A catch comparison study on different codend designs to evaluate bycatch reduction in the North-East Atlantic deep-water shrimp (Pandalus borealis) fishery

Abstract

Currently, there is a growing interest in the North-East Atlantic deep-water shrimp (Pandalus borealis) fishery with more actors expected to take part in the coming years. As the species and size of targeted shrimp varies globally, selectivity in this fishery is based on a grid system in front of a small mesh sized codend to avoid bycatch while simultaneously maintaining shrimp catches. However, small fish can still pass through the grid and risk being retained in the codend. Thus, the aim of this study was to analyze the selectivity of a modified shrimp trawl codend using shortened lastridges, an increased mesh size and a four panel codend in combination with the Nordmøre grid with the aim of reducing bycatch while simultaneously maintaining the retention of shrimp. This was carried out using a catch comparison analysis between the different treatment codends versus the compulsory two panel, 35 mm diamond mesh codend used in the fishery today. We found that applying shortened lastridge ropes, along with a four panel codend significantly improved the exclusion of redfish at approximately 50 % in length groups below 7.5 cm while simultaneously maintaining shrimp catches. However, a significant increase in catch efficiency for the Greenland halibut occurred. When all treatments were applied, a significant reduction in shrimp was observed as well as a significant reduction in both redfish and Greenland halibut. An additional experiment was undertaken observing the effect of shortened lastridge ropes while the baseline codends used were configured with four panels rather than two. This caused a significant reduction in shrimp as well as redfish and Greenland halibut in the treatment codend.

The results from this thesis demonstrates that applying 30% shortened lastridge ropes along with a four panel codend may be a potential solution for the industry in reducing bycatch, but further exploration regarding the exclusion of flatfishes is needed. Reducing the percentage of lastridge shortening may offer some more clarity for these species’.