Food depletion causes die-offs or spurs emigration to new areas. This is the largest threat to shellfisheries. As food competition increases, subdominant male otters are forced to the outskirts of their established range. Eventually females spread into the vacated male areas, the population builds, and the cycle repeats, wavelike. While sea otters don t remove all shellfish, leaving very small individuals and those hidden increvicesbeyond their reach, they do preclude nearshore fisheries.
Human harvest is regulated by size limits, season and gear restrictions, even sex of the species.
The initial direct effects of sea otter foraging are indisputable. Biologists have documented the impacts of sea otter foraging on fisheries. In Prince William Sound, Alaska, individual otters were observed eating over 80 clams and 12 Dungeness crabs daily, altering their habits to forage at night, when crab are active. The Alaska Department of Fish and Game closed the Orca Inlet Dungeness fishery for the first time in 1980. It remains closed today.