The effect of different sweep lengths on the length composition of bottom-sampling trawl catches
Abundance estimates of Northeast Arctic cod ( Gadus morhua L.) and haddock ( Melanogrammus aeglefinus L) are compiled annually from combined bottom-trawl and acoustic surveys. Both survey methods use data from bottom-trawl catches in the calculations. The surveys are conducted in the Barents Sea and...
| Published in: | ICES Journal of Marine Science |
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| Main Authors: | , |
| Format: | Text |
| Language: | English |
| Published: |
Oxford University Press
1989
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| Subjects: | |
| Online Access: | http://icesjms.oxfordjournals.org/cgi/content/short/45/3/263 https://doi.org/10.1093/icesjms/45.3.263 |
| Summary: | Abundance estimates of Northeast Arctic cod ( Gadus morhua L.) and haddock ( Melanogrammus aeglefinus L) are compiled annually from combined bottom-trawl and acoustic surveys. Both survey methods use data from bottom-trawl catches in the calculations. The surveys are conducted in the Barents Sea and the Svalbard area with the same bottom trawl, but with different sweep lengths. The bottom-trawl indices are calculated for both areas assuming an effective path width of 25 m. In this paper results from parallel trawling experiments with the standard sampling trawl equipped with different sweep lengths are analysed. The results show that the total catch increases with increasing sweep length. Small fish are relatively underestimated by the trawl with the longer sweeps, and a slight species selection was indicated. It is concluded that combining survey results without compensating for the effect of using different sweep lengths will bias the estimates. |
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