Sea otter conservation

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Sea otters in the Olympic Coast National Marine Sanctuary are descendants of otters translocated from Alaska in 1969 and 1970.

Modern efforts in sea otter conservation began in the early 20th century, when the sea otter was nearly extinct due to large-scale commercial hunting. The sea otter was once abundant in a wide arc across the North Pacific ocean, from northern Japan to Alaska to Mexico. By 1911, hunting for the animal's luxurious fur had reduced the sea otter population to fewer than 2000 individuals in the most remote and inaccessible parts of its range.

During the 20th century, sea otter populations recovered from remnant populations in the far east of Russia, western Alaska, and California. Beginning in the 1960s, efforts to translocate sea otters to previously populated areas were also successful in restoring sea otters to other parts of the west coast of North America. Populations in some areas are now thriving, and the recovery of the sea otter is considered one of the greatest successes in marine conservation.^[1]

In two important parts of its range, however, sea otter populations have recently declined or have plateaued at depressed levels. In the Aleutian Islands, a massive and unexpected disappearance of sea otters has occurred in recent decades. The cause of the decline is not known, although the observed pattern of disappearances is consistent with a rise in orca predation. In the 1990s, California's sea otter population stopped growing for reasons that are probably different from the difficulties facing Alaska's otters. A high prevalence of infectious disease in juveniles and adults has been found to cause many sea otter deaths, however it is not known why California sea otters would be more vulnerable to disease than populations elsewhere. Other threats to sea otters are well-known. In particular, sea otters are highly vulnerable to oil spills, and a major spill can rapidly kill thousands of the animals. The IUCN lists the sea otter as an endangered species.

[edit] Background

Main article: Sea otter

Once on the verge of extinction, the recovery of the sea otter is considered one of the greatest successes in marine conservation.

The sea otter (Enhydra lutris) is a marine mammal living near the shores of the North Pacific, from northern Japan, the Kuril Islands and Kamchatka east across the Aleutian Islands and along the North American coast to Mexico. It has the thickest fur in the animal kingdom. Between 1741 and 1911, a period of extensive hunting for sea otter pelts, known as "the Great Hunt", brought the world population to 1,000 – 2,000 individuals in a fraction of the species' historic range. Since then, most commercial hunting of the species has been banned, although a limited amount of hunting by indigenous peoples has been permitted.

The sea otter preys mostly upon invertebrates such as sea urchins, diverse mollusks and crustaceans, and some species of fish. In most of its range, it is a keystone species, with a stabilizing effect on its local ecosystem that is disproportionate to its size and abundance. Specifically, sea otters control sea urchin populations, which would otherwise inflict extensive damage to the kelp forest ecosystems that provide crucial habitat and food for other marine organisms and help contain coastal erosion.

Because of the sea otter's crucial ecological role, as well as the animal's aesthetic and cultural value, particular efforts have been made to protect the species and to expand its range. However, conservation of the sea otter is complicated by the fact that some of its preferred prey species, such as some species of abalone, crabs, and clams, are also eaten by humans. Because of the species' reputation for depleting shellfish resources, advocates for commercial, recreational, and subsistence shellfish harvesting have often opposed allowing the sea otter's range to increase, and there have even been instances of fishermen and others illegally killing them.^[2]

The sea otter's range is currently discontinuous. It is absent from about a third of its former range, including all of Oregon and northern California. It has only recently begun to reappear in Mexico and northern Japan. Sea otters can do well in captivity, and are featured in over 40 public aquaria and zoos.^[3]

Sea otters rely on clean fur to stay warm. If the fur is polluted from an oil spill, however, the otter ingests the oil when grooming.

[edit] Conservation issues

The IUCN describes the significant threats to sea otters as oil pollution, predation by orcas, poaching, and conflicts with fisheries. Sea otters can drown if entangled in fishing gear.^[4] They can also be stressed by well-meaning human watchers who approach too closely. The most significant threat to sea otters is oil spills.^[5] Sea otters are particularly vulnerable, as they rely on their fur to keep warm. When their fur is soaked with oil, it loses its ability to retain air, and the animal quickly dies from hypothermia.^[5] The liver, kidneys, and lungs of sea otters also become damaged after they inhale oil or ingest it when grooming.^[5]

The small geographic ranges of the sea otter populations in California, Washington, and British Columbia mean that a single major spill could be catastrophic for that state or province.^[6][7][8] Prevention of oil spills, and preparation for rescue of otters in the event of one, are major areas of focus for conservation efforts. Increasing the size and the range of sea otter populations will also reduce the effects of catastrophic oil spills.

Sea Otter in the Yukon Delta National Wildlife Refuge.

Marine protected areas provide good habitat in which activities such as dumping waste and drilling for oil are not permitted.^[9][10] The sea otter population within the Monterey Bay National Marine Sanctuary is estimated to be more than than 1,200. ^[11] The at the Olympic Coast National Marine Sanctuary is over 500. ^[12]

[edit] Russia

Before the 19th century there were around 20,000 to 25,000 sea otters in the Kuril Islands, with more on Kamchatka and the Commander Islands. After the years of the Great Hunt, the population in these areas, currently part of Russia, was only 750.^[13] As of 2004, sea otters have repopulated all of their former habitat in these areas, with an estimated total population of about 27,000. Of these, about 19,000 are in the Kurils, 2000 to 3500 on Kamchatka and another 5000 to 5500 on the Commander Islands.^[13] Growth has slowed slightly, suggesting that the numbers are reaching carrying capacity.^[13] The success of the sea otter's recovery in Russia has been credited to large-scale and long-term protection, enlargement of the species's range, and human emigration from the islands.^[13]

[edit] Alaska

In the wake of the Exxon Valdez oil spill, heavy sheens of oil covered large areas of Prince William Sound.

Colonies were discovered around Alaska's Aleutian Islands and Prince William Sound in the 1930s. A sanctuary was created in Amchitka Island, whose sea otter population grew to outstrip its supply of prey.^[14] By the mid-1960s, Amchitka Island was being used a site for nuclear testing, which eventually killed many sea otters in the area. In advance of a major test in 1968, the U.S. Atomic Energy Commission agreed to move hundreds of the animals to other parts of the coast. Seven hundred sea otters were transplanted in the 1960s and 1970s, with survival rates improving as scientists became more knowledgeable about how to safely transport the animals.^[15] In 1973, the sea otter population in Alaska was estimated at between 100,000 and 125,000 animals.^[16]

[edit] Declines in the Aleutian Islands

In recent decades, the sea otter population the Aleutian Islands of western Alaska has plummeted. In the 1980s, the area was home to an estimated 55,000 to 100,000 sea otters, but the population fell to around 6,000 animals by 2000.^[17] One controversial hypothesis is that orcas have been eating the otters. The evidence in support of this explanation is circumstantial: It is unlikely that the otters have been dying from disease or starvation, as few bodies of sick or emaciated otters have been recovered.^[17] Also, populations have declined in areas of open water frequented by orcas, but not in nearby lagoons where orcas are absent.^[18]

Some Alaska orcas specialize in preying on marine mammals and others on fish. The orcas that prefer marine mammal prey usually attack seals, sea lions, and small cetaceans, and have occasionally been seen preying on grey whale calves. The small, furry sea otter offers little nutrition for an orca, however orcas are so large that a handful of individual whales on a diet of sea otters would account for the disappearance of thousands of otters. According to one theory known as "sequential megafauna collapse", orcas may have started eating otters due to shortages of their usual, much larger, prey. The region's population of large whales was decimated by commercial whaling in the 1960s. Then stocks of harbor seals and Steller sea lions experienced massive declines in the 1970s and 1980s, respectively, which may have forced orcas to seek smaller prey.^[19] The theory that orca predation has been responsible for these declines remains controversial, and so far there has been no direct evidence that orcas prey on sea otters to any significant extent.^[18]

[edit] Exxon Valdez oil spill

The 1989 Exxon Valdez oil spill devastated the sea otter population in Prince William Sound. Over 1,000 oiled sea otter carcasses were recovered,^[20] with the actual number of deaths estimated to be several times that number.^[6][21] Approximately 350 oiled sea otters were rescued, and over the next five months given intensive rehabilitation.^[22] Each otter was tranquilized and thoroughly washed and dried. Those which had swallowed a lot of oil were treated with activated charcoal. The effort saved about 200 of the 350 rescued sea otters, although many later died after being released.^[22] Although few sea otters were saved in the rescue effort, much knowledge was gained about how to successfully rehabilitate oiled sea otters. A 2006 report from the Exxon Valdez Oil Spill Trustee Council named the sea otter as one of several species still being affected by the lingering oil in the area.^[23]

The thick fur of the sea otter once made it a target for large-scale hunting, and makes it vulnerable to oil spills today.

[edit] Current status

As of 2006, there are an estimated 73,000 sea otters in Alaska. In August 2005, the "southwest Alaska Distinct Population Segment" of the sea otter was listed as "threatened" under the Endangered Species Act.^[24] A little over a year later, the Arizona-based Center for Biological Diversity filed a lawsuit arguing that the U.S. Fish and Wildlife Service had failed to designate critical habitat for the species, as required by the Endangered Species Act.^[25]

[edit] British Columbia, Washington, and Oregon

Between 1969 and 1972, 89 sea otters were flown or shipped from Alaska to the west coast of Vancouver Island, British Columbia. They established a healthy population, estimated to be over 3,000 as of 2004, and their range is now from Tofino to Cape Scott.^[26] However, the First Nations people in the area had not been consulted before the relocations took place. Although the translocated sea otters improved the general health of the ecosystem, they depleted shellfish and sea urchins that local indigenous communities had come to reply upon, and many in these communities came to regret the return of the otters.^[27]

In 1989, a separate colony was discovered in the central B.C. coast. It is not known if this colony, which had a size of about 300 animals in 2004, was founded by translocated otters or by survivors of the fur trade.^[26] The sea otter is considered a threatened species in Canada and is protected under the federal Species at Risk Act (SARA).^[28] In April 2007, the Committee on the Status of Endangered Wildlife in Canada changed its assessment of the sea otter from "threatened" to "special concern". The committee's assessment reflects the ongoing strength of the B.C. population and may lead to a reduction of its legal status under SARA.^[29]

59 sea otters were translocated from Amchitka Island to Washington State in 1969 and 1970, with annual surveys between 2000 and 2004 recording between 504 and 743 individuals.^[8] The state has listed the sea otter as an endangered species since 1981.^[8] Attempts were made to move 93 sea otters to the Oregon coast in the 1970s, however none have been seen since the early 1980s.^[15] It is not known if they died or moved away.^[15]

[edit] California

In 1938, the population in California was only about 50 animals. It has rebounded to around 3,000, still far below the estimated pre-fur trade population of 16,000.

California is the only location where the southern sea otter (Enhydra lutris nereis) subspecies is found in significant numbers. In 1938, a couple testing a telescope discovered a group of about 50 of these animals in a remote part of the coast near Big Sur, California.^[30] With conservation efforts, this group has since grown and expanded its range.^[20] However, recovery has been slow in comparison to sea other populations elsewhere, and also in comparison to sympatric marine mammal species such as California sea lions and harbor seals.^[31] Its average growth rate between 1914 and 1984 was only 5%, and fluctuated or declined in the late 1990s.^[32] The southern sea otter was listed under the Endangered Species Act as an threatened subspecies in 1977. A survey taken in the spring of 2007 counted a little over 3,000 sea otters in California, up slightly from previous years but down from an estimated pre-fur trade population of 16,000.^[33] For the subspecies to be delisted from the list of threatened species, the count must average 3,090 or more over three years.^[33]

The expansion of the sea otter population brought it into conflict with shellfish fisheries. Beginning in the 1980s, the U.S. Fish and Wildlife Service attempted to manage the competition between sea otters and fishermen by creating an "otter-free zone" from Point Conception to the U.S.-Mexico border. In this zone, only San Nicolas Island was designated as sea otter habitat, and sea otters found elsewhere in the area were supposed to be captured and relocated. These plans were abandoned after it proved impractical to capture the hundreds of otters which ignored regulations and swam into the zone.^[17]

[edit] Population health

The causes of the recent difficulties for California's sea otters are not well understood. As the birth rate in California is comparable to rates in other, rapidly growing sea otter populations, the decline is attributed to high rates of mortality.^[31] Unusually high mortality rates amongst adult and young adult otters, particularly females, have been reported.^[33] Disease is believed to be a leading cause, and other possible mortality factors include water contamination and drowning in fishing nets.^[34]

In California, adults of breeding age have experienced high levels of mortality in recent years.

Although the bodies of dead sea otters often sink at sea, necropsies of beached carcasses provide some insights into the causes of mortality. A study of 105 sea otters that had washed ashore between 1998 and 2001 determined the major causes of death to be protozoal encephalitis, acanthocephalan parasite infection, shark attack, and cardiac disease.^[31] Infectious disease alone caused 63.8% of deaths, and in most of these cases the disease was caused by parasites. Infection, particularly Toxoplasma gondii encephalitis, was often present in otters that had died of cardiac disease, suggesting that infection may have contributed to the onset of cardiac disease.^[31] T. gondii encephalitis was also strongly associated with shark bites, perhaps because the disease causes abnormal behavior that increases the likelihood of shark attack.^[31]

In one study, 42 percent of live sea otters surveyed had antibodies to the T. gondii parasite, an almost certain sign of infection.^[35] The parasite, which is often fatal to sea otters, is carried by wild and domestic cats. As the parasite can be carried into the ocean via the sewage system, cat owners are encouraged to dispose of droppings in the trash rather than flushing them.^[36]

Although it is clear that disease has contributed to the deaths of many of California's sea otters, it is not known why the California population would be more vulnerable to disease than populations in other areas. It has been proposed that a low level of genetic variation of the population, due to its history of population bottlenecks, may be a contributing factor.

[edit] References

[edit] Bibliography

• Kenyon, Karl W. (1969). The Sea Otter in the Eastern Pacific Ocean. Washington, D.C.: U.S. Bureau of Sport Fisheries and Wildlife. 
• Love, John A. (1992). Sea Otters. Golden, Colorado: Fulcrum Publishing. ISBN 1-55591-123-4. 
• Nickerson, Roy (1989). Sea Otters, a Natural History and Guide. San Francisco, CA: Chronicle Books. ISBN 0-87701-567-8. 
• Silverstein, Alvin; Silverstein, Virginia and Robert (1995). The Sea Otter. Brookfield, Connecticut: The Millbrook Press, Inc.. ISBN 1-56294-418-5. 
• VanBlaricom, Glenn R. (2001). Sea Otters. Stillwater, MN: Voyageur Press Inc.. ISBN 0-89658-562-X. 

[edit] External links

• The Otter Project
• Friends of the Sea Otter