Weddell Seal, Leptonychotes weddellii
The Weddell seal (Leptonychotes weddellii) is a large true seal in the Lobodontini tribe. It is native to Antarctica, with its range consisting of a large “ring” that surrounds Antarctica. This seal will spend most of its time in the water instead of on land. The Weddell seal appears on the IUCN Red List with a conservation status of “Least Concern”. It is estimated this seal numbers over 800,000 individuals in the wild.
First discovered in 1820s by a British sealing captain named James Weddell, the Weddell seal has been placed in the Lobodontini tribe along with three other seals. All four seals share a common ancestor, as well as an adapted tooth structure that allows the seals to pull in the Antarctic krill that make up large portions of their diet.
Adult Weddell seals can grow to be an average of 8.2 to 11.5 feet and can weigh between 880 and 1360 pounds. Typically, females are larger than males, and the cat like faces of these seals differ slightly in length, with males bearing noses that are slightly longer. The noses of the species turn upwards, giving the appearance that it is smiling. Each Weddell seal bares a thin coat that can vary in color as the seal ages. Pups are born with gray fur that darkens within the first three to four weeks of age. Adults are typically brown in color, with pale underbellies, and the brown will fade in older seals.
The Weddell seal prefers to gather in small groups that will surround holes in the ice, or in larger groups that dwell on continental pack ice. During the harsh winters of its range, it will spend its time in the water, only stretching its head through small holes in the ice to breath. When on land, these docile seals can be seen relaxing on the ice.
The reproduction habits of the Weddell seal vary depending upon location. Seals inhabiting areas of higher latitudes will typically give birth between the months of September and December, while those living in lower latitudes will give birth in earlier months. Most of these seals are able to mate at six to eight years of age, but some individuals can mate earlier. Although breeding occurs underwater, calls can be felt through the ice. During breeding, females are often bitten on the neck. The Weddell seal is one of the few species of seals that often gives birth to twins. Pups are able to swim at around two weeks of age, and are weaned at seven weeks.
The Weddell seal is skilled at diving, and can swim to a depth of up to 2,300 feet. After taking a large breath from an ice hole, the seal will dive down, slowly descending for up to 164 feet. These seals are able to remain underwater for up to eighty minutes. These adventures consist of foraging for food and searching out cracks in the ice that could be potential breathing holes and are made possible by the increased amount of myoglobin in the muscles.
It is thought that this seal can stay underwater for so long with limited oxygen due to a process known as anaerobic metabolism. This process causes lactic acid to build up and remain in the muscles until it surfaces, when the acid then travels into the bloodstream. This is accomplished when the capillaries shrink, but it is though that this process is not the most efficient because it requires a longer recovery period for the seal.
Another way that the Weddell seal is able to remain underwater is an increased oxygen carrying capability. This is possible by having an increased amount of red blood cells, as well as having more blood than other animals. Together with an oxygen reserve in the spleen, adjustments in heart rate and PH balance of the blood, this seal can remain underwater longer than other seals.
The diet of the Weddell seal consists of many creatures including krill, fish, bottom-feeding prawns, squid, and occasionally penguins. During the warmer months of the year, these seals will rely on eyesight to hunt and forage for food, but when blizzards occur during winter, they must use their whiskers and other senses to locate food.
On the fast ice, the Waddell seal has no natural predators, but in the water or on pack ice leopard seals and killer whales will hunt sub-adults and pups. The lifespan of this seal is significantly shorter than most seals that live an average of forty years. Because the Weddell seal scrapes ice with its teeth, it will eventually wear them down, and will live an average of 20 years. It is protected by the Convention for the Conservation of Antarctic Seals and the Antarctic Treaty.
Image Caption: Weddell Seal. Credit: Samuel Blanc/Wikipedia(CC BY-SA 3.0)