Escapement from a Diamond IX midwater trawl during acoustic surveys for capelin (Mallotus villosus) in the Northwest Atlantic
Escapement from different parts of the Diamond IX midwater trawl was measured using experimental bags made of 6.3-mm-square mesh nylon attached to the outside of the trawl. The objective was to quantify the amount of escapement and to determine its effect on estimating the species composition and le...
| Published in: | ICES Journal of Marine Science |
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| Main Author: | |
| Format: | Text |
| Language: | English |
| Published: |
Oxford University Press
1990
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| Subjects: | |
| Online Access: | http://icesjms.oxfordjournals.org/cgi/content/short/47/1/76 https://doi.org/10.1093/icesjms/47.1.76 |
| Summary: | Escapement from different parts of the Diamond IX midwater trawl was measured using experimental bags made of 6.3-mm-square mesh nylon attached to the outside of the trawl. The objective was to quantify the amount of escapement and to determine its effect on estimating the species composition and length frequency of capelin populations encountered during capelin acoustic surveys. Escapement was restricted primarily to the third and fourth bellies near the codend. Escapement was not related to the catch weight in the codend. Differences were observed in length frequencies between the experimental bags and codend catches of capelin. Length frequencies were skewed to the left towards the smaller lengths for experimental bag catches compared with the codend regardless of the size of capelin encountered. In some instances, there were differences in species composition between the codend and the experimental bags, especially when sand lance and Arctic cod were present. Escapement was greatest from the top of the trawl compared with the bottom and side in the vicinity of the fourth wedge and belly. A bias in the length frequency of the capelin catch or in the catch composition due to escapement is of concern when biomass estimates of capelin are calculated from acoustic surveys. |
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