Fur seals are marine mammals that primarily inhabit the open ocean. Their diet consists almost entirely of marine organisms, as they actively hunt a variety of prey.
Primary Prey
The diet of fur seals predominantly consists of fish, cephalopods, and crustaceans. Northern fur seals, for instance, consume midwater fish and squid species. Their specific fish prey in the North Pacific includes Pacific sand lance, Pacific herring, northern smoothtongue, Atka mackerel, and Pacific salmon. Off the West Coast, their diet expands to include mackerel, octopus, squid, sardine, and anchovy. Walleye pollock is a significant food source for Northern fur seals foraging over the Bering Sea shelf.
Antarctic fur seals primarily feed on krill, fish, and squid. Krill is a major component, particularly for nursing mothers near South Georgia, but their diet can also include myctophids (lanternfish), icefish, and notothenioids. Some southern fur seal species also include seabirds, such as penguins. South American fur seals often consume anchovies, weakfish, cutlassfish, and other small pelagic fish, alongside shrimp, lobster krill, and various cephalopods like squid. Australian fur seals mainly target bony fish species, squid, and octopus.
Dietary Adaptations and Variations
A fur seal’s diet varies significantly based on species, geographic location, seasonal prey availability, and the individual seal’s age or reproductive status. Northern fur seals consume different prey depending on their foraging location and the time of year. For example, their diet over the Bering Sea shelf emphasizes walleye pollock, while foraging over the slope or in off-shelf waters leads to greater consumption of oceanic fish and squid.
Antarctic fur seal diets vary by season and location; krill is particularly important for nursing mothers during the breeding season. However, Antarctic fur seals in other regions, like those south of the Indian Ocean, consume more squid and fish. Juvenile South American fur seals, for instance, may feed on different types of demersal fish compared to adults, likely due to differences in prey accessibility.
Foraging Behavior
Fur seals employ various strategies to capture food in marine environments. They feed mainly at night, when many prey species, such as small schooling fish and squid, are closer to the ocean surface. Fur seals can dive to considerable depths in pursuit of prey. Northern fur seals are recorded diving up to 200 meters (656 feet), and Australian fur seals up to 150 meters. Female Antarctic fur seals typically dive to around 30 meters but can exceed 100 meters, remaining submerged for 2 to 5 minutes.
Their sensory capabilities contribute to their foraging success. Fur seals possess highly sensitive whiskers, known as vibrissae, which are crucial for detecting prey in low-light or murky waters. These whiskers allow them to sense water movements and hydrodynamic cues produced by swimming prey. When capturing prey, fur seals primarily use raptorial biting and may also employ suction feeding for smaller items. Larger prey items are often grasped and thrashed to break them into manageable pieces before being swallowed, often whole.