Sharks ended up in Med after 'navigational error'

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The Independent Online

Australian great white sharks have ended up in the Mediterranean after going "walkabout", a study has shown.

Four of the deadly predators found off the coasts of Turkey, Tunisia and Sicily had DNA which showed they belonged to a family from Down Under.

Scientists believe their ancestors turned up near the popular holiday destinations after making a navigational error. They may then have found themselves trapped in the enclosed sea.

Later generations stayed in the Med - thankfully in low numbers - because, like salmon, great whites like to return to their birth place.

Dr Les Noble, a member of the research team from the University of Aberdeen, said: "We were absolutely astonished - it was a moment of scientific serendipity.

"We looked at the DNA signature of the sharks and found they were all from the same extended family. The founding mothers had the same DNA as great white sharks found off the coast of Australia."

Two of the sharks were caught in the Bay of Edremit, Turkey, two years ago. The third was found off Tunisia in 2006 and the fourth off Sicily 20 years ago.

The original journey to Europe was probably made by a few pregnant females as long as 450,000 years ago, according to the scientists.

They may have taken a "wrong turn" due to a number of factors including climate change, high sea levels and unusual ocean eddy-currents called Agulhas rings.

Scientists already knew that sharks frequently swim between Australia and Africa, and navigate by following currents.

In this case, instead of returning home from Africa, the sharks are believed to have continued heading west.

They may have been led astray by Agulhas rings which, due to climate change at the time, would have been much more powerful than they are today.

Only after entering the Atlantic Ocean and becoming free of the currents would the sharks have turned around. But by then their path would have been blocked by the west coast of Africa.

Following the coast eastwards they would eventually have reached the Straits of Gibraltar, and the mouth of the Mediterranean.

Swordfish and bluefin tuna - food for the great whites - are thought to have arrived in the Mediterranean the same way.

The findings are published today in the journal Proceedings of the Royal Society B.

Dr Cathy Jones, a shark geneticist from the University of Aberdeen's School of Biological Sciences, said: "We discovered that genetically Mediterranean white sharks are effectively a displaced Australian population which was probably a consequence of a historical navigational error by a few pregnant females during a time of global climate change.

"Once they got to the Mediterranean they may have become trapped because its peninsulas and channels make it like a giant lobster pot."

Colleague Dr Chrysa Gubili said: "It is an incredible journey that we believe is historical and not happening now, but was prompted by a period of climatic instability.

"Some might say they could have entered the Med via the Suez Canal, but this apparently obvious route is unlikely because of high temperatures and hypersalinity."

Dr Noble said the Mediterranean great whites were now an endangered population which needed protection.

"They are big fish in a small pond and are at the top of the food chain in a sea where they have moulded the ecosystem," he added.