Spatiotemporal distribution and fishing ground driving mechanism of swimming crab Portunus trituberculatus in Hangzhou Bay and its adjacent waters.

The marine ecological environment of Hangzhou Bay and its adjacent waters ( 30°-31° N, 121.5-123.5° E ) shaped by various factors, serves as a spawning and feeding ground for diverse species of fish, shrimp and crabs, including a traditional gillnet fishing area for the gazami crab, Portunus trituberculatus. The study investigates spatiotemporal distribution and the mechanisms underlying the formation of these fishing grounds of P. trituberculatus using single bottom trawl survey data from 31 stations in Hangzhou Bay and its adjacent waters across four seasons in 2014, gillnet survey data during the period 25-29 July 2019 to 2021 and gillnet vessel fishing logs from September 2020 to January 2021. Seasonal variations and spatiotemporal distributions of P. trituberculatus abundance and body mass were analysed. A generalised additive model was applied to assess the influence of external factors identifying key drivers of fishing ground formation. Gillnet monitoring and fishing log data were used to explore inter-annual trends in population characteristics and catch per unit effort (CPUE). The findings revealed pronounced seasonal patterns in P. trituberculatus abundance and distribution, with notable seasonal differences in spatial and temporal dynamics. The primary external factors affecting abundance were season and bottom salinity, followed by latitude and surface chlorophyll a content. Bottom salinity emerged as the critical environmental factor driving the formation of the gillnet fishing grounds. Significant inter-annual differences were observed in P. trituberculatus carapace length (P < 0.05), although no significant differences were found between sexes within the same year. Monthly variation in CPUE 0.49-1.38 kg/net and carapace length 75.6-82.1 mm were also significant (P < 0.05). This study elucidates the spatiotemporal distribution patterns and environmental drivers shaping P. trituberculatus fishing grounds in Hangzhou Bay and its adjacent waters, providing insights for sustainable management and conservation of these fishery resources.