Southern Elephant Seal

Southern Elephant Seal
Male (Bull)
Female (Cow)
Conservation status

Least Concern (IUCN 3.1)[1]
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Suborder: Pinnipedia
Family: Phocidae
Genus: Mirounga
Species: M. leonina
Binomial name
Mirounga leonina
Linnaeus, 1758

The Southern Elephant Seal (Mirounga leonina) is one of two species of elephant seal. It is not only the most massive pinniped but also the largest member of the order Carnivora living today. The seal gets its name from its great size and the large proboscis of the adult males, which is used in making extraordinarily loud roaring noises, especially during the mating season.

Contents

Description

The Southern elephant seal is distinguished from the Northern elephant seal by its greater body mass and a wider proboscis. There is a great sexual dimorphism in size, possibly the largest of any mammal, with the males much larger than the females.[2] While the females average about 400-900 kg (880-1,980 lb) and 2.6-3 m (8.6-10 feet) long, the bulls average around 2,200-4,000 kg (4,847-8,800 lb) and 4.2-5 m (13-16.5 feet) long.[3][4] The record bull, shot in Possession Bay, South Georgia in 1913, was 5,000 kg (11,000 lb) and 6.9 m (22.5 feet) long. The maximum size of a female is 1,000 kg (2,210 lb) and 3.7 m (12.2 ft).

Close-up of juvenile Southern Elephant seal, showing face and mouth detail

The eyes are large, round and black. The width of the eyes and a high concentration of low light pigments suggest that sight plays an important role in the capture of prey. Like all seals, elephant seals have hind limbs whose ends form the tail and tail fin. Each of the "feet" can deploy five long webbed fingers. This agile, dual palm is used to propel water. The pectoral fins are used little while swimming. While the hind limbs are unfit for locomotion on land, elephant seals use their fins as support to propel their bodies. They are able to propel themselves quickly (as fast as 8km/h) in this way for short-distance travel, to return to water, catch up with a female or chase an intruder.

Pups are born with fur and are completely black. Their coat is unsuited to water but protects infants by insulating them from the cold air. The first moulting accompanies weaning. After moulting, the coats may turn grey and brown, depending on the thickness and moisture of hair. Among older males, the skin takes the form of a thick leather which is often scarred.

Like other seals, elephant seals have a bloodstream adapted to the cold in which a mixture of small veins surround arteries capturing heat from them. This structure is present in extremities such as the hind legs.

Range and population

The world population is approximately 650,000 animals. Studies have shown the existence of three geographic subpopulations, one in each of the three oceans.

Tracking studies have indicated the routes traveled by elephant seals, thereby demonstrating that their main feeding area is at the edge of the Antarctic continent. While elephant seals may come ashore in Antarctica occasionally to rest or even to mate, they gather to breed in subantarctic locations.

Southern elephant seal harem on a beach on the Kerguelen Islands

The largest subpopulation is in the South Atlantic, with more than 400,000 individuals, including approximately 113,000 breeding females on South Georgia[5]; the other breeding colonies are located on the Falkland Islands and Valdes Peninsula in Argentina (the only continental breeding population).

The second subpopulation, in the south Indian Ocean, consist of up to 200,000 individuals, three-quarters of which breed in the Kerguelen Islands and the rest in the Crozet Islands, Marion and Prince Edward Islands, and Heard Island. Some individuals also breed on Amsterdam Island. The third sub-population of about 75,000 seals are found in the sub-Antarctic islands of the Pacific Ocean south of Tasmania and New Zealand, mainly Macquarie Island.

Colonies once existed in Tasmania, Saint Helena and the Juan Fernández Islands off the coast of Chile. Sometimes individuals at the time of moulting have been found in South Africa or Australia. There have also been reports from time to time of animals lost on the shores of Mauritius. There are two reports from the Río Guayas estuary area in Ecuador.

After the end of large scale seal hunting in the 19th century, the southern elephant seals recovered to a sizable population in the 1950's; since then there has been an unexplained decline in the subpopulations of the Indian Ocean and Pacific Ocean. The population now seems to be stable; the reasons for the fluctuation are unknown. Suggested explanations include a phenomenon of depression following a rapid demographic rebound that depletes vital resources, a change in climate, competition with other species whose numbers also varied, or even an adverse influence of scientific monitoring techniques.

Behavior

Feeding and diving

Thanks to satellite tracking, it was found that the animals spend very little time on the surface, usually a few minutes for oxygen. They dive repeatedly, each time for more than twenty minutes, to hunt their prey, squid and fish, between 400 and 1000 m deep. The diving records were recorded in nearly two hours for the duration and more than 1400 m in depth.

King Penguins and Southern Elephant Seal at South Georgia Island.

As far as duration, depth and the sequence of dives, the Southern elephant seal is the best performing seal. In may regards, they exceed even most cetaceans. These capabilities result from non-standard physiological adaptations, common to marine mammals, but particularly developed in elephant seals. The coping strategy is based on two pillars: increase the storage of oxygen and reduce its consumption.

Southern Elephant seal (just weaned pup): first bath

In the ocean, the elephant seals apparently live alone. Males seem to prefer to feed at the edge of the Antarctic continent, while females circulate widely. Individuals will return annually to the same hunting areas. The feeding of elephant seals is still not well known. We know that their diet is primarily composed of fish and squid, caught in the deep dives. But the direct observation of hunts during those long periods of quiet and pelagic life is impossible. While hunting in the dark depths, it is partly thanks to the use of vision that the elephant seals seem to locate their prey; the bioluminescence of some prey animals can facilitate their capture. Elephant seals have not developed a system of echolocation in the manner of cetaceans, but it is assumed that their vibrissae, which are sensitive to vibrations, play a role in search of food.

When attending the sub-Antarctic coast or Antarctic, the elephant seals can also consume shellfish isopods, ascidians, krill, mollusks or even algae. The elephant seal's only predators are orcas and possibly great white sharks, both of which are most likely to target pups.

Reproduction and pup life

Southern Elephant seal (females) : one is giving birth
Southern Elephant seal (young males): collective mudbath during moulting

Elephant seals are among the seals that can stay on land for the longest periods of time, as they can stay dry for several weeks consecutively each year. Females enter beaches in the sub-Antarctic early in the austral spring, starting in September. Generally, the pups are born rather quickly. Immediately, the newborn begins to suckle. Breastfeeding lasts an average of 23 days. Throughout this period, the female fasts. Newborns weigh about 40 kg at birth reached 120 to 130 kg when they are weaned. The mother loses significant weight during this time. Even before all the pups are born, the males have also joined the colonies. The strongest known bulls, the alpha males, have established their harems of several dozen females. Beta males are also present and have smaller harems. The least successful males have no harems but will go as far as to try to seduce an alpha or beta male's females when the male is not looking. An elephant seal must stay in his territory to defend it, which could mean months without eating and having to live on its blubber storage. Two fighting males use their weight and canines against each other. The outcome is rarely fatal and the defeated bull will flee. However bulls can suffer severe tears and cuts.

Young seals that are weaned gather in nurseries until losing their birth coat. They enter the water to practice swimming, generally starting their apprenticeship in estuaries or ponds. In summer, the elephant seals come ashore to molt. This happens sometimes directly after reproduction. Some males can stay ashore for more than 3 months without food.

Conservation

Play fight

After their near extinction due to hunting in the 19th century, total population is about 600,000, but all the populations seem to be declining at present. The reasons for this are unclear, but it may simply be that once protection from hunting was established, the species recovered so fast that it overshot its equilibrium numbers. Most of their most important breeding sites are now protected by international treaty, as UNESCO World Heritage Sites, or by national legislation.

Minazo

One of the most famous southern elephant seals is Minazo, who lived in Japan's Enoshima Aquarium from when he was a half-year old until his death in 2005.[6] Minazo became popular for his signature bucket-holding, tongue-lolling pose. In 2006, Minazo was memorialized by the Japanese noise musician Masami Akita, AKA Merzbow, in a two volume album (vol. 1, vol. 2) with artwork by Jenny Akita showing Minazo holding his beloved bucket. In 2007, Minazo became the subject of an image macro similar to lolcat called lolrus. In his liner notes, Masami Akita suggests that Minazo's frequent and demanding performances left him exhausted, contributing ultimately to his death. Akita's intention in celebrating Minazo was to highlight the plight of captive animals used for performance before public audiences.[7] Minazo has also featured on several t-shirt designs. In 2009 the t-shirt site mrcloud.com recreated their Beatles' "I Am The Walrus" t-shirt to feature Minazo holding his signature bucket.[8]

See also

Notes

  1. ↑ Campagna, C. (IUCN SSC Pinniped Specialist Group) (2008). Mirounga leonina. In: IUCN 2008. IUCN Red List of Threatened Species. Downloaded on 22 March 2009. Database entry includes a brief justification of why this species is of least concern
  2. ↑ http://books.google.com/books?id=2rkHQpToi9sC&pg=PA23&lpg=PA23&dq=elephant+seal+greatest+sexual+dimorphism&source=bl&ots=hCivHt0aAr&sig=sbBEbl5k0bdE6b1Kh06GoxNIrKA&hl=en&ei=OlH4SeSkGoOltge6irjtDw&sa=X&oi=book_result&ct=result&resnum=2
  3. ↑ http://www.pinnipeds.org/species/selephnt.htm
  4. ↑ http://animaldiversity.ummz.umich.edu/site/accounts/information/Mirounga_leonina.html
  5. ↑ Boyd, I.L., Walker, T.R., Poncet, J. (1996) Status of Southern Elephant seals, Mirounga leonina at South Georgia. Antarctic Science. 8(3): 237-244.
  6. ↑ Minazo album press release (Important Records 2006)[1]
  7. ↑ "Popular Enoshima aquarium seal dies after 10 1/2-year run" (Japan Times 2005-10-05)[2]
  8. ↑ http://www.mrcloud.com/walrus-tshirt-bukkit-tshirt-lolrus-p-337.html

References

External links