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Article Excerpt
ABSTRACT: We tested the survival and growth of three young-of-the-year (YOY) estuarine resident (mummichog, sheepshead minnow, winter flounder) and a southern migrant (silver perch) fish species to determine the influence of winter temperatures. Under ambient winter temperatures with daily feeding, mortality did not occur for mummichog and sheepshead minnow, was low for winter flounder (25%) and high for silver perch (100%). There was little or no growth for any species that survived during the winter. As expected, silver perch were least tolerant to cold temperature, supporting the hypothesis that this species needs to migrate out of Middle Atlantic Bight estuaries in the fall to avoid low winter temperatures and survive.
KEYWORDS: winter mortality, young-of-the-year, fishes, estuaries, growth
INTRODUCTION
The ability of temperate young-of-the-year (YOY) fishes to survive the first winter of life may be an important determinant of recruitment success. Investigators have shown that winter survival of YOY may be size dependent and for some species may be dependent on a critical minimum winter temperature below which YOY cannot survive (Conover and Present, 1990; Hales and Able, 2001; Henderson et al., 1988; Kooka et al., 2007; Post et al., 1998; Sogard, 1997). A recent review noted that most research currently addresses winter mortality in freshwater fishes, but that there is increasing interest in marine and estuarine fishes (Hurst, 2007). Responses in these contrasting environments may differ, in part, because extensive migrations to thermal refugia are possible for estuarine and marine fishes, but not for freshwater fish (Hurst, 2007). In addition, the general warming associated with climate change can result in warmer winters and reduced winter mortality and enhanced recruitment to the adult population (Hare and Able, 2007; Hurst, 2007).
This study compares winter survival rates among the YOY of four species that have different patterns of estuarine use. Bairdiella chrysoura Lacepede (silver perch) are resident in the summer, but are not found in winter because they migrate out of estuaries and move south as temperatures cool in the fall (Able and Brown, 2005; Able and Fahay, 1998). We hypothesized that YOY silver perch would be intolerant of cold water temperatures. In contrast, three year-round, estuarine species, Fundulus heteroditus Linnaeus (mummichog), Cyprinodon variegatus Lacepede (sheepshead minnow), and Pseudopleuronectes americanus Walbaum (winter flounder) (Able and Fahay, 1998; Smith and Able, 1994) were hypothesized to be tolerant of low winter temperatures because they are considered resident. We also determined growth rates for all these species as another index of their response to low temperatures in winter. Our goal was to determine the influence of winter temperatures on growth and survival rates for all four species.
MATERIALS AND METHODS
Winter Flounder and Silver Perch Experiments
Young-of-the-year winter flounder and silver perch were collected in Great Bay/Little Egg Harbor estuary in southern New Jersey from August to November 1995. All fish were held in the laboratory at ambient temperature in a flow-through seawater system and were fed a diet of chopped Menidia menidia Linnaeus (Atlantic silverside) and Artemia sp. (brine shrimp) daily until the start of the experiment. The flow rate of ambient sea water, which was filtered and UV treated, was approximately 0.61 [min.sup.-1] and a drainage hole in the side of each aquarium maintained water volume at a constant level....
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