Sea otter conservation
Encyclopedia
Sea Otter
The sea otter is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between 14 and 45 kg , making them the heaviest members of the weasel family, but among the smallest marine mammals...
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
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
to Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
to Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
. 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
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
, western Alaska, and California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
. 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
Marine conservation
Marine conservation, also known as marine resources conservation, is the protection and preservation of ecosystems in oceans and seas. Marine conservation focuses on limiting human-caused damage to marine ecosystems, and on restoring damaged marine ecosystems...
.
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
Orca
The killer whale , commonly referred to as the orca, and less commonly as the blackfish, is a toothed whale belonging to the oceanic dolphin family. Killer whales are found in all oceans, from the frigid Arctic and Antarctic regions to tropical seas...
predation. Sea otters give live birth. 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 spill
Oil spill
An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially marine areas, due to human activity, and is a form of pollution. The term is mostly used to describe marine oil spills, where oil is released into the ocean or coastal waters...
s, and a major spill can rapidly kill thousands of the animals. The IUCN lists the sea otter as an endangered species
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
.
Background
Marine mammal
Marine mammals, which include seals, whales, dolphins, and walruses, form a diverse group of 128 species that rely on the ocean for their existence. They do not represent a distinct biological grouping, but rather are unified by their reliance on the marine environment for feeding. The level of...
living near the shores of the North Pacific
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
, from northern Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, the Kuril Islands
Kuril Islands
The Kuril Islands , in Russia's Sakhalin Oblast region, form a volcanic archipelago that stretches approximately northeast from Hokkaidō, Japan, to Kamchatka, Russia, separating the Sea of Okhotsk from the North Pacific Ocean. There are 56 islands and many more minor rocks. It consists of Greater...
and Kamchatka
Kamchatka Peninsula
The Kamchatka Peninsula is a peninsula in the Russian Far East, with an area of . It lies between the Pacific Ocean to the east and the Sea of Okhotsk to the west...
east across the Aleutian Islands and along the North American
North American
North American generally refers to an entity, people, group, or attribute of North America, especially of the United States and Canada together.-Culture:*North American English, a collective term used to describe American English and Canadian English...
coast to Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
. 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 urchin
Sea urchin
Sea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or "test", is round and spiny, typically from across. Common colors include black and dull...
s, diverse mollusks and crustaceans, and some species of fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
. In most of its range, it is a keystone species
Keystone species
A keystone species is a species that has a disproportionately large effect on its environment relative to its abundance. Such species play a critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem and helping to determine the types and...
, 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
Kelp forest
Kelp forests are underwater areas with a high density of kelp. They are recognized as one of the most productive and dynamic ecosystems on Earth. Smaller areas of anchored kelp are called kelp beds....
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
Abalone
Abalone , from aulón, are small to very large-sized edible sea snails, marine gastropod molluscs in the family Haliotidae and the genus Haliotis...
, crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s, and clam
Clam
The word "clam" can be applied to freshwater mussels, and other freshwater bivalves, as well as marine bivalves.In the United States, "clam" can be used in several different ways: one, as a general term covering all bivalve molluscs...
s, 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.
The sea otter's range is currently discontinuous. It is absent from about a third of its former range, including all of Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...
and northern California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
. 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
Aquarium
An aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...
and zoo
Zoo
A zoological garden, zoological park, menagerie, or zoo is a facility in which animals are confined within enclosures, displayed to the public, and in which they may also be bred....
s.
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. They can also be stressed by well-meaning human watchers who approach too closely. The most significant threat to sea otters is oil spillOil spill
An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially marine areas, due to human activity, and is a form of pollution. The term is mostly used to describe marine oil spills, where oil is released into the ocean or coastal waters...
s. 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
Hypothermia
Hypothermia is a condition in which core temperature drops below the required temperature for normal metabolism and body functions which is defined as . Body temperature is usually maintained near a constant level of through biologic homeostasis or thermoregulation...
. The liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
, kidneys, and lungs of sea otters also become damaged after they inhale oil or ingest it when grooming.
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. 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.
Marine Protected Area
Marine Protected Areas, like any protected area, are regions in which human activity has been placed under some restrictions in the interest of conserving the natural environment, it's surrounding waters and the occupant ecosystems, and any cultural or historical resources that may require...
s provide good habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
in which activities such as dumping waste and drilling for oil are not permitted. The sea otter population within the Monterey Bay National Marine Sanctuary
Monterey Bay National Marine Sanctuary
The Monterey Bay National Marine Sanctuary is a US Federally protected marine area offshore of California's central coast around Monterey Bay....
is estimated to be more than 1,200. The at the Olympic Coast National Marine Sanctuary
Olympic Coast National Marine Sanctuary
The Olympic Coast National Marine Sanctuary is one of 14 marine sanctuaries administered by the National Oceanic and Atmospheric Administration , an agency of the U.S. Department of Commerce. It is located along the Olympic Peninsula of Washington state...
is over 500.
Russia
Before the 19th century there were around 20,000 to 25,000 sea otters in the Kuril IslandsKuril Islands
The Kuril Islands , in Russia's Sakhalin Oblast region, form a volcanic archipelago that stretches approximately northeast from Hokkaidō, Japan, to Kamchatka, Russia, separating the Sea of Okhotsk from the North Pacific Ocean. There are 56 islands and many more minor rocks. It consists of Greater...
, with more on Kamchatka and the Commander Islands. After the years of the Great Hunt, the population in these areas, currently part of Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
, was only 750. 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. Growth has slowed slightly, suggesting that the numbers are reaching carrying capacity
Carrying capacity
The carrying capacity of a biological species in an environment is the maximum population size of the species that the environment can sustain indefinitely, given the food, habitat, water and other necessities available in the environment...
. 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.
Alaska
Prince William Sound
Prince William Sound is a sound off the Gulf of Alaska on the south coast of the U.S. state of Alaska. It is located on the east side of the Kenai Peninsula. Its largest port is Valdez, at the southern terminus of the Trans-Alaska Pipeline System...
in the 1930s. A sanctuary was created in Amchitka Island, whose sea otter population grew to outstrip its supply of prey. By the mid-1960s, Amchitka Island was being used a site for nuclear testing
Nuclear testing
Nuclear weapons tests are experiments carried out to determine the effectiveness, yield and explosive capability of nuclear weapons. Throughout the twentieth century, most nations that have developed nuclear weapons have tested them...
, 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. In 1973, the sea otter population in Alaska was estimated at between 100,000 and 125,000 animals.
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. 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. Also, populations have declined in areas of open water frequented by orcas, but not in nearby lagoons where orcas are absent.Some Alaska orcas specialize in preying on marine mammals and others on fish. The orcas that prefer marine mammal prey usually attack seals
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...
, sea lion
Sea Lion
Sea lions are pinnipeds characterized by external ear-flaps, long fore-flippers, the ability to walk on all fours, and short thick hair. Together with the fur seal, they comprise the family Otariidae, or eared seals. There are six extant and one extinct species in five genera...
s, 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 whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...
s was decimated by commercial whaling
Whaling
Whaling is the hunting of whales mainly for meat and oil. Its earliest forms date to at least 3000 BC. Various coastal communities have long histories of sustenance whaling and harvesting beached whales...
in the 1960s. Then stocks of harbor seal
Harbor Seal
The harbor seal , also known as the common seal, is a true seal found along temperate and Arctic marine coastlines of the Northern Hemisphere...
s and Steller sea lions experienced massive declines in the 1970s and 1980s, respectively, which may have forced orcas to seek smaller prey. 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.
Exxon Valdez oil spill
The 1989 Exxon Valdez oil spillExxon Valdez oil spill
The Exxon Valdez oil spill occurred in Prince William Sound, Alaska, on March 24, 1989, when the Exxon Valdez, an oil tanker bound for Long Beach, California, struck Prince William Sound's Bligh Reef and spilled of crude oil. It is considered to be one of the most devastating human-caused...
devastated the sea otter population in Prince William Sound
Prince William Sound
Prince William Sound is a sound off the Gulf of Alaska on the south coast of the U.S. state of Alaska. It is located on the east side of the Kenai Peninsula. Its largest port is Valdez, at the southern terminus of the Trans-Alaska Pipeline System...
. Over 1,000 oiled sea otter carcasses were recovered, with the actual number of deaths estimated to be several times that number. Approximately 350 oiled sea otters were rescued, and over the next five months given intensive rehabilitation. 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. 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.
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 ActEndangered Species Act
The Endangered Species Act of 1973 is one of the dozens of United States environmental laws passed in the 1970s. Signed into law by President Richard Nixon on December 28, 1973, it was designed to protect critically imperiled species from extinction as a "consequence of economic growth and...
. A little over a year later, the Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
-based Center for Biological Diversity
Center for Biological Diversity
The Center for Biological Diversity based in Tucson, Arizona, is a nonprofit membership organization with approximately 220,000 members and online activists, known for its work protecting endangered species through legal action and scientific petitions...
filed a lawsuit arguing that the U.S. Fish and Wildlife Service had failed to designate critical habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
for the species, as required by the Endangered Species Act.
Sea otter sound off of prince of wales island is home to at least 50,000 additional sea otters.
British Columbia, Washington, and Oregon
Between 1969 and 1972, 89 sea otters were flown or shipped from Alaska to the west coast of Vancouver IslandVancouver Island
Vancouver Island is a large island in British Columbia, Canada. It is one of several North American locations named after George Vancouver, the British Royal Navy officer who explored the Pacific Northwest coast of North America between 1791 and 1794...
, 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
Cape Scott Provincial Park
Cape Scott Provincial Park is a provincial park located at the cape of the same name, which is the northwestern tip of Vancouver Island, British Columbia, Canada. First established in 1973 with c. of area, later boundary revisions form an area of 22,290 ha...
. However, the First Nations
First Nations
First Nations is a term that collectively refers to various Aboriginal peoples in Canada who are neither Inuit nor Métis. There are currently over 630 recognised First Nations governments or bands spread across Canada, roughly half of which are in the provinces of Ontario and British Columbia. The...
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.
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. The sea otter is considered a threatened species in Canada and is protected under the federal Species at Risk Act
Species at Risk Act
The Species at Risk Act is a piece of Canadian federal legislation which became law in Canada on December 12, 2002. It is designed to meet one of Canada's key commitments under the International Convention on Biological Diversity. The goal of the Act is to protect endangered or threatened...
(SARA). In April 2007, the Committee on the Status of Endangered Wildlife in Canada
Committee on the Status of Endangered Wildlife in Canada
The Committee on the Status of Endangered Wildlife in Canada ; French: Le Comité sur la situation des espèces en péril au Canada, is an independent committee of wildlife experts and scientists whose "raison d’être is to identify species at risk" 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.
59 sea otters were translocated from Amchitka Island to Washington in 1969 and 1970, with annual surveys between 2000 and 2004 recording between 504 and 743 individuals. The state has listed the sea otter as an endangered species since 1981. Attempts were made to move 93 sea otters to the Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...
coast in the 1970s, however none have been seen since the early 1980s. It is not known if they died or moved away.
California
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 SurBig Sur
Big Sur is a sparsely populated region of the Central Coast of California where the Santa Lucia Mountains rise abruptly from the Pacific Ocean. The name "Big Sur" is derived from the original Spanish-language "el sur grande", meaning "the big south", or from "el país grande del sur", "the big...
, California. With conservation efforts, this group has since grown and expanded its range. 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 lion
California Sea Lion
The California sea lion is a coastal sea lion of western North America. Their numbers are abundant , and the population continues to expand about 5% annually. They are quite intelligent and can adapt to man-made environments...
s and harbor seal
Harbor Seal
The harbor seal , also known as the common seal, is a true seal found along temperate and Arctic marine coastlines of the Northern Hemisphere...
s. Its average growth rate between 1914 and 1984 was only 5%, and fluctuated or declined in the late 1990s. The southern sea otter was listed under the Endangered Species Act
Endangered Species Act
The Endangered Species Act of 1973 is one of the dozens of United States environmental laws passed in the 1970s. Signed into law by President Richard Nixon on December 28, 1973, it was designed to protect critically imperiled species from extinction as a "consequence of economic growth and...
as a 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. For the subspecies to be delisted from the list of threatened species, the count must average 3,090 or more over three years.
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
Point Conception
Point Conception is a headland along the Pacific coast of U.S. state of California, located in southwestern Santa Barbara County. It is the point where the Santa Barbara Channel meets the Pacific Ocean, and as the corner between the mostly north-south trending portion of coast to the north and the...
to the U.S.-Mexico border. In this zone, only San Nicolas Island
San Nicolas Island
San Nicolas Island is the most remote of California's Channel Islands. It is part of Ventura County. The 14,562 acre island is currently controlled by the United States Navy and is used as a weapons testing and training facility, served by Naval Outlying Field 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.
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. Unusually high mortality rates amongst adult and young adult otters, particularly females, have been reported. Disease is believed to be a leading cause, and other possible mortality factors include water contamination and drowning in fishing nets.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
Encephalitis
Encephalitis is an acute inflammation of the brain. Encephalitis with meningitis is known as meningoencephalitis. Symptoms include headache, fever, confusion, drowsiness, and fatigue...
, acanthocephalan parasite infection, shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
attack, and cardiac disease. Infectious disease alone caused 63.8% of deaths, and in most of these cases the disease was caused by parasites. Infection, particularly Toxoplasma gondii
Toxoplasma gondii
Toxoplasma gondii is a species of parasitic protozoa in the genus Toxoplasma. The definitive host of T. gondii is the cat, but the parasite can be carried by many warm-blooded animals . Toxoplasmosis, the disease of which T...
encephalitis, was often present in otters that had died of cardiac disease, suggesting that infection may have contributed to the onset of cardiac disease. T. gondii encephalitis was also strongly associated with shark bites, perhaps because the disease causes abnormal behavior that increases the likelihood of shark attack
Shark attack
A shark attack is an attack on a human by a shark. Every year around 60 shark attacks are reported worldwide, although death is quite unusual. Despite the relative rarity of shark attacks, the fear of sharks is a common phenomenon, having been fueled by the occasional instances of serial attacks,...
.
In one study, 42 percent of live sea otters surveyed had antibodies to the T. gondii parasite, an almost certain sign of infection. 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.
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
Genetic variation
Genetic variation, variation in alleles of genes, occurs both within and among populations. Genetic variation is important because it provides the “raw material” for natural selection. Genetic variation is brought about by mutation, a change in a chemical structure of a gene. Polyploidy is an...
of the population, due to its history of population bottleneck
Population bottleneck
A population bottleneck is an evolutionary event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing....
s, may be a contributing factor.