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

Abstract

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 searobin (Prionotus evolans: Linnaeus) and young-of-the-year (YOY) winter flounder (Pseudopleuronectes americanus: Walbaum). Striped sea robins (121–367 mm total length [TL]) were present in Sandy Hook Bay but absent from the Navesink River in biweekly gillnet surveys conducted from May through October, 1998. However, juvenile winter flounder were present throughout the estuary during periodic beam trawl surveys. Although mysids and sand shrimp (Crangon septemspinosa, Say: 10–49 mm TL) were the numerically predominant prey 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 predators 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 by predator esophageal width. When winter flounder (40–60 mm TL) and sand shrimp (30–50 mm TL) were offered at different densities to searobins, the predators 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 excavate buried winter flounder. Our field and laboratory observations indicate that striped searobins consume large numbers of winter flounder in vulnerable size classes (15–70 mm TL) in habitats where the two species co-occur. Patterns in the distribution of the two species in the NSHES suggest that predation probably varies spatially in the estuary, with flounder more at risk in nurseries in Sandy Hook Bay than in the Navesink River, which may serve as a spatial refuge for winter flounder from searobin predation during some years.