212 J
.P. Manderson et al. J. Exp. Mar. Biol. Ecol. 242 1999 211 –231
refuge for winter flounder from searobin predation during some years.
1999 Elsevier Science B.V. All rights reserved.
Keywords : Predator–prey; Prey choice; Size selection; Trigilid; Flatfish predator
1. Introduction
Predation risk is a critical factor determining the suitability of nursery habitats, including those used by commercially important flatfish Gibson, 1994. Following
settlement, flatfish face a suite of invertebrate, fish and bird predators that typically narrows in composition as the prey grow. While newly settled flatfish suffer high
mortality from crustacean predators Pihl and van der Veer, 1992; Seikai et al., 1993; Witting and Able, 1995, later stage juveniles are primarily preyed upon by piscivorous
fishes Ansell and Gibson, 1993; Ellis and Gibson, 1995, 1997; Gibson and Robb, 1996; Bax, 1998. Variations in the identity and capability of piscivorous fish in flatfish
nurseries, along with changes in the relative size of predators and prey, are likely to result in important temporal and spatial variations in predation intensity. While
relationships between predatory fish and European flatfish have been studied Gibson and Robb, 1996; Bax, 1998, there have been no systematic studies of the potential
impacts of piscivorous fish in northwest Atlantic flatfish nurseries.
The striped sea robin Prionotus evolans is common on soft-bottom continental shelf and estuarine habitats in the Mid-Atlantic Bight and co-occurs with a number of flatfish
including the commercially important winter flounder Pseudopleuronectes americanus McBride and Able, 1994; Rountree and Able, 1997; McBride et al., 1998. Although
young-of-the-year YOY winter flounder and other flatfishes have been reported in the searobin’s diet Marshall, 1946; Richards et al., 1979, the interaction between the two
species has not been studied. Small flatfish are known dietary components for a number of other triglid species searobins and gurnards Richards et al., 1979; Meyer and
Smale, 1991; Ellis and Gibson, 1995. Triglids are opportunistic predators that use modified anterior pectoral fin rays equipped with tactile and chemosensory receptors to
search soft substrata for epibenthic prey, particularly crustaceans Bardach and Case, 1965; Silver and Finger, 1984; Ross, 1977. The ability of triglids to use finrays to
search for and flush prey could make them particularly effective predators of juvenile flatfishes, which use soft sediment as refuge and burial as an escape response Gibson
and Robb, 1992; Minami et al., 1994.
In this study we report on the dietary patterns of striped searobins collected in shallow-water habitats in a mid-Atlantic estuarine system. We also present results of
laboratory experiments testing the following null hypotheses: •
1 H : Prey size selectivity of striped searobins for juvenile winter flounder prey is similar in the presence and absence of fine sand subtratum.
• 2 H : Searobins consume equivalent numbers of winter flounder and sand shrimp
Crangon septemspinosa during both daytime and nighttime experiments.
J .P. Manderson et al. J. Exp. Mar. Biol. Ecol. 242 1999 211 –231
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• 3 H : The proportions of winter flounder and sand shrimp consumed by searobins
are not different from the proportions of the two prey at the start of experiments. Finally, we report on video observations of the search and attack strategies of
searobins feeding on juvenile winter flounder.
2. Materials and methods
