A diving zookeeper tries to measure a hammerhead shark at the Sea Life aquarium in Hanover January 28, 2008. The number of sharks in the Mediterranean has fallen by 97 percent in the last 200 years, putting the sea's ecological balance at risk, a report released on Wednesday said. REUTERS/Christian Charisius

ROME (Reuters) - The number of sharks in the Mediterranean has fallen by 97 percent in the last 200 years, putting the sea’s ecological balance at risk, a report released on Wednesday said.

The report, by the Washington-based Lenfest Ocean Program, used records such as fishermen’s logs, shark landings, museum specimens and visual sightings to estimate the number and size of the Mediterranean sharks over the last two centuries.

There was only enough data on five of the 20 big shark species present in the Mediterranean to be useful to the study -- the hammerhead, thresher, blue and two species of mackerel shark, which averaged a decline of 97 percent.

“It will have a major impact on the ecosystem because large predatory sharks are at the top of the food chain,” said Francesco Ferretti, the report’s lead author.

Losing the top of the food chain can mean smaller fish thrive and consume more of their prey, upsetting the ecological balance. “If we lose these sharks we are going to lose this important portion of the ecosystem functioning,” said Ferretti.

A report last month by the International Union for Conservation of Nature found 11 kinds of shark faced extinction due to overfishing, partly caused by booming demand for shark fin soup in Asia.

Fishers from all over the world catch and trade sharks for their lucrative fins, often discarding their carcasses, the report said, noting Indonesia and Spain are among the top culprits.

Ferretti said the practice was not thought to be common in the Mediterranean due to the small numbers of sharks now present there. More of a problem was “by-catch” -- where sharks are caught in long-line fishing meant to snag tuna and swordfish.

“The Mediterranean has been fished since Roman times, it’s a historical thing,” said Ferretti. “But now (modern) fishing has put big impact on the shark population.”