The Influence of Temperature and Forage Availability on Growth and Habitat Selection of a Pelagic Piscivore

Abstract

Habitat characteristics influencing growth of fishes often affect habitat selection because behaviors leading to rapid growth are under selective pressure. For pelagic piscivores such as striped bass Morone saxatilis stocked into southern reservoirs, temperature and prey density will likely be the most important factors influencing growth and spatial distribution. The traditional paradigm used to understand reservoir striped bass has focused on unsuitable physical conditions that may develop during summer stratification when hypolimnetic hypoxia forces fish into warm epilimnetic water. This study investigates how forage availability modifies the effects of physical conditions on this species. Striped bass in Badin Lake, NC, tagged with temperature-sensing transmitters tolerated temperatures above 27 degrees Celcius for two months to avoid hypolimnetic hypoxia but still displayed rapid growth. Bioenergetics models showed that high consumption rates allowed these fish to allocate energy to growth even during the summer and to grow rapidly during the fall as temperatures cooled. In contrast, striped bass in Lake Norman, NC, had slower growth despite experiencing warm summer temperatures for two to four weeks less. Lake Norman striped bass had lower consumption rates, and bioenergetics model simulations in which habitat conditions were exchanged between the reservoirs indicated that differences in forage availability had a greater relative effect on growth of striped bass than differences in thermal regime. These results suggest that criteria for determining the suitability of reservoirs for striped bass should incorporate a measure of prey availability. As with growth, habitat selection of Badin Lake striped bass was not solely dependent on temperature. Growth rate potential (the rate of growth of a predator occupying a particular location characterized by temperature and forage fish density) provided a better explanation of the spatial distribution of striped bass than did temperature or forage fish density alone. These results suggest growth rate potential can help us understand how fish integrate information on temperature and forage fish density, but it is important to note that growth rate potential was not a perfect predictor of the spatial distribution of striped bass so we cannot assume fish will optimize their patch choice with respect to this variable under all circumstances.