Shallow water predation risk for a juvenile flatfish (winter flounder; Pseudopleuronectes americanus, Walbaum) in a northwest Atlantic estuary John P. Manderson a, * , Jeffrey Pessutti a , John G. Hilbert a , Francis Juanes b a James J. Howard Marine Sciences Laboratory, Behavioral Ecology Branch, Department of Commerce, NOAA/National Marine Fisheries Service, Highlands, NJ 07732, USA b Department of Natural Resources Conservation, University of Massachusetts, Amherst, MA 01003-9285, USA Received 8 April 2003; received in revised form 3 May 2003; accepted 15 December 2003 Abstract 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 >35 mm standard length (SL) were concentrated in habitats f1m 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 ( < 1 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. Published by Elsevier B.V. Keywords: Predation refuge; Nursery habitat quality; Tethering; Juvenile fish mortality 0022-0981/$ - see front matter. Published by Elsevier B.V. doi:10.1016/j.jembe.2003.12.004 * Corresponding author. Tel.: +1-732-872-3057; fax: +1-732-872-3088. E-mail address: john.manderson@noaa.gov (J.P. Manderson). www.elsevier.com/locate/jembe Journal of Experimental Marine Biology and Ecology 304 (2004) 137 – 157