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The Mediterranean Sea, says Francesco Ferretti, is “a very dangerous place for a shark.”

So dangerous that in the past two centuries, the shark population there has plummeted by more than 97 percent, according to a study by the graduate student, two colleagues at Dalhousie University in Nova Scotia and an Italian researcher.

They based their conclusion on evidence scoured from an unusually wide variety of records, including documents drawn from universities and archives, from fish markets and recreational fishing clubs, and from local accounts of shark sightings.

The paper, co-authored with the late Dalhousie marine biologist Ransom A. Myers and others, is only the latest evidence that some of the oceans' most feared predators are themselves in dire danger.

Another team of scientists has shown in recent months that the peril is global, concluding that all but two of 21 species of open-ocean sharks and their cousins, the rays, are facing the risk of extinction. Another found that the decline of sharks at the top of the food chain is disrupting marine ecosystems around the globe.

“Sharks are just one part of the ocean's web of life,” said Margaret Bowman, who directs the nonprofit Lenfest Ocean Program, which helped fund all three studies. “But these studies show if you pull out that one thread, the whole web suffers.”

The shark researchers – from Australia, Canada, New Zealand, the United States and several European countries – are engaged in a huge detective project, much of it inspired by Myers, who pioneered the first global shark assessment before his death in late 2006.

Culling both unconventional and traditional sources such as fishing data, museum records and scientific studies, they are tracking not only how drastically sharks' numbers have dropped in recent decades but also how their disappearance is transforming the marine world.

Several factors help explain why the shark population has declined in the Mediterranean, Ferretti said in a telephone interview from his native Italy. Fishing vessels are targeting them to meet the Asian demand for shark-fin soup, while simultaneously trying to compensate for the fact that they have depleted other fisheries.

“Some fishers have decided to switch to sharks because they cannot make up their product with bony fish,” he said, noting that the presence of so many countries bordering the Mediterranean has contributed to the fishing pressure there.

“At these levels, these sharks can be considered functionally extinct, meaning that they cannot perform their role of top predators in the Mediterranean marine ecosystems anymore,” he said. Ferretti and his colleagues published their findings in the journal Conservation Biology.

Shark populations all over the world have plummeted because of intentional fishing for their fins, which are eaten and used for medicines in Asia, and "bycatch," in which sharks are accidentally caught when fishermen target other species.

For this study, published in the March 30 issue of the journal Science, the researchers looked at surveys of populations of 11 great shark species, conducted between 1970 and 2005. Every species had substantially declined in just those few decades.

The smallest observed decline was in sandbar shark populations, which had decreased nonetheless by 87 percent. Other species, including the bull, dusky and smooth hammerhead sharks, may have declined by more than 99 percent.

"They're all down dramatically," said study co-leader Charles Peterson of the University of North Carolina.

Two of the shark species studied have been Endangered Species Act candidates since 1997, but have yet to be added to the list, Baum said.

Domino effect

When one predator disappears from an ecosystem, others that eat the same prey usually take over and keep the balance of the ecosystem in check.

But in this case, where not one, but all, of the top predators are rapidly disappearing, "you lose the resiliency and buffering capacity of one species to step in for another," Peterson told LiveScience.

The loss of top predators has a domino effect on the rest of the ecosystem; populations of lower-level predators, such as rays, skates and smaller sharks, aren't kept in check, allowing them to overeat and wipe out their own prey.

DOUG wrote:Sharks hate them they worry me more than crocs do and poop ya when they eat a good fish your fighting !!! Does anyone think sharks are mor abundant now that they used to be?? I'd take a big set for the jaws have to be big though !!