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How Many Sharks Are Enough?

"Palmyra Atoll is one of the few places left on earth where sharks and other large predators dominate ocean waters."

 

Anyone lucky enough to jump in to the ocean near Palmyra Atoll will immediately see lots and lots of sharks.

While some people may find this experience disconcerting, visitors and scientists revel in their presence. Even Kydd Pollock, who was bitten by a shark in 2010, wants more sharks in the ocean. Palmyra Atoll is one of the few places left on earth where sharks and other large predators dominate ocean waters.

With so many sharks in one place, and so few humans, it is possible to learn new things that can be used to improve shark populations and marine systems elsewhere. The Nature Conservancy is working with partners from the Palmyra Atoll Research Consortium  to determine how shark populations are changing over time, where sharks spend their time, over what distances and depths they travel, and when they move.

One study using acoustic, radio and satellite signals found that sharks spend the daytime at depths below 100 meters – well below where humans can dive – and come up into shallower water at night. Led by PARC Chair Dr. Jenn Caselle with the Marine Science Institute at the University of California Santa Barbara, this research provides new insights into shark behavior.

But in recent years, scientists have become concerned about a possible decline in shark populations around the atoll. When researchers jump in the water today, they see fewer sharks overall, and the sharks aren’t surrounding them as they once did. While this may sound like a good thing to some of us, a declining shark population could mean there are unseen problems in Palmyra’s marine wilderness.

One hypothesis for why we are seeing fewer sharks is that they have become accustomed to people and no longer surround humans curiously. Another is that they travel much further and more frequently than previously thought; Stanford researcher Doug McCauley tagged several sharks at Palmyra that have been caught by fishermen more than 90 miles away.

To understand just what is happening to Palmyra’s sharks, Dr. Eric Conklin, the Conservancy’s director of marine science for Hawai‘i and Palmyra, is leading a team of researchers to tag and recapture reef sharks over several years. This work will create the first accurate baseline of shark populations at the atoll and, ultimately, help us better understand changes in shark populations to inform management at Palmyra and elsewhere throughout the Pacific.

Purchased by the Conservancy in 2000, Palmyra Atoll is now a marine national monument and center for scientific study.

 

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