Feeding habits and dietary overlap of age-0 winter flounder (Pseudopleuronectes americanus) and summer flounder (Paralichthys dentatus) in southern New England tidal rivers


David L. Taylor and Carissa L. Gervasi
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Age-0 winter flounder (Pseudopleuronectes americanus; 20– 90 mm in total length [TL]) and summer flounder (Paralichthys dentatus; 19–172 mm TL) were collected from the Seekonk and Taunton Rivers (in Rhode Island and Massachusetts, respectively) from May through September during 2009–2015, and stomach content analysis was used to assess diet composition and resource overlap for these species. Winter and summer flounder underwent ontogenetic dietary shifts. Winter flounder <40 mm TL predominantly fed on copepods, transitioning to amphipods, isopods, and bivalves with increasing size. Polychaetes also were consumed frequently by winter flounder, irrespective of size. The principal prey of summer flounder <60 mm TL were mysid shrimp and copepods, whereas sand shrimp (Crangon septemspinosa), amphipods, and fish were the dominant prey of larger conspecifics. There was minimal dietary overlap for the flounder species when comparisons were made independent of body size, indicating food niche segregation. For winter and summer flounder of equivalent sizes, however, dietary overlap was inversely related to TL. Moderate to high resource overlap occurred for small winter and summer flounder (<40 mm TL) and was attributed to their mutual reliance on copepods and amphipods. Despite evidence of dietary overlap, it is unlikely that shared prey resources were diminished enough to negatively affect either flounder species.