Seal

Seals are a semi-aquatic species, also commonly referred to as pinnipeds. There are three general categories of seals, classified as Phocidae, consisting of the true seals, Otariidae, consisting of fur seals and sea lions, and Odobenidae, which currently includes only walruses. They are easily recognized from their finned feet and distinct build, allowing them to thrive in the sea.

These animals have long captured the public consciousness due to their striking appearance and playful nature and are prominently featured in exhibits worldwide.

List of the Common Types of Seals

There are 34 known species of seals in the world. These consist of 18 true or earless seals, 15 eared seals, which include fur seals and sea lions, and the walrus.

Physical Description and Appearance

Size: Length: 3 -16 ft (1 – 5 m)

Weight: 99 – 7100 lb (45 – 3200 kg)

The Baikal seal is the smallest at 3ft and 99lbs, while the male Southern Elephant seal is the largest, measuring 16ft and 7100lbs.

Flippers: All seals have four fin-like appendages called flippers, which help them move on land and sea. Seals and walruses have shorter flippers, while sea lions have longer ones.

Ears: Only the otariids have external ears, as evident from their name eared seals. On the other hand, the phoecids and walruses lack external ear flaps and have only ear holes.

Teeth: They have fewer teeth than most carnivores, especially incisors and molars, but have pointed, sharp canines. Walruses have two very easily identifiable protruding tusks.

Body and Coloration: Males are generally larger than females, except for some like crabeater and leopard seals. They have a streamlined and spindle-shaped body, alongside rounded heads, short snouts, and small tails. Most of them are covered with dense fur and have whiskers.

While colors widely vary from white to brown to gray to black, a general characteristic among all seals is that the dorsal region is darker while the ventral area has a lighter shade.

Distribution

They are found in seas and oceans worldwide, mostly preferring the colder waters of the Arctic and Antarctic regions. Some are also found in inland lakes in Finland, Russia, and Siberia. The exceptions are the monk seals, which live in tropical waters, and the Baikal seal, which is exclusive to the freshwater lake Baikal.

Habitat

Though they spend long periods in water, they will come on land for short periods to rest, breed, or shed. Those living in polar regions can be spotted on ice floes or large floating ice sheets, while those in more temperate climes are seen on boulders or rocky outcrops close to the sea.

How long do they live

Seals have high longevity and can live up to 25-30 years. The longest living seal recorded is a female Gray seal off the coast of the Shetland Isles in Scotland who lived up to 46 years.

What do they eat

Carnivorous in nature, their diet consists of seafood like crabs, krill, mackerel, mollusks, octopi, salmon, and squid. They also hunt birds, especially penguins, and even prey upon juvenile seals.

Some pinnipeds have more specific tastes, such as the crabeater seal, which, contrary to its name, is a filter feeder sustaining on krill. The walrus uses its teeth to feed on clams.

Behavior

• All three types of seals have unique forms of vocalization – sea lions bark, other eared as well as earless seals grunt and slap water, and walruses produce gong-like noises.
• These pinnipeds have developed several feeding strategies, including pierce feeding, grip and tear feeding, suction feeding, and filter-feeding. However, they are known to employ multiple strategies at once, depending on the availability of the prey.
• They are very social creatures but don’t form close relationships. Groups can be massive with over a hundred members, though hunting tends to be solitary.
• The seal is a very intelligent animal, capable of remembering patterns for about 18 seconds and repeating them verbatim. They are among the few species that show rhythmic entrainment, i.e., a response to musical rhythms.

Adaptations

• In order to survive in harsh cold environments, seals have a layer of extra fat referred to as blubber. This layer helps them maintain their body temperature by regulating blood flow, passing blood from the interiors to the external layers of fat when it is warmer, and migrating back when the temperatures are lower.
• Most seals have a layer of dense fur to provide insulation. Only walruses are sparsely covered in fur.
• Seals are semi-aquatic mammals, having adapted to life in the ocean. The bodies of true seals and walruses are shaped like a torpedo, with physical features like ears internalized and short flippers, which allows them to reach high speeds underwater, while that of a sea lion is more maneuverable and allows for better mobility on land due to larger fore flippers.
• To prevent a bout of decompression sickness as a result of nitrogen bubbles getting trapped in the blood while resurfacing, seals will collapse their lungs to release any stored air when they dive.

How do they reproduce

Seals mate annually and are generally promiscuous, though monogamy has been observed in certain species. Breeding can take place both on land and sea after forming a colony. Both sexes build up extra blubber reserves – the males need additional energy for courting a mate and warding off competitors, while the females need it to nurse and take care of their newborns.

Courtship varies from species to species, as some, like the California sea lions, use a lek system while others, like the male northern fur seal, maintain entire territories between which the females can freely move.

Life Cycle

After breeding, the females will give birth to a single pup. They then have to take care of the baby seals independently as males do not generally help raise the offspring.  The mother will haul on land to nurture and feed the young, fasting during lactation, with walruses being the only exception as they wean their pups at sea. Once the weaning period is over, she abandons the pup, leaving it to fend for itself.

Baby seals reach up to three times their weight during feeding and use the excess fat to strengthen themselves to survive. This is a precarious period for them, as they become easy prey for killer whales, polar bears, and other seals. During this time, pups do not eat or drink, surviving off the body fat provided to them while weaning.

Males reach sexual maturity at around 3 – 4 years of age, while females do so at 3 – 6 years.

Conservation

According to the IUCN’s classifications, seven seal species are “Endangered” or “EN”  including the Hawaiian fur seal, the Galapagos fur seal, and the Australian sea lion. Three are categorized as “Vulnerable” or “VU” – the northern fur seal, the hooded seal, and the walrus. There are several threats to them, including getting caught in fishing nets, global warming causing habitat loss, marine pollution, and indiscriminate hunting for their blubber, fur, and meat.

There have been several acts passed to protect seals. These include the Marine Mammal Protection Act of 1972 (MMPA) in the United States and the Convention for the Conservation of Antarctic Seals.

Seals – FAQs

Interesting Facts

• Seals have a lot of carbon monoxide in their blood. This is a result of staying underwater for long periods.
• Two seals went extinct relatively recently – the Caribbean monk seal in 1996 and the Japanese sea lion, whose last recorded sighting was that of a juvenile in 1974.
• Due to their appealing appearance and behavior, seals have been prominently featured in popular culture. This includes the legend of the selkies, the Inuit goddess Sedna, and modern animated features such as Madagascar and Ice Age.
• Seals have been historically easy to tame and are often seen in zoos and marine parks. They have also been used in scientific research and also by the military.