Shark attacks are on the rise in the U.S.—but it’s not because sharks are getting fiercer.

The increase in attacks—59 last year, up from 31 in 2011—is connected to climate change, experts say. According to a study by Progress in Oceanography, climate change is pushing sharks and other marine species northward. At the same time, warm weather means people are more likely go swimming, a potentially fatal combination. According to the Florida Program for Shark Research, seven people have died from shark attacks since 2005.

“Each year we should have more attacks than the last because there’s more humans entering the water, and more hours spent in the water,” said George Burgess, director of the Florida Program for Shark Research. “What you see is more of a human activity than a shark activity.”

Most shark attacks take place in Florida, California and Hawaii, where tourists often visit beaches. The number of tourists in Florida, where the most shark attacks take place, has risen every year since 2009, to 106 million last year. Meanwhile, there’s also been a gradual increase in the number of sharks in the water.

In the last few decades, sharks have been increasingly exploited. Sharks were caught as bycatch starting in the 1960s, meaning they were incidentally caught during the commercial fishing of other fish. Later, sharks became targets in fisheries that expanded rapidly in the 1980s. As a result, shark populations have declined. Now, thanks to fishery regulations in the U.S., shark populations have been gradually increasing since the start of this century, but recovery is slow.

“To get them back to manageable levels is going to take decades for many of these species,” Burgess said. “We’re talking 30 years or more.”

But even as shark attacks have risen, an individual’s chance of getting attacked by a shark has not, Burgess said, because the human population is increasing faster than the shark population.

“The key here is, human plus shark equals attack,” Burgess said. “The number of humans and number of sharks influence the chances of them coming together. … With more on each side, the greater the chance of the two coming together and having an attack.”

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