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A shark that was once the most common warm-water oceanic species in the world has virtually disappeared from the Gulf of Mexico, a new study authored by Canadian scientists has found.

"Researchers in the 1960s suggested that oceanic white tip sharks were the most common large species on Earth," said Ransom Myers, a fisheries biologist at Dalhousie University and co-author of the study. "What we have shown is akin to the herds of buffalo disappearing from the Great Plains and no one noticing."

Comparing data of accidental catch taken aboard commercial fishing vessels in the 1950s and the late 1990s, the authors of the study estimate that the population of oceanic white tip shark has declined more than 99 per cent in the gulf, a figure that they say can be extrapolated beyond the region.

"We're not dealing with a U.S. issue, we're dealing with something much wider," Dr. Myers told globeandmail.com on Wednesday. "All the indications are that this probably represents a similar decline in the tropical areas of Atlantic," he added, noting the species are also found around Cuba, the coast of West Africa, Brazil and the southern United States.

In the cover story of the February issue of the journal Ecology Letters, Dr. Myers and his Dalhousie colleague, Julia Baum, write that the proportion of white tip and silky sharks caught on fishing lines in the gulf had declined to 0.3 per cent from 15 per cent in the more than 40 years under study. The study was part of the Pew Global Shark Assessment, a three-year, $1.5-million systematic inventory of sharks around the world.

Dr. Myers attributes the disappearance of the species to the practice of catching sharks for their fins, the chief ingredient in the Chinese delicacy shark fin soup. The soup, which takes two days to prepare and can cost up to $100 a bowl, has an unremarkable taste but is regarded as a status symbol.

In the United States, where direct fishing of open-water sharks has been banned since 1993, most white tip shark killings are the result of bycatch - accidental trappings in lines (up to 80 kilometres long and containing thousands of hooks) that are intended to trap tuna and swordfish.

But shark fishing in international waters seems to be the main cause of the decline of the white tip, which are known to migrate hundreds of kilometres, Dr. Myers said.

China, Japan, Korea and Spain are among the countries that legally catch sharks and cut off their fins before throwing them back to the ocean. They then sell the fins, mainly in the lucrative Chinese market.

"It's like cutting their arms and legs off - they can't swim and they sink to the bottom of the ocean," Dr. Myers said. " It's an incredibly cruel practice, and they're basically driving the species extinct for a senseless luxury."

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