An apparent increase in shark attacks may well have a human cause, with low-cost air travel but also over-fishing and possibly global warming among the hidden suspects, say experts.

Headlines this week were grabbed by a decision to close beaches in the Seychelles after a shark savaged a British honeymooner before the horrified gaze of his spouse, in the second fatal attack there in 15 days.

In Russia's Pacific coastal region of Primorye, a shark mauled a 16-year-old boy a day after a man lost his forearms defending his wife. In the Caribbean, a woman vacationing in Puerto Rico received a 30-centimetre (foot-long) shark bite as she swam in a tourist haunt, the bioluminescent bay of Vieques.

According to the International Shark Attack File (ISAF), compiled at the University of Florida, 79 unprovoked shark assaults occurred around the world in 2010, six of which were fatal.

This was the highest number in a decade, amounting to an increase of 25 percent on 2009, when there were 63 attacks with six fatalities, and 49 percent over 2008, which had 53 recorded attacks, four of them mortal.

So far this year, there have been six deaths and seven cases of injuries, according to an unofficial toll compiled by AFP from news reports.

Compared to deaths from smoking, road accidents, lightning strikes or even from other animals, the risk is minute, say experts.

"The attention from shark attacks is completely overblown," said Agathe Lefranc, a scientist with a French group, the Association for the Study and Conservation of Salachians (APECS), a category that includes sharks and rays.

Marine biologists say there is little research into the causes of shark attacks but point to several possibilities, all linked to humans themselves.

No. 1 is quite simply the growth in mobility, with cheap air travel and package vacations enabling people to swim, snorkel, surf or dive in places that previously had no human presence.

"The growth in shark attack numbers does not necessarily mean that there is an increase in the rate of shark attacks," says ISAF.

"Rather it most likely is reflective of the ever-increasing amount of time spent in the sea by humans, which increases the odds of interaction between the two affected parties."

David Jacoby, a specialist at the Marine Biological Association (MBA) in Plymouth, southwestern England, said shark attacks were events that had local causes and often were poorly investigated, if at all.

One case that stands out occurred in the Egyptian resort of Sharm el-Sheikh, where sharks made five attacks in a week in November-December last year, one of which was fatal.

The finger of blame was pointed at a passing livestock transport ship that had dumped sheep carcasesses overboard and at operators who illegally fed sharks to thrill the tourists.

Another question -- but again, lacking sufficient data to answer it -- is the impact on shark behaviour from overfishing and from global warming, which affects ocean temperatures and currents.

"We know that these animals are opportunistic and they go to where food sources are available, and those resources do move, and they are dependent on currents, nutrient-rich patches," said Jacoby.

"It's not just sharks that do this, but all large pelagic predators are drawn to areas where there is high food availability. But whether this is a case of increased human activity is unclear."

A hugely successful fish in evolutionary terms, with a lineage dating back more than 400 million years, the shark is under relentless attack from humans themselves.

A third of open-water shark species, including the great white and the hammerhead, are facing extinction, driven in part by demand in Asia for shark-fin soup, according to the International Union for the Conservation of Nature (IUCN).

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