---SEALS, SEA LIONS AND WALRUSES

Seals, sea lions and walruses, often collectively referred to as pinnipeds, all belong to the order Pinnipedia. Pinnipedia literally means "fin-footed", which refers to their fin-shaped limbs.

Picture: Harbor Seals having a rest.

The pinnipeds are mammals, and are related to the carnivores, but are usually not included in this order. Pinnipeds usually spend most of their time in or near the oceans (although there are some species living near fresh water lakes), and therefore they are considered marine (or more generally, aquatic) mammals.

Whales and dolphins, as well as the sirenians (manatees and dugongs) have invaded the oceans earlier than the pinnipeds and therefore more adapted to an aquatic lifestyle: they cannot survive on
land for more than a few hours. Pinnipeds developed some 25 million years ago. The relationship between the pinniped groups is somewhat unclear. It is commonly thought that seals evolved in the
North Atlantic, while the sea lions and walruses developed in the Pacific. The sea lion and walrus lines diverged some 20 million years ago. The seals are probably related to the mustelids (which included the marten and the otter), whereas the sea lions are more closely related to bears.

Pinnipeds can be found worldwide. Seals can be found in the North Atlantic and Pacific and around the Antarctic. Walruses only occur in the Arctic waters of the Atlantic and Pacific. Sea lions can be found throughout the Pacific and in the South Atlantic. There are no sea lions in the North Atlantic.

Like the whales and dolphins, the pinnipeds have a thick blubber layer to protect them from hypothermia in the cold water and to give them a more hydrodynamic shape. Unlike the whales, most pinnipeds have fur. In the walrus it is barely visible, in fur seals (sea lion species), the fur is very thick. They all have obvious whiskers, which they probably use for underwater (close range) navigation and foraging. There is a lot of variation in size. The smallest is the ringed seal (1.5 m long and weighing about 68 kg) and the largest is the Southern elephant seal (5 m long and weighing over 3500 kg).

Their adaptation to living both on land and in the ocean is illustrated in an extreme form in the behaviour of the Northern elephant seal. This seal spends months out in the ocean on foraging trips. During that period they never come close to shore and sleep underwater. They are excellent divers, which on average dive to a depth of about 300 m, but they can dive as deep as 1500 m and stay submerged for more than an hour (about 66 minutes). In some periods of the year, they come ashore to give birth and raise their pups, to mate and to moult. Especially during the moult, they stay on land for a few weeks and do not enter the water at all. During that period, they use their large blubber layer as food storage.There are three families of pinnipeds: the (true) seals, the eared seals (sea lions and fur seals) and the walruses, with in total 35 species (one of which, the Caribbean monk seal, is considered to be extinct). Some species are divided into a number of subspecies.

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True seals (Phocidae)

True seals have a torpedo-shaped body. They have no external ears. Their hind-flippers are pointed backwards and their fore-flippers are short. They have a small, distinct tail. On land, they move by
"hopping" on their bellies. They swim by moving their hind-flippers left and right. They don't use their fore-flippers while swimming. This group is divided into two subfamilies: the northern phocids (Phocinae) and the southern phocids (Monachinae). There are some anatomical differences between the two groups.

Picture: Northern Elephant Seals.

Northern phocids (Phocinae). To this group belong well-known seal species like the harbour seal, the grey seal, the harp seal and the ringed seal (the Saimaa seal, which lives in the Finnish freshwater lake Saimaa, is a subspecies of ringed seal). Southern phocids (Monachinae). To this group belong the endangered Mediterrean and Hawaiian monk seals, and a number of Antarctic seals, such as the Weddell seal and the leopard seal.

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Eared seals: Sea Lions and Fur Seals (Otariidae)

The eared seals have a more elongated body than true seals. They have small external earlobes. Their fore-flippers are larger and they use these for moving around on land. Their hind-flippers and be folded forward. They can support their bodies on their fore- and hind-flippers. They have a small tail. Underwater they propel themselves with their fore-flippers and use their hind-flippers only for steering. This group is divided into two subfamilies: the fur seals (Arctocephalinae) and the sea lions (Otariinae). The anatomical differences between these subfamilies are not big.

Picture: Australian Sea Lion.

Fur Seals (Arctocephalinae)

Fur seals are usually smaller than sea lions and have a thick fur. They are sometimes referred to as sea bears. To this group belong the Northern or Pribiloff fur seal and the South African fur seal.

Sea Lions (Otariinae)

Sea lions are usually fairly large and in some species the males have a thick mane, somewhat like a lion, which gave them their common name. To this group belong the well-known California sea lion and the Southern or Patagonian sea lion.

Walruses (Odobenidae)

Picture: Walrus.

Walruses have no external ears. They have large fore-flippers, which they use to support themselves on land. Their hind-flippers can be folded forward. Their tail is hidden. Underwater they propel themselves using their hind-flippers, like true seals. Their most remarkable features are the large tusks. There is only one species of walrus, with two subspecies: the North Atlantic and the (somewhat larger) North Pacific walrus.

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Finnish seals

In the Baltic Sea and its adjacent waters around Finland, there are three seal species: the harbour seal (only occasionally) , the grey seal and a ringed seal subspecies: the Baltic ringed seal. In Lake
Saimaa (Northeast of Helsinki, close to the Russian border), there is another, unique ringed seal subspecies: the Saimaa seal. This subspecies only occurs in this freshwater lake system.

There is one seal at the Särkänniemi Aquarium. Wilhelmi is a harbour seal, who was born in the Zoo in Stuttgart (Germany) in 1968. For a harbour seal, he is very old, since harbour seals usually
do not become older than 25 years.

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