Long, slim body, with disproportionately large head separated from body by marked constriction at neck. 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.
Leopard seals have a muscular, somewhat reptilian head, with a sinuous neck, highly arched back and long powerful flippers. The body is dark grey above and light grey below and they have white throats with black spots. These distinctive spots are what give the Leopard seal its name. As one might expect, Leopard seals have impressively long, sharp teeth which are well-adapted for cutting and tearing the flesh of prey. Their streamlined bodies are built for speed and power; their smooth, impermiable skin allowing them to easily slice through the water on pursuit dives. These characteristics combined with excellent sight and smell have established Leopard seals as one of the consummate predators of the Antarctic.
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.
Scientists still have much to learn about the reproductive behaviors of Leopard seals due to the difficulty of monitoring breeding sites on the shifting pack ice of the Antarctic. Solitary animals, by nature, Leopard seals come on land only during the breeding season and then only in pairs or small groups. Females dig a hole in the ice early in the austral summer where they give birth to single pup after a 9 month gestation. The female protects the pups until they can take care of themselves.
Leopard seals may live for 26 years or more. Their only known natural predator is the Killer Whale..
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.
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.
Leopard seals use different food sources when they become available or when opportunities to take other, more sought after prey, are few. For some individuals krill can make up the largest proportion of their diet, particularly during the winter months when other food types are not abundant, where others use penguins and fish more heavily in their diet.
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. gazelle) and southern sea lions (Neophoca cinerea and Phocarctes 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 carcinophagus) 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.
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.