Zalophus californianus
The one you have already heard, barking from a pier somewhere on the Pacific coast.
If you have ever stood on a pier in San Francisco or Monterey, you heard California sea lions before you saw them. Males bark, loudly and repeatedly, to hold territory and to advertise themselves. It is a genuinely doglike sound and it carries a long way.
Females and pups do something more precise. Each mother and each pup has a call unique to that individual, and each also has a distinct scent. When a mother returns from days at sea to a beach holding hundreds of pups, she calls, listens for the one reply that matches, walks to it, and sniffs the pup as a final check before letting it nurse. Voice first, smell to confirm.
That two step check matters because a nursing pup is expensive. A mother stays ashore with a newborn for about a week, then settles into a rhythm of two to three day foraging trips followed by one to two days back at the rookery. Nursing can last one to two years. Feeding another female's pup would waste an enormous amount of her effort, and she rarely makes that mistake.
California sea lions are eared seals, family Otariidae, not true seals, and the difference is easiest to see when one hauls out on a marina dock. It does not slither. It stands up. In an eared seal the hip and ankle joints allow the hind flippers to rotate forward underneath the body and carry weight, so the animal walks on all four limbs with its chest and head held clear of the ground. A true seal cannot do this at all. Its hind flippers trail permanently behind, and it crosses land by humping along on its belly like a caterpillar.
Watch the front end too. Small rolled ear flaps sit flat against the head just behind the eye, which is where the family gets its name. True seals have only an ear hole. And a California sea lion swims with those long black hairless front flippers, rowing them downward and backward like a bird's wings, while a true seal pushes with its rear end and steers with the front. This is why a sea lion can chase a fish through kelp and then sprint up a dock ladder, and a harbour seal can do neither.
The sexes look almost like different animals. A male weighs three to four times what a female weighs, and above his eyes sits a sagittal crest, a bony ridge along the top of the skull that grows with age and pushes the forehead into a high rounded dome. The dome is crowned with a tuft of blonde hair on an otherwise dark head, and it is the fastest way to spot a bull. Females have no crest at all and a smooth sloping forehead.
California sea lions were hunted heavily through the nineteenth and early twentieth centuries. In 1964 the breeding population on the California Channel Islands was estimated at only about 35,000 animals. Then in 1972 the United States passed the Marine Mammal Protection Act, and the numbers began climbing. Between 1975 and 2014 the US stock grew at up to 7 percent a year.
It is still climbing. The species is listed as Least Concern, and researchers think the US portion may be approaching the maximum number the environment can support. Two figures get quoted and they are not in conflict: the IUCN assessment gives about 387,646 animals across the whole range, while NOAA's stock assessment for the US stock alone gave 257,606 animals in 2014. Different areas, different years.
Success brings its own problems. More sea lions means more contact with people. They haul out on docks, jetties and buoys, sometimes sinking small boats under their combined weight. They take fish off sport fishing lines and out of nets. At Bonneville Dam on the Columbia River they learned to intercept migrating salmon and steelhead at exactly the point where the fish are funnelled and vulnerable, which puts a protected predator directly against protected prey. There is no clean answer to that.
In the spring of 1998, sea lions began coming ashore along the central California coast in a strange condition. They were well fed, not starving, but they were having seizures, arching their backs, losing coordination and dying. Between 15 May and 19 June, 70 California sea lions and one northern fur seal stranded between San Luis Obispo and San Mateo County. Forty eight of the seventy died despite treatment.
The cause was domoic acid, a natural toxin produced by a microscopic alga, the diatom Pseudo-nitzschia australis. When conditions favour it the alga blooms in huge numbers. Northern anchovies filter it out of the water and concentrate it. Sea lions eat the anchovies. The toxin attacks the brain, and particularly the hippocampus, which handles memory and navigation.
This was the first time domoic acid poisoning was conclusively documented in any marine mammal, and it changed how scientists think about harmful algal blooms. Animals that survive an acute episode can be left with permanent brain damage and may strand again and again. The blooms are tied to ocean conditions and nutrient supply, and they are now a recurring feature of the California coast rather than a single strange event.
California sea lions are among the most studied minds in the ocean, partly because they are large, tolerant of people and highly trainable, and partly because they keep turning out to be good at things nobody expected.
The clearest example is a female named Ronan, studied at the Long Marine Laboratory at the University of California, Santa Cruz. In work published in 2013, Ronan learned to bob her head in time to a musical beat, then kept time to tempos and to songs she had never heard before. Until then, keeping a beat was thought to require vocal learning, the ability to copy new sounds, which is why parrots can do it and most mammals cannot. A sea lion does not learn its calls that way, so Ronan sent researchers back to rethink where rhythm comes from in the animal brain.
Other work has looked at how these animals sort objects into categories, how long they remember what they have learned, and how they use their whiskers to detect the faint water disturbance a swimming fish leaves behind. Sea lion whiskers sit on a mobile muzzle and are actively steered rather than held passively, a pinniped skill that reaches its extreme in the walrus.
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