HALIFAX, Nova Scotia, Jan. 16 (UPI) -- Sharks are on the verge of disappearing from the Atlantic Ocean, a Canadian study released Thursday reports.
"They're declining at phenomenal rates over really short time periods," Julia Baum, a biology graduate student at Dalhousie University in Halifax and lead author of the study, told United Press International. "We're seeing declines as much as 90 percent for the hammerhead sharks in 15 years."
The study, which appears in the Jan. 17 issue of the journal Science, used a combination of scientific observations, analyses of catches by fishing boats and a mathematical model, found three populations of sharks -- scalloped hammerheads, whites, and threshers -- have declined by about 75 percent between 1986 and 2000. Blue shark populations declined by about 60 percent over the same period.
The declines are seen from as far north as Newfoundland to northern Brazil and as far west as the Gulf of Mexico, Baum said.
Many of the sharks are taken by pelagic -- that is, open ocean -- long-line fishing methods designed to catch tuna and swordfish, which are important commercial fish. "They're getting sharks incidentally because they are set to target these large marine predators," said Baum.
Pelagic long-line fishing methods involve lines as long as 20 nautical miles in the open ocean with approximately 500 baited hooks.
"Chilling," is how Reg Watson, a scientist with the Fisheries Center at the University of British Columbia, characterized the results of the study. The results show "the way in which these stocks have been decimated over such a remarkably short period of time," he said.
Enric Cortes, a shark specialist with the U.S. National Marine Fisheries Service, noted there have been declines in the shark population, but does not agree they have been dramatic.
"If you¹re basing all your conclusions only on one data set, and you're talking about all these species, those are some pretty wide, sweeping statements, I would say," Cortes, told UPI, noting he did agree with Baum that the loss of a "top consumer" -- the animal at the top of a food chain -- can have serious consequences for an ecosystem.
"If we think of an ecosystem as an intricate machine with many different interconnected parts that we don't understand, and then we're removing a very big component of that machine, we can't expect it to function optimally," Baum said. Because so little is known about the biology of sharks, she said scientists cannot predict the impact of their decline on the web of life in the ocean.
Regarding proposals to set aside marine reserves -- ocean areas that are off-limits to fishing -- to protect sharks and other endangered species, Baum said she disagreed they would be an effective way to protect the sharks. She said she and colleagues performed a computer simulation of the impact of such reserves and the result was they would only intensify fishing elsewhere.
A better solution to the problem, Baum said, is to cut back on the amount of fishing done for tuna and swordfish. That, she explained, would reduce pressure on sharks. However, in the face of heavy demand for high-value fish such as tuna, such action would be "difficult," she said.
(Reported by Harvey Black, UPI Science News, in Madison, Wis.)