Study says shark gone from Gulf
Others disagree that whitetip nearly extinct
By Dina Capiello
Houston Chronicle Environment Writer
February 4, 2004
A shark that was once as common in the Gulf of Mexico as bloodthirsty mosquitoes along the Texas coast is now virtually extinct from the region, according to research published today in the journal Ecology Letters.
By comparing data collected in the 1950s to accidental catch taken in the 1990s aboard commercial fishing vessels, two Canadian scientists estimate that the population of oceanic whitetip sharks has declined in the Gulf by more than 99 percent -- a number that the federal government said Tuesday was likely overestimated.
The study spells more trouble for big fish and sharks, which are slow-growing species that give birth to few young and are already on the decline elsewhere. In the Gulf of Mexico, the whitetip joins green turtles and blue fin tuna on the locally extinct list, although the shark still exists in the warm waters of the world's oceans.
"What we have shown is akin to the herds of buffalo disappearing from the Great Plains and no one noticing," said Ransom Myers, a leading fisheries biologist based at Dalhousie University in Nova Scotia who wrote the paper with colleague Julia Baum as part of a global assessment of sharks.
"There are so few of them, whatever functions they served in the ecosystem they are no longer serving," he said.
In their study, the scientists documented that the proportion of whitetip and silky sharks caught on fishing lines in the Gulf had declined from 15 percent to 0.3 percent during the past 40 years, a trend that they say means fewer sharks are in the Gulf.
Part of the reason for the decline, however, also could be increasing regulations to protect open-water species such as sharks. In the mid-1980s, the Gulf was closed to foreign fishing fleets casting long lines for tuna. In 1993, catching sharks just for their fins was banned in the United States, diminishing the market for shark.
As a result, whitetip shark killings in the Gulf and elsewhere in the United States are now largely the result of bycatch -- fish caught unintentionally in the long lines set for tuna and swordfish. These lines can extend as far as 50 miles and contain thousands of hooks.
"In respect to open-water sharks, we've eliminated any direct fishing," said Michael Sissenwine, the chief scientific adviser for the National Marine Fisheries Service, the government agency that manages shark populations in U.S. waters.
Sissenwine questioned the study's numbers.
"I wouldn't put a lot of confidence in the specific numbers," he said. "It's only the Gulf of Mexico, and the species being discussed here has a broad range. To know what is happening to this population, one needs to know what is happening everywhere."
Since the shark migrates hundreds of miles, the legal taking of whitetip sharks in international waters could also be contributing to their absence in the Gulf. While Sissenwine says that commercial fishing is targeting sharks less, the researchers found that had little effect on how many sharks were caught.
Advocates for ocean conservation said the study should result in better shark management, either by closing areas with high bycatch or adding whitetip sharks to the list of species that can't be fished.
"You can see them as canaries in the coal mine, and a real signal that we are overexploiting our ocean resources," said Sonja Fordham, the international fish conservation program manager for The Ocean Conservancy in Washington, D.C.
The National Marine Fisheries plans to conduct a shark population study in the entire Atlantic Ocean, something that has been delayed by a lack of cooperation from the international community, which still catches oceanic whitetips for their fins.
But Myers said that in many cases, data for other areas do not exist.
http://www.chron.com/cs/CDA/ssistory.mpl/metropolitan/2386421
