308 



Fishery Bulletin 100(2) 



lock in the western and central GOA (defined as the area 

 between 147°W and 170°W), from 1984 to 1996. Catch per 

 unit of effort (CPUE) (number of fisli/km'-) was used as a 

 measure of density throughout our analysis. 



We also examine changes in species associations and the 

 distribution of pollock. Analysis is limited to the summer 

 months because the source of our pollock data were sum- 

 mer research surveys. 



4000 



- 3000 - 



2000 



1000 



L1I1IJIIII....I1..II....I1 





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4000 



o 3000 



2000 



g 1000 





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4000 



3000 



2000 ^ 



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Methods 



Data source 



Data were collected from triennial bottom trawl surveys in 

 the GOA conducted by the Alaska Fisheries Science Center 

 of the U.S. National Marine Fisheries Service (RACE divi- 

 sion trawl sui-vey relational database, MundellM. The use 

 of bottom trawl data to assess juvenile pollock 

 abundance and distribution has many prece- 

 dents. In the Bering Sea, bottom trawl sui-vey 

 data have been used to determine estimates 

 of age-1 pollock, which were used as indices 

 of recruitment (Wespestad-). Others have used 

 the same data to evaluate the relationship 

 between juvenile pollock and the movement of 

 the ice edge in the Bering Sea (Wyllie-Echever- 

 ria and Wooster, 1998). Bottom trawl estimates 

 have also been used to explore the relationships 

 between different age groups of pollock in She- 

 likof Strait (Schumacher and Kendall, 1991). 



Brodeur and Wilson (1996) modeled the depth 

 distribution of pollock in the GOA during their 

 first year and showed that age-1 pollock were 

 found near bottom. Acoustic surveys of spawn- 

 ing pollock in Shelikof Strait have detected 

 age-1 pollock in both nearbottom and pelagic 

 layers. These data suggest that some age-1 pol- 

 lock may reside off bottom. Therefore, juvenile 

 pollock data from bottom trawl surveys are 

 used as an index rather than an absolute mea- 

 sure of abundance (Bailey and Spring, 1992; 

 Guttormsen and Wilson^). 



Survey design 



Triennial bottom trawl sui-veys were conducted 

 during the summer months (May-Sep) of 1984, 

 1987, 1990, 1993, and 1996. These surveys 

 have consistently been conducted in a strat- 

 ified random sampling pattern (Martin and 

 Clausen. 1995; Munro and Hoff 1995; Stark 

 and Clausen, 1995; Martin, 1997). The GOA is 

 divided into 49 strata according to water depth 



I I I I I 





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Year 



Figure 1 



Data for walleye pollock in Gulf of Alaska, 1969-1997: pollock recruit- 

 ment (A), biomass estimates from stock assessment analysis (B), and 

 biomass estimates from triennial bottom trawl sui-veys IC). Data are 

 from Dorn, M. W., A. B. Hollowed. E. Brown, B. Megrey. C. Wilson, and 

 J. Blackburn. 2000. Walleye pollock. In Stock assessment and fishery 

 evaluation report for the 2000 Gulf of Alaska groundfish fishery. 60 p. 

 North Pacific Fishery Management Council. P.O. Box 10:3136. Anchor- 

 age. Alaska 99.510. 



• Mundell. G. 1999. Personal commun. Alaska 

 Fisheries Science Center, NMFS/NOAA, 7600 Sand 

 Point Way NE, Seattle, WA 98115. 



- Wespestad. V. 199,5. Walleye pollock. //; Plan 

 team for groundfish fisheries of the Bering Sea/ 

 Aleutian Islands stock assessment and fishery eval- 

 uation report for the groundfish resources of the 

 Bering Sea/Aleutian Islands region as projected for 

 1996, 35 p. North Pacific Fishery Management 

 Council, PO. Box 103136, Anchorage. AK 99510. 



3 Guttormsen, M. A., and CD. Wilson. 1999. Echo 

 integration-trawl survey results for walleye pollock 

 in the Gulf of Alaska during 1998. In Stock assess- 

 ment and fishery evaluation report for the 1998 

 Gulf of Alaska groundfish fishery, 25 p. North 

 Pacific Fishery Management Council, 605 W 4"' 

 Avenue, Suite 306, Anchorage, Alaska 99501. 



