The influence of warp length on trawl dimension and catch of walleye pollock Theragra chalcogramma in a bottom trawl survey

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,...

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Bibliographic Details
Published in:Fisheries science 2005-08, Vol.71 (4), p.738-747
Main Authors: Fujimori, Y. (Hokkaido Univ., Sapporo (Japan)), Chiba, K, Oshima, T, Miyashita, K, Honda, S
Format: Article
Language:English
Subjects:
Fish
Fisheries
Fisheries research
Fishing
FISHING NETS
footgear contact
Marine
Polls & surveys
SURVEYS
THERAGRA CHALCOGRAMMA
trawl dimension
trawl survey
TRAWLING
walleye pollock
warp length
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Summary: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 wilt 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.
ISSN:0919-9268
1444-2906
DOI:10.1111/j.1444-2906.2005.01023.x