A study of optimum positioning of square-mesh escape panels in Irish SeaNephrops trawls

摘要

The position of a square-mesh panel in a 70-mm Nephrops trawl of the type widely used in the Irish Sea was varied to examine the effect on catch rates of whiting (Merlangius merlangus) of different sizes. Panels of 75-mm mesh size and 3 m length were positioned either 1 m in front of the cod-end extension, conforming with United Kingdom (UK) legislation, or 7 m in front of the extension, conforming with Irish (IRL) legislation. Forty-three tows of a twin Nephrops trawl were carried out from a commercial fishing vessel of the type using this gear in the Irish Sea, with different panel positions in the two nets. In a subsequent experiment, the twin trawl was separated into two single trawls and 40 parallel hauls were carried out from two smaller commercial trawlers typical of the single-rig Nephrops fleet in the Irish Sea. In each experiment, the trawls were deployed over a range of depths. Rigged as a twin trawl, the IRL net consistently caught fewer whiting below the minimum landing size (MLS) of 27 cm than did the UK net (mean catch rates of 72 +/- 10 and 131 +/- 14 fish per hour, respectively). Catch rates above MLS were almost identical in most hauls. In contrast, the panel position had no significant effect on catch rates of whiting of all sizes when the same nets were towed in parallel by the two smaller vessels. Possible reasons for these differences in results are discussed. As catch rates of whiting above MLS were not affected by panel position in both sets of trials, it is concluded that the more forward panel position would be most appropriate for Nephrops fisheries involving both single and twin trawls.