Fish-Nursery Use in Georgia Salt-Marsh Estuaries: The Influence of Springtime Freshwater Conditions

Abstract

The fish assemblage using shallow nursery habitats in the Ogeechee River-Ossabaw Sound salt-marsh estuary, Georgia, was investigated during the winter and spring of two successive years. High river discharges during these periods produced fully freshwater conditions (all tidal stages and amplitudes) in the upper portion of the study area for up to 4 months. Abundances of Atlantic croaker Micropogonias undulatus, southern flounder Paralichthys lethostigma, silver perch Bairdiella chrysoura, and hogchoker Trinectes maculatus recruits were highest in the upper estuary. Spots Leiostomus xanthurus were more evenly distributed, but continued to use upper-estuary nursery areas during periods of high river discharge. Although the recruitment of several species likely was inhibited during discharge peaks, only striped mullet Mug//cephalus avoided freshwater conditions. Spots, southern flounder, Atlantic menhaden, and silver perch utilized shallow nursery areas on a size-specific basis. Recruitment and utilization patterns of fishes spawned in deeper areas generally were maintained throughout prolonged periods (up to 100 days) of freshwater conditions. The precise function of upper-estuary nursery areas is governed by the timing and magnitude of discharge events, but remains essentially intact through the seasonal encroachment of fresh water. Extensive and highly productive salt-marsh estuaries are a dominant feature along much of the Atlantic and Gulf of Mexico coasts of the southeastern United States. Shallow areas within estuaries provide habitat for fish assemblages that are highly dynamic both spatially and temporally. Some species are resident year-round, but an important component of these assemblages is a transient group of young-of-the-year clupeiform, perciform, and pleuronectlform fishes that are spawned in deeper estuarine, nearshore, and offshore waters (Turner and Johnson 1973). These species enter the shallow portions of estuaries primarily in the winter and early spring, occur in very high densities during their recruitment and residence periods, and leave the shallows as they grow or as the water begins to cool in late summer and early fall (Herke 1971; I Present address: University of Delaware, College of Marine Studies, Lewes, Delaware 19958. • Present address: South Carolina Wildlife and Marine Resources Department, Post Office Box 12559, Dean 1980; Weinstein2 et al. 1980; Weinstein and Brooks 1983). Comparisons of their spatial and temporal nursery use between studies are complicated by differences in habitats sampled, timing of sampling with respect to tidal-lunar cycles, and gear design and efficiency. However, it is apparent that fishes generally exhibit similar patterns throughout the region. "Waves" of recruitment and peaks of abundance unique to each species are separated through time during the late fall, winter, spring, and early summer (Weinstein2 et al. 1980). Each species associates with particular ranges of physicochemical and biotic factors, including salinity, substrate composition, veget...

Correspondence between environmental gradients and summer littoral fish assemblages in low salinity reaches of the Chesapeake Bay, USA

“…This coenocline is similar to patterns observed in other temperate and tropical zone coastal faunas (Weinstein et al 1980, Rogers et al 1984, Smith et al 1984, Felley 1987, Peterson & Ross 1991, Winemiller & Leslie 1992, and is characterized by a series of species supplements and replacements in successive downstream locations. Fish assemblages generally grade smoothly into each other with one notable exception; the freshwater interface is a boundary with a markedly increased rate of species turnover.…”

“…Previous estuarine studies differ in their estimation of the importance of salinity gradients to the distribution of estuarine fishes in mid-Atlantic waters (Weinstein et al 1980, Rogers et al 1984, Rozas & Hackney 1984, Bulger et al 1993). These disagreements have been attributed to seasonal alterations in large-scale gradients, and the integration of sequential recruitment of species throughout the year.…”

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“…These habitats serve as nurseries and feeding areas for endemic, marine, and freshwater species so that population structure, numbers of species and individuals, and the average size of fishes vary seasonally within fish communities (Dahlberg and Odum, 1970;Conover and Ross, 1982;Rogers, Targett, and Vansant, 1984;Levin et al, 2001). Young fishes are more flexible and better able to tolerate the wide variations in estuarine conditions than are adults, which may be able to use the estuary only for short periods of time.…”

“…Juvenile red drums subsequently mature in estuarine and shallow nearshore waters while schools of adults move between inshore and offshore areas. Rogers, Targett, and Vansant (1984) report that numerous species use upper estuarine nursery areas near freshwater river discharges in the Ossabaw Sound estuary, at the northern end of Ossabaw Island. Other patterns may be related to river discharge, temperature, food availability, or depth (Rogers, Targett, and Vansant, 1984;Smith and Wenner, 1985;Jassby et al, 1995).…”

“…Rogers, Targett, and Vansant (1984) report that numerous species use upper estuarine nursery areas near freshwater river discharges in the Ossabaw Sound estuary, at the northern end of Ossabaw Island. Other patterns may be related to river discharge, temperature, food availability, or depth (Rogers, Targett, and Vansant, 1984;Smith and Wenner, 1985;Jassby et al, 1995). St. Catherines is different from most barrier islands because it does not receive a significant influx of fresh water from a nearby large river, contrasting with such islands as Ossabaw, Sapelo, St. Simons, and Cumberland that receive inputs of fresh water from rivers such as the Ogeechee, Altamaha, and St. Marys (Oertel, 1979;Howard and Frey, 1985).…”