(Hombron & Jacquinot, 1842) - Crabeater seal
In Crabeater seals, the head and muzzle are moderately long and thin relative to the animal's overall size. The eyes are set fairly far apart and the head tapers to the base of the straight muzzle, forming a slight forehead in profile. The nostrils are on top of the muzzle, just back from the end. The line of the mouth is virtually straight. The vibrissae are short, pale to clear, and inconspicuous. The foreflippers are long, oar shaped, and pointed, like those of otariids. The first digits are elongated and robust, and the fifth digit is reduced. Many crabeaters bear long dark scars, either singly or as a parallel pair, attributable to attacks by leopard seals.
The coat of a freshly moulted crabeater has a rich sheen, with light to dark tones of silvery grey to yellowish brown. There are irregular patches of spots and rings, often in clusters on the sides, flippers, and around the insertions of the flippers. These markings produce a reticulated, or web-like, pattern on many crabeaters. The flippers can be so heavily marked with spots and rings that they appear darker than the rest of the body. As the year progresses, crabeaters fade dramatically, virtually eliminating the contrast between top and bottom. As these seals become older they become paler overall, and some look faded all year. Pups are born with a soft woolly coat that is greyish brown, with darker colouring on the flippers. Moult begins in about 2 to 3 weeks and the pup sheds into a subadult pelage similar to that of the adult. Most crabeaters have at least a few and often many long scars on the body, which are most often seen in pairs, parallel or near to each other. These scars are thought to be the result of unsuccessful leopard seal attacks on the seals as juveniles. Additionally many older animals are extensively scarred on the neck, face, and around the lower jaws.
All of the post-canine teeth are ornate, with multiple accessory cusps. Upper and lower teeth interlock to form a network for straining krill from the water.
The dental formula is I 2/2, C 1/1, PC 5/5.
Can be confused with
Crabeater seals are most likely to be confused with leopard and Weddell seals. The former has a massive reptilean head, long foreflippers, and huge maw. The latter has a very small head, relative to the rotund body, and a distinctly spotted coat. Only crabeaters occur routinely in large groups.
Adults reach 2.6 m in length and, although little data is available, weigh an estimated 200 to 300 kg. Neonates are thought to be at least 1.1 m and 20 to 40 kg.
The distribution of crabeater seals is tied to the seasonal fluctuations of the pack ice. They can be found right up to the coast of Antarctica, as far south as McMurdo Sound, during late summer ice break-up, and as vagrants as far north as New Zealand and the lower reaches of Africa, Australia, and South America.
Biology and Behaviour
Pups are born from September to December, and mating most likely occurs from October through December (although little is known about their reproduction). There are no specific rookeries; females haul out on ice, give birth, and aggressively ward off other seals, particularly males.
Crabeaters are frequently encountered alone or in small groups of up to 10 on the ice or in the water. However, much larger groups of up to several thousands have been observed. Occasionally, they can be seen traveling together in herds, breathing and diving almost synchronously. They are known for their ability to move rapidly on ice, with sinuous serpentine motions of the back, aided by the flippers. When agitated, their response is to arch their back and raise their neck and head, and often point the nose upwards at a slight angle in an alert posture.
Recent research has revealed that crabeater seals can dive to 430 m and for 11 minutes, although most feeding dives were much shallower and shorter. It is believed that crabeaters feed with greatest intensity at night, mostly on krill.
Crabeater seals have never been seriously exploited by humans. They continue to be taken for scientific research and to feed sled dogs kept at Antarctic bases. They are probably the most numerous pinniped, and may be the most numerous large mammal on earth besides humans. It has been speculated that the population of crabeater seals is at an all time high due to the demise of the large stocks of krill-eating baleen whales.