The two species of Mako shark, an oceanic group, were the only ones that declined by less than 50 percent.
All sharks falling into the category of large coastal species also dwindled by more than half. "Coastal species are going downhill because fisheries are covering their entire range," Baum said.
The result: a gloomy forecast for sharks around the ocean. "We found they're declining at a phenomenal rate," said co-author Ransom Myers, a biologist at the University of Dalhousie, Nova Scotia.
Myers and other researchers are now comparing the current shark numbers to counts gathered from U.S. government fisheries surveys in the 1950s. This snapshot of the sharks' past provides an even bleaker view on their present state, Myers said. "When we go back, it's even worse."
The shark paper "packs quite a wallop and is very much to the point," said Mark Grace, a biologist at the National Marine Fisheries Service Laboratory in Pascagoula, Mississippi. Grace, who has conducted shark surveys in recent years for NMFS, said these findings are in line with many researchers' suspicions about sharks.
However, Grace said studies like these need to take into account how fishing gear is used and what environmental conditions might affect the catch, potentially swaying shark numbers.
Sharks Sensitive to Overfishing
Some people see sharks as the sea's scariest fish.
"We have this idea of sharks being really fierce predatorsand they are. They're at the top of the food chain," Baum said. "But they're also really fragile."
These oft-feared sea creatures grow extremely slowly, taking years to reach maturity. A shark has only a few offspring during its lifetime, compared to other fish, making it difficult to jumpstart a dwindling population. While the sharks have survived as the kings of the ocean for millions of years, their slow-growing populations make them especially sensitive to a recently introduced predatorhumans.
"Sharks are the most vulnerable species in the ocean," Myers said. "They're going to be the first thing you'll see eliminated."
Sharks get hooked as a byproduct of other fisheries. In addition, there are market for the sharks themselves. Commercial fisheries catch some species for dinner-plate appearances. Shark fins, used in delicacies like shark fin soup, rake in profits on the Asian market.
Both the United States and Canada have recently banned finning, but that doesn't mean the shark fin trade has stopped. "There's really high incentive to keep them, because they're one of the most highly valued products," Baum said.
Fisheries managers have turned to fishing regulations and marine reserves to aid other ailing species. In July 2001, concern about the endangered leatherback sea turtle sparked the closure of a large fishing area off the coast of Newfoundland. The researchers used simulations of the fisheries data to see if closing this spot might change shark catches.
While blue sharks and mako sharksspecies of lower conservation concernappeared to be protected by the closure, the researchers' models predicted catches of other shark species would shoot up in the remaining open areas.
If fishermen have to go to new areas to catch the same amount of fish, they're going to affect other species, Baum said.
Designing protected areas for a single species leaves out the complicated web of creatures swimming under the waves, and could shift pressure to other threatened species, she said. "Single-species conservation isn't going to work."
Protected places that shelter several highly threatened species might help shelter species in trouble. "Reserves could play an important role," said Baum. "But what's really needed here is a reduction in fishing effort."
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Nationalgeographic.com Resources on Sharks
Shark "Photo of the Year" is E-mail Hoax
Shark Gives "Virgin Birth" in Detroit
Satellite Tags Keep Track of Great White Sharks
Shark-Soup Boom Spurs Conservationist DNA Study
Great Whites May Be Taking the Rap for Bull Shark Attacks
Crittercams Provide Insights Into Nurse Shark Behavior includes photo gallery
Researchers Tag Sharks to Study Breeding Habits includes photo gallery
Scientists Study Nurse Shark Mating Habits includes photo gallery
Shark Nursery Yields Secrets of Breeding includes photo gallery
"Jaws" Author Peter Benchley Talks Sharks hear Benchley read from his new book
Oceans of Plenty: South Africa's Teaming Seas from National Geographic magazine
The Crittercam Chronicles: Sharks
Field Tales: Filming Great White Sharks
National Geographic Animals and Nature Guide
Shark Safari Online Quiz for Kids
Creature Feature: Great White Sharks
Ten Cool Things That You Didn't Know About Great White Sharks
Print 'N' Go Coloring Book: Great White Sharks
Use this National Geographic News article in your classroom with the Xpeditions lesson plans:
Lesson Plan: A Trip to the Beach?
Lesson Plan: Are Sharks As Dangerous As We Think They Are?
Lesson Plan: Does the Hammer Help?
Lesson Plan: SharksSetting the Record Straight
Lesson Plan: SharksShould They Be Afraid of Us?
Lesson Plan: What's the Hammer For?
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