Early-life density-dependent mortality in the Gulf of Thailand

Density-dependent mortality is a key mechanism regulating fish population dynamics, yet empirical evidence from tropical systems remains limited. This study investigated density-dependent survival during early life stages of 25 dominant taxa from trawl landings in the Gulf of Thailand, a productive tropical system dominated by multispecies and multi-gear fisheries, where trash fish (TF) catches from trawlers comprise proportions of juveniles. Temporal variation in the abundance of fish at ages smaller than L25 was linked to subsequent survival patterns to evaluate compensatory dynamics. Growth parameters revealed wide interspecific variation in life-history strategies, ranging from fast-growing (Encrasicholina spp.) to a slower-growing demersal group (Sciaenidae). Most taxa exhibited a negative density- survival relationship, with 11 taxa (including Rastrelliger kanagurta, Atule mate, and Lutjanus lutjanus) showing strong and significant compensatory density dependence (p < 0.001), indicating elevated mortality at higher juvenile densities. Evidence for depensatory dynamics was weak and statistically unsupported. These results provide empirical biological evidence that compensatory density-dependent mortality commonly operates during early life stages in tropical multispecies and multi-gear fisheries. The findings suggest that juvenile removal via TF catches does not uniformly translate into reduced long-term productivity, highlighting the importance of incorporating early-life density dependence into stock assessment and management frameworks.