Hydroacoustic and fishing surveys for walleye pollock (Theragra chalcogramma) in Dixon Entrance and northern Hecate Strait, January 22-February 9, 1979 / by F.H.C. Taylor and R. Kieser.: Fs97-4/1624E-PDF

"The G.B. REED carried out a hydroacoustic survey of Dixon Entrance and northern Hecate Strait from January 22-February 9, 1979, to determine the distribution and abundance of pollock during the period of the major winter fishery. The chartered trawler ARCTIC HARVESTER fished the same area at the same time to identify the midwater fish signs seen on the echosounder, to determine the species composition of the midwater stocks, and to obtain biological information on them. In January walleye pollock were found concentrated in a narrow band inside the 100 fm (183 m) contour from Rose Spit to Zayas Island. Six other small concentrations most probably of yellowtail rockfish were encountered, 3 between Capes Chacon and Muzon and 3 from Massett to Langara Island. Fish were very sparsely distributed over the remainder of the area. In northern Hecate Strait four small concentrations of fish were located. The hydroacoustic estimate of midwater fish in Dixon Entrance was only 1600 t, a marked decline from the estimated 15,000 t of July, 1978. There were 965 t of pollock, 122 t of yellowtail rockfish, and 94 t of ratfish. In northern Hecate Strait there were 356 t of fish, of which 264 t were considered to be herring. Part of the area between Rose Spit and Zayas Island was surveyed twice, a week apart. Only 625 t of pollock were located, compared to 1105 t in the same area on the first survey. On both surveys 95 t of yellowtail rockfish were found. A marked decrease in biomass was found at night both in Dixon Entrance and in northern Hecate Strait. The variance of the daytime density estimate in the area surveyed on the two occasions was ±23% to ±34% on the first survey and ±10% to ±19% on the second survey, dependant on the method used to make the calculation. The higher estimates resulted from the method considered the most appropriate. These estimates are of the same order as those obtained by other surveys or by other workers on similar species"--Abstract, page iii.

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