The Crabeater Seal is one of the most common seals in the world — with one of the most unusual feeding processes. That process, which involves using its teeth like a filter, is explained after the jump!
Sorry for the belated Pinnipednesday, but I was traveling yesterday for business. By the time I got home, I just didn't have the energy to write, even about creatures as wonderful as pinnipeds. So to make up for it, I will start with a sealfie:
The Crabeater Seal (Lobodon carcinophagus) is true seal (meaning earless seal) that can be found in the Antarctic. They are typically found on the ice packs that freeze and extend into the ocean along the coasts of Antarctica, which is a crucial element of their habitat. Despite what you might think their name implies, they do not eat crabs.
Instead, their unique tooth structure allows them to feed primarily on krill, which comprises about 90% of their diet. They are able to strain water through their mouths and capture the tiny crustaceans (specifically Euphausia superba, a type of krill endemic to the Antarctic).
Adult Crabeater Seals are unique in that females are just slightly larger than males, growing up to 7.6 feet (2.3 meters) in body length, with males just a scarce 2.5 inches (6 cm) shorter. Females will weigh in at about 400 pounds (200 kg), which is about 17 pounds (8 kg) heavier than males. Of course, the average weights of adults fluctuate depending on the season. Females expend some of their body weight while they are nursing pups, and males will lose body weight from fasting as they attend to their mating females and drive away rival males.
Crabeater Seals move remarkably efficiently on land in the right conditions, able to achieve speeds of around 12-16 miles per hour (19-26 km/h) over short distances. Like other seals, they have been observed performing specific swimming maneuvers like porpoising (leaping out of the water) and spyhopping (poking their heads out of the water to better see things above the surface). They typically gather in large numbers, with groups of hundreds of animals swimming together and nearly 1,000 hauling out on the same patch of ice or coastline.
During the birthing season, however, female Crabeater Seals prefer to haul out on isolated ice packs, separating themselves from others rather than forming rookeries like other pinnipeds. This happens during the Southern Hemisphere springtime, from September to December. Females will come into estrus about one to two weeks after giving birth, so males will hang around mother-pup pairs until the females are ready to mate again. The gestation period is approximately 11 months. The remains of Crabeater Seals have been found farther inland than any other species of pinniped - about 62 miles (100 km) and about 3,280 feet (1,000 meters) above sea level, causing scientists to believe that they are fairly comfortable with wandering about on land.
Crabeater Seals have a healthy population, but their pups are preyed upon by Leopard Seals. The mortality rate of the pups during their first year of life is very high, about 80%, and it's not unusual to see adult Crabeater Seals bearing the scars of Leopard Seal attacks. They are also prey for orcas, but this has not been widely observed.