In California, River Otters (Lontra canadensis) are most commonly associated with food-rich lowland aquatic habitats where they forage primarily on fish and crustaceans. Their distribution in high-elevation montane regions of the state, areas in which fish and crayfish were absent historically, is largely unknown. We compiled occurrence records of River Otters in California from elevations >1100 m, and evaluated them using evidentiary standards. Based on 126 records, we report the widespread presence of River Otters in the Klamath, southern Cascades, and Sierra Nevada mountain ranges, including at elevations exceeding 3000 m. Sixty-three percent of the records met our definition as verified, and the remaining 37% were considered unverified. The distribution of observations through time and habitats in which observations were made were similar between verified and unverified records. River Otter records spanned the period from 1900 to 2017, with 50% occurring between 1991 and 2010. Ninety-three percent of the water bodies with records of River Otters contained nonnative prey (fish and crayfish). Those lacking nonnative prey all supported native prey, including amphibians and reptiles. Based on records that contained River Otter foraging observations, nonnative fishes and crayfish were represented in 89% of the total accounts, and native frogs and invertebrates were represented in 22%. It remains unclear whether River Otters occurred in Californias high-elevation water bodies prior to the introduction of fish and crayfish, and additional research is needed to understand the possible influence of nonnative prey in allowing River Otters to expand their distribution in these habitats.
