Crabeater Seal, Lobodon carcinophagus
The crabeater seal (Lobodon carcinophagus) is a true seal that can be found around the whole of Antarctica. Its range also includes small areas in South America, New Zealand, Africa, and Australia. It resides on the pack ice zone for the entire year, even as it shifts seasonally, and prefers to stay in the continental shelf area in water with a depth of less than 1,968 feet. Because the populations are so wide spread and are sufficiently mixed, there have been no subspecies found.
Because of a shared ancestor, the crabeater seal and three other species of Antarctic seal are classified in the Lobodontini tribe of seals. The teeth structures of each seal in this tribe are similar, and show adaptations for pulling small prey, like krill, out of the water.
The crabeater seals can grow to have an average body length of 7.6 feet and an average weight of 440 pounds, although weight can vary depending on seasons, sex, and activity. Typically, females can be up 2.5 inches longer and may weigh up to 17 pounds more than males. The color and texture of the coat depends on age, with pups appearing to be soft and brown in color until their first molting, after which they are chocolate brown in color. Adult seals are typically light in color, with cream bellies, and during the summer, an adult seal’s fur can be all cream in color.
The crabeater seal is a sociable species, occurring in land groups of up to 1,000 individuals, but these are usually younger seals. In the water, these groups are smaller, numbering in the hundreds, and they can be seen breathing and diving in almost complete synchronicity. Adult seals can be seen in groups of up to three individuals, but are typically solitary.
Crabeater seals will typically give birth between the months of September to December, the Antarctic spring. Instead of forming groups when giving birth and rearing young, females will separate in the ice and give birth individually. A male will protect the mother and her pup until the female is able to mate again, and this typically occurs around one to two weeks after the pup is weaned. The mating habits of this seal have not been observed, but it is thought that they occur underwater.
The crabeater seal has a distinctive gait that can be considered serpentine. It leaves a noticeable track when moving about on land, and on cold days, it can move at speeds of up to sixteen miles per hour. This speed is reduced to seven miles per hour in the water, although what this seal lacks in speed it makes up for in agility, leaping completely out of the water in a manner similar to a dolphin and lifting itself vertically out of the water to scout for threats.
Although the name suggests that it eats crabs, the crabeater seal actually feeds mainly on Antarctic krill, which take up ninety percent of its diet. There are no seasonal distinctions between types of prey, but it has been found that the crabeater seal may eat more male and adult krill. They will also feed on many Antarctic species of fish, as well as some cephalopods, like squid.
Because of specialist diet of the crabeater seal, there is little to no competition for food between the three other species that share its range, which are the Ross, Weddell, and leopard seals. Two species of baleen whales that also share its range include the minke whale and the blue whale. It is though that a nine percent increase in seal populations of this area may have been the result of increased whale hunting during a period known as industrial whaling.
The crabeater seal suffers great losses from the leopard seals who share its range, and many young individuals are left with visible scarring from violent encounters. Most of these attacks occur within the first year of a crabeater seal’s life, with up to eighty percent of these pups perishing. The scarring diminishes as the seals increase in age, and it is thought that the large groups of young seals are a form of protection from leopard seal attacks. Predation also occurs from killer whales, although this has not been well documented. Occasionally, whales will group together to create waves that knock the seals off the ice and into the water. The crabeater seal has been listed on the IUCN Red List as of “Least Concern”.
Image Caption: Lobodon carcinophagus, Crabeater Seal. Credit: Mike Cameron/Wikipedia