Prey Preference of the North American River Otter (Lontra Canadensis) Evaluated According to Optimal Foraging Theory

Prey preference of the North American river otter (Lontra canadensis) was studied in a captive population and evaluated according to optimal foraging theory. Live sunfish (Lepomis spp.), brown trout (Salmo trutta), and crayfish (Cambaridae spp.) were released in a pool, and the search, chase, and handling/eating times of two otters were recorded. When provided with choice of sizes, otters showed a significant preference for catching and eating large prey first. When given a choice of species, otters significantly preferred to catch and eat brown trout first; this preference remained when offered dead prey. Using the rate of energy intake, the preference for brown trout was expected as it provided significantly more energy per unit time, but size preferences only fit predictions after metabolic rate was incorporated, as an otter expends more energy chasing prey in the water than when eating on land. The net energy gained was significantly greatest for large prey in all the size trials and for brown trout in the species trials. Captive river otters exhibit prey preferences that match our predictions based on optimal foraging theory, which can provide insight into dietary habits of wild otter populations.