MEPS 228:227-239 (2002)  -  doi:10.3354/meps228227

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: x-distance [D] = 12.3 km, SD = 3.6, n = 2; between sectors: x-D = 4.3 km, SD = 1.3, n = 6; between stations: ×-D = 1.8 km, SD = 0.8, n = 12). Three 12 d enclosure experiments were performed over 40 consecutive days from mid-May through June 1999. Flounder growth (range = 0 to 0.9 mm SL d^-1 enclosure^-1) was dynamic at a regional spatial scale. Generalized additive modeling indicated that growth was most rapid at relatively cool temperatures (<21°C) and low salinities (<24”). However, spatial analysis of partial growth indicated that the relative influences of temperature and salinity changed over time. Salinity effects were strongest during the earliest experiment (May 20 to June 1) when temperatures were cool (<20°C) throughout the estuary. During this period, salinities were conducive for rapid growth throughout the river. From June 4 to 16, salinities remained optimal in the river, but as the system warmed, temperatures conducive for rapid growth contracted into the bay and temperature effects became stronger than salinity effects. Growth was more rapid in the bay, but not as high as that measured during the first experiment in the river where optimal salinities and temperatures overlapped within the estuary. With continued warming and curtailed freshwater runoff, temperatures were sub-optimal throughout the estuary, salinities were conducive for rapid growth only in the upper river, and from June 18 to 30 growth rates were relatively low. Our analysis suggests that habitat suitability for the growth of juvenile fish can be spatially dynamic because multiple regulatory factors vary simultaneously in space and time. Rapid growth occurs at sites and times when optimal conditions for regulatory factors intersect in space, but the spatial coincidence of optimal conditions can be ephemeral.

KEY WORDS: Essential fish habitat · Dynamic habitat · Spatial scale · Winter flounder · Pleuronectes americanus