The Weddell seal (Leptonychotes weddelli) is the southernmost pinniped in the world. There are an estimated 800,000 of these animals in the waters off the Antarctic continent. While the overall population is stable, some colonies have seen a decline in numbers over the last decade. Hunting of the Weddell seal is permitted for commercial purposes; however, the 1972 convention for the conservation of Antarctic seals has set catch limits and prohibited the taking of individuals over the age of one year from September 1 to January 31.
A male Weddell seal reaches sexual maturity in 3 to 6 years and a female in 2-6 years. There are many variables in when, exactly, individuals are ready to breed: availability of food, density of population, etc. Weddell seals breed during the austral spring, with the peak pupping falling between September and November and the peak mating period following immediately thereafter, through early December. The seals breed in colonies, often in fast ice or shore fast ice--away from predators, including orcas and leopard seals, which roam the open waters and ice floes of the South Atlantic. In what is known as reverse sexual dimorphism, males are generally smaller than females. One theory suggests that this relates to agility in swimming and, hence, success in breeding--where actual mating takes place under water. Important to the success of breeding males is their ability to defend aquatic territory, or maritory. Maritories describe areas in the vicinity of breathing holes and the competition is fierce. Weddell seal males are known to not only display, but to aggressively attack other male intruders, leaving bloody wounds in the tail flippers as they give chase.
Weddells give birth to one pup at a time
A female ovulates towards the end of her lactation period, as a pup is being weaned--usually about 48 days after giving birth. An adaptation in response to a number of ecological circumstances, known as delayed implantation--that is the time between conception and implantation, may last for as long as 90 days. During this time the fertilized egg is in a sort of suspended animation. From implantation, the gestation period is 10.25 months, on average. Weddells give birth to one pup at a time; although two instances of twins were recorded in the McMurdo Sound study area this year. A newborn pup has a coat of long hair, called lanugo, which they will shed within the first month as the protective layer of blubber is developed. They nurse often on milk that contains between 30 and 60% fat. At about 3 weeks, they are learning to swim and at about 5-6 weeks they are weaned and on their own.
Weddell seals have a varied diet which includes mostly fish, such as Atlantic cod, and invertabrates. They also feed on cephalopods, such as squid and octopuses and are known to forage occasionally on krill. As prey, Weddells and most other seals are a staple of orcas, or killer whales. Leopard seals are also known to feed on pups and subadults.
Among the pinnipeds, Weddell seals are outstanding in the range and variety of their vocalizations. Researchers have classified 12 types of calls with 34 discrete phrases and calls--from booming territorial sounds, to birdlike chirps and whistles. Their frequency range is remarkable, with lower frequency calls registering around 0.1KHz and others reaching up to 70KHz--well beyond human hearing which levels out at about 18KHz. Males generally have a broader repertoire of calls which are heard most often during the mating season, as a display to competing males and to attract females. Weddell seal sounds can be heard above and below the ice and they communicate on land as well as in water.
To listen to a examples of Weddell seal vocalizations, please select from the samples below.
Weddell Seal Vocal Sample #1
Weddell Seal Vocal Sample #2
Weddell Seal Vocal Sample #3
Weddell Seal Vocal Sample #4
Weddell Seal Mothers and Pups
A few Weddell seal facts...
For more information about Weddell seals and other pinnipeds, I highly recommend Marianne Riedman's wonderful book, where I found most of this information:
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