A rapid bycatch assessment framework for small-scale fisheries: A case study on horseshoe crab (Tachypleus tridentatus) bycatch

Timely bycatch data is crucial for detecting rare and endangered species impacted by small-scale fisheries, supporting sustainable management. Horseshoe crabs (Tachypleus tridentatus), valued for the utility of their blood cells for detecting bacterial endotoxins, continue to be harvested despite their demographically vulnerable status and declining populations. Timely bycatch monitoring is crucial to limit further fishery mortality and enforce species-specific bycatch quotas. By combining local ecological knowledge surveys, deep learning algorithms, and remote sensing techniques, this study developed a framework for rapidly assessing T. tridentatus bycatch and associated indicators. The framework estimates that at least 9120 ± 315 T. tridentatus are bycaught annually in Leizhou Bay, China, with a catch per unit effort (CPUE) of 0.29 ± 0.01 T. tridentatus per vessel per month. Bycatch rates are significantly higher in gillnet fisheries than in trawl fisheries, and the probability of incidental capture is notably greater during the spring and autumn seasons. Additionally, bycatch intensity exhibits significant spatial heterogeneity, indicating areas where protection efforts should be prioritized. The results of this study underscored the severity of T. tridentatus bycatch in coastal regions and indicate measures to reduce bycatch at the institutional, technical, and operational levels. These recommendations, while focused on T. tridentatus, offer a broader framework for conserving other vulnerable species.