habitat_narrative
Terrestrial|Marine
Adult Crabeater Seals reach 2.6 m in length and weigh an estimated 200â300 kg. Neonates are thought to be at least 1.1 m and 20â40 kg. The mean age of sexual maturity in females varies from 2.5 to 4.2 years and these variations may be related to changes in food abundance (Bengtson and Laws 1985, HÃ¥rding and Härkönen 1995). Annual adult mortality is about 3â10% (Boveng 1993). Crabeater Seal births occur mainly during the second half of October. They do not use specific rookeries. Instead, adult females haul out singly on an ice floe where they give birth, and they are joined by a male shortly after (Siniff et al. 1979, Adam 2005). Adult males attend female-pup pairs and stay with the female until her oestrous begins one to two weeks after the pup is weaned. Mating has not been witnessed and presumably occurs in the water.Pups are born from September to December (Southwell et al. 2003) in a soft woolly coat that is greyish-brown in colour and has been described as light, milk coffee brown, with darker colouring on the flippers. Adult females fast during lactation, and wean their pups after an average of three weeks (Southwell 2004, Adam 2005) at which time pups are moulting from the lanugo coat into a sub-adult pelage similar to that of the adult. Adults and subadults moult in January and February, and a large proportion of the animals in an area are thought to be hauled out during the annual moult.
Mortality is high in the first year, possibly reaching 80%. Much of this mortality is attributed to Leopard Seal predation, and up to 78% of Crabeaters that survive through their first year have injuries and scars from Leopard Seal attacks (Siniff and Bengtson 1997). The presence of long scars and sets of parallel scars that are readily visible on the pale, relatively unmarked pelage of Crabeaters, are testimony to the frequency of these attacks on young of this species. Leopard Seal attacks appear to fall off dramatically after Crabeaters reach one year of age (Siniff and Stone 1985).
Recent research has revealed that Crabeater Seals can dive up to 600 m and stay submerged for 24 minutes, although most feeding dives occur within the top 50 m, and are shorter in duration (Burns et al. 2004, 2008). Foraging occurs primarily at night (Bengtson and Stewart 1992), and instrumented seals have been recorded to dive continuously for periods up to 16 hours. Dives at dawn and dusk are deeper than at night, and indicate that Crabeater feeding activity is also tied to the daily vertical migrations of Krill. They have a general pattern of feeding from dusk until dawn, and hauling-out in the middle of the day.
Crabeater Seals feed primarily on Antarctic Krill, Euphausia superba, which accounts for over 90% of their diet, with the remainder made up of fish and squid. New information indicates that the diet composition of the Crabeater Seal can display some plasticity, and they can compensate when Krill availability decreases by incorporating more fish (> 25% of their diet; Hückstädt et al. 2012). All of the post-canine teeth are ornate, with multiple accessory cusps that interlock to form a network for straining Krill from the seawater. A ridge of bone on each mandible fills the gap in the mouth behind the last upper post-canine teeth and the back of the jaw, which helps prevent the loss of Krill from the mouth when feeding.
Crabeater Seals are frequently encountered alone or in small groups of up to three on the ice or in the water. Much larger groups of up to 1,000 hauled-out together have been observed. They can be seen swimming together in herds estimated to be up to 500 animals, breathing and diving almost synchronously.
