Schultz Mischa, Hoffmayer Eric R, Sulikowski James A, Byrne Michael E
School of Natural Resources, University of Missouri, Columbia, Missouri, United States of America.
Southeast Fisheries Science Center, National Marine Fisheries Service, Pascagoula, Mississippi, United States of America.
PLoS One. 2025 Sep 2;20(9):e0330999. doi: 10.1371/journal.pone.0330999. eCollection 2025.
Severe population declines of shortfin mako sharks (Isurus oxyrinchus) in the Atlantic Ocean have led to the implementation of conservation measures, notably fishing retention bans and live-release regulations, aimed at substantially reducing fishing mortality to allow stock recovery. While retention bans can eliminate harvest mortality, their effectiveness can be reduced if survival of sharks encountered as bycatch and not retained is low. We quantified at-vessel survival (AVS) and post-release survival (PRS) and estimated overall bycatch survival probability of mako sharks for the U.S. Atlantic pelagic longline fishery. Based on fisheries observer records (n = 7821) between 2000-2020, we found AVS varied regionally from 0.77 (95% CI: 0.74-0.80) in the northmost observation region to 0.65 (95% CI: 0.61-0.69) in the Gulf of Mexico (GOM). We found significant negative correlations between AVS and soak time, surface temperature, mainline length, and shark size. Based on pop-up archival satellite tags (n = 27) deployed from pelagic longline vessels in the WNA during 2022-2024, PRS was 0.87 (95% CI: 0.74-0.93). Overall mean bycatch survival probability varied regionally from 0.64 (95% CI: 0.51-0.68) in the northmost observation region to 0.59 (95% CI: 0.49-0.64) in the GOM, which given the low productivity rates of mako sharks may be low enough to hinder recovery efforts if mako sharks are encountered as bycatch in significant numbers. Pairing retention bans with actions that reduce incidence of bycatch would likely provide the greatest benefit to population recovery. Our research highlights the importance of quantifying survival regionally and between fleets, as variability in fishing practices and environmental conditions can result in different bycatch survival outcomes, which can be important considerations in stock assessment.
大西洋短鳍灰鲭鲨（Isurus oxyrinchus）数量严重下降，促使人们实施了保护措施，特别是捕捞留存禁令和放生活体规定，旨在大幅降低捕捞死亡率，以使种群得以恢复。虽然留存禁令可以消除捕捞死亡，但如果作为兼捕物捕获但未留存的鲨鱼存活率较低，其有效性就会降低。我们对美国大西洋远洋延绳钓渔业中灰鲭鲨的船上存活率（AVS）和放归后存活率（PRS）进行了量化，并估计了兼捕鲨鱼的总体存活概率。根据2000年至2020年间渔业观察员记录（n = 7821），我们发现AVS在区域上有所不同，最北部观察区域为0.77（95%置信区间：0.74 - 0.80），墨西哥湾（GOM）为0.65（95%置信区间：0.61 - 0.69）。我们发现AVS与浸泡时间、表层温度、主线长度和鲨鱼大小之间存在显著负相关。根据2022年至2024年期间在西大西洋区（WNA）从远洋延绳钓船上部署的弹出式存档卫星标签（n = 27），PRS为0.87（95%置信区间：0.74 - 0.93）。总体平均兼捕存活概率在区域上有所不同，最北部观察区域为0.64（95%置信区间：0.51 - 0.68），墨西哥湾为0.59（95%置信区间：0.49 - 0.64），鉴于灰鲭鲨的低繁殖率，如果大量灰鲭鲨作为兼捕物被捕获，这个概率可能低到足以阻碍恢复工作。将留存禁令与减少兼捕发生率的行动相结合，可能会给种群恢复带来最大益处。我们的研究强调了在区域和船队之间量化存活率的重要性，因为捕捞方式和环境条件的差异可能导致不同的兼捕存活结果，这在种群评估中是重要的考虑因素。
