Researchers taking deep dive into why sharks are migrating from Southern to Northern California

ByTim Didion & Spencer Christian via KGO logo
Thursday, September 29, 2022
Why are sharks migrating from Southern to Northern CA?
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Researchers are looking at why young sharks are moving hundreds of miles north of Southern California to the waters off Monterey Bay.

SAN FRANCISCO (KGO) -- For young sharks, the sandy beaches of Southern California, often act as juvenile nurseries. That's where they can feed and congregate before they develop into fully grown hunters. This offers beach-goers, and researchers an up-close opportunity.

"There's so many people and so many sharks, that we have the capacity to gather huge amounts of data, to look at how they interact and behave around people. And that's primarily for juveniles up to maybe nine feet long," says shark researcher Chris Lowe, Ph.D. of California State University, Long Beach.

Now, Professor Lowe and his team are studying an apparent nursery much closer to the Bay Area. As we first reported earlier this year, Lowe, along with researchers at the Monterey Bay Aquarium, are trying to understand what's drawing an increasing number of young juveniles hundreds of miles north to the waters off Monterey Bay.

"So what are the sharks doing close to the shoreline? How long are they going to be there? How close might they get to people? What depths do they prefer? Those sorts of questions," Professor Lowe explained. "And of course, what we want to know is when it gets cold up there in the winter, where do they go?"

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Researchers believe climate change may be a partial driver. A number of so-called marine heat waves, popularly known as ocean blobs, may also play a role in warming waters. But the migration seems to have continued in cooler cycles. And experts caution that marine forces are complicated and not fully understood.

"The ocean is so dynamic, we don't know why they're here," says researcher Sammy Andrzejaczek, Ph.D., of Stanford's Hopkins Marine Station. "Yeah, it could be temperature, it could be their prey shifting."

To help answer those kinds of questions, Dr. Andrzejaczek and her colleagues at the Hopkins Marine Station are reexamining shark habitat from the top down. By using a three-dimensional, vertical model, they're trying to discover the different ways sharks and other marine creatures behave and use the ocean at different depths.

This could potentially unlock secrets of feeding patterns, preferred temperatures, and oxygen levels.

"And so they need to go down, they need a certain three dimensional environment with food, or they need to regulate their body temperature, there's oxygen limitations as you dive down. So we really need to understand that additional dimension to understand how they move and why they're moving and how that may change in the future," says Andrzejaczek.

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The two shark studies are not connected, but some of the questions clearly overlap. Professor Lowe is using both tags and drones to locate Shark off Monterey. And he agrees a vertical understanding is key as well.

"So if they're going to those beaches, because that's a safe place for them. Then when you have that heavily stratified water column with warm water at the surface, and cooler water down deep, that gives them options. So we're just starting to analyze the datasets that we have over the last couple of years to look at how that might affect where they spend their time," says Lowe.

Stanford researchers are also hoping their work can lead to better management practices at depths where sharks and other marine creatures are endangered by threats including commercial fishing.

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