Fur seals and sea lions are marine mammals that share many superficial similarities, leading to common confusion. This article will clarify their taxonomic relationship and highlight the distinct features that allow for their proper identification.
Not the Same: Understanding the Family Tree
Fur seals and sea lions are closely related but distinct species. Both belong to the family Otariidae, known as “eared seals,” which distinguishes them from “true seals” (Phocidae) and walruses (Odobenidae) by the presence of external ear flaps. The Otariidae family encompasses 15 species across seven genera.
Traditionally, the Otariidae family was divided into two subfamilies: Otariinae for sea lions and Arctocephalinae for fur seals. This classification was primarily based on the presence of a thick underfur layer in fur seals. However, recent genetic studies suggest that this traditional subfamily distinction may not fully reflect their evolutionary relationships, with some fur seal species being more closely related to sea lions than to other fur seals.
Telling Them Apart: Key Distinctions
One of the most noticeable differences between fur seals and sea lions lies in their coat. Fur seals possess a dense underfur layer with longer guard hairs, giving them a much thicker and more luxurious coat. In contrast, sea lions have a coarser, shorter coat of hair without the same dense underfur, relying more on a layer of blubber for insulation.
Size and build also offer distinguishing characteristics. Sea lions are generally larger and more robust than fur seals. For instance, a female Galapagos fur seal might weigh 27-33 kg, while a female Galapagos sea lion can range from 55-75 kg. Furthermore, sea lions typically have longer snouts and their eyes are set further back, whereas fur seals have shorter muzzles and larger, more bulbous eyes.
Their flippers and locomotion patterns also differ. Sea lions use their large fore flippers for propulsion in the water, moving them in a powerful, sweeping motion like oars. Fur seals, while also using their fore flippers, have proportionally longer flippers, and some species are noted for extremely long hind flippers. On land, sea lions are more agile, able to “walk” or even gallop, while fur seals appear stockier due to their smaller overall body size.
Vocalization provides another clear distinction, particularly for California sea lions, which are known for their characteristic loud barks. Fur seals tend to be quieter, communicating with softer grunts, growls, or hisses.
Shared Characteristics and Habitat
Despite their differences, fur seals and sea lions share several common traits as members of the Otariidae family. They also both have the ability to rotate their hind flippers forward, allowing them to move on all fours on land, which true seals cannot do. This adaptation provides them with greater mobility on terrestrial surfaces compared to true seals, which “galumph” or wriggle on their bellies.
These marine mammals are found across various coastal waters, typically in subpolar, temperate, and equatorial regions of the Pacific, Southern, Indian, and Atlantic Oceans. They are semi-aquatic, spending time both in the ocean for feeding and on land or ice for breeding and resting. They often congregate in large groups, particularly during breeding seasons, forming rookeries on beaches or rocky substrates, often on islands. Their diet primarily consists of fish, squid, and krill, though specific prey items can vary by species and location.