150-420: The sea otter ( Enhydra lutris ) 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 (30 and 100 lb), making them the heaviest members of the weasel family , but among the smallest marine mammals. Unlike most marine mammals, the sea otter's primary form of insulation is an exceptionally thick coat of fur ,
300-487: A blubber layer, while their oil glands help matt down their fur and keep it from holding air. Thick bones also prove crucial in increasing buoyancy, as sea otters spend long hours floating atop the ocean. In a study, southern and northern Sea Otter populations were compared against the African clawless otter , and it was determined that aquatic traits like loss of smell and hair thickness independently evolved, evidencing
450-400: A metabolic rate two or three times that of comparatively sized terrestrial mammals. It must eat an estimated 25 to 38% of its own body weight in food each day to burn the calories necessary to counteract the loss of heat due to the cold water environment. Its digestive efficiency is estimated at 80 to 85%, and food is digested and passed in as little as three hours. Most of its need for water
600-415: A pinna and hair . Whales have an elongated head, especially baleen whales , due to the wide overhanging jaw. Bowhead whale plates can be 9 metres (30 ft) long. Their nostril(s) make up the blowhole , with one in toothed whales and two in baleen whales. The nostrils are located on top of the head above the eyes so that the rest of the body can remain submerged while surfacing for air. The back of
750-405: A blunt snout and reduced dentition rely on suction feeding . Though carnivorous, they house gut flora similar to that of terrestrial herbivores, probably a remnant of their herbivorous ancestry. Baleen whales use their baleen plates to sieve plankton, among others, out of the water; there are two types of methods: lunge-feeding and gulp-feeding. Lunge-feeders expand the volume of their jaw to
900-570: A complex genome of polygenic traits resulting in complex systems. This study was only able to take place after sequencing of Sea Otter nuclear genomes and through phylogeny to find a close ancestor with which to compare genomes. Previously, it was suspected that sea otters came from the same evolutionary branch as earless seals , such as harbor and monk seals . Sea Otters have experienced numerous population bottlenecks throughout their history, with significant numbers being wiped out 9,000-10,000 generations ago and 300–700 generations ago, long before
1050-418: A distinct molting season. As the ability of the guard hairs to repel water depends on utmost cleanliness, the sea otter has the ability to reach and groom the fur on any part of its body, taking advantage of its loose skin and an unusually supple skeleton . The coloration of the pelage is usually deep brown with silver-gray speckles, but it can range from yellowish or grayish brown to almost black. In adults,
1200-627: A divergence of the Monachinae (monk seals) and Phocinae lineages 22 mya. Fossil evidence indicates the sea otter ( Enhydra ) lineage became isolated in the North Pacific approximately two mya, giving rise to the now-extinct † Enhydra macrodonta and the modern sea otter, Enhydra lutris . The sea otter evolved initially in northern Hokkaidō and Russia, and then spread east to the Aleutian Islands , mainland Alaska , and down
1350-601: A factor in the ability to produce sounds used in echolocation. Mysticeti, who don't have the ability to echolocate, possess general symmetry of the skull and facial region, while Odontoceti display a nasofacial asymmetry that is linked to their echolocating abilities. Differences in the level of asymmetry also seem to correlate with differences in the types of sounds produced. Mysticeti have exceptionally thin, wide basilar membranes in their cochleae without stiffening agents, making their ears adapted for processing low to infrasonic frequencies. The initial karyotype includes
1500-471: A few are specialists. They typically hunt non-schooling fish, slow-moving or immobile invertebrates or endothermic prey when in groups. Solitary foraging species usually exploit coastal waters, bays and rivers. When large schools of fish or squid are available, pinnipeds hunt cooperatively in large groups, locating and herding their prey. Some species, such as California and South American sea lions, may forage with cetaceans and sea birds. The polar bear
1650-501: A few eat other mammals. While the number of marine mammals is small compared to those found on land, their roles in various ecosystems are large, especially concerning the maintenance of marine ecosystems, through processes including the regulation of prey populations. This role in maintaining ecosystems makes them of particular concern as 23% of marine mammal species are currently threatened. Marine mammals were first hunted by aboriginal peoples for food and other resources. Many were also
SECTION 10
#17327805305471800-496: A home range a few kilometres long, and remain there year-round. The sea otter population is thought to have once been 150,000 to 300,000, stretching in an arc across the North Pacific from northern Japan to the central Baja California Peninsula in Mexico. The fur trade that began in the 1740s reduced the sea otter's numbers to an estimated 1,000 to 2,000 members in 13 colonies. Hunting records researched by historian Adele Ogden place
1950-439: A large melon and multiple, asymmetric air bags. River dolphins , unlike most other cetaceans, can turn their head 90°. Most other cetaceans have fused neck vertebrae and are unable to turn their head at all. The baleen of baleen whales consists of long, fibrous strands of keratin. Located in place of the teeth, it has the appearance of a huge fringe and is used to sieve the water for plankton and krill. Sperm whales have
2100-584: A latitudinal basis to move between seasonal habitats. For example, the gray whale migrates 10,000 miles (16,000 km) round trip. The journey begins at winter birthing grounds in warm lagoons along Baja California, and traverses 5,000–7,000 miles (8,000–11,300 km) of coastline to summer feeding grounds in the Bering, Chuckchi and Beaufort seas off the coast of Alaska. Conscious breathing cetaceans sleep but cannot afford to be unconscious for long, because they may drown. While knowledge of sleep in wild cetaceans
2250-581: A male sea otter took up residence at Simpson Reef off of Cape Arago for six months. This male is thought to have originated from a colony in Washington, but disappeared after a coastal storm. On 18 February 2009, a male sea otter was spotted in Depoe Bay off the Oregon Coast . It could have traveled to the state from either California or Washington. The historic population of California sea otters
2400-606: A mate. The species exhibits a variety of vocal behaviors. The cry of a pup is often compared to that of a gull . Females coo when they are apparently content; males may grunt instead. Distressed or frightened adults may whistle, hiss, or in extreme circumstances, scream. Although sea otters can be playful and sociable, they are not considered to be truly social animals . They spend much time alone, and each adult can meet its own hunting, grooming, and defense needs. Sea otters are polygynous : males have multiple female partners, typically those that inhabit their territory. If no territory
2550-508: A mother may be forced to abandon a pup if she cannot find enough food for it; at the other extreme, a pup may be nursed until it is almost adult size. Pup mortality is high, particularly during an individual's first winter – by one estimate, only 25% of pups survive their first year. Pups born to experienced mothers have the highest survival rates. Females perform all tasks of feeding and raising offspring, and have occasionally been observed caring for orphaned pups. Much has been written about
2700-698: A number of features for efficient locomotion such as torpedo-shaped bodies to reduce drag; modified limbs for propulsion and steering ; tail flukes and dorsal fins for propulsion and balance. Marine mammals are adept at thermoregulation using dense fur or blubber , circulatory adjustments ( counter-current heat exchange ); and reduced appendages, and large size to prevent heat loss. Marine mammals are able to dive for long periods. Both pinnipeds and cetaceans have large and complex blood vessel systems pushing large volumes of blood rich in myoglobin and hemoglobin , which serve to store greater quantities of oxygen . Other important reservoirs include muscles and
2850-438: A number of terrestrial habitats, both continental and island. In temperate and tropical areas, they haul-out on to sandy and pebble beaches, rocky shores , shoals , mud flats , tide pools and in sea caves . Some species also rest on man-made structures, like piers , jetties , buoys and oil platforms . Seals may move further inland and rest in sand dunes or vegetation, and may even climb cliffs. Most cetaceans live in
3000-629: A period of glaciation in the Pleistocene or from the eastern part of Siberia , (from Kamchatka and the Kolym Peninsula). The oldest known polar bear fossil is a 130,000-to-110,000-year-old jaw bone, found on Prince Charles Foreland in 2004. The mitochondrial DNA (mtDNA) of the polar bear diverged from the brown bear roughly 150,000 years ago. Further, some clades of brown bear, as assessed by their mtDNA, are more closely related to polar bears than to other brown bears, meaning that
3150-442: A seal to appear. When the seal exhales, the bear smells its breath, reaches into the hole with a forepaw, and drags it out onto the ice. The polar bear also hunts by stalking seals resting on the ice. Upon spotting a seal, it walks to within 100 yards (90 m), and then crouches. If the seal does not notice, the bear creeps to within 30 to 40 feet (9 to 10 m) of the seal and then suddenly rushes to attack. A third hunting method
SECTION 20
#17327805305473300-457: A separate colony was discovered in the central British Columbia coast. It is not known if this colony, which numbered about 300 animals in 2004, was founded by transplanted otters or was a remnant population that had gone undetected. By 2013, this population exceeded 1,100 individuals, was increasing at an estimated 12.6% annual rate, and its range included Aristazabal Island , and Milbanke Sound south to Calvert Island . In 2008, Canada determined
3450-537: A set of chromosomes from 2n = 44. They have four pairs of telocentric chromosomes (whose centromeres sit at one of the telomeres ), two to four pairs of subtelocentric and one or two large pairs of submetacentric chromosomes. The remaining chromosomes are metacentric—the centromere is approximately in the middle—and are rather small. All cetaceans have chromosomes 2n = 44, except the sperm whales and pygmy sperm whales , which have 2n = 42. Cetaceans are found in many aquatic habitats. While many marine species, such as
3600-697: A specific body of water. The southern right whale dolphin and the hourglass dolphin live only in the Southern Ocean . The narwhal and the beluga live only in the Arctic Ocean. Sowerby's beaked whale and the Clymene dolphin exist only in the Atlantic and the Pacific white-sided dolphin and the northern straight dolphin live only in the North Pacific. Cosmopolitan species may be found in
3750-426: A terrestrial mammal breathing out on a cold day, a small cloud of 'steam' appears. This is called the 'spout' and varies across species in shape, angle and height. Species can be identified at a distance using this characteristic. The structure of the respiratory and circulatory systems is of particular importance for the life of marine mammals . The oxygen balance is effective. Each breath can replace up to 90% of
3900-430: A volume bigger than the original volume of the whale itself by inflating their mouth. This causes grooves on their throat to expand, increasing the amount of water the mouth can store. They ram a baitball at high speeds in order to feed, but this is only energy-effective when used against a large baitball. Gulp-feeders swim with an open mouth, filling it with water and prey. Prey must occur in sufficient numbers to trigger
4050-654: Is bicornuate . Cetacean eyes are set on the sides rather than the front of the head. This means only species with pointed 'beaks' (such as dolphins) have good binocular vision forward and downward. Tear glands secrete greasy tears, which protect the eyes from the salt in the water. The lens is almost spherical, which is most efficient at focusing the minimal light that reaches deep water. Odontocetes have little to no ability to taste or smell, while mysticetes are believed to have some ability to smell because of their reduced, but functional olfactory system . Cetaceans are known to possess excellent hearing. At least one species,
4200-447: Is an infraorder of aquatic mammals belonging to the order Artiodactyla that includes whales , dolphins and porpoises . Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel themselves through the water with powerful up-and-down movement of their tail which ends in a paddle-like fluke, using their flipper-shaped forelimbs to maneuver. While
4350-515: Is considered to be functionally extinct due to human activity. The two parvorders, baleen whales (Mysticeti) and toothed whales (Odontoceti), are thought to have diverged around thirty-four million years ago. Baleen whales have bristles made of keratin instead of teeth . The bristles filter krill and other small invertebrates from seawater. Grey whales feed on bottom-dwelling mollusks. Rorqual family (balaenopterids) use throat pleats to expand their mouths to take in food and sieve out
4500-540: Is established, they seek out females in estrus. When a male sea otter finds a receptive female, the two engage in playful and sometimes aggressive behavior. They bond for the duration of estrus, or 3 days. The male holds the female's head or nose with his jaws during copulation. Visible scars are often present on females from this behavior. Births occur year-round, with peaks between May and June in northern populations and between January and March in southern populations. Gestation appears to vary from four to twelve months, as
4650-410: Is fairly short, thick, slightly flattened, and muscular. The front paws are short with retractable claws, with tough pads on the palms that enable gripping slippery prey. The bones show osteosclerosis , increasing their density to reduce buoyancy. The sea otter presents an insight into the evolutionary process of the mammalian invasion of the aquatic environment , which has occurred numerous times over
Sea otter - Misplaced Pages Continue
4800-530: Is herding, where a pod squeezes a school of fish into a small volume, known as a bait ball . Individual members then take turns plowing through the ball, feeding on the stunned fish. Coralling is a method where dolphins chase fish into shallow water to catch them more easily. Killer whales and bottlenose dolphins have also been known to drive their prey onto a beach to feed on it. Killer whales have been known to paralyze great white sharks and other sharks and rays by flipping them upside down. Other whales with
4950-430: Is home to elongated spindle neurons that, prior to 2019, were known only in hominids . In humans, these cells are thought to be involved in social conduct, emotions, judgment and theory of mind. Cetacean spindle neurons are found in areas of the brain homologous to where they are found in humans, suggesting they perform a similar function. The cetacean skeleton is largely made up of cortical bone , which stabilizes
5100-433: Is limited, toothed cetaceans in captivity have been recorded to exhibit unihemispheric slow-wave sleep (USWS), which means they sleep with one side of their brain at a time, so that they may swim, breathe consciously and avoid both predators and social contact during their period of rest. A 2008 study found that sperm whales sleep in vertical postures just under the surface in passive shallow 'drift-dives', generally during
5250-400: Is met through food, although, in contrast to most other marine mammals, it also drinks seawater. Its relatively large kidneys enable it to derive fresh water from sea water and excrete concentrated urine. The sea otter is diurnal . It has a period of foraging and eating in the morning, starting about an hour before sunrise, then rests or sleeps in mid-day. Foraging resumes for a few hours in
5400-594: Is most likely to mate if he maintains a breeding territory in an area that is also favored by females. As autumn is the peak breeding season in most areas, males typically defend their territory only from spring to autumn. During this time, males patrol the boundaries of their territories to exclude other males, although actual fighting is rare. Adult females move freely between male territories, where they outnumber adult males by an average of five to one. Males that do not have territories tend to congregate in large, male-only groups, and swim through female areas when searching for
5550-421: Is neither particularly acute nor poor. An adult's 32 teeth , particularly the molars , are flattened and rounded for crushing rather than cutting food. Seals and sea otters are the only carnivores with two pairs of lower incisor teeth rather than three; the adult dental formula is 3.1.3.1 2.1.3.2 . The teeth and bones are sometimes stained purple as a result of ingesting sea urchins. The sea otter has
5700-632: Is not known, although orca predation is suspected. The sea otter population in Prince William Sound was also hit hard by the Exxon Valdez oil spill , which killed thousands of sea otters in 1989. In 1969 and 1970, 59 sea otters were translocated from Amchitka Island to Washington , and released near La Push and Point Grenville . The translocated population is estimated to have declined to between 10 and 43 individuals before increasing, reaching 208 individuals in 1989. As of 2017,
5850-418: Is scarce. West Indian manatees eat up to 60 different species of plants, as well as fish and small invertebrates to a lesser extent. Sea otters are a classic example of a keystone species; their presence affects the ecosystem more profoundly than their size and numbers would suggest. They keep the population of certain benthic (sea floor) herbivores, particularly sea urchins , in check. Sea urchins graze on
6000-424: Is so well-adapted for both air and water that some blind specimens can survive. Some species, such as sperm whales, are well adapted for diving to great depths. Several species of toothed whales show sexual dimorphism , in which the males differ from the females, usually for purposes of sexual display or aggression. Cetacean bodies are generally similar to those of fish, which can be attributed to their lifestyle and
6150-759: Is swallowed whole. Teeth are shaped like cones (dolphins and sperm whales), spades ( porpoises ), pegs ( belugas ), tusks ( narwhals ) or variable (beaked whale males). Female beaked whales' teeth are hidden in the gums and are not visible, and most male beaked whales have only two short tusks. Narwhals have vestigial teeth other than their tusk, which is present on males and 15% of females and has millions of nerves to sense water temperature, pressure and salinity. A few toothed whales, such as some orcas , feed on mammals, such as pinnipeds and other whales. Toothed whales have well-developed senses – their eyesight and hearing are adapted for both air and water, and they have advanced sonar capabilities using their melon . Their hearing
Sea otter - Misplaced Pages Continue
6300-408: Is the development of echolocation in whales and dolphins. Toothed whales emit a focused beam of high-frequency clicks in the direction that their head is pointing. Sounds are generated by passing air from the bony nares through the phonic lips. These sounds are reflected by the dense concave bone of the cranium and an air sac at its base. The focused beam is modulated by a large fatty organ known as
6450-559: Is the heaviest mustelid. Male sea otters usually weigh 22 to 45 kg (49 to 99 lb) and are 1.2 to 1.5 m (3 ft 11 in to 4 ft 11 in) in length, though specimens up to 54 kg (119 lb) have been recorded. Females are smaller, weighing 14 to 33 kg (31 to 73 lb) and measuring 1.0 to 1.4 m (3 ft 3 in to 4 ft 7 in) in length. The average weight for adult sea otters that are in more densely populated areas, at 28.3 kg (62 lb) in males and 21.1 kg (47 lb) in females,
6600-428: Is the most carnivorous species of bear, and its diet primarily consists of ringed ( Pusa hispida ) and bearded ( Erignathus barbatus ) seals. Polar bears hunt primarily at the interface between ice, water, and air; they only rarely catch seals on land or in open water. The polar bear's most common hunting method is still-hunting: The bear locates a seal breathing hole using its sense of smell, and crouches nearby for
6750-447: Is the only marine animal capable of lifting and turning over rocks, which it often does with its front paws when searching for prey. The sea otter may also pluck snails and other organisms from kelp and dig deep into underwater mud for clams . It is the only marine mammal that catches fish with its forepaws rather than with its teeth. A Misplaced Pages editor has observed Otters pulling clusters of gooseneck barnacles and mussels from piers at
6900-720: Is the only marine mammal that catches fish with its forepaws rather than with its teeth. Under each foreleg, sea otters have a loose pouch of skin that extends across the chest which they use to store collected food to bring to the surface. This pouch also holds a rock that is used to break open shellfish and clams, an example of tool use . The sea otters eat while floating on their backs, using their forepaws to tear food apart and bring to their mouths. Marine otters mainly feed on crustaceans and fish. Pinnipeds mostly feed on fish and cephalopods , followed by crustaceans and bivalves , and then zooplankton and warm-blooded prey (like sea birds ). Most species are generalist feeders, but
7050-437: Is to raid the birth lairs that female seals create in the snow. They may also feed on fish. Sirenians are referred to as "sea cows" because their diet consists mainly of seagrass. When eating, they ingest the whole plant, including the roots, although when this is impossible they feed on just the leaves. A wide variety of seagrass has been found in dugong stomach contents, and evidence exists they will eat algae when seagrass
7200-416: Is unique among the mustelids in not making dens or burrows , in having no functional anal scent glands , and in being able to live its entire life without leaving the water. The only living member of the genus Enhydra , the sea otter is so different from other mustelid species that, as recently as 1982, some scientists believed it was more closely related to the earless seals . Genetic analysis indicates
7350-412: Is vital for deep diving, since beyond a depth around 100 m (330 ft), the lung tissue is almost completely compressed by the water pressure. The stomach consists of three chambers. The first region is formed by a loose gland and a muscular forestomach (missing in beaked whales); this is followed by the main stomach and the pylorus . Both are equipped with glands to help digestion. A bowel adjoins
7500-428: The Aleutian Islands and California have recently declined or have plateaued at depressed levels. For these reasons, the sea otter remains classified as an endangered species . The sea otter is the heaviest (the giant otter is longer, but significantly slimmer) member of the family Mustelidae , a diverse group that includes the 13 otter species and terrestrial animals such as weasels , badgers , and minks . It
7650-459: The Amazon river dolphin . The collarbone is completely absent. Cetaceans have a cartilaginous fluke at the end of their tails that is used for propulsion. The fluke is set horizontally on the body and used with vertical movements, unlike fish and ichthyosaurs, which have vertical tails which move horizontally. Cetaceans have powerful hearts. Blood oxygen is distributed effectively throughout
SECTION 50
#17327805305477800-572: The Eocene . Their evolutionary link to terrestrial mammals was unknown until the 2007 discovery of † Puijila darwini in early Miocene deposits in Nunavut , Canada. Like a modern otter, † Puijila had a long tail, short limbs and webbed feet instead of flippers. The lineages of Otariidae (eared seals) and Odobenidae (walrus) split almost 28 mya. Phocids (earless seals) are known to have existed for at least 15 mya, and molecular evidence supports
7950-486: The Indian Ocean . The variation observed in range size is a result of the different ecological requirements of each species and their ability to cope with a broad range of environmental conditions. The high degree of overlap between marine mammal species richness and areas of human impact on the environment is of concern. Most marine mammals, such as seals and sea otters, inhabit the coast. Seals, however, also use
8100-551: The North Atlantic right whale , are critically endangered . Other than being hunted, marine mammals can be killed as bycatch from fisheries, where for example they can become entangled in nets and drown or starve. Increased ocean traffic causes collisions between fast ocean vessels and large marine mammals. Habitat degradation also threatens marine mammals and their ability to find and catch food. Noise pollution , for example, may adversely affect echolocating mammals, and
8250-551: The North Ronaldsay sheep ( Ovis aries ) which normally eats seaweed outside the lambing season, the Eurasian otter ( Lutra lutra ) which is usually found in freshwater but can be found along coastal Scotland , and others. Marine mammals form a diverse group of 129 species that rely on the ocean for their existence. They are an informal group unified only by their reliance on marine environments for feeding. Despite
8400-574: The Old World (such as cetaceans ). The first known quadrupedal sirenian was † Pezosiren from the early middle Eocene. The earliest known sea cows, of the families † Prorastomidae and † Protosirenidae , were both confined to the Eocene, and were pig-sized, four-legged, amphibious creatures. The first members of Dugongidae appeared by the middle Eocene. At this point, sea cows were fully aquatic. Pinnipeds split from other caniforms 50 mya during
8550-653: The Russian-American Company snuck Aleuts into San Francisco Bay multiple times, despite the Spanish capturing or shooting them while hunting sea otters in the estuaries of San Jose , San Mateo , San Bruno and around Angel Island . The founder of Fort Ross , Ivan Kuskov , finding otters scarce on his second voyage to Bodega Bay in 1812, sent a party of Aleuts to San Francisco Bay, where they met another Russian party and an American party, and caught 1,160 sea otters in three months. By 1817, sea otters in
8700-532: The beaked whale family, several species of the porpoise family, orcas, pilot whales , eastern spinner dolphins and northern right whale dolphins show this characteristic. Males in these species developed external features absent in females that are advantageous in combat or display. For example, male sperm whales are up to 63% percent larger than females, and many beaked whales possess tusks used in competition among males. Hind legs are not present in cetaceans, nor are any other external body attachments such as
8850-664: The blue whale , the humpback whale and the orca , have a distribution area that includes nearly the entire ocean, some species occur only locally or in broken populations. These include the vaquita , which inhabits a small part of the Gulf of California and Hector's dolphin , which lives in some coastal waters in New Zealand. Most river dolphin species live exclusively in fresh water. Many species inhabit specific latitudes, often in tropical or subtropical waters, such as Bryde's whale or Risso's dolphin . Others are found only in
9000-522: The hippopotamuses . Sirenians, the sea cows, became aquatic around 40 million years ago. The first appearance of sirenians in the fossil record was during the early Eocene, and by the late Eocene, sirenians had significantly diversified. Inhabitants of rivers, estuaries, and nearshore marine waters, they were able to spread rapidly. The most primitive sirenian, † Prorastomus , was found in Jamaica, unlike other marine mammals which originated from
9150-404: The melon as a head buckle. This is filled with air sacs and fat that aid in buoyancy and biosonar . The sperm whale has a particularly pronounced melon; this is called the spermaceti organ and contains the eponymous spermaceti , hence the name "sperm whale". Even the long tusk of the narwhal is a vice-formed tooth. In many toothed whales, the depression in their skull is due to the formation of
SECTION 60
#17327805305479300-399: The southern sea otter , is native to central and southern California. The Asian sea otter is the largest subspecies and has a slightly wider skull and shorter nasal bones than both other subspecies. Northern sea otters possess longer mandibles (lower jaws) while southern sea otters have longer rostrums and smaller teeth. The sea otter is one of the smallest marine mammal species, but it
9450-404: The sperm whale , and the poorly understood beaked whales ) and the filter feeding Mysticeti or baleen whales (which includes species like the blue whale , the humpback whale and the bowhead whale ). Despite their highly modified bodies and carnivorous lifestyle, genetic and fossil evidence places cetaceans as nested within even-toed ungulates , most closely related to hippopotamus within
9600-643: The spleen which all have the capacity to hold a high concentration of oxygen. They are also capable of bradycardia (reduced heart rate), and vasoconstriction (shunting most of the oxygen to vital organs such as the brain and heart) to allow extended diving times and cope with oxygen deprivation. If oxygen is depleted ( hypoxia ), marine mammals can access substantial reservoirs of glycogen that support anaerobic glycolysis . Sound travels differently through water, and therefore marine mammals have developed adaptations to ensure effective communication, prey capture, and predator detection. The most notable adaptation
9750-433: The tucuxi or Guiana dolphin, is able to use electroreception to sense prey. The external ear has lost the pinna (visible ear), but still retains a narrow ear canal . The three small bones or ossicles that transmit sound within each ear are dense and compact , and differently shaped from those of land mammals. The semicircular canals are much smaller relative to body size than in other mammals. A bony structure of
9900-558: The "sea beaver ". Three subspecies of the sea otter are recognized with distinct geographical distributions. Enhydra lutris lutris ( nominate ), the Asian sea otter , ranges across Russia's Kuril Islands northeast of Japan, and the Commander Islands in the northwestern Pacific Ocean. In the eastern Pacific Ocean, E. l. kenyoni , the northern sea otter , is found from Alaska's Aleutian Islands to Oregon and E. l. nereis ,
10050-430: The 'melon'. This acts like an acoustic lens because it is composed of lipids of differing densities. Marine mammals have evolved a wide variety of features for feeding, which are mainly seen in their dentition. For example, the cheek teeth of pinnipeds and odontocetes are specifically adapted to capture fish and squid. In contrast, baleen whales have evolved baleen plates to filter feed plankton and small fish from
10200-597: The Kurils, 2,000 to 3,500 at Kamchatka and another 5,000 to 5,500 at the Commander Islands. Growth has slowed slightly, suggesting the numbers are reaching carrying capacity . Along the North American coast south of Alaska, the sea otter's range is discontinuous. A remnant population survived off Vancouver Island into the 20th century, but it died out despite the 1911 international protection treaty, with
10350-464: The North American coast. In comparison to cetaceans, sirenians, and pinnipeds, which entered the water approximately 50, 40, and 20 mya, respectively, the sea otter is a relative newcomer to marine life. In some respects though, the sea otter is more fully adapted to water than pinnipeds, which must haul out on land or ice to give birth. Polar bears are thought to have diverged from a population of brown bears , Ursus arctos , that became isolated during
10500-675: The Pacific, Atlantic and Indian Oceans. However, northern and southern populations become genetically separated over time. In some species, this separation leads eventually to a divergence of the species, such as produced the southern right whale , North Pacific right whale and North Atlantic right whale . Migratory species' reproductive sites often lie in the tropics and their feeding grounds in polar regions. Thirty-two species are found in European waters, including twenty-five toothed and seven baleen species. Many species of whales migrate on
10650-697: The Russian east coast, Alaska, British Columbia, Washington, and California, with reports of recolonizations in Mexico and Japan. Population estimates made between 2004 and 2007 give a worldwide total of approximately 107,000 sea otters. Adele Ogden wrote in The California Sea Otter Trade that western sea otter were hunted "from Yezo northeastward past the Kuril Group and Kamchatka to the Aleutian Chain ". "Yezo" refers to
10800-624: The abalone shell using a large stone, with observed rates of 45 blows in 15 seconds. Releasing an abalone, which can cling to rock with a force equal to 4,000 times its own body weight, requires multiple dives. Although each adult and independent juvenile forages alone, sea otters tend to rest together in single-sex groups called rafts . A raft typically contains 10 to 100 animals, with male rafts being larger than female ones. The largest raft ever seen contained over 2000 sea otters. To keep themselves from drifting out to sea when resting and eating, sea otters may wrap themselves in kelp . A male sea otter
10950-449: The afternoon and subsides before sunset, and a third foraging period may occur around midnight. Females with pups appear to be more inclined to feed at night. Observations of the amount of time a sea otter must spend each day foraging range from 24 to 60%, apparently depending on the availability of food in the area. Sea otters spend much of their time grooming, which consists of cleaning the fur, untangling knots, removing loose fur, rubbing
11100-402: The amount of brain mass available for cognitive tasks. Allometric analysis of the relationship between mammalian brain mass (weight) and body mass for different species of mammals shows that larger species generally have larger brains. However, this increase is not fully proportional. Typically the brain mass only increases in proportion to somewhere between the two-thirds power (or the square of
11250-522: The animal in the water. For this reason, the usual terrestrial compact bones, which are finely woven cancellous bone , are replaced with lighter and more elastic material. In many places, bone elements are replaced by cartilage and even fat, thereby improving their hydrostatic qualities. The ear and the muzzle contain a bone shape that is exclusive to cetaceans with a high density, resembling porcelain . This conducts sound better than other bones, thus aiding biosonar . The number of vertebrae that make up
11400-663: The area were practically eliminated and the Russians sought permission from the Spanish and the Mexican governments to hunt further and further south of San Francisco. In 1833, fur trappers George Nidever and George Yount canoed "along the Petaluma side of [the] Bay, and then proceeded to the San Joaquin River ", returning with sea otter, beaver, and river otter pelts. Remnant sea otter populations may have survived in
11550-401: The base. Unlike most other marine mammals, the sea otter has no blubber and relies on its exceptionally thick fur to keep warm. With up to 150,000 strands of hair per square centimetre (970,000/in), its fur is the densest of any animal. The fur consists of long, waterproof guard hairs and short underfur; the guard hairs keep the dense underfur layer dry. There is an air compartment between
11700-1036: The bay until 1840, when the Rancho Punta de Quentin was granted to Captain John B. R. Cooper , a sea captain from Boston, by Mexican Governor Juan Bautista Alvarado along with a license to hunt sea otters, reportedly then prevalent at the mouth of Corte Madera Creek . Marine mammal Marine mammals are mammals that rely on marine (saltwater) ecosystems for their existence. They include animals such as cetaceans ( whales , dolphins and porpoises ), pinnipeds ( seals , sea lions and walruses ), sirenians ( manatees and dugongs ), sea otters and polar bears . They are an informal group, unified only by their reliance on marine environments for feeding and survival. Marine mammal adaptation to an aquatic lifestyle varies considerably between species. Both cetaceans and sirenians are fully aquatic and therefore are obligate water dwellers. Pinnipeds are semiaquatic; they spend
11850-439: The body wall. The stable lumbar and tail include the other vertebrae. Below the caudal vertebrae is the chevron bone . The front limbs are paddle-shaped with shortened arms and elongated finger bones, to support movement. They are connected by cartilage. The second and third fingers display a proliferation of the finger members, a so-called hyperphalangy. The shoulder joint is the only functional joint in all cetaceans except for
12000-416: The body. They are warm-blooded, i.e., they hold a nearly constant body temperature. Cetaceans have lungs, meaning they breathe air. An individual can last without a breath from a few minutes to over two hours depending on the species. Cetacea are deliberate breathers who must be awake to inhale and exhale. When stale air, warmed from the lungs, is exhaled, it condenses as it meets colder external air. As with
12150-403: The brain folds around the insula and expands more laterally than in terrestrial mammals. As a result, the cetacean prefrontal cortex (compared to that in humans) rather than frontal is laterally positioned. Brain size was previously considered a major indicator of intelligence . Since most of the brain is used for maintaining bodily functions, greater ratios of brain to body mass may increase
12300-461: The cetaceans genetically and morphologically fall firmly within the Artiodactyla (even-toed ungulates). The term "Cetartiodactyla" reflects the idea that whales evolved within the ungulates. The term was coined by merging the name for the two orders, Cetacea and Artiodactyla, into a single word. Under this definition, the closest living land relative of the whales and dolphins is thought to be
12450-439: The chance of deleterious genetic drift . Pteronura (giant otter) Lontra (4 species) Enhydra (sea otter) Hydrictis (spotted-necked otter) Lutra (2 species) Aonyx (African clawless) Amblonyx (Asian small-clawed) Lutrogale (smooth-coated) The first scientific description of the sea otter is contained in the field notes of Georg Steller from 1751, and
12600-556: The clade Whippomorpha . Cetaceans have been extensively hunted for their meat, blubber and oil by commercial operations. Although the International Whaling Commission has agreed on putting a halt to commercial whaling, whale hunting is still going on, either under IWC quotas to assist the subsistence of Arctic native people or in the name of scientific research, although a large spectrum of non-lethal methods are now available to study marine mammals in
12750-751: The country (namely Kamchatka and Sakhalin Island ), occasionally being seen in and around the Sea of Okhotsk . Before the 19th century, around 20,000 to 25,000 sea otters lived near the Kuril Islands , with more near Kamchatka and the Commander Islands . After the years of the Great Hunt, the population in these areas, currently part of Russia, was only 750. By 2004, sea otters had repopulated all of their former habitat in these areas, with an estimated total population of about 27,000. Of these, about 19,000 are at
12900-416: The course of mammalian evolution. Having only returned to the sea about 3 million years ago, sea otters represent a snapshot at the earliest point of the transition from fur to blubber. In sea otters, fur is still advantageous, given their small nature and division of lifetime between the aquatic and terrestrial environments. However, as sea otters evolve and adapt to spending more and more of their lifetimes in
13050-542: The cube root) and the three-quarters power (or the cube of the fourth root) of the body mass. m brain ∝ ( m body ) where k is between two-thirds and three-quarters. Thus if Species B is twice the size of Species A, its brain size will typically be somewhere between 60% and 70% higher. Comparison of a particular animal's brain size with the expected brain size based on such an analysis provides an encephalization quotient that can be used as an indication of animal intelligence. The neocortex of many cetaceans
13200-488: The densest in the animal kingdom. Although it can walk on land, the sea otter is capable of living exclusively in the ocean. The sea otter inhabits nearshore environments, where it dives to the sea floor to forage . It preys mostly on marine invertebrates such as sea urchins , various mollusks and crustaceans , and some species of fish . Its foraging and eating habits are noteworthy in several respects. Its use of rocks to dislodge prey and to open shells makes it one of
13350-521: The diversity in anatomy seen between groups, improved foraging efficiency has been the main driver in their evolution . The level of dependence on the marine environment varies considerably with species. For example, dolphins and whales are completely dependent on the marine environment for all stages of their life; seals feed in the ocean but breed on land; and polar bears must feed on land. The cetaceans became aquatic around 50 million years ago (mya). Based on molecular and morphological research,
13500-436: The evolution of numerous traits to create hallmark features like thick and oily fur and large bones, compared to their freshwater sister species. Sea otters require these traits to survive the cold waters of the northern Pacific Ocean , in which they spend their entire lives despite occasionally coming out of the water as pups. Sea otters have the thickest fur of any animal (~1,000,000 hairs per square inch), as they do not have
13650-501: The evolutionary future of sea otters. The sea otter propels itself underwater by moving the rear end of its body, including its tail and hind feet, up and down, and is capable of speeds of up to 9 kilometres per hour (5.6 mph). When underwater, its body is long and streamlined, with the short forelimbs pressed closely against the chest. When at the surface, it usually floats on its back and moves by sculling its feet and tail from side to side. At rest, all four limbs can be folded onto
13800-531: The eyes are open, ten teeth are visible, and the pup has a thick coat of baby fur. Mothers have been observed to lick and fluff a newborn for hours; after grooming, the pup's fur retains so much air, the pup floats like a cork and cannot dive. The fluffy baby fur is replaced by adult fur after about 13 weeks. Nursing lasts six to eight months in Californian populations and four to twelve months in Alaska, with
13950-460: The few mammal species to use tools. In most of its range, it is a keystone species , controlling sea urchin populations which would otherwise inflict extensive damage to kelp forest ecosystems . Its diet includes prey species that are also valued by humans as food, leading to conflicts between sea otters and fisheries. Sea otters, whose numbers were once estimated at 150,000–300,000, were hunted extensively for their fur between 1741 and 1911, and
14100-530: The fin are for stabilization and steering in the water. The male genitals and the mammary glands of females are sunken into the body. The male genitals are attached to a vestigial pelvis . The body is wrapped in a thick layer of fat, known as blubber . This provides thermal insulation and gives cetaceans their smooth, streamlined body shape. In larger species, it can reach a thickness up to one-half meter (1.6 feet). Sexual dimorphism evolved in many toothed whales. Sperm whales, narwhals , many members of
14250-812: The floor or to stay submerged. Surface-living animals (such as sea otters) need the opposite, and free-swimming animals living in open waters (such as dolphins) need to be neutrally buoyant in order to be able to swim up and down the water column. Typically, thick and dense bone is found in bottom feeders and low bone density is associated with mammals living in deep water. Some marine mammals, such as polar bears and otters, have retained four weight-bearing limbs and can walk on land like fully terrestrial animals. All cetaceans are carnivorous and predatory . Toothed whales mostly feed on fish and cephalopods , followed by crustaceans and bivalves . Some may forage with other kinds of animals, such as other species of whales or certain species of pinnipeds . One common feeding method
14400-511: The fur to squeeze out water and introduce air, and blowing air into the fur. To casual observers, it appears as if the animals are scratching, but they are not known to have lice or other parasites in the fur. When eating, sea otters roll in the water frequently, apparently to wash food scraps from their fur. The sea otter hunts in short dives, often to the sea floor . Although it can hold its breath for up to five minutes, its dives typically last about one minute and not more than four minutes. It
14550-442: The fur trade. These previous genetic bottlenecks are responsible for already low genetic diversity amongst species members, making the secondary bottleneck caused by the fur trade more significant. These primary bottlenecks were most likely caused by disease, a common cause for genetic bottlenecks. Estimates place these bottlenecks at leaving around ten to forty animals for about eight to forty-four years. This led to genetic drift , as
14700-454: The globe, but their distribution is patchy and coincides with the productivity of the oceans. Species richness peaks at around 40° latitude, both north and south. This corresponds to the highest levels of primary production around North and South America , Africa , Asia and Australia . Total species range is highly variable for marine mammal species. On average most marine mammals have ranges which are equivalent or smaller than one-fifth of
14850-403: The group's members. For example, the blue whale reaches a maximum confirmed length of 29.9 meters (98 feet) and a weight of 173 tonnes (190 short tons), making it the largest animal ever known to have existed. There are approximately 89 living species split into two parvorders : Odontoceti or toothed whales (containing porpoises , dolphins , other predatory whales like the beluga and
15000-405: The habitat conditions. Their body is well-adapted to their habitat, although they share essential characteristics with other higher mammals ( Eutheria ). They have a streamlined shape, and their forelimbs are flippers . Almost all have a dorsal fin on their backs, but this can take on many forms, depending on the species. A few species, such as the beluga whale , lack them. Both the flipper and
15150-427: The head, throat, and chest are lighter in color than the rest of the body. The sea otter displays numerous adaptations to its marine environment. The nostrils and small ears can close. The hind feet, which provide most of its propulsion in swimming, are long, broadly flattened, and fully webbed . The fifth digit on each hind foot is longest, facilitating swimming while on its back, but making walking difficult. The tail
15300-901: The health of coastal ecosystems, and similar changes have been observed as sea otter populations recovered in the Aleutian and Commander Islands and the Big Sur coast of California. However, some kelp forest ecosystems in California have also thrived without sea otters, with sea urchin populations apparently controlled by other factors. The role of sea otters in maintaining kelp forests has been observed to be more important in areas of open coast than in more protected bays and estuaries . Cetacea ( see text for families) Cetacea ( / s ɪ ˈ t eɪ ʃ ə / ; from Latin cetus ' whale ', from Ancient Greek κῆτος ( kêtos ) ' huge fish , sea monster ')
15450-529: The ice further north that remains frozen year-round. Seals may also migrate to other environmental changes, such as El Niño , and traveling seals may use various features of their environment to reach their destination including geomagnetic fields, water and wind currents, the position of the sun and moon and the taste and temperature of the water. Baleen whales famously migrate very long distances into tropical waters to give birth and raise young, possibly to prevent predation by killer whales. The gray whale has
15600-493: The island province of Hokkaido , in northern Japan, where the country's only confirmed population of western sea otter resides. Sightings have been documented in the waters of Cape Nosappu , Erimo , Hamanaka and Nemuro , among other locations in the region. Currently, the most stable and secure part of the western sea otter's range is along the Russian Far East coastline, in the northwestern Pacific waters off of
15750-434: The largest brain mass of any animal on Earth, averaging 8,000 cm (490 in ) and 7.8 kg (17 lb) in mature males. The brain to body mass ratio in some odontocetes, such as belugas and narwhals, is second only to humans. In some whales, however, it is less than half that of humans: 0.9% versus 2.1%. In cetaceans, evolution in the water has caused changes to the head that have modified brain shape such that
15900-592: The last sea otter taken near Kyuquot in 1929. From 1969 to 1972, 89 sea otters were flown or shipped from Alaska to the west coast of Vancouver Island. This population increased to over 5,600 in 2013 with an estimated annual growth rate of 7.2%, and their range on the island's west coast extended north to Cape Scott and across the Queen Charlotte Strait to the Broughton Archipelago and south to Clayoquot Sound and Tofino . In 1989,
16050-437: The level of devotion of sea otter mothers for their pups – a mother gives her infant almost constant attention, cradling it on her chest away from the cold water and attentively grooming its fur. When foraging, she leaves her pup floating on the water, sometimes wrapped in kelp to keep it from floating away; if the pup is not sleeping, it cries loudly until she returns. Mothers have been known to carry their pups for days after
16200-528: The longest recorded migration of any mammal, with one traveling 14,000 miles (23,000 km) from the Sea of Okhotsk to the Baja Peninsula . During the winter, manatees living at the northern end of their range migrate to warmer waters. Marine mammals have a number of physiological and anatomical features to overcome the unique challenges associated with aquatic living. Some of these features are very species-specific. Marine mammals have developed
16350-401: The lower stems of kelp , causing the kelp to drift away and die. Loss of the habitat and nutrients provided by kelp forests leads to profound cascade effects on the marine ecosystem. North Pacific areas that do not have sea otters often turn into urchin barrens , with abundant sea urchins and no kelp forest. Reintroduction of sea otters to British Columbia has led to a dramatic improvement in
16500-422: The majority of cetaceans live in marine environments, a small number reside solely in brackish water or fresh water . Having a cosmopolitan distribution , they can be found in some rivers and all of Earth's oceans, and many species inhabit vast ranges where they migrate with the changing of the seasons. Cetaceans are famous for their high intelligence , complex social behaviour, and the enormous size of some of
16650-476: The majority of their time in the water but need to return to land for important activities such as mating , breeding and molting . Sea otters tend to live in kelp forests and estuaries. In contrast, the polar bear is mostly terrestrial and only go into the water on occasions of necessity, and are thus much less adapted to aquatic living. The diets of marine mammals vary considerably as well; some eat zooplankton , others eat fish, squid, shellfish, or seagrass, and
16800-459: The meat in shellfish. To eat large sea urchins, which are mostly covered with spines, the sea otter bites through the underside where the spines are shortest, and licks the soft contents out of the urchin's shell. The sea otter's use of rocks when hunting and feeding makes it one of the few mammal species to use tools. To open hard shells, it may pound its prey with both paws against a rock on its chest. To pry an abalone off its rock, it hammers
16950-469: The middle and inner ear, the auditory bulla , is composed of two compact and dense bones (the periotic and tympanic). It is housed in a cavity in the middle ear; in the Odontoceti (apart from in the physeterids , this cavity is filled with dense foam and completely surrounds the bulla, which is connected to the skull only by ligaments. This may isolate the ear from sounds transmitted through the bones of
17100-467: The modern sea otter, Enhydra lutris . One related species has been described, Enhydra reevei , from the Pleistocene of East Anglia . The modern sea otter evolved initially in northern Hokkaidō and Russia, and then spread east to the Aleutian Islands , mainland Alaska , and down the North American coast. In comparison to cetaceans , sirenians , and pinnipeds , which entered the water approximately 50, 40, and 20 million years ago, respectively,
17250-522: The mother beginning to offer bits of prey at one to two months. The milk from a sea otter's two abdominal nipples is rich in fat and more similar to the milk of other marine mammals than to that of other mustelids . A pup, with guidance from its mother, practices swimming and diving for several weeks before it is able to reach the sea floor. Initially, the objects it retrieves are of little food value, such as brightly colored starfish and pebbles. Juveniles are typically independent at six to eight months, but
17400-541: The oceans, which have also evolved several specialized aquatic traits. In addition to the above, several other mammals have a great dependency on the sea without having become so anatomically specialized, otherwise known as "quasi-marine mammals". This term can include: the greater bulldog bat ( Noctilio leporinus ), the fish-eating bat ( Myotis vivesi ), the arctic fox ( Vulpes lagopus ) which often scavenges polar bear kills, coastal gray wolf ( Canis lupus ) populations which predominantly eat salmon and marine carcasses,
17550-858: The ongoing effects of global warming degrade Arctic environments. Procaviidae Elephantidae Dugongidae (dugongs) Trichechus manatus (West Indian manatee) Trichechus senegalensis (African manatee) Trichechus inunguis (Amazonian manatee; freshwater species) Hippopotamidae Mysticeti (baleen whales) Odontoceti (toothed whales, except river dolphins ) Ruminantia Perissodactyla Pholidota Feliformia Canidae Ursus maritimus (polar bear) all other ursids Enhydra lutris (sea otter) Lontra felina (marine otter) † Neogale macrodon (sea mink) all other mustelids Otariidae (eared seals) Odobenidae (walruses) Phocidae (earless seals) The term "marine mammal" encompasses all mammals whose survival depends entirely or almost entirely on
17700-621: The open ocean, and species like the sperm whale may dive to depths of −1,000 to −2,500 feet (−300 to −760 m) in search of food. Sirenians live in shallow coastal waters, usually living 30 feet (9.1 m) below sea level. However, they have been known to dive to −120 feet (−37 m) to forage deep-water seagrasses . Sea otters live in protected areas, such as rocky shores, kelp forests , and barrier reefs , although they may reside among drift ice or in sandy, muddy, or silty areas. Many marine mammals seasonally migrate. Annual ice contains areas of water that appear and disappear throughout
17850-541: The polar bear might not be considered a species under some species concepts . In general, terrestrial amniote invasions of the sea have become more frequent in the Cenozoic than they were in the Mesozoic. Factors contributing to this trend include the increasing productivity of near-shore marine environments, and the role of endothermy in facilitating this transition. Marine mammals are widely distributed throughout
18000-694: The population was estimated at over 2,000 individuals, and their range extends from Point Grenville in the south to Cape Flattery in the north and east to Pillar Point along the Strait of Juan de Fuca . In Washington, sea otters are found almost exclusively on the outer coasts. They can swim as close as six feet off shore along the Olympic coast. Reported sightings of sea otters in the San Juan Islands and Puget Sound almost always turn out to be North American river otters , which are commonly seen along
18150-466: The populations of northern and southern sea otters were cut off from one another by thousands of miles, leading to significant genomic differences. However, the modern population bottleneck caused by the fur trade of the eighteenth and early twentieth centuries presents the most significant concern to scientists and conservationists attempting to recover population numbers and genetic diversity. Each bottleneck has lowered genomic diversity and thus increased
18300-444: The pups' deaths. Females become sexually mature at around three or four years of age and males at around five; however, males often do not successfully breed until a few years later. A captive male sired offspring at age 19. In the wild, sea otters live to a maximum age of 23 years, with lifespans ranging from 10 to 15 years for males and 15–20 years for females. Several captive individuals have lived past 20 years. The Seattle Aquarium
18450-531: The sea otter and its closest extant relatives, which include the African speckle-throated otter , Eurasian otter , African clawless otter and Asian small-clawed otter , shared an ancestor approximately 5 million years ago. Fossil evidence indicates the Enhydra lineage became isolated in the North Pacific approximately 2 million years ago, giving rise to the now-extinct Enhydra macrodonta and
18600-429: The sea otter find prey by touch when waters are dark or murky. Researchers have noted when they approach in plain view, sea otters react more rapidly when the wind is blowing towards the animals, indicating the sense of smell is more important than sight as a warning sense. Other observations indicate the sea otter's sense of sight is useful above and below the water, although not as good as that of seals. Its hearing
18750-545: The sea otter is a relative newcomer to a marine existence. In some respects, though, the sea otter is more fully adapted to water than pinnipeds, which must haul out on land or ice to give birth. The full genome of the northern sea otter ( Enhydra lutris kenyoni ) was sequenced in 2017 and may allow for examination of the sea otter's evolutionary divergence from terrestrial mustelids. Following their divergence from their most common ancestor five million years ago, sea otters have developed traits dependent on polygenic selection, or
18900-499: The sea, the convergent evolution of blubber suggests that the reliance on fur for insulation would be replaced by a dependency on blubber. This is particularly true due to the diving nature of the sea otter; as dives become lengthier and deeper, the air layer's ability to retain heat or buoyancy decreases, while blubber remains efficient at both of those functions. Blubber can also additionally serve as an energy source for deep dives, which would most likely prove advantageous over fur in
19050-534: The seashore. However, biologists have confirmed isolated sightings of sea otters in these areas since the mid-1990s. The last native sea otter in Oregon was probably shot and killed in 1906. In 1970 and 1971, a total of 95 sea otters were transplanted from Amchitka Island , Alaska to the Southern Oregon coast. However, this translocation effort failed and otters soon again disappeared from the state. In 2004,
19200-467: The shore. They are found most often in areas with protection from the most severe ocean winds, such as rocky coastlines, thick kelp forests , and barrier reefs . Although they are most strongly associated with rocky substrates , sea otters can also live in areas where the sea floor consists primarily of mud, sand, or silt. Their northern range is limited by ice, as sea otters can survive amidst drift ice but not land-fast ice . Individuals generally occupy
19350-426: The skull is significantly shortened and deformed. By shifting the nostrils to the top of the head, the nasal passages extend perpendicularly through the skull. The teeth or baleen in the upper jaw sit exclusively on the maxilla . The braincase is concentrated through the nasal passage to the front and is correspondingly higher, with individual cranial bones that overlap. In toothed whales, connective tissue exists in
19500-908: The skull, something that also happens in bats . Cetaceans use sound to communicate , using groans, moans, whistles, clicks or the 'singing' of the humpback whale. Odontoceti are generally capable of echolocation . They can discern the size, shape, surface characteristics, distance and movement of an object. They can search for, chase and catch fast-swimming prey in total darkness. Most Odontoceti can distinguish between prey and nonprey (such as humans or boats); captive Odontoceti can be trained to distinguish between, for example, balls of different sizes or shapes. Echolocation clicks also contain characteristic details unique to each animal, which may suggest that toothed whales can discern between their own click and that of others. While differences in ear structure associated with echolocating abilities are found amongst Cetacea, cranial asymmetry has also been found to be
19650-411: The species is capable of delayed implantation followed by four months of pregnancy. In California, sea otters usually breed every year, about twice as often as those in Alaska. Birth usually takes place in the water and typically produces a single pup weighing 1.4 to 2.3 kilograms (3 lb 1 oz to 5 lb 1 oz). Twins occur in 2% of births; however, usually only one pup survives. At birth,
19800-547: The species was described by Carl Linnaeus in his landmark 1758 10th edition of Systema Naturae . Originally named Lutra marina , it underwent numerous name changes before being accepted as Enhydra lutris in 1922. The generic name Enhydra , derives from the Ancient Greek en /εν "in" and hydra /ύδρα "water", meaning "in the water", and the Latin word lutris , meaning "otter". It was formerly sometimes referred to as
19950-457: The spine varies by species, ranging from forty to ninety-three. The cervical spine , found in all mammals, consists of seven vertebrae which, however, are reduced or fused. This fusion provides stability during swimming at the expense of mobility. The fins are carried by the thoracic vertebrae , ranging from nine to seventeen individual vertebrae. The sternum is cartilaginous. The last two to three pairs of ribs are not connected and hang freely in
20100-404: The status of sea otters to be "special concern". Alaska is the central area of the sea otter's range. In 1973, the population in Alaska was estimated at between 100,000 and 125,000 animals. By 2006, though, the Alaska population had fallen to an estimated 73,000 animals. A massive decline in sea otter populations in the Aleutian Islands accounts for most of the change; the cause of this decline
20250-500: The stomachs, whose individual sections can only be distinguished histologically . The liver is large and separate from the gall bladder . The kidneys are long and flattened. The salt concentration in cetacean blood is lower than that in seawater, requiring kidneys to excrete salt. This allows the animals to drink seawater. The urinary bladder is proportionally smaller in cetaceans than in land mammals. The testes are located internally, without an external scrotum . The uterus
20400-474: The target for commercial industry, leading to a sharp decline in all populations of exploited species, such as whales and seals. Commercial hunting led to the extinction of the Steller's sea cow , sea mink , Japanese sea lion and Caribbean monk seal . After commercial hunting ended, some species, such as the gray whale and northern elephant seal , have rebounded in numbers; conversely, other species, such as
20550-421: The thick fur and the skin where air is trapped and heated by the body. Cold water is kept completely away from the skin and heat loss is limited. However, a potential disadvantage of this form of insulation is compression of the air layer as the otter dives, thereby reducing the insulating quality of fur at depth when the animal forages. The fur is thick year-round, as it is shed and replaced gradually rather than in
20700-436: The torso to conserve heat, whereas on particularly hot days, the hind feet may be held underwater for cooling. The sea otter's body is highly buoyant because of its large lung capacity – about 2.5 times greater than that of similar-sized land mammals – and the air trapped in its fur. The sea otter walks with a clumsy, rolling gait on land, and can run in a bounding motion. Long, highly sensitive whiskers and front paws help
20850-427: The total lung volume. For land mammals, in comparison, this value is usually about 15%. During inhalation, about twice as much oxygen is absorbed by the lung tissue as in a land mammal. As with all mammals, the oxygen is stored in the blood and the lungs, but in cetaceans, it is also stored in various tissues, mainly in the muscles. The muscle pigment, myoglobin , provides an effective bond. This additional oxygen storage
21000-459: The water. Polar bears, otters, and fur seals have long, oily, and waterproof fur in order to trap air to provide insulation. In contrast, other marine mammals—such as whales, dolphins, porpoises, manatees, dugongs, and walruses—have lost long fur in favor of a thick, dense epidermis and a thickened fat layer (blubber) to prevent drag . Wading and bottom-feeding animals (such as manatees) need to be heavier than water in order to keep contact with
21150-705: The water. Balaenids ( right whales and bowhead whales ) have massive heads that can make up 40% of their body mass. Most mysticetes prefer the food-rich colder waters of the Northern and Southern Hemispheres, migrating to the Equator to give birth. During this process, they are capable of fasting for several months, relying on their fat reserves. The parvorder of Odontocetes – the toothed whales – include sperm whales, beaked whales, orcas, dolphins and porpoises. Generally their teeth have evolved to catch fish, squid or other marine invertebrates , not for chewing them, so prey
21300-556: The westernmost limit of the hunting grounds off the northern Japanese island of Hokkaido and the easternmost limit off Punta Morro Hermosa about 21 + 1 ⁄ 2 miles (34.6 km) south of Punta Eugenia , Baja California's westernmost headland in Mexico . In about two-thirds of its former range, the species is at varying levels of recovery, with high population densities in some areas and threatened populations in others. Sea otters currently have stable populations in parts of
21450-409: The whale's interest, be within a certain size range so that the baleen plates can filter it, and be slow enough so that it cannot escape. Otters are the only marine animals that are capable of lifting and turning over rocks, which they often do with their front paws when searching for prey. The sea otter may pluck snails and other organisms from kelp and dig deep into underwater mud for clams . It
21600-671: The wharf in Santa Cruz, California. Under each foreleg, the sea otter has a loose pouch of skin that extends across the chest. In this pouch (preferentially the left one), the animal stores collected food to bring to the surface. This pouch also holds a rock, unique to the otter, that is used to break open shellfish and clams. At the surface, the sea otter eats while floating on its back, using its forepaws to tear food apart and bring it to its mouth. It can chew and swallow small mussels with their shells, whereas large mussel shells may be twisted apart. It uses its lower incisor teeth to access
21750-407: The wild. Cetaceans also face severe environmental hazards from underwater noise pollution , entanglement in abandoned ropes and nets, collisions with ships, plastic and heavy metals build-up, to accelerating climate change , but how much they are affected varies widely from species to species, from minimally in the case of the southern bottlenose whale to the baiji (Chinese river dolphin) which
21900-453: The world population fell to 1,000–2,000 individuals living in a fraction of their historic range. A subsequent international ban on hunting, sea otter conservation efforts, and reintroduction programs into previously populated areas have contributed to numbers rebounding, and the species occupies about two-thirds of its former range. The recovery of the sea otter is considered an important success in marine conservation , although populations in
22050-483: The year as the weather changes, and seals migrate in response to these changes. In turn, polar bears must follow their prey. In Hudson Bay , James Bay , and some other areas, the ice melts completely each summer (an event often referred to as "ice-floe breakup"), forcing polar bears to go onto land and wait through the months until the next freeze-up. In the Chukchi and Beaufort seas, polar bears retreat each summer to
22200-431: Was considerably lighter than the average weight of otters in more sparse populations, at 39.3 kg (87 lb) in males and 25.2 kg (56 lb) in females Presumably less populous otters are more able to monopolize food sources, For its size, the male otter's baculum is very large, massive and bent upwards, measuring 150 mm ( 5 + 7 ⁄ 8 in) in length and 15 mm ( 9 ⁄ 16 in) at
22350-657: Was estimated at 16,000 before the fur trade decimated the population, leading to their assumed extinction. Today's population of California sea otters are the descendants of a single colony of about 50 sea otters located near Bixby Creek Bridge in March 1938. Their principal range has gradually expanded and extends from Pigeon Point in San Mateo County to Santa Barbara County . Sea otters were once numerous in San Francisco Bay . Historical records revealed
22500-404: Was home to both the oldest recorded female, Etika, who lived to the age of 28, and the oldest recorded male, Adaa , who lived to be 22 years 8 months. Sea otters in the wild often develop worn teeth , which may account for their apparently shorter lifespans. Sea otters live in coastal waters 15 to 23 metres (49 to 75 ft) deep, and usually stay within a kilometre ( 2 ⁄ 3 mi) of
#546453