DISTRIBUTION AND ABUNDANCE OF ROCKFISH DETERMINED FROM A SUBMERSIBLE AND BY BOTTOM TRAWLING

A manned submersible was used in the eastern Gulf of Alaska to observe spatial distributions of Pacific ocean perch Sebastes alutus and othe r Sebastes spp., and count rockfish for comparison with bottom-trawl c atch rates. Twenty submersible dives were completed in 1988 and 1989 a t depths of 188-290 m. Approximately 80% of the 5317 rockfish observed from the submersible were Pacific ocean perch. Most adult Pacific oce an perch were in groups of 2-200 over flat, pebble substrate. Fish wit hin a group were 1-4 m apart, usually oriented into the current, and 0 -7 m above bottom. Most juvenile Pacific ocean perch, and juveniles an d adults of other Sebastes spp., were associated with rugged habitat ( cobble, boulders, pinnacles, and coral). Densities of Pacific ocean pe rch estimated from bottom-trawl catches were approximately twice those observed from the submersible, indicating that the bridles and otter doors herded fish into the trawl. Bottom-trawl surveys may overestimat e Pacific ocean perch abundance because of this possible herding effec t and the preference of adult Pacific ocean perch for smooth (trawlabl e) substrate.