Northern elephant seal (Mirounga angustirostris)

KingdomAnimalia
PhylumChordata
ClassMammalia
OrderCarnivora
FamilyPhocidae
GenusMirounga (1)
SizeMale length: 4 - 5 m (2)
Female length: 2 - 3 m (2)
Male weight: 2,000 - 2,700 kg (2)
Female weight: 600 - 900 kg (2)

The northern elephant seal is classified as Least Concern (LC) on the IUCN Red List (1).

On land, this enormous marine mammal may be a lumbering mass of blubber, but once in water the northern elephant seal (Mirounga angustirostris) transforms into a graceful swimmer and remarkable diver. One of the most striking features of the northern elephant seal is the pronounced differences between the sexes (3). Males are not only significantly larger and heavier than females, but they also have (like their namesakes) a prominent, trunk-like proboscis, and a region of thickened, scarred skin on the neck, chest and shoulders called a ‘chest shield’, the result of numerous fights with other males (3).

The short, stiff hair of males is dark grey, fading to a rusty greyish-brown throughout the year (2). Females are generally darker than males, having a brown coat with a lighter area around the neck, which is actually scarring from being repeatedly bitten by the male during mating (2). Like other true seals (those belonging to the Phocidae family), the northern elephant seal has long, webbed feet, providing effective propulsion through the water, and forelimbs that are used to steer whilst swimming or to drag themselves across land (4).

The northern elephant seal occurs in the eastern Pacific Ocean, where it breeds on approximately 15 islands and a few mainland beaches situated between northern California and the Baja California Peninsula in Mexico (2) (3). This species has also been recorded breeding further north at Race Rocks, an ecological reserve in the Strait of Juan de Fuca (5).

When not breeding, many northern elephant seals migrate north, along the North American coast to the Gulf of Alaska and the Aleutian Islands (3).

Sandy or gravel beaches, far from human activity, are the preferred breeding sites of the northern elephant seal (2). When feeding at sea, males tend to be found over continental shelves whereas females inhabit deeper open water (3).

The annual breeding cycle of the northern elephant seal begins in December, when the huge males haul out onto deserted beaches. Large numbers of pregnant females soon follow the males, aggregating into large groups known as harems, with each group presided over by a large, dominant male (3). Competition for this dominant position is intense (3), with males establishing their supremacy through stares, gestures, and snorts and grunts amplified by the inflation of their proboscis (2). Spectacular fights may ensue, with males delivering serious, but rarely fatal, blows with their large canine teeth (2).

Between two and five days after arriving at the colony, each female will give birth to a single pup (3). For the next 27 days (2), the female will stay with her new pup, feeding it large quantities of rich, fatty milk, while she relies on her own thick blubber for sustenance (3). Shortly before the young are weaned, the females come into oestrus and mate with the dominant male. After weaning their young, the females return to sea, leaving the pups to fend for themselves (3). For the next four to six weeks, the pups practice swimming and diving, before leaving the beach where they were born to spend the next six months at sea. Northern elephant seal pups are highly vulnerable at this time, with around 30 percent perishing (3).

After breeding, many northern elephant seals travel north towards Alaska to feed. Northern elephant seals feed primarily on deepwater fish and squid, a diet that necessitates an exceptional diving ability (3). They can dive down to over 1,500 metres, remaining underwater for up to an extraordinary 120 minutes, although most dives are to shallower depths and last for around 20 minutes (3). More than 80 percent of the year is spent feeding at sea, in order to build up their essential blubber stores to provide energy for breeding and moulting, times at which the seals do not feed (3).

Northern elephant seals return to their southern breeding ground to moult, a process in which the very outer layer of skin is shed in addition to the hair. As rich supplies of blood are pumped to the skin to enable the growth of the new skin and hair, conserving body heat becomes essential, and so the seals do not enter the water to feed for the next three to five weeks (3). Following moulting, northern elephant seals travel northwards once more, before returning to their breeding colonies to commence the breeding cycle again. This remarkable journey, undertake twice each year, covers an impressive 10,000 kilometres (3).

In the past, the northern elephant seal suffered intense exploitation for its thick blubber which yields high quality oil (3). Hunting started around 1818 and by the 1860s about 250,000 seals had been killed, leaving numbers too low to make hunting worthwhile (2). On a number of occasions it was thought that the species had gone extinct, and by 1892, just a single population of about 100 individuals remained on Guadalupe Island, off northern Baja California (2). Thankfully, the implementation of legal protection allowed numbers to recover, and the northern elephant seal population slowly spread north and south until they reoccupied most of the original range (2).

Today, northern elephant seals continue to increase in both number and range (3). There is some concern that commercial fisheries may be competing with the northern elephant seal for its preferred prey, but otherwise, this species faces no negative interactions with humans (3). Possibly the most serious potential threat to the northern elephant seal is the significant lack of genetic diversity in populations, the result of the drastic declines they underwent in the past. This may leave the northern elephant seal ill equipped to adapt to any changes in their environment (2).

Complete legal protection for the northern elephant seal was implemented in Mexico in 1922 (2), and subsequently, the severely depleted populations went on to display one of the most incredible recoveries ever observed in a mammal (3). The northern elephant seal is also protected in the United States under the Marine Mammal Protection Act (6).(1)

For further information on the northern elephant seal see:

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  1. IUCN Red List (November, 2008)
    http://www.iucnredlist.org
  2. Nowak, R.M. (1999) Walker's Mammals of the World. Johns Hopkins University Press, Baltimore, Maryland.
  3. Hindell, M.A. (2002) Elephant seals. In: Perrin, W.F., Würsig, B. and Thewissen, J.G.M. (Eds) Encyclopedia of Marine Mammals. Academic Press, London.
  4. Macdonald, D.W. (2006) The Encyclopedia of Mammals. Oxford University Press, Oxford.
  5. Race Rocks - Elephant seals (Mirounga angustirostris) at Race Rocks (December, 2012)
    http://www.racerocks.ca/wp/marine-mammal-problems/elephant-seals-mirounga-angustirostris-at-race-rocks/
  6. Western Pacific Regional Fishery Management Council (September, 2008)
    http://www.wpcouncil.org/protected/species_mammals.html#top