for National Geographic News
This story is one of a series looking at National Geographic Crittercam research. Crittercam is a research instrument worn by wild animals and equipped with a video camera and other information-gathering equipment. (Get the basics on underwater and terrestrial Crittercams.)
Ask Tracey Rogers, director of the Australian Marine Mammal Research Centre at Sydney's Taronga Zoo, to name a special someone who influenced her career path and she might mention a leopard seal named Astrid.
Rogers said it was an encounter with Astrid while she worked as a seal trainer at the zoo that inspired her to pursue a Ph.D. The pivotal moment came when Rogers entered the leopard seal pool for the first time. An emergency forced her to leave the confines of the safety cage, and Astrid followed, quick to notice the fish still lodged under Rogers's arm.
Rogers said she froze, realizing that a very large predator was after the fish she carried. "I basically was panicking," Rogers recalled. "I was thinking, 'I'm going to get really bitten here.'" Rogers closed her eyes, only to open them moments later to a barrage of air bubbles. Astrid had indeed come closer but was gently nudging the fish with her nose out from underneath Rogers's arm. When it floated clear, Astrid ate it, then turned to look back into Rogers's mask.
"I thought, 'Oh God, you're a smart seal. You guys are great!'" Rogers said the encounter swayed her not only to pursue her Ph.D. but to study leopard seals in particular after she realized they were "really special."
Leopard seals (Hydrurga leptonyx) certainly live up to the "leopard" part of their name. These Antarctic marine hunters are stealthy and skilled predators. They are the only seal known to hunt other warm-blooded animals. Leopard seals typically feed on penguins and the pups of other seal species but will eat "just about everything they come across," Rogers said.
Their hunting tactics depend on the element of surprise. Attacking from behind, a leopard seal will use its powerful jaws to grab a seal pup by the head and crush its skull. To catch penguins, a leopard seal will lurk near the water's edge just under the surface to watch shadows on the ice above. Spotting a penguin, it will lung out of the water and onto the ice to snatch its prey and drag it back into the water. The seals will also back into alcoves along the ice or beach, coil up into an S-shape, and then spring forward "like a crocodile," Rogers said.
Leopard seals have highly specialized mouths that are well equipped to handle a wide variety of prey, including fish and krill. Their front canine teeth are large and feline, perfect for grasping prey and slashing it open. Each molar has three distinct cusps that interlock when their jaw is closed, forming a sieve for straining krill from the water.
Krill compose approximately 40 percent of a leopard seal's diet. However, in Prydz Bay, Antarctica, where Rogers has conducted her studies, leopard seals appear to bypass these tiny crustaceans in favor of abundant small mammals and birds.
Rogers has found that individual seals seem to develop a specialty for hunting particular species. So while one individual might be good at catching seal pups, another might be adept at catching penguins.