Weddell seal (Leptonychotes weddellii) pup lying next to mother on fast sea ice in spring sunshine. Temperature minus 30 degrees Celsius. Ross Sea, Antarctica. Weddell seals have the most southerly distribution of any mammal, found as far south as McMurdo Sound (77°S). Weddell seals can grow 3 meters long and weigh between 400600 kg. The pups are around half the length of their mother at birth, and weigh 25 to 30 kg (55 to 66 lb). They gain around 2 kg (4.4 lb) a day, and by 67 weeks old they