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Sharks Travel "Superhighways," Visit "Cafes"

Anne Minard in Boston, Massachusetts
for National Geographic News
February 19, 2008
 
Sharks follow well-traveled "superhighways" among feeding hot spots, new research suggests. The discovery should allow scientists to create better conservation strategies for the fish.

Some great white sharks travel predictable pathways, spending long winters in two areas near Hawaii, according to research led by Salvador Jorgensen of Stanford University in California.

Jorgensen and colleagues suggest that other shark species have the same habits, and other research already supports the idea.

Peter Klimley of the University of California, Davis, for example, has noticed that scalloped hammerhead sharks in the Gulf of California use islands as stepping-stones, spending six to ten months at a time at certain islands before moving on.

Understanding shark migration routes can be key to saving the declining fish, experts say.

Many shark species are listed as endangered on the World Conservation Union (IUCN) Red List. And that doesn't count hundreds of vulnerable, deep-water species which are the hardest to study.

"We should concentrate [on] protection [of shark-rich] islands," said Klimley, who has received funding from the National Geographic Society's Committee for Research and Exploration and Expeditions Council. (National Geographic News is part of the National Geographic Society.)

The researchers presented their findings last week at the annual meeting of the American Association for the Advancement of Science in Boston, Massachusetts.

In Deep Water

The new insight into shark migration comes at a time when numbers of imperiled shark species have skyrocketed.

(Related: "Mediterranean Sharks, Rays Facing Oblivion, Study Says" [November 16, 2007].)

The fish are threatened mostly by overfishing. Demand for shark fins and meat, recreational shark fishing, and tuna and swordfish fishing that ensnares unwanted sharks are particular concerns.

In 2008 the IUCN's Red List of threatened and endangered sharks will add five new species that live in the open ocean. The group believes 16 of 21 open-ocean shark and ray species are threatened or nearly threatened.

The situation may be worse for deep-water sharks.

Colin Simpfendorfer, a researcher at James Cook University in Queensland, Australia, said his new research suggests deep-water sharks, rays, and skates may take much longer to recover from overfishing than their shallow-water kin.

"On average, deep-water sharks are half as good at withstanding fishing pressure," Simpendorfer said.

"Deep-water shark fisheries could have rapid and substantial effects on shark populations."

But numbers are spotty, he said: Scientists have enough data to understand what's happening with only 13 of the 581 known deep-ocean species.

Jaws Café

Stanford's Jorgensen and his colleagues tagged and tracked more than a hundred great white sharks along the central California coast.

The sharks have access to a year-round supply of seals and sea lions—but that's apparently not enough to keep them from voyaging.

The researchers have tracked the sharks to two winter hotspots: one off the Hawaiian coast and another at a point in the middle of the ocean, halfway between California and Hawaii.

Though they're not sure whether the draw is food or reproduction, they've dubbed the area the White Shark Café.

"We started calling it the café because that is where you might go to have a snack or maybe just to 'see and be seen.' We are not sure which," Jorgensen said in a statement.

"These animals appear again and again at very specific areas," he said. "This is really important in terms of management."

By figuring out sharks' migration routes and where the highly mobile fish congregate, researchers can provide valuable information to help fisheries managers decide which ocean regions are the highest priorities for protection.

Stepping-Stones

UC Davis's Klimley and his team have also found that scalloped hammerhead sharks stop along a series of pre-established island sites between Mexico and Ecuador for extended periods of time.

Creating reserves around such islands will go a long way toward protecting hammerheads, he said, and "will provide the public with places for viewing sharks in their habitat."

The scalloped hammerhead—new on the 2008 IUCN list—is one of the most at-risk open-ocean species, said Julia Baum, a marine ecologist at Scripps Institution of Oceanography of the University of California San Diego.

No international limits exist on shark fishing, Baum said, though a United Nations resolution calls for catch limits and a strict ban on the practice of slicing off shark fins for use in soup. Finned sharks are often tossed back in the ocean to die.

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