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的影响，是实现渔业可持续管理的关键环节。尽管既往研究已揭示开发利用中的鱼类种群存在年龄或体型截短现象，但捕捞对种群统计学特征的其他影响——例如通过改变种群生活史与种群密度——却较少受到关注。本研究以标志性过度捕捞物种——太平洋蓝鳍金枪鱼（Pacific bluefin tuna, *Thunnus orientalis*）为研究对象，探讨捕捞通过改变繁殖权衡关系进而影响成体种群统计学特征的效应。研究结果与预期相悖：延绳钓渔业的捕捞个体平均体长随时间推移呈上升趋势，而围网渔业的捕捞个体平均体长则未呈现此类上升趋势。我们提出假说：成体金枪鱼产卵洄游的体型依赖能耗，以及产卵场升高的捕捞死亡率，可能会驱动体型依赖型的弃产行为，进而介导观测到的捕捞个体体长变化。本研究利用基于个体的生态遗传模型，证实捕捞诱导的弃产行为演化与体型截短效应相互作用，共同塑造了金枪鱼捕捞个体平均体长的时间变化模式。小型成体的弃产行为使得延绳钓渔业的捕捞个体平均体长上升，而围网渔业对小型成体的捕捞截短则可抵消这一变化趋势。本研究结果凸显了捕捞对种群统计学特征影响的生态演化动态，并警示：在太平洋蓝鳍金枪鱼及其他洄游性物种的渔业管理中，不应仅以种群统计学特征作为管理依据。