Estuarine diet of North American river otters (Lontra canadensis) in Makah Bay on the Makah Indian Reservation in Washington

The North American river otter (Lontra canadensis) is mainly an opportunistic forager inhabiting coastal areas throughout the Pacific Northwest of the United States. Using parts from scat samples, collected along the estuaries of the Wa’atch and Tsoo-Yess Rivers in Washington State during the summer of 2018 and the spring and summer of 2019, we analyzed the diet of this species in estuaries of Makah Bay. We documented one of the most diverse diets of North American river otters in Washington: 45 prey species were identified among 17 fish families and 10 decapod taxa. Pacific staghorn sculpin (Leptocottus armatus), saddleback gunnel (Pholis sp. cf. ornata), and starry flounder (Platichthys stellatus) were the 3 most prevalent species in the diet of North American river otters (>47% frequency of occurrence for each of the 3 species). We suggest that the variation among prey species in the diet was driven primarily by habitat, followed by prey abundance and availability. Limited incidences of subtidal prey species, instances of high-volume predation on dense aggregations of fish prey, and the presence of commercially important species open interesting insights into foraging behavior or prey species distribution. Our study resulted in the first description of the diet of North American river otters in the area.