Seal vs Sea Lion: Key Differences and How to Tell Them Apart

Key differences at a glance

Seals, sea lions and walruses together make up the pinnipeds, a group of meat-eating, fin-footed mammals that live mostly in the sea but come ashore to rest and breed. Genetic studies show that all pinnipeds share a single common ancestor, and their closest living land relatives are the weasels and their kin. There are 34 living species in three families:

• True seals (Phocidae), also called earless or crawling seals, with about 18–19 species, including the harbor seal, gray seal and elephant seals.
• Eared seals (Otariidae), with about 15 species: the sea lions, such as the California sea lion, and the fur seals.
• Walruses (Odobenidae), with a single living species.

In everyday speech, “seal” can mean any pinniped, which is why sea lions are sometimes called seals. Biologists use the families above, and the differences below apply to true seals versus sea lions.

Ears, flippers and whiskers

Sea lions have small, rolled external ear flaps on the sides of the head. True seals have no ear flaps at all, only a small ear opening behind each eye that is easy to miss.

The front flippers are just as telling. A sea lion’s front flippers are long, leathery and mostly hairless, almost like wings. A seal’s front flippers are short and covered in fur, with strong claws that it uses to grip ice and rocks, scratch and hold prey.

Even the whiskers differ. Sea lion whiskers are smooth, while those of most true seals, including harbor seals, have a wavy, beaded outline. Researchers think this shape reduces vibration as the seal swims, making it easier for the whiskers to pick up water movements from prey.

Walking on land

Sea lions can turn their hind flippers forward under the body. That lets them stand up on their front flippers, walk, gallop and even climb rocks, harbor docks and stairs. Over short distances, a sea lion can move faster on land than many people expect.

True seals cannot do this. Their hind flippers always point backward, so on land they move by hunching forward on their bellies, using the front flippers for support, in a movement often described as caterpillar-like or galumphing. NOAA notes that this awkward movement is normal and does not mean a seal is injured. On ice, though, many seals slide along quite quickly.

Swimming: hind flippers vs front flippers

In the water the roles are reversed. Sea lions “fly” through the water with powerful strokes of their long front flippers, using the hind flippers mainly to steer. They are agile and acrobatic, often twisting, turning and leaping clear of the surface when traveling fast.

True seals swim by sweeping their hind flippers and lower body from side to side, like a fish’s tail, and keep the front flippers close to the body or use them to steer. This style is very efficient for long and deep dives, and true seals include the deepest divers of all pinnipeds, the elephant seals.

Sounds and social life

Sea lions are famously noisy. California sea lions bark almost constantly in their colonies, especially breeding males defending territories, and mothers and pups find each other by their calls, as explained in Why do sea lions bark? They are very social, piling together on beaches, rocks and docks and often resting in groups at sea.

Most true seals are much quieter in air. Harbor seals mainly grunt, growl and snort on land, although males make low roaring calls underwater in the breeding season, and some seals, such as Weddell and bearded seals, produce long underwater songs. Harbor seals haul out in groups, but they keep some space between them and usually hunt alone.

Raising pups is different too. Sea lion mothers alternate trips to sea with days of nursing for many months, often most of a year. True seal mothers nurse for a short, intense period on very rich milk: about 4–6 weeks in the harbor seal and only about 4 days in the hooded seal, the shortest nursing period known in any mammal.

Which is bigger, a seal or a sea lion?

It depends on the species. Comparing the two most familiar ones in North America, a harbor seal is about 1.5–1.9 m (5–6.2 ft) long and weighs roughly 50–170 kg (110–375 lb), with males and females of similar size. A male California sea lion is bigger, up to about 2.4 m (7.9 ft) and 390 kg (860 lb), though females are much smaller, at about 90–110 kg (200–240 lb).

At the extremes, though, true seals win. The largest pinniped is the southern elephant seal, whose bulls can weigh several tonnes, and the northern elephant seal is not far behind. The largest sea lion, the Steller sea lion, has bulls of up to about 1,100 kg (2,500 lb).

Where seals and sea lions live

True seals live in cold and temperate seas around the world, from the Arctic to the Antarctic, and a few species live in freshwater lakes or warm waters, such as the monk seals. Sea lions and fur seals live mainly in the Pacific Ocean and the Southern Hemisphere, including the coasts of South America, southern Africa, Australia and New Zealand.

There are no wild sea lions or fur seals in the North Atlantic. Any seal you see on a beach in Europe or on the US East Coast is a true seal, most often a harbor seal or a gray seal. On the Pacific coast of North America, both groups live side by side: harbor seals rest on quiet beaches and rocks, while California and Steller sea lions crowd onto docks, buoys and jetties, famously at San Francisco’s Pier 39, described in Why are there sea lions at Pier 39?

What about walruses?

The walrus is the third kind of pinniped and has a mix of features. Like sea lions, it can turn its hind flippers forward and walk on all fours. Like true seals, it has no external ear flaps and swims mainly with its hind flippers. Walruses are easy to recognize by their long tusks, bristly whiskers and nearly hairless, wrinkled skin, and they live only in the Arctic. Read more in the profile of the walrus.