Impacts of sea otter (Enhydra lutris) predation on commercially important sea cucumbers (Parastichopus californicus) in southeast Alaska

Abstract

Sea cucumbers (Parastichopus californicus), which are an important commercial, subsistence, and ecological resource, are negatively affected by an expanding sea otter (Enhydra lutris) population in southeast Alaska. A few hundred sea otters were reintroduced into southeast Alaska in the late 1960s after their extirpation during the 18th and 19th century fur trade. In the ensuing decades after recolonization, the sea otter population grew exponentially in number and distribution, and sea cucumbers declined in density in areas with otters, suggesting an inverse relationship between sea otter numbers and sea cucumber density. We evaluated the interaction and effects of sea otters on sea cucumbers using sea otter foraging observations, sea otter population survey data, and sea cucumber density data. Our results indicate that sea cucumber density declined with and without sea otter presence and that the extent of the decline depends on the duration and magnitude of sea otter presence, with 100% decline in areas occupied by sea otters since 1994. Sea otter predation should be included in sea cucumber fishery management as a step toward ecosystem-based management.