The influence of temperature and forage availability on growth and habitat selection of a pelagic piscivore

Habitat characteristics influencing growth of fishes often affect habitat selection because behaviors leading to rapid growth are frequently under strong selective pressure. For a pelagic piscivore such as striped bass Morone saxatilis stocked into southern reservoirs, temperature and forage fish density are likely to be the most important factors influencing realized growth, and the spatial distribution of these environmental variables would be expected to influence their spatial distribution. The traditional paradigm used to explain striped bass growth and habitat selection has focused exclusively on physical habitat, specifically unsuitable habitat conditions that may develop during summer stratification when hypolimnetic dissolved oxygen levels are too low and epilimnetic temperatures are too warm to provide suitable conditions for adult fish. This study improves our understanding of reservoir striped bass, and pelagic predators in general, by investigating how prey availability modifies the effects of physical conditions on growth and habitat selection of this species.; Using relocations of striped bass tagged with temperature-sensing sonic transmitters in Badin Lake, NC, I demonstrated that striped bass will occupy temperatures above 27°C for up to two months in order to avoid low dissolved oxygen levels. However, Badin Lake striped bass did not occupy the minimum temperature with at least 2 mg/l dissolved oxygen, the minimum tolerance of the species. Rather, tagged fish of all sizes were consistently found at slightly higher temperatures and higher dissolved oxygen levels just above the oxycline, indicating that reservoir striped bass may not tolerate minimum dissolved oxygen levels for an extended period and may have greater thermal plasticity that originally believed even in systems with highly unsuitable summer habitat. Using bioenergetics modeling, I showed that growth is possible even at the high temperatures experienced by the Badin Lake population if fish can attain sufficient consumption rates.; The conclusion that the effects of warm temperatures on growth will be mediated by forage availability was supported by the results of bioenergetics model simulations of the Badin Lake striped bass population, which experienced fairly rapid growth, and the population in Lake Norman, NC, which displayed much slower growth despite experiencing warm temperatures for a shorter period over the summer. High consumption rates allowed Badin Lake striped bass of all sizes to allocate some energy to growth even during the summer and to achieve rapid growth during the fall as temperatures cool. Lake Norman striped bass in older age classes did not consume sufficient prey resources to allocate energy to growth over the summer, and consumption rates of striped bass of all ages declined more over the fall than in Badin Lake, preventing these fish from experiencing any season with conditions conducive to rapid growth. Bioenergetics model simulations in which habitat conditions from Badin Lake and Lake Norman were exchanged indicated that differences in forage availability between the systems 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, and poor growth and condition should be considered an indicator of imbalance between the predatory demand of the striped bass population and prey supply.; As with growth, habitat selection of Badin Lake striped bass was not solely dependent on temperature. Striped bass were found throughout the range of cooler temperatures just above the oxycline that were available during the summer, rather than selecting the minimum temperatures available. Growth rate potential (the rate of growth expected for a predator occupying a particular location characterized by temperature and forage fish density) provided a bett...