Climate change and fishing are pulling the functional diversity of the world's largest marine fisheries to opposite extremes.

Aim: Marine biodiversity is increasingly threatened by overfishing and climate change, but it is still unclear how these drivers have shaped the functional diversity (FD) of marine fish. Here, we explore how the FD of commercial marine fish communities responds to climate change and fishing pressure. Major taxa studied: Marine fish. Location: China Seas. Time period: 1989–2018. Methods: We used a catch database of four individual species and 12 species groups that were reported continuously in China from 1989 to 2018. Seven traits were selected to calculate FD. We adopted generalized linear mixed models to analyse the complex relationship among climate change, fishing pressure and several metrics of marine fish FD. We identified the percentage change in diversity for communities to assess the relative contribution of each species or species group by removing individual species or a species group from the dataset. Results: Climate change and fishing pressure exerted statistically significant opposing effects on the functional evenness (FEve) and functional divergence (FDiv) of commercial fish communities. Increasing sea surface temperature had a significant positive effect on FEve but a negative effect on FDiv. In contrast, increasing fishing pressure had the opposite effects on FEve and FDiv. These results were driven by the significantly varying relative contributions of fish species or species groups to the functional space, whereby low‐trophic‐level pelagic fish species or species groups are closer to the boundaries of the functional trait space than high‐trophic‐level demersal fish species or species groups. Main conclusions: The FD of commercial marine fish communities responds significantly to climate warming and increasing fishing pressure, with opposite effects driven by different response patterns of fish species or species groups. Our results suggest that management actions should address the two issues simultaneously, because considering only one will unleash greater functional changes in the other. [ABSTRACT FROM AUTHOR]