Sea Otters are playful animals that spend almost all their time in the sea. They eat, sleep, and even have their babies in the water. In the daytime sea otters float on their backs eating Abalone, their favorite food. To open the Abalone shell they place a small rock on their chest and smash the shell against it. Sea otters are one of the few mammals, beside humans, that use tools. They will use strands of kelp to tie themselves into the kelp beds for a secure night’s sleep. They love to frolic with other otters and seals. Unlike seals and walrus, sea otters have no blubber to keep them warm in the cold arctic waters. Air trapped in their fur keeps them warm and bouyant. Oil spills can damage this fine fur and cause the otter to get very cold and die. That is why volunteers cleaned the sea otters so carefully after the oil spills in Alaska.
Sea otters also faced great dangers from hunters who wanted their valuable coats. They were hunted so heavily in the 18-19th Centuries that they had to be placed on the U.S. government endangered species list. Now the populations have come back to a large extent, but conservationists would like to continue to protect them. Fishermen would like them off the endangered species list in order to protect the abalone harvest
IUCN RED LIST
The Sea Otter is considered to be Endangered due its vulnerability to large-scale population declines. The species is believed to have undergone a decline exceeding 50% over the past 30 years (approximately three generations). The world-wide population of Sea Otters decreased to approximately 2,000 animals by the end of the commercial fur trade in 1911 (Kenyon 1969). The population recovered from 11 remnant populations located in Russia (Bering Island, Kamchatka Peninsula, and Kuril Islands) and in the United States (in Alaska (Aleutian Islands, Alaska Peninsula, Kodiak archipelago, and Prince William Sound) and California). The remnant populations were small and widely dispersed, as a result, this species has low genetic diversity (Ralls et al. 1983). Since the 1980s, the species had been recovering in many areas thanks to intensive management and regulatory efforts by several governments. However contemporary issues (oil spills, potential fisheries interactions, predation, and disease events), have either prevented Sea Otter populations from thriving or have caused population declines throughout much of the species range. In the United States, two subspecies of Sea Otters are listed as threatened (E. lutris kenyoni in SW Alaska and E. lutris nereis in California) due to precipitous population declines in Alaska and slow growth (and vulnerability to anthropogenic factors) of a small population in California.
In Alaska, precipitous population declines occurred in the Aleutian Islands beginning in the late 1980s–2005. By 2000, counts of Sea Otters had decreased by 90% with a declining trend through 2005 (Doroff et al. 2003, Estes et al. 2005, Burn et al. 2003). The probable cause of the decline was increased predation by killer whales (Orcinus orca) (Estes et al. 1998). More recent Sea Otters surveys indicate the population trend has increased since 2005, however, counts remain well below carrying capacity for this region (D.M. Burn pers. comm. 2010). Population counts also remain low for the Alaska Peninsula (Burn and Doroff 2005, U.S. Fish and Wildlife Service Stock Assessment Reports). The population in the Kodiak archipelago and lower Cook Inlet appeared stable or increasing during the same period that population declines were documented in the Aleutian Islands and Alaska Peninsula (Kodiak and lower Cook Inlet are part of the Southwest population stock), however, this habitat has not been surveyed since 2004.
Recent studies have found infectious disease to be an important mortality factor in California Sea Otter populations (Conrad et al. 2005, Johnson et al. 2009). Information collected from forensic-level necropsies of dead Sea Otters and sampling of free-ranging Sea Otters indicate a strong link to protozoan parasites,Toxoplasma gondii and Sacrocystis neurona, that are known to breed in cats and opossums (Thomas and Cole 1996, Conrad et al. 2005) thus sources of mortality for the Sea Otter population include land-based factors. Other factors identified as causing significant mortality include acanthocephalan peritonitis, protozoal encephalitis, bacterial and fungal infections (Thomas and Cole 1996).
The situation in the Russian Federation is clearer now. The Sea Otter number on the Commander Islands reached maximum since last 150 years period (A. Burdin and S.V. Zagrebelny pers. comm. 2006). In 2007, the direct count revealed around 8,000 otters in both Bering and Medny Islands. The Commanders Island population of Sea Otter was never so abundant, but in 2008, it was found that the population was on decline. In 2004 the Kuril Islands population of Sea Otter was estimated around 19,000 (Kornev and Korneva 2004), but later count have shown sever decline (up to 40–50% in different locations). Though the causes of such decline are not very clear, the threat due to poaching can’t be ruled out.
Throughout their range, Sea Otters use a variety of near shore marine environments and 84% of foraging occurs in water ≤ 30m in depth (Bodkin et al. 2004) and throughout much of their range, foraging occurs within a kilometer of the shore. Their classic association is with rocky substrates supporting kelp beds, but they also frequent soft-sediment areas where kelp is absent (Riedman and Estes 1990, DeMaster et al. 1996, Burn and Doroff 2005). Kelp canopy is 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, such as rocky coastlines, thick kelp forests, and barrier reefs. 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 home range a few kilometers long, and remain there year-round. 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 82m 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.
The diet of Sea Otter 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 crabs and giant 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 will make up 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 items 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. Only in the Aleutian archipelago were Sea Otters observed to regularly eat fish, which could comprise up to 50% of their diet. 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). Bivalve molluscs 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 (Kenyon 1969, Jameson and Johnson 1993, Monson et al. 2000, Monson and DeGange 1995, von Biela 2007). 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). 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 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).
19th Century Naturalist
Edward Nelson Recounts:
“In 1760-65 when Bering and his party first explored the Aleutian Islands, they found the Sea Otters so numerous that the Aleuts wore long mantles made of their skins and a scrap of old iron was enough to secure the finest skin. In 1840 Veniaminov wrote that the Sea Otters in these islands are distinguished above everything on account of their great value and small numbers. There was a time when they were killed in thousands, now only by hundreds. There are plenty of places where before there were great numbers of Sea Otters; now not one is to be seen or found. The reason for this is most evident; every year hunted without rest they have fled to places unknown and without danger.
When the Fur Seal Islands were discovered the sea otters there were very numerous, and two sailors killed five thousand there the first year. The next year less than one thousand were killed, and from the end of the next six years to the present day the Sea Otter has been unknown there. From the Aleutian Islands south to Oregon the Russians found these otters so numerous that they were obtained in numbers running from two to three thousand kills per year. This great increase in the catch during the later years is entirely due to the greater vigor with which the animal has been hunted, and the introduction of fine long-range rifles. Good rifles now replace to a great extent, the primitive spears.
There is little doubt that in the course of a few years under the present regulations and mode of hunting, this valuable animal will be exterminated, and in place of affording the Aleuts a livelihood will leave them dependent upon the Government.”
Asian Small Clawed Otter
Status and Distribution
All otters in Thailand are severely threatened due to habitat destruction, pollution of waterways, and human encroachment. Two species, the Eurasian otter and the hairy-nosed otter, may already have disappeared from Thailand.
The Asian small-clawed otter is still found in many wildlife sanctuaries and national parks in Thailand, where it frequents streams, rivers, marshy wetlands, and the sea coasts. Outstanding numbers are found in the western forested areas and in the marshy wetlands in southern Thailand, including Nung Tung Tong Reserve and Pattani and Songkla Provinces.
The smooth otter still occurs in the Huay Kha Khaeng Reserve in western Thailand; in the Tapi River, Phru-Toa-Dang Peat Swamp Forest, Bang Lan Dam and Ao Phangnga National Park in the south; and in the Mun River in the northeast.
All four otter species were officially declared protected wild animals of the first category by the Ministerial Regulation No. 10 in 1975, in accordance with the Wild Animals Reservation and Protection Act B.E. 2503 (1960). According to this act, no persons shall kill protected wild animals of the first category except for educational purposes or scientific research. Trading of otter skins and carcasses is also prohibited by law.
- Municipal, agricultural, and industrial wastes in most waterways throughout Thailand have severely threatened the otter populations.
- Habitat destruction, including logging and hydroelectric projects which alter river systems, have reduced the habitat available to otters. The hydroelectric dams replace natural rivers with steep-sided reservoirs devoid of surrounding cover and thus unsuitable for otter habitation. The changing of mangrove forest into shrimp and fish aquaculture projects also diminishes otter habitats and puts otters in more direct competition with man.
- Competition with people for fish supplies has resulted in direct killing of otters in areas where they would otherwise occur.
- Insufficient enforcement of existing wildlife laws and reserved areas provide little more than “paper” protection for otters and their remaining habitats.
- A complete survey of otters and their remaining habitats needs to be initiated quickly to pinpoint areas of critical concern for each otter species. Efforts should be made to determine areas where small pockets of the Eurasian otter and the hairy-nosed otter might still occur.
- Habitats that still contain otter populations should be declared “otter reserves” and legal action should be taken to protect these areas. Existing protected areas also need to be more closely monitored and protected.
- Public education programs should be initiated to develop awareness of the importance of conservation of otters and other wetland inhabitants and of a clean environment in general.
- Reintroduction programs should not be considered at this time; efforts should focus instead on protecting the habitats of the remaining otters in Thailand. Only if and when the overall pollution problems are solved, can otters be reintroduced into areas where they now no longer occur.