Fishing Fleets Are Targeting Sharks Where They’re Most Vulnerable

Researchers find that some fishing fleets operate in 80 percent of shark hot spots.
(Photo: Neil Hammerschlag)
Jan 25, 2016· 1 MIN READ
Katharine Gammon has written for Nature, Wired, Discover, and Popular Science. A new mom, she lives in Santa Monica.

Sharks have long been accidentally caught in nets intended for lucrative fish such as tuna. Now new research shows that commercial fishing boats are purposely targeting shark habitat, with disastrous results for the increasingly imperiled animals.

The study, published Monday in Proceedings of the National Academy of Sciences, found that fishing fleets operate in 80 percent of shark hot spots. “We were surprised to find such a large overlap, because for many years we’ve been told that fishermen weren’t going looking for sharks,” said David Sims, a researcher at The Marine Biological Association of the U.K. and senior author of the study.

The researchers analyzed GPS data supplied by Spanish and Portuguese fishing fleets from 2005 to 2009. Each ship, which stays at sea for months at a time, broadcasts a signal with its location every hour.

“The boats have large refrigeration and technology that people don’t realize,” said Sims. “They purchase the satellite images of sea surface temperatures so they can see where the cold and warm waters meet—and that is often where sharks prefer to hang out.”

Longline fishing boats set out lines more than 60 miles long, with 1,200 baited hooks on each line. “Millions and millions of hooks are being deployed each year,” Sims said.

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The researchers also gathered data from 99 sharks fitted with GPS trackers. They then calculated how often ships and sharks were in the same place.

Finding an 80-percent overlap led Sims to believe the sharks are being tracked throughout the year. “That raises the concern that shark hot spots are at risk,” he noted. The researchers discovered that the Spanish fleet sold shark fins to Asia and shark meat to Europe.

As stocks of large fish decline, fishers increasingly turn to other sources of income, Sims explained. “The amount of tuna and swordfish these fishermen catch is minimal, so the shark is now the dominant catch, maybe making up three-quarters of the total,” he said. “This is not insignificant anymore.”

Other research has estimated that shark populations are in sharp decline, with as many as 100 million killed each year.

Sims cautioned that the study underestimates the risk to sharks, given that the researchers only studied Spanish and Portuguese fishing vessels and that five other nations operate larger fleets.

He said marine-protected areas aren’t likely to help sharks because they roam so widely, but other measures may aid conservation of mako and blue sharks, which make up the majority of catches. For example, fishing vessels can deploy hooks made of materials that deter sharks from taking bait.