Partial migration of striped bass: revisiting the contingent hypothesis

Partial migration, by which contingents within populations undertake divergent migrations, is common in marine fishes but remains poorly documented. Intrapopulation groups of fish with similar seasonal migration behaviors were noted early in the fisheries literature and have attracted increased interest for their role in population resilience to environmental change and fishing. Here, we used acoustic telemetry to test historical hypotheses on contingent structure for striped bass Morone saxatilis in the Hudson River, New York (USA), which harbors one of the largest populations of this species. Season and region of release were used as design elements to evaluate 3 principal contingents. In total, 51 implanted striped bass were detected in New York Harbor (NYH), Hudson River, and other estuarine and coastal receiver arrays from June 2010 through December 2011. Multivariate analyses of >500 000 recoveries confirmed predictions of 3 broad contingent behaviors, viz. those that principally utilized (1) the Upper Hudson River Estuary, (2) the NYH and Lower Hudson River Estuary, and (3) coastal waters, but commingled in upper Hudson River spawning habitats during late spring. All contingents occupied NYH, but their transit routes into and out of the harbor varied significantly. Further behavioral diversity was observed within contingents, including size-specific differential migration, multiple natal origins (natal divergence), and non-annual (skipped) spawning. Contingent structure within Hudson River striped bass likely distributes the influences of regional fisheries, pollution, and other en vironmental forces, promoting stability and persistence in the overall population.