Great white sharks have long navigated the waters between South Africa and Australia. Like other famous ancient mariners, there was a time when they misjudged their location. About 450,000 years ago, Carcharodon carcharias discovered the Mediterranean Sea.
An abnormally strong current caused by ancient climate change and high sea levels may have confused the great whites, report marine evolutionary biologists from Scotland and Turkey in the Proceedings of the Royal Society Biological Sciences. The ocean current, called the Agulhas, may have formed an eddy, called an Agulhas ring, which the sharks likely mistook for the actual current.
By the time the eddy tapered off, the sharks had traveled too far north and would have encountered the western coast of Africa rather than the southern tip of the continent. In an effort to continue their eastern migration to reach the Australian waters where they were born, the great white sharks would have instinctively followed the African coast until they could travel east.
Genetic markers allowed Les Noble, a shark geneticist at the University of Aberdeen, to compare the Mediterranean sharks with the other populations.
“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,” Noble said in a press release.
The geography of the Mediterranean made it a shark trap. There was only a small entrance in at the Straits of Gibraltar, and plenty of peninsulas, islands, and channels to block navigation out. The scientists do not believe any more great white’s are entering the Mediterranean now.
“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,” said Cathy Jones, a shark geneticist from the University of Aberdeen in a press release.
Luckily for the sharks, the similar eddies may have brought swordfish and bluefin tuna into the Mediterranean as well. Thus the sharks would have had familiar food to chow down on while they adapted to the new-found ecosystem.
The Mediterranean’s top natural predator is now in danger from the seas’ top modern predator, humans.
“This is an endangered population and should be afforded protection in what is a highly polluted and overfished sea,” said Noble, “These white sharks are a crucial part of their marine ecosystem.”
Top Photo: Great White Shark; iStockphoto
Bottom Photo: The Aghulas Current; NOAA