The influence of warp length on trawl dimension and catch of walleye pollock <Emphasis Type="Italic">Theragra chalcogramma</Emphasis> in a bottom trawl survey |
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Authors: | Email author" target="_blank">Yasuzumi?FujimoriEmail author Kenji?Chiba Tatsuki?Oshima Kazushi?Miyashita Satoshi?Honda |
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Institution: | Graduate School of Fisheries Science, Hokkaido University, Hakodate, Hokkaido 041-8611,;Marine Fisheries Research and Development Department, Fisheries Research Agency, Yokohama, Kanagawa 220-6115,;Field Science Center for Northern Biosphere, Hokkaido University, Hakodate, Hokkaido 041-8611 and;Hokkaido National Fisheries Research Institutes, Fisheries Research Agency, Kushiro, Hokkaido 085-0802, Japan |
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Abstract: | ABSTRACT: Variations in trawl dimension, bottom contact, and catch with differing warp lengths during walleye pollock surveys conducted by the Fisheries Research Agency were examined. The ratio of warp length to fishing depth (scope ratio) was set at 2.5, 3.0 and 3.5 at depths of 110 m. At a 2.5 scope ratio, the net mouth shape and footgear contact fluctuated, as the trawl door did not contact the bottom. Footgear contact was complete when the scope ratio was 3.0 or more. Walleye pollock, sculpins and flatfishes were the main catch in all tows, and the catch increased with scope ratio. There was no difference in the length frequency of walleye pollock ( n = 300) captured at 2.5 and 3.0 scope ratio. However, the length frequency at 3.5 was significantly different from that of other scope ratios. These results suggest that at a scope ratio of 3.0 or more, the trawl door will not leave the bottom at any depths. To compliment echo surveys for walleye pollock, a 3.0 scope ratio would be optimal, since the catch data for a 3.5 scope ratio was dissimilar from that of scope ratios. |
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Keywords: | footgear contact trawl dimension trawl survey walleye pollock warp length |
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