Head to head
Otter vs Seal
A sleek brown animal rolling in the surf could be an otter or a seal, and the two are often confused, especially the larger sea otter. They took to the water from different ancestors and solved the same problems in different ways.
| Otter | Seal | |
|---|---|---|
| Family | Mustelidae, the weasel family | Pinnipeds; closest to bears |
| Species | 13 otter species | ~33 seal, sea lion, and walrus species |
| Insulation | Dense fur, no blubber; groomed constantly | Thick blubber layer |
| Limbs | Four webbed feet plus a strong tail | Front and rear flippers, no real tail |
| On land | Walks, runs, and bounds normally | Hitches along on the belly or waddles on flippers |
| Typical weight | 1 to 45 kg (sea otter largest) | 30 kg to over 3000 kg (elephant seal) |
| Mostly found | Rivers, lakes, marshes, and Pacific kelp forests | Coasts and open ocean of every sea |
| External ears | Small ear openings, no flaps | Ear flaps in sea lions and fur seals; none in true seals |
Otter vs Seal: common questions
How do I tell a sea otter from a seal?
A sea otter usually floats on its back at the surface, often with its paws and hind feet lifted clear of the water, and it may be grooming, cracking a shell on a rock balanced on its chest, or wrapped in kelp. It has a small, round, distinctly furry face with prominent whiskers, and a visible tail. A seal at rest floats vertically or lies hauled out on rocks or a beach, has a sleeker, wetter-looking head, no visible tail, and is generally much larger. If it is on land and moving, an otter walks on four legs while a seal either bellies along or, if it can walk, does so on flippers.
Are otters and seals related?
Distantly. Both are in the order Carnivora, and both belong to the dog-like branch of it, Caniformia. Within that branch, seals and their relatives are thought to be closest to bears, having evolved from a bear-like land ancestor that returned to the sea around 25 million years ago. Otters are mustelids, which are also caniforms and not far from the seal and bear group, so an otter is a closer relative of a seal than a cat is, but the two still last shared an ancestor tens of millions of years ago and adapted to water separately.
Which is the better swimmer?
The seal, for sustained speed, depth, and endurance. Seals are streamlined, powerfully muscled, and propelled by large flippers or a sculling rear body, and species such as the elephant seal dive to more than 1500 metres and stay down for over an hour. Otters are agile and quick in water and well suited to hunting in rivers and kelp, using body undulations and webbed feet, but they are shallow, short-duration divers by comparison, typically working within a minute or two of the surface. The otter has the edge on versatility, being genuinely at home both in the water and on land, whereas a seal is built overwhelmingly for the water and pays for it ashore.