Variation in diet and activity of river otters (Lontra canadensis) by season and aquatic community

Abstract Keystone predators can impact many prey species, including those that are endangered. A requisite to assess the have on different populations is identify species being consumed in types of communities, while accounting for possible seasonal variation consumption. Here we used analysis North American river otter (Lontra canadensis) scat otters their populations, particularly endangered salmonids and migrating birds. We analyzed composition 1,411 scats collected from 10 sites Humboldt County, California, between 2011 2012. Analysis items placed study into four distinct clusters based diet. Fish, mostly families Gasterosteidae, Cottidae, Pholidae, formed primary component, crustaceans, birds, amphibians, insects, also were important components Salmonids constituted < 5% overall diet, but largest percentage salmon during spawning season at inland cluster where spawn. Scat marking intensity varied seasons, with most autumn fewest winter/spring, except pattern activity was reversed. River may be responding migrations threatened salmonids. Diet surveys this type useful monitoring resource use by top aquatic ecosystems.