Predator-prey relations between age-1 + summer flounder (Paralichthys dentatus, Linnaeus) and age-0 winter flounder (Pseudopleuronectes americanus, Walbaum): predator diets, prey selection, and effects of sediments and macrophytes

Laboratory experiments and weekly trammel net surveys in the Navesink River , New Jersey (USA) were used to examine the predator-prey interaction betwe en age-1 + summer flounder (Paralichthys dentatus) and age-0 winter flounde r (Pseudopleuronectes americanus). Winter flounder (24-67 mm TL) were the d ominant piscine prey of summer flounder (n = 95, 252-648 mm TL) collected i n trammel nets. We observed a temporal shift in summer flounder diets from sand shrimp (Crangon septemspinosa) and winter flounder, dominant during Ju ne and early July, to blue crabs (Callinectes sapidus) and other fishes (pr imarily Atlantic silversides, Menidia menidia and Atlantic menhaden, Brevor tia tyrannus) later in the summer. Variations in prey selection appeared to be related to changes in the spatial distribution of predators and spatiot emporal variation in prey availability. In laboratory experiments, summer f lounder (271-345 mm total length, TL) preferred demersal winter flounder to a pelagic fish (Atlantic silversides) and a benthic invertebrate (sand shr imp) prey, and the vulnerability of winter flounder increased with increasi ng prey body size from 20 to 90 mm TL. Experiments testing habitat effects showed that mortality of winter flounder in three different size classes (2 0-29, 40-49, 60-69 mm TL) was not influenced by sediment grain sizes permit ting differential burial of the prey. However, vegetation enhanced survival , with fish suffering lower mortality in eelgrass (Zostera marina, 15+/-0.0 4%) than in sea lettuce (Ulva lactuca, 38+/-0.04%) or bare sand (70+/-0.07% ) when the macrophytes were planted to produce similar leaf surface areas ( 5000 cm(2) m(-2)). Prey vulnerability appeared to be related to the role of vision in the predator's attack strategy and prey activity levels. (C) 200 0 Elsevier Science B.V. All rights reserved.