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To investigate the spatial-temporal distribution characteristics of Harpadon nehereus in the Yangtze River Estuary (YRE) and its relationship with environmental factors, this study used the data from resource and environmental surveys conducted in the YRE and adjacent waters during August (summer) and November (autumn), 2017-2022. Generalized additive models (GAM) were employed to analyze the relationships between the relative resources of H. nehereus and environmental factors and to predict the spatial-temporal distribution of H. nehereus resources in 2022. Our results revealed that the best model deviance explained in summer and autumn was 64.89% and 49.90%, with average effect sizes of 0.75 and 0.70, respectively, for cross-validated regression slopes. Water temperature and salinity were identified as the key environmental factors influencing the relative resources of H. nehereus in the YRE. Overall, there were notable seasonal differences in the relationship between the relative resources of H. nehereus and environmental factors. The relative resources of H. nehereus in the YRE were higher in the summer than in autumn. In summer, both water temperature and salinity exhibited multi-wave nonlinear relationships with the relative resources of H. nehereus, while in autumn, the relative resources of H. nehereus showed a positive linear relationship with water temperature and a nonlinear relationship with salinity. Additionally, the predicted and observed values of the relative resources of H. nehereus in 2022 showed similar spatial distribution patterns. The relative resources of H. nehereus was higher in the northern branch than in the southern branch and the offshore regions compared to the near-estuary regions. Altogether, our study provides a scientific basis for conservation management and sustainable utilization of H. nehereus resources in the YRE, thereby contributing to the restoration and management of fishery resources in the region. [ABSTRACT FROM AUTHOR]

Coastal waters provide an important spawning and nursery ground for offshore marine organisms. To understand the suitable habitat and distribution of Harpadon nehereus, a key nearshore species, this study assessed the survey data of fishery resources and environment in Zhejiang’s nearshore fishery in Spring of 2017 to 2020. We used the generalized additive model (GAM) and random forests model (RF) to analyze the environmental factors affecting the selection of spawning habitats by H. nehereus and analyzed the suitable habitat characteristics of H. nehereus in nearshore fisheries. Our results indicate that H. nehereus is widely distributed in Zhejiang’s nearshore and that its density is higher in waters near islands and reefs. Among the relative importance scores of predictors calculated based on RF, seawater salinity is an important environmental factor affecting the distribution of H. nehereus in April (surface seawater salinity was 38.67% and bottom seawater salinity was 34.5%), followed by depth (34.19%), whereas the change in water temperature had no obvious effect on H. nehereus distribution. The suitable habitat characteristics of H. nehereus mainly include high salinity near a water depth of 40 m and a water area with sea bottom dissolved oxygen levels < 6 mg/L. The prediction results of the model indicate that the suitable habitat of H. nehereus is mainly located in the region near Zhoushan Islands in the north of the fishing grounds. Overall, these results may serve as a basis for determining the protection strategies of key nearshore species and enhancing fishery management units.