Evaluation of a Modified Codend Configuration for a Marine Mammal Bycatch Reduction Device in a Midwater Trawl Gear

Marine mammal Bycatch Reduction Devices (BRDs) can result in the escape of target fish species. In the present study, a modified single-layer codend configuration developed from previous studies was evaluated using BRDs with guide net angles of 30° and 45°. Catch was collected separately from the codend and the BRD cover to estimate catch loss rates and characteristics. For caught species, catch loss rates based on the number and weight of individuals were 9% and 13% for herring with the 30° guide net and 16% and 18% with the 45° guide net, respectively. For Korean pomfret, catch loss rates were 24% and 23% at 30° and 4% at 45°. These results suggest that further modification of BRD is necessary. In contrast, catch loss rates of mackerel with the 30° guide net reached 56%, whereas hairtail showed loss rates of 60% and 65% with the 45° guide net. Underwater observations indicated that catch loss was influenced by swimming behavior and entanglement with the guide net. Despite the modification of the codend to a single layer, the present study still observed high catch loss rates. However, no bycatch of marine mammals occurred during the experimental operations.