The maritime fur trade practically wiped out the sea otter populations of North America’s Pacific Northwest. But the otters, who are shellfish predators, have recovered, thanks to federal laws that forbid hunting them. Now a new problem has arisen. Local indigenous communities hold constitutionally protected rights to harvest the same shellfish, which have been decimated by the now-protected predators.
Recent research has shown that indigenous people managed their relationships with sea otters and shellfish with great care. Most likely there was a patchwork of sea otters along the coast, with plenty in some areas, virtually none in others. Researchers from Simon Fraser University in British Columbia measured ancient mussel shells from coastal sites spanning 6,000 years. Then they compared them with sizes at sites with and without sea otters today. This approach worked, because sea otters focus on larger mussels, so their presence is a sign that the predators were plentiful. Mussels of the size selected by the otters are only found in areas where otters have been absent for more than century.
Over a wide area from the Aleutian Islands to southern California, otters were absent or rare before the fur trade. The new research suggests that traditional conservation practices by the Haida Indians and other groups paid attention to controlling otter populations through hunting, thereby protecting a critical part of their diet. The new findings firmly dismiss a widely held assumption that sea otter populations were living near carrying capacity over their entire range. They were not: traditional conservation practices ensured an abundance of large molluscs.