Feeding ecology and diet

As stated previously, fur seals tend to forage on the high seas, and sea lions tend to forage near the coast. Fur seals are

Galápagos sea lion (Zalophus wollebaeki) subadults, sparring. (Photo by Tui De Roy. Bruce Coleman, Inc. Reproduced by permission.)

fairly small (females average less than 110 lb [50 kg]), and can thrive on large numbers of small fish (like myctophids) and squid that rise to the surface at night in association with the deep scattering layer. The Antarctic fur seal exploits eu-phausids (krill) that undergo similar vertical migrations. Fur seal females can dive to 656 ft (200 m) or so, which enables the largest of them to feed on the bottom where the continental shelf is broad and productive.

Sea lion females may dive to 1,312 ft (400 m) or so, and generally take small numbers of larger fish and squid that are

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The New Zealand fur seal (Arctocephalus forsteri) on land. (Photo ©Tony Wu/www.silent-symphony.com. Reproduced by permission.)
A Callifornia sea lion (Zalophus californianus) congregation in Monterey Bay, California, USA. (Photo by Jeff Foott. Bruce Coleman, Inc. Reproduced by permission.)

part of the continental shelf fauna. Unlike fur seals, which suspend feeding in the middle of the day when their prey are at maximum depth, sea lions may forage night and day without stopping. Their greater energy needs may preclude them from exploiting the smaller organisms of the deep scattering layer. Both groups are capable of exploiting silvery schooling fish, such as herring, anchovy, or sardines, wherever they are encountered.

The length of the mothers' feeding absence depends on the foraging environment they use, and therefore tends to be longer for fur seals than for sea lions. The shortest trips are made by the equatorial species that feed locally (a few hours to one day). The longest trips are made by the temperate fur seals (Guadalupe, Juan Fernández, subantarctic, and some populations of the New Zealand fur seal) that feed on organisms of the deep scattering layer. Pup fasting ability varies accordingly.

Most sea lion species (males only) have been observed preying on other species of seals, but fur seals have not. Both groups occasionally eat birds. Otariids are visual feeders; echolocation has not been demonstrated for any species, although researchers have looked for this ability in the laboratory.

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