ABSTRACT:The relationship between the growth of early juvenile winter flounder (Psuedopleuronectes americanus, Walbaum; 17 to 27 mm standard length [SL]) and the spatial dynamics of estuarine gradients immediately following larval settlement was examined using field enclosure techniques in a temperate nursery. Enclosures (n = 60; 3 fish per enclosure) were deployed throughout the Navesink River/Sandy Hook Bay estuarine system, New Jersey, in a nested spatial design that allowed measurement of growth variation in time at 3 spatial scales (between regions: × -distance [D]

Small individuals <500 mm TL were likely to remain in the estuary longer at warmer temperatures than were large individuals. Size-dependent temperature responses were similar to optimal temperatures for growth reported in previous studies. Freshwater discharge also influenced residence time. All species were likely to remain in the estuary until freshwater discharge rates fell to a value associated with the transition of the estuarine state from a partially to fully mixed state. This transition weakens flows into the upstream salt front where prey concentrations usually are high. Time of estuarine residence appeared to be regulated by temperatures that controlled scopes for growth and the indirect effects of freshwater discharge on prey productivity and concentration. Changes in the seasonal phenology of temperature, precipitation, and human water use could alter the durations over which small estuarine tributaries serve as suitable habitats.