The Weddell seal is a large seal with a bulky body, and a relatively small head with a short, wide snout. Adults are brown to dark gray with light and dark patches on the back and silvery-white on the belly. The front flippers are smallish relative to body size. The fur color of pups is light gray or sometimes golden.
Weddell seals inhabit Antarctic and sub-Antarctic waters. They do not migrate and winters are spent under the ice of the Antarctic Sea, emerging through blowholes and cracks to breathe. They congregate in large groups on pack ice. They are found in areas further south than all other mammals, 1,287 km (800 miles) distant from the South Pole in McMurdo Sound waters.
Outside of the breeding season Weddell seals usually spend time singly but tend to form small groups around breathing holes and cracks in the ice. This is its lifeline, as the hole is essential for both resurfacing for air and diving for food. When on ice, a seal will rarely travel more than three meters away from its hole. Most of its activities happen at night under water. The seals can dive down as far a 600 m, and stay under water for as long as an hour. They are especially noisy underwater, with a constant barrage of sounds. Vocalizations made by the male are more complex than the female's noises and can be heard as far as 20 miles away. Such sounds could be for territorial defense.
Weddel seals are carnivores (piscivores) and their diet includes mostly fish and squid. In summer, they hunt a little more at night and dive to forage for food. They get enough water from metabolizing seawater or from their food but sometimes individuals will eat snow.
Weddell seals return to fast ice colonies during the spring for birthing and breeding. It is suggested that they are polygynous breeders and don't form pairs. Birthing occurs from September to December after the gestation period of 9-10 months. A single pup is usually born but sometimes twins are produced. The mother and pup then stay together. The pups first enter the water around 1-2 weeks old. Breeding males stay in the water under the ice, defending territory and a breathing hole until pups are weaned at 6 weeks old. The pup is then left to learn to hunt. The mother goes off to mate again. Weddell seal females become reproductively mature as early as 3 years old, but both females and males don't usually breed until they're about 7.
Weddell seals face no immediate or significant threats. Potential threats are climate change and global warming. Weddell seal numbers may decline with increasing temperatures if Antarctic sea ice is significantly reduced. Disturbance by vessel noise and a close approach by people may also harm this seal.
According to IUCN, the global population of Weddell seals has been variously estimated at 200,000 to 1,000,000 individuals. The ICUN classifies the Weddell seal as "Least Concern".