The sea otter (Enhydra lutris) is a marine mammal hunted to near extinction during the 1800s. Despite their well-known importance as a keystone species, we know little about historical sea otter ecology. Here, we characterize the ecological niche of ancient southern sea otters (E. lutris nereis) using d13C and d15N analysis of bones recovered from archaeological sites spanning ~7,000 to 350 years before present (N=112 individuals) at five regions along the coast of California. These...