Winter Feeding as an Overwintering Survival Strategy in Young-of-the-Year Winter Flounder

Abstract

For fish, the first winter of life can be a period of high mortality prior to recruitment. When resources are limiting or when fish are unable to feed due to low temperatures, starvation can often lead to size-dependent overwintering mortality. Larger individuals are typically better able to survive starvation because they have a higher percentage of energy reserves and a lower metabolic rate per unit of body mass than small individuals. Alternatively, fish that can feed during the winter are able to maintain their lipid stores and reduce their chance of starvation. The aim of this study was to examine the overwintering mortality and physiology of young-of-the-year (age-0) winter flounder Pseudopleuronectes americanus in relation to body size. Size-dependent mortality was investigated with 17 years of length-frequency data. In addition, I sampled the diet and whole-body crude lipid content of 309 age-0 winter flounder over the course of 1 year. Samples were taken in three estuaries in the northeastern USA during October–April. Whole-body crude lipid content ranged from 4.7% to 12.4% of dry weight. Larger age-0 winter flounder did not have higher lipid stores, and the age-0 fish did not exhibit size-dependent overwintering mortality. Age-0 winter flounder fed on amphipods and polychaetes throughout the winter, and their whole-body crude lipid content was maintained through the fall and winter. The physiology data lack temporal replication, but the spatial coherence in results (i.e., consistency among the three estuaries, representing two different stocks) suggests that the consumption and energy allocation patterns are real and that age-0 winter flounder follow an alternative overwintering survival strategy.

Received March 25, 2011; accepted January 4, 2012

ACKNOWLEDGMENTS

I gratefully acknowledge the hard work of the individuals who collected fish during the four trawl surveys, including Erin Bohaboy (URI-GSO weekly fish trawl); RIDEM; Don Danila (Dominion Nuclear Connecticut, Inc., Millstone Environmental Laboratory); and Normandeau Associates, Inc. I thank Chong Lee (Food Sciences, URI) for providing laboratory space and techniques for processing fish lipids; I am also grateful to Chris Calabretta, Sheldon Pratt, and Jason Graff for assisting with benthic invertebrate identification. Manuscript comments and suggestions by Jeremy Collie are greatly appreciated. The manuscript was also greatly improved by three reviewers. The Nature Conservancy provided funding for this project.