during

1973-88. Average incidental catch rates of dead

northern sea lions during 1973-77 were also higher

in the Gulf of Alaska than in the Bering Sea during

all years from 1973 to 1988 (Fig. 11).

Incidental Take by Month and Time of Day-Northern sea lions were caught in nets in all months of the

year-seasonal peaks occurring by region and type of

fishery. In the Bering Sea, foreign trawlers caught

29% of their annual incidental take of northern sea

lions from February to May and 55% from September to December (Fig. 12A). Joint venture vessels

caught 62% of their annual incidental take in the

Bering Sea during April-May (Fig. 12B). In the Gulf

of Alaska, foreign trawlers caught 65% of their incidental take from September to November (Fig. 12C).

Joint venture vessels caught 92% of their incidental

take of northern sea lions in the Gulf of Alaska, primarily in Shelikof Strait, from February to April

(Fig. 12D).

Total reported incidental take by both fisheries

during late spring and summer (June to August) in

both regions was lower «25%) than in the remainder of the year combined, even though fishing effort

was not low during summer months (38% of annual

total). There was a significant difference (chi-square

test; P <0.001) between summer months and the

remainder of the year in the number of observed

hauls with incidental mortality of northern sea lions

versus the number of hauls without sea lions. Incidental take of northern sea lions during summer

months was presumably low because that is the time

of year when these animals breed and remain near

rookeries.

Nearly 60% of northern sea lions caught incidentally in fishing operations in Alaskan waters

by foreign and ]V fisheries were caught at night

(Table 11). Data from the]V fisheries i~ the Bering

Sea (Table 11) suggest that an equal likelihood of
Perez and Loughlin: Incidental Catch of Marine Mammals 35

Month

Age and Size-Male northern sea lions caught during

1977-87 in the U.S. EEZ off Alaska ranged from 1 to

at least 13 years of age (n=273 aged teeth; Fig. 14A).

The mean age of males caught in the Bering Sea was

5.2 years during 1977-81 and 5.9 years during 1982-

87 (Table 12); this was not a statistically significant

increase (P=0.131). As expected, the mean lengths

(standard) of males were larger than those of females, but sample sizes were low for some ages (Fig.

15, A and B). The mean length of male northern sea

lions incidentally caught in the Bering Sea during

1973-87 was 242.8 cm (standard) and 253.6 cm (curvilinear). Although there is an apparent increase in

the mean standard length for all males in the 1980s,

t-tests were not significan t owing to low sample sizes

and differences among observers in technique of

length measurement.

Unlike the case for the Bering Sea, the mean age

of males caught in the Gulf of Alaska significantly

decreased from 6.2 years during 1977-81 to 4.7 years

during 1982-87 (i-test; P=0.004). The mean length of

male northern sea lions incidentally caught in the

Gulf of Alaska during 1973-87 was 214.0 cm (standard) and 226.7 cm (curvilinear). The standard and

curvilinear lengths significantly (t-tests; P<0.03) decreased in the 1980s as would be expected with decreasing mean age of incidentally caught animals

(Table 12).

Female northern sea lions caught during 1977-87

in the U.S. EEZ off Alaska ranged from 1 to 25 years

of age (n=414 aged teeth; Fig. 14B). The mean

length of females taken during 1973-87 in the Bering

Sea was 199.1 cm (standard) and 207.5 cm (curvilinear) (Table 12). As was the case with male sea lions,

the mean age of females may have increased from 4.6

years (n=32) in 1977-81 to 5.4 years (n=51) in 1982-

87, but the t-test results were not significant

differs almost inversely with the trend in sea lion incidental catch (Fig. 13A). A greater proportion of

hauls were retrieved in daylight than at night; however, fishing did occur throughout the 24-hour period (Fig. 13A).

The duration of fishing averaged from three to five

hours throughout the day and night. Generally,

fishing time was greater (by almost an hour per haul)

for hauls retrieved three to four hours before or after

sunrise in the ]V fisheries, and about a half-hour

longer at night in the foreign fisheries (Fig. 13B). It

is not known if there is a relationship between length

of fishing time and incidental catch of northern sea

lions, but the rate of catch of sea lions may be higher

when the fishing duration is longer. In any case, the

frequency of northern sea lions caught during

fishing operations was greater for hauls retrieved after sunset.

'-'.

Bering Sea (Foreign)

Gulf of Alaska (Foreign)

.--'--

Bering Sea (Joint venture)

Gulf of Alaska (Joint venture)

".",..... -'--'--'--'- ......-. O+--.-.-r--+-....;p.;~-,.......~:...,-""""t---;

Jan Feb Mar Apr May Jun Jul Aug Sep Del Nov Dec

o+-""'T'"--t'--r-,..--r---r-r-,..--r=-'~

Jan Feb Mar Apr May Jun Jul Aug Sep Del Nov Dec

O~'-~-'~~:::;:=:::;:::::;::"'---r-~ Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

10

30

20

40

10

40

30

20

20

40

30

B 20

10 ;'

,. --

40

o 30

c

A

incidental catch between day and night may have occurred since 1985, but this likelihood may be an artifact of the low rates of incidental catch of northern

sea lions in recent years. Also, the fact that time of

day was not available for all northern sea lions

caught, especially prior to 1985, makes it difficult to

compare changes in catch rates by year by diurnal

period. The diel trend in number of hauls retrieved

10

O+--r-ir=-"",-r-;<--.--.---r-.--.--;

Jan Feb Mar Apr May Jun Jul Aug Sep Del Nov Dec

l----1lead sea lion catch .- .- Number of net haulsI

Figure 12

Percent of total by month of the number of incidentally

taken northern sea lions (reported by U.S. fishery observers; no decomposed animals) which died during trawl

fishing operations and the total number of net retrievals

(hauls) when observers were present in the U.S. Exclusive

Economic Zone during 1978-88 (years combined): (A) on

foreign vessels (no motherships) in the Bering Sea and

Aleutian Islands region; (B) on joint venture vessels in the

Bering Sea and Aleutian Islands region; (C) on foreign

vessels (no motherships) in the Gulf of Alaska; and (D) on

joint venture vessels in the Gulf of Alaska.
36 NOAA Technical Report NMFS 104

Table II

Number of northern sea lions incidentally caugh t by foreign fisheries during 1978-87 and joint venture fisheries during

1985-88 in the U.S. Exclusive Economic Zone off Alaska with respect to diurnal period. a

Fishery Number Number Total Percent

diurnal period dead b alive taken total

Bel ing Sea and Aleutian Islands

Foreign

Daytime Il4 80 194 37.4

Nighttime 196 128 324 62.6

Total 310 208 518 100.0

Joint venture

Daytime 75 75 53.6

Nighttime 62 3 65 46.4

Total 137 3 140 100.0

Gulf of Alaska

Foreign

Daytime 55 31 86 37.9

Nighttime 107 34 141 62.1

Total 162 65 227 100.0

Joint venture

Daytime 29 29 27.9

Nighttime 73 2 75 72.1

Total 102 2 104 100.0

Total-Alaska

Foreign

Daytime 191 III 302 38.9

Nighttime 313 162 475 61.1

Total 504 273 777 100.0

Joint venture

Daytime 82 82 38.7

Nighttime 125 5 130 61.3

Total 207 5 212 100.0

a Only animals for which the time of net retrieval was recorded were included. There was no foreign fishery in the U.S. Exclusive

Economic Zone off Alaska during 1988.

b Decomposed animals were not included.

Table 12

Average age, standard length and curvilinear length by sex, region and fishery years for incidentally caught northern

sea lions in Alaska during 1977-87. Data are x ± 2 SE. The sample size is shown in parentheses below the mean.

Bering Sea and

Aleutian Islands Gulf of Alaska

Measurement Male Female Male Female

1977--81

Age (years) 5.2 ± 0.73 4.6 ± 1.00 6.2 ± 0.89 7.0 ± 1.45

(40) (32) (22) (7)

Standard length (em) 235.7 ± 15.73 198.0±15.17 236.1 ± 22.62 209.7 ± 41.77

(15) (8) (7) (3)

Curvilinear length (em) 261.0 ± 22.95 199.0 ± 15.76 255.7 ± 18.89 243.0

(19) (22) (10) (1)

1982--87

Age (years) 5.9 ± 0.54 5.4 ± 0.91 4.7 ± 0.41 6.6 ± 0.40

(109) (51) (102) (323)

Standard length (em) 245.3 ± 12.14 199.5 ± 11.22 208.0 ± 11.22 198.2 ± 5.68

(42) (24) (26) (96)
Perez and Loughlin: Incidental Catch of Marine Mammals 37

Table 12 (continued)

Bering Sea and

Aleutian Islands Gulf of Alaska

Measurement Male Female Male Female

Curvilinear length (em) 251.1 ± 10.81

(55)

216.5 ± 8.73

(21)

1r.!1.9 ± 8.62

(61)

206.1 ± 3.46

(214)

All years (1977-87)

Age (years)

Standard length (em)

Curvilinear length (em)

5.7 ± 0.44

(149)

242.8 ± 9.85

(57)

253.6 ± 9.93

(74)

5.1 ± 0.68

(83)

199.1 ±9.12

(32)

207.5 ±9.41

(43)

5.0 ± 0.38

(124)

214.0 ± 10.70

(33)

226.7 ± 8.31

(71)

6.6 ± 0.39

(330)

198.6 ± 5.62

(99)

206.2 ± 3.46

(215)

(P=0.287). Average standard body length did not increase appreciably with increasing age for females

(the increase in mean curvilinear length was also insignificant; t-test, n=43, P=0.061) during the 1980s,

but this was most likely due to low sample size

(n<50). Unlike the case for males, there was no statistically significant decrease (P=0.747) in mean age of

incidentally caught female northern sea lions in the

Gulf of Alaska (Table 12).

There were no statistically significant differences

(with t-tests) in the mean age, standard length or

curvilinear length of northern sea lions caught in the

periods 1977-81 and 1982-87 by foreign fisheries in

either the Bering Sea or Gulf of Alaska (Table 13) .

There was a significant difference (t-test; P=O.Oll) in

mean age for sea lion males in the Gulf of Alaska

between the foreign and]V fisheries (Table 13) during 1982-87, but limited sample sizes prevented statistical analysis of length differences. The difference

in measurements for incidentally caught male nonhern sea lions between the two fisheries was probably

related to the difference in primary fishing areas

since the]V fisheries were more common in Area-IV,

Chirikof, and Kodiak during recent years than were

the foreign fisheries (Table 4).

The sizes (standard and curvilinear length) by age

of female northern sea lions taken incidentally in

trawl fishing operations in the Gulf of Alaska during

._-- Dead see lion cetch

- Number 01 net hauls

Figure 13

Percent throughout the 24-hour period during day

and night hours of: (A) the total observed number of

incidentally taken northern sea lions (reported by U.S.

fishery observers; no decomposed animals) which died

during trawl fishing operations (solid line) and the total number of net retrievals (hauls) when observers

were present (dotted line) on for"eign (no motherships) and joint venture vessels (both fisheries combined) in the U.S. Exclusive Economic Zone during

1978-88; and (B) the average fishing time of hauls

(net in the water) by time of net retrieval for independent foreign stern trawlers during 1980-87 (solid line)

andjoint venture vessels during 1985-88 (dotted line).

SUnrl..

SUnrise

...-... ...-- .. ,.,.......""

- Foreign

.._- Joint venture

Nlghtlme

Sun••t Nightime

Sunset

,------ ---~_ ......

10

8

A c 6

e

If 4

2

0

Sunrl.. Daytime

::I

0

:5.5

"5

01

4

8-

B 3

g'2

:E

..

'; 1 co

III

;;; 0

Sunrl.. Daytime
38 NOAA Technical Report NMFS 104

80

Male northern sea lions

70

60

! 50

A E 40

z 30

20 Figure 14

10 Number by age and sex of incidentally taken

0 northern sea lions (observed only; no decom2 3 4 5 6 7 8 9 10 11 12 s13 posed animals) which died during trawl fishing

operations of foreign and joint venture vessels

80

Female northern sea lions in the U.S. Exclusive Economic Zone in Alaska

70 during 1978-87 (years and areas combined)

60 based only on data from teeth specimens coliU 50 lected by U.S. observers: (A) male northern sea

.Q lions, and (B) female northern sea lions. E 40

B z 30

20

10

0

2 3 4 5 6 7 9 10 11 12 13 14 15 S16

Age

Male northern sea lions

550 (2) (2)

500 (2)

A 450

E 400 (5)

350 I

(3\ z: 300 (13) (11) (13) (5) (6) I i5l

c: I 250 (10)(18) I I I I

"E 200 as I I "0

c: 150

Sl 100

50

0

0 1 2 3 4 5 6 7 8 9 10 11 12

550

500 Female northern sea lions

(2)

B 450

E 400

350

300 (4) (4) (2) (2) j1 250 (4) (20) (34) (10) (14) (9) (8) (8) I I I 200 I

(9) I I I I

-g 150 I I I I

Sl 100

50

0

0 1 2 3 4 5 6 7 8 9 1C 11 12 13 14 15

Years

Figure 15

Standard length (em; mean ± 95% confidence

intervals) by age and sex of incidentally taken

northern sea lions which died during trawl

fishing operations of foreign and joint venture

vessels in the U.S. Exclusive Economic Zone in

Alaska during 1977-87 (years combined) based

only on animals from which teeth specimens

were collected by U.S. observers: (A) males,

and (B) females. The sample size is shown in

parentheses above each data set.
Perez and Loughlin: Incidental Catch of Marine Mammals 39

Table 13

Average age, standard length and curvilinear length by sex, region, years and fishery for northern sea lions taken

incidental to fishing operations in the U.S. Exclusive Economic Zone off Alaska, 1977-87. Data are x ± 2 SE. The

sample size is shown in parentheses below the mean.

Male Female

Years Age Standard Curvilinear Age Standard Curvilinear

fishery (years) length (em) length (em) (years) length (em) length (em)

Bering Sea and Aleutian Islands

1977-81

Foreign 5.2 ± 0.73 235.7 ± 15.73 261.0 ± 22.95 4.6 ± 1.00 198.0 ± 15.18 199.0 ± 15.76

(40) (15) (19) (32) (8) (22)

JV

1982-87

Foreign 5.8 ± 0.69 257.7 ± 17.16 246.2 ± 13.28 6.7 ± 2.47 203.6 ± 16.83 210.6 ± 18.31

(62) (20) (35) (17) (8) (7)

JV 6.1 ± 0.87 234.0 ± 16.02 259.8 ± 18.37 4.7 ± 0.48 197.4 ± 14.84 219.5 ± 9.51

(47) (22) (20) (34) (16) (14)

Gulf of Alaska

1977-81

Foreign 6.2 ± 0.89 236.1 ± 22.63 255.7 ± 18.89 6.8 ± 1.67 209.7 ± 41.77 243.0

(22) (7) (10) (6) (3) (1)

JV

1982-87

Foreign 6.3 ± 1.16 225.0 247.1 ± 32.61 15.0 235.0

(10) (1) (9) (1) (1)

JV 4.6 ± 0.42 207.3 ± 11.59 217.5 ± 7.98 6.5 ± 0.40 197.9 ± 5.69 206.1 ± 3.46

(92) (25) (52) (322) (95) (214)

Table 14

Estimated mortality of five commonly encountered marine mammal species caught in trawls by foreign and joint

venture fisheries in the U.S. Exclusive Economic Zone of the Bering Sea and Aleutian Islands during 1978-88.

Mortality rates based on U.S. fishery observer data by area and fishery are listed in part B. * = the estimated lower 95%

confidence level was less than the number of animals reported by U.S. observers (the latter was used as the minimum

estimate); ** = the estimated lower 95% confidence level was less than zero (the number of animals reported caught by

U.S. observers was used as the minimum estimate).

Part A Estimated Mortality-ratio estimate p'iRs) and the lower (L]) and upper (L2 ) 95% confidence limitsa

Northern Harbor and Dall's

Walrus fur seal b Ribbon seal spotted seals C porpoise

Year YRs L, L, YR, L, L2 YR, L, L2 YRs L, L2 YRs L, L2

1978 7 5 9 10 8 12 31 1 ** 65 5 4 6 3 2 4

1979 6 5 7 18 2 34 27 1 ** 60 4 3 5 23 1 ** 56

1980 28 1 * 56 58 13 103 6 4 8 4 3 5 1 0 2

1981 40 2 ** 96 24 1 ** 52 5 3 7 4 3 5 1 0 2

1982 3 2 4 28 12 44 14 2 26 2 1 3 1 0 2

1983 13 6 20 20 11 29 21 12 30 29 17 41 6 2 * 11

1984 4 2 6 31 23 39 24 16 32 7 4 10 9 4 14

1985 27 16 38 9 4 14 5 1 9 15 9 21 2 1 ** 5

1986 13 7 19 8 4 * 13 0 0 0 6 4 * 10 1 0 2

1987 32 21 43 5 3 * 9 0 0 0 7 4 * 12 1 0 2

1988 17 10 24 6 2 10 0 0 0 3 2 * 6 I 0 2

Total 190 124 256 217 157 277 133 82 184 86 71 101 49 15 83
40 NOAA Technical Report NMFS 104

Table 14 (continued)

Part B Observed incidental mortality rate per 10" t of groundfish catch-ratio (R) ± twice the standard error (s(R» of observed incidental take to observed fish catch. Refer to Figure 1 for the locations of the areas in the left column. FF =

foreign fishery (rates for independent stern trawlers only):]V = joint venture fishery (U.S.-foreign).

R±2 s(R)

(X 10-4)

Northern Harbor and Dall's

fur seal b Ribbon seal spotted sealsc porpoise

0.123 ± 0.057 0.031 ± 0.029 0.143 ± 0.062 0

0.045 ± 0.044 0 0 0.067 ± 0.070

0.039 ± 0.020 0 0.061 ± 0.024 0.006 ± 0.008

0.165 ± 0.088 0.231 ± 0.112 0.033 ± 0.039 0.066 ± 0.056

0 0 0 0

0.022 ± 0.032 0 0 0

0 0 0 0

Number

of hauls

Area observedd

fishery (n) Walrus

Area-I

FF,1978-87 54,310 0.143 ± 0.062

]V, 1980-84 3,772 0.045 ± 0.044

]V, 1985-88 62,931 0.195 ± 0.050

Area-II

FF,1978-87 54,648 0.082 ± 0.074

]V, 1980-84 160 0

]V, 1985-88 10,277 0.044 ± 0.044

Area-III

FF,1978-87 22 0

]V, 1980-84 0

]V, 1985-88 0

Area-IV

FF, 1978-87 11,969

]V, 1980-84 719

]V, 1985-88 6,299

0.134 ±0.166

0.134 ±0.148

0.245 ±0.150

o

o

0.123 ±0.106

o

o

o

a The ratio estimates in Part A of the table are the sums of the separate ratio estimates for all strata. The strata (subgroups) for

northern sea lion data (Table 4) were used for all mar:ne mammal species.

b Ribbon seals were often misidentified by observers as northern fur seals, and thus some of the estimated fur seal take may include

some ribbon seals.

C Observers were often unable to distinguish between harbor seals and spotted seals, and both species have been grouped.

d The sample size was the number of hauls observed, except for the joint venture fisheries during 1980-84 where the sample size was

the number of fishing days with observer coverage.

'----------------------------

Table 15

Estimated number of dead animals of three commonly encountered marine mammal species caught in trawls by foreign

and joint venture fisheries in the U.S. Exclusive Economic Zone of the Gulf of Alaska during 1978-88. Mortality rates

based on U.S. fishery observer data by area and fishery are listed in part B. * = the estimated lower 95% confidence

level was less than the number of animals reported by U.S. observers (the latter was used as the minimum estimate);

** = the estimated lower 95% confidence level was less than zero (the number of animals reported caught by U.S.

observers was used as the minimum estimate).

Part A Estimated Mortality-ratio estimate (YR,) and the lower (1-,) and upper (L2) 95% confidence limitsa.

Northern Dall's

fur seal Harbor seal porpoise

Year fib L, L2 fib L1 4, fib L 1 L2

1978 14 1 ** 39 0 0 ** 1 0 0 0

1979 6 1 ** 16 11 1 ** 32 0 0 0

1980 0 0 ** 2 0 0 ** 1 0 0 0

1981 2 0 4 0 0 ** 1 0 0 0

1982 0 0 ** 1 0 0 0 0 0 0

1983 0 0 ** 1 0 0 0 0 0 0

1984 5 3 * 10 1 I * 2 0 0 0

1985 1 1 ** 3 0 0 0 0 0 0

1986 0 0 0 0 0 0 1 1 * 2

1987 0 0 ** 1 0 0 0 0 0 ** 1

1988 0 0 0 0 0 0 0 0 0

Total 28 6 * 55 12 2 ** 33 1 * 2
Part B

Perez and Loughlin: Incidental Catch of Marine Mammals 41

Table 15 (continued)

Observed incidental mortality rate per 104 t of groundfish catch-ratio rfl-) ± twice the standard error (srfl-») of observed

incidental take to observed fish catch. Refer to Figure 1 for the locations of the areas in the left column. FF = foreign

fishery (rates for independent stern trawlers only);]V = joint ven ture fishery (U.S.-foreign).

iU2srfl-)

(X 10-4)

Number

of hauls

Area observed b Northern Dall's

fishery (n) fur seal Harbor seal porpoise

Shumagin

FF, 1978-85 6,011 0.107 ± 0.184 0.107 ± 0.184 0

]V, 1978-84 275 0 0 0

]V, 1985-88 954 0.343 ± 0.432 0 0.343 ± 0.432

Chirikof

FF, 1978-85 5,757 0.248 ± 0.441 0 0

]V, 1978-84 1,682 0 0.032 ± 0.040 0

]V, 1985-88 3,730 0 0 0

Kodiak

FF, 1978-85 7,839 0.226 ± 0.402 0 0

]V, 1978-84 1,075 0.243 ± 0.298 0 0

]V, 1985-88 1,357 0 0 0

Yakutat

FF,1978-85 1,025 0 0 0

]V, 1978-84 6 0 0 0

Southeastern

FF, 1978-85 871 0 0 0

]V, 1978-84 2 0 0 0

a The ratio estimates in Part A of the table are the sums of the separate ratio estimates for all strata. The strata (subgroups) for

northern sea lion data (Table 5) were used for all marine mammal species.

b The sample size was the number of hauls observed, except for the joint venture fisheries during 1978-84 where the sample size was

the number of fishing days with observer coverage. There were no]V fisheries in the Yakutat or Southeastern areas during 1985-88,

and there were no foreign fisheries in the Gulf of Alaska during 1986-88.

1982-84 were smaller than sizes reported by the

Alaska Department of Fish and Game (ADF&G) from

animals collected from haul-out sites near Kodiak

during 1975-78 and smaller than animals taken from

haul-out sites near Kodiak during 1985-86 (Calkins

and Goodwin 1988) (Fig. 16, A through C). Analysis

of covariance tests (P<0.05) and nonoverlapping 95%

confidence intervals (primarily between ages 3 and 7)

suggest that mean lengths were smaller during 1982-84

than in 1975-78, and possibly also smaller than in

1985-86.

Other Marine Mammal Species in Alaska

Incidental catch of marine mammals other than

northern sea lions taken by both the foreign and]V

fisheries was very low in Alaska during 1978-88. Besides northern sea lions, walruses, northern fur seals,

ribbon seals, harbor seals (possibly also spotted seals,

Phoca largha), and Dall's porpoises were most commonly encountered (Tables 1-3). During the period

1978-88, a total of 190 walruses, 217 northern fur

seals, 133 ribbon seals, 86 harbor (and spotted) seals,

and 49 Dall's porpoises were estimated to have died

during trawl operations in the Bering Sea region

(Table 14). In the Gulf of Alaska, 28 northern fur

seals, 12 harbor seals, and I Dall's porpoise were estimated to have died during 1978-88 (Table 15). Unlike northern sea lions which have been caught in all

statistical areas of Alaska,. some marine mammal species have limited distributions. For example, walruses, ribbon seals, and spotted seals generally occur

only in Area-I, Area-II, or Area-III of the Bering Sea.

Northern fur seals, harbor seals (except Area-III),

and Dall's porpoises may be encountered in all statistical areas, but these species were not observed in

hauls in all areas during 1978-88 (Tables 14 and 15).

Incidental catch rates of these other marine mammal species during 1978-88 averaged less than one

animal caught dead (excluding decomposed animals) per 40,000 t of groundfish caught in the Bering

Sea and less than one dead mammal per 30,000 t of

groundfish in the Gulf of Alaska (Tables 14 and 15).
42 NOAA Technical Report NMFS 104

As previously mentioned, average incidental catch

rates for northern sea lions were significantly higher

(Tables 4, 5, and 6). For example, at least 25 or more

northern sea lions were caught for each northern fur

seal taken in Area-IV, and 10 northern sea lions for

each walrus taken in Area-I of the Bering Sea. However, in Area-II of the Bering Sea average incidental

catch rates of ribbon seals and northern fur seals

were only 4-5 times lower than catch rates for the

northern sea lion. These average catch rates reflect

the distribution of these mammals since northern sea

lions are not very abundant in Area-II. Itshould also

be noted that observers occasionally misiqentified

ribbon seals as northern fur seals. Although northern

fur seals were incidentally caught in Area-II of the

Bering Sea, the average catch rate for northern fur

seals may be lower and the catch of ribbon seals

higher than that shown in Table 14; however, the total for both species combined would be the same.

Figure 16

Standard length of female northern sea lions in the Gulf of

Alaska based on measurements taken during three time

periods: (A) during 1975-78 for data collected by ADF&G

and reported by Calkins and Goodwin (1988) for animals

taken on haul sites; (B) during 1982-84 from incidentally

taken animals which died during fishing operations by

trawl fisheries; and (C) during 1985-86 for data collected

by ADF&G and reported by Calkins and Goodwin (1988)

for animals taken on haul sites. The sample size is shown in

parentheses above each data set.

Years

Incidental take of marine mammals in trawl nets off

the coast of Washington, Oregon, and California was

low during all years. A total of 36 marine mammals

(7 northern s~a lions, 1 California sea lion, 1 northern fur seal, 5 harbor seals, 3 Pacific white-sided dolphins [Lagenorhynchus obliquidens], 9 Dall's porpoises,

and 10 unidentified small cetaceans) were observed

caught dead or alive in the catch during 1973-88

(Table 1). Nearly 80% of this incidental take occurred in the Columbia fishing area, the remainder

in the Eureka fishing area (Fig. 1). Most (78%) of

this incidental take occurred in the foreign fishery.

The incidental catch rate has remained low for the]V

fisheries, even though the total annual fish catch

(Fig. 5A) and number of vessel days (Fig. 6A) since

1984 in the region is similar to or greater than that of

the foreign fisheries prior to 1981.

California sea lions were not observed taken in

trawl operations until 1988. Although some of the

reported northern sea lions caught during 1973-88

off Washington, Oregon, and California could have

been California sea lions, several were indeed northern sea lions based on identification of canine teeth

collected by u.S. fishery observers.

The west coast fisheries have always had low incidental mortality rates (compared with Alaska): less

than one marine mammal per 104 t during 1973-77

(Table 16) and one marine mammal per 104 t during

1978-88 (although some country-specific rates by

area and year were as high as 68 mammals per 104 t;

Table 17). Only 35% of the total fish catch during

1973-88 in the west coast fishery was monitored by

U.S. fishery observers (Table 1). Using the same approach as for northern sea lions in Alaska, an estimated total of 99 marine mammals (all species combined) died during fishing operations by the foreign

trawl fisheries off Washington, Oregon, and California during 1978-88 (Table 18). Similarly, for the]V

fisheries there, the estimated total incidental mortality of marine mammals during 1978-88 was

7 (Table 18).

Marine Mammal Species in

Washington, Oregon, and California

(8) (6) (5) (1) (5)

I I I . I

1975-78 (ADF&G)

(3) (3) (3) (3)

I (i) I I' '1

1982-84 (Incidental take)

(4)

I

1985-86 (ADF&G)

(3) (6) (7) (6) (7) (7) (6) I z :J: :J: x I

(7) (9) (20) I I :J:

(4)

(7) (4)

(5) (9) :J: I

TI I

50

O+--.-----r-r--r-...,----,,....--r--.-----ro 2 3 4 5 6 7 8 9 10

150

100

50

o-\-....,....--..--r--r-...,----,,....--r---.---..-

o 2 3 4 5 6 7 8 9 10

200

O+-....,....--..-,.,..--r-...,----,,....--r-....,....----r---,

o 2 3 4 5 6 7 8 9 10

300

250

100

150

200

300

250

50

100

150

200

250

300

c

A
Perez and Loughlin: Incidental Catch of Marine Mammals 43

Table 16

Number of marine mammals reported by U.S. fishery observers incidentally caught by vessel class and nation in t~e

U.S. Exclusive Economic Zone off Washington, Oregon, and California during 1973-77. a Catch rates are the ratio (ft.)

± twice the standard error (s(R)) of observed incidental take of only dead animals to observed groundfish catch (per

10,000 metric tons (t) basis).

Groundfish Marine mammals

Vessel

nation

yearb

Observed

catch C

(t)

Number

of

observer

days (n)

Number

dead

reported

in catchd

k±2srft)

(X 1O-4)e

Small stern trawler

Japan

1976

Large freezer trawler

Japan

1975

1976

Poland

1976

1977

U.S.S.R.

1976

1977

Freezer mothership

U.S.S.R.

1977

318.2 17 0 0

966.0 38 0 0

1,637.0 65 0 0

10,029.2 204 I 1.00 ± 1.99

7,416.5 251 0 0

1,045.6 72 0 0

21,730.2 681 I 0.46 ±0.92

1,191.3 34 0 0

a Only fisheries with observer coverage during 1973-77 are listed.

b Small stern trawler: trawl vessel <1,500 gross tons; large freezer trawler: trawl vessel>1,500 gross Ions which produces frozen whole

fish and fillet products; freezer mothership: vessel with a fleet of catcher boats which produces frozen whole fish or frozen products.

C Total daily catch; includes hauls not monitored by observers for fish composition or presence of marine mammals.

d Does not include decomposed marine mammals.

e The observed sampling fraction of the total fishery is not known by vessel class from 1973 to 1977, but was assumed to be low at that

time. This parameter was ignored in the calculation of standard errors of incidental take rates for this time period. The effect of

ignoring the correction for the observed sampling fraction is to overestimate the standard error of the ratio estimate (Cochran

1977).

Discussion _

During the period 1978-81 the estimated average annual take of northern sea lions by foreign vessels was

724 animals (Loughlin et al. 1983). In the 1982-84

walleye pollock JV fishery in Shelikof Strait, Alaska,

the estimated number of mortalities resulting from

incidental catch ranged from 216 to 1,436 from January to April (Loughlin and Nelson 1986). The estimates reported in this study are somewhat higher because the analysis was based on subregions (statistical

areas) for which estimated catch totals were summed,

as opposed to the annual average method used in the

earlier study. Although some data corrections have

been made in the years since the previous studies

were made, the results of each of the studies are essentially similar.

Northern sea lions caught by foreign vessels between 1978 and 1981 were principally females between 2 and 10 years of age, 65% of which were probably sexually mature (Loughlin et al. 1983). The average age for first ovulation and for first pregnancy for

female northern sea lions in the Gulf of Alaska is 4-5

years (Pitcher and Calkins 1981). Any female age 4-5

years or older and caught incidentally was probably

sexually mature; but only by examination of reproductive tracts, which was not possible, could this be

verified. Jorthern sea lions caught in Shelikof Strait

between 1982 and 1984 were predominantly female;

an estimated 79% were sexually mature with an average age of 6.4 years for all females (n =228, range in

age from 1 to 25 years old; Loughlin and Nelson

1986). Sexually mature males were rarely caught.

In the Shelikof Strait JV fishery, northern sea lions

were usually caught during nighttime-73% caught

between 2000 and 0500 hours (Loughlin and Nelson

1986). Analysis of the location of dead animals in the

net suggested that they were caught during net as-
44 NOAA Technical Report NMFS 104

Table 17

Number of marine mammals (species combined) reported by U.S. fishery observers incidentally caught by subgroup

(area, vessel class, nation, and year) in the U.S. Exclusive Economic Zone off the coast of Washington, Oregon, and

California,J 978-88, and an estimation of thAe total incidental take of marine mammals in the fishery. a Catch rates are

the ratio (ft.) ± twice the standard error (s(ft.» of observed inAcidental take to observed groundfish catch (per 10,000

metric tons (t) basis). Estimated takes are the ratio estimate (YR ) ± the 95% confidence limits (L95%). Refer to Figure 1

for the locations of the areas in the left column. * = the estimated lower 95% confidence level was less than the number

of animals reported by U. S. observers; ** = the estimated lower 95% confidence level was less than zero.

Groundfish Marine mammals

Number

Vessel Total Observed Percent of hauls umber

nation catch catch( of catch observedd reported R± 2 sift)

year b (t) (t) observed (n) in catch' (X 10-4) YR ± L.:JS%

Vancouver

Joint venture mothership (countries combined)

1980 2,736.2 1,868.4 68.3 48 0 0

1981 2,168.2 1,522.6 70.2 37 0 0

1982 31,927.2 24,232.6 75.9 459 0 0

1983 27,850.4 24,839.3 89.2 447 0 0

1984 9,056.1 7,770.9 85.8 142 0 0

198sf 7,005.4 4,711.4 67.2 319 0 0

19861' 11,687.3 9,093.2 77.8 666 0 0

1987! 7,058.9 5,697.4 80.7 380 0 0

198sf 12,642.0 8,632.7 68.3 492 0 0

Columbia

Large freezer trawler

Bulgaria

1981 3,665.4 1,577.3 43.0 184 6.34 ± 9.62 2±4 ** 1982 6,732.0 5,039.0 74.9 258 1.98 ± 2.00 1 ± 1 *

People's Republic of China

1987 5.0 2.6 52.0 2 0 0

Republic of Korea

1987 1,412.7 578.6 41.0 42 0 0

Poland

1978 20,325.9 6,259.4 30.8 634 0 0

1979 12,271.1 2,320.0 18.9 326 0 0

1980 45,393.0 5,966.5 13.1 628 0 0

1981 43,000.7 7,098.4 16.5 862 0 0

1984 14,607.9 9,613.0 65.8 653 0 0

1985 43,660.2 29,608.8 67.8 2,583 1 0.34 ± 0.38 1 ± 1 * 1986 42,228.2 30,122.9 71.3 2,316 0 0

1987 48,830.4 32,815.1 67.2 2,564 3 0.91 ± 0.60 4±3 * 1988 17,142.6 13,426.5 78.3 1,115 4 2.98 ± 2.20 5±4 *

U.S.S.R.

1978 51,559.1 12,671.3 24.6 1,502 0 (2) 0

1979 51,262.3 11,209.1 21.9 1,510 9 8.03 ± 14.20 41 ± 72 **

1984 470.7 325.5 69.2 27 0 0

Joint venture mothership (countries combined)

1978 894.2 893.5 99.9 46 0 0

1979 8,826.8 4,771.7 54.1 182 0 0

1980 13,268.6 10,672.3 80.4 273 1 0.94 ±0.83 1 ± 1 * 1981 12,697.3 4,424.2 34.8 120 0 0

1982 30,164.8 27,423.2 90.9 543 0 0

1983 39,903.3 36,546.2 91.6 633 0 0

1984 66,798.3 62,194.7 93.1 1,127 0 0

198sf 25,027.8 17,539.5 70.1 1,358 1 0.57 ± 0.62 1 ± 1 * 19861' 67,805.3 47,757.2 70.4 3,370 3 0.63 ± 0.39 4±3 *
Perez and Loughlin: Incidental Catch of Marine Mammals 45

Table 17 (continued)

Groundfish Marine mammals

Number

Vessel Total Observed Percent of hauls Number

nation catch catch C of catch observedd reported fu 2 sift)

yearb (t) (t) observed (n) in catch e (X 10-4) YR ±Lg5%

1987/ 100,092.0 74,082.5 74.0 4,837 0 0

198sf 98,256.0 68,224.6 69.4 4,249 I 0.15 ±0.16 I ± I *

Eureka

Large freezer trawler

Bulgaria

1981 3,447.5 1,249.5 36.2 99 0 0

1982 521.5 448.0 85.9 23 0 0

Poland

1978 6,248.5 3,089.3 49.4 402 o (1) 0

1979 6,134.0 2,146.3 35.0 238 0 0

1980 1,535.2 418.9 27.3 59 0 0

1981 21,193.1 3,692.2 17.4 346 2 5.42 ±6.98 II ± 15 ** 1985 6,539.0 4,634.4 70.9 308 0 0

1986 28,524.6 21,710.5 76.1 1,577 0 0

1987 145.0 145.0 100.0 17 I 68.97

1988 1,195.6 806.6 67.5 49 0 0

U.S.S.R.

1978 19,870.2 4,412.9 22.2 475 0 0

1979 38,087.1 9,098.9 23.9 1,046 3 3.30 ±4.29 13 ±16 ** 1984 3.3 2.2 66.7 2 0 0

Joint venture motbership (countries combined)

1979 226.9 46.4 20.4 7 0 0

1980 12,465.6 9,960.4 79.9 234 0 0

1981 30,275.1 10,965.3 36.2 246 0 0

1982 6,953.2 4,773.3 68.6 120 0 0

1983 2,253.4 931.1 41.3 20 0 0

1984 3,778.9 3,097.2 82.0 55 0 0

19861 3,241.6 1,939.5 59.8 135 0 0

198sf 25,255.0 17,807.7 70.5 1,024 0 0

Monterey

Large freezer trawler

Poland

1978 676.0 11.0 1.6 3 0 0

1979 216.1 21.0 9.7 1 0 0

U.S.S.R.

1979 71.7 4.4 6.1 0 0

Joint venture motbership (countries combined)

1982 108.2 108.2 100.0 5 0 0

1983 3,238.0 2,663.8 82.3 48 0 0

1984 19.5

19861 93.1 93.1 100.0 7 0 0 0

198sf 740.0 315.1 42.6 8 0 0

a There were no foreign trawl fisheries off Was\lington, Oregon and California during 1983.

b Joint venture mothership: processing vessel of the joint venture fisheries which receives catches from U.S. fishing vessels; large

freezer trawler: trawl vessel >1,500 gross tons which produces frozen whole fish and fillet products.

C Observed ton~age listed for motherships (all years) and joint venture vessels (1978-84) are total daily catch, and include hauls not

sampled for fish composition nor monitored for presence of marine mammals.

d Data are fishing days with observer coverage for motherships (all years) and joint venture vessels during 1978-84.

e Totals include only dead animals (excludes "decomposed in catch"); numbers in parentheses are additional animals caught and

released back to sea still alive.

/ Observer data were based on hauls observed for joint venture vessels during 1985-88.
46 NOAA Technical Report NMFS 104

Table 18

Estimated incidental mortality of marine mammals (all species combined) in the foreign and joint venture groundfish

trawl fisheries (all countries combined) in the U.S. Exclusive Economic Zone off Washington, Oregon, and California

during 1978-88. Estimates of the number of dead marine mammals are the ratio estimate (l7R,s) a and the lower (L\)

and upper (L2) 95% confidence limitsb. * = the estimated lower 95% confidence level was less than the number of

animals reported by U.S. observers (the latter was used as the minimum estimate); ** = the estimated lower 95%

confidence level was less than zero (the number of animals reported caught by U.S. observers was used as the

minimum estimate).

Foreign fisheries Joint venture fisheries

Estimated number of Estimated number of

Percent dead marine mammals Percent dead marine mammals

Total fish Total fish

groundfish catch groundfish catch

Year catch (t) < observed YRs L, L. catch (t) < observedd YRs L, L.

1978 98,680 26.8 8 4 12 894 99.9 0 0 0

1979 108,042 23.0 55 12 ** 128 9,054 53.2 0 0 0

1980 46,928 13.6 4 1 7, 28,470 79.0 1 1 * 2

1981 71,307 19.1 17 3 * 32 45,141 37.5 0 0 0

1982 7,254 75.6 I 1 * 2 69,153 81.8 0 0 0

1983 no fishery 73,245 88.7 0 0 0

1984 15,082 65.9 1 1 1 79,653 91.7 0 0 0

1985 50,199 68.2 1 1 ** 3 32,033 69.5 1 1 ** 3

1986 70,753 73.3 2 1 3 82,827 71.1 4 3 * 7

1987 50,393 66.6 5 4 * 8 107,151 74.5 0 0 0

1988 18,338 77.6 5 4 * 9 136,893 69.4 1 1 ** 3

Total 536,976 39.8 99 25 * 174 664,515 74.6 7 6 * 11

a The sum of estimates for the strata (area, vessel class, country and year) in Table 17.

b Sample size (number of hauls observed, or observed fishing days for joint venture fisheries during 1978-84) can be summed from

the data by area, vessel class, country and year in Table 17.

<Trawl catches (metric tons) during 1978-88.

d Values for the percent of fish catch observed during 1978-84 listed in this column are higher than true values (unknown) since joint

venture data for those years were based on total daily fish catch rather than hauls observed.

cent or while the net was near the surface during

haulback (Loughlin and Nelson 1986).

The changes over the years in the observed and

estimated totals of incidental catch of northern sea

lions in Alaska may be due to a number of probable

causes: 1) the northern sea lion population size has

declined every year, and this has the effect of reducing the number of animals that could be caught; 2)

fisheries may have shifted their fishing locations to

localities away from areas of high concentration of

northern sea lions (e.g., there has been less fishing in

Shelikof Strait in recent years and more fishing effort

in Area-I and Area-II of the Bering Sea); 3) there had

been more daytime fishing in recent years compared

to early years (but this may not be a significar.t factor

because recently]V fisheries in the Bering Sea seem

to catch an equal number of sea lions in either the

day or night); 4) fishing techniques have improved to

prevent incidental mortality and catch of marine

mammals; 5) changes in fishing gear, vessel size, or

catch per haul have reduced incidental catch rates

(although there has been no significant relationship

between vessel class and average catch size); or 6) the

animals may be learning to avoid being caught in the

nets.

Using limited data on groundfish catches by trawl

gear, country (data for foreign countries other than

Japan were only available as a combined total), statistical fishing area, and year, we calculated estimates of

the northern sea lion mortality by foreign trawl

fisheries in Alaska during 1966-77 using observed average rates for 1973-77 (Table 19). We assumed that

sea lions were probably caught also in the side trawls

which were discontinued in 1972. We used 1966 as

the first year because it was the first year there were

data with which to exclude catch data by other
Perez and Loughlin: Incidental Catch of Marine Mammals 47

Table 19

Estimated incidental mortality of northern sea lions in the foreign groundfish trawl fisheries (all countries combined)

in Alaska during 1966-77, based on the incidental take rates during 1973-77.a Estimates of the number of dead

northern sea lions are the ratio estimate d'R) and the lower (L) and upper (/-'2) 95% confidence limits.

Bering Sea and Aleutian Islandsb Gulf of Alaska C

umber of dead sea lions umber of dead sea lions

Total Total

groundfish groundfish

Year YR catch (t) d,e YR L) 4 catch (t)d L, 4

1966 326,200 260 220 300 159,000 320 180 460

1967 579,700 470 390 550 142,300 290 160 420

1968 650,800 540 460 620 127,600 240 140 340

1969 808,300 670 560 780 100,900 140 100 180

1970 1,201,300 990 840 1,140 72,900 90 70 110

1971 1,772,600 1,450 1,220 1,680 94,000 150 100 200

1972 1,900,200 1,560 1,310 1,810 151,000 290 170 410

1973 1,779,600 1,470 1,230 1,710 149,100 270 160 380

1974 1,740,100 1,410 1,170 1,650 165,900 330 190 470

1975 1,455,500 1,190 1,000 1,380 171,700 390 200 580

1976 1,413,400 1,150 960 1,340 175,400 410 210 610

1977 1,051,300 490 330 650 178,500 260 90 430

Total 14,793,849 11,650 11,040 12,260 1,894,427 3,180 2,730 3,630

a The estimated incidental take represents only northern sea lions which died incidental to fishing operations, and excludes those

which were caught and released alive. Totals may include some animals caught outside the U.S. Exclusive Economic Zone (which was

not established until 1977). Estimated incidental take was calculated for all trawl gear types during 1966-77 (i.e., stern, pair, and side

trawls) using observed rates based only on stern trawl catches; but observers did report incidental take during pair trawl operations

in mothership-based fisheries during 1973-86 (side trawls were not used during 1973-86). Estimates were rounded to the nearest 10.

b Estimates for 1966-76 were calculated with the following incidental take rates based on combined U.S. observer data from foreign

trawlers in the Bering Sea during 1973-77: For Japan, R= 8.58 (L, = 6.11, 4 = 11.06) sea lions per 104 t of groundfish caught

(sr,R) = 1.26, n = 1,328 days); and for other countries (combined),R = 6.69 (L, = 2.76, 4 = 10.62) sea lions Rer 104 t of groundfish

caught (sr,R) = 2.00, n = 419 days). Estimates for 1977 were calculated with the rates for only 1977: ForJapan, R= 4.31 (L) = 1.02, L2 =

7.61) sea lions per 104 t of groundfish caught (sr,R) '; 1.65, n =549 days); and for other countries (combined), R=7.26 (L) =2.73, 4 = 11.77) sea lions per 104 t of groundfish caught (s(fi) =2.26, n =362 days).

C Estimates for 1966-76 were calculated with the following incidental take rates based on combined U.S. observer data from foreign

trawlers in the Gulf of Alaska during 1973-77: For Japan, R= 9.56 (L) = 3.63, 4 = 15.49) sea lions per 104 t of groundfish caught

(sr,R) = 3.02, n = 716 days); and for other countries (combinedJ,R = 32.45 (L, = 14.18, 4 = 50.72) sea lions per 104 t of groundfish

caught (sr,R) =9.28, n = 262 days). Estimates for 1977 were calculated with the rates for only 1977: ForJapan, R=~.65 (L) =0.68, L2 =

10.63) sea lions per 104 t of groundfish caught (s(fi) =?49, n = 427 days); and for other countries (combined), R = 22.80 (L, = 4.99,

4 = 40.61) sea lions per 104 t of groundfish caught (s(R) =8.91, n = 184 days).

d Estimated catch totals include some catches of groundfish by longline vessels (the available data precluded exclusion of these catches

which were low relative to trawl catches), but these totals exclude estimated catches of groundfish with Danish seine gear. Groundfish

catch data were taken from Murai et a!. (1981) for 1966-76, Berger et a!. (1986) for 1977, and Sueto Murai (Alaska Fisheries Science

Center, NMFS, OAA, 7600 Sand Point Way E, Seattle, WA 98115, unpub!. data) for Japanese catch data by gear type and INPFC

statistical area data during 1966-77. Excludes fishing by Canada. Groundfish catch estimates were rounded to the nearest hundred.

e Excludes catches of Pacific herring (classified with groundfish) because of separate pelagic foreign fisheries during some of these

years.
48 NOAA Technical Report NMFS 104 _. _

fisheries (e.g., pelagic herring fisheries, hali bu t

fisheries) for the Bering Sea and Gulf of Alaska. It

was also about the time the trawl fisheries began to

increase their effort in Alaska and was one of the

peak years of abundance for the northern sea lion;

sea lion abundance began to decline in the early

1970s (Merrick et al. 1987).

We estimated a total of 11,650 northern sea lions

died incidentally in trawl fishing from 1966 to 1977

in the Bering Sea, and a total of 3,180 northern sea

lions died incidentally with fishing effort in the Gulf

of Alaska at the same time (Table 19). These estimates for 1966-77 and the estimates for 1978-88 are

illustrated as a time series in Figure 17. Estimated

takes of northern sea lions by year were higher before 1977 (the year the FCMA took effect) than for

most years (except 1982) (Fig. 17). We have used

these estimates to assess the possible impact of incidental take on the northern sea lion population in

the absence of other controlling factors.

York (1990) has prepared a stable population life

table for adult female northern sea lions based

largely on data from Calkins and Pitcher (1982),

Calkins and Goodwin (1988), and Loughlin and

Nelson (1986) (see Table 20). York's fecundity rates

are one-half the values in Calkins and Pitcher (1982).

We used York's stable-age life table and estimates of

the population size of adult female northern sea lions which we derived using data in Merrick et al.

(1987) to calculate the effects of the estimated incidental mortality of northern sea lions on the population since 1966. These effects can only be considered

hypothetical because the true population size, age

and sex distribution by year and region of the sea

2,500

lion population in Alaska, and the actual sex and age

of each animal caught in the trawl fisheries are not

known. However, declines in the northern sea lion

populations of Alaska since the 1960s are real, based

on actual population counts; only the level of impact

due to incidental take is hypothetical.

In producing this analysis, we used the average age

and sex composition of incidentally caught dead

northern sea lions from Area-IV (Aleutian Islands)

and the Chirikof area (based primarily on animals

incidentally caught in Shelikof Strait whose teeth

were aged) as an estimate (=mean estimate) for the

Bering Sea and Gulf of Alaska regions, respectively

(Table 21, columns 3 and 5). Minimum rates of

change were calculated using the average age and sex

composition for the entire Bering Sea or Gulf of

Alaska in their respective analyses (Table 21, columns

2 and 4). By using the observed fishing effort and

incidental catch figures by month during 1978-88 for

each region, and assuming both equal effort and incidental catch for each month during 1966-77, the

estimated incidental take each year was apportioned

between the first and last six months of the year (all

births were estimated to occur on June 15, which was

also used as the end of the first six-month period).

For females estimated caught and found dead in

fishing trawls from June 16 to December 31 each

year, their pups were also considered to have subsequently died that year because they would not have

been weaned and able to survive on their own. Natural mortality rates (York 1990) were applied to the

estimated population on 15 June in order to calculate the number of survivors each year if the population were stable. Incidental-take mortality was sub2.500

Ul

c

o 2.000 'C

'0

VI 1.500 't:l

c

III

:::J ! 1.000

.r:

VI

=6

§ 500

2

Cl

VI

C

,g

2.000

E

1.500 '5c

'0

..

Ql

1.000 :::J

C

't:l

500 E

w

Figure 17

Total groundfish catch and estimated total

number of incidentally taken northern sea

lions which died during fishing operations of

all foreign and joint venture trawl fisheries in

Alaska during 1966-88.

o 0

19666768697071727374757677 78 79 80 818283 8485

Year

- Groundflsh catch • Estimated incidental catch
Perez and Loughlin: Incidental Catch of Marine Mammals 49

Table 20

Stable population life table parameters for the female component of the northern sea lion population in Alaska, and

the estimated size of the female population in 1965 for the Bering Sea and Gulf of Alaska. a These data were used to

develop a hypothetical model of the trend in population size with the estimated level of incidental mortality of

northern sea lions in trawl fisheries during 1966-88 discussed in this study.

Stable population life table for northern sea lions Estimated 1965 population size

from York (1990) of female northern sea lionsd

Ages b Bering Sea

Cumulative Annual Percent and Aleutian

Al A Z survival survival Fecundityc at age Islands Gulf of Alaska

0 I 1.000 0.782 0.000 16.251 13,100 14,980

I 2 0.782 0.782 0.000 12.709 10,244 11,715

2 3 0.612 0.782 0.000 9.938 8.011 9,161

3 4 0.478 0.930 0.101 7.772 6,265 7,164

4 5 0.445 0.909 0.180 7.228 5,826 6,662

5 6 0.404 0.895 0.261 6.570 5,296 6,056

6 7 0.362 0.884 0.315 5.880 4,740 5,420

7 8 0.320 0.875 0.315 5.198 4,190 4,791

8 9 0.280 0.867 0.315 4.548 3,666 4,193

9 10 0.242 0.859 0.315 3.943 3,179 3,635

10 11 0.208 0.853 0.315 3.388 2,731 3,122

11 12 0.178 0.847 0.315 2.889 2,329 2,663

12 13 0.150 0.841 0.~15 2.447 1,973 2,256

13 31 s 0.150e P(x)! 0.315 11.239 9,058 10,358

Total 100.000 80,608 92,176

a York (1990) derived the stable population parameters and survival rates using exponential and Weibull models based on northern

sea lion data collected during 1975-78 in the Gulf of Alaska (Calkins and Pitcher 1982).

b AI is the age for which the population size estimates and pup production values were calculated, and A2 is the age of survival based

on the survival rates. Animals in the population were assumed to not live past age 31 in this study, hence the survival rate for age 31

was zero.

c The fecundity rates are one-half the values in Calkins and Pitcher (1982).

d The 1965 base year population sizes were based on pup count and population trend data for the northern sea lion in Alaska

(Merrick et al. 1987), assuming a constant average annual rate of decline among all rookeries in the Bering Sea and Gulf of Alaska

since the 1950s proportioned to the total rate of decline. The female component of the estimated total pup level was calculated

assuming a sex ratio of 0.485 for females (Calkins and Pitcher 1982). Values for ages 1-31 were calculated using the percent age

values in column 6. 'll'

e S = n P(i).

! P(;;"= /IncG[l/a, «x+l)/t)a] - IncG[l/a, (x/t)a]}//lncG[l/a, (x/t)a] - IncG[l/a, «x-l)/t)a]}; IncG is the incomplete Gamma

function, a =1.37, and t =8.41.

tracted from this calculated number of survivors.

Density dependence was not considered.

Figure 18 shows the rate of change due only to

incidental take in the trawl fisheries (other population size factors were not considered) in the Bering

Sea. A minimum estimate of 6.7% for the decline

during 1966-89 was calculated for the Bering Sea

based on the annual trawl catches by stern trawl gear

and the estimated adult female component of the

lower 95% confidence level estimates of incidental

take during each year. The mean estimate of the

probable decline since 1966 due solely to incidental

take was 16.3% in the Bering Sea, when all trawl

catches (including pair and side trawls) and the upper 95% confidence limit of estimated annual incidental take was used in the calculations. A similar

exercise for the Gulf of Alaska (Fig. 19) yielded a

minimum decline of 3.6% since 1966 and a mean

estimate of 6.4% for the decline in the northern sea

lion population solely on account of incidental take.

The peak (1972) estimated upper 95% confidence

limit of 2,120 dead northern sea lions in the catch

throughout Alaska may be lower than the true level

of incidental take during the early 1970s. It is unlikely that during 1973-77 observers reported all marine mammals incidentally caught because of limited

opportunity to view and record such occurrences. Because the catch rates for the early 1970s were based
50 NOAA Technical Report NMFS 104

on the number of sea lions reported caught per total

tonnage of groundfish caught (all hauls whether

monitored or not) during the entire time the observer was aboard the vessel, the incidental take rates

prior to 1978 can be considered underestimates

(catch rates since 1978 were based only on th,e monitored portion of the groundfish catch).

An early estimate of incidental take based only on

a few observations and the effort of fishing in the

North Pacific Ocean and Bering Sea during the early

1970s suggested that perhaps 4,400 northern sea lions died in the Japanese trawl fisheries in 1971 (Letter dated 15 August 1973 from D. L. Alverson [then

Director of the t'-:orthwest and Alaska Fisheries Center, NMFS, NOAA, Seattle, WA] to W. F. Royce [then

Associate Director for Resource Research, NMFS,

NOAA, Washington, D.C.]). This early estimate may

not have been far from the truth, and at the time,

even that level of take was considered possibly low.

For example, the greatest incidental mortality levels

actually observed and reported by U.S. fishery observers during 1973-88 occurred in 1982 in Shelikof

Strait when it was not uncommon for 50 or more

dead sea lions to be found in a single haul. A U.S.

fishery observer in 1973 reported that he was informed by the captain of the Japanese trawler

Haruna Maru that the vessel had caught 60 northern

sea lions in a single haul in March 1972 near the

Pribilof Islands in the Bering Sea. Similar occurrences may have occurred at other times in the

Bering Sea during the early 1970s when the northern

sea lion population size was still high.

If these higher take estimates were indeed likely,

then the data in Table 20 and Figures 18 and 19

suggest that incidental mortality may be a more important factor in the population decline of northern

sea lions in Alaska than previously suspected. It is

unlikely that it is the only factor or necessarily the

principal factor, but it is certainly a contributing

cause of the population decline since the 1960s. It is

unfortunate that the necessary database for biological assessments of the status of the northern sea lion

,or data collection on observations of incidental catch

did not improve until about 1980, after the bulk of

the population decline occurred. It is now difficult to

assess the role of each factor which may have contributed to the reduced stocks of northern sea lions in

Alaska.

Table 21

Estimated age composition (based on tooth samples) of the female component (relative to the total population) of the

incidental catch of northern sea lions in the foreign and joint venture trawl fisheries (1966-88) of Alaska used in a

hypothetical model of the population trend of northern sea lions during since 1965. a

Bering Sea and

Aleutian Islands Gulf of Alaska

Entire Entire Chirikof

Age region Area-IV region area

1 0.4 0.0 1.5 1.7

2 3.0 6.8 5.0 5.4

3 8.1 20.5 7.2 8.0

4 7.3 15.9 12.3 12.4

5 6.0 12.5 6.1 6.3

6 3.4 5.7 8.8 9.5

7 3.0 4.5 7.7 7.5

8 1.3 0.0 4.4 4.6

9 0.9 1.1 3.1 3.4

10 0.4 0.0 6.8 7.5

11 0.4 1.1 1.8 1.9

12 0.0 0.0 1.5 1.7

13-31 0.0 0.0 3.1 3.4

Total b 34.2 68.1 69.3 73.3

a Estimates based on aged canine teeth collected by U.S. fishery observers from dead northern sea lions (no decomposed animals)

incidentally caught by foreign and joint venture trawl fisheries (1977-87). A zero value does not indicate there were no animals of

that age group.

b Total percent values represent only the female component of the total northern sea lion population. The male component is the

difference from 100%.
Perez and Loughlin: Incidental Catch of Marine Mammals 51

Annual

Figure 18

Yearly change in the size of the population of

female northern sea lions in the Bering Sea

and Aleutian Islands region during 1965-89

based on a stable life table (York 1990), an estimated baseline 1965 population of 80,608 females, the average age and sex of dead northern sea lions incidentally caught in trawl

fisheries, and the total estimates of incidental

mortality of northern sea lions presented in

this paper: (A) annual rate of change (percent), and (B) cumulative percent of change.

The mean estimate was based on the ratio estimate of incidental take and the minimum estimate was based on the lower confidence limit

of the ratio estimate.

Cumulative

.......

.., .., ..- _ .

69 71 73 75 77 79 81 83 85 87 89

-2.0 .J...,...........-r-.........---r.............--.,r--T--.-r-T""""1--r-r--.--r-T-r.--T"""1".--.

1965 67

o

8, -5.0 r::::

CII

s::.

u

'0 -10.0

'E

Gl

Q. -15.0

0.0

Gl -0.5 Cl

r::::

CII

s::.

u

'0 -1.0

'E

Gl

l:!

Gl

Q. -1.5

A

B

-20.0...L,--.--.--r-T-r,-T"""1".-.,-.,...-,-r-r--.--r-T-r.--T"""1".-.

1965 67 69 71 73 75 77 79 81 83 85 87 89

Year

1 __Mean estimate .•..••.. Minimum estimate I

The high estimated catch of northern sea lions

during the 1970s by foreign fisheries may partially

account for the reported decline of their populations

in the Aleutian Islands region and the western Gulf

of Alaska at that time, but except for the 1982-84

Shelikof Strait fishery, incidental catch in recent

years by ]V fisheries is low and does not explain the

present continuing decline.

Summary _

U.S. fishery observers reported 17 marine mammal

species caught incidentally in groundfish operations

by foreign and ]V trawl vessels during the period

1973-88 in the U.S. EEZ of the North Pacific Ocean

and Bering Sea. Most of the 3,661 mammals caught

died in the nets, but some were released alive (422)

or decomposed (previously dead; 284). Northern sea

lions represented 87% of the total observed marine

mammal incidental take during the study period. Excluding decomposed animals, 42.8% of 3,077 northern sea lions observed incidentally taken during

1973-88 were caught in the Bering Sea; 57.0% were

caught in the Gulf of Alaska; and 2.0% were caught

off Washington, Oregon, and California.

Incidental take of marine mammals in trawl gear

off the coast of Washington, Oregon, and California

was low during all years; a total of 106 mammals (all

species combined) were estimated to have died in

fishing operations during 1973-88. Incidental catch

of marine mammals, other than northern sea lions,

by both the foreign and]V fisheries was also very low

in Alaska during the same time period. The total estimated incidental take of each species (excluding sea

lions) in Alaska was less than 217 for all years combined since 1978.

Northern sea lions were caught in nets during all

months of the year. However, reported incidental

take of sea lions in Alaska during late spring and

summer (June to August) was lower «25%) than in
52 NOAA Technical Report NMFS 104

Annual

0.0

Ql -0.5 Cl

c:

ell

.r:

A u

'0 -1.0

E

Ql

l:!

Ql

Q. -1.5

-2.0

1965 67 69 71 73 75 77 79 81 83 85 87 89

0 --.--. --- ..... Cumulative

_.._--- --- -_.. Ql -5.0 Cl

c:

ell

.r:

B u

'0 -10.0

E

Ql

l:!

Ql

Q. -15.0

Figure 19

Yearly change in the size of the population of

female northern sea lions in the Gulf of Alaska

region during 1965-89 based on a stable life

table (York 1990), an estimated baseline 1965

population of 92,176 females, the average age

and sex of dead northern sea lions incidentally

caught in trawl fisheries, and the total estimates

of incidental mortality of northern sea lions

presented in this paper: (A) annual rate of

change (percent), and (B) cumulative percent

of change. The mean estimate was based on the

ratio estimate of incidental take and minimum

estimate was based on the lower confidence

limit of the ratio estimate.

-20.0 .............-ro-r,-,..-,-,.....,....,.......-.-,-,..-,-,.,..-,....,.......-.-T'"

1965 67 69 71 73 75 77 79 81 83 85 87 89

Year

1--Mean estimate .•-._... Minimum estimate I

the remainder of the year. The low catch in late

spring and summer is probably due to the animals

remaining near rookeries then.

Nearly 60% of northern sea lions reported caught

incidentally in trawl fishing operations were caught at

night (after sunset). The diel trend in number of

hauls retrieved differs almost inversely with the trend

in sea lion incidental catch.

Based on canine tooth samples, nearly 60% of the

sea lions incidentally taken in the Gulf of Alaska were

adult females (?:4 years of age), whereas less than

25% of the sea lions reported caught in the Bering

Sea were adult females. However, at least 40% of the

sea lions caught in Area-IV of the Bering Sea were

adult females.

On the average, observed rates of incidental take

of northern sea lions during 1973-88 were higher in

the Gulf of Alaska region than in the Bering Sea.

There was a nearly 50% reduction in catch rates by

successive, approximately four-year periods during

1973-88. The observed rate of incidental mortality of

northern sea lions was 25 times higher for the

Chirikof area of the Gulf of Alaska than for Area-I of

the Bering Sea where the total groundfish catch in

the fishery was over eight times greater. However, because of the greater fishing effort in the Bering Sea,

the total estimated take of northern sea lions in

trawls in Area-I was half of what it was in the Chirikof

area during 1978-88.

A total estimate of 6,543 (95% confidence limits,

5,728 to 7,358) northern sea lions were incidentally

caught and died in trawls of both the foreign and]V

fisheries throughout Alaska during 1978-88. This information is based on U.S. observer data. We estimated that an additional total of 14,830 (95% confidence limits, 14,070 to 15,590) northern sea lions
Perez and Loughlin: Incidental Catch of Marine Mammals 53

died incidentally in trawl fishing in Alaska during

1966-77, based on the average observed incidental

catch rates during 1973-77.

Incidental take was a contributing cause of the

population decline of northern sea lions in Alaska

accounting for a decline of 16% in the Bering Sea

and 6% in the Gulf of Alaska. However, because the

actual population decline in Alaska based on counts

of animals on land at rookeries has exceeded 80%

since 1960, it is unlikely that incidental take is the

only factor or n.ecessarily the principal factor in the

decline.

Acknowledgments _

We thank the hundreds of observers who spent thousands of hours aboard foreign fishing vessels for their

patience and diligent effort in monitoring the incidental take of marine mammals in catches, including

the collection of teeth specimens and measurement

of animal lengths and the recording of these data.

We thank J. Berger, R. Carlson, S. Murai, R. Nelson

Jr., J. Wall, and H. Weikart for providing data on the

fishery catch and observer effort necessary for the

completion of this report. We thank G. Antonelis, Jr.,

R. DeLong, P. Gearin, H. Kajimura, and R. Merrick

for their assistance in the ageing of pinniped teeth.

We also thank J. Breiwick for assistance with the statistical treatment of the data. H. Braham, M.

Dahlheim, R. DeLong, R. Nelson Jr., and S. Syrjala

provided valuable comments during the preparation

of the manuscript.

Citations _

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Berger,j.D.,j.E. Smoker, and KA. King.

1986. Foreign and joint venture catches and allocations in

the Pacific Northwest and Alaska fishing area under the

Magnuson Fishery Conservation and Management Act,

1977-84. NOAA Tech. Memo. NMFS F/NWC-99, 53 p.

Calkins, D., and E. Goodwin.

1988. Investigation of the declining sea lion population in

the Gulf of Alaska. Unpubl. rep., 76 p. Alaska Dep. Fish

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Calkins, D.G., and KW. Pitcher.

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Cochran, W.G.

] 977. Sampling techniques. 3rd ed., John Wiley and Sons,

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Loughlin, TR., and R. Nelson Jr.

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]988, Univ. Alaska, Fairbanks, Sea Grant Rep. AK-SG-89-1, p.

679-700.

Loughlin, TR., L. Consiglieri, R.L. DeLong, and A.T Actor.

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the Gulf of Alaska and Aleutian Islands during June

]989. NOAA Tech. Memo. NMFS F/NWC-] 76, 26 p.

Merrick, R.M., TR. Loughlin, and D.G. Calkins.

] 987. Decline in abundance of the northern sea lion

(Eumetapias jubatus) in Alaska, ]95&-86. Fish. Bull., U.S.

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Murai, S., H.A. Gangmark, and R.R. French.

] 981. All-nation removals of groundfish, herring, and

shrimp from the eastern Bering Sea and northeast Pacific

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40 p.

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54 NOAA Technical Report NMFS 104

Appendix 1

References For Groundfish Catch Data, 1978-88

1978

Foreign Fisheries Observer Program.

[1979]. Summaries of provisional 1978 foreign groundfish

catches in the Northeast Pacific Ocean and Bering Sea.

Unpubl. data booklet, 96 p. Foreign Fisheries Observer

Program, Alaska Fisheries Science Center, NMFS, NOAA,

7600 Sand Point Way N.E., Seattle, WA 98115.

French, R., R Nelson Jr., and]. Wall.

1979. Observations of foreign and joint venture fishing fleets

off the coast of Washington, Oregon, and California, 1978.

Document submitted to the annual meeting of the International North Pacific Fisheries Commission, Anchorage,

Alaska, October 1979, 16 p. Alaska Fisheries Science Center, NMFS, NOAA, 7600 Sand Point Way N.E., Seattle, WA

98115.

Nelson, R.Jr., R. French, and]. Wall.

1979. Summary of U.S. observer sampling on foreign fishing

vessels in Bering SealAleutian Islands region, 1978. Document submitted to the annual meeting of the International

North Pacific Fisheries Commission, Anchorage, Alaska, October 1979, 75 p. Alaska Fisheries Science Center, NMFS,

NOAA, 7600 Sand Point Way N.E., Seattle, WA 98115.

Wall,]., R. French, and R. Nelson Jr.

1979. Observations of foreign fishing fleets in tt.e Gulf of

Alaska, 1978. Document submitted to the annual meeting of

the International North Pacific Fisheries Commission, Anchorage, Alaska, October 1979, 60 p. Alaska Fisheries Science Center, NMFS, OAA, 7600 Sand Point Way N.E.,

Seattle, WA 98115.

1979

French, R., R. Nelson Jr., and]. Wall.

1980. Observations of foreign and joint venture fishing fleets

off the coast of Washington, Oregon, and California, 1979.

Document submitted to the annual meeting of the International North Pacific Fisheries Commission, Anchorage,

Alaska, October 1980, 27 p. Alaska Fisheries Science Center, NMFS, 7600 Sand Point Way N.E., Seattle, WA 98115.

Nelson, RJr., R. French, and]. Wall.

1980.. Summary of U.S. observer sampling on foreign fishing

vessels in Bering SealAleutian Islands region, 1979. Document submitted to the annual meeting of the International

North Pacific Fisheries Commission, Anchorage, Alaska, October 1980, 85 p. Alaska Fisheries Science Center, NMFS,

NOAA, 7600 Sand Point Way .E., Seattle, WA 98115.

Nelson, R.Jr., R. French,]. Wall, and]. Berger.

[1980]. Summaries of provisional 1979 foreign grouridfish catches in the Northeast Pacific Ocean and Bering

Sea. Unpubl. data booklet, 150 p. Foreign Fisheries

Observer Program, Alaska Fisheries Science Cen ter,

NMFS, NOAA, 7600 Sand Point Way N.E., Seattle, WA

98115.

Wall,]., R. French, and. R. NelsonJr.

1980. Observations of foreign fishing fleets in the Gulf of

Alaska, 1979. Document submitted to the annual meeting

of the International North Pacific Fisheries Commission,

Anchorage, Alaska, September 1980, 78 p. Alaska Fisheries

Science Center, NMFS, NOAA, 7600 Sand Point Way N.E.,

Seattle, WA 98115.

1980

French, R., R. NelsonJr., and]. Wall.

1981. Observations of foreign and joint venture fishing fleets

off the coast of Washington, Oregon, and California, 1980.

Document submitted to the annual meeting of the International North Pacific Fisheries Commission, Vancouver,

Canada, October 1981,18 p. Alaska Fisheries Science Center, NMFS, NOAA, 7600 Sand Point Way N.E., Seattle, WA

98115.

French, R, R Nelson Jr.,]. Wall,]. Berger, and B. Gibbs.

[1981]. Summaries of provisional foreign gr-oundfish catches

(metric tons) in the Northeast Pacific Ocean and Bering

Sea, 1980. Unpubl. data rep., 188 p. Alaska Fisheries Science Center, NMFS, NOAA, 7600 Sand Point Way N.E., Seattle, WA 98115.

Nelson, R. Jr., R. French and]. Wall.

1981. Summary of U.S. observer sampling on foreign fishing

vessels in the Bering SealAleutian Islands region, 1980.

Document submitted to the annual meeting of the International North Pacific Fisheries Commission, Anchorage,

Alaska, September 1981, 69 p. Alaska Fisheries Science

Center, NMFS, NOAA, 7600 Sand Point Way N.E., Seattle,

WA 98115.

Wall,]., R. French, and R. Nelson Jr.

1981. Observations of foreign fishing fleets in the Gulf of

Alaska, 1980. Document submitted to the annual meeting of

the International North Pacific Fisheries Commission,

Vancouver, B.C., Canada, September 1981, 60 p. Alaska

Fisheries Science Center, NMFS, NOAA, 7600 Sand Point

Way N.E., Seattle, WA 98115.

1981

Berger,]., R. NelsonJr., and]. Wall.

1982. Summary of U.S. observer sampling on foreign and

joint venture fisheries off the coast of Washington, Oregon,

and California, 1981. Document submitted to the annual

meeting of the International North Pacific Fisheries Commission, Tokyo, Japan, October 1982, 32 p. Alaska Fisheries Science Center, NMFS, NOAA, 7600 Sand Point Way

.E., Seattle, WA 98115.

French, R., R. NelsonJr.,]. Wall,]. Berger, and B. Gibbs.

1982. Summaries of provisional foreign and joint-venture

groundfish catches (metric tons) in the Northeast Pacific

Ocean and Bering ~ea, 1981. Unpubl. data rep., 183 p.

Alaska Fisheries Science Center, NMFS, NOAA, 7600 Sand

Point Way N.E., Seattle, WA 98115.

Nelson, R.Jr.,]' Wall, and]. Berger.

1982. Summary of U.S. observer sampling of foreign and

joint venture fisheries in the Bering SealAleutian Islands

region, 1981. Document submitted to the annual meeting

of the International North Pacific Fisheries Commission,

Tokyo,Japan, October 1982, 81 p. Alaska Fisheries Science

Center, NMFS, NOAA, 7600 Sand Point Way N.E., Seattle,

WA 98115.

Wall,]. R elsonJr., and]. Berger.

1982. Observations of foreign fishing fleets in the Gulf of

Alaska; 1981. Document submitted to the annual meeting of

the International North Pacific Fisheries Commission,

Vancouver, B.C., Canada, September 1982, 72 p. Alaska
Perez and Loughlin: Incidental Catch of Marine Mammals 55

Fisheries Science Center, NMFS, NOAA, 7600 Sand Point

Way N.E., Seattle, WA 9S115.

1982

Nelson, RJr.,]. Wall,]. Berger, and B. Gibbs.

19S3. Summaries of provisional foreign and joint-venture

groundfish catches (metric tons) in the Northeast Pacific

Ocean and Bering Sea, 19S2. Unpubl. data rep., 167 p.

Alaska Fisheries Science Center, NMFS, NOAA, 7600 Sand

Point Way N.E., Seattle, WA 9S115.

Nelson R.Jr.,]. Wall, and]. Berger.

19S4. Summary of U.S. observer sampling of foreign and

joint-venture fisheries in the Northeast Pacific Ocean and

eastern Bering Sea, 19S2. Document submitted to the annual meeting of the International North Pacific Fisheries

Commission, Anchorage, Alaska, October 19S3, 224 p.

Alaska Fisheries Science Center, NMFS, NOAA, 7600 Sand

Point Way N.E., Seattle, WA 9S115.

1983

Berger,]',]. Wall, and R. Nelson Jr.

19S4. Summary of U.S. observer sampling of foreign and

joint-venture fisheries in the Northeast Pacific Ocean and

eastern Bering Sea, 19S3. Document submitted to the annual meting of the International North Pacific Fisheries

Commission, Vancouver, B.C., Canada, October 19S4,

211 p. Alaska' Fisheries Science Center, NMFS, NOAA,

7600 Sand Point Way N.E., Seattle, WA 9S115.

Nelson, R.Jr.,]. Wall,]. Berger, and B. Gibbs.

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groundfish catches (metric tons) in the Northeast Pacific

Ocean and Bering Sea, 19S3. tJnpubl. data rep., 172 p.

Alaska Fisheries Science Center, NMFS, NOAA, 7600 Sand

Point Way N.E., Seattle, WA 9S115.

1984

Berger,]., R NelsonJr., and]. Wall.

19S5. Summaries of provisional foreign aJ:ld joint-venture

groundfish catches (metric tons) in the Northeast Pacific

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Alaska Fisheries Science Center, NMFS, NOAA, 7600 Sand

Point Way N.E., Seattle, WA 9S115..

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joint-venture fisheries in the Northeast Pacific Ocean and

eastern Bering Sea, 19S4. Document submitted to the annual meting of the International North Pacific Fisheries

Commission, Tokyo, Japan, October 19S5, 225 p. Alaska

·Fisheries Science Center, NMFS, NOAA, 7600 Sand Point

Way N.E., Seattle, WA 9S115.

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groundfish catches (metric tons) in the Northeast Pacific

Ocean and Bering Sea, 19S5. Unpubl. data rep., 162 p.

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Point Way N.E., Seattle, WA 98115.

Berger,]. D.,]. Wall, and R Nelson Jr.

1987. Summary of U.S. observer sampling of foreign and

joint venture fisheries in the Northeast Pacific Ocean and

eastern Bering Sea, 1985. NOAA Tech. Memo. NMFS,

F/NWC-112, 169 p.

1986

Berger,]., S. Murai, R. NelsonJr., and]. Wall.

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groundfish catches (metric tons) in the Northeast Pacific

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176 p. Alaska Fisheries Science Center, NMFS, NOAA,

7600 Sand Point Way N.E., Seattle, WA 98115.

Berger,]., R. NelsonJr.,]' Wall, H. Weikart, and B. Maier.

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joint venture fisheries in the Northeast Pacific Ocean and

eastern Bering Sea, 19S6. NOAA Tech. Memo. NMFS,

F/NWC-128, 167 p.

Clancy, T.]., and R. E. Nelson Jr.

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foreign and joint venture fisheries in the Northeast Pacific

Ocean and eastern Bering Sea, 1986. NWAFC Processed

Rep. 87-12, 43 p. Resource Ecology and Fisheries Management Division, Alaska Fisheries Science Center, NMFS,

NOAA, 7600 Sand Point Way N.E., Seattle, WA 9S115.

1987

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joint venture fisheries in the Northeast Pacific Ocean and

eastern Bering Sea, 19S7. NOAA Tech. Memo. NMFS,

F/NWC-148, 141 p.

Berger,]., H. Weikart, and S. Murai.

1988. Summaries of foreign and joint venture groundfish

catches (metric tons) in the Northeast Pacific Ocean and

Bering Sea, 1987. NWAFC Processed Rep. 8S-08, 114 p.

Alaska Fisheries Science Center, NMFS, NOAA, 7600 Sand

Point Way N.E., Seattle, WA 98115.

Clancy, T.]., and RE. NelsonJr.

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foreign and joint venture fisheries in the Northeast Pacific

Ocean and eastern Bering Sea, 19S7. NWAFC Processed

Rep. SS-07, 43 p. Resource Ecology and Fisheries Management Division, Alaska Fisheries Science Center, NMFS,

NOAA, 7600 Sand Point Way N.E., Seattle, WA 9S115.

1988

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joint venture fisheries in the Northeast Pacific Ocean and

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Berger,]., S. Murai, and M. Guttormsen.

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catches (metric tons) in the Northeast Pacific Ocean and

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56 NOAA Technical Report NMFS 104

Appendix 2

Estimates of incidental catch rates and mortality were obtained by ratio estimates of pooled data (1973-77 and summary rate

comparisons) and stratified sampling by INPFC statistical area, vessel class, country, and year (subgroup = stratum, indexed

by the letter h). Sampling units (indexed by the letter i) were defined as hauls for foreign trawlers (all years) and for ]V

vessels since 1985, and days for foreign motherships (all years) and for]V vessels during 1978-84. The phrase "marine

mammals" below refers only to the marine mammal species for which catch rates were calculated in each analysis, unless

specifically stated otherwise in the text. Since the catch rates (incidental take ratios) calculated with the equations below

were all decimals less than one, they were multiplied by 10,000 to facilitate readability. Catch rates for pooled data analyses

(1973-77 and annual averages for areas) were calculated by considering the data as a single stratum. Equations for ratio

estimates were based on Cochran (1977).

Given

J

x·1

Yi

number of strata analyzed (total for year or region),

lower 95% confidence limit,

upper 95% confidence limit,

number of observed sampling units in stratum h,

total number of sampling units in the fishery in stratum h (including those not observed),

metric tons of groundfish observed in sampling unit i,

mean number of metric tons of groundfish observed in stratum h,

total metric tons of groundfish caught in the fishery in stratum h,

number of marine mammals observed in sampling unit i,

mean number of marine mammals observed in stratum h,

the sampling fraction (nh/Nh) (since Nh is unknown for most years and areas, fwas approximated by the

proportion of total groundfish catch observed),

observed incidental take ratio (catch rate) for stratum h,

standard error of observed incidental take ratio (catch rate) for stratum h,

ratio estimate of total incidental take for stratum h,

stratified random sampling ratio estimator for total incidental take obtained by summing the separate ratio

estimates from Jstrata,

variance of ratio estimate for stratum h, and

variance of stratified random sampling ratio estimator from Jstrata.

Catch rates and ratio estimates were obtained from:

(1)

(2)
Perez and Loughlin: Incidental Catch of Marine Mammals 57

2 A A 2 2 2:Yj - 2Rh2:YjXj+R h2:Xj

nh_l

(3)

(4)

(5)

(6)

(7)

Confidence intervals (CI) between L1 and were estimated with the appropriate value of Student's t:

95% CI=R±t[s(11)]

95% CI= }\± t [YVrYR)]

(8)

(9)

(10)