NOAA Technical Memorandum NMFS-AFSC-43

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Alaska Fisheries Science Center

September 1994

by

R. C. Ferrero and L. W. Fritz

Comparisons of Walleye Pollock,

Theragra chalcogramma, Harvest

to Steller Sea Lion, Eumetopias jubatus,

Abundance in the Bering Sea

and Gulf of Alaska
NOAA Technical Memorandum NMFS

The National Marine Fisheries Service's Alaska Fisheries Science Center uses the

NOAA Technical Memorandum series to issue informal scientific and technical

publications when complete formal review and editorial processing are not

appropriate or feasible. Documents within this series reflect sound professional

work and may be referenced in the formal scientific and technical literature.

The NMFS-AFSC Technical Memorandum series of the Alaska Fisheries Science

Center continues the NMFS-F/NWC series established in 1970 by the Northwest

Fisheries Center. The new NMFS-NWFSC series will be used by the Northwest

Fisheries Science Center.

This document should be cited as follows:

Ferrero, R. C., and L. W. Fritz. 1994. Comparisons of walleye pollock,

Theragra chalcogramma, harvest to Steller sea lion, Eumetopias

jubatus, abundance in the Bering Sea and Gulf of Alaska. U.S. Dep.

Commer., NOAA Tech. Memo. NMFS-AFSC-43, 25 p. 

Reference in this document to trade names does not imply endorsement by the

National Marine Fisheries Service, NOAA.
September 1994

NOAA Technical Memorandum NMFS-AFSC-43

by

 R. C. Ferrero and L. W. Fritz

 Comparisons of Walleye Pollock,

Theragra chalcogramma, Harvest

to Steller Sea Lion, Eumetopias jubatus,

Abundance in the Bering Sea

and Gulf of Alaska

Alaska Fisheries Science Center

7600 Sand Point Way N.E., BIN C-15700

Seattle, WA 98115-0070

U.S. DEPARTMENT OF COMMERCE

Ronald H. Brown, Secretary

National Oceanic and Atmospheric Administration

D. James Baker, Under Secretary and Administrator

National Marine Fisheries Service

Rolland A. Schmitten, Assistant Administrator for Fisheries
This document is available to the public through:

National Technical Information Service

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ABSTRACT

Steller sea lion, Eumetipias jubatus, counts made on

rookeries in the Gulf of Alaska, Aleutian Islands, and the Bering

Sea from 1976 to 1991 were compared to annual estimates of

walleye pollock, Theragra Chalcogramma, harvest to examine

possible relationships between Steller sea lion abundance and

commercial pollock fishing. Comparisons were made between

Steller sea lion counts and pollock fishery data from the same

year and from 1 to 5 years prior. Two sets of study areas were

used, one encompassing 60 nmi or 120 nmi blocks around six major

rookeries and another with 13 sites defined by 20 nmi radius

rings around major rookeries. Lacking accurate measures of local

pollock biomass, harvest data were used as approximations of

annual differences in pollock abundance. Following methods used

in Loughlin and Merrick (1989), correlation coefficients were

calculated using a linear model and tested for significance using

a 2-tailed null hypothesis (=O.O5). However, since the data are

probably not normally distributed, Kendall's coefficients of rank

correlation were also calculated and tested for significance

(=0.05).

Using the parametric approach, some significant positive

-correlations were obtained comparing sea lion counts to pollock

harvests 1 to 5 years prior (2 in the first set of comparisons

and 8 in the second). These may indicate circumstances where

pollock abundance was adequate to sustain the fishery while sea
iv

lion abundance remained unaffected. Significant negative

correlations (2 in each set of comparisons) may suggest instances

where areas of low pollock biomass were effectively harvested,

but the low or reduced availability of prey, or the fishing

activity itself, could have affected Steller sea lion abundance 3

to 5 years later.

Only two of the significant correlations found in the

parametric approach were detected using Kendall's rank

correlation test. We conclude that any potential relationship

between sea lion abundance and pollock harvest can not be

properly determined from these data.
V

CONTENTS

Page

Introduction...........

Methods 2

Update of Loughlin and Merrick (1989) 3

Comparisons of Sea Lion Counts from 13 Study Areas

to Pollock

Analytical Approach................ 7

Results 8

Update of Loughlin and Merrick (1989) 8

Comparisons of Sea Lion Counts from 13 Study Areas

to Pollock Harvest 8

Discussion

Interpretation of Positive Correlations ............. 10

Interpretation of Negative Correlations..... 11

Acknowledgments.. l 13

Citations 14

Tables 18

Figures 24
INTRODUCTION

Major growth in the commercial fishery for walleye pollock,

Theragra chalcogramma, in the Gulf of Alaska and the Bering Sea

from the mid-1960s to the present (Megrey and Wespestad 1990)

occurred at about the same time the Steller sea lion, Eumetiopias

population declined in those areas (Merrick et al.

1987) l The relationship between Steller sea lion abundance and

the commercial harvest of walleye pollock is unknown, but it has

been repeatedly speculated that removal of sea lion prey by

commercial trawl fisheries has contributed to the decline of

Steller sea lion abundance (Braham et al. 1980, Lowry 1982,

Merrick et al. 1987, Loughlin and Merrick 1989).

Loughlin and Merrick (1989) compared sea lion counts and

pollock harvest statistics in seven areas surrounding eight major

rookeries to test the hypothesis that commercial catches of

pollock influenced sea lion abundance. Direct comparisons of

data from the same years, and lagged comparisons where pollock

harvest data was paired against sea lion counts 1 - 5 years later

were examined for patterns of significant negative correlations.

The results were equivocal; few significant correlations were

detected and they were both positive and negative.

Loughlin and Merrick (1989) noted a number of problems

with their data set which may have confounded detection of

significant correlations if they existed. These included the

limited availability of sea lion count data, geographical

differences in the utilization or recruitment of pollock stocks,
2

positive and negative trends in pollock stock abundance during

the study period, and the variable timing of pollock harvests

relative to the fixed timing of sea lion counts during the

breeding season, Furthermore, the application of statistical

tests which include a normality assumption to these data (which

are probably not normally distributed) has since been questioned,

suggesting the need to also conduct tests using a more

conservative non-parametric approach,

The purpose of this paper was to retest the Loughlin and

Merrick (1989) hypothesis that commercial catches of pollock were

correlated with sea lion abundance in light of additional sea

lion count and pollock harvest data collected since 1987 using

both the original and non-parametric statistical tests, Our

approach also differs fundamentally from the original study in

that we do not focus solely on detection of negative

correlations. Instead, we discuss possible interpretations for

both positive and negative relationships. We also emphasize that

significant correlations, either positive or negative, do not

indicate causal relationships.

METHODS

Two comparisons are included in this study, each subjected

to both the parametric and non-parametric tests:

1 l an update of Loughlin and Merrick's (1989) analyses,

including recent sea lion count and pollock harvest data
from 1987 to 1991;

3

2 l a comparison of sea lion counts from 13 study areas

encompassing most major rookeries from the Barren Islands

(Gulf of Alaska) to the western Aleutian Islands, with

pollock harvests that occurred within 20 nm of those areas.

Update of Loughlin and Merrick (1989)

The first set of analyses based on the Loughlin and Merrick

(1989) data set, include sea lion counts and harvest records from

1987 to 1991. The total study period extended from 1976 to 1991.

Study area boundaries followed those defined in the original

study (Fig. 1, Table 1), although two sites, Marmot Island and

Forrester Island, were omitted. The original comparisons of sea

lion pup counts with pollock harvest were not repeated.

The Marmot Island time series was used by Loughlin and

Merrick (1989) to study the effects of the joint venture (JV;

partnerships between domestic catcher boats and foreign

processing ships) pollock fishery in Shelikof Strait. However,

because the JV fishery did not occur in the area immediately

surrounding Marmot Island, the hypothesis of a causal

relationship between sea lion counts and pollock catches in the

vicinity of Marmot Island could not be tested.

Since there has been no directed pollock fishing near

Forrester Island since the early 198Os, we assumed that the

relationship between sea lion counts and pollock-harvest in the

eastern Gulf of Alaska had not changed since 1988 and the
4

information in Loughlin and Merrick (1989) was still valid. The

original data set was also modified to exclude Chowiet Island for

1976 because the datum reported for it was a rough ocular

estimate and not a true count.

Sea lion count data were obtained from surveys conducted by

the National Marine Fisheries Service (NMFS) and the Alaska

Department of Fish and Game. The most recent counts were

obtained from aerial surveys conducted in 1987 (NMFS, unpubl.

data), 1989 (Loughlin et. al. 1990), 1990 (Merrick et. al.

1991), and 1991 (Merrick et. al. 1992) (Table 2). All counts

represent the number of sea lions appearing in aerial photographs

of the sites at the time of the surveys; there were no ocular

estimates. All surveys except those at Walrus Island were

conducted during late June and early July at the peak of breeding

season Counts on Walrus Island were. generally conducted in midJuly or early August, beyond the optimal survey time frame, but

they are probably still representative (Richard Merrick, NMML,

pers, comm.).

Pollock catch data from 1976 to 1986 were obtained from

Loughlin and Merrick (1989). To estimate study area pollock

catches for 1987-91, data from three sources were used. The

first source was the data collected by observers aboard foreign,

JV and domestic vessels, which include amount of pollock caught

and latitude and longitude of hauls sampled.

The second source of information was the Pacific Fisheries
5

Information Network (PacFINl), from which the pollock catch in

each International North Pacific Fisheries Commission (INPFC)

statistical area was obtained. Study areas were located in three

INPFC areas. Because of a lack of observer coverage aboard

domestic vessels that delivered pollock to shore-side processing

plants in 1987 to 1989, catch estimates were supplemented by data

filed by shore-side processors. Study area catch estimates, C,

for 1987 to 1991 were made by adjusting the observed catch in

each study area by the ratio of the total to observed catches in

the surrounding INPFC area:

where OF and OD are the observed pollock catches in each study

area by foreign/JV and domestic components, respectively; IF and

ID are the observed pollock catches by foreign/JV and domestic

components, respectively, in the three INPFC statistical areas in

which the study areas were located; TF and TD are total pollock

catches in the INPFC statistical area by each fishery component;

and P is the pollock catch reported by domestic shore-side

processors for appropriate 1⁄2° latitude by lo

 longitude blocks for

each study area. The estimated pollock catches from 1976 to 1991

in each study area are listed in Table 3.

1

PacFIN is maintained by the Pacific States Marine Fisheries

Commission, 7600 Sand Point Way, N.E., Seattle, WA 98115
6

Comparisons of Sea Lion Counts from 13 Study Areas

to Pollock Harvest

The second set of comparisons examined pollock harvest and

sea lion abundance for 13 study areas encompassing 20 nmi radii

around major rookeries rather than a 60 nmi or 120 nmi blocks

(Fig. 2). Smaller and more numerous study areas were created to

provide finer resolution comparisons. A distance of twenty

nautical miles was chosen to define the study areas because this

is approximately the maximum distance travelled away from the

rookery by satellite-tagged post-partum female sea lions in

summer (Merrick et al., 1994). A distance of 20 nmi also

corresponds to the size of the eastern Aleutian Islands and

Seguam Pass trawl exclusion zones currently enacted as a sea lion

conservation measure during the BSAI Region pollock roe fishery.

Sea lion counts for each area were obtained from the same

survey sources used by Loughlin and Merrick (1989) (Table 4).

Catches of pollock (C) within 20 nmi of the 13 study areas (Table

5) were estimated as:

where OF and OD are totals of observed foreign/JV and domestic

pollock catches in each of the 13 study areas, respectively; AFT

and ADT are actual totals of foreign/JV and domestic pollock

catches in the GOA or BSAI Regions (as appropriate for each study

area); and OFT and ODT are total observed foreign/JV and domestic

pollock catches in the GOA or BSAI Regions (as appropriate for
7

each study area). This was then compared to sea lion abundance

for each rookery or rookery group. There were two study areas

(UAA=Ugamak, Akun and Akutan and OA=Ogchul and Adugak) which

straddled both North Pacific Fishery Management Council (NPMFC)

districts (GOA and BSAI). In these two cases, estimates of

actual catch were summed across districts.

Analytical Approach

Direct comparisons of data collected within the same year

were conducted (lag year 0), along with correlations of sea lion

counts with pollock harvests 1 to 5 years previous. We

calculated correlation coefficients (r) using a linear model and

tested for significance using a 2-tailed null hypotheses

(a=0.05). Kendall's rank correlation coefficients were also

calculated and tested for significance using a 2-tailed null

hypothesis (a=0.05)

In the update of Loughlin and Merrick's (1989) analyses,

adding three new years of sea lion counts increased the total

number of observations per correlation analysis in lag years 0

and 1. However, no net increase was achieved in lag comparisons

2 - 5 where no pollock harvest data for years prior to 1977 were

available to pair with the first years of sea lion data in the

time series.. Consequently, as lag years increase, the number of

observations per correlation run decreases (to a minimum of 4),

and the relationship is more dependent on data collected since

1985, particularly 1989 to 1991.
8

RESULTS.

Update of Loughlin and Merrick (1989)

Four parametric comparisons provided significant

correlations; 2 were positive and 2 were negative (Table 6). The

significant negative correlations occurredin lag years 2 and 3

at Seguam Island. The two significant positive correlations

occurred in lag years 3 and 4 at Chowiet/Chirikof Islands.

Three non-parametric comparisons provided significant

negative correlations (Table 7). All were at Bogoslof Island,

lag years 0, 1 and 5.

Comparisons of Sea Lion Counts from 13 Study Areas

to Pollock Harvest

In the parametric tests, ten significant correlations were

detected; 2 were negative and 8 were positive (Table 8). The

significant negative correlations were detected at Sea Lion Rocks

(lags 4 and 5). The significant positive correlations were found

at Chowiet (lag 4), Chirikof (lags 0, 2, and 4), in the

Atkins/Chernabura area (lag 3), the Ogchul/Adugak area (lags 3

and 5), and the Gramp/Tag/Ulak area (lag 4).

Using the non-parametric tests, 3 significant correlations

were detected; 2 were negative and 1 was positive (Table 9). The

negative correlations were found at Sea lion Rocks (lag 4) and

Bogoslof Island (lag 0); the positive correlation at Atkins and

Chernabura (lag 3).
9

DISCUSSION

With the exception of the significant negative correlation

at Sea Lion Rocks (lag 4) and the significant positive

correlation at Atkins and Chernabura (lag 39, the non-parametric

test series indicates that the relationship between sea lion

abundance and pollock harvest data sets detected using the

parametric approach can not be confirmed using a more

conservative, and perhaps more applicable test. We also

emphasize, however, that even the parametric analyses resulted in

far more nonsignificant correlations than significant ones and

consistent patterns were elusive. The nature of the variables

themselves, ranging over several orders of magnitude, and the

very low sample sizes ultimately limit their utility in examining

possible relationships between commercial pollock fisheries and

the Steller sea lion decline. Furthermore, other synergistic

effects such as changes in oceanographic conditions or fish

community structure complicate the issue and reduce the

likelihood of firm conclusions in this kind of analysis.

Too few significant correlations were detected using the

non-parametric tests to exclude explanation by random chance

alone. However, since the few significant results were both

positive and negative, a limited interpretation of the direction

of significance is useful, particularly if better, more complete

data sets can be compared using these approaches in the future.
10

Interpretation of Positive Correlations

Loughlin and Merrick (1989) did not offer a biological

rationale for the occurrence of significant positive correlations

since they were focusing on pollock harvest as a possible

negative impact on sea lion abundance. They did suggest that

inconsistencies in the sign of correlations across lag years at a

given site may have been an artifact of the study time frame.

The largest sea lion declines occurred prior to 1976; when those

data were paired with pollock harvest, which also diminished

through the mid-1970's, positive correlations resulted.

We suggest that significant positive correlations may

indicate circumstances where pollock harvest paralleled pollock

abundance and that the available pollock biomass satisfied both

harvest and sea lion needs. However, we can not explain

significant positive correlations in direct comparisons (lag 0)

lacking evidence to suggest that adult and juvenile sea lion

survival is directly effected by pollock abundance in the same

year or that pollock harvest directly benefits sea lions in any

way.

The results of modelling (e.g., York 1994; Pascual and

Adkison, 1994) and field studies (e.g., Castellini et al. 1993;

Richard Merrick, NMML, unpubl. data) suggest that an increase in

mortality of weaned pups and juveniles is the most likely

proximate cause of sea lion declines. This implies that a

correlations between harvest data and sea lion data (positive or

negative) are more likely to surface in lagged comparisons,
11

particularly at 3-5 years.

Interpretation of Negative Correlations

Loughlin and Merrick (1989) viewed the effect of pollock

harvest as the removal of prey otherwise available for sea lions,

but noted-that they would have preferred to compare sea lion

abundance to a measure of pollock biomass remaining after

harvest. Such a measure still does not exist. However, we

suggest that significant negative correlations using the harvest

statistic are informative in that they may indicate circumstances

where pollock biomass was adequate to meet the needs of the

fishery, but not sea lions. Alternatively, other factors such as

vessel disturbance or coincidental environmental processes could

have impacted sea lion abundance independent of pollock biomass.

Even so, we can not rule out the possibility that developments in

fishing technology (e.g. hydroacoustics, and net design and

construction) and increases in numbers of vessels may have

enabled fishermen to sustain catches even as the target stock

declined in the local area fished (Laevastu and Favorite 1988;

Angelsen and Olsen 1986). Where pollock biomass may have been

low to begin with and/or where harvests were exceptionally

efficient, the result could have been localized depletions that

ultimately impacted sea lion survival. These circumstances would

explain significant negative correlations in lagged comparisons.

Negative correlations in direct comparisons can not be

explained in the same way. If a large, direct reduction of sea
12

lions occurred prior to the counts (e.g., high incidental takes

early in the year), lag 0 could be explained, but such is not the

case, Incidental takes did occur in the study period, but they

were not high enough nor consistent from year to year to appear

as a factor in sea lion counts (Perez and Loughlin 1991).

Therefore, we can not determine a biological explanation for

them.
13

ACKNOWLEDGMENTS

The authors wish to thank Tom Loughlin, Richard Merrick and

Anne York and for their assistance in formulating and reviewing

these analyses. Additional reviews provided by Howard Braham,

Rod Hobbs, Grant Thompson, Anne Hollowed, Russ Kappenman, Richard 

Marasco and Richard Methot significantly improved the manuscript.

We also thank Gary Duker and James Lee for their technical

reviews and Charles Leap for assistance with the figures.
14

CITATIONS

Angelsen, K. K., and S. Olsen. 1986 l Impacts of fish density

and effort level on efficiency of fishing gear, p. 437-445.

In M. Alton (compiler), A workshop on comparative biology,

assessment, and management of gadoids from the North Pacific

and Atlantic Oceans, 24-28 June 1985, Alaska Fisheries

Science Center, NMFS, 7600 Sand Point Way, N.E., Seattle, WA

98115.

Braham, H. W., R. D. Everitt, and D. J. Rugh. 1980, Northern

sea lion population decline in the eastern Aleutian Islands.

J. Wild. Manage. 44:25-33.

Castellini, M. A., R. W. Davis, and T. R. Loughlin. 1993 l The

health status of Steller sea lion pups in the Gulf of

Alaska: Blood chemistry and body condition. Mar. Mammal

Sci. 9:202-208.

Laevastu, T., and F. Favorite. 1988. Fishing and Stock

Fluctuations. Fishing News Books, Ltd., Farnham, Surrey,

England. 239 p.
15

Loughlin, T. R., A. S. Perlov, and V. A. Vladimirov. 1990.

Survey of northern sea lions (Eumetopias jubatus) in the

Gulf of Alaska and Aleutian Islands during June 1989. U.S.

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Loughlin, T. R., and R. L. Merrick. 1989. Comparison of

commercial harvest of walleye pollock and northern sea lion

abundance in the Bering Sea and Gulf of Alaska, p. 679-699.

In L. Lowery (ed.), Proc. Int. Symp. Mgmt. Walleye Pollock,

Alaska Sea Grant Rept. No. 89-1, Univ. Alaska, Anchorage AK.

Lowry, L. F. 1982 l Documentation and assessment of marine

mammal-fishery interactions in the Bering Sea, p. 300-311.

In Kenneth Sobol (ea.), Transactions of the Forty-seventh

North American Wildlife and Natural Resources Conference,

Wildlife Management Institute, Washington, D.C.

Megrey, B. A., and V. G. Wespestad. 1990. Alaskan groundfish

resources: 10 years of management under the Magnuson

Fishery Conservation and Management Act. North Amer. Jour.

Fish. Manage. 10:125-143.
16

Merrick, R. L., T. R. Loughlin, and D. G. Calkins. 1987.

Decline in abundance of the northern sea lion, Eumetopias

jubatus, in Alaska, 1956-86. Fish. Bull., U.S. 85:351-365.

Merrick, R. L., L. M. Ferm, R. D. Everitt, R. R. Ream, and L. A.

Lessard. 1991. Aerial and ship-based surveys of northern

sea lions (Eumetopias jubatus) in the Gulf of Alaska and

Aleutian Islands during June and July 1990. U.S. Dep.

Commer., NOAA Tech. Memo. NMFS F/NWC-196, 34 p.

Merrick, R. L., D. G. Calkins, and D. C. McAllister. 1992.

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(Eumetopias jubatus) in Southeast Alaska, the Gulf of

Alaska, and Aleutian Islands during June and July 1991. U.S.

Dep. Commer., NOAA Tech. Memo. NMFS-AFSC-1, 41 p.

Merrick, R. L., T. R. Loughlin, G. A. Antonelis, and R. Hill.

1994. Use of satellite-linked telemetry to study Steller

sea lion and northern fur seal foraging. Polar Research

13:105-114,
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Pascual, M. A., and M. D. Adkison. 1994. The decline of

northern sea lion populations: Demography, harvest, or

environment. Ecological Applications 4:393-403.

Perez, M. A., and T. R. Loughlin. 1991. Incidental catch of

marine mammals by foreign and joint venture trawl vessels in

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1975-1985. Mar. Mammal Sci. 10:31-37.
18

Table 1. Definition of 5 study areas used to estimate catches of

pollock modeled after areas in Loughlin and Merrick 1989.

Longitude Latitude INPFC

Study Area from to from to Area

Table 2. Sea lion counts from 1976 to 1991 for 5 study areas modeled after

areas in Loughlin and Merrick 1989.
Table 3. Estimated catches of walleye pollock (in metric tons) in each study areas listed in Table 1.

Year

Seguam Bogoslof Walrus Ugamak Chirikof

Island Island Island Island Island
Table 4. Sea lion counts from 1977 to 1991 for the following 15 study areas surrounding rookeries from the Barren

Islands to the western Aleutian Islands: SM=Sugarloaf and Marmot; CHT=Chowiet; CHF=ChirFkof; AC=Atkins and

Chernabura; PC=Pinnacle and Clubbing Rocks; SLR=Sea Lion Rocks (near Amak Island); UAA=Ugamak, Akun and

Akutan; BO=Bogoslof; OA=Ogchul and Adugak; Y=Yunaska; SA=Seguam and Agligadak; K=Kasatochi; GTU=Gramp Rock,

Tag and Ulak (Delarof Islands).

Year SM CHT CHF AC PC SLR UAA BO OA Y SA GTU
Table 5. Estimated catches of walleye pollock (metric tons) within 20 nmi of each of the following study areas or

rookery groups: SM=Sugarloaf and Marmot; CHT=Chowiet; CHF=Chirikof; AC=Atkins and Chernabura; PC=Pinnacle

and Clubbing Rocks; SLR=Sea Lion Rocks (near Amak Island); UAA=Ugamak, Akun and Akutan; BO=Bogoslof;

OA=Ogchul and Adugak; Y=Yunaska; SA=Seguam and Agligadak; K=Kasatochi; GTU=Gramp Rock, Tag and Ulak

(Delarof Islands).

Year SM CHT CHF AC PC SLR UAA BO OA Y SA GTU
Table 6. Correlation coefficients (r) for Steller sea lion counts and 0 to 5 year

lags of pollock harvest for 5 study areas modeled after Loughlin and

Merrick 1989. Significant correlations (a=0.05) are marked with an asterisk.

Ch/Ch stands for Chowiet and Chirikof Islands.

Table 7. Kendall's coefficients of rank correlation (t) between Steller sea ‘lion counts

and 0 to 5 year lags of pollock harvests for 5 study areas modeled after

Loughlin and Merrick 1989.

an asterisk.

Significant correlations (a=0.05) are marked with

Ch/Ch stands for Chowiet and Chirikof islands.
Table 8. Correlation coefficients (r) between Steller sea lion counts at 15 rookery sites and 0-5 year

lags of pollock harvest within 20 nmi of each site.

with an asterisk.

Significant correlations (cx=O.O5) are marked

Table 9. Kendall's coefficients of rank correlation (I) between Steller sea lion counts at 15 rookery sites

and 0 to 5 year lags of pollock harvest within 20 nmi of each site.

are marked with an asterisk. Significant correlations (a=O.O5) 

Figure 2. Study areas as defined in this study.
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