Throughout their range, Sea Otters use a variety of near shore marine environments and 84% of foraging occurs in water ≤30 m in depth (Bodkin et al. 2004) and most of their foraging occurs within a kilometre of the shore. Their classic association is with mixed rocky intertidal substrates supporting kelp beds, but also frequent soft-sediment dominated areas where kelp is absent (Riedman and Estes 1990, DeMaster et al. 1996, Burn and Doroff 2005). Kelp canopy is thought to be an important habitat component, used for foraging and resting (Riedman and Estes 1990). They are found most often in areas with protection from the most severe ocean winds and swells, such as rocky coastlines, thick kelp forests, barrier reefs and refuges such as inlets, bays and estuaries. Although they are most strongly associated with rocky substrates, Sea Otters can also live in areas where the sea floor consists primarily of mud, sand, or silt. Individuals generally occupy a relatively small home range a few to tens of kilometres long and have high site fidelity, remaining there year-round, however, some individuals, primarily males, do make long distance (more than hundreds of kilometers) movements and migrations (Rathbun et al. 2000; Tinker et al. 2008, 2019). Sea Otters forage in rocky and soft-sediment communities on or near the ocean floor. The maximum confirmed depth of dive was 97 m (Newby 1975); however, recent studies using time-depth recorders implanted in Sea Otters indicate average maximum forage depths of 54 m for female and 82 m for male Sea Otters (Bodkin et al. 2004).

Sea Otters are weakly territorial (Kenyon 1969) with fighting and aggression rare (Loughlin 1980). Only adult male Sea Otters establish territories. Males patrol territorial boundaries and attempt to exclude other adult males from the area. Females move freely between and among male territories. Groups of male and female Sea Otters generally rest separately. Sea Otter annual home ranges can occupy up to 0.8 km² (80 ha) and extend along 16 km of coastline (Kenyon 1969, Loughlin 1980). Typically, female sea otter home ranges are about 1.5–2 times larger than resident adult males during the breeding season; however, females have smaller annual or lifetime home ranges than males (Riedman and Estes 1990). Jameson (1989) found that territorial adult males occupied a mean home range of 40.3 ha during the summer-fall period (when home range size was considered equal to territory size); and mean coastline length was 1.1 km. Winter-spring mean home range size of territorial adult males that remained in female areas was 78.0 ha, with a mean coastline length of 2.16 km.

Sea Otter diet consists almost exclusively of marine invertebrates, including sea urchins, a variety of bivalves such as clams and mussels, abalone, other molluscs, crustaceans, and snails. Its prey ranges in size from tiny limpets and snails, to kelp and cancer crabs, to giant Pacific octopuses (Estes 1980). Sea urchins, abalones and rock crabs are the principal prey of Sea Otters in newly reoccupied habitats of central California (Vandevere, 1969), whereas, clams and crab make up the majority of the diet in soft-sediment habitats (Kvitek et al. 1992, Doroff and DeGange 1994). Where prey such as sea urchins, clams, and abalone are present in a range of sizes, Sea Otters tend to select larger prey over smaller ones of similar type (Kvitek et al. 1992). In California, it has been noted that Sea Otters ignore Pismo clams smaller than 3 inches (7 cm) across. One exception is in the Aleutian archipelago were Sea Otters were observed to regularly eat fish, which could comprise up to 50% of their diet in some seasons. The fish species eaten were usually bottom dwelling and sedentary or sluggish forms, such as the Red Irish Lord and Globefish (Estes 1980). They also consume crab, clam, mussels, turban snails, sea cucumbers, squid, octopus, chitons, tubeworms, large barnacles, scallops, and sea stars (Wild and Ames 1974, Riedman and Estes 1990). Burrowing bivalve molluscs such as clams are excavated by digging in sand or mud bottoms and are the most common prey in soft-sediment communities (Calkins 1978, Kvitek et al. 1992, Doroff and DeGange 1994).

Male Sea Otters reach sexual maturity around age five or six, but probably do not become territorial or reproductively successful for two or three subsequent years (Riedman and Estes 1990). Most female Sea Otters are sexually mature at age four or five, though some are mature as early as 2.5 years (Kenyon 1969, Jameson and Johnson 1993, Monson et al. 2000, Monson and DeGange 1995, von Biela 2007). Thus, it is thought that Sea Otter generation length is approximately seven years (Gagne et al. 2018). Sea Otters apparently are polygynous, although the exact nature of the mating system may vary. Females normally give birth to a single pup that weighs 1.4 to 2.3 kg at birth (Riedman and Estes 1990). Gestation has been documented to be approximately six months with an obligatory two to three-month delayed implantation phase and a four-month implanted phase when fetal growth occurs (Riedman and Estes 1990). Twinning has been documented in Sea Otters (Williams et al. 1980); however, litters larger than one are rare, and when they occur, neither pup is likely to survive (Jameson and Bodkin 1986). Pups are precocial and remain dependent upon their mothers for about six months (Jameson and Johnson 1993). Longevity in Sea Otters is estimated to be 15 to 20 years for females and 10 to 15 years for males (Riedman and Estes 1990).

Historically, Sea Otters occurred across the North Pacific Rim, ranging from Hokkaido, Japan, through the Kuril Islands, the Kamchatka Peninsula, and the Commander Islands, the Aleutian Islands, peninsular and south coastal Alaska and south to Baja California, Mexico (Kenyon 1969). In the early 1700s, the worldwide population was estimated to be between 150,000 (Kenyon 1969) and 300,000 individuals (Johnson 1982). Although it appears that First Nations’ harvests periodically led to significant 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 throughout the range. When Sea Otters were afforded protection by the International Fur Seal Treaty in 1911, it is thought that fewer than 2,000 animals remained in 13 remnant colonies (Kenyon 1969). Remnant populations were located in Russia (Kuril Islands, Kamchatka Peninsula, and the Commander Islands) in Alaska (Southwestern Alaska population stock (the Aleutian Islands (two remnant colonies), Alaska Peninsula (three remnant colonies), and Kodiak Island (one remnant colony), the South-central population stock (Prince William Sound), in Canada (Queen Charlotte Islands), in central California, and in Mexico (San Benito Islands) (Kenyon 1969, Estes 1980). However, the Queen Charlotte, Canada and San Benito Island, Mexico remnant Sea Otter populations have presumably died out and likely did not contribute to the recolonization of the species following near extirpation (Kenyon 1969).

In North America, the current Sea Otter’s range is fairly continuous from the Aleutian Islands to Prince William Sound with population gaps along the Gulf of Alaska until Yakutat (which was a translocated population) then another gap in the population’s distribution until the outer islands of Southeast Alaska (also a translocated population with Sea Otters from the Aleutian Islands and Prince William Sound). The next gap in the Sea Otter population distribution is between Southeast Alaska and British Columbia, Canada. Translocation efforts were successful in Washington State but not in Oregon, thus there is a large population gap between the small sea otter population in Washington and that of central California.

Enhydra lutris nereis is listed on CITES Appendix I. All other populations are included in CITES Appendix II. In Canada, sea otters are protected and managed under the Species at Risk Act (SARA). In the United States, Sea Otters are protected by the Marine Mammal Protection Act of 1972 (MMPA) and in Southwest Alaska and California, the Endangered Species Act of 1973 (ESA). The US Fish and Wildlife Service (Service) is the federal agency responsible for their conservation and management. The ESA also makes it illegal to buy, sell or possess any part of endangered species or items made from them. However, both the ESA and the MMPA allow for coastal Native people in Alaska to harvest Sea Otters for personal use, trade, barter, and the development of cottage industry. Native subsistence harvest of sea otters is monitored by the Service through a Marking, Tagging and Reporting program. The Service and Native organizations conduct joint population surveys and dialog on important conservations issues. The MMPA also mandates that efforts must be made to recover the species, which means creating and implementing a plan for returning them to healthy population levels.