Fur seals are hunters of fish, squid and, in the far south, krill, and they take whatever is plentiful near their home island. That means two colonies of the same species can eat almost completely different things. Their hunting ranges from quick sucks of small fish to shaking big prey apart at the surface, and a few individuals hunt seabirds.
The Main Foods Fur Seals Eat
Most fur seal meals fall into three groups: small schooling fish, squid, and krill, which are small shrimp-like animals that swarm in cold southern seas. In South African waters, fish turned up in nearly 9 of every 10 Cape fur seal droppings.1University of Cape Town Open Access. Variability in the diet of cape fur seals and their interaction with fisheries off the South African coast, 2010-2019 Squid appeared in only about 1 in 20, and crabs or shrimp almost never.2University of Cape Town Open Access. Variability in the diet of cape fur seals and their interaction with fisheries off the South African coast, 2010-2019 Antarctic fur seals at South Georgia in winter split between krill, fish, or both, with roughly a third of droppings in each group.3Antarctic Science. The diet of Antarctic fur seals (Arctocephalus gazella Peters 1875) during winter at South Georgia
Schooling fish such as anchovy and sardine pack tightly, so a single dive can yield several catches. They’re small enough to swallow whole without surfacing, and they’re oily, which gives a lot of energy per bite to an animal that has to stay warm in cold water.
Krill are finger-length crustaceans that form huge swarms in Antarctic waters. Where krill are scarce, seals switch to fish instead.
Most of what we know comes from the seals’ droppings, which hold fish ear bones, squid beaks and prey DNA.4Marine Ecology Progress Series. Combining hard-part and DNA analyses of scats with biologging and stable isotopes can reveal different diet compositions and feeding strategies within a fur seal population DNA from droppings can even identify prey that left no hard parts behind.5PubMed. Analysis of Australian fur seal diet by pyrosequencing prey DNA in faeces
Fish ear bones are tough and keep their shape through digestion, so experts can often match them to a species and estimate the fish’s size. Soft prey leaves little behind, so a diet judged only from hard parts can understate how much soft-bodied food a seal ate. And droppings show only the last day or two of eating, which is why researchers collect many samples across a season to see the wider pattern.
How Diet Differs by Species and Location
Young walleye pollock, a cod relative, is the main food for northern fur seals on most Pribilof Island colonies.6PubMed Central. Biological and Physical Environmental Drivers of Diet Variation in Northern Fur Seals Pollock made up roughly 40 to 75 percent of what these seals ate by weight in recent decades.7PubMed Central. Current and future habitat suitability of northern fur seals and overlap with the commercial walleye pollock fishery in the eastern Bering Sea But on Medny Island, which sits next to deep ocean water, the same species mostly eats squid.8Journal of Zoology. Inter‐island variation in the diet of female northern fur seals (Callorhinus ursinus) in the Bering Sea St. George Island, with waters in between, gets a mix of pollock and squid.9Journal of Zoology. Inter‐island variation in the diet of female northern fur seals (Callorhinus ursinus) in the Bering Sea Off Japan, northern fur seals feast on firefly squid that come into shallow water to spawn in winter and spring.10Fisheries Research. Squid in the diet of northern fur seals, Callorhinus ursinus, caught in the western and central North Pacific Ocean
The shape of the seafloor explains much of this. Islands on wide shallow shelves give seals easy access to pollock and other shelf fish, while islands near the deep shelf edge put open-ocean squid within reach. Seals don’t travel far from breeding colonies while nursing, so nearby waters dominate the menu. Currents and temperature decide which fish and squid gather near an island, and when local prey changes over the years, a colony’s menu changes with it.
Antarctic fur seals show a similar split around krill. At South Georgia they eat mainly krill, while at Heard and Macquarie Islands they eat mainly fish and some squid.11Australian Antarctic Program. Fur seals The difference is strong enough that colonies have adapted genetically to their local prey.12Marine Ecology Progress Series. Prey differences drive local genetic adaptation in Antarctic fur seals
Cape fur seals in southern Africa eat mostly anchovy, horse mackerel, sardine and hake.13University of Cape Town Open Access. Variability in the diet of cape fur seals and their interaction with fisheries off the South African coast, 2010-2019 At Plettenberg Bay, sand tongue-fish, a small flatfish, joins that list.14African Journal of Marine Science. Diet of the Cape fur seal Arctocephalus pusillus pusillus at the Robberg Peninsula, Plettenberg Bay, and implications for local fisheries
When scientists compare colonies, a diet is usually described as the share of droppings containing each prey type. That tells you how often a food turned up, not how much of it was eaten. Two colonies can both eat mostly fish and still differ, because one may rely on a single species while the other eats many. Seasons matter too, so a diet measured in winter may not match the same colony’s summer menu.
How Fur Seals Catch and Eat Their Prey
Fur seals pull small prey into their mouths by suction alone, but larger prey is grabbed with the teeth.15Marine Mammal Science. Prey capture and processing behaviors vary with prey size and shape in Australian and subantarctic fur seals Anything deeper than about 7.5 cm (3 inches) top to bottom is taken to the surface and shaken apart.16Marine Mammal Science. Prey capture and processing behaviors vary with prey size and shape in Australian and subantarctic fur seals
The seal grips the fish in its back teeth and whips its head side to side until it tears in two.17PubMed Central. Australian Fur Seals (Arctocephalus pusillus doriferus) Use Raptorial Biting and Suction Feeding When Targeting Prey in Different Foraging Scenarios One half flies off while the seal swallows the other, then goes back for the pieces.18PubMed Central. Australian Fur Seals (Arctocephalus pusillus doriferus) Use Raptorial Biting and Suction Feeding When Targeting Prey in Different Foraging Scenarios A flexible, muscular neck makes the quick whipping motion possible while the jaws hold on.
Fur seals do little chewing. Their pointed teeth are built for gripping slippery prey, and food goes down in chunks.
At an aquarium or on a boat trip, a seal that surfaces and thrashes its head is usually breaking up a large fish. Gulls often gather to grab the flung pieces.
How Deep and How Long Fur Seals Dive
Female Cape fur seals usually dive to around 40 to 60 m and stay down about 2 minutes.19PubMed Central. Dive behaviour and foraging effort of female Cape fur seals Arctocephalus pusillus pusillus The deepest dive recorded was 454 m and the longest nearly 10 minutes.20PubMed Central. Dive behaviour and foraging effort of female Cape fur seals Arctocephalus pusillus pusillus Dives that hit the seafloor are the ones most likely to push a seal past its comfortable breath-hold limit.21PubMed Central. Dive behaviour and foraging effort of female Cape fur seals Arctocephalus pusillus pusillus
Most dives stay shallow for a practical reason. Going deeper costs more time swimming down and back up, which leaves less time to feed at the bottom. A seal that finds prey near the surface gains more food per breath, so the record dives are exceptions.
Light changes the picture. Northern fur seals dive deeper in daylight and under bright moonlight.22PubMed Central. The Sun, Moon, Wind, and Biological Imperative–Shaping Contrasting Wintertime Migration and Foraging Strategies of Adult Male and Female Northern Fur Seals (Callorhinus ursinus) Many prey animals rise toward the surface in darkness and sink in light. Bright moonlight can keep prey deeper, so a seal following them has to dive deeper.
Males and females hunt differently too. Male Antarctic fur seals are much bigger and often hunt on or near the seafloor, which females don’t do.23Animal Behaviour. Segregation between the sexes: Antarctic fur seals, Arctocephalus gazella, foraging at South Georgia
Hunting trips can be long. Nursing mothers leave pups ashore and go to sea for days. Antarctic fur seal mothers travel about 600 km on trips lasting around a week, and the pup fasts until she returns.
Do Fur Seals Eat Penguins and Other Seabirds
Seabird hunting is real. At one Namibian island, Cape fur seals were seen killing gannets, cormorants and penguins thousands of times over nine years.24South African Journal of Wildlife Research. Seabird predation by individual seals at Ichaboe Island, Namibia At Dyer Island, South Africa, seals killed about 7 percent of adult African penguins each year, mostly because penguins are caught returning at dusk to feed chicks.25Ostrich. An assessment of the impact of predation by Cape fur sealsArctocephalus pusillus pusilluson seabirds at Dyer Island, South Africa In Australia, penguin DNA appeared in about 1 in 10 long-nosed fur seal droppings at one site.26Frontiers in Marine Science. Quantifying wildlife conflicts with metabarcoding and traditional dietary analyses: applied to seabird predation by long-nosed fur seals A seal typically ambushes from below near the colony, then shakes the bird at the surface the way it would a large fish.
Bird hunting is not a normal behavior for every seal. Individuals develop their own targets and techniques.27South African Journal of Wildlife Research. Seabird predation by individual seals at Ichaboe Island, Namibia It is mostly young males, and the habit may be learned from others or grow out of play.28South African Journal of Wildlife Research. Seabird predation by individual seals at Ichaboe Island, Namibia Seabirds still make up a small share of the overall Cape fur seal diet, appearing in under 1 in 10 droppings.29University of Cape Town Open Access. Variability in the diet of cape fur seals and their interaction with fisheries off the South African coast, 2010-2019
For African penguins, which are endangered, even a few specialist seals can harm a colony. Losses concentrate in breeding season and among fledglings leaving islands. Managers sometimes target problem individuals rather than whole seal populations.
How Young Fur Seals Learn to Hunt
Galápagos fur seal pups at six months rely entirely on milk and dive only about 5 m.30Behaviour. Ontogeny of Diving Behaviour in the Galápagos Fur Seal By one year they dive near 50 m and start catching some of their own food.31Behaviour. Ontogeny of Diving Behaviour in the Galápagos Fur Seal Two-year-olds reach about 70 m and are the youngest to be weaned.32Behaviour. Ontogeny of Diving Behaviour in the Galápagos Fur Seal Reaching a depth is not the same as feeding there, since a pup must also stay down long enough to catch something.
Their bodies set the limit. Australian fur seal pups near weaning can reach adult depths but can’t stay as long.33PubMed. The physiological and behavioural development of diving in Australian fur seal (Arctocephalus pusillus doriferus) pups Their muscles hold less than a quarter of an adult’s stored oxygen at nine months.34PubMed. The physiological and behavioural development of diving in Australian fur seal (Arctocephalus pusillus doriferus) pups
Weaning time varies because pups need enough dive capacity to reach prey before their mothers stop feeding them. Where prey is deep or patchy, nursing lasts longer. Young seals often hunt at night, when prey rises closer to the surface.
Fisheries, Climate and Threats to Their Food
Northern fur seal hunting grounds overlap heavily with the commercial pollock fishery.35PubMed Central. Current and future habitat suitability of northern fur seals and overlap with the commercial walleye pollock fishery in the eastern Bering Sea But overlap alone doesn’t prove the seals go hungry.36PubMed Central. Current and future habitat suitability of northern fur seals and overlap with the commercial walleye pollock fishery in the eastern Bering Sea A fishery and a seal colony may use the same fish stock while taking different sizes or ages of fish, and whether the seals suffer depends on whether the fish are scarce enough for the catch to matter. Judging that means comparing seal condition, fish numbers and the amount caught over time.
The scale of seal appetite is large. South African fur seals were estimated to eat about 125,000 tonnes of anchovy and 120,000 tonnes of hake a year.37South African Journal of Marine Science. Diet of the South African fur seal (1974–1985) and an assessment of competition with fisheries in southern Africa In the Falklands, fur seals dive harder where trawlers catch the most squid and hake.38Global Ecology and Conservation. Spatial overlap between South American fur seal foraging effort and commercial trawl fisheries in the Falkland Islands
Warm water shifts the menu. El Niño warming changes what Peruvian fur seals eat.39Frontiers in Marine Science. Peruvian Fur Seals as Archivists of El Niño Southern Oscillation Effects During the 2015 El Niño, Guadalupe fur seals spent less time ashore, likely because food was harder to find.40PubMed Central. Impact of the 2015 El Niño-Southern Oscillation on the Abundance and Foraging Habits of Guadalupe Fur Seals and California Sea Lions from the San Benito Archipelago, Mexico When krill were scarce at South Georgia, mothers’ trips doubled in length and cost more energy.41Ecology. Foraging Energetics of Antartic Fur Seals in Relation to Changes in Prey Availability A mother away twice as long leaves her pup fasting longer. Seals that already dive deep have little room to dive deeper if prey moves.42PubMed Central. Diving deep into trouble: the role of foraging strategy and morphology in adapting to a changing environment
Seals tangled in net fragments burn more energy and spend more time at sea.43Marine Pollution Bulletin. Marine debris and northern fur seals: A case study Entanglement has contributed to the Pribilof population’s decline.44Marine Pollution Bulletin. Marine debris and northern fur seals: A case study Fur seals can also compete with Steller sea lions for the same prey.45Canadian Journal of Zoology. Prey competition between sympatric Steller sea lions (<i>Eumetopias jubatus</i>) and northern fur seals (<i>Callorhinus ursinus</i>) on Lovushki Island, Russia
People can help by choosing seafood certified as sustainably fished, cutting and disposing of fishing line and net properly, and reporting entangled seals to local wildlife authorities rather than approaching them.