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Five shark attacks in a week - all in places where the predators are unusual - have foxed experts.
Some marine scientists said the attacks - on a British honeymooner in the Seychelles and four others in Russia and Puerto Rico - could be a result of warmer waters caused by climate change.
Others believe overfishing or more people swimming may be to blame.
But they all agree science does not yet fully understand the behaviour and movement of sharks.
Sydney Aquarium's Amy Wilkes said that, despite the uncertainty, swimmers in Australia should not worry too much as shark attacks were still rare occurrences.
"Worldwide we only have an average of 10 deaths a year from shark attacks - it's a very small number.
"I don't think we can say because there've been attacks in other places that we are likely to have more [in Australia] because it's going to be different sharks in different areas."
A wildlife expert said the shark attacks off the Russian coast may have been the result of warmer currents from the southern seas.
"It might have migrated there following fish stocks or squids," World Wildlife Foundation expert Konstantin Zgurovsky told Kommersant FM radio, Reuters reported.
But Ms Wilkes said the attacks in Russia and the Seychelles were likely to be from predatory sharks common to the local area, rather than sharks that were migrating from other spots.
"In terms of the water temperature ... it's just that different species tend to live in different types of temperatures. So it's not definitely something you could say that's attributable to climate change."
David Jacoby of the Marine Biological Association in Plymouth, south-western England, told Agence France-Presse shark attacks were usually the result of local causes, and these were poorly investigated.
One example was the spate of five attacks - in which one person died - off the coast of the Egyptian resort of Sharm el-Sheikh in December, which were blamed on a livestock ship throwing sheep overboard and at tourist companies feeding sharks to attract tourists.
It was also not clear if overfishing in the world's oceans has changed shark behaviour.
"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," Mr Jacoby said to AFP.
"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."
The International Shark Attack File, compiled by the Florida Museum of Natural History at the University of Florida, said there were 79 recorded unprovoked shark attacks across the world last year, AFP reported. Six were fatal, it added.
It was an increase of 25 per cent from 2009, which had 63 attacks and six deaths, and an increase of 49 per cent from 2008, which had 53 attacks with four fatalities.
More human-shark encounters?
But the International Shark Attack File said the rising number of attacks were likely to be caused by an "ever-increasing amount of time spent in the sea by humans, which increases the odds of interaction between the two affected parties".
The International Union for the Conservation of Nature said a third of open-water shark species such as the great white and the hammerhead were threatened by extinction, in part due to the demand for shark fin soup in Asia, AFP reported.
- with wires
Avoiding shark attacks Avoid swimming around dawn and dusk - times when there are less people in the water. There's less help available if something does happen. With some shark species, for example bull sharks, it's also a time when they might be more actively hunting for food. Attacks can occur as a case of mistaken identity as well because there is less light. Swim between the flags. Avoid swimming among schools of fish. In summer, we often see more attacks also because the patterns of fish movements change. People do tend to thrash about on the surface a bit, which tends to mimic the patterns of a shark's natural prey. If people do feel concerned that they have seen a shark, they should calmly swim into shore and not panic.
(Suggestions by Amy Wilkes)