Changes in the length compositions of some fish species as a consequence of alterations in the groundgear of the GOV-trawl

摘要

Experiments using bagnets under the groundgear have shown that the efficiency of sampling trawls for different species and length groups of fishes varies with the type of groundgear. Critics of the results claim that properties of the sampling gear change due to the attachment of the collection bags. The present contribution addresses these criticisms by comparing the length distributions of selected species obtained from catches with the same net but different rollergear. The results generally confirm the original bagnet experiments. In agreement with earlier bagnet results for some bottom dwelling fishes, the same changes in efficiency of the sampling trawl depending on fish length could be detected. For other species-also in agreement with existing knowledge- there was no effect when groundgear was changed. Furthermore, the present results hint at an increased efficiency for capture of larger fish of some species in the case of fishing lines lifted by groundgear. Possible reasons for this phenomenon are discussed.