Dynamics of early juvenile winter flounder predation risk on a North West Atlantic estuarine nursery ground

In an effort to determine the characteristics of estuarine habitats suitable for early juvenile winter flounder Pseudopleuronectes americanus survivorship, we examined piscivorous fish distributions and diets, and flounder predation risk along estuarine gradients in the Navesink River/Sandy Hook Bay estuarine system, New Jersey, USA. Demersal fish, striped searobin Prionotus evolans and summer flounder Paralichthys dentatus, were more important predators of winter flounder than pelagic fish (Pomatomus saltatrix, Cynoscion regalis, Morone saxatilis) based on diet analysis of 4 yr of gill (1998 and 1999) and trammel net (2001 and 2002) fish collections. From April through June newly settled winter flounder <20 mm standard length (SL) were eaten by striped searobin that were common in habitats with salinities ≥ 20‰. Fish >20 mm standard length (SL) were consumed by summer flounder in shallow habitats in June and July. In May and June tethering experiments, Age-0 winter flounder predation risk was high in habitats with salinities >19‰ and temperatures >20°C. In 3 yr, salinities were <20‰ in the upstream reach of estuary which probably served as a predator refuge for settling flounder. During 2002, however, historically low freshwater discharge associated with a spring drought produced high salinities ≥20‰ in upstream habitats where searobins ate large numbers of settling winter flounder and predation risk was high. These results suggest that the volume of estuarine habitat suitable for early juvenile flounder survivorship is determined, in part, by predator and prey responses to spatially dynamic physico-chemical gradients. Because gradient dynamics are controlled by climate forcing, climate variation may cause nursery habitat volumes to contract or expand resulting in variation in the local production of Age-0 recruits.
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