Hydroacoustic and fishing surveys for walleye pollock in Dixon Entrance and nearby areas, July 5-23, 1978 / by F.H.C. Taylor and R. Kieser.: Fs97-4/1572E-PDF

"The G.B. REED conducted a hydroacoustic survey of Dixon Entrance, Chatham Sound, and northern Hecate Strait from July 5-23, 1978, to determine the distribution and abundance of pelagic fish especially walleye pollock. The chartered trawler, NEMESIS, fished the same areas at the same time to determine the species composition of the midwater fish stocks and to obtain biological information on them. Walleye pollock were distributed throughout Dixon Entrance in a layer between 90 and 140 m (50-77 fm). They occurred infrequently where the water depth was less than 100 m (55 fm). About 90% of the pollock in Dixon Entrance were in midwater. Two main concentrations were located, one from Dundas Island to McIntyre Bay centered on the Two Peaks grounds, the other off Cape Chacon. The hydroacoustic estimate of midwater fish in Dixon Entrance was 15,000 t. Of this, 10,000 t were considered pollock, 2,800 t rockfish, 1,000 t herring, and 500 t eulachon. In northern Chatham Sound near Boston Islands the estimate of 1,400 t of pollock is possibly too large. In northern Hecate Strait 2,100 t of pelagic fish were located, about 60% herring, and 40% dogfish. Pollock were not encountered here in midwater but occurred in bottom trawl tows. Ages of pollock, determined from pectoral fin ray sections, ranged from 0-11 yr. Age 0 fish were found entangled in the mesh in several localities. Age 1 fish were widespread but not abundant. Ages 2 and 3 were rare. Ages 6 and 7 were the most numerous age groups. Adult age groups were not distributed evenly throughout Dixon Entrance. The age data suggest a high rate of natural mortality, and a high Brody growth coefficient. Pollock were feeding actively on zooplankton, principally euphausiids. Scars from lamprey wounds were noted on some pollock. They were more frequent on pollock caught near the surface in deep water off the Boston Island than elsewhere"--Abstract, page iii.

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