Graduate student Francesco Ferretti, two colleagues at Dalhousie University in Nova Scotia and an Italian researcher collected data from university and other archival sources, as well as from fish markets, recreational fishing clubs and local accounts of shark sightings, The Washington Post reported Monday.

In a paper published in the current issue of the journal Conservation Biology -- co-authored with the late Dalhousie marine biologist Ransom A. Myers and others -- the researchers reported that the shark population has been dropping drastically and that the trend is having a broader effect on marine life in general.

Another research team recently concluded that 19 of 21 open-ocean shark species, along with their cousins, the ray, face the risk of extinction, the Post said. Yet another team reported that the diminishing number of sharks at the top of the food chain is having a disruptive effect on marine ecosystems worldwide.

"Sharks are just one part of the ocean's web of life," said Margaret Bowman, director of the non-profit Lenfest Ocean Program, which helped fund the studies. "But these studies show if you pull out that one thread, the whole web suffers."