Empirical Salmonid Habitat Suitability Criteria and Bioenergetics Predictions Compared

Daily net energy intake (DNEI) was calculated using a drift-foraging model that incorporated water depth, water velocity, diel fluctuating water temperature, turbidity, drift density, and drift size.  The DNEI predictions of high-energy habitat matched the observed habitat utilization of a wide size range of rainbow/redband trout (Oncorhynchus mykiss spp.) in the Klamath River, California/Oregon, USA, and cutthroat trout (O. clarki) in St. Charles Creek, Idaho, USA.  DNEI predictions also matched empirical habitat suitability criteria (HSC) developed for adult rainbow trout from four west slope Sierra Nevada rivers in Northern California, USA (Middle Fork Stanislaus River, North Fork Stanislaus River, South Fork American River, upper North Fork Feather River).  Both the DNEI model predictions and the empirical data indicate that fish sizes that can achieve maximum daily consumption should preferentially occupy lower velocity, energy-efficient habitats.  Conversely, fish sizes that cannot achieve daily maximum consumption should preferentially occupy higher velocity habitats.  Previous energetics foraging models, based on short-term net energy intake (NEI) (e.g., joules/hr), predict that fish should occupy only the higher velocity habitats, contrary to the empirical data presented in this paper.