A Shiver of Sharks

Why have so many juvenile white sharks made the California coast their home?

chris lowe, shark lab
Tod Seelie

On a cloudy summer day, Chris Lowe boards a small open-bow Boston Whaler and heads out from San Diego Bay to Coronado Beach. Forty minutes into the trip, he and his team spot their targets: dorsal fins in a known hot spot for juvenile white sharks. A drone, piloted by another team on the beach, guides Lowe and his crew to the exact location of the sharks. Lowe’s been a marine biologist for decades, but the sight of a group of sharks—known as a shiver—can still make his heart race. This is all the more remarkable given that since 1998, Lowe has been the head of Cal State Long Beach’s Shark Lab, 100 miles north of here.

The captain steers the small boat beside one of the sharks. Lowe dips a long pole strapped with a GoPro camera into the murky water to take a peek at the shark’s underside and check for claspers—a male shark’s genitalia. The drone operator measures the shark (six feet long), using the length of the boat as a ruler, and also looks for any identifying marks. Then Lowe uses a modified pole spear to dart the shark, inserting a transmitter into its back near the dorsal, where it dangles off like an earring. Lowe’s encounter with the shark—approaching it three times in a burst—is like a dance, he says. His final move: using a biopsy dart to take a small plug of skin and muscle, which, when analyzed, will reveal what the creature has been eating.

Dr. Lowe joined Alta Live.


White sharks—juveniles and adults—are thriving in California waters, and Lowe and his team want to understand why. They tagged 53 sharks in 2020—triple the previous year’s number, and researchers in Northern California report a similar rise. A simple explanation may be warmer water temperatures, which juvenile whites rely on to keep their bodies heated. They’re only about five feet long at birth and have an easier time swimming in shallow waters—which are both warmer and home to more stingrays, which juveniles eat rather than the mammals preferred by adult white sharks. Previously, they had to travel to Mexico to find warmer temperatures. Better water quality here and a California law that protects white sharks from being hunted in state-controlled waters, enacted in 1994, have also allowed their population to increase.

This article appears in the Fall 2021 issue of Alta Journal.

When the Shark Lab was established in 1966, sharks in these waters were overfished and unprotected, teetering on the edge of existence. The lab’s founder, marine biologist Donald Nelson, was a pioneer in the field of shark senses (and a mentor to Lowe). The U.S. Navy recruited Nelson to study how to best protect oceangoers from sharks. Nelson had big questions but limited data. He’d been a champion spear fisher as a child, and all he—or any biologist, for that matter—could do was dive with sharks and dissect them. The lab started to develop transmitters, but even those offered minimal data—researchers would know that a shark had gone from one place to another, but not how it had gotten there.

shark lab tank
A shark in one of the research tanks at the Shark Lab. In 2020, researchers tagged three times as many white sharks off the California coast as in the previous year.
Tod Seelie

Today, the lab utilizes drones, gyrometers, magnetometers, acoustic transmitters, and underwater tracking robots to understand shark behavior, and it is always developing new tech. “We have the ability to put transmitters on animals with all this information,” Lowe says. “Now we have context, and that helps us understand how they make decisions.”

That information is essential to Sean Carey, a lifeguard captain with the City of Coronado who collaborates with the Shark Lab. Until 2017, he didn’t worry too much about sharks. But now? He thinks about them all the time. On his beach, there’s a shark sighting nearly every week, he says. “We went from zero sharks to a lot of sharks in a four-to-five-year period.”

A shark’s tag will ping off buoys or underwater receivers near shore, sending a live alert to lifeguards and researchers if sharks are close to humans in the water, a sort of early warning system. In Coronado, Carey downloads the data monthly and sends it to the Shark Lab, which develops maps and timelines of shark incidents. Juvenile white sharks—which swim closer to shore than their elders—mostly avoid people; the stingrays they gobble up are a far bigger risk, statistically, to oceangoers. The overall likelihood of a shark encounter has gone down from 1950 to now, even as the human population in coastal California has tripled.

Off Coronado, as the shark disappears back into the murk, Lowe says his research “allows us to live in their skin and figure out why they are staying here and, when they leave, what they are using as a cue to go. By using this technology, we are starting to answer those questions for the first time.”

The lab is not only studying shark behavior; it is also eager to understand another animal: humans. It’s seeking volunteers to participate in a survey about perceptions of wildlife and beach safety. With more people in the water than ever before, researchers want to put the data together to create a credible shark forecast; to say, in essence, whether it’s going to be a sharky week out there.•

Katharine Gammon is a freelance science writer based in Santa Monica.
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