Lying on a fine line between ocean and land, seals and sea lions belong to a group of closely related semi-aquatic mammals called pinnipeds (a Latin term that roughly translates to “buoyancy”). On an evolutionary timeline, it is believed that pinnipeds separated from other predators (such as dogs and felines) about 50 million years ago. Their huge flippers, thick layer of fat and long mustache allow them to survive in the harsh conditions of cold ocean water.
The taxonomy of this group can be a little tricky to analyze, but pinnipeds are divided into three distinct families. The Phocidae family contains all true seals; they are sometimes called creeping seals or earless seals to distinguish them from other types of seals. The Otariidae family includes 16 species of fur seals and sea lions (the third family, named Odobenidae, is dedicated exclusively to tusked walruses).
Many are confused by the fact that, despite their name, seals are anatomically and behaviorally closer to sea lions than real seals. Basically, seals and sea lions differ from real seals in body shape and social behavior. But fur seals differ from sea lions in that they have a thick layer of fur (not just hairless fat) that protects them from cold water. To make it clear for this article, whenever the term “seal” is used, it usually refers to actual seals. The term “sea lion” can refer to both sea lions and seals.
Comparison of seals and sea lions
Here’s a quick rundown of the main differences between a seal and a sea lion.
| Seal | Sea lion | |
|---|---|---|
| The size | 110 to 8,500 lbs. (50 to 3850 kg) | 150 to 2200 lbs. (From 70 to 1000 kg) |
| Social behavior | Mostly solitary, except during the breeding season | Lives in larger colonies |
| Habitat | Polar, subpolar and temperate waters; Baikal seal is the only freshwater species | Subpolar, temperate and equatorial waters |
| Number of species | 18 species including elephant seals and ringed seals | 16 species including the California sea lion and Steller’s sea lion |
| Body | Streamlined body with rear fins facing back. | Sea lions have external earplugs and pivoting rear fins. |
5 main differences between seals and sea lions
While seals and sea lions are very difficult to distinguish with the untrained eye, there are five important differences between the two that should aid identification. These differences mainly boil down to body shape and social organization. Size or body color alone will not help you determine which one is which (except for a really massive elephant seal, the largest of all pinnipeds).
Keep in mind that there are huge differences both between and between families. Some species may have certain adaptations that are simply lacking in closely related species.
Seals vs. Sea Lions: Land and Water Adaptations
True seals are more adapted to aquatic life than to life on land. Their more streamlined bodies allow them to slice through the water quickly, and their rear fins are angled backward to propel them forward. They clumsily move on the ground, crawl on their stomachs and drag forward with their front flippers. In contrast, sea lions are generally better adapted to life on land, as their hind fins rotate forward and act more like legs. While seals rely more on full-body movement in the water, sea lions mostly swim by rotating their hind flippers.
Seals vs. Sea Lions: Earflaps
Real seals do not have visible earplugs; instead, they have two holes on the sides of their heads. Both sea lions and fur seals have small outer cuffs on their heads.
Seals vs. Sea Lions: Flipper Size
Seals have shorter flippers than sea lions. They also have short claws surrounded by bare skin, whereas sea lions have long claws with tufts of fur on their front fins.
Seals vs. Sea Lions: Social Behavior
Sea lions are more likely to gather together in large, noisy colonies throughout the year. True seals, on the other hand, prefer to live and hunt alone; they usually come ashore only once a year to mate.
Seals vs. Sea Lions: Vocalizations
Real seals make soft grunting sounds, sometimes amplified by impacts on the water, but otherwise quite quiet. On the other hand, sea lions emit loud barks to communicate. When a colony goes berserk, it can be a cacophony of barking and grunting.
Seals vs. Sea Lions: 5 Key Differences, FAQs Explained (Frequently Asked Questions)
What is the difference between a seal and a sea lion?
The main difference is that true seals are better adapted to more solitary life, hunting and long-term survival in harsh seas. Its streamlined body is more ergonomic and devoid of external headphones, and its rear fins cannot rotate, making it awkward on land.
Which is more aggressive, a seal or a sea lion?
It is difficult to say which one is more aggressive because behavior can vary greatly depending on the species. Both seals and sea lions can become aggressive if they feel threatened or provoked. Since even the smallest pinnipeds are about the size of a man, they should not be approached in the wild unless absolutely necessary.
Do sea lions kill seals?
Fatalities between seals and sea lions are usually quite rare. The Steller sea lion (the largest of all sea lions, weighing up to 2,200 pounds) is known to kill and eat much smaller seals, but this is the exception rather than the rule. Given the same size of a seal and a sea lion, one does not usually hunt the other. Territorial disputes are a little more common, but even then they very rarely end in death. One population usually just drives off another.