ALL ISSUES     |     FALL 2017

Where the Wild Sharks Are

By Salvador Jorgensen, PhD, Senior Research Scientist

White sharks are incredibly predictable creatures of habit. These long-distance navigators spend most of their time in remote areas of the open ocean, where much about their lives is a mystery to us. But northeastern Pacific white sharks have returned—like clockwork—to their favorite spots along the California coast year after year, for decades. Amazingly, their primary feeding areas and pupping grounds lie at the doorstep of two of the largest metropolitan areas in California: San Francisco and Los Angeles.

Thanks to advanced technologies in tracking, and analyzing their movements and behaviors in the wild, we're learning more about the vital role white sharks, and sharks in general, play in the global ocean. Over the past 15 years, we've made some amazing discoveries and learned a lot about where white sharks go and when they go there.

Now we're switching gears to understand more about why they use these specific areas, how they interact with their environment and how we can protect the safety of both white sharks and humans in the ocean.

Each fall, our team of researchers and Aquarium partners heads out to the elephant seal rookeries around the Farallon Islands to photograph as many white sharks as possible (up to 75 each year). Each shark fin is like a fingerprint; it has a unique series of notches and ridges that allows us to distinguish one shark from another.

Shark dorsal fins remain unchanged over decades, so if we get a good ID we can identify that shark five, 10, 15, even 20 years later. For three sharks, we have matches spanning a quarter of a century.

Recently we've begun using electronic tags with activity trackers (think Fitbit) to understand how frequently white sharks feed. We've learned that eating large, blubber-rich seals allows white sharks to pack on some reserves, which they store in their oil–rich livers. They then tap into those reserves while making the journey to the mysterious White Shark Cafe, halfway between the West Coast and Hawaii. The journey takes up to a month, during which they may not feed at all.

When they return from the Cafe, the males come straight to the feeding grounds. The females follow a longer and more circuitous route that eventually takes them near southern California and Baja, where they give live birth to four-foot-long pups that show up off the beaches.

Working with our partners at California State University, Long Beach; Stanford University; and the Ensenada Center for Scientific Research and Higher Education in Mexico, we've been tracking the newborn and juvenile sharks, and have identified important nursery areas between Ventura and San Diego, and another farther south in Baja, in the Bay of Vizcaino.

These spots are vital as nurseries because they are the only coastal areas in the northeastern Pacific with abundant food and just the right water temperature for small white sharks to maintain their warm core body temperatures.

During the most recent El Niño, we saw this optimal temperature band shift north into central California, which is why we began seeing some of these smaller sharks in Monterey Bay.

Even as we learn more about why these areas are so vital to California white sharks, we've also been investigating the rare interactions when an ocean-going person is mistakenly bitten. In collaboration with our Stanford partners, we analyzed 50 years of shark-bite records and found that even as shark sightings seem to be more common off the coasts of Los Angeles and San Francisco, the overall risk of shark encounters has decreased by 90 percent over the past half of a century.

We've learned we can coexist with these vital ocean predators and share their habitat, but we should respect them and remember that the ocean is a wilderness deeply imbued with mystery where we are visitors, not masters.

In a Shorelines online exclusive, read more about Sal tracking white sharks by their fin-gerprints here.

Left: White shark biologists Salvador Jorgensen (left) and Scot Anderson use their arms to demonstrate the girth of a large white shark.  Right: Satellite pop-up tags provide us with important data on white shark behavior.

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