Spawning Site Selection By Winter Flounder in the Gulf of Maine: Implications for Connectivity and Recruitment

Winter flounder (Pseudopleuronectes americanus) in the Gulf of Maine were historically considered to be obligate estuarine spawners.  Spawning in estuaries was thought to promote larval retention and local population structure.  However, using acoustic telemetry we observed two sympatric contingents of winter flounder, which exhibited divergent spawning migrations.  One contingent spawned in coastal waters, while a smaller contingent of winter flounder was observed migrating to estuarine habitats to spawn.  Individual-based modeling explored how spawning site choice by adult winter flounder affects larval dispersal and rates of connectivity between habitats.  Spawning was simulated at three coastal spawning grounds in the Gulf of Maine (Ipswich Bay, Jeffreys Ledge, and Stellwagen Bank) from 2005 to 2009, to infer transport success of larvae and rates of connectivity between spawning sites and settlement areas.  Despite interannual variability, results suggest that certain coastal spawning sites likely serve as an important source of larvae to estuarine nursery grounds.  Such connectivity can influence the resilience and dynamics of local estuarine populations, and help sustain these populations.  Results also suggest that coastal spawning behavior enhances gene flow within the Gulf of Maine, which may preclude genetic differentiation from occurring between proximate estuarine populations of winter flounder.