An Interdisciplinary Assessment of Winter Flounder(Pseudopleuronectes americanus) Stock Structure

An interdisciplinary review was undertaken to evaluate the stock structure and management of winter flounder (Pseudopleuronectes americanus) throughout its geographic range in the northwest Atlantic. Information on morphology, tagging studies, genetics, larval dispersal, life history traits, environmental signals and meristics was considered. In the coastal waters of the United States, winter flounder are managed as three stock units; Georges Bank, Gulf of Maine and Southern New England/Mid-Atlantic. In Canadian waters, winter flounder are managed as three stock units: western Scotian Shelf (NAFO Div. 4X), eastern Scotian Shelf (NAFO Div. 4VW), and the southern Gulf of St. Lawrence (NAFO Div. 4T). Estuarine spawning, which likely plays an important role in reproductive isolation and population structure, is non-existent on Georges Bank and Browns Bank, variable in more northern habitats and may be obligate in southern New England. Contingent groups are likely present in several regions, and merit further research. Despite evidence for local population structure, information from tagging, meristic analysis, and life history studies suggest extensive mixing within stock units, thereby supporting the current U.S. management units. Genetic analysis and parasite markers indicate that Canadian management units are distinct. However, examination of inshore and offshore winter flounder within Division 4X suggests little interchange occurs between these groups. Based on their distribution and life history traits, several flounder stocks likely exist within the Div. 4T management area. A stock composition analysis of mixed-stock fisheries would be useful to facilitate the management and assessment of winter flounder in both U.S. and Canadian waters.