Harvesting that Preserves Large Fish Might Help Mitigate the Worst Impacts of Warming

ABSTRACT Fishing and oceanic warming significantly impact fish populations worldwide. Understanding their interactive effects is crucial for managing harvested populations. Here, we first review current knowledge of harvest and warming interactions, focusing on experimental applications that provide unique insights into short‐ and long‐term effects difficult to study in wild populations. We then present findings from a multi‐generational experiment exposing 18 zebrafish populations to combined harvest and warming selection. Treatments included three types of size‐selective fishing (~80% mortality) and two temperatures (26°C ‘control’ and 30°C ‘warmed’). Warmed populations exhibited expected temperature‐size‐rule responses: juveniles grew 18% faster and matured earlier, while adults were 3%–5% shorter and ~10% lighter. Gaussian selectivity (removing medium‐sized fish) led to adults that were 5% longer and 18% heavier, while sigmoidal selectivity (removing large fish) resulted in 4% shorter and 15% lighter adults. Fishing and warming had increasingly interactive impacts on body sizes across generations. At the end of the treatment generations, warming combined with sigmoidal selectivity produced the smallest fish (6% shorter, 20% lighter), while Gaussian selectivity compensated for warming‐induced size declines. Juvenile body size changes were mostly reversible but warming and fishing induced an evolved change in adult body size. Warming caused a 15% reduction in maximum yield‐per‐recruit, while Gaussian selectivity increased maximum yield by 20%, and sigmoidal selectivity reduced it by 11%. Our work demonstrates both synergistic and antagonistic impacts of fishing and warming on fish sizes and yields, and suggests that warming effects can be partially mitigated by fishing practices that protect large individuals.