Spatio-temporal shifts in the habitat suitability of Atlantic tomcod in its southernmost extent of distribution

Atlantic tomcod (Microgadus tomcod) is a resilient and genetically unique species capable of surviving in the Hudson River Estuary (HRE) despite historically high levels of contaminants. The HRE represents the southernmost extent of tomcod's range in the northeastern United States, making it a critical habitat for this species. However, rising temperatures and habitat degradation threaten the persistence of tomcod in this region. Understanding habitat suitability for tomcod, particularly in their post-yolk-sac larval (PYSL) and young-of-year (YOY) stages, is essential for conservation and management efforts. The Hudson River Biological Monitoring Program, including the Long River Survey (LRS) and the Water Quality Survey, has provided decades of data on tomcod abundance and environmental conditions. Using the LRS-calibrated dataset, which removes the impacts of changes in sampling protocols over time, we compared different configurations of habitat suitability index (HSI) models through cross-validation to identify the best-performing HSI model for PYSL and YOY tomcod. Using the best-performing HSI model, we examined changes in tomcod habitat suitability across three time periods: past (1985–2000), recent (2001–2017), and projected future (near-term, medium-term, and long-term). This study indicates a spatial contraction and a northward shift in suitable tomcod habitat over time, which is projected to continue under future climate scenarios. These findings provide insights into how projected spatiotemporal species distributions can be incorporated into conservation planning to improve tomcod management in the Hudson River Estuary, and yield transferable approach applicable to other species and aquatic ecosystems facing environmental change.