Mediterranean’s sharks originated in Australia
THE GREAT WHITE sharks of the Mediterranean Sea may be descended from Aussie sharks that lost their way during a period of global climate change almost half a million years ago.
The results of DNA testing on four great whites snared by fishermen off the coasts of Turkey, Tunisia and Sicily “astonished” scientists from Scotland’s University of Aberdeen. They believe a “navigational error” by a few pregnant females about 450,000 years ago explains their unlikely origin.
“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,” says shark geneticist Dr Les Noble. “The founding mothers had the same DNA as great white sharks found off the coast of Australia.”
Astonishing result
Great whites (also called white pointers) are known to migrate between Australia and Africa, using cues from currents to navigate.
The researchers believe that – instead of returning eastwards – a number of Australian sharks were caught in a fast-flowing eddy of water called an Agulhas ring that drove them into the Atlantic Ocean. From there they made their way north along the west coast of Africa until they reached the Straits of Gibraltar, which opens into the Mediterranean.
Once there, the population remained static because the shape of the Mediterranean (enclosed by southern Europe, North Africa and the Middle East) made it difficult for them to find their way out, and because female great whites typically return to their own birthplace to give birth.
“Once they got to the Mediterranean they may have become trapped because its peninsulas and channels make it like a giant lobster pot,” says Dr Cathy Jones, another of the experts behind the research. “But because white shark females return to the area where they give birth, once they birth in the Mediterranean, they become a fixture, shaping and rebalancing the ecosystem.”
Giant lobster pot
Dr Terry Walker from the Marine and Freshwater Fisheries Institute of Victoria, who was not involved in the study, says the sharks’ apparent Australian ancestry is fascinating and further evidence of trans-oceanic migration.
The DNA analysis in the new report confirms that they are closely related, he says. “The fact that they’ve turned up in the Mediterranean is remarkable, but perhaps not surprising because there is evidence they can cross oceans.”
The team’s findings are published this week in the journal Proceedings of the Royal Society B.
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