Spatiotemporal distribution characteristics of Konosirus punctatus spawning grounds in Daya Bay Based on a Two-stage GAM

To analyze the response of marine fish reproduction to environmental changes and understand the early recruitment process of Konosirus punctatus, we investigated its reproductive cycle, identified spawning gravity centers and migration trajectories via center of gravity analysis, and explored the relationship between egg distribution and environmental factors using a Two-stage Generalized Additive Model (GAM). Data were collected from year-round sampling in the spawning and nursery grounds investigation of Daya Bay from May 2022 to April 2023. The results indicate that the reproductive period of K. punctatus in Daya Bay extended from December to the following April, with the peak spawning season occurring from January to March. Significant spatiotemporal variations were observed in egg distribution (p<0.05), with high-abundance areas mainly concentrated in the northwestern and southwestern nearshore waters. The spawning gravity center of K. punctatus in Daya Bay migrated around Jixin Island, Xuzhou, and Yuanzhou, forming a trajectory from the northern Central Islands to the northwestern nearshore waters, then to the southwestern waters, eventually returning to the Central Islands. The spatial heterogeneity results were consistent with the elliptic centroid analysis, showing a decreasing abundance trend from the northwest to the southeast. The two-stage GAM reveals that month, longitude, latitude, and zooplankton abundance were the main factors influencing the probability of egg occurrence (p<0.05). Month, zooplankton abundance, longitude, latitude, sea surface temperature (SST), sea surface salinity (SSS), and offshore distance significantly affect abundance distribution of K. punctatus eggs. Zooplankton abundance exhibited a significant positive linear effect on egg distribution. The SST and SSS of the high-abundance areas ranged from 18°C to 24°C and 32.5‰ to 34.0‰, respectively. The findings provide an important scientific basis and support for the investigation and protection of K. punctatus spawning grounds in Daya Bay, as well as for the refined management of the Daya Bay sea area.