Eumetopias jubatus
The biggest eared seal alive, and a species pulling in two directions at once.
In 1741 a German naturalist named Georg Wilhelm Steller sailed east from Kamchatka with Vitus Bering to find out what lay between Asia and America. The voyage failed badly. The ship wrecked, Bering died, and the survivors spent a winter marooned on a treeless island. Steller filled the time describing animals no European had recorded. He wrote up this sea lion in 1742, and it has carried his name ever since.
The scientific name is a description in itself. Eumetopias means broad forehead. Jubatus means maned. Broad forehead, maned. That is the animal: a wide, fairly flat skull sloping into a short blunt muzzle, and on a mature bull a heavy shaggy ruff of coarse hair over the chest, shoulders and back.
The coat is a warm tawny colour, light blonde to reddish brown, and it stays pale even when the animal is soaking wet. That is a useful field mark, because the flippers, muzzle tip and eye rims are jet black by contrast.
Steller sea lions belong to the family Otariidae, the eared seals, and they are built on a completely different plan from the harbour seals and elephant seals in the other half of this archive. Look for the ear first. An eared seal has two small external ear flaps, short rolled cones of skin lying flat behind the eye. A true seal has only a hole. On a big Steller bull the flaps almost vanish into the ruff, but they are there.
The bigger difference is how the animal moves. A Steller sea lion swims by rowing with its front flippers, which are long, broad, black and leathery, roughly a quarter of the body length, and beaten downward and backward like wings. A true seal does the opposite, sweeping its rear end side to side and using the front flippers mainly to steer. On land the Steller's hip and ankle joints let the hind flippers swing forward under the body and take weight, so the animal stands on all four limbs, holds its chest and head high, walks, and climbs. Stellers are regularly found on rock ledges far above the sea, in places a true seal could never reach, because a true seal can only hump along on its belly.
Then there is size. A Steller bull weighs about three times what a female weighs and grows 20 to 25 percent longer. NOAA gives a maximum male weight of about 1,100 kg. Most true seals are nowhere near this lopsided, and in several ice seal species the female is actually the larger sex.
Between the late 1970s and 1990 the western population of Steller sea lions fell by about 70 percent. NOAA puts the total decline from the 1970s to the early 2000s at roughly 77 to 81 percent. Hundreds of thousands of animals disappeared from the Gulf of Alaska and the Aleutian Islands, and the species was listed under the US Endangered Species Act in 1990.
Scientists tested one explanation after another. Were commercial fisheries taking the pollock and mackerel the sea lions needed? Were killer whales, short of great whales after industrial whaling, switching to smaller prey? Was the whole North Pacific shifting under a change in ocean climate? Disease, contaminants and illegal shooting were all examined too. Evidence turned up for several of these, and the honest current answer is that no single cause accounts for the crash.
What makes it stranger is that over the same years the eastern population, from Southeast Alaska down to California, was growing at about 4.25 percent a year. Two halves of one species, sharing a coastline, moving in opposite directions.
Steller sea lions breed at traditional sites called rookeries, mostly rocky islands, ledges and gravel beaches. Bulls arrive in spring and claim territories they will hold for the entire breeding season. Holding a territory means not leaving it, and not leaving it means not eating. A mature bull may fast for one to two months.
That fast explains why so much of this animal's biology is about bulk. A male is sexually mature somewhere between three and eight years old, but he is usually not big enough to hold ground until nine or ten. He needs enough stored fat and muscle to outlast every rival who wants his patch, and only a small fraction of adult males ever breed. That is the pressure that produced the size gap between the sexes.
Females arrive from mid May. Pups are born between mid May and mid July, peaking in June, and mothers mate again within about two weeks of giving birth. Most pups wean before their first birthday, though some keep nursing for as long as three years. Females can live to about 30, males to about 20.
More than a hundred fish species have been recorded in the Steller sea lion diet, along with squid and octopus: walleye pollock, Atka mackerel, Pacific cod, salmon, herring, sand lance, flatfish and rockfish among them. They have also been recorded killing and eating young northern fur seals at the Pribilof Islands, and harbour and ringed seals. Mothers with small pups feed mostly at night and switch to any time of day once the season ends.
Adult females average dives of about 45 m, though the deepest documented dive is about 427 m, roughly 1,400 feet. Most dives last two minutes or less but can run past 13 minutes. Diving ability builds with age. The diving of adult males has essentially never been studied, which is a good reminder that even a closely watched species still has blanks in its file.
At sea they gather in loose groups called rafts, and one will often lie at the surface with a flipper held straight up in the air. This is not distress. Flippers are poorly insulated, with blood vessels close to the skin, so a raised flipper works as a solar panel in the sun and as a radiator in the water.
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