Loutre de mer

In the early 1700s, the worldwide population was estimated to be between 150,000 (Kenyon 1969) and 300,000 individuals (Johnson 1982), occurring along the North Pacific from northern Japan to the central Baja Peninsula in Mexico. Its abundance was greatly reduced by human exploitation. Although it appears that First Nations harvests periodically led to local reductions of Sea Otters (Simenstad et al. 1978, Jones et al. 2011), the species remained abundant throughout its range until the mid-1700s. Following the arrival in Alaska of Russian explorers in 1741, extensive commercial harvest of Sea Otters over the next 150 years resulted in the near extirpation of the species. When sea otters were afforded protection by the International Fur Seal Treaty in 1911, probably fewer than 2,000 animals remained in 13 remnant colonies (Kenyon 1969): two in the Kuril Islands and Kamchatka; one in the Commander Islands; a total of 10 in the following areas: Aleutian Islands (2) and along the Alaska Peninsula (3); Kodiak Archipelago (1), Prince William Sound (1), the Queen Charlotte Islands (1), central California (1), and San Benito Islands (1). However, the Queen Charlotte, Canada and San Benito Island, Mexico remnant Sea Otter populations became extinct and likely did not contribute to the recolonization of the species following near extirpation (Kenyon 1969).

Sea Otters currently have established populations in parts of the Kuril Islands, the Russian east coast, throughout coastal Alaska, British Columbia, Washington, and California, and there have been reports of single-animal observations in Mexico and Japan (a recent maximum of 20 in the latter). Population estimates and counts made between 2000–2018 give a generalised worldwide estimate of 128,902 Sea Otters. However, many populations have not been surveyed regularly or recently. The biggest change during this time being the decrease in the northern Kuril Islands and the Kamchatka Peninsula which have declined from approximately 22,000 Sea Otters to approximately 12,100 since the early 2000s (Kornev 2007, Kornev 2010), representing a decline of approximately 55% for this subpopulation within the last 21 years (three generations). This is a long-established region for Sea Otters (holding approximately 9–10% of the global population) and there are no documented reasons for this decline. The population in the Commander Islands is believed to be stable and had one of the longest time-series for population surveys for the species—however, this region has not been surveyed since the late 1990s. It is thought that budget restrictions have prevented any current population assessments for the species in this region.

In Alaska, precipitous population declines occurred in the Aleutian Islands beginning in the late 1980s–2005. In the 1980s, around 90,000 Sea Otters were thought to occur in the Aleutian Islands. By 2000,this population had decreased by 90% (to around 9,000), with a declining trend continuing through to 2005 and an estimated loss to the population of 62,000–90,000 Sea Otters (Burn et al. 2003, Doroff et al. 2003, Estes et al. 2005, Burn and Doroff 2005). The probable cause of the decline was increased predation by Killer Whales (Orcinus orca) (Estes et al. 1998). To date, there is no indication of further declines in counts and no real indication that the population is showing signs of significant recovery. Population counts also remain low for the Alaska Peninsula (Burn and Doroff 2005, U.S. Fish and Wildlife Service Stock Assessment Reports). In this listed population, the Kodiak archipelago and lower Cook Inlet appeared stable or increasing during the same period that population declines were documented in the Aleutian chain. A generalised estimate of Sea Otter numbers in Alaska is 98,780 (representing around 77% of the global population); in addition to ~9,000 in the Aleutian Islands, there are ~16,340 on the Alaskan Peninsula, ~46,700 in the Gulf of Alaska, and 25,700 in Southeast Alaska, however, many of these areas have not been surveyed thoroughly for over a decade (S. Larson pers. comm. 2021).

Between 1969 and 1972, 89 Sea Otters were translocated from Alaska (66% from Prince William Sound and 33% from Amchitka Island in the Aleutians) to the west coast of Vancouver Island, British Columbia, where they established a healthy population. Sea Otter range expansion has continued and in 2008 it was documented that they have left Vancouver Island and moved into northern Queen Charlotte Strait and the adjacent British Columbia mainland coast and in some portions of the central British Columbia mainland coast. The most recent population estimate is 6,754 (Nichol et al. 2015), representing around 7–8% of the global population.

During 1969 and 1970, 59 Sea Otters were translocated from the remnant population of Amchitka Island to Washington State. The most recent surveys in 2019 indicate the population is approximately 2,785 (around 2% of the global population) with an estimated average annual growth rate of 9.8% and continued range expansion is expected (Jefferies et al. 2019).

California's Sea Otters are the descendants of a single colony of about 50 southern Sea Otters discovered near Big Sur in 1938. The southern Sea Otter population in California is recovering to near its threshold for delisting under the Endangered Species Act (1973), however, the present distribution is only a fraction of the historic distribution (Tinker et al. 2019). The latest survey results report a three-year average of 2,962 Sea Otters (around 2% of the global population), including the mainland and the San Nicolas Island population, which represents a <1% growth rate per year (Hatfield et al. 2019). Population range expansion has been greatly impacted by shark-bite mortality in the northern end of the subspecies’ range (Hatfield et al. 2019). The Pacific Northwest has had major reductions in canopy-forming kelp in the past decade due to the loss of sea stars through a wasting disease and now an abundance of urchins that graze intensively on kelp (Roger-Bennett and Catton 2019). The giant kelp likely afforded Sea Otters protection from shark predation, and the loss of this habitat has been a factor intensifying the predation. On the southern end of the range, at San Nicolas Island, the reintroduced population originally established in the mid-1980s from the Central California population is now well established, numbering over 100 animals, and has an estimated annual growth rate of 10.5% for the past five years (Hatfield et al. 2019). Schramm et al. 2014, based on reports of sea otters in Baja California, Mexico, suggested that a higher frequency of Sea Otters than in the past.

In Japan, small numbers of Sea Otters (E. l. lutris) have been observed regularly on the eastern side of Hokkaido Islands since the 1970s (Hattori et al. 2005). The most recent estimate is 20 individuals, but at present this is not believed to be an established population.