Dynamics of fish populations and communities within the Tonle Sap flood pulse system

Abstract The Tonle Sap Lake (TSL) is the most fish‐diverse lake in Southeast Asia and ranks among the world's richest inland fisheries. Although previous studies have described broad changes in fish abundance and community composition across the lake's annual flood pulse, the spatiotemporal dynamics of individual species and their co‐occurrence patterns remain poorly understood. Fish have traditionally been grouped into three migratory guilds: (1) resident species, (2) lateral migrants (short‐distance movers between lake and floodplain), and (3) longitudinal migrants (long‐distance movers in and out of the lake). If this classification holds, species within the same guild should exhibit similar population dynamics. To test this, we analyzed weekly fish catch data from 2012 to 2015 across five sites, focusing on 71 common species. Using population synchrony analysis and probabilistic models, we found pronounced seasonal variations in both species abundance and occurrence, especially among long‐distance migrators, which increased during high‐ and receding‐water periods. Resident and short‐distance migrators also showed seasonal changes, leading to seasonal shifts in community composition. However, these temporal patterns varied across locations, likely due to differences in environmental conditions and habitat availability. This spatial variation led to low synchrony in population dynamics across sites, though some species showed heightened synchrony during particular hydrological periods. Within sites, species belonging to the same migratory guild, especially resident species, tended to be more synchronized during high‐ and rising‐water periods, suggesting shared responses to local abiotic drivers. Co‐occurrence analyses further revealed periodic shifts in species associations, with more positive associations during high‐ and receding‐water stages. Collectively, these results demonstrate strong seasonal restructuring of fish populations and communities in TSL, but inconsistent spatial patterns. Our findings indicate that guild‐based classifications only partially capture the dynamics of TSL fish assemblages and that effective fishery management should incorporate additional ecological and habitat‐specific factors.