Elephant seal

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Elephant seal
See elefanten edit.jpg
Male and female northern elephant seals
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Clade: Pinnipedia
Family: Phocidae
Tribe: Miroungini
Genus: Mirounga
Gray, 1827
Species

M. angustirostris
M. leonina

Elephant seals are large, oceangoing earless seals in the genus Mirounga. The two species, the northern elephant seal (M. angustirostris) and the southern elephant seal (M. leonina), were both hunted to the brink of extinction by the end of the 19th century, but their numbers have since recovered.

Contents

The northern elephant seal, somewhat smaller than its southern relative, ranges over the Pacific coast of the U.S., Canada and Mexico. The most northerly breeding location on the Pacific Coast is at Race Rocks, at the southern tip of Vancouver Island in the Strait of Juan de Fuca. The southern elephant seal is found in the Southern Hemisphere on islands such as South Georgia and Macquarie Island, and on the coasts of New Zealand, South Africa, and Argentina in the Peninsula Valdés. In southern Chile, there is a small colony of 120 animals at Jackson Bay, Admiralty Sound (Seno Almirantazgo), Tierra del Fuego. [1] The oldest known unambiguous elephant seal fossils are fragmentary fossils of an unnamed member of the tribe Miroungini described from the late Pliocene Petane Formation of New Zealand. [2] Teeth originally identified as representing an unnamed species of Mirounga have been found in South Africa, and dated to the Miocene epoch; [3] [4] however Boessenecker & Churchill (2016) considered these teeth to be almost certainly misidentified odontocete teeth. [2]

Elephant seals breed annually and are seemingly faithful to colonies that have established breeding areas. [5]

Description

Elephant seals are marine mammals classified under the order Pinnipedia, which, in Latin, means feather- or fin-footed. [6] Elephant seals are considered true seals, and fall under the family Phocidae. [7] Phocids (true seals) are characterized by having no external ear and reduced limbs. [7] The reduction of their limbs helps them be more streamlined and move easily in the water. [6] However, it makes navigating on land a bit difficult because they cannot turn their hind flippers forward to walk like the Otariids. [6] In addition, the hind flipper of elephant seals have a lot of surface area, which helps propel them in the water. [6] Elephant seals spend the majority of their time (90%) underwater in search of food, and can cover 60 miles a day when they head out to sea. [7] When elephant seals are born, they can weigh up to 80 pounds and reach lengths up to 4 feet. [7] Sexual dimorphism is extreme, with male elephant seals weighing up to 10 times more than females, [8] and having a large proboscis. [7]

Elephant seals take their name from the large proboscis of the adult male (bull), which resembles an elephant's trunk, and is considered a secondary sexual characteristic. [9] The bull's proboscis is used in producing extraordinarily loud roaring noises, especially during the mating season. More importantly, however, the nose acts as a sort of rebreather, filled with cavities designed to reabsorb moisture from their exhalations. [10] This is important during the mating season when the seals do not leave the beach to feed, and must conserve body moisture as there is no incoming source of water. They are very much larger than other pinnipeds, with southern elephant seal bulls typically reaching a length of 5 m (16 ft) and a weight of 3,000 kg (6,600 lb), and are much larger than the adult females (cows), with some exceptionally large males reaching up to 6 m (20 ft) in length and weighing 4,000 kg (8,800 lb); cows typically measure about 3 m (10 ft) and 900 kg (2,000 lb). Northern elephant seal bulls reach a length of 4.3 to 4.8 m (14 to 16 ft) and the heaviest weigh about 2,500 kg (5,500 lb). [11] [12]

The northern and southern elephant seal can be distinguished by various external features. On average, the southern elephant seal tends to be larger than the northern species. [8] Adult male elephant seals belonging to the northern species tend to have a larger proboscis, and thick chest area with a red coloration compared to the southern species. [8] Females do not have the large proboscis and can be distinguished between species by looking at their nose characteristics. [8] Southern females tend to have a smaller, blunt nose compared to northern females. [8]

Extant species

ImageScientific nameCommon NameDistribution
Mirounga angustirostris, Point Reyes.jpg M. angustirostris Northern elephant seal Eastern Pacific Ocean
Southern Elephant Seal (5797958581).jpg M. leonina Southern elephant seal South Atlantic

Physiology

Skull of a northern elephant seal. Miroungaskull.jpg
Skull of a northern elephant seal.

Elephant seals spend up to 80% of their lives in the ocean. They can hold their breath for more than 100 minutes [13] [14] – longer than any other noncetacean mammal. Elephant seals dive to 1,550 m (5,090 ft) beneath the ocean's surface [13] (the deepest recorded dive of an elephant seal is 2,388 m (7,835 ft) by a southern elephant seal). [15] The average depth of their dives is about 300 to 600 m (980 to 1,970 ft), typically for around 20 minutes for females and 60 minutes for males, as they search for their favorite foods, which are skates, rays, squid, octopuses, eels, small sharks and large fish. Their stomachs also often contain gastroliths. They spend only brief amounts of time at the surface to rest between dives (2–3 minutes). [7] Females tend to dive a bit deeper due to their prey source. [7]

Male elephant seals fighting for mates.

Elephant seals are shielded from extreme cold more by their blubber than by fur. Their hair and outer layers of skin molt in large patches. The skin has to be regrown by blood vessels reaching through the blubber. When molting occurs, the seal is susceptible to the cold, and must rest on land, in a safe place called a "haul out". Northern males and young adults haul out during June to July to molt; northern females and immature seals during April to May.

Elephant seals have a very large volume of blood, allowing them to hold a large amount of oxygen for use when diving. They have large sinuses in their abdomens to hold blood and can also store oxygen in their muscles with increased myoglobin concentrations in muscle. In addition, they have a larger proportion of oxygen-carrying red blood cells. These adaptations allow elephant seals to dive to such depths and remain underwater for up to two hours. [16]

Elephant seals are able to slow down their heartbeat (bradycardia) and divert blood flow from the external areas of the body to important core organs. [7] They can also slow down their metabolism while performing deep dives. [7]

Elephant seals have a helpful feature in their bodies known as the countercurrent heat exchanger to help conserve energy and prevent heat loss. [7] In this system, arteries and veins are organized in a way to maintain a constant body temperature by having the cool blood flowing to the heart warmed by blood going to external areas of the animal. [7]

Milk produced by elephant seals is remarkably high in milkfat compared to other mammals. After an initially lower state, it rises to over 50% milkfat (human breast milk is about 4% milkfat, and cow milk is about 3.5% milkfat). [17]

Adaptations

Elephant seals have large circular eyes that have more rods than cones to help them see in low light conditions when they are diving. [6] [7] These seals also possess a structure called the tapetum lucidum, which helps their vision by having light reflected back to the retina to allow more chances for photoreceptors to detect light. [6]

Their body is covered in blubber, which helps them keep warm and reduce drag while they are swimming. [7] The shape of their body also helps them maneuver well in the water, but limits their movement on land. [7] Also, elephant seals have the ability to fast for long periods of time while breeding or molting. [7] The turbinate process, another unique adaptation, is very beneficial when these seals are fasting, breeding, molting, or hauling out. [7] This unique nasal structure recycles moisture when they breathe and helps prevent water loss. [7]

Elephant seals have external whiskers called vibrissae to help them locate prey and navigate their environment. [7] The vibrissae are connected to blood vessels, nerves, and muscles making them an important sensing tool. [6]

Due to evolutionary changes, their ear has been modified to work extremely well underwater. [6] The structure of the inner ear helps amplify incoming sounds, and allows these seals to have good directional hearing due to the isolation of the inner ear. [6] In addition to these adaptations, tissues in the ear canal allow the pressure in the ear to be adjusted while these seals perform their deep dives. [6]

Breeding season

Dominant males arrive at potential breeding sites in November, and will spend 3 months on the beach fasting to ensure that they can mate with as many females as possible. [7] Male elephant seals use fighting, vocal noises, and different positions to determine who will be deemed the dominant male. [7] [18] When males reach 8 to 9 years of age, they have developed a pronounced long nose, in addition to a chest shield, which is thickened skin in their chest area. [7] Showing off their noses, making loud vocalizations, and altering their posture are a few ways males show off their dominance. [7] [18] When battles come into play, seals will stand tall, and ram themselves into one another using their chest plates and sharp teeth. [7]

When the pregnant females arrive, the dominating males have already selected their territory on the beach. [7] Females cluster in groups called harems, which could consist of up to 50 females surrounding one alpha male. [7] Outside of these groups, a beta bull is normally roaming around on the beach. [7] The beta bull helps the alpha by preventing other males accessing the females. [7] In return, the beta bull might have an opportunity to mate with one of the females while the alpha is occupied. [7]

Birth on average only takes a few minutes, and the mother and pup have a connection due to each other's unique smell and sound. [7] The mothers will fast and nurse up to 28 days, providing their pups with rich milk. [7] The last two to three days, however, females will be ready to mate, and the dominant males will pounce on the opportunity. [7] During this exhaustive process, males and females lose up to a third of their body weight during the breeding season. [7] The gestation period for females is 11 months, and the pupping seasons lasts from mid December through the middle of February. [7] The new pups will spend up to ten additional weeks on land learning how to swim and dive. [7]

Life history

The average lifespan of a Northern Elephant Seal is 9 years, while the average lifespan of a Southern Elephant Seal is 21 years. [19] Males reach maturity at five to six years, but generally do not achieve alpha status until the age of eight, with the prime breeding years being between ages 9 and 12. The longest life expectancy of a male northern elephant seal is approximately 14 years.

Females begin breeding at age 3–6 (median=4), and have one pup per breeding attempt. [20] Once they begin breeding, 79% of adult females breed each year. [21] Breeding success is much lower for first-time mothers relative to experienced breeders. [21] Annual survival probability of adult females is 0.83 for experienced breeding females, but only 0.66 for first-time breeders indicating a significant cost of reproduction. [21] More male pups are produced than female pups in years with warmer sea surface temperature in the northeastern Pacific Ocean. [22]

Molting

Once a year, elephant seals go through a process called molting where they shed the outer layer of hair and skin. [7] This molting process takes up to a month to complete. [7] When it comes time to molt, they will haul out on land to shed their outer layer, and will not consume any food during this time. [7] The females and juveniles will molt first, followed by the sub adult males, and finally the large mature males. [7]

Predators

The main predator of elephant seals is the great white shark. [7] Orcas are also another predator of elephant seals. [7] Cookie cutter sharks can even take notorious bites out of their skin. [7]

Status

The IUCN lists both species of elephant seal as being of least concern, although they are still threatened by entanglement in marine debris, fishery interactions, and boat collisions. Though a complete population count of elephant seals is not possible because all age classes are not ashore at the same time, the most recent estimate of the California breeding stock was approximately 124,000 individuals. In the United States, the elephant seal, like all marine mammals, is protected under the Marine Mammal Protection Act (MMPA), passed in 1972, which outlaws hunting, killing, capture, and harassment of the animal. [23]

See also

Related Research Articles

Earless seal family of mammals

The seals, phocids or true seals are one of the three main groups of mammals within the seal lineage, Pinnipedia. All true seals are members of the family Phocidae. They are sometimes called crawling seals to distinguish them from the fur seals and sea lions of the family Otariidae. Seals live in the oceans of both hemispheres and, with the exception of the more tropical monk seals, are mostly confined to polar, subpolar, and temperate climates. The Baikal seal is the only species of exclusively freshwater seal.

Fur seal subfamily of mammals

Fur seals are any of nine species of pinnipeds belonging to the subfamily Arctocephalinae in the family Otariidae. They are much more closely related to sea lions than true seals, and share with them external ears (pinnae), relatively long and muscular foreflippers, and the ability to walk on all fours. They are marked by their dense underfur, which made them a long-time object of commercial hunting. Eight species belong to the genus Arctocephalus and are found primarily in the Southern Hemisphere, while a ninth species also sometimes called fur seal, the northern fur seal, belongs to a different genus and inhabits the North Pacific.

California sea lion the fastest living species pinniped in the world

The California sea lion is a coastal eared seal native to western North America. It is one of six species of sea lion. Its natural habitat ranges from southeast Alaska to central Mexico, including the Gulf of California. Sea lions are sexually dimorphic; males are larger than females, and have a thicker neck, and protruding sagittal crest. They mainly haul-out on sandy or rocky beaches, but they also frequent manmade environments such as marinas and wharves. Sea lions feed on a number of species of fish and squid, and are preyed on by killer whales and great white sharks.

Pinniped Infraorder of mammals

Pinnipeds, commonly known as seals, are a widely distributed and diverse clade of carnivorous, fin-footed, semiaquatic marine mammals. They comprise the extant families Odobenidae, Otariidae, and Phocidae. There are 33 extant species of pinnipeds, and more than 50 extinct species have been described from fossils. While seals were historically thought to have descended from two ancestral lines, molecular evidence supports them as a monophyletic lineage. Pinnipeds belong to the order Carnivora and their closest living relatives are believed to be bears and the superfamily of musteloids, having diverged about 50 million years ago.

Steller sea lion The largest living sea lion and eared seal in the world

The Steller sea lion, also known as the Steller's sea lion and "northern sea lion", is a near-threatened species of sea lion in the northern Pacific. It is the sole member of the genus Eumetopias and the largest of the eared seals (Otariidae). Among pinnipeds, it is inferior in size only to the walrus and the two species of elephant seals. The species is named for the naturalist Georg Wilhelm Steller, who first described them in 1741. The Steller sea lion has attracted considerable attention in recent decades, owing to significant and largely unexplained declines in their numbers over an extensive portion of their northern range in Alaska.

Grey seal species of seal

The grey seal is found on both shores of the North Atlantic Ocean. It is a large seal of the family Phocidae which are commonly referred to as "true seals" or "earless seals". It is the only species classified in the genus Halichoerus. Its name is spelled gray seal in the US; it is also known as Atlantic seal and the horsehead seal.

Leopard seal Species of mammal

The leopard seal, also referred to as the sea leopard, is the second largest species of seal in the Antarctic. Its only natural predator is the killer whale. It feeds on a wide range of prey including cephalopods, other pinnipeds, krill, birds and fish. It is the only species in the genus Hydrurga. Its closest relatives are the Ross seal, the crabeater seal and the Weddell seal, which together are known as the tribe of Lobodontini seals. The name hydrurga means "water worker" and leptonyx is the Greek for "small clawed".

Northern elephant seal The second largest living pinniped in the world

The northern elephant seal is one of two species of elephant seal. It is a member of the family Phocidae. Elephant seals derive their name from their great size and from the male's large proboscis, which is used in making extraordinarily loud roaring noises, especially during the mating competition. Sexual dimorphism in size is great. Correspondingly, the mating system is highly polygynous; a successful male is able to impregnate up to 50 females in one season.

Hooded seal species of mammal

The hooded seal is a large phocid found only in the central and western North Atlantic, ranging from Svalbard in the east to the Gulf of St. Lawrence in the west. The seals are typically silver-grey or white in Color, with black spots that vary in size covering most of the body. Hooded seal pups are known as "blue-backs" because their coats are blue-grey on the back with whitish bellies, though this coat is shed after 14 months of age when the pups molt.

Northern fur seal The largest fur seal in the northern hemisphere

The northern fur seal is an eared seal found along the north Pacific Ocean, the Bering Sea, and the Sea of Okhotsk. It is the largest member of the fur seal subfamily (Arctocephalinae) and the only living species in the genus Callorhinus. A single fossil species, Callorhinus gilmorei, is known from the Pliocene of Japan and western North America.

Antarctic fur seal species of mammal

The Antarctic fur seal, is one of eight seals in the genus Arctocephalus, and one of nine fur seals in the subfamily Arctocephalinae. Despite what its name suggests, the Antarctic fur seal is mostly distributed in Subantarctic islands and its scientific name is thought to have come from the German vessel SMS Gazelle, which was the first to collect specimens of this species from Kerguelen Islands.

Subantarctic fur seal species of mammal

The subantarctic fur seal is found in the southern parts of the Indian, Pacific, and Atlantic Oceans. It was first described by Gray in 1872 from a specimen recovered in northern Australia—hence the inappropriate specific name tropicalis.

Juan Fernández fur seal species of mammal

The Juan Fernández fur seal is the second smallest of the fur seals, second only to the Galápagos fur seal. They are found only on the Pacific Coast of South America, more specifically on the Juan Fernández Islands and the Desventuradas Islands. There is still much that is unknown about this species. Scientists still do not know the average life span of this species, or the diet and behavior of males apart from the breeding season.

Brown fur seal species of fur seal

The brown fur seal, also known as the Cape fur seal, South African fur seal, and Australian fur seal, is a species of fur seal.

South American sea lion species of mammal

The South American sea lion, also called the Southern Sea Lion and the Patagonian sea lion, is a sea lion found on the Ecuadorian, Peruvian, Chilean, Falkland Islands, Argentinean, Uruguayan, and Southern Brazilian coasts. It is the only member of the genus Otaria. Its scientific name was subject to controversy, with some taxonomists referring to it as Otaria flavescens and others referring to it as Otaria byronia. The former eventually won out, although that may still be overturned. Locally, it is known by several names, most commonly lobo marino (es)/lobo marinho (pt) and león marino (es)/leão marinho (pt) and the hair seal.

Weddell seal species of mammal

The Weddell seal is a relatively large and abundant true seal with a circumpolar distribution surrounding Antarctica. The Weddell seal was discovered and named in the 1820s during expeditions led by British sealing captain James Weddell to the area of the Southern Ocean now known as the Weddell Sea. The life history of this species is well documented since it occupies fast ice environments close to the Antarctic continent and often adjacent to Antarctic bases.

Caspian seal species of mammal

The Caspian seal is one of the smallest members of the earless seal family and unique in that it is found exclusively in the brackish Caspian Sea. They are found not only along the shorelines, but also on the many rocky islands and floating blocks of ice that dot the Caspian Sea. In winter, and cooler parts of the spring and autumn season, these marine mammals populate the Northern Caspian. As the ice melts in the warmer season, they can be found on the mouths of the Volga and Ural Rivers, as well as the southern latitudes of the Caspian where cooler waters can be found due to greater depth.

Ribbon seal Species of mammal

The ribbon seal is a medium-sized pinniped from the true seal family (Phocidae). A seasonally ice-bound species, it is found in the Arctic and Subarctic regions of the North Pacific Ocean, notably in the Bering Sea and Sea of Okhotsk. It is distinguished by its striking coloration, with two wide white strips and two white circles against dark brown or black fur.

Southern elephant seal Species of mammal

The southern elephant seal is one of the two species of elephant seals. It is the largest member of the clade Pinnipedia and the order Carnivora, as well as the largest extant marine mammal that is not a cetacean. It gets its name from its massive size and the large proboscis of the adult male, which is used to produce very loud roars, especially during the breeding season. A bull southern elephant seal is about 40% heavier than a male northern elephant seal, more than twice as heavy as a male walrus, and six to seven times heavier than the largest living terrestrial carnivorans, the polar bear and the Kodiak bear.

Harbor seal Species of mammal

The harbourseal, also known as the common seal, is a true seal found along temperate and Arctic marine coastlines of the Northern Hemisphere. The most widely distributed species of pinniped, they are found in coastal waters of the northern Atlantic, Pacific Oceans, Baltic and North Seas.

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