Diet of winter flounder in a New Jersey estuary: Ontogenetic change and spatial variation

Juvenile and adult winter flounder, Pseudopleuronectes americanus Walbaum ( Pleuronectidae), from the Navesink River and Sandy Hook Bay, New Jersey, U. S., were examined for ontogenetic, seasonal, and spatial variation in dieta ry content. Fish (n = 1291 non-empty) were placed by cluster analysis of di etary content into three size groups: 15-49, 50-299, and greater than or eq ual to 300 mm total length. Clear ontogenetic patterns were revealed, in pa rticular the disappearance of calanoid copepods from the diet as fish grew >50 mm and an increase in number of taxa in the diet with growth. Fish in s ize group 1 fed upon spionid polychaetes, the calanoid copepod Eurytemora a ffinis, and ampeliscid amphipods. Fish in size group 2 added various specie s of polychaetes, amphipods, and siphons of the bivalve Mya arenaria to the ir diets. Size group 2 was present during all months of the survey, but onl y minor seasonal differences in their diet were apparent. One obvious chang e was the increase in consumption of the shrimp Crangon septemspinosa in su mmer and fall. Size group 3 fish, collected mainly in fall, ate large volum es of M. arenaria and glycerid polychaetes. Cluster analysis showed a large -scale spatial pattern in diet among fish of size group 1, related to the p resence of E. affinis in winter flounder diets in the river and a marsh cov e in the bay. Small-scale spatial differences in diets of fish in size grou p 2 were possibly related to prey distribution.