Biomass survey of rockfish stocks in the Dixon Entrance-southeast Alaska region, July 5-22, 1983 (R/V G.B. Reed and M/V Free Enterprise No. 1) / by B.M. Leaman and D.A. Nagtegaal.: Fs97-6/1510E-PDF

"Two vessels were used to survey rockfish aggregations on the outer continental shelf (180-640 m) between 54°10'N - 55°30'N, using echo sounder and bottom trawl gear. Both stratified-systematic and encounter-response search patterns were employed to detect and map significant aggregations. Rockfish density in the survey area was very low with only two areas showing extensive rockfish echo soundings. One large aggregation (~9 M² ) was observed near 55°10'N and a second area of higher density was detected between 54°10' - 54°25'N. No estimation of the biomass in the northern aggregation was possible due to rough bottom. Individual schools in the southern area were mapped and sampled. Extrapolation of catch rates over school dimensions suggests a minimum biomass of ~1200 t ± 67%, composed primarily (89%) of Sebastes alutus. Catch rates ranged from 1000-16,000 kg/h. Biomass estimates for comparable areas of a 1979 survey showed both major and minor decreases over the 1979 estimates, depending on area. In addition the commercial fishery has removed approximately four times the total 1983 estimate, during the 1983-1985 period. The value of swept-area surveys for rockfishes is reviewed in light of these results"--Abstract, page iii.

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