Humpback whale sightings in bay thrill boaters, alarm biologists

Lauri Duke, a volunteer at the Marine Mammal Center and Golden Gate Cetacean Research, snapped this picture of a surfacing humpback whale from Fort Point. “I had never seen humpback whales before, and it was awesome,” Duke said. less Lauri Duke, a volunteer at the Marine Mammal Center and Golden Gate Cetacean Research, snapped this picture of a surfacing humpback whale from Fort Point. “I had never seen humpback whales before, and it was ... more Image 1 of / 25 Caption Close Humpback whale sightings in bay thrill boaters, alarm biologists 1 / 25 Back to Gallery

Humpback whales have been swimming into San Francisco Bay in unprecedented numbers over the past two weeks — even leaping out of the water near Alcatraz — in a sight that has thrilled boaters, alarmed marine biologists and harked back to a famous wayward whale three decades ago.

As many as four humpbacks at a time have been spotted flapping their tails and breaching in bay waters, apparently feeding on anchovies and other schooling fish during incoming tides.

“I had never seen humpback whales before, and it was awesome,” said Lauri Duke, 54, of Rocklin (Placer County), who volunteers at the Marine Mammal Center and Golden Gate Cetacean Research and happened to spot the leviathans during visits over the past two weekends.

“There were at least three in the bay and out in the channel last Sunday, and four or five the Sunday before that,” said Duke, who photographed the animals from Fort Point. “They were mostly coming partially out of the water, showing their tails.”

Marine expert surprised

Mary Jane Schramm, the spokeswoman for the Greater Farallones National Marine Sanctuary, said she saw humpbacks in the bay from her desk off Crissy Field Beach in the Presidio.

“I’ve been in this game for a lot of decades, and this is the first time I’ve heard of this many humpbacks coming in this far,” she said.

It’s normal, Schramm said, for gray whales to wander into the bay, but humpbacks generally feed farther offshore and are not accustomed to navigating shallow water and narrow straits like those in San Francisco Bay.

She and other marine experts are concerned that the beasts could swamp boats while breaching, be hit by a ship or get spooked by looky-loos who paddle or sail out to see them.

“If they head any direction except west they could get into big trouble,” said Schramm, adding that the potential for disease and skin problems is greater in fresh and brackish water. “The deeper they get into the bay, the more acoustically confusing it becomes.”

Schramm’s biggest fear is that the giant bay intruders will go the way of Humphrey, the famous 40-ton humpback who caused pandemonium in 1985 when he swam through the Carquinez Strait, up the Sacramento River and into a creek near Rio Vista.

The Solano County city became the focal point of a whale craze, attracting 10,000 people a day as experts tried desperately to turn the lost animal around.

Humphrey went back to sea after 25 days, only to return in the fall of 1990, getting stuck on mud flats near Double Rock, just off the Candlestick Park parking lot. He remained stuck for 25 hours, until volunteers, helped by a 41-foot Coast Guard boat, pulled him free and sent him back to the ocean.

Delta and Dawn swim in

In 2007, a mother humpback and her calf, later dubbed Delta and Dawn, also lost their bearings and swam up the Sacramento River all the way to the ship-turning basin in the capital. The whales found their way out again but suffered wounds, probably from boat propellers.

The recent influx, experts said, may be the result of an unusual concentration of anchovies near shore — a phenomenon that also occurred last year, when fishermen and whaling boats reported large numbers of the cetaceans near the Golden Gate.

Unlike gray whales, which generally make a beeline to Alaska, humpbacks slowly move north after giving birth in Mexico and Central America, feeding all along their migration route, Schramm said.

Humpbacks are unique among whales, known for their complex vocalizations that sound like singing and for their acrobatic breaching, an apparently playful activity in which they lift nearly their entire bodies out of the water before splashing down.

Before 1900, an estimated 15,000 humpbacks lived in the North Pacific, but the population was severely reduced by commercial whaling. In the 20th century, their numbers dwindled to fewer than 1,000.

An international ban on commercial whaling was instituted in 1964 and the whale population has since rebounded. Between 75,000 and 80,000 humpbacks now live in the world’s oceans, and many of those survivors migrate through the Greater Farallones National Marine Sanctuary.

The recent gathering of humpbacks is just the latest head-scratching happening off the Golden Gate. Last year at this time, an unusually large number of dead whales, including grays, a humpback and a sperm whale, turned up along the Northern California shoreline.

Marine scientists are looking at a variety of factors, including environmental changes, food distribution, predator behavior and the practices of the shipping industry.

For now, Schramm urged boaters, paddleboarders and news helicopters to stay away from the whales.

“If you are in a small boat and a humpback breaches near you, you could be swamped or it could land on you,” she said. “It’s dangerous, so for your own safety and to prevent wildlife disturbance, don’t approach them.”

Peter Fimrite is a San Francisco Chronicle staff writer. Email: pfimrite@sfchronicle.com Twitter: @pfimrite