Hydrurga leptonyx (Blainville, 1820)

Leopard seals may live for 26 years or more. Their only known natural predator is the Killer Whale.

Species details

Identification

Long, slim body, with disproportionately large head separated from body by marked constriction at neck. They are dark grey above; lighter below; with light and dark grey spots on throat and sides. They have a characteristic 'reptilian' appearance to their head; a wide gape of jaws and characteristically three-pronged teeth, which makes identification easy. The teeth of the leopard seal have a dual role; the large re-curved canines and incisors are designed for gripping and tearing prey, whereas the upper and lower tricuspid (three cusped) molars interlock to provide an efficient krill sieve. Leopard seals are sexually dimorphic, the females are larger than the males growing up to 3.8 m in length and weighing up to 500 kg, whereas males grow up to 3.3 m in length and weigh up to 300 kg.

Species distribution

Distribution info

While the majority of the leopard seal population remains within the circumpolar Antarctic pack ice the seals are regular, although not abundant, visitors to the sub-Antarctic islands of the southern oceans and to the southern continents. The most northerly leopard seal sightings are from the Cook Islands. Juveniles appear to be more mobile, moving further north during the winter. Because it does not need to return to the pack ice to breed, the leopard seal can escape food shortages during winter by dispersing northwards. Every 4 to 5 years the number of leopard seals on the sub-Antarctic islands oscillates from a few to several hundred seals. The periodic dispersal could be related to oscillating current patterns or resource shortages in certain years. By comparison, adult seals that remain in Antarctica are much less mobile and remain within the same region throughout the year.

Habitat

During summer, leopard seals breed on the outer fringes of the pack ice where they are solitary and sparsely distributed. Their density is inversely related to the amount of pack ice available to the seals as haul-out platforms. Pack ice cover varies with the season, from a maximum between August and October to a minimum between February and March. Population densities are greatest in areas of abundant cake ice (ice floes of 2 to 20 m in diameter) and brash ice (ice floes greater than 2 m in diameter), whereas they are least in areas with larger floes. Densities range from 0.003 to 0.151 seals/km2, and there is an age-related difference in their spatial behaviour. Due to intra-specific aggression there is a greater degree of spatial separation among older seals.

Feeding Behaviour

Leopard seals' main source of food is penguins and they can often be seen cruising in the vicinity of Adelie, Chinstrap, and Gentoo colonies. Typically, they will lie in wait by an icy ledge or rock outcrop, pouncing on the first penguin to dive into the water. Leopards will also hunt fish, squid and krill, and occasionally other seals like the Crabeater seal.
Leopard seals capture and eat juvenile crabeater seals in particular, but also prey on Weddell (Leptonychotes weddellii), Ross (Ommatophoca rossii), southern elephant (Mirounga leonina), sub-Antarctic and Antarctic fur seals (Arctocephalus tropicalis and A. gazella) and southern sea lions (Neophoca cinerea and Phocarctos hookeri).
Leopard seals are responsible for more predation on warm-blooded prey than any other pinniped, they are catholic feeders taking a diverse range of prey, including fish, cephalopods, sea birds, and seals. They use different food sources when they become available or when opportunities to take other, more sought after prey, are few. During the winter leopard seals must compete directly with krill-feeding specialists, such as the crabeater seal (Lobodon carcinophaga) and Adélie penguin (Pygoscelis adeliae) which may be a time of potential food shortage and cause some juvenile leopard seals to move north from the pack ice during the austral winter.
Newly weaned crabeater seals are taken from November to February when they are most vulnerable. Crabeater seal survivors bear characteristic parallel paired rake scars from leopard seal attacks, and a large proportion of the adult population, approximately 78%, bear leopard seal rake marks.

Reproductive

Male leopard seals are sexually mature by 4.5 years and females by 4 years of age. Females give birth to their pups and wean them on the ice floes of the Antarctic pack ice. Males do not remain with the females; only mother-pup groups are observed on ice floes. Length at birth is approximately 120 cm, with rapid growth through the first 6 months postpartum. Births are believed to occur from October to mid-November and mating from December to early January, after the pups have weaned. Lactation is believed to last for up to 4 weeks but maybe shorter than this. Mating in the wild has been observed rarely, but captive seals mount only when in the water. There is a period of delayed implantation from early January to mid-February. Implanted fetuses are found after mid-February when the corpus luteum (glandular structure in the ovary) has begun to increase in size and the corpus albicans (scar from ovarian glandular structure) from the previous pregnancy has continued to regress.