Diversity and variations of the catches from gillnet fisheries in two large rivers in Thailand: insight from long-term monitoring data

Fish diversity and functional diversity of the catches from gillnet fisheries of the Chao Phraya River (CPR) and the Bang Pakong River (BPR) in the central of Thailand were analyzed, using the monitoring data from 2010 to 2023 and 2007 to 2023, respectively. The study focuses on the inter-annual assessment of fish community dynamics at the whole-river scale, which aims to provide essential insights for the sustainable management of both rivers. Long- and short-term variations as well as the stress of fish assemblages were also assessed. A total of 93,998 individual fish were recorded from 121 species in the CPR, and 108 species in the BPR, in which the species from family Cyprinidae were most diverse in both rivers. Both rivers exhibited substantial species diversity and functional trait diversity, with the CPR generally supporting higher abundance and diversity indices than the BPR. The long-term variation indicated that most species were stable in the catches. Meanwhile short-term variations were influent by fishing pressure year by year. Abundance-biomass comparisons revealed that the fish assemblages in both rivers were minimal disturbance, except for occasional specific years, suggesting localized or temporal stress events. Overall, results indicate that fish assemblages in both the CPR and BPR remain largely intact, with functional diversity contributing to ecosystem resilience despite high fishing pressure and other ongoing anthropogenic influences.