What’s the Difference Between Seals and Sea Lions?

As part of our summer internship responsibilities, we are required to complete a project that will be useful to the NMLC after we’ve gone back to school. I’m doing a three-part “What’s the Difference?” educational poster/presentation series on seals v. sea lions, dolphins v. porpoises, and toothed whales v. baleen whales. I’m nearing completion of my seal v. sea lion interactive poster, but I can’t use everything that I’ve learned on the poster, so I thought I’d share what I’ve learned in this week’s blog.

What they have in common

Both seals and sea lions are called Pinnipeds, which means “fin-footed.” They are mammals, a group of animals that includes humans that have live young, produce milk, have hair/fur on their bodies, are air breathing, and are “endothermic” or able to control their body temperature. Both types of animals are also semi-aquatic, which means that they spend part of their lives on land, and part of their lives in the ocean. Seals and sea lions are protected by the Marine Mammal Protection Act, which requires that no one harass the animals – which includes getting too close! They also have similar diets, although a few things are different, and they use their specialized whiskers to feel the movement of their prey in the water. They are preyed upon by orcas, polar bears and sharks.

Seals

Seals are more adapted for water travel than for land travel because they can’t rotate their back flippers to walk on land, so they move like a caterpillar. The major distinction between seals and sea lions is their lack of external ear flaps.

Photo credit: www.eol.org

Seals also use their back and front flippers differently from sea lions while swimming. Seals use their front flippers to steer, and their back flippers for power. From far away, you might be able to tell a sea lion from a seal because seals frequently have many colors in their fur, and they can’t lift the front part of their body off the ground the way that sea lions can.

Photo credit: http://www.hedweb.com/animimag/sealpup.htm

Seals reach sexual maturity at 3+ years. Females build up a blubber reserve for the nursing period because many species don’t feed while with their pups. This period can be as short as 4 days, and as long as a few weeks. The mating system in phocids (seals) seems to be more complex than otariids (sea lions). They may have more of a lek-type system in some species, where a male displays to a female or makes underwater vocalizations to attract females, and so she is able to choose her mate. More commonly, however, the dominant male in the area will choose 3-8 females to be a part of his harem. Seals can live to be 14 years old.

Sea Lions

Sea lions include animals referred to as “fur seals.” Fur seals are named misleadingly because they are apart of the Otariid family with sea lions. Sea lions do have external ear flaps – you can see it on the side of the head in both of the pictures below as well as other morphological similarities between sea lions:

California Sea Lion. Photo credit: http://pt-lobos.parks.state.ca.us/MarineMammals.html

Northern fur seal. Photo credit: www.eol.org

They are more adapted for life on land than seals, as they can rotate their back flippers to make it possible for them to walk and run on land. Sea lions can only dive as deep as 450m, but dives further than 200 are uncommon, and they can’t store as much oxygen in their lungs as seals can.   Sea lions’ flippers have no hair or claws so that they can more easily grip the surface of rocks, and many of their mating areas are on rocky terrain. The way they use their flippers to swim is different from seals – it’s actually the exact opposite. Sea lions use their long, strong front flippers for power while they swim, and their back flippers for steering. This gives them an advantage when escaping orcas because if the orca were to bite their back flippers, they could still swim quickly to get away, where if a seal had its back flipper bitten, it would no longer have the “power” flippers to keep it moving forward. Sea lions are also usually monochromatic – or they only have one color in their fur, while seals typically have many colors.

The mating system in sea lions is polygynous, which means that there are many females per male. A ratio of 10 females per male is fairly common. The males will defend a patch of land, called a territory, and then all the females on his land are the ones that he mates with. The older and more experienced the male: the better location he has and the more females that want to give birth and nurse their pup on his land. Both otariids and phocids (sea lions and seals) have post partum estrus, or are ready to mate immediately after giving birth. The uterus in females is shaped like a “y”, with one horn holding the full-term fetus and the other preparing to receive the new blastocyst within a few days  of birth of the fetus.  The females become receptive for mating between 4 and 23 days postpartum. In the Steller sea lion, it has been noted the females that have lost a pup will adopt another. Sea lions are different from seals in that the females will continue eating while lactating, seals fast during this time, and also in that pups stay with the females between 4-12 months, depending on the species. Sea lions also tend to have a little longer lives than seals – they can live to be 15-20 years old.

So that may be more than you ever wanted to know about seals and sea lions! Feel free to come by the center at the end of the summer to see the exhibit I’m designing that will sum up this information and have an interactive component!