Grid-net design that successfully reduces discarded catch and damage to benthic species in the veined rapa whelk beam trawl fishery

Abstract

In this study, a grid-net design (GND) with three different bar spacings was compared with the commercial beam trawl used in the veined rapa whelk fishery to minimize the discarded catch amount and the loss of commercial product. In addition, the damage and mortality rates of the species that entered the tested fishing gear were determined to understand whether the tested fishing gear has a possible negative effect on benthic species. In the grid-net design, a rectangular metallic grid positioned 6 cm off the ground substituted half of the codend to allow the escape of discard species. Sea trials were carried out in the south-eastern Black Sea between 13 and 24 October 2021. Results showed that the discarded catch amount was significantly reduced by each GND (P < 0.05). Compared with the commercial fishing gear, the reductions in the discarded catch amounts (in terms of number) were 91.6%, 92.2%, and 95.0% for 22, 25, and 28 mm GNDs, respectively. The minimum commercial product loss was determined at 22 mm GND. In addition, it was seen that each GND compared to commercial gear caused statistically significantly less damage and mortality on the discarded species. In conclusion, 22 mm GND was the most successful design among the tested gears in minimizing commercial product loss and reducing the discarded catch amount. Recommendations are given for this design to be adopted by the commercial fleet.