Stock composition and movement patterns of striped bass in the Saco River Estuary, Maine, USA, using acoustic telemetry

Diversity in fish migration across space and time can buffer populations against environmental variability and promote long-term resilience. Considerable effort has been focused on understanding anadromous mixed-stock populations of striped bass on the east coast of the United States; yet a key knowledge gap remains in identifying which spawning populations contribute to northern habitats during seasonal migrations. Here, we used acoustic telemetry and network analyses to investigate the migratory behavior of striped bass utilizing northern habitats. We compared fine-scale movements and broad coastal migrations of striped bass populations present within Southern Maine, USA. Our specific goals were to identify spawning populations present in Southern Maine, characterize estuarine habitat use, and compare migratory patterns among populations. Results revealed a mixed-stock assemblage in the Saco River Estuary composed primarily of Hudson River, New York, USA (42.3 - 59.6%) and Delaware Bay, Delaware and New Jersey, USA (5.7 - 32.6%) origin fish, with fewer fish from the Chesapeake Bay population, Maryland, USA (1.9 - 3.8%), and 3.8% of individuals whose spawning population origin could not be confidently estimated. Fine-scale habitat use varied among individuals and size classes and shifted seasonally, with fish exhibiting both long- and short-term residency. Despite overlapping seasonal residency within the estuary, network analyses indicated that Hudson River and Delaware Bay striped bass largely maintained distinct migratory pathways (8-20% network similarity) and habitat connections, converging within shared northern foraging habitats. These findings demonstrate that Maine provides important seasonal habitat for multiple Atlantic coast spawning populations and highlight population-specific differences in movement, habitat connectivity, and site fidelity.