An Interdisciplinary Assessment of Winter Flounder Stock Structure

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Stock structure and management of winter flounder (Pseudopleuronectes americanus) was evaluated throughout its geographic range in the northwest Atlantic. Information on genetics, morphology, meristics, larval dispersal, life history traits, applied mark experiments and environmental signals was reviewed. Winter flounder in U.S. waters are currently managed as three separate units; Georges Bank, Gulf of Maine and Southern New England/Mid-Atlantic. Estuarine spawning, which likely plays an important role in reproductive isolation and population structure, appears to be obligate in southern New England, non-existent on Georges Bank and variable in the Gulf of Maine. Despite evidence for reproductively isolated estuarine groups, information from tagging, meristic analysis, and life history studies suggest extensive mixing, thereby supporting the current U.S. management regimen. In Canadian waters, winter flounder are managed as three units: western Scotian Shelf (NAFO Div. 4X), eastern Scotian Shelf (NAFO Div. 4VW), and the southern Gulf of St. Lawrence (NAFO Div. 4T). Genetic analysis and parasite markers indicate that these Canadian management units are distinct. However, examination of inshore and offshore winter flounder within division 4X suggests little interchange occurs between these groups. Several separate stocks probably exist within the 4T management area as well. Stock assessment and fishery management would likely benefit from stock composition analysis of mixed-stock fisheries of both U.S. and Canadian fishery resources.