Spatiotemporal shifts in American Eel population in a changing Hudson River estuary.

This article investigates spatiotemporal shifts in the American Eel (Anguilla rostrata) population within the Hudson River estuary (HRE) over a 44-year period (1974–2017), focusing on how changing estuarine water quality variables—specifically dissolved oxygen, water temperature, and conductivity—influence the distribution of young-of-year (age 0) and yearling-or-older (age 1+) eels. Using data from the Long River Ichthyoplankton Survey and the Hudson River Biological Monitoring Program, the study found that both age classes’ population centers shifted downstream at average rates of approximately 1.1 km/year (age 0) and 0.41 km/year (age 1+), despite generally higher temperatures and lower dissolved oxygen near the estuary’s mouth. Statistical models indicated that mean dissolved oxygen and water temperature significantly relate to population center locations, with dissolved oxygen explaining more variance, while conductivity had little effect. However, the downstream shifts do not appear to result from eels tracking stable dissolved oxygen or temperature conditions, especially for age 0 individuals, suggesting that other environmental, ecological, or anthropogenic factors—such as freshwater flow, salinity-driven productivity gradients, sex-specific habitat preferences, or pollution remediation—may contribute to these distributional changes. The findings underscore the need for further research incorporating additional biological and environmental variables to better understand and manage this globally distributed and declining species in the context of rapidly changing estuarine ecosystems.