Spatiotemporal dynamics of spawning habitat distribution of American shad (Alosa sapidissima) in the Hudson River Estuary under multi stressors

Diadromous fishes, known for their extensive migrations between freshwater and marine ecosystems, are highly vulnerable to environmental fluctuations and human activities, making them prone to population declines. Despite awareness of climate change impacts and habitat limitations, the remaining spawning habitat’s biogeography is understudied. The present study focuses on the Hudson River Estuary (HRE) American shad (Alosa sapidissima) population which is experiencing historically low stock levels, as a case study to investigate the spatiotemporal distribution of its existing spawning habitat. Generalized additive models were used to investigate the effect of some environmental (e.g., temperature, river bottom type) and sampling variables (e.g., sampling location and time) on the spatial distribution of the American shad. Our results provide compelling evidence of an optimal spawning habitat for the American shad, suggesting that environmental factors may not be the primary drivers shaping the distribution of their spawning grounds. The significant relationships between the distribution of spawning habitat and spawning stock biomass indicates that factors beyond the HRE are likely to play the most significant roles in the shad population.