A large number of tourists over the weekend in San Francisco Bay watched a great white shark devouring a seal just a few feet off the Alcatraz Island, and while the spectacle was thrilling to watch on video, it signaled a lot more to marine scientists about changing ecosystems in the area.
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This great white shark attack on a seal is the first ever recording of such events in the San Francisco Bay, and it marked the few times sharks would venture out into the area largely used by swimmers, windsurfers, and kayakers.
Some scientists are of the considered view that it signaled this year’s El Nino’s influence in driving sharks into uncharted northern territory.
“It’s Jaws! It’s Jaws!” bellowed an unseen boy beside tourist Meredith Coppolo Shindler who videoed the scene from an overhead dock. “That’s the awesomest thing I’ve ever seen in my life!”
Marine biologists say the shark’s foray meant that other sharks are coming into Monterey Bay, Farallon Islands, and Bodega Head, an area known as Red Triangle. Great white sharks have been spotted during fall, off the coast of San Francisco, but none had been documented by camera lens or seen visually inside the Golden Gate.
“This is the first recorded predation event I know of in the San Francisco Bay,” said David McGuire, a research associate at the California Academy of Sciences who directs the San Francisco-based conservation group, Shark Stewards. “It definitely looks like a white shark, about 8-10 feet, from the phone video sent to us. The tourists were pretty excited.”
Averaging about 15-16 feet in length, great white sharks can sometimes grow as long as 21 feet and weigh around 7,000 pounds. They have been sighted this year in Monterey Bay and in some other places off the coast of San Francisco, and they come to the Farallon Islands around September-October to feed every year.
“It’s not so much the abundance of sharks. It’s that the center of gravity has shifted somewhat north,” said Sean Van Sommeran, the executive director and founder of the Pelagic Shark Research Foundation in Santa Cruz. He thinks El Nino is causing the ocean to warm up, causing sharks to foray farther. “Some of the fishing camps in Baja, the small fishing villages in the Sea of Cortez, that used to have white sharks are now empty.”
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“For me it’s pretty exciting and a sign that health is returning to the San Francisco Bay ecosystem,” said Salvador Jorgensen, a research scientist for the Monterey Bay Aquarium who, together with other researchers, started seeing sharks in the bay as soon as they began tracking them with acoustic pinger tags in 2006.