By Kelly Stewart
Crowded together on rocks near La Jolla Cove, these animals attract attention with their loud barking and theatrical movements while jostling for the best sunny spot. Because these marine mammals are readily trained, this is the “seal” most commonly found as the funny sidekick in aquarium and zoo animal shows, although it’s in a different family than the true seals.
Sea lions differ from the local harbor seals in a couple of important ways. Sea lions have ears with external flaps (seals do not), and they are able to walk along on all four flippers, rather than lurching along on their bellies the way the seals do. One other difference that is perhaps more noticeable here in La Jolla is that the sea lions are very social and like to lie heaped together on rocks and other haul-out locations. Harbor seals on the other hand, lie together in groups but do not like to be touching at all.
Male sea lions are easily recognized because they are larger than females, they have a darker coat and they are more vocal. As well, as a male matures, he develops a bony lump on the top of his skull (a sagittal crest) that gives him a large bulbous head. Females look much gentler and demurely pose on rocks with other members of their group. Pups are born on offshore islands in June and July and are dark brown when born, although they lighten up within a few months. Each mother has a unique call for her pup so they can easily recognize each other.
Eating many kinds of fish and squid, sea lions are active swimmers and are very acrobatic underwater, sometimes encountering, playing with and investigating scuba divers. You may see them floating (rafting) together in the water — usually snoozing. Often while rafting, they will raise their flippers out of the water (looking a bit like shark fins at first sight) to regulate their body temperature. Their flippers have a lot of blood flow and are less insulated than the rest of their body, so they are able to warm their blood using the sun and then distribute that warmed blood throughout the rest of their body.
Kelly Stewart, Ph.D. is a postdoc with NOAA’s Southwest Fisheries Science Center. Contact her at NaturalLaJolla@gmail.com.