Vertical distribution and acoustic estimation of biomass of walleye pollock Theragra chalcogramma, and anchovy Engraulis japonicus in the Pacific coast of eastern Hokkaido [Japan]
1996
Ohshimo, S. (Seikai National Fisheries Research Inst., Nagasaki (Japan)) | Hamatsu, T.
We estimated the biomass of walleye pollock and anchovy using a quantitative echo sounder combined with analysis of midwater trawling catches. The acoustic survey, conducted from October to November 1994, was executed along 8 transact lines. Trawling was done at 7 stations, and CTD or XBT castings were executed at 48 sites. The vertical thermocline at about 100 m depth was cleared by CTD or XBT castings. The water temperatures above and under the thermocline were 5 to 15 degrees C and 2 to 5 degrees C, respectively. Anchovy (Engraulis japonicus) occurred in the shallow water layer. Small walleye pollock (Theragra chalcogramma) about 200 mm in total length occurred at the thermocline, and larger pollock (about 350 mm in total length) were below the thermocline. Based on results from the otolith readings, the smaller walleye pollock were 0 to 1 year old, and the larger pollock ranged from 2 to 5 years old. In the present survey area, the estimated biomass of the anchovy was 890,000 tons. The 0 and 1 age, and 2 to 5 years old walleye pollock were 139,000 and 23,400 tons, respectively (6,115 square-kilometer, degree of coverage = 5.68 and C.V. = 0.25)
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