Seasonal Energy Dynamics of Young-of-the-Year Hudson River Striped Bass

Abstract

Mortality of young-of-the-year (age-0) temperate fish during the winter has often been attributed to depletion of energy reserves, which results in starvation. We examined the seasonal energy cycle in age-0 Hudson River striped bass Morone saxatilis with field collections and laboratory experiments to determine if winter mortality could be attributed to starvation. Compositional analyses of wild fish showed that age-0 striped bass stored energy in the form of lipids prior to winter and then experienced an energy deficit, losing 7 and 16% of total body energy, respectively, in the two winters examined. Compositional analyses were performed on fish from a laboratory experiment in which age-0 striped bass were exposed to ambient winter conditions. Mortality was associated with low energy levels in unfed treatments but not when food was provided daily. In neither treatment did starvation appear to be the ultimate cause of death, as wild fish were captured with energy levels lower than those observed among mortalities in either experimental treatment. Our results suggest that starvation is not the only cause of winter mortality that produces the observed size-dependent patterns among age-0 striped bass. Other stresses associated with overwintering likely interact with the energy deficit to determine the size-dependent patterns of winter mortality that are observed in temperate fishes.