Great white sharks found in the Mediterranean were originally from Australia, researchers have discovered.
Stephen Adams 17 Nov 2010
They got there because a few pregnant females got lost around the Cape of Good Hope some 450,000 years ago and ended up in the Atlantic Ocean, according to scientists from Aberdeen Universtiy.
DNA analysis of four great whites captured across the Mediterranean showed that they were all closely related to the current Australian population.
Shark tagging has shown that Great Whites regularly swim between Australia and Africa, with Australian females instinctively heading home eastwards to give birth.
The scientists believe some sharks could have been thrown into the Southern Atlantic by a particularly strong eddy at the foot of the warm Agulhas Current, which sweeps down the east coast of Africa.
Once in the Atlantic they would have tried in vain to head east again, all the while being taken up the west coast of Africa by the cold Benguela Current.
A handful eventually reached the Mediterranean by swimming eastwards through the Straits of Gibraltar.
Once inside they were effectively trapped, said Dr Cathy Jones, a shark geneticist from Aberdeen University’s school of biological sciences.
She 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.
“But because white shark females return to the area where give birth, once they birth in the Mediterranean they become a fixture, shaping and rebalancing the ecosystem.”
Their research, conducted with colleagues from Istanbul in Turkey, is published today in the journal Proceedings of the Royal Society B.
Great white walkabout – Aussie sharks in Mediterranean
Malcolm Holland November 18, 2010
THEY are the accidental migrants, great white sharks originally from Western Australia living half a world away in the waters of the Mediterranean.
Astonished researchers from the University of Aberdeen have found the great whites of the Mediterranean share the same DNA as those in WA.
It’s believed a few pregnant females made a “navigational error” about 450,000 years ago during a time of global climate change and were pushed up Africa’s west coast by a strong current until they entered the Mediterranean via the Straits of Gibraltar.
The females then gave birth, and the great whites have stayed in the Med – although in low numbers – because, like salmon, they return to their place of birth.
The scientists analysed the DNA of four great whites caught in the Med – two caught in the Bay of Edremit off Turkey two years ago, another off Tunisia in 2006 and the fourth off Sicily 20 years ago.
“We were absolutely astonished – it was a moment of scientific serendipity,” geneticist Dr Les Noble said.
“We looked at the DNA signature of the sharks and found they were all from the same extended family.”
Recent research using tagged sharks found that great whites frequently swim back and forth between Western Australia, where many give birth, and the southeast coast of Africa.
But the research team believe about 450,000 years ago great whites at the bottom of Africa were caught in a huge eddy of water called the Agulhas ring, which pushed them into the powerful Benguela Current and then up Africa’s west coast.
They still had an inbuilt desire to swim eastwards – as they would when returning to WA from African waters – but could not until they hit the Straits of Gibraltar.
“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,” shark geneticist Dr Cathy Jones said.
“Once they got to the Mediterranean they may have become trapped because its peninsulas and channels make it like a lobster pot.
“Because white shark females return to the area where they birth, once they birth in the Mediterranean they become a fixture, shaping and rebalancing the ecosystem.”
Florida Museum of Natural History’s International Shark Attack File lists 23 confirmed, unprovoked attacks by great white sharks in the Mediterranean between 1907 and 2008, the last in 1989.
Of these, 11 were fatal.