Predation by striped searobin (Prionotus evolans, Triglidae) on young-of-the-year winter flounder (Pseudopleuronectes americanus, Walbaum): examiningprey size selection and prey choice using field observations and laboratory experiments

Laboratory experiments and field observations in shallow water habitats in the Navesink River/Sandy Hook Bay estuarine system (NSHES), New Jersey, USA , were used to examine the predator-prey relationship between the striped s earobin (Prionotus evolans: Linnaeus) and young-of-the-year (YOY) winter fl ounder (Pseudopleuronectes americanus: Walbaum). Striped sea robins (121-36 7 mm total length [TL]) were present in Sandy Hook Bay but absent from the Navesink River in biweekly gillnet surveys conducted from May through Octob er, 1998. However, juvenile winter flounder were present throughout the est uary during periodic beam trawl surveys. Although mysids and sand shrimp (C rangon septemspinosa, Say: 10-49 mm TL) were the numerically predominant pr ey of searobins, winter flounder (15-57 mm TL) accounted for an average of 17% (+/-3) of prey by weight and were found in the diets of 69% of predator s collected in June. In the laboratory, searobins (212-319 mm TL) presented with a range of winter flounder sizes (30-114 mm TL) selected prey < 70 mm TL (24% of predator TL) and maximum prey size appeared to be constrained b y predator esophageal width. When winter flounder (40-60 mm TL) and sand sh rimp (30-50 mm TL) were offered at different densities to searobins, the pr edators fed opportunistically, consuming the prey in proportions similar to initial relative abundances. Laboratory observations showed that searobins rely on modified pectoral finrays to detect, flush, and occasionally excav ate buried winter flounder. Our field and laboratory observations indicate that striped searobins consume large numbers of winter flounder in vulnerab le size classes (15-70 mm TL) in habitats where the two species co-occur. P atterns in the distribution of the two species in the NSHES suggest that pr edation probably varies spatially in the estuary, with flounder more at ris k in nurseries in Sandy Hook Bay than in the Navesink River, which may serv e as a spatial refuge for winter flounder from searobin predation during so me years. (C) 1999 Elsevier Science B.V. All rights reserved.