Sea otter Enhydra lutra

In the 1980s, along many of the magically beautiful coasts of north-east Asia, Alaska and British Columbia, and along the much busier shores as far south as California, sea otters were a common occurrence once more. At any time of day, right inshore or often far out at sea, one might come across a mother otter afloat on her back, carrying a cub on her chest, sometimes leaving it briefly on the surface while she dived deep, deep down, perhaps some 40 metres to

Figure 2.5 Sea otter in California. Note thick, dense fur. © Jane Vargas.

the bottom. Now, early in the twenty-first century, the animals face serious problems again.

Sea otters are very different from all the other otters, and spectacular in many ways. Recognized as such by many scientists, they are also studied more extensively than any of the others, and there is a large amount of information about them.

To mention a few of the unique points of the sea otters that excite researchers: they are more aquatic even than seals, not necessarily coming ashore, usually even giving birth in water. They drink sea water, dive to great depths, use tools to access their food, mothers carry their pup on their belly whilst floating on the surface, they may aggregate in huge 'rafts' of several hundred animals, and their shaggy, extremely dense, fur is quite different from that of any other otter. The abundant twentieth-century populations have a substantial effect on their marine environment and on the human use of resources therein. Recently, however, a dramatic decline set in.

Sea otters are larger than other otters, average adult males and females weighing 29 and 20 kg respectively (the largest male recorded was 42 kg), with mean total lengths of 129 and 120 cm. They are the largest existing members of the mustelid family. Their tail is short, less than one-third of body length, the hind feet are proper flippers, whereas the front feet have sharp, partly retractable, claws not found as such in any other otter. The teeth are blunt, with large flattened molars (for crunching molluscs). The extremely thick fur gives the animals a rather grizzled appearance.

Active in daytime and spending almost all of their life out at sea, mostly floating belly-up on the surface, the animals are very vulnerable to human exploitation—and exploited they have been. The original geographical range is along coasts of the northern Pacific Ocean, from Mexico to Japan; it is somewhat smaller now (Fig. 2.6). After they were 'discovered' and from about 1780 onwards, they were 'harvested' until, in about 1820, they were more or less gone. At the beginning of the twentieth century only about 1000 to 2000 sea otters remained in their entirely vast range of coast, in small pockets here and there, with little hope for their survival.

South of Alaska there was only one remnant population, in central California.

Sea otters belong to a species that has influenced history more than any of the other otters. Their fur was reputed to be the best of all animals, and over a fairly short time in the eighteenth century a vast trade built up along the American north-west shores, motivated by large profits from the one species. Hundreds of thousands of otters were slaughtered by Indians, and sold to British and American trading ships. These then progressed to Canton to sell the furs at vast gain in China. The Indian tribes, in the meantime, were betrayed and harassed, persecuted and literally decimated by smallpox, syphilis and tuberculosis brought in by the sailors. Sea otters were driven almost to extinction in the course of just a few decades.

After an effective alarm was raised, legal protection took hold in 1911, and the sea otter population expanded again immediately, in many places at a rate of around 20% per year. In the 1990s it was estimated that sea otters were back again in numbers of approximately 50,000. At the end of the century numbers were falling again, with good evidence that this was caused by a large increase in predation on the otters by killer whales.

Sea otters do not go into fresh water, nor do they go much into oceanic depths further than about 30 metres (although dives of about 100 metres have been recorded). They are often in and around kelp beds, where they sleep and forage. Rocky coasts are their favourites, especially where there are large underwater reefs, and they may haul out on land on rocky points, staying close to the shore. However, they do not wash in freshwater pools, as other otters do where they live in the sea, nor do they have to rely on fresh water for

Figure 2.6 Geographical range of the sea otter: along coasts from north of Japan to Baja, California.

drinking: sea water will do. Perhaps to make up for the fact that sea otters live without access to fresh water for washing, they spend an inordinate amount of time grooming whilst afloat in the sea, even blowing bubbles into their fur to retain insulation.

Feeding behaviour is unusual, and has profound implications for the environment. Their diet consists mostly of sea urchins, crabs and large molluscs such as abalones and clams, and fish, but it varies hugely between regions, with availability of the different foods strongly affected by the sea otter itself. For instance, sea otters have decimated populations of sea urchins in places, which in turn had the effect of inducing the growth of large kelp beds (sea urchins can remove these completely), followed by further changes in prey populations (see Chapter 8). Interestingly, some shellfish appear to be protected against sea otter predation by toxins from algal blooms, and there is evidence that sea otters avoid such areas.

Clams and abalones are carried several at a time in the otter's armpit, often from great depths to the surface, opened and consumed whilst the predator is floating belly-up. To open shells, the animals often use a tool, a small rock, which is also carried up from the ocean floor in the armpit. Even a long way away one can hear the shells being bashed by the otters.

Dive times of sea otters can be up to 4 minutes (average 74 seconds). Because of the large amount of heat loss from the body in this environment, their rate of heat production is two to three times higher than that of land mammals of similar size, and food consumption is correspondingly high at 20-30% of bodyweight per day (some 5-6 kg per day for an average otter).

Sea otters are usually alone, but they may be very gregarious, especially males; amazingly, the largest group ('raft') reported contained about 2000 animals. Sometimes females form 'nursery groups' of mothers and pups, of more than 100 otters. These groups have a very fluid composition with otters coming and going, but clearly the animals are highly social at times, even to the extent of actively defending one another against predators, or against people trying to capture them. The animals are quite vocal, with many different and loud calls. With their kind of lifestyle, scent communication is out of order, and, although I found their faeces at haul-out sites, they are probably not left as scent marks, as 'spraints'—they are mere eliminations.

Males and females live in more or less separate areas and groupings, but some solitary males defend territories, in areas with rafts of females, and they attempt to herd females to keep them in their area. Females take a long time to become sexually mature, some 4-5 years, then have a gestation period that varies in length from 4 to 12 months (because of delayed implantation). The animals copulate in the water, and occasionally the mating process is so vigorous that the female drowns, or gets badly injured as the male bites her face.

Once the single pup has been born (often in water, rarely on land), the length of time that the mother looks after it is also highly variable, from 4 to 9 months in California (where they feed mostly on shellfish and crabs) to well over a year in Alaska (significantly, in some areas feeding mostly on fish there). The mother is in constant attendance of the pup, carrying it on her belly, vigorously defending it against all comers, but she has to abandon it when diving for food. That is the time when some ofthe pups are taken by bald eagles. Orphaned pups are sometimes adopted by other otters, even by males.

At times, sea otter populations showed significant mortality rates from oil pollution, drowning in nets, and starvation. In California, disease has caused long-term declines. However, all of these changes are small compared with the more recent disaster that has overtaken their populations in Alaska, with killer whales causing a reduction in places of more than 90%. It is difficult to be optimistic about the fate of these wonderful animals.

General references for sea otters

Estes 2002; Gibson 1992; Kenyon 1969; Riedman and Estes 1990; VanBlaricom and Estes 1988.

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