A group of tourists recently witnessed a rare and bloody spectacle when a great white shark attacked and ate a sea mammal just off a dock on Alcatraz.
KTVU has obtained two videos of the incident shot by tourists.
One video posted to YouTube on October 10th by Chris Shindler shows a great white shark attacking a seal or sea lion. It is hard to tell which in the video.
A young boy on board can be heard shouting with excitement, "That's a great white!" At the end he remarks, "That's the best thing I've ever seen in my life!"
The boy might not have known how rare a sight it was. Shark experts say it's the first known predatory attack of a white shark inside the Bay.
"It's actually a sign that maybe the San Francisco Bay is getting a little healthier, that you have top predators like white sharks coming in," said David McGuire of Shark Stewards. "It's the first known predation of a sea lion or seal that I know of in San Francisco Bay in historical times."
That doesn't mean sharks haven't entered San Francisco Bay. Researchers have tagged and tracked white sharks.
"One shark came in four times, so they're probably coming around the front of the Bay, following prey, and then exiting," explained McGuire. "There is the myth of shark infested waters, but we like to say shark inhabited waters."
You may know the species at great white shark, but that's not the name those who study them use.
"They need no superlative," said McGuire. "They are great, so we just call them white Sharks."
People swimming in the Bay off Crissy Field were shocked to hear about the sighting.
"A great white shark?" asked Megan Meloni. "I didn't know that those come into the Bay. That's pretty scary actually!"
Surfer Nick Lee was equally surprised.
"I always think they stop at the Golden Gate, that they can't get past the bridge," he said. "I guess they can."
They can and do, but McGuire says that doesn't mean they're trolling the shores for a human snack.
"There are people swimming around the Bay every day without risk of shark attack," McGuire said. "There's much higher risks, like getting hit by a boat."
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Those who study white sharks are hoping someone else captured the predatory attack on video so they can study and learn from it.
"Well I think it’s very unusual obviously to see that kind of thing going on in the Bay. I think what was most impressive was that young boy’s response. This is may be the best day of his life in his opinion. And that’s just setting him up to be an enthusiast for the ocean and hopefully a marine biologist or someone who cares deeply about our ocean," said marine biologist Wallace Nichols.