Sea Otter
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| Enhydra lutris (Linnaeus, 1758) |
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 Modern and historical range
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The Sea Otter (Enhydra lutris) is a large otter native to the North Pacific, from northern Japan and Kamchatka east across the Aleutian Islands south to California. The heaviest of the otters, Sea Otters are the only species within the genus Enhydra.
Hunted extensively for their luxurious fur—the densest of all mammals with up to 394,000 hairs per square centimeter— from 1741 onwards, sea otter populations were greatly reduced to the point of extermination in many parts of their historic range. By 1911 the world population was estimated to be just 1,000-2,000 individuals. Although several subspecies are still endangered, the otters have since been legally protected, and reintroduction efforts have shown positive results.
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[edit] Physical description
With long, streamlined bodies, Sea Otters are built for life at sea. Exceptionally dense brown fur insulates the animal and retains air, creating an effective barrier between the water and the skin; this is important, as the otters lack insulating fat. Underneath each powerful front flipper is a pouch of skin used to temporarily store food collected during extended dives to the bottom. The front flippers also have retractile claws, while the hind flippers are longer, broadly flattened and webbed. They have a fairly short, thick, muscular tail.
Sea Otters have compact molars with smooth cusps; they are the only carnivores with no more than four lower incisors. Male sea otters may reach a maximum weight of 45 kilograms (nearly 100 pounds) and a length of up to 1.5 metres (nearly 5 feet). Females are smaller.
[edit] Habitat and diet
Generally sticking to shallow coastal waters of no more than about 55 metres in depth, Sea Otters are found most often in areas with rocky coastline and thick kelp forests; barrier reefs and intertidal areas are also inhabited. These otters may be considered a keystone species — they control the population of certain invertebrates which would otherwise run amok if unchecked. Chief among these invertebrates are sea urchins and abalone, a favourite prey of the otters. To eat prey in shells they often use rocks, which sit on their stomach, to break open the shell in order to get the creature inside.
Crabs, mussels, scallops, cephalopods, fish, chiton and snails are also prey to the Sea Otter. Individuals may show finicky preferences; despite this, they require 20-25% of their body weight in food each day.
Otters are taught feeding practices by their mothers, and groups of otters often show matrilineal differences in food preferences. Some lineages of otters are noted for their preference for gulls or sand crabs as food sources.
The otters themselves are threatened mostly by humans, sharks and Orcas.
Otters frequently eat while floating on the surface of the water. Otters like to relax and groom themselves this way after a hunt, and also use this method to fill up their fur with warm air bubbles for insulation.
[edit] Behavior and reproduction
Sea Otters may be either solitary or in groups called rafts when resting and cling to kelp so they do not float away while they are taking a nap. Females avoid males outside of breeding periods. Conflicting data regarding home range and migration of Sea Otters suggests their movements are dependent on availability of resources. Home ranges may be as large as 5.4 square kilometres, with most animals travelling found within 1-2 kilometres of the previous day's location.
Diurnal animals, most of a Sea Otter's day is taken up by foraging and grooming. Feeding activity peaks in the early morning and evening (crepuscular feeding); dives are fairly short, typically lasting no more than about 90 seconds. The otters wrap themselves in mats of kelp, securing them from the sway of currents while resting and feeding. Floating on their backs, the otters wash and (if necessary) pry open their prey with a favoured rock they keep in their pouch. Sea Otters present a rare example of mammalian tool use.
No set breeding season is observed, but peaks occur from May to June in northern populations and January to March in southern populations. Sea Otters are polygynous: that is, males have multiple female partners. Bonding does occur between the sexes during the female's estrus, which lasts all of three days. During these periods males will defend their territories; there is very rarely actual fighting involved, with most disputes being settled by raucous posturing. Females have characteristic scars on the nose from the males' habit of holding the former's muzzle in their jaws during copulation.
Courtship between otters is very playful. When males and females are courting they swim and dive together, with the male twisting and doing corkscrews in the water to let the female know he is interested. The male will also swim facedown and they will swim more quickly than they would usually. Mating is said to be rough, the male biting the female on the side of the face or on the muzzle.
Gestation is approximately 218 days, although it can be prolonged from several days to several months if the fertilized egg does not immediately imbed itself in the uterine wall. During this suspension period, the egg remains unmoving. This may occur because the stormy tendencies of seas may disrupt the implantation. Gestation usually ends in a single birth; twins are a rarity, and usually only one of them survives. Pups are born weighing up to 2.3 kilograms; they are able to eat solids very soon after birth. The brownish yellow pups are cared for exclusively by the mother whom they are dependent upon for six months or more. The mother is responsible for teaching the pups how to hunt, dive, and groom effectively.
[edit] The Great Hunt
In the 1600s to the 1700s, Russia was heavily involved in the sable fur trade. Peter the Great declared that Russia should have the monopoly in sable furs, and that they should find new populations of sable to hunt. The Russians conquered Kamchatka, in the eastern edge of Russia, where they could harvest sable and sea otter fur. The Russians continued to explore the north Pacific, looking for sea routes to Japan and America. Vitus Bering and Alexi I. Chirikov, two Navy officers, were given the task of mapping the Arctic coast and finding a way to America. Chirikov managed to return to Kamchatka in 1741, after much difficulty. Bering's sailors suffered from scurvy, and were marooned on Bering Island, in the Commander Islands, where Bering died. There, the surviving crew spent the winter hunting sea otters and gambling with otter pelts. They finally returned home in 1742 with 900 sea otter pelts, enough to pay for the entire expedition. It was Bering's expedition that set off the Great Hunt that was to continue for another hundred years.
The Russians sent many ships to harvest otter furs, and soon depleted all of the otter populations in the Commander Islands. They moved on to the Aleutian Islands, which were already inhabited by the Aleuts. Since the Aleuts could not repel the Russians, the Russians did everything they could to get their hands on otter fur, even taking hostages and forcing the islanders to hunt for them. It wasn't only otters that were hunted; the Russians wiped out the local fox population, along with the Aleuts. It wasn't until 1776, when Captain James Cook reached the north Pacific that other nations joined in the hunt. Captain Cook was killed in Hawaii by natives, but his crew sailed on to the lively trading port of Guangzhou in China, where they found merchants offering outrageous amounts of money for even the smallest scrap of otter fur. The sailors almost mutinied in their desire to return for more otters. It was then that the English discovered the value of these skins.
The Great Hunt continued, with Russians, Americans, and other Europeans competing amongst each other for that prized commodity. The Alaskas were almost completely depleted of sea otters, causing the Russians to sell it to the United States in 1867. Now, the sea otters were being slaughtered by the Americans. It wasn't until 1911 that an international treaty was signed to stop the hunting of sea otters. So few otters remained, some estimate only 1,000-2,000 in the wild, that many assumed they would become extinct. In 1938, biologists found a group of sea otters along the coast south of Carmel, California. This group and other surviving groups would form the nucleus for the restoration of the sea otters.
[edit] Oil spills
Even though otters are no longer at risk because of hunters, oil threats are increased. Otters rely on their fur for heat, and oil spill cause their air pockets to break. This can cause hypothermia and even death. Also, because of otters' constant grooming habits, if they ingest this oil, they can receive damage to the liver, kidneys, eyes, and other organs. Main causes for oil spills are tankers, and the waste that is thrown out after cleaning them.
[edit] References
- Estes (2000). Enhydra lutris. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 11 May 2006. Database entry includes justification for why this species is endangered
- Enhydra lutris (TSN 180547). Integrated Taxonomic Information System. Accessed on 18 March 2006.
[edit] External links
- Animal Diversity Web: Enhydra lutris
- OceanInfo: Sea otters
- CNN: Alaskan Sea Otter population falls 70% in eight years
- The Otter Project
- Save The Otters
