Sea otter reintroductions into previously occupied habitat, Northeast Pacific, USA and Canada

Summary

Sea otters once numbered about 300,000 around the north Pacific rim before a 170-year commercial fur harvest, ending in 1911, reduced them to roughly 1,000 animals. Between 1937 and 1989, nine reintroductions moved otters into vacant historic habitat, of which six established self-sustaining populations that today account for about 30 percent of the species' 125,000 estimated total and over half its historic range. Early attempts, moving otters from Amchitka Island to the Pribilofs and Attu Island in the 1950s, failed, likely from poor husbandry and too few animals; from 1965 onward, larger releases from Amchitka and Prince William Sound succeeded in the Pribilofs, southeast Alaska, British Columbia and Washington, though a parallel effort in Oregon failed and a 1987 release of 139 otters to California's San Nicolas Island stalled for nearly two decades before recovering. Across all reintroductions, roughly 90 percent of released otters were typically lost early on to emigration or mortality, but survivors then grew at close to the species' maximum rate of about 20 percent a year, since abundant, decades-undisturbed prey favoured the newcomers even as it created conflict with shellfish fisheries. Where otters re-established, they suppressed sea urchin grazing and allowed kelp forests to recover, restoring a more complex nearshore ecosystem. The authors count six of nine reintroductions successful and credit mixing otters from genetically distinct source populations with restoring diversity lost during the fur trade, while noting a large stretch of unoccupied habitat in California and Oregon still awaits a further attempt.