The effect of temperature and forage fish density on distribution of an aquatic piscivore.
Thompson, Jessica1, Rice, James1, 1 North Carolina State University, Raleigh, NC
ABSTRACT- Habitat selection can give particular insight into how individuals approach trade-offs present in the environment when habitat conditions are substantially less than ideal. Such is the case for many populations of striped bass (Morone saxatilis) in southern reservoirs. During summer stratification, hypoxia in the lower water column limits available habitat, forcing fish into surface water with temperatures well above their preferred range while potentially isolating them from the regions of the reservoir that contain the highest forage fish densities. To evaluate the relative influence of forage fish density and temperature on reservoir striped bass habitat selection, we examined the distribution of striped bass tagged with sonic transmitters in Badin Lake, a eutrophic reservoir in the piedmont region of North Carolina. Fish locations were compared to water column temperatures, dissolved oxygen constraints, and forage fish densities interpolated across the reservoir using geostatistical techniques, in the summers of two consecutive years that displayed substantially differing severity of stratification and associated thermal conditions. Distribution of striped bass was most strongly associated with the coolest temperatures and highest forage fish densities in the summer with the best thermal conditions. In the year with warmer surface water temperatures, striped bass still avoided areas of the reservoir with the warmest temperatures, but they did not always optimize their habitat decisions relative to forage fish density. This result, along with lower movement rates observed in this summer, suggests that fish may not fully integrate all habitat options across the system when thermal conditions are most limiting.
Key words: aquatic ecology, habitat selection, piscivore
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