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25 April, 2000

Pinnipeds (seals) 1 Question 66: How are crabeater and leopard seals like baleen whales? Seals do well in polar climates because their dense fur and the layer of blubber beneath the skin form an effective thermal (heat) insulator in extremely cold water or air. They feed at sea and need to haul out on land only for short rest periods or to have their young. The Antarctic seals can use the area's extensive ice cover instead of land so they have been able to colonize a larger geographic area that closely mirrors their prey distribution. This is also true in the Arctic for the seals that live and breed in the pack ice. Seals in other areas of the world can't get too far away from their coastal breeding areas. All Antarctic seals belong to the order Pinnipedia. They fall into two sub-groups in the order, Family Otariidae--eared seals (eight species of Southern Fur Seal) and Family Phocidae--true seals (Crabeater Seal, Ross Seal, Leopard Seal, Weddell Seal, and Southern Elephant Seal). The Crabeater, Ross, Leopard and Weddell Seals are estimated to make up 56% of the world's seal stock and, because of their relatively large size, more than 79% of the total biomass of seals worldwide. The habitat preferences of these seals determine the depth of our knowledge about their biology. We know the most about those that breed on beaches and on fast ice (Elephant, Fur and Weddell Seals). Crabeater and Leopard Seals are less well known as they inhabit the changing pack ice environment. Icebreakers rarely get deep into the thickest pack ice, so we see the Ross Seals the least often and know little about them. Crabeater Seals are very active seals that typically feed in the upper water column. Adults grow to around 230-260 cm in length and weigh up to 227 kg. The males are slightly smaller than the females, a fact true for all Antarctic seals except the Elephant and Fur Seals. The Crabeater Seals we saw in the Palmer area were a light gray color and looked fuzzy, like a velveteen stuffed animal. We saw them hauled out alone on ice and shore and swimming in groups in the water. Immature seals can form extremely large groups. Pups are born in early October and are fed by their mother for the first month. During that time the mother loses approximately 50% of her weight, the pup increases its weight from 20 to 113 kg, and the male defends a territory around the family group to keep out other adult males and Leopard Seals. Crabeater Seals make up an important part of the Leopard Seal Diet. Ross seals are thought to be deep, nocturnal divers for food as they have oversized eyes, have been found with large squid in their stomachs, and tend to be hauled out in the middle of the day. They also eat fish and some krill. Ross Seals are usually solitary, although some small groups have been observed. They seem to haul out on larger ice floes than other seals. Few pups have ever been seen; they are probably born in November. Ross Seals have not been measured in large numbers but the largest female on record weighed 204 kg and was 256 cm long. Their front flippers are nearly a quarter of the length of the entire body, the longest of any seal in this group. Leopard Seal females generally average 290 cm in length and 367 in weight (males, 180 cm and 324 kg), but the largest specimen on record was 358 cm long; that is over 11 feet! They are long, lithe and graceful and are very mobile on land or in the water. They have a huge gape (mouth opening) and a very large head for their body size. They are usually solitary in the summer and are usually found near a food source (i.e. the edge of the pack ice). Along the Antarctic Peninsula pups are born on ice floes in November and December. The mother stays with the pup until it is weaned. Leopard Seals eat krill, penguins, other seal species (usually juveniles), fish, and cephalopods (i.e. squid). The proportions of each of these components change seasonally as the availability of easy prey changes (i.e. young penguins or young seals going to sea for the first time). Continued 4/25/00... Answer 65: The fin whale, which can reach a speed of 16-20 km/hr during its migration.


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