Leopard seals are the largest by far of the Antarctic seals. Their bodies are sinuous and their powerful jaws open widely to show extremely long canine teeth. They have a large, reptile-like head with a long, flexible neck. The overall body shape is long and slender, which makes them very agile when in the water. Their coloring is different dorsally to ventrally, as their back is dark gray, their underside is silvery gray, and there are dark and light spots over the entire body. The coat of juveniles much softer and thicker, and has a dorsal stripe, with a light gray underside scattered with dark spots. Although males and females are similar in appearance, which is unusual for a seal, females are slightly larger than males.
Leopard seals can be found in the circumpolar area in the Antarctic pack ice. A small number are found year round on the nearby sub-Antarctic islands just beyond the pack ice. Some have also been observed around coasts as far north as South Africa, South America, Australia and New Zealand. But its main habitat is in Antarctica on the pack ice, or associated ice bergs and ice floes
Leopard seals are diurnal, meaning they are active during the day and sleep at night. They are solitary, both on the ice and at sea, with groups only forming by temporary mating pairs or by pairs of mothers and pups. The density of leopard seals on and near pack ice increases at the time of the mating season and also when the pups are born, as mothers give birth and look after their young in these places. Otherwise, leopard seals mainly remain in the water. They are graceful swimmers, and use powerful, long simultaneous strokes with their flippers. They can stay underwater for 15 to 30 minutes, sometimes sleeping under water and coming to the surface for air without waking up. They hunt in shallow water; they do not dive deeply. Leopard seals are usually quiet on the ice. When underwater they make trills, grunts, growling noises and low frequency moans.
Leopard seals are polygynous, one male mating with multiple females. Groups form only for temporary mating pairs or they are mother and pup pairs. Breeding takes place during the middle of the southern hemisphere's summer, with births occurring from early October and January. Gestation lasts for 8 to 9 months, and a single pup is born. Females generally stock up on food prior to giving birth, which takes place in a hole amongst the pack ice. Pups are fed on rich fatty milk, which enables them to grow quickly. Within a month a pup molts its first coat and can go to sea. The mother protects her pup until it can take care of itself; male seals do not take part in parental care. Females are sexually mature at 2 to 6 years of age and males at 3 to 7.
At present the Leopard seal faces no major threats but there are several factors of concern for their future, including increasing disturbance from tourism, the spread of disease, commercial harvesting of krill, and probably of most importance, the unknown effects of climate change. Reduction in the amount of pack-ice as a result of global warming would likely affect the extent of habitat available for seals to pup and rest, as well as the availability of their prey species.
According to the IUCN Red List, the total Leopard seal population number is more than 35,000 individuals and it is classified as Least Concern (LC).
As apex predators, these seals play an important role feeding on the large animals of the extreme Antarctic system, thus controlling their populations.