The great 2014 Pier 39 sea lion disappearance

The sea lions have once again disappeared from Pier 39 in San Francisco, much like they did in 2009 (above). The sea lions have once again disappeared from Pier 39 in San Francisco, much like they did in 2009 (above). Photo: Brant Ward, The Chronicle Photo: Brant Ward, The Chronicle Image 1 of / 1 Caption Close The great 2014 Pier 39 sea lion disappearance 1 / 1 Back to Gallery

There was an eerie silence off the docks of Pier 39 on Friday.

The buzz of marine life - represented for more than two decades by the loud barks of hundreds of sea lions and the oohs and aahs of San Francisco tourists - was absent. The famed 700-pound pinnipeds were gone, having blubbered off for reasons unknown.

"Where are they?" asked Grayson Prince, 14, a visitor from Atlanta.

He and his 15-year-old sister, Gabrielle, counted just one large male sea lion sitting alone on a barge.

"We could have gone to the zoo or something," she chimed in.

About a week into the disappearance, no one knows for certain where the sea lions went. But the prospects of their returning seem promising after a similar migration 4 1/2 years ago.

Last week, just as in December 2009, the sea lions were out lazing in the sun and posing for photos one day - and then, without notice, they disappeared. In their wake, they left not only wood docks stained with white scat and hordes of disappointed sightseers, but also questions about the uncertain ways of the wild.

On one hand, it's not unusual for the sea lions around Fisherman's Wharf to leave their docks, particularly at this time of year, said marine scientists. The early summer months are when the animals migrate, mostly south to the Channel Islands off the Southern California coast to rear their young.

But for so many to go at once - even the sea lions that are too young to breed - is odd, said Monica DeAngelis, a marine mammal biologist with the National Oceanic and Atmospheric Administration.

"If they don't come back in a few days, that will pique people's interest even further," DeAngelis said Friday.

The sea lions have become a fixture in San Francisco. Since their arrival in 1990, when marine experts believe the animals were lured by a trophy run of herring, they have been a marquee attraction - alongside sourdough bowls of clam chowder and ferries to Alcatraz.

While the animals continue to be somewhat mobile, at least as much as food and mating require, the bay environment has proved quite hospitable, and many have cut short their travel plans to spend more time in the city.

"A lot of them just call it home and really don't need to go anywhere else," DeAngelis said.

In 2009, the population of sea lions peaked at 1,700 before their initial disappearance.

On Friday, tourists speculated about why so many sea lions might vanish again. One person suggested an earthquake. Another figured it could have been great white sharks.

Marine experts pointed to many possible explanations. Beyond the annual breeding pattern, they said, a disturbance such as a construction project - or sheer appetite - may have triggered the exodus.

"They might have received some signal that there was a food source for them to find," said Shawn Johnson, director of veterinary science at the Marine Mammal Center in Sausalito. "The amazing thing is: How did they all receive word that it was time to go?"

The Marine Mammal Center, which treats injured sea lions, has taken in a near-record number of weak, hungry pups this year - 433 so far, compared with 296 all of last year, Johnson said. Food, he said, remains an especially strong driver of behavior.

In all likelihood, the sea lions will return soon, the experts said. When they disappeared in December 2009, also with little explanation, the animals were back three months later.

"It's natural," said Stephanie Furness, who works at the Global Candle Gallery on the pier. "Yeah, it's an attraction. But it seems silly to be concerned about that as a business point."