DTU Aqua, National Institute for Aquatic Resources, Technical University of Denmark, Kemitorvet 1, 2800 Kongens Lyngby, Denmark.
SLU, Department of Aquatic Resources, Swedish University of Agricultural Sciences, Lysekill 45330, Sweden.
Proc Biol Sci. 2023 Jul 12;290(2002):20222570. doi: 10.1098/rspb.2022.2570.
Incidental captures (bycatch) remain a key global conservation threat for cetaceans. Bycatch of harbour porpoise in set gillnets is routinely monitored in European Union fisheries, but generally relies on data collected at low spatio-temporal resolution or over short periods. In Denmark, a long-term monitoring programme started in 2010 using electronic monitoring to collect data on porpoise bycatch and gillnet fishing effort at a fine spatial and temporal scale, including time and position of each fishing operation, together with every associated bycatch event. We used these observations to model bycatch rates, given the operational and ecological characteristics of each haul observed in Danish waters. Data on fishing effort from the Danish and Swedish gillnet fleets were collected to predict fleet-wide porpoise bycatch in gillnets at regional level. Between 2010 and 2020, yearly total bycatch averaged 2088 animals (95% Cl: 667-6798). For the Western Baltic assessment unit, bycatch levels were above sustainability thresholds. These results demonstrate that fishing characteristics are key determinants of porpoise bycatch and that classical approaches ignoring these features would produce biased estimates. It emphasizes the need for efficient and informative monitoring methods to understand possible conservation impacts of marine mammal bycatch and to implement tailored mitigation techniques.
偶然捕获（副渔获物）仍然是全球保护鲸目动物的主要威胁。在欧盟渔业中， routinely 监测港口鼠海豚在定置刺网中的副渔获物，但通常依赖于在低时空分辨率或短时间内收集的数据。在丹麦，自 2010 年以来，一项长期监测计划开始使用电子监测来收集有关海豚副渔获物和刺网捕鱼努力的精细时空尺度数据，包括每次捕捞作业的时间和位置，以及每次相关的副渔获物事件。我们使用这些观测值来建模副渔获率，给定在丹麦水域观察到的每个拖网的操作和生态特征。从丹麦和瑞典刺网船队收集了关于捕捞努力的数据，以预测区域范围内刺网中船队范围的海豚副渔获物。2010 年至 2020 年间，每年的总副渔获物平均为 2088 只（95%Cl：667-6798）。对于西部波罗的海评估单元，副渔获物水平高于可持续性阈值。这些结果表明，捕捞特征是海豚副渔获物的关键决定因素，而忽略这些特征的传统方法将产生有偏差的估计。它强调了需要有效的和信息丰富的监测方法来了解海洋哺乳动物副渔获物对保护可能产生的影响，并实施有针对性的缓解技术。
