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Marine biologists have finally uncovered why California’s great white sharks make an annual pilgrimage to an area of open ocean between California and Hawaii previously thought to be the ocean equivalent of a “vast desert.”

Years ago scientists nicknamed the area the “shark café,” assuming the remote area in the Pacific might be particularly important for breeding or feeding. The most curious part, though, that initially puzzled researchers was how male and female white sharks would behave at the “café” – some male sharks moving up and down the water column upwards of 120 times a day. Female sharks, on the other hand, were tracked diving to deeper water during the day and rising to shallower water by night.

So, what explains the strange behavior?

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Well, in a recent expedition to the shark café led by scientists from Stanford University and the Monterrey Bay Aquarium, the team made a discovery. Instead of barren ocean, they found a vast community of tiny light-sensitive creatures – perfect for the white sharks to chow on and tantalizing enough to cause the sharks to cross the sea en masse annually to do so.

The white sharks swim up and down an area of ocean known as the “mid-water zone” with depths ranging from 660 feet to several miles to feed on these light-sensitive creatures like squid and phytoplankton.

“It’s the largest migration of animals on Earth—a vertical migration that’s timed with the light cycle,” Salvador Jorgensen, a research scientist at the Monterey Bay Aquarium, told SFGate on Tuesday. “During the day they go just below where there is light and at night they come up nearer the surface to warmer, more productive waters under the cover of darkness.”

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Last fall, researchers tagged 36 great white sharks with the intention of tracking them to the shark café. The tags were designed to pop off and float to the surface. This spring, oceanographers, marine ecologists, and microbiologists from five academic institutions boarded the research vessel Falkor in an attempt to intercept the tags, tracking the sharks to their mysterious café.

“Just as we predicted, the sharks showed up,” lead researcher and marine biologist Barbara Block told NPR back in May.

Block and her team were able to retrieve 10 of 22 tags that floated to the surface signaling the Falkor they had successfully detached. Many questions remain, but the sheer amount of data the team acquired is astounding.

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“We now have a gold mine of data. We have doubled the current 20-year data set on white shark diving behaviors and environmental preferences in just three weeks,” Block told SFGate. This “will help us better understand the persistence of this unique environment and why it attracts such large predators.”

 

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