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Expect More Shark Attacks as More Humans Flock to Water

Image: A man stands on the beach in Les Aigrettes

A man stands on the beach in Les Aigrettes, on the western coast of the French Indian Ocean island of La Reunion, at the spot where a 13-year-old boy was attacked and killed by a shark on Sunday. RICHARD BOUHET / AFP - Getty Images

Cases like the Sunday death of a 13-year-old surfing champion in a shark attack off a French island in the Indian Ocean may be giving sharks a bad rap. Though the number of "unprovoked" shark attacks has been rising steadily for more than a century, it’s not because sharks have become more aggressive, experts say.

Rather, it boils down to simple math: The presence of more humans boosts the likelihood of more shark-human interactions. There are now more than 7 billion people on Earth, and that number could approach 11 billion by 2050, according to U.N. projections.

"If we look at the number of shark attacks in any given place in any given year and compare that to population growth in those areas, we find that shark attacks match the growth curve of the human population in that region," George H. Burgess, director of the Florida Program for Shark Research and curator of the International Shark Attack File, told NBC News. "As long as the human population continues to increase, we can expect to see numerically more shark bites."

Emergency Responders Arrive at Scene of Lethal Shark Attack 0:28

"As the human population (and tourist population) continues to grow, some shark populations that were severely overfished have increased in recent decades as they recover following successful management," said Dean Grubbs, associate director of Research at Florida State University Coastal and Marine Laboratory. "Therefore, more sharks and people are likely to be in close proximity to one another leading to more numbers of attacks, but to my knowledge, the rate of shark attacks (e.g. number of attacks per 100,000 beach-goers) has not changed."

Burgess said the marine animal that attacked the teen surfer off the Indian Ocean island of Reunion was likely a bull or tiger shark. Surfers, Burgess said, are the No. 1 group victimized by sharks.

"That’s chiefly because, one, those folks spend more time in sea in areas where those sharks are most common, and second, the activity itself provides essentially a provocation with the kicking of feet and splashing of hands, which are very attractive to sharks," Burgess said.

There were 72 "unprovoked" shark attacks on humans worldwide in 2014, according to the International Shark Attack File. Though that's the lowest annual global total since 2009, the figure has been trending steadily upward since 1900, with each decade having more attacks than the previous. ISAF notes: "The numerical growth in shark interactions ... most likely reflects the ever-increasing amount of time spent in the sea by humans, which increases the opportunities for interaction between the two affected parties."

The U.S. accounts for two-thirds of world shark attacks in any given year and Florida accounts for more than half of the U.S. total.