Climate change impacting migration of juvenile great white sharks in Pacific

Researchers are watching a weather pattern in the Pacific that has become a force in recent years. Its effect has not only influenced the weather that arrives off our coast, but something else, juvenile great white sharks, also referred to as white sharks.

For swimmers, and surfers in parts of Southern California, juvenile white sharks are becoming almost constant companions. They are often spotted in large groups, along beaches that are part of a warm water nursery habitat stretching up from Mexico.

"From the spring until the late fall, it's every single day and they could be aggregating at a very busy public beach and they just don't seem to care," observes professor Chris Lowe.

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Lowe directs the Shark Lab at California State University Long Beach, where he's monitored the juvenile nurseries for years. But lately, much of the focus is shifting north after a study led by the Monterey Bay Aquarium was released earlier this year. In it, Lowe and his colleagues document a startling migration. Increasing numbers of juvenile white sharks, now populating areas as far north as Monterey Bay.

"And that particular part of Monterey Bay is known to be the warmest part. And that is probably acting as a thermal refuge. That's one of the things that's drawing them there," says Lowe.

John McCosker, is a longtime marine researcher at the California Academy of Sciences in San Francisco.

"They presume it's related to climate change. And it's easy to make that relationship because there's an elevated sea surface temperature," he says.

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McCosker Francisco believes water temperature may be only part of the equation. But for the past several years, it's been the most intriguing part.

"This great difference is going to be felt more and more commonly at shark ally and the places the surfers like to surf," says McCosker.

The question now: How long is the shift likely to last? And might greater numbers of juvenile great whites move even closer to the Bay Area?

The answer may hinge on a specific type of weather event. They are masses of warm water, which can raise temperatures along our coast several degrees. They are now popularly referred to as "blobs" after a major heat event in 2014.

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Researchers at the National Oceanic and Atmospheric Administration more accurately refer to these "blobs," as marine heatwaves. They're believed to be caused by deviations in wind circulation, ocean currents, and sea surface temperatures. One recent blob actually raised west coast sea surface temperatures by nearly five degrees Fahrenheit.

And several recent encounters with surfers and divers may preview the challenges of northward migration. If the ocean heatwaves, or rising ocean temperatures, do create a lasting path, experts believe those of us in Northern California may have to adjust to living in closer quarters with juvenile sharks.

"If water temperatures continue to warm the way they are, then we might expect to see these nurseries get pushed further and further north. And white sharks showing up in places where people haven't historically seen them, mainly because the habitat is conducive," says professor Lowe.

How conducive remains to be seen, and could depend on global factors, experts are still struggling to fully understand.

Currently, there have been indications pointing to another possible Blob event building in the northern Pacific. Researchers we spoke with say the jury's still out on whether it will expand or move into the California coastline. But what's really key they say, is understanding whether these marine heat waves are now becoming cyclical, a new normal if you will, with the need to keep monitoring them in the way we do with cycles like El Nino.

To learn more about Marine Heat Waves and the juvenile shark research from the Monterey Bay Aquarium, as well as a new exhibit on sharks at the California Academy of Sciences check out the links below:



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