Maegan Reid, Melissa Dragon, Jodie Calain

 A paper for MSCI 375, Biology of Marine Mammals, submitted December 2, 1998

 The sea otter, Enhydra lutris is adapted to living in the coastal waters of the north Pacific and can spend their whole life at sea, only coming ashore during storms. The sea otters belong to the group of carnivores called the Mustelidae, which also includes weasels, skunks, and badgers. It is one of the smallest species of marine mammals (VanBlaircom and Estes, 1990). They have blunt heads, with short, thick necks. There is no blubber beneath the skin, and they are adept swimmers and divers. They have folded valve-like ears, loose skin with dense fur, and retractable front claws. Their tail is short, straight, and flattened with a rounded tip (Paine and Foott, 1993). Sea otters are the only carnivore that have four incisor teeth in it’s lower jaw, but rely predominantly on molars for crushing shellfish (Sea Otter Information,1998). They eat, sleep, and rest while floating on their backs. There isn’t much time for anything else considering they groom themselves for up to 48% of the daylight hours. They groom by rubbing their fur with their forepaws. Their strong claws combs the fur, and then they roll over into the water to smooth it down (Animal Bytes,1998).

Sea otters have been heavily exploited in the past. In 1741 the Bering expedition survivors returned with sea otter furs. By 1911, hundreds of thousands had been slaughtered for their valuable pelts, and an estimated 500-1000 individuals remained. It was at this point that the Fur Seal Treaty, which included protective legislation for the sea otter, was signed by the United States, Britain, Russia, and Japan. Since then sea otters have made a comeback. In 1986 there was an estimated population of nearly 20,000 in Alaska. Many have also returned, or have been reintroduced to parts of their historic range. This extends from Japan in the west, through the Aleutian Islands, to the coast of the North American mainland, and south to Baja, California (Love, 1990).

Although the Alaskan and Californian sea otters have a lot of similarities, they also have some distinct differences. The biggest physical difference between the Californian and Alaskan sea otter is size. As a whole, they are sexually dimorphic. The males are 34% heavier and 8% longer than the females. On the average Alaskans are quite bigger than the Californians, and have a larger skull. Alaskan males weigh about 85 pounds and are a little more than four and a half feet in length, while California males only weigh about 60 pounds and are a little less than 4 and a half feet long. This same idea applies to the females. Alaskan females weigh about 55 pounds and are slightly greater than 4 feet long. California females weigh considerably less only about 45 pounds and are about 4 feet long. These numbers may change a bit in areas where sea otters are heavily populated in Alaska. In this situation, although they are still bigger than the Californians, many weigh less than them because of competition for food. (Riedman and Estes, 1990)

Alaskan sea otters seem to live slightly longer than the Californians. Alaskan females live between 15 and 20 years, whereas California females live to be 15 or 16 years. Alaskan males live between 10 and 15 years, and California males only live to be 11 or 12 (Riedman and Estes, 1990).

Sea otters participate in a polygynous mating system in which the males hold territories. They form pair bonds with multiple females. They can only give birth to one pup at a time, and twins are rare. In these special cases one pup usually dies because the mom can’t take care of both.

Both Alaskan and Californian otters reach sexual maturity at about the same times. Females reach it usually between the ages of four and five, but some as early as three. Males are not sexually mature until a little later; between five and six years, and do not reach social maturity until they are even a little older; between eight and ten. Sexually mature females can be distinguished by scars on their nose. These scars are the result of the male biting the female’s nose during mating (Riedman, 1990).

The California and Alaskan sea otters also differ in the time in which they breed. Although it occurs throughout the year in both, there are months in which it is very pronounced. These are called peak seasons. Californians give birth annually and their breeding season peaks in January and lasts through March. A second peak occurs from July to October, due to high pup mortality in the winter. This high mortality is predominantly due to harsh weather conditions in the winter months. There are also slight variations to these times, depending on the area of California. As for the Alaskan, who only gives birth about every two years, their peak season occurs from March to May when climate conditions are not as harsh. Few births occur in late fall and winter (Riedman and Estes, 1990).

Sea otters also exhibit what is called delayed implantation. Once a female conceives, implantation and any further development is delayed. It is speculated that this is an adaptation for birth to occur in favorable conditions (Riedman, 1990). This may also be the cause of gestation periods differing between the two. The Californians give birth most often in water, but also do so on land when kelp beds are sparse. Their gestation period is about six months and the newborn pup weighs about 5 pounds. Alaskans give birth on land more often than Californians, and their gestation period is quite longer. It ranges between 10 and 12 months, depending on the age and health of the mom, and the abundance of food. These newborns weigh about the same as Californians, maybe slightly more. Once the females have given birth the pups are dependent on their moms for food. Californians nurse their pups for five to eight months, while Alaskans are dependent on their moms quite a lot longer; at least a year. This is also very dependent on the health of the mom and the abundance of food (Riedman and Estes, 1990).

Looking at what the two groups eat can also tell you a lot about them and their environment. Like humans, sea otters have their favorite foods. If they have over 50 options, for example, each otter will only specialize in two or three of them. Since there are different kinds of food in the waters of Alaska versus those in California, these two groups feed on different kinds of prey. Alaskans feed on a lot of epibenthic fish. This is primarily because of their abundance and scarcity of invertebrates, especially sea urchins. Although they eat both, their main source depends on the area of Alaska in which they live and the relative abundance of species. Californians, however, eat primarily abalone, rock crabs, and large red sea urchins, which all have lots of rich calories. Once their favorite foods become scarce they will eat other prey, such as kelp crabs, clams, mussels, along with some others, and even the occasional sea bird. They also take advantage of some seasonal prey, like the pelagic red crabs, and squid. Again, the types of things they eat is most highly influenced by the environment, even though they do have their favorites (Riedman, 1990).

What is more interesting than what they eat is how they eat it. Californians use a lot of tools to pry open their food, or bang on it like a hammer until it breaks open. They use such things as rocks, old shells, driftwood, crab carcasses, and even glass bottles to dislodge shellfish. Alaskans, on the other hand, are not as crafty as the Californians when it comes to tool use. It is not because they are not able to, but because they don’t really have to. For one they eat a lot of fish, and any shellfish they do eat, their shells are soft enough that they can break through with their teeth (Riedman and Estes).

Rather than looking at what they eat, you also have to take into consideration who eats them. Since Alaskans and Californians live in different areas, you would think that they have different predators. Well, they do! Great White sharks are responsible for 10% to 15% of California sea otter deaths each year, and Alaskans have others to worry about such as coyotes, bald eagles (eat pups), and brown bears (Riedman, 1990). The killer whale is also a new predator recently added to their list. Although killer whales do not normally feed on sea otters, the recent decline of the stellar sea lions and harbor seals, their usual prey, has caused them to turn to sea otters for food (Estes and others, 1998).

Other causes of mortality other than predators are pathological diseases which include enteritis, the inflammation of the intestinal tract. Enteritis is associated with other diseases, poisoning and various types of stress. Pneumonia, infection of nasal wounds inflicted during mating, and injuries in males caused from fighting are also causes of death. Environmental influences such as starvation, harsh weather conditions during the winter season, and paralytic shellfish poisoning (PSP) caused by blooms of toxic dinoflagellates also have an effect on mortality.

Human interaction is responsible for some sea otter deaths such as drownings in commercial set nets, shooting incidents and oil spills. Oil spills that have occurred along the Alaskan coastline were reported to have fouled the sea otters’ fur causing insulation loss and loss of buoyancy. Studies have shown that partial oil contamination of fur equal to 30% of total body surface results in death. Oil spills also cause a loss of habitat, food resources, and pathological abnormalities and disorders due to oil consumption. No oil spills have occurred along the Californian coastline, but it is assumed that the same effects would result among the Californian sea otter population.

Sea otters usually inhabit areas with rocky substrates between shoreline and the outer limits of the kelp canopy which generally corresponds to a 18m depth contour. In areas of Alaska, water shallow enough for sea otter foraging may extend many miles offshore. Kelp canopies in Alaska are formed entirely by Alaria fistulosa. In California sea otters are occasionally found at the 36m depth curve, but rarely are found many miles offshore. In California rocky bottom substrates normally support average population densities of 5 sea otters per km and sandy bottoms support .8 sea otters per km. California sea otters prefer Giant kelp communities (Macrocystis pyrifera) as opposed to Bull kelp (Nereocystis leutkeana). The record dive depth for sea otters was made by an Alaskan sea otter off the Aleutian Islands where the sea otter was found, drowned in a King Crab pot at 100m depth.

Sea otters have a strong influence on the ecology of kelp forests. Many species of fish occur at higher densities in kelp habitats than in sea urchin barrens. These fish constitute an important element of the Alaskan sea otters’ diet, as do invertebrates when available. When urchins are abundant, the sea otters eat them therefore increasing the kelp community and fish diversity. When urchins are scarce there is still a strong kelp community and fish become the dominant prey item. Californian sea otters feed primarily on invertebrates including sea urchins which feed on kelp. The urchin population is controlled by sea otter predation which increases the kelp community.

Haulout sites are characterized by low relief algae covered rocks exposed at lowtide. Sand and cobble beaches are also sites for hauling out. Females haulout frequently during their estrus period. Frequency of haulout in both males and females varies among individuals. Californian sea otters do not haulout as frequently or as in large groups as do Alaskan sea otters.

Both Alaskan and Californian sea otters have specialized glands that secrete oil and enhance the water repellent quality of the fur. Also both sea otters lack erector pili muscles in the epidermis allowing the hair the lie flat and close to the skin when immersed in water. Molting occurs gradually throughout the year although peak periods for Alaskan sea otters occurs in the spring. Vigorous grooming bouts occur before and after feeding and rest periods.

Communication and interaction between sea otters is similar in both Alaskan and Californian sea otters. Scent, physical contact by nosing, nuzzling and head jerking, and distinct vocalizations between mothers and their pups facilitate recognition between sea otter individuals. Sea otters have 8 types of vocalizations: the baby cry, scream, whistle or whine (from distress or frustration), coo and grunt (from satisfaction in grooming and feeding), snarl or growl (when captured), and hiss and bark (when frightened or frustrated) (Reidman and Estes, 1990).

After looking over the comparisons and contrasts between the two, we need to conclude with whether or not an Alaskan sea otter would fit in in California. We feel that it would fit in California because many of the differences are behavioral and these are influenced mainly by their environments. For example; Alaskan sea otters haul out on land more often than Californians. In warmer climate conditions, they would not have to do so. Although it is difficult to transplant the otters, once it got there, we feel it will be able to adapt to the differences.

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