Leopard Seals Are Apex Predators of the Antarctic

A leopard seal lounges on an ice floe on Pleneau Island in the Antarctic Peninsula. Wolfgang Kaehler/LightRocket/Getty Images

Everybody is terrified of something, and often it has to do with whatever's most likely to cause an unpleasant and untimely death. If you're living in the Cretaceous Period, a T-rex might be the stuff of nightmares, while a mountain goat living today in the European Alps might constantly be on high alert for a golden eagle swooping down and dropping them off a cliff. But if you're an animal — almost any animal — living off the coast of Antarctica, the real horror show begins when the leopard seals show up.

Leopard seals (Hydrurga leptonyx) are apex predators and the second largest seal in the Antarctic coastal ecosystems, after the southern elephant seal (Mirounga leonina). They are extremely agile, fast swimmers with long, muscular bodies. Their common name references the big, spotted cats of Africa and Asia, because they are both terrifying apex predators with giant, powerful jaws filled with sharp teeth, and their coats are also speckled.

"Leopard seals eat almost everything, from krill to penguins to seals and fur seals," says Daniel Costa, director of the Institute of Marine Sciences UC Santa Cruz, who studies movement patterns, diving behavior, physiology and diet in leopard seals. "They typically hang out at penguin and fur seal colonies. When the penguins or fur seals go into the water the leopard seal very slowly sneaks up on them and catches them. They then swim further offshore and begin to tear the seal or penguin apart. Leopard seals also attack and kill juvenile crabeater seals — we've seen adult crabeater seals that have been mauled by leopard seals."

Leopard seals are stealthy hunters, but tiny krill are more difficult to sneak up on than a fish or a floating sea bird. However, their front teeth are sharp and great for ripping and tearing, but they also have specialized molars they use to filter krill out of the water while they swim around.

A study published in 2019 in the Canadian Journal of Zoology found leopard seals cache their prey like cats, sometimes killing a fur seal pup and stashing it somewhere safe to eat later when they're hungry.

The Life Cycle of the Leopard Seal

Leopard seals are pagophilic, meaning they mostly live on ice packs, and they're primarily found in Antarctica, though they have been sighted off Australia, South America, New Zealand and South Africa. They live on their own for most of their lives, with the exception of when a mother is with her pup.

"Not much is known about the reproductive biology of leopard seals," says Costa. "We know they give birth in the pack ice during the austral spring [spring in the Southern Hemisphere] in October and November. They give birth to a single pup. If they are like other pack ice seals they suckle their pup while fasting and do so over a period of a few weeks. Their milk is probably very high in fat — 40 to 50 percent fat."

Their breeding system is equally mysterious. Male leopard seals spend many hours each day making loud, underwater calls during the austral summer, November through March, possibly as a way to fend off intruders to their territory and to call in potential mates.

In their romantic lives, leopard seals probably practice what we call serial monogamy, says Costa:

"A male stays with a female while she has her pup, waiting for her to come into estrus. Once they breed, he goes looking for another female to breed with. There is very little known about this, but males do have a very high frequency vocalization that is probably related to social display."

Conservation Pressures

As predators at the top of the food chain with no real threats other than humans and the killer whale, leopard seals do pretty well for themselves. But, like virtually every other animal that relies on Antarctic pack ice for its livelihood, the threat of climate change looms large over the long-term survival of leopard seals.

"There are no direct threats to leopard seals, other than climate change potentially reducing the abundance or the distribution of their prey," says Costa. "In one of the fur seal colonies I have worked on, the number of leopard seals has increased dramatically from a few to over 30 individuals. We don't know if this is because the population has increased, or that they are now focusing on a few fur seal and penguin colonies because other food resources are less available."