Weddell seal

Introduction to Weddell Seals

One of the most common seals you may see on a TravelWild Antarctica cruise, the Weddell seal (Leptonychotes weddelli) also has the distinction of being the most southern dwelling of all mammals—except for Homo sapiens on a research base located at the South Pole!

Weddell seal fur color is variable Copyright © John Shaw
Weddell seal fur color is variable

Weddell seals spend much of their time in the water, but on most cruises they are often seen on large flat chunks of floating pack ice or on gently-sloping beaches around Antarctica and adjacent islands. Preferring in-shore habitats, Weddell seals emerge through breathing holes early in the Antarctic spring onto the huge sheets of pack ice and fast ice (sea ice attached to land) to rest, molt or give birth.

Ironically, the Weddell seal’s name commemorates James Weddell, a 1800s British sailor—and professional seal hunter.

Weddell Seals Physical Characteristics and Identification

With a face resembling a smiling cat and an endearingly placid and docile disposition on the ice, the Weddell seal is a “true” “earless” seal, belonging to the Phocidae family. On shore they often allow the close approach of people. Like other phocids, the Weddell seal has no external ear flaps. Its large streamlined body is perfect for deep diving. Weddell seal teeth are distinctive and have evolved to allow it to chew holes in the ice, which are used for breathing and for access to the ice surface.

Its variable-colored coat can be a combination of gray, buff and brown. The coat may be streaked and blotched—sometimes with distinctive spots that cause the seals, at a distance, to be confused with leopard seals. Weddell seals molt at the beginning of summer and their coat can lighten a bit with prolonged sun exposure and with age.

As one of the largest true seals, the Weddell seal weighs 850-1000 lbs (400-450kg), with males being slightly smaller than females—a reverse sexual dimorphism of the norm for most mammals.

Weddell Seal Distribution and Migration

Seal pups gain as much as 5 pounds per day Copyright © Joe Van Os
Seal pups gain as much as 5 pounds per day

The Weddell seal is found in circumpolar Antarctica and is most abundant near the Antarctic coast. In the austral winter it moves northward with the expansion of the pack ice, staying in the water to avoid blizzards and poking its head through breathing holes.

Weddell Seal Habitat

Like other true seals, Weddell seals are more at home in the water than on land. Inhabiting the pack ice and coastal fast ice they can leave the water through the holes they make and maintain with their teeth. The Weddell seal’s hole is its lifeline: critical for both diving for food and resurfacing for air. When on ice, the seal rarely travels beyond three meters from its hole. Since there are no polar bears in Antarctica, these seals do not use their breathing holes to escape from terrestrial predators such as those found in the Arctic.

Weddell Seal Diet

The Weddell seal feeds mainly on fish, as well as cephalopods and crustaceans, and hunts below the ice. The diet varies with the season and the available prey. The Weddell seal’s high-speed swimming capability and keen eyesight facilitate hunting, aided by its whiskers or vibrissae, which are complicated sense organs that can detect the wake of swimming fish. During the almost total darkness of the Antarctic winter, the vibrissae are crucial to capturing prey.

Weddell Seal Behavior

Mothers stay with pups for up to 50 days Copyright © Joe Van Os
Mothers stay with pups for up to 50 days

Weddell seals are especially noisy underwater, producing a constant stream of sounds. Male vocalizations are more complex than those of the female and can be detected up to 20 miles away. The sounds may be part of territorial defense.

The Weddell seal has been called the “consummate diver”—able to dive to depths of 2,000 feet (610m) for up to an hour. They spend most of their time underwater. To surface they use their teeth to chew and maintain their breathing holes in the ice. This chewing wears down their teeth and, by 20 years of age, the Weddell seal may no longer have viable teeth and, unable to hunt or maintain its breathing hole, may die.

When not breeding, the Weddell seal is not particularly social, but will share the ice at comfortable distances.

Weddell Seal Breeding and Mating

Weddell seals attain sexual maturity at age 3-6 years for males and 2-6 years for females, depending on availability of food, population density and other environmental factors.

Weddell seals are calm on shore allowing close observation Copyright © Joe Van Os
Weddell seals are calm on shore allowing close observation

The pupping and breeding season takes place mid-September–December, when female Weddell seals can be found in loose “colonies” of up to 100 individuals giving birth on the fast ice. Births occur in 1-4 minutes and are usually single pups, although the Weddell seal is one of the few seals known to give birth to twins.

At birth, the pup lacks insulating blubber. For protection against the cold, its coat is made up of a thick layer of very fine gray fur, called the lanugo coat. This coat is shed relatively quickly as the pup fattens up on high-fat milk from its mother. (It is the pearly white lanugo coat on harp seal pups in the western North Atlantic that has caused them to be hunted for the fur trade.)

The mother and pup are rarely separated, except for short dives by the mother for food. Lactation lasts approximately 50 days—considerably longer than that of other Antarctic seal species. This prolonged period constitutes a significant drain on the mother’s fat reserves and necessitates the mother hunt between nursing times. A newborn pup weighs 55-66 lbs (25-30kg) and gains 4-5 lbs (2kg) per day. Upon weaning the pup may weigh well over 220 lbs (100kg), whereas the female may lose 200-300 pounds (100-150kg) during this time.

After weaning, the pup is left on its own to learn to hunt while the mother mates again.

Breeding males wait in the water beneath the ice, defending an aquatic territory and breathing hole against other bulls until pups are weaned. Mating takes place underwater, and a single bull can breed with a large number of females. Like other phocids, the female Weddell seal becomes pregnant immediately after mating, but embryonic blastocyst implantation is delayed so the pup is born almost a full year later.

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