Functional dynamics of the world's largest indiscriminate fishery over the last two decades

This is the authors' abstract. We don't add key points for this paper.

Understanding how biological diversity responds to global environmental change is a central question in modern ecology. However, our ability to predict how the functional structure of fish communities responds to human disturbances remains limited. This study investigated the long-term trends in fish community diversity and functional structure in the Tonle Sap Lake system (Mekong Basin, Cambodia), which has the world's largest indiscriminate fishery. Using the longest available fish monitoring dataset from the dai (stationary trawl) fishery (2003–2022), we applied multivariate analysis on relative abundance data to examine temporal changes in both taxonomic (species richness, inverse Simpson index) and functional (fish maximum body length, functional guild, life history strategy) community structure. Our results reveal two key findings: (1) a clear and concerning decline in fish community diversity and change in community composition over the past two decades, and (2) novel evidence of long-term shifts in functional traits, particularly in fish functional guilds and life history strategies. Specifically, the fish community shifted from long-to short-distance migrant species, and from floodplain spawners to generalist guilds and estuarine/marine visitors. Additionally, large-bodied species with equilibrium and periodic strategies have been replaced by smaller-bodied, fast-growing, opportunistic species. These findings suggest a temporal shift from K-selected to r-selected communities. New management strategies, including reducing fishing pressure, are urgently needed to preserve the ecosystem function and ensure the long-term sustainability of Tonle Sap Lake's fishery. • The world's largest indiscriminate fishery, Tonle Sap Lake, suffers from overfishing. • We investigated taxonomic and functional structure driven by overfishing. • Fishing pressure reduced fish diversity and changed community composition. • Fishing pressure could drive a shift from K-selected to r-selected communities. • Management measures to reduce fishing pressure are needed for fishery sustainability.