Southern Elephant Seal
|Distribution and Numbers
The Southern elephant seal is the largest of the pinnipeds and gets its name from the male's inflatable elephant-like trunk. Its main breeding grounds are the subantarctic islands near the Antarctic Polar Front, the population at South Georgia being the largest and containing approximately half of the entire species. Other important populations are at Macquarie Island, Heard Island and the Kerguelen Islands. Rare births have also been reported from New Zealand, Australia and South Africa, and some individuals have been known to wander as far north as the equator. The total population has been calculated at about 600,000.
Photo: Tom Arnbom,
University of Stockholm
The Southern elephant seal was heavily exploited in the 19th and 20th centuries for its blubber as a source of oil, reducing its numbers considerably. A controlled hunt of adult males continued at South Georgia until 1964. Any killing of the species south of 60�S is now regulated by the Convention for the Conservation of Antarctic Seals (CCAS), while the species is also protected by legislation in various countries within its range. The Southern elephant seal is listed as an Appendix II species under CITES.
|Southern elephant seal numbers have decreased significantly over the last forty years, e.g. by 50% on Heard Island, 84% on Marion Island, 57% on Macquarie Island, 90% on Campbell and Signy Islands, and up to 80% on some of the Kerguelen Islands. Numbers at the South Georgia colony have remained relatively stable during this time, while the colony in Argentina is the only one that appears to have been increasing. The reasons for this decline in some populations are not yet understood and the effect seems to be specific to Southern elephant seals rather than other animals in the Southern Ocean. Some have suggested that the problem may be due to competition with other marine predators or due to ocean environmental change but both of these are currently speculative. There is currently not much support for the explanation that the problem is due to direct competition with commercial fisheries since, for example, there is no commercial fishing for deep water species in the feeding areas of the declining Macquarie Island population. However any future increase in fishing in the region could certainly cause problems for the species. In 1999 an Argentinean marine mammal scientist warned that overfishing is threatening the survival of the Pen�nsula Vald�s population, expressing concern about the ever-increasing volume of squid caught by commercial fishermen at the seals' feeding grounds along the edge of the continental shelf.|
|The explanation that is perhaps most currently favoured is that the Southern elephant seal populations overshot their sustainable population levels after recovering from the previous period of commercial sealing, and that they are now regaining their equilibrium constrained by the finite food resources available. Research is however continuing to determine the causes and the decline in populations may well be a complex combination of factors. The Pen�nsula Vald�s colony faces the additional problem of disturbance caused by relatively uncontrolled tourism, some seals there also having been seen with pieces of net around their necks and oil on their bodies.|
|It was reported in March 2000 that the Australian Environment Minister had ordered that the hot iron branding of Southern elephant seals by scientists on Macquarie Island be stopped. The action came after a report indicated that the brands had created large weeping sores and infected wounds on many seals, branded seals being almost three times as likely to be in poor physical condition as unbranded seals. Around 14,000 weaned Southern elephant seal pups had been branded since 1993 with an identifying code for the purposes of helping to understand the population decline. In March 2001 it was also announced by the Tasmanian Government that, due to allegations of cruelty, all invasive research on elephant seals on Macquarie Island had been banned until a full review of the research could be undertaken. The allegations involved "undue levels of effort" by scientists using sticks to separate groups of seals in order to reach particular individuals. The only research to be allowed to continue in the meantime would be population counts and the chance retrieval of data loggers shed by seals at their annual moult.|
Photo: Michael Bryden,
University of Sydney
|In 1999 UNESCO's World Heritage Committee designated
Argentina's Pen�nsula Vald�s, an important site for the species, as a World Heritage
Southern elephant seals on World Heritage listed Macquarie Island were afforded additional protection in 2000 by the creation of a new federal 16 million hectare Marine Park on the eastern side of the island. In addition, the Tasmanian government announced in 2000 an extension to the Macquarie Island Nature Reserve to cover all Tasmanian waters out to three nautical miles surrounding the island.
Southern elephant seals give birth and breed in September-November, the larger males arriving a month before the females and other males in order to fight for dominance and the right to a harem of females. Only the largest 2-3% of males each year gain this right and the number of breeding females to which the successful males have access is large, sometimes exceeding 100. The female gives birth between 0-10 days after coming ashore and does not leave the beach to feed until her pup is weaned. During this time she depends on her stored reserves to sustain her and loses an average of 35% of her body weight, a weight loss of 8kg per day. The pup is born with dark brown-black fur which it moults at 3-4 weeks to be replaced by shorter silver-grey hair. The nursing period lasts an average of about 23 days and the pup puts on weight very quickly during this period, gaining about 3.5 - 4kg per day. The mother mates up to 5 days before her pup is weaned, most matings concentrated in the three days before weaning, and then once her pup is weaned she abandons it and returns back out to sea. The pup leaves the beach about 3-8 weeks later to begin the process of teaching itself to feed. Suitable food may not be near at hand for the pup which means that the amassed body reserves of the pup are an important aspect in its survival. The weaned size of pups is very variable, some being three times the weight of others.
|Although elephant seal mothers only give birth to one pup in each breeding season they have sometimes been seen to nurse two pups. Many pups die on the crowded breeding beaches. Adult males, up to 10 times the size of breeding females, also do not feed during the breeding season and may lose up to more than 40%, 12kg per day, of their body weight while ashore. The amount of time spent ashore by males during the breeding season varies greatly, some breeding males spending more than 60 days and up to 90 days on shore (the females only spend 25-30 days ashore). After an intensive period of feeding the adults return to moult for an average of 30-40 days in January-February. They do not enter the water to feed while moulting. Some non-breeding bulls moult on the Antarctic continent itself.|
|Adult Southern elephant seals range in colour from dark grey to brown
with a lighter underside. The Southern elephant seal is a creature of the open sea when
not breeding or moulting, and spends ten months a year intensively foraging over wide
areas in the waters of the Antarctic for squid and fish. The seals dive continuously, day
and night, for the entire trip to sea, diving to average depths of 300-600m and for
average periods of 20-22 minutes. They spend 90% of their time underwater, spending only
2-3 minutes at the surface between dives. The deepest dives are made during the day. Adult
Southern elephant seals make two return migratory trips of up to 2,000km each way to their
Antarctic feeding grounds each year, once after breeding and the second time after
moulting. An exception to this is the Argentinean population which feeds in the southern
Atlantic Ocean rather than in Antarctic waters. Weaned pups and juveniles are preyed upon
by killer whales and sometimes leopard seals.
Southern elephant seals show a great difference in size between the sexes and also within each sex. The average weight of fully grown adult males is 2,200kg (maximum over 4,000kg), while their average length is 4.2m (maximum 6.2m). Male elephant seals at Argentina's Pen�nsula Vald�s are significantly smaller than those in the Falkland Islands and South Georgia. Females typically weigh 500kg (maximum 1,000kg) and measure an average of 2.7m in length (maximum 3.7m). Pups are born about 1.3m long, the males slightly heavier at about 50kg compared to 45kg, but both sexes weigh roughly the same, about 135-140 kg, by the time that they are weaned. Southern elephant seals are known to dive as deep as 2,000m for as long as 2 hours. Most females reach sexual maturity at 2-4 years of age. Males may reach sexual maturity at 3-6 years of age but few of them breed until 10 years of age. Southern elephant seals can live for up to 23 years.
Photo: Michael Bryden,
University of Sydney