Facts about elephant seal

Elephant seal group, Campbell Island

The southern elephant seal (Mirounga leonina) is the largest species of seal in the world. They are dark grey immediately after moulting, fading through the year to a rusty greyish brown. Their most outstanding feature is the inflatable proboscis (snout) which reaches full development in adult males, and is thought to increase the effectiveness of the bull elephant seal's roar.

Elephant seals use their teeth during fighting to rake the necks of opponents. Large bulls can be heavily scarred from fights with other males during the breeding season. The nails on their forelimbs help the elephant seal climb over rocks and are also used for scratching dry skin and irritation caused by parasites.

Adult males: length 4-5 m, weight 3,600 kg
Adult females: length 2-3 m, weight 900 kg

Range

Southern elephant seals range throughout the Southern Ocean around the Antarctic continent and on most sub-Antarctic islands. The New Zealand population is concentrated on the Antipodes Islands and on Campbell Island. In winter, they frequently visit the Auckland, Antipodes and Snares Islands, less often the Chatham Islands and occasionally various mainland locations, from Stewart Island to the Bay of Islands.

Southern elephant seals haul-out on sand or gravel beaches with easy access as large males in particular find movement on land challenging.

When visiting local coastlines to moult, young elephant seals may stay in an area for months, giving people an opportunity to observe these animals. They can be an impressive sight, and young seals can be very playful. Enjoy their visits, but remember they are wild animals, and should be respected as such.

Population

There has been a long-term, annual decline of 5-11% of elephant seals at most colonies in the southern oceans. The reason for this is unknown, the two major theories being:

• decline is related to commercial exploitation of prey stocks; and
• the population is returning to pre-sealing levels after having recovered to abnormally high levels.

The total population was estimated at 607,000 in 1990 compared to 768,000 in 1985.

The New Zealand breeding stock is small; the Campbell Island population was numbered at 417 in the late 1940s and has since declined by 97%.

Diet and foraging

Elephant seals feed on animals such as squid, cuttlefish and large fish, including sharks.

Elephant seals are deep-sea feeders. At sea, they spend about 90% of their time underwater. Most dives are to depths of between 300 and 800 m and last 20-27 minutes. Surface intervals between dives are much shorter at only 2-4 minutes. Dives during the day tend to be much deeper than at night. Their high blood volume and oxygen capacity suggests they are capable of deep diving. Elephant seals are not particularly agile even in the water but can swim at speeds up to 20-25 km/h.

Life history

Breeding males arrive at rookeries in August, and pregnant females arrive in September and October. Males do not maintain territories but do establish dominance hierarchies structured primarily by age, secondarily by size, and to some extent, by previous experience. Males threaten each other visually and vocally.

Males are sexually mature at 3-6 years, but few breed before they are 10 years old. Only the largest two or three males breed in a given year. Many males will never breed with 90% dying before reaching sexual maturity. Females are sexually mature at 2-4 years old and may then give birth annually for 12 years. Breeding males may mate with 100 females in a season.

Females give birth to a single pup shortly after coming ashore in September or October and will then remain ashore for the next 23 or so days nursing her pup. A few weeks later the females mate and then depart, abruptly weaning their pups. Females then remain at sea feeding for 70 days before coming ashore to moult. Pups remain ashore for a period of 50 days before finally going to sea to feed.

Life expectancy is approximately 23 for females and 20 for males.

Seals normally come ashore to rest after long periods at sea or sometimes when they are sick, injured or tangled up in debris or nets. Young elephant seals come ashore to moult in summer. During moulting, they normally don't feed, rarely go back to the sea, and can stay in one location for several months. Moulting usually takes place in the tussock above beaches where they wriggle around in dry sand to slough off old skin.

Adult females moult slightly later in the season followed by the males in the autumn to winter months. Adult moulting takes place in deep, muddy wallows, shared with many others.

Leopard seals occasionally attack and kill pups, and killer whales may prey on pups and older seals, though neither are believed to have any significant affect on the population.

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