Our Disappearing Reef Sharks

A new survey of nearly 400 coral reefs worldwide reveals sharks once common in those waters are vanishing, a troubling sign that they are at a much greater risk of going extinct than previously thought.

Populations of five common reef sharks have declined between 60 percent and 73 percent over the past half-century, a team of 150 researchers report in Science June 15.

"It's absolutely jaw-dropping," said Arizona State University's marine biologist David Shiffman. "If you look at all the reef sharks at all the reefs everywhere, you get a very similar pattern."

The culprit is rampant overfishing. In much of Asia, fishers chop off fins for shark fin soup. In other areas, fishing fleets inadvertently suppress sharks by targeting their prey.

From reefs in East Africa to Australia's Great Barrier Reef to the Caribbean, researchers dropped GoPro cameras underwater alongside bags of bait, recording more than 20,000 hours of footage. An army of volunteers pored over the video to tally the sharks that showed up, focusing on the Caribbean reef shark, nurse shark, grey reef shark, blacktip reef shark, and whitetip reef shark.

The declines were at their starkest in less wealthy nations with lax regulations. Many more sharks teemed in the waters off richer countries and in designed protected areas. Among the worst area is Jamaica's coast, where local fishermen catch grouper and snapper upon which sharks prey. A big hurdle to protecting sharks in Jamaica is that every report of a shark biting a human created fears among the public, making it harder to enact policies to protect them." They see sharks as vicious.

In places without many sharks, species of rays became the top predator. But rays are no replacement for sharks, which foster biodiversity in coral reefs by feeding on prey populations numerous in size, giving other fish a chance to thrive.

One encouraging finding: Many reefs bereft of sharks are close to other reefs filled with them. By reducing overfishing, those healthy populations could recolonize the shark-depleted waters.

- Dino Grandoni, Washington Post