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California sea lions started showing up in great number at Sea Lion Caves in Oregon last fall just about the time they began disappearing from San Francisco Bay's Pier 39.


Now, they're leaving Oregon, and showing up in -- San Francisco. The headlines out of San Francisco read like an Agatha Christie plot:

"Sea lions mysteriously disappear from Pier 39."

"S.F.'s vanishing sea lions baffles experts."

"Where did the city's ever-present sea lions go?"

Yes, a big, blubbery mammalian mystery has brewed for weeks around San Francisco Bay. Now, clues point toward Oregon.

Or do they?

Every salty whodunit must start somewhere and this one begins a little more than 20 years ago, in September 1989, when California sea lions, Zalophus californianus, started consistently hauling their bulbous bods onto a dock at Pier 39, an attraction as thick with tourists as it is with San Francisco-themed tchotchkes. That month, only a handful of sea lions hung around, sunning, snoozing and inconveniencing fishermen.

By mid-January 1990, 150 of their friends had joined them. By February, they numbered about 250 and by March, more than 400.

Fishing vessels moved out of the way, but that spring, so did the sea lions, migrating south to breeding grounds in the Channel Islands near Santa Barbara, Calif.

That summer, the gargantuan beasts -- males grow to 7 feet and can reach 1,000 pounds -- returned, as they have annually, according to the Marine Mammal Center, a nonprofit rescue and research operation in Marin County, Calif.

Tourists may come to taste San Francisco's rambunctious character and sensuous fog, but for the sea lions, food and safety have been the draws. Until recently, winter herring runs provided plenty of forage. Orcas and great white sharks, which dine on sea lions, don't enter the busy bay.

The noisy, intelligent, playful, pungent mammals thrived. They grew so abundant that their original favorite dock submerged under their weight and fell apart.

Knowing a good tourist draw when they saw it, the folks who operate Pier 39 provided new housing, a cluster of 10-foot-by-12-foot floats within camera clicking distance from shore. Sea lions squeezed aboard, barking their approval.

The Marine Mammal Center got so many questions it opened a kiosk nearby. And for years, tourists stopped for a look and an earful.

On Oct. 23, 2009, volunteers counted more than 1,700 California sea lions at Pier 39.

Clue: Gaze ocean-ward along Oregon's central coast and you might notice vast rafts of sea lions frolicking, says Dan Harkins, general manager at Sea Lion Caves, between Yachats and Florence. The caves, more typically home to the larger Steller sea lions, have operated as a tourist attraction for 78 years, and "all of a sudden we're seeing numbers that nobody remembers seeing," he says.

Typically in January, 500 to 700 California and Steller sea lions hang out in and around the caves, feasting on anchovies, sardines and such. This week, Harkins says, estimates climbed toward 1,500.

Lost Beach, between the caves and Heceta Head, has been so jam-packed on some days that the sand was scarcely visible between the animals' chocolate or golden brown bodies.

"We don't have license plates on 'em to be able to tell if they're from California," he says. "It's all speculation right now, but it seems to be tied in. They disappeared there. We've got record numbers up here."

Scientists are disinclined to jump to such a tidy conclusion.

California sea lions always cruise through Oregon waters in search of food, says Bruce Mate, director of the Marine Mammal Institute at Oregon State University's Hatfield Marine Science Center in Newport. Typically they start to arrive in late summer, peak in October, then move on to waters off Washington and British Columbia.

But with small, schooling bait fish such as anchovies and sardines abundant off Oregon at the moment, Mate says, the ravenous Californians may simply have selected to stay.

El Niño conditions might be a factor. Warmer water in California last summer and fall may have pushed prey species north, inspiring sea lions to follow.

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After squeezing into Sea Lion Caves in record numbers, wedging flipper-to-flipper along Lost Beach and bobbing in vast rafts off the central Oregon coast this winter, thousands of California sea lions have mostly moved on.

At the same time, sea lions that abruptly vacated San Francisco Bay last fall appear to be slowly returning to Pier 39, where for decades tourists have watched their slippery antics, listened to their noisy barks and snapped their pictures.

California sea lions range widely, hunting in the Northwest, breeding and pupping in Southern California's Channel Islands. But the sudden disappearance of a huge number of animals was so unusual it made headlines around the world.

Their population ballooned in San Francisco Bay over the past two decades. Merchants at Pier 39 accommodated the behemoths -- males grow to 7 feet and can reach 1,000 pounds -- by installing floats for the sea lions to use.

Scientists speculated that El Nino conditions might have contributed to their exodus, or that the sea lions may simply have gone hunting.

Herring counts fell so precipitously in San Francisco Bay that officials cancelled this winter's commercial herring fishery. Meanwhile, schooling bait fish such as anchovies and sardines were ample off Oregon. The sea lions may have liked the sound of the menu.

Sea Lion Caves, of course, still attracts sea lions -- the California variety and Steller sea lions, which breed and raise their young along Oregon's coast. Tuesday afternoon, Saubert estimated the caves still held 30 or 40 California sea lions and perhaps 100 remained in the area.

"They folded up their chaise lounges and put away their umbrella drinks," Saubert said. "They have decided that maybe vacation's over."

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