Escape of fish under the fishing line of a Norwegian sampling trawl and its influence on survey results
The Institute of Marine Research, Bergen, has carried out combined bottom-trawl and acoustic surveys for cod and haddock in the Barents Sea and the Svalbard area since 1981. The results have demonstrated clearly that the current trawl and acoustic survey methods considerably underestimate the young...
| 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/45/3/269 https://doi.org/10.1093/icesjms/45.3.269 |
| Summary: | The Institute of Marine Research, Bergen, has carried out combined bottom-trawl and acoustic surveys for cod and haddock in the Barents Sea and the Svalbard area since 1981. The results have demonstrated clearly that the current trawl and acoustic survey methods considerably underestimate the young age groups of cod, partly because of low gear efficiency for the smaller fish. This paper describes the results of experiments with small bags to collect fish that escape under the trawl. Catches of several different species were obtained in the small bags. Comparison between trawl and bag catches reveals a length-dependent escape of cod and haddock under the trawl; i.e., small fish are severely underrepresented in the trawl catches. The escape also has a considerable effect on the species composition, because cod, more than haddock, tend to dive under the fishing line. To improve the efficiency of the sampling trawl, a rockhopper ground gear was introduced. Comparison of the trawl fitted with standard bobbins gear and with rockhopper gear showed that escape under the standard equipment was of similar magnitude as that in the bag experiment. |
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