Availability of Commercial Fish Species as Food....
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GRANT NUMBER: NA47FD0351           NMFS NUMBER: 93-AKR-010

REPORT TITLE:  Availability of Commercial Fish Species as Food for Marine Mammals

AUTHOR:  Norcross, Brenda L.

PUBLISH DATE:  December 1, 1995

AVAILABLE FROM:  National Marine Fisheries Service, Alaska Region, P.O. Box 21668, Juneau, AK 21668.  PHONE: (907) 586-7224


The objective of this project was to investigate the abundance of commercial fish species as a food supply for marine mammals, particularly Steller sea lions.  Bottom trawl surveys were conducted near three rookeries in the Gulf of Alaska.  Small demersal fishes were targeted within foraging range of the sea lion rookeries on Akun, Atkins and Marmot Island. The most abundant species in the total catch from all gear types were rock sole, northern sculpin, Pacific halibut, walleye pollock, butter sole, Aleutian alligator fish, arrowtooth flounder, and fourhorn poacher.  Catch-per-unit-effort (CPUE) was estimated as number of fish per 10 min. tow and was found to differ among gear types and mesh sizes. Species composition and abundances differed significantly among rookeries when CPUE's from the most frequently used gear type were compared. Rock sole, mostly age-0 fish, was the most abundant species at Akun Island, whereas northern sculpin was most abundant at Atkins and Marmot Islands.  The observed patterns of CPUE by sampling location indicated a decreasing trend in CPUE from west to east for most species.   Observed species composition and abundances do not reflect all pre available to juvenile Steller sea lions within feeding range of the rookeries because only trawlable areas were sampled and because the size range of fishes sampled is smaller than the average size of prey in sea lion stomachs. Nevertheless, differences are believed to reflect real differences in prey availability among rookeries that potentially affect sea lion feeding.

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