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

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 (<i>P</i> &lt; 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.

本研究针对脉红螺渔业中所使用的商用桁拖网，设计了三种不同栅条间距的网栅设计（Grid-net Design, GND）并与之对比，旨在最大限度减少兼捕丢弃量与商品渔获损失。此外，本研究测定了进入受试渔具的物种的损伤率与死亡率，以明确受试渔具是否会对底栖物种产生潜在负面影响。该网栅设计中，将距海底6厘米的矩形金属栅替代了一半网囊，以使兼捕物种得以逃逸。本研究于2021年10月13日至24日在黑海东南部开展海上试验。试验结果表明，所有受试网栅设计均显著降低了兼捕丢弃量（P<0.05）。相较于商用桁拖网，栅条间距22mm、25mm、28mm的网栅设计的兼捕丢弃量（按数量统计）分别降低了91.6%、92.2%与95.0%。其中22mm间距的网栅设计的商品渔获损失最低。此外，相较于商用渔具，所有受试网栅设计对兼捕物种造成的损伤与死亡率均具有统计学显著性降低。综上，在所有受试渔具中，22mm间距的网栅设计在降低商品渔获损失与减少兼捕丢弃量两方面均表现最优。本研究建议该设计被商业捕捞船队推广采用。