Cute, Fat, Lazy Slugs...AKA: Weddell Seals

“Of the lunacies earth can boast, The one that must please the devil the most is pride reduced to the whimsical terms of causing the slugs to despise the worms”~~Unknown

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Latin Name: Leptonychotes weddellii

Family: Phocidae

Genus: Leptonychotes

The Weddell seal was discovered and named in the 1820s by James Weddell, a British sealing captain. Captain Weddell discovered the seal in the parts of the Southern Ocean now known as the Weddell Sea. However, the seals are found around the entire Antarctic continent. 

 

Weddell seals have the most southerly distribution of any mammal, with a habitat that extends as far south as McMurdo Sound (at 77°S). It is the only member of the Antarctic tribe of lobodontine (Lobodontine means "lobed tooth") seals to prefer in-shore habitats where there is fast ice (An Ice Shelf) and free-floating pack ice. It is estimated that there are approximately 800,000 seals today. Due to their large numbers, docile behavior, and penchant for hauling out on fast ice, they can be easily approached by humans therefore, making them the best studied of the Antarctic seals.

Weddell seals are one of the species most studied by scientists here at McMurdo Station. I had the opportunity of driving a group of scientists from Seward, AK that was down here for a couple of months researching the seals. Due to the fact that Seward is such a small town, it just so turned out that I knew the woman that was the head of the research team down here. She had been a guest speaker for the kayak company I work for in Seward. In Seward, she works with the Stellar sea lion and Harbor seal populations that are found in that part of Alaska. Again, it proves that we live in a small world.

But I digress…back to the seals :).
 

Physical Appearance:

The males weigh less than the females, although they are generally about the same size and length. Weddell seals measure about 8.2-11.5 ft long and weigh between 880-1360 lbs. The male seals tend to have a thicker neck and a broader head and muzzle than the females. The Weddell seal face has been compared to that of a cat due to a short mouth line and similarities in the structure of the nose and whiskers. Their upturned mouths give them the appearance of smiling. 

 

Mother and pup

 

The Weddell seal grows a thin fur coat around their whole body except for small areas around the flippers. The color and pattern of the coat varies, often fading to a duller color as the seal ages. This coat molts around the beginning of summer. Adults are generally brown, with lighter belly coloring. They are mottled with large darker and lighter patches, those on the belly being silvery white. Adult males usually bear scars, most of them around the genital region.

Young Weddell seals have gray coloring for the first 3 to 4 weeks; later they turn a darker color. The pups reach maturity at 3 years of age. The pups are around half the length of their mother at birth, and weigh 55 to 66 lb. They gain around 4.4 lb a day, and by 6–7 weeks old they can weigh around 220 lb. 

 

Weddell Seal Pup separated from its mother and found on the road to the Ice Runway

 

Behavior and Breeding:

Weddell seals gather in small groups around cracks and holes in the ice. These animals can also be found in large groups on ice attached to the continent. In the winter months, they stay in the water to avoid blizzards, with only their heads poking through breathing holes in the ice. This seal is often observed lying on its side, when on land. 

 

The smile of satisfaction

Weddell Seals with Mt. Erebus in the background and pressure ridges near Scott Base

 

Depending on the latitude it inhabits, this marine mammal gives birth from early September through November, with those living at lower latitudes giving birth earlier. During the mating season, Weddell seals make noises that are loud enough to be felt through the ice. Copulation has only been observed to occur underwater, where the female is often bitten on the neck by her partner. The seals are normally around six to eight years old when they first breed, but this can be much earlier for some females. The Weddell seal is one of the only breeds of seals that can give birth to twin pups. Birth of the pup only takes around one to four minutes. The pups take their first swim at around one to two weeks old. They can hold their breath for five minutes, enabling them to dive to depths of 330 ft. After six to seven weeks they are weaned and begin to hunt independently. 

 

 

Diving:

The Weddell seal is known for its very deep dives, which may reach some 2,300 ft. After dropping away from a breathing hole in the ice, the seals become negatively buoyant in the first 30 to 50 meters, allowing them to dive with little effort as they make their descent.

They can also stay underwater for approximately 80 minutes. Such deep dives involve foraging sessions, as well as searching for cracks in the ice sheets that can lead to new breathing holes. The seals can remain submerged for such long periods of time because of high concentrations of myoglobin in their muscles.

Weddell seals metabolism is relatively constant during deep water dives, meaning there must be another way to account for functioning with a lack of oxygen over an extended period of time. Seals, unlike other mammals (such as humans) can undergo anaerobic metabolism for these extended dives, which causes a buildup of lactic acid in the muscles. The lactic acid does not enter the bloodstream; however, until after the animal has surfaced. This is done by constricting the capillaries going from the muscles to the veins. This requires a longer recovery time though, which in the long run, may be less efficient than quicker, aerobic metabolic dives.

These seals also compensate for prolonged lack of available oxygen by increasing their oxygen carrying capacity. This is done by having more red blood cells per unit volume of blood, as well as having more blood relative to other mammals. Typical oxygen concentration levels in human blood at sea level are about 15cc; where as Weddell Seals can have 60cc. They can also release oxygenated blood from their spleen into the rest of their body acting as an oxygen reserve. Muscle cells also contain more myoglobin, which has a high affinity for oxygen.

Other circulatory adjustments include reducing their heart rate. The seals do not send blood to where it is not needed while diving. Essential structures like the brain still receive blood, while the gut and lungs may not (oftentimes they will collapse their lungs at great depths due to such high pressure). It is important to understand that diving mammals are not able to dive for long periods of time because of a higher lung capacity, but more importantly, because of increased oxygen carrying capacity in the blood and muscles.
 

Diet and Predation:

Weddell seals eat an array of fish, krill, squid, bottom-feeding prawns, cephalopods, crustaceans and sometimes penguins. A sedentary adult will eat around 22 lb a day, while an active adult will eat over 110 lb a day.

Scientists believe Weddell seals rely mainly on eyesight to hunt for food when light is available. However, during the Antarctic winter darkness, when there is no light under the ice where the seals forage, they rely on other senses, primarily vibrissae or whiskers, which are not just hairs but very complicated sense organs with more than 500 nerve endings that attach to the animal’s snout. The hairs allow the seals to detect the wake of swimming fish and use that to capture prey. Kind of like a cat.

Weddell seals have no natural predators when on fast ice. At sea or on pack ice, they become prey for killer whales and leopard seals, which prey primarily on juveniles and pups. The Weddell seal is protected by the Antarctic Treaty and the Convention for the Conservation of Antarctic Seals.

Lifespan:

The Weddell seal has a shorter lifespan than most other pinnipeds. On average, the Weddell seal lives for 20 years, compared to an average life expectancy of 40 years for most other seals. This is because the Weddell seals survive by scraping the ice to keep their breathing holes open with its teeth. This has the effect of wearing down its teeth over time. Once a Weddell seal's teeth have worn down to a certain level, the seal is unable to eat and eventually starves to death.

 

A bouquet of flowers for the seals