Great White Sharks in the Mediterranean Came from Australia

A new study carried out by an international team of scientists discovered that great white sharks now live in the Mediterranean because hundreds of thousands years ago, a few pregnant females got lost along the way.

This is the first genetic analysis of this shark population, showing a descendant from shark communities living near Australia.

Evolutionary biologist Andrew Martin of the University of Colorado at Boulder, co-author of the paper published November 16 in the journal Proceedings of the Royal Society B, and his colleagues, gathered tissue from four Mediterranean sharks and carried out an analysis of the mitochondrial DNA, which is passed on from mother to offspring.

They concluded that Mediterranean sharks are more closely related to shark populations in the Pacific and Indian ocean, than they are to those in the Atlantic.

Their explanation is that the female ancestors of the Mediterranean sharks arrived here after a very long trip around the globe.

Apparently, a group of very stubborn females reached the Mediterranean after an extreme climate change some 450,000 years ago, during the late Pleistocene era.

The climate change triggered abnormal currents that confused the sharks during navigation, or displaced their prey, forcing them to follow it to distant lands.

The theory says that the pregnant females swam down the east coast of Africa, when a strong current pushed them on the other side of the continent.

They carried on their journey toward west along the current and ended up in the Atlantic Ocean.

As the sharks had a tendency of swimming east, towards their native grounds, they reached the Strait of Gibraltar and the Mediterranean, instead of Australia, their birthing ground.

These sharks stay loyal to their breeding grounds so the females must have settled quickly into the new surroundings.

This trip was rather unusual as normally the females stay very close to breeding areas and the males are the ones taking long trips across ocean basins, said Martin.

Another discovery made by the team of scientists was the lack of genetic variability among these sharks, and Martin told LiveScience that this must be due to the long history of intense fishing in the area.

He said that “all we're seeing today are the descendants of a few individuals that survived,” and one day these populations could disappear too, because of overfishing and local pollution of this lake-like environment.

Martin explained that “a huge number of people draw on it [the Mediterranean] for resources, and as a consequence, the top predators there compete with human beings.

“We can lose animals like the white sharks because we keep chipping away at the base of the food chain.”

Instead of “doing our best to make this world a much more unstable place”, we should learn to “appreciate the lives of the organisms we share the planet with”, Martin added.