How one wrong turn 450,000 years ago brought us great white sharks in the Med

Published on 16/11/2010 13:44

THEY are the ocean's most feared and deadliest predator. And, in a major scientific breakthrough, Scottish scientists have discovered the great white sharks found in the Mediterranean owe their existence to a wrong turn taken about 450,000 years ago.

• The fearsome great whites, like salmon, are programmed to return to the place of their birth. Picture AFP/Getty

Shark geneticists at Aberdeen University have found that DNA samples taken from greats whites caught in both the Mediterranean and the waters off Australia are almost an exact match - and that they share a common ancestry.

In a report, published in the scientific journal Proceedings of the Royal Society B, the Scottish scientists reveal the presence of the great whites in the Mediterranean was probably caused by a navigational error made during a time of significant global climate change, which led to a small group of "confused" sharks - probably a handful of pregnant females - heading north up the coast of Africa, following a strong ocean current, instead of heading east towards the Antipodes.

And they have stayed in the Med because, like salmon, they return to their place of birth. The peninsulas and narrow channels of the Med may also have made it difficult for the sharks to make their way back out into the Atlantic.

Dr Les Noble, a shark geneticist from Aberdeen University's School of Biological Sciences, led the groundbreaking research in collaboration with scientists from Turkey, the United States and Plymouth in Devon.

He 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."

Dr Noble explained that the research team believed a "quirky" combination of factors, such as climatic instability, high sea levels and an unusually fast flowing eddy periodically "spun off" the Agulhas Current - the largest western boundary current in the world - had been to blame for the wrong turn made by a small group of Australian great white sharks almost half a million years ago.

He said: "The relationship with the Australian animals is undeniable.

"We found that the Mediterranean and Australian shark populations had been separated for 450,000 years by looking at the number of mutations in the DNA that had occurred between the two groups."

Dr Noble said the founding group may have comprised just one single pregnant female who gave birth to several young once she reached the Mediterranean. Swordfish and bluefin tuna may also have arrived in the Med via the unusual currents, providing the founding white shark population with a ready supply of food.'BIG FISH IN A SMALL POND'

THE largest great white shark ever caught was landed on the Mediterranean island of Malta in 1987, and it measured a staggering 23.4ft.

But little is known of the Med's white sharks. "This is an endangered population and should be afforded protection in what is a highly polluted and overfished sea," Dr Les Noble said.

"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. These white sharks are a crucial part of their marine ecosystem and look to be critically endangered."

He went on: "If the Mediterranean was to lose an apex predator - something that is right at the top of the food chain - then you could get a phenomena known as 'ecological cascade', which means animals further down the food chain reach unsustainable numbers. The fate of the Mediterranean is tied to these sharks."