Data from: Fishing-induced changes in adult length are mediated by skipped-spawning

Elucidating fishing effects on fish population dynamics is a critical step toward sustainable fisheries management. Despite previous studies that have suggested age or size truncation in exploited fish populations, other aspects of fishing effects on population demography, e.g., via altering life histories and density, have received less attention. Here, we investigated the fishing effects altering adult demography via shifting reproductive trade-offs in the iconic, overexploited, Pacific bluefin tuna Thunnus orientalis. We found that, contrary to our expectation, mean lengths of catch increased over time in longline fisheries. On the other hand, mean catch lengths for purse seine fisheries did not show such increasing trends. We hypothesized that the size-dependent energetic cost of the spawning migration and elevated fishing mortality on the spawning grounds potentially drive size-dependent skipped spawning for adult tuna, mediating the observed changes in the catch lengths. Using eco-genetic individual-based modeling, we demonstrated that fishing-induced evolution of skipped spawning and size truncation interacted to shape the observed temporal changes in mean catch lengths for tuna. Skipped spawning of the small adults led to increased mean catch lengths for the longline fisheries, while truncation of small adults by the purse seines could offset such a pattern. Our results highlight the eco-evolutionary dynamics of fishing effects on population demography and caution against using demographic traits as a basis for fisheries management of the Pacific bluefin tuna as well as other migratory species.

阐明捕捞对鱼类种群动态（population dynamics）的影响，是实现渔业可持续管理（sustainable fisheries management）的关键环节。尽管此前已有研究指出受捕捞压力的鱼类种群存在年龄截短（age truncation）或体型截短（size truncation）现象，但捕捞对种群统计学（population demography）特征的其他影响维度——例如通过改变生活史（life histories）策略与种群密度——却较少受到关注。本研究以兼具标志性与过度捕捞现状的太平洋蓝鳍金枪鱼（Thunnus orientalis）为研究对象，探讨了捕捞通过改变繁殖权衡（reproductive trade-offs）进而影响成体种群统计学特征的效应。研究结果显示，与预期相悖，延绳钓渔业（longline fisheries）的渔获平均体长随时间推移呈上升趋势；与之相对，围网渔业（purse seine fisheries）的渔获平均体长并未呈现此类上升趋势。我们提出假说：成体金枪鱼产卵洄游（spawning migration）的体型依赖型能量成本，以及产卵场（spawning grounds）的捕捞死亡率升高，可能共同驱动了体型依赖型的跳过产卵（skipped spawning）行为，进而介导了观测到的渔获体长变化。本研究采用基于个体的生态遗传模型（eco-genetic individual-based modeling），证实了跳过产卵行为与体型截短的捕捞诱导进化（fishing-induced evolution）二者相互作用，共同塑造了金枪鱼渔获平均体长的观测时间序列变化。小型成体的跳过产卵行为提升了延绳钓渔业的渔获平均体长，而围网捕捞对小型成体的截杀则可抵消这一趋势。本研究结果凸显了捕捞对种群统计学特征的生态进化动态（eco-evolutionary dynamics）效应，并警示：在太平洋蓝鳍金枪鱼乃至其他洄游性物种的渔业管理中，不应单纯以种群统计学特征作为管理依据。