6 research outputs found
Dynamics of early juvenile winter flounder predation risk on a North West Atlantic estuarine nursery ground
Relation between the level of self-mutilation and theconcentration of fecal metabolites of glucocorticoids incaptive chimpanzees (Pan troglodytes)
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Shallow water predation risk for a juvenile flatfish (winter flounder; Pseudopleuronectes americanus, Walbaum) in a northwest Atlantic estuary
Many small fish, including several juvenile Atlantic flatfish, are most abundant in shallow areas presumable because these habitats enhance survivorship and/or growth. In this study, we investigated size-dependent depth distributions and the role of shallow habitats as predator refuges for age-0 winter flounder (Pseudopleuronectes americanus) in a northwest Atlantic estuarine nursery. Analysis of trawl surveys performed during the larval settlement period throughout the Navesink River and Sandy Hook Bay, New Jersey, showed that as fish increased in size, depth of occurrence gradually decreased, so that individuals \u3e35 mm standard length (SL) were concentrated in habitats ∼1 m deep. Tethering in structurally simple and adjacent shallow and deep habitats showed that predation risk for flounder (30–50 mm SL) was low in shallow water (\u3c1 m) and increased rapidly with depth. Summer flounder (Paralychthys dentatus), which were more abundant in trammel nets in deep habitats and included winter flounder in their diets, appeared to be important consumers of tethered fish. Our results indicate that following larval settlement, winter flounder emigrate from or suffer high mortality in deeper water to become concentrated in shallow habitats that can serve as predator refuges even when they lack complex physical structures. These results highlight the potential for functional habitat loss when natural and/or anthropogenic factors make shallow habitats unavailable to young fish
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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 \u3c20 mm standard length (SL) were eaten by striped searobin that were common in habitats with salinities ≥ 20‰. Fish \u3e20 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 \u3e19‰ and temperatures \u3e20°C. In 3 yr, salinities were \u3c20‰ 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