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PROTECT: Sea Otters


Sea Otter
Enhydra lutris

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





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

Aonyx cinerea


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.

Legal Status
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.


  1. Municipal, agricultural, and industrial wastes in most waterways throughout Thailand have severely threatened the otter populations.

  2. 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.

  3. Competition with people for fish supplies has resulted in direct killing of otters in areas where they would otherwise occur.

  4. Insufficient enforcement of existing wildlife laws and reserved areas provide little more than “paper” protection for otters and their remaining habitats.

Conservation Priorities

  1. 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.

  2. 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.

  3. 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.

  4. 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.


 In the last few decades the range of Asian small clawed otter has shrunk particularly in its western portion, as evident from the published literature. The Vulnerable status of the species is based on past population decline rates under criterion A2acd. Given the extent of loss of habitat that is occurring in south and southeast Asia and the intensity of poaching the reduction in population has been observed in many parts of its range (Hussain 1993; Melisch et al. 1996; Hussain 2002). Although quantitative data on population sizes or trends are lacking, it is suspected that the global population of the smooth-coated otter has declined by> 30% over the past 30 years. The threats to small-clawed otter is prominent in its western range so much so that since last 60 years its range has been shrunk considerable moving west to east from Himachal Pradesh to Assam (Hussain 2007). They were once common in the mangroves of east Calcutta and Sunderbans (Sanyal 1991) is now believed to be locally extinct.


The Asian small-clawed otter has a large distribution range, extending from India in South Asia east ward through entire Southeast Asia up to Palawan (Philippines) and Taiwan and southern China in the north (Mason and Macdonald 1986, Wozencraft 1993, Hussain 2000). In recent years, in England it has established itself in the wild after escaping from captivity (Jefferies 1990 and 1991). In India it occurs in the Himalayan foothills of Himachal Pradesh (Kulu), West Bengal, Assam and Arunachal Pradesh as well as in southern Indian hill ranges of Coorg (Karnataka), Ashambu, Nilgiri and Palni hills (Tamil Nadu) and some places in Kerala (Pocock 1941, Prater 1971, Hussain 2000).

In most of their range the Asian small-clawed otter is sympatric with smooth-coated and Eurasian otters. In India, all the three species occur in Western Ghats and in the Northeast India where the species occur in small group of two to four individuals. In Western Ghats they are mostly found along the hill streams. They were once common in the mangroves of east Calcutta and Sunderbans (Sanyal 1991). The Asian small-clawed otters occur in freshwater and peat swamp forests, rice fields, lakes, streams, reservoirs, canals, mangrove and along the coast (Sivasothi and Nor 1994). In Malaysia and Indonesia they occur in coastal wetlands, and along the banks of paddy fields. Comparable data from Java, Myanmar, and India revealed that the Asian small-clawed otters have a high climatic and trophic adaptability in south and Southeast Asian tropics, occurring from coastal wetlands up to mountain streams (Melisch et al., 1996). A reliable population estimate of the Asian small-clawed otter is lacking. As many as 15 individuals were seen in a group in Malaysia (Wayre 1978), four to eight in coastal Sabha (Mason and Macdonald 1986) and two to four in India.


The typical habitats of the Asian small-clawed otter in west Java are wetland systems having pools and stagnant water, including shallow stretches, with depth less than 1 m. These habitats are represented by freshwater swamps, meandering rivers, mangroves and tidal pools. Muller (1839) observed small-clawed otter from slow-flowing lowland streams to submontane streams dominated by rocks and boulders in forested areas. Irrigated rice fields with many crab species (Brachyura) are extensively used by small-clawed otter if proper shelter for them is available. These can act as suitable man made habitats (Melisch et al., 1996). In Thailand, the rapid-flowing upper areas of the Huay Kha Khaeng are dominated by L. lutra, the slowly meandering river near the dam and the dam itself were used by L. perspicillata while the Asian small-clawed otter occurred mostly in the middle sections, but also at the upper reaches. When different otter species occurred in the same site there was evidence of difference in use of the habitats. Signs of the of small-clawed otter were found wandering further away from the river than the two other species, between patches of reeds and river debris where crabs were more likely to be found (Kruuk et al. 1994).

In west Java, its presence is positively correlated with slow flowing and stagnant broad rivers and smaller streams, depicting a distinct decline in preference from slow to deep-water bodies. On the other hand, they also use shallow fast-flowing mountain creeks narrower than 5 m, particularly when the course of the streams includes natural pools. In rice fields, they chose slow-flowing irrigation channels narrower than 2 m and with a varied, moderate or low vegetation structure. Like smooth-coated otter the Asian small-clawed otter dislike bare and open areas that do not offer any shelter (Melisch et al. 1996). It prefers pond areas and rice fields than the rivers, whereas it uses mangroves and lakes in proportion to their availability (Melisch et al. 1996). In riverine systems it prefers moderate and low vegetation structure, though their presence was also observed from banks with poor vegetation cover. Neither in ponds nor in rice field areas did they show preference for any of the vegetation structure categories, though poor nor bare structural conditions were the least favoured both in riverine and pond areas and along the rice fields.

The small-clawed otter is adapted to feed on invertebrates as evident from the last two upper teeth (pm4 and m3) which are larger in size for crushing the exoskeleton of crabs and other hard shelled prey. The small clawed otter feeds mainly on crabs, snails and other molluscs, insects and small fish such as gouramis and catfish (Pocock 1941, Wayre 1978). They supplement their diet with rodents, snakes and amphibians too. 

During a study in Malaysia, Foster-Turly (1992) examined 328 scats and found that around 80.8% of the scats consisted of crabs, 77.8% fish, 12.5% insects and 4.0% snails. This is the first study in which quantitative information on the diet of wild small-clawed otter was made. This study revealed that though the small-clawed otter is adapted for an invertebrate diet it substantiates its diet with large quantity of fish. Apart from crabs, the major prey item for small-clawed otter was the mudskipper (Gobioidei). This was recorded in the 48% of the scats. The other important prey was Trichogaster spp. and Anabantidae fish, which were represented in 27.4% scats. As evident from the scats the major fish prey were Trichogaster spp 20.7%, Anabis testudineus 5.2%, Clarius spp 2.4% and Channa striatus 1.5%. Apart from these the small-clawed otter in Malaysia also fed on snakes, frogs and insects. Foster-Turly (1992) also examined the diet composition at four different times of the year coinciding with different water levels in the rice fields and concluded that the diet of the small-clawed otter was significantly different at different times of the year. Only the relatively rare dietary components of rodents, snails and snakehead fish (Clarius spp.) showed no significant difference among seasons. Crabs were always the most prevalent food items, but the frequency of occurrence in scats varied from 70.4% to 93.2%. Similarly, though the mudskippers were the second most important food items, they were consumed in significantly different amounts in different seasons from a low of 27.3% to 63.6%. The amount of Trichogaster, Anabis and the Anbantidae also varied considerably. This difference in the use of these prey are most likely due to difference in the life cycle and availability of these prey at different times of the year.

Preliminary analysis of the small-clawed otter spraints from west Java showed their preference for crabs in both natural and man-made habitats (Melisch et al. 1996). In 87% of all collected spraints, crabs formed the dominant prey. Remaining part of the spraints consisted of fish bones and scales, ribs and vertebrae, unidentified mammalian hair, shrimps, insects and snake scales.In the Huay Kha Khaeng, Thailand almost 90% of the spraints of small-clawed otter contained remains of crabs Potamon smithianus, whereas 5% scats contained each of Fish and Amphibians. Apart from this, in few scats evidences of rodents and other arthropods were also found. Kruuk et al. (1994) estimated the preference for various size classes of crabs eaten by small-clawed otter. Of the 92 scats, 14 scats had crabs size 10-14 cm, 42 scats had 15-19 cm, 26 had 20-24 cm, 12 had 25-29 cm, 4 had 30-34 and 1 had 40-44 cm. The size distribution of crabs taken by small-clawed otter was similar to what was available, and there was not much evidence for selection of specific size. In west Java a preliminary estimate of preferred size confirmed an average of 3-4 cm carapace width (Melisch et al. 1996). 

The sexual behaviour of small clawed otter has been observed in as young as 18 months old. In captivity, successful breeding has been reported for 2.1 year females and 2.8 year males. The youngest animal to reproduce was a female of 13 months captive born at Bronx Zoo, and the oldest was a 15 years male at the National Zoo, USA (Foster-Turley and Engfer 1988). In the females oestrous cycle has duration of anywhere from 28 to 30 days, with breeding occurring the year round (Lancaster 1975). Some facilities report this cycle extending to ?every few months? with older animals. Oestrus lasts from one to thirteen days. Behavioural signs of the onset of oestrus may include increased rubbing and marking. 

In captivity mating usually takes place in the water, but has also been observed on land on a few occasions. In most cases the exact gestation period could not be ascertained but it is believed to be around 60-86 days (Lancaster 1975, Sobel 1996). The litter size ranges from 2-7. Life span in captivity is around 11 years (Crandall 1964).



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