A test of a generalized, optimal habitat selection model for drift-feeding fishes: brook charr

Optimality theory is useful for modeling habitat use in animals, although many models have not been rigorously tested. We evaluated the ability of the Grossman et al. net-energy-intake (NEI) optimal foraging model for drift-feeding stream fishes, to predict the holding velocity (microhabitat) of native brook charr (BC; Salvelinus fontinalis) inhabiting a southern Appalachian stream. This model postulates that fish choose holding velocities that maximize their NEI, and is broadly applicable to stream fishes, many of which are drift-feeders. We used laboratory prey capture success versus water velocity data to quantify the relationship between prey capture success, water velocity, and holding velocity of BC (N = 21, mean standard length = 147 mm +/- 14 sd). Parameterization of the Grossman et al. model yielded an optimal holding velocity prediction of 18.5 cm center dot s(-1). Based on fitting criteria from previous work, the model prediction was successful because it fell within the 95% confidence interval (13.5-20.5 cm center dot s(-1)) of mean holding velocities (17.0 cm center dot s(-1), N = 26) of BC in Lynn Camp Prong, Tennessee. Consequently, NEI maximization likely is a causal factor affecting BC habitat choice. Our result argues strongly for the general usefulness of this model.