Sea otters are the smallest marine mammals; they are furry creatures that spend almost all of their lives in the ocean. Although they resemble small seals, sea otters are not related to seals. They are actually related to weasels, badgers, and minks. They belong to the family "Mustelidae" and the species "Enhydra lutris," from the Greek "en hydra," meaning "in the water," and the Latin "lutris," meaning otter. There are three subspecies of the sea otter: the southern sea otter (Enhydra lutris nereis), the Alaskan sea otter (Enhydra lutris lutris), and the Asian sea otter (Enhydra lutris gracilis). The main difference between the three subspecies is the shape of the skull and the size of the otter (Alaskan otters tend to be larger). There are also other types of otters, such as the river otter, but sea otters are distinctly different from other otters. They are adapted to living their entire lives in the water, whereas other otters live on land and merely hunt in water.
Unlike other marine mammals, such as seals and dolphins, sea otters do not rely on a layer of fat to insulate their bodies from the cold water. Instead, they have a thick fur which keeps them warm. Adult sea otters average about 1.3 meters (4 feet) in length and about 20-45 kilograms (45-100 pounds) in weight. Their normal position, when in the ocean, is floating on their backs with their paws sticking up out of the water. They do this to conserve heat (since their paws aren't covered with fur). When an otter sleeps, it will generally wrap itself in kelp, in order to keep itself from drifting away.
Sea otters can be found in the Pacific Ocean along the coast of California, up to Alaska, along the eastern coast of Russia (what used to be called Russia), and all the way to northern tip of Japan. They live only in a narrow band of coastal waters, never straying into the deep ocean, except in rare instances when they might travel between islands and mainland. Kelp beds are a favored habitat of the sea otter. In fact, sea otters help create kelp beds, by eating urchins and other kelp-eating animals.
Otters are usually found congregated together into groups called "rafts". Male otters form separate rafts from female otters. Not all otters live in rafts. For instance, some male otters are territorial and will stake out regions for themselves apart from other males. A raft of sea otters can vary in size from tens of otters (typical around California) to hundreds of otters (in Alaska). The largest raft ever spotted was two thousand otters, in Bristol Bay, Alaska. The main purpose of forming rafts seems to be socialization. Sea otters do not need numbers to protect themselves from enemies, nor do they need to band together to hunt prey. But they do seem to have a need to socialize with other otters.
The best place to view sea otters in California is at Monterey Bay. There are hundreds of sea otters around that area, many easily visible from the shore. For a closer look, you can rent a kayak, although you are prohibited from approaching within 50 feet of an otter. One otter named Josephine blatantly ignores this restriction and has been known to jump into a kayak, no doubt creating some interesting moments for the startled kayaker. Josephine has also been known to push harbor seals out of her way when she wants to rest on a particular rock. A very un-otterlike behavior!
There used to be hundreds of thousands of sea otters ranging all along the coast, from Baja California to Hokkaido, Japan. Unfortunately, due to their luxurious fur, they were viciously hunted in the 18th and 19th centuries. In 1911, laws were passed which protected otters, but the devastation had already been done. Only thirteen colonies of sea otters survived in sporadic locations along the original range.
It was once thought that the southern sea otter (of California) had become extinct from the fur trade. But luckily, a small group of otters survived near Big Sur. This single group was responsible for the repopulation of otters in California. There are now roughly 2,000 sea otters living in a 250 mile range along the central coast. This represents only a tenth of the original population of 20,000. The 250 mile range represents only a tiny portion of the original range, which used to extend from Canada to Baja California. For an unknown reason, the current population of the southern sea otter has been growing very slowly at a rate of only 5% a year. There is an ongoing effort to relocate otters to areas they once populated (such as Oregon and Washington), but so far success has been limited.
The Alaskan sea otter has fared much better. There may be as many as 150,000 sea otters living in Alaska today. In recent times, the population has been growing by as much as 20% a year. Even in Alaska, though, the sea otter has not fully reoccupied its former range, and it seems that it will take quite a few decades before otters will migrate and repopulate the unoccupied areas.
The sea otter is now a protected species, and it is illegal to even harass a sea otter, much less kill one. Sadly though, even today some sea otters are found shot, and others are killed by boaters who drive speed boats through their territories (sometimes intentionally!). There is also pressure from the shellfish and urchin industries to limit the range of the sea otter. Ironically, these industries only exist because the hunting of the otter allowed shellfish and urchin populations to grow in areas where they had never grown before. Now, these industries blame the otter for eating their harvest, as if this were a new "threat," rather than the natural ecological balance. After all, otters have been living in these waters for thousands of years and should have the right to return to their former territories. Indeed, otters may do more good than harm, by promoting the growth of kelp beds. Not only do kelp beds provide shelter for multitudes of marine life, but kelp itself can be harvested and used. The kelp industry in California is a multi-million dollar industry, and it surely benefits from the repopulation of the sea otter.
Sea otters depend on their fur to keep warm. Their fur is the densest fur of all the animals. There may be up to 1 million hairs per square inch (150,000/cm2). That's more hairs than you have on your entire body! But even with such thick fur, it takes an effort to keep the otter warm. The sea otter spends hours each day grooming its fur. The otter needs to squeeze any water out, and to blow air into the fur. The air makes the fur waterproof, so that the otter's skin can stay dry and warm. Cleaning is also essential. Dirty fur can get wet easily and put the otter in danger of dying from the cold. In fact, early attempts to relocate otters failed because the otters' fur became dirty while being transported. After being released, many otters quickly died from the cold, and the others had to be retrieved before they too died.
In addition to thick fur, sea otters have another defense against the cold, ocean waters. The otter has a high body temperature (around 38 C or 100 F) which requires a fast metabolism. As a result, otters need to eat a lot. They may eat up to 25% of their body weight each day. This is the equivalent of a human eating about 100 hamburgers!
One major threat to the sea otter is an oil spill. When an otter becomes covered with oil, the oil destroys the insulating properties of the fur. A soiled otter will quickly die of cold, and even if it manages to lick the oil off, it will be sick from poisoning. About the only thing that can be done after an oil spill is for humans to rescue the otters and wash the oil off. The Exxon Valdez disaster in Alaska killed thousands of otters. Even heroic attempts by volunteers to save the otters failed to prevent the massive death toll.
Experts worry that an oil spill in California may wipe out the southern sea otter. Because of this, there is now a program to preserve the otter at San Nicolas Island (a small island about 70 miles west of Los Angeles, south of the otter's current range). Attempts have been made to relocate some otters to the island in order to start a new colony there. Of 137 otters relocated there, only about 14 otters remain. Several otters swam all the way back to the mainland. Others did not survive the unusually harsh storms which hit in the first few years. Many simply disappeared, and their fates are unknown.
The Friends of the Sea Otter has also produced a sea otter rescue video, from their experience with the Exxon Valdez disaster. They have trained volunteers who will be ready to assist in the event of an oil spill.
Otters eat a variety of foods, including shellfish, sea urchins, fish, and many different types of invertebrate sea life. Interestingly, individual otters seem to have distinct food preferences. One otter may eat only sea urchins, while another might eat only crabs and abalone. Otters spend a lot of time diving for food, as they must constantly eat to survive. Otters can dive to hundreds of feet for several minutes. However, they prefer to stay in shallower waters and make quicker dives instead.
Capturing their prey is not always an easy task. Although some prey need simply to be found and gathered, other prey, such as abalones, cling fiercely to rocks. Still others, such as clams, hide themselves under the ocean floor. The otter, a highly intelligent animal, is nevertheless capable of finding ways to capture these hard-to-get prey.
Smaller shellfish clinging to rocks can be pried off by the otters' strong arms. The otter is quite strong and could probably win an arm wrestling contest with a human. Yet even this strength is not enough to defeat the larger abalone, which clings fiercely to rocks. Humans diving for abalone need to use a crowbar to pry off this stubborn shellfish. Otters, not to be outdone, use rocks as hammers to knock off the abalone. Several good strikes from the side are required to dislodge the victim. Often, an otter will dive repeatedly to work on a single abalone.
Underground food, such as clams, can be obtained by digging. Otters can dig with their forepaws, like dogs, and they will sometimes use rocks to help dig as well. The otters' sensitive whiskers are used to help feel around for food. With the combination of whiskers and paws, the otter seems to have no problem finding and gathering clams in the cloudy waters. Otters have a little pouch under their left armpit in which they can store things like rocks and food while are swimming. Actually they have a pouch under each armpit, but they seem to be right-handed, so they tend to use the left armpit to store things.
Once the otter has found its food, it brings it to the surface to eat. But not all foods can be eaten right away. Although the otter has strong teeth which can bite through crab shells and some shellfish, other prey such as abalones have to be cracked open first. Individual otters seem to have preferences as to which method they choose accomplish the task. Some otters will place a big rock on their chest like an anvil, and then smash their prey on the rock until the shell breaks open. Other otters will reverse this and place their prey on their chest and smash the rock against it. Some otters will use several short, quick strikes; other otters will use a few strong blows. One otter was spotted carrying around its "favorite rock," which it used for twelve consecutive dives. Another otter used six different rocks to open forty-four mussels. Alaskan otters do not use rocks as the southern sea otters do, probably because the shellfish there have much thinner shells. But research has shown that Alaskan otters are capable of using rocks, if they are required to.
Another curious behavior of the otter is its sense of tidiness when it is eating. Often as an otter is eating, it will roll over in the water to clear its chest of any waste scraps. After all, one can't get one's fur dirty! Seagulls and fish often gather around a feasting otter in order to get at the scraps left behind.
Otters are very resourceful and intelligent. They are the only mammals other than primates to use tools. In addition to using tools, otters display a remarkable ability to adapt to the environment. For example, sea otters have discovered that discarded aluminum cans on the sea floor often contain small octopuses. One otter was observed gathering eight cans in fifteen minutes, with five cans being occupied by unfortunate octopuses. Another otter acquired a taste for sea birds. This otter developed a technique for sneaking up on birds from underwater and catching them by their legs. Other otters nearby were later spotted capturing birds as well, suggesting that otters learn food gathering techniques from each other.
Some otters (usually male) steal food from other otters (usually female), saving themselves the work of gathering the food themselves. While I wouldn't quite characterize this behavior as intelligent (rather lazy and greedy in fact), one stealing technique is particularly interesting. A male otter will wait for a mother with a pup to dive for food. The male will then "kidnap" the pup, and wait for the mother to surface. The pup is released only after the mother hands over her food. It is unlikely that the male will actually harm the pup, but this "hostage technique" seems to work nonetheless.
The resourcefulness of the otter is one of the reasons that the otter manages to survive so well in an ever-changing ocean environment. Unfortunately, the greatest threat to the sea otter comes not from the natural environment, but from mankind. We have already once put the sea otter on the verge of extinction, and today we must maintain a constant vigilance, lest an oil spill or other man-made disaster threaten the species again.
There are only a few animals that prey on sea otters, the main two being bald eagles and sharks.
In certain parts of Russia and Alaska, bald eagles will eat otter pups, whom they snatch from the surface when their mothers dive for food. In one study, it was found that about 10% of the otter pups in a certain region were being killed by bald eagles. However, eagles never attack adult otters, though they may occasionally steal food from them.
Great white sharks attack otters occasionally, but probably only because they mistake them for seals. The thin furry otter is not as good a meal as the large blubbery seal. Some evidence indicates that sharks may toss aside otters after discovering their mistaken identities. For instance, although otters with shark bite scars are quite common, to date no one has ever found an otter in the belly of a shark. In California, great white sharks seem to be responsible for about 10-15% of the otters that die each year.
Other predators include killer whales, coyotes, and bears. Killer whales generally ignore sea otters, and like sharks they probably only attack when mistaking an otter for a seal. Coyotes in Alaska will catch young sea otters if they haul out onto land. Brown bears in Russia will similarly attack hauled-out otters, especially at the end of winter when the bears are hungry from hibernation and the otters are weakened by the winter storms.
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