Data report: National Marine Fisheries Service longline surveys, 1991-96

Abstract

This report summarizes the results of the 1991-96 National Marine Fisheries Service longline surveys of the Gulf of Alaska and eastern Aleutian Islands. Sablefish, Anoplopoma fimbria, was the principal target species, although shortspine thornyhead, Sebastolobus alascanus, rougheye rockfish, Sebastes aleutianus, and shortraker rockfish, Sebastes borealis, populations appear to have been sampled adequately to derive meaningful abundance indices. The survey area in the Gulf of Alaska extends from Islands of Four Mountains (170°W long.) eastward to Dixon Entrance (133°25'W long.) and covers the upper continental slope and selected gullies. Beginning in 1996, the eastern Aleutian Islands were surveyed from Amchitka Pass (178°58'W long.) to the western end of Umnak Island (170°12'W long.).

Sablefish abundance indices (relative population number, RPN) for the Gulf of Alaska declined slightly from 1991 to 1996. The two large annual declines in 1992 and 1994 were followed by slight increases in 1993 and 1995. Sablefish relative biomass (relative population weight, RPW) changes were similar to those for sablefish RPN in the Gulf of Alaska. The length compositions for both sexes of sablefish increased from 1991 to 1996.

Gulfwide, shortspine thornyhead RPN and RPW increased during 1996 to the highest number for any survey year, exceeding the previous high in 1992. For all years, their length modes changed slightly.

Gulfwide, RPN and RPW for rougheye rockfish varied without a discernable trend from 1991 to 1994, then increased substantially in 1995 and 1996. Their length modes were generally 42-44 cm fork length (FL).

Shortraker rockfish RPN and RPW declined from 1991 to 1994 and then increased in 1995 and 1996. Their length modes were generally 56-63 cm FL.


View Online.  (.pdf, 1.66 MB).