Photograph by Doug Perrine, Nature Picture Library/Corbis

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A tiger shark (Galeocerdo cuvier) is pictured above. Hawaii has faced a spate of shark attacks on humans this year, raising safety concerns.

Photograph by Doug Perrine, Nature Picture Library/Corbis

Maui Death Raises Questions About Spike in Hawaiian Shark Attacks

Two shark attack fatalities this year are Hawaii's first since 2004.

A shark killed a fisherman off the Maui coast on Monday, Maui County Ocean Safety officials reported, when it bit his foot, which he had dangled over the side of his kayak.

The attack was the eighth near Maui and the thirteenth in Hawaiian waters this year—more than triple the 20-year average of about four unprovoked shark incidents each year.

Patrick Briney, the fisherman, was Hawaii's second shark attack fatality this year, following an August attack on a German snorkeler. Prior to 2013 there hadn't been a single fatal shark attack in Hawaii since 2004.

This year's attacks, on top of ten Hawaiian attacks last year, have people asking whether there's been a recent statistical anomaly or whether more shark attacks are Hawaii's new normal.

Yannis Papastamatiou, a marine biologist at the University of St. Andrews in Scotland, said it's nearly impossible to know what's behind the rise in attack numbers.

"The problem with shark bites is that the numbers are so low it's hard to do any type of statistical analysis," he said. "There may be something behind it. It may be due to natural fluctuations or chance.

"It's especially hard to answer with only one or two years of data," he continued. "If it would continue for years, we may be able to learn more." Hawaiian attacks spiked previously, during the 1990s, he said, before returning to previous levels.

Papastamatiou authored a recent seven-year tagging and tracking study of the migration patterns of tiger sharks in the Hawaiian Islands and uncovered a possible connection to attacks in the area, though that was not the focus of his study.

"We noted that there did seem to be a spike in shark bites during October, and that does overlap with the time of year when we now believe that there are pregnant female sharks coming down from the northwestern Hawaiian Islands to the main Hawaiian Islands, potentially to give birth," he said.

Data from the University of Florida's International Shark Attack File (ISAF) show that since 1926, the highest numbers of attacks around Hawaii took place in October, November, and December.

But Papastamatiou, previously at the University of Florida and the Florida Museum of Natural History, stressed that this correlation doesn't prove causation: "Whether one has anything to do with the other is very difficult to say."

Shark Attacks Around the World

Regardless of where in the world you swim, odds of becoming shark bait are very, very slim.

Using 2000 data as a typical example, the ISAF estimates that a person's odds of being bitten by a shark are about 1 in 11.5 million. (Related: "How Should We Respond When Humans and Sharks Collide?")

Worldwide, shark attack fatalities averaged between just four and five a year from 2001 to 2010.

The U.S. saw 53 shark attacks in 2012, according to the International Shark Attack File report, the most since 2000. But shark attack fatalities around the world remained flat, the authors found.

(By comparison, conservationists estimate that as many as 100 million sharks are killed every year in fisheries, primarily to feed Asia's appetite for shark fin soup.)

Still, shark attack numbers have slowly risen since 1900, according to ISAF statistics. That's because the growing human population has put many more people into the waters where sharks swim, experts say.

Learning exactly where and when those sharks swim in abundance might be one way to help keep people safe and explain why some attacks occur—including the recent spate in Hawaii.

Just 80 unprovoked attacks were recorded worldwide in 2012, according to the ISAF, even though people and sharks spent billions of hours sharing the water. While waters overall are statistically safe, ISAF director George Burgess said that some localities have developed problematic situations and are the site of repeated attacks, according to the press release announcing the report.

"What I've seen in all situations when there's been a sudden upswing in an area is that human-causative factors are involved," Burgess said in the release, "such as changes in our behavior, changes in our abundance, or an overt shark-attracting product of something that we're doing."

Shark attack variables—like weekend weather or the economy impacting the number of people in the water, or ocean conditions enticing sharks from one location to another—can change dramatically in the short term

That's why experts stress that studying attacks over the long term offers a much clearer picture of where human-shark problems lie, rather than looking at a short-term spike like the rise in Hawaiian attacks.