Recolonizing sea otters spatially segregate from pinnipeds on the Canadian Pacific coastline: The implications of segregation for species conservation

The reintroduction and recolonization of species extirpated from former ranges are key components of species conservation. Resource availability affects recolonization success and resulting distribution patterns, but top-down processes may also play a role through density-mediated or trait-mediated indirect effects that may exclude a species from otherwise suitable habitat. We predicted that the spatial distribution of recolonizing sea otters, Enhydra lutris, on the Canadian Pacific coastline was explained by resources as well as interspecific interactions – spatial segregation from pinnipeds, the preferred prey of killer whales Orcinus orca. We surveyed the summer occurrence of sea otters and pinnipeds on Vancouver Island, Canada. We quantified coastline density and bathymetry at multiple spatial scales as indices of habitat complexity and foraging habitat availability. We used generalized linear model selection to test hypotheses about sea otters’ spatial relationship to resources and heterospecifics. Pinniped presence negatively predicted sea otter presence, even after accounting for complexity and foraging habitat. Sea otters may segregate from pinnipeds due to trait-mediated indirect effects of predation, leading us to hypothesize apparent competition between sea otters and pinnipeds. Research is needed to test this hypothesis; if true, refuge from apparent competitors may be a key component of recolonization habitat for sea otters. Species distribution models should quantify resource landscapes but also species-scapes: the spatial plane of species interactions that combines with resources to drive species distributions. Conservation plans based on recolonization models that include only resources may overestimate available habitat, carrying capacity, and recolonization success.