Sea Otter and Nearshore Community
When the Russian fur traders and the Aleut hunters they had enslaved sailed to southeast Alaska in the late 1700s, this part of the Pacific coast was home to tens of thousands of sea otters. By the mid 1800s there were none. The species was hunted from an estimated population of 150,000 to 300,000 sea otters to numbers so few that people thought they were extinct. This harvest had taken place (with help from the Americans in the south) throughout the otter's range, from northern Japan and the Kuril and Aleutian Islands in the west, all along the Pacific coast to Baja California in the south. The object of all this harvest was the pelt of the sea otter.
The sea otter's fur is the densest of any mammal, twice as dense as the next most densely furred mammal, the fur seal, and it became extremely valuable in trade with China, where it was known as "warm gold". Long guard hairs cover and keep dry a dense underfur that traps an insulating layer of air. This warm, waterproof coat is one of the many adaptations of the otter that enable them to live their whole lives, from birth to death, in the sea, and the reason they were hunted almost to extinction.
Sea otters, Enhydra lutris, are members of the Mustelid family, the family that also has as members the river otter, the weasels, the mink, the marten and the wolverine. Sea otters, which are true marine mammals, are sometimes confused with their more terrestrial cousins, the river otter, which in coastal areas such as southeast Alaska spend a lot of time feeding in and along the sea. River otters and sea otters are close to the same length, around 120 cm. (47 inches) but sea otters are much heavier. At 20 to 40 kilograms (44 to 88 lbs.), they weigh three to four times as much as a river otter. Sea otters have developed long webbed flippers on their hind feet, making them powerful and graceful swimmers and slow, clumsy walkers. The sea otter has a lung capacity almost three times that of a terrestrial animal the same size, making them much more buoyant when eating and resting at the surface and giving them a greater oxygen capacity for diving. They also don't have to drink fresh water or come on land to mate or give birth.
Otters can mate at any time of year, but most otters give birth to one pup in the spring after a 6 month gestation, and the mother spends another 6 months raising the pup. The young otters are then on their own. In areas like southeast Alaska where new territory is available, groups of young males will usually leave to explore and move into new areas. The male otter will stay among the bachelors until he is ready to mate and defend a territory. Young females usually reach sexual maturity at age two or three and have their first pup when they're three or four. When prey is abundant and environmental conditions are good, young females can have a pup every year. This may explain why otters are able to increase their numbers so quickly in newly colonized areas with abundant food resources, such as southeast Alaska.
Sea otters are efficient predators, eating almost any invertebrate or fish they can find and catch. They must be efficient, for they need to eat the equivalent of almost 20% of their body weight in a day. In areas with rocky bottoms the preferred species are sea urchins and abalone. In areas with softer bottoms they eat clams and crabs. Biologists are unsure of how deep they are capable of diving but they are known to dive to greater than 300 feet and are able to stay down for up to five minutes.
To search for its prey on the sea floor or within the kelp beds, the otter uses not only its eyes but its dexterous front paws and the sensitive whiskers on its face. In the dim light of the sea floor they must quickly dig out with their mitt-like paws the clams in the soft bottom, or feel along cracks in the rocks and under kelp for chitons or abalone, before they run out of air and have to return to the surface. If they find something that's hard to get open, as is the case with many of their prey, they may bring a rock with them to the surface, hold it on their bellies as they float on their backs, and use the rock as an anvil upon which to break open the clam or sea urchin.
Concern for the near-extinct sea otter was finally shown in the early 1900s. Legislation banning the killing of sea otters and the sale of their pelts was signed in 1911. Searching along the Pacific coast, people later found that a few sea otters had survived. Thirteen remnant populations numbering less than 2,000 otters were scattered along the original range, most of them in the isolated Kuril, Commander, and Aleutian Islands of the north Pacific. Some of those populations dwindled and died out, but others grew and thrived. It was from such a population on Amchitka Island in the Aleutians that 412 otters were relocated to Southeast Alaska in the late 1960s. Many of those transplants survived and spread. It is now thought that the whole outer coast of southeast Alaska, from Yakutat to Dixon Entrance, has sea otters. In the early 1990s otters began moving into inside waters such as Icy Straits, and the mid-1990s saw the first sea otters in Glacier Bay.
It is with great interest and some concern that biologists, fisheries managers and commercial shellfish harvesters watch this recolonization of the Glacier Bay area, for it is far from the simple addition of the sea otter to the near shore community. The otter has a profound effect on its environment. Because the Glacier Bay area had been studied intensively for many years before the otters were relocated, biologists have the chance to watch the process and see the changes that follow the otters.
Several studies were done in the shallow rocky subtidal on the outer coast of Glacier Bay in the 1970s, before the otters had moved into the area. One study showed that invertebrate herbivores, mainly sea urchins, were consuming most of the macroscopic algae, and seemed to be preventing the development of large kelp beds and the organisms associated with them. When urchins were removed and kept out of an area, a diverse and productive kelp forest developed within a year. On that site during the second year after urchin removal, the perennial kelp species Laminaria groenlandica became dominant. On deeper sites, or on sites with an unstable substrate, the bull kelp Nereocystis took over during the second year. Not only do these kelp forests provide a stable and diverse habitat for many species of fish and invertebrates but they dampen wave action and protect intertidal communities from storm damage. A substantial quantity of the organic matter produced by the kelp bed ends up as detritus and dissolved organic nutrients, which is likely to disperse widely and support organisms throughout the community and beyond.
In the years following these studies, transplanted sea otters began recolonizing the area. Observers found that otters became established, increased in numbers, and very quickly decimated the urchin population. Within three years dense stands of Nereocystis and Laminaria had replaced all but the smallest and best hidden of the urchin beds. Once otters had eaten all of this abundant and easily caught prey they moved on to another unexploited piece of coast or switched to hunting other species. Many of the otters moved along the coast; those who stayed began eating more bivalves and chitons while keeping the urchin population low enough to maintain the kelp forest.
In the spring of 1996 researchers in Glacier Bay found that the colonization of Glacier Bay by sea otters had changed from a few small groups at the mouth of the bay and the Beardslee Islands at the lower end of the bay, to the northern Beardslee Islands and the Marble Islands in the mid-bay. A group of 87 otters was seen off the Marble Islands and it is assumed that others were missed. In Prince William Sound, sea otters are seen living up very near the glacier fronts and on this basis it is thought they may eventually utilize all of Glacier Bay. The 1996 observers identified 23 different prey species being taken by otter. A large percentage of those were horse mussels, butter clams, tanner crab, and green sea urchins.
The recolonization of southeast Alaska by sea otters is certainly a success story for the species not everyone is celebrating that success. One of the first of the shellfish industries to fall prey to the sea otter's appetite was the red urchin fishery on the outer coast of southeast Alaska. The urchin roe is considered a delicacy in Japan where it commands a very high price. Red Urchins, Strongylocentrotus franciscanus, are one of three species of urchins found in southeast Alaska waters. They prefer the wave-beaten outer coast, and waters with strong currents. Urchins are herbivores, grazing in rocky areas on macroscopic algae. They are classified as echinoderms ("spiny skin"), related to the starfish and sea cucumbers. The urchin has hundreds of suction cup-tipped tube feet which it uses for locomotion and attaching itself to rocks. It is also covered with stiff spines which it uses for protection and for moving food to its mouth on the underside of the body. The spines work to protect the urchin from almost everything but the fisherman and the sea otter. Since the sea otters became established along the outer coast of the region, the Red Urchin populations have fallen below the level that is worth harvesting commercially.
Northern or Pinto abalone, Haliotus kamtschatkana, have much the same range and habitat requirements as the Red Sea Urchin, and have suffered much the same fate in terms of sea otter and human predation. Abalone are large, thick-shelled, univalve mollusks, herbivores with a rasping mouth called a radula that they use to scrap algae off of rocks. They are able to escape most predation by holding on to rocks with a suction equal to 4,000 times their own weight. Abalone are more prone to local extinctions through overhavesting because of the very short dispersal distance of their larval stage — about 150 meters. If all of the adults in an area are harvested, then there will not soon be a new recruitment of abalone to take their place.
Soon after sea otters recolonized eastern Prince William Sound the commercial Dungeness crab fishery there collapsed. It's too soon to say if the same will happen in the Glacier Bay area. Regular monitoring of the crab populations of the area is being done by a multi-agency research team.
After almost two centuries of absence, the sea otter is returning to the Glacier Bay ecosystem. Some people see them only as adorable creatures in marine aquariums, some see them as oil-soaked victims of the Exxon Valdez oil spill, some see them as competitors for shellfish. Hopefully, someday, more people will see them as the well-adapted, important components of the nearshore marine ecosystem that they are.
