North Atlantic Sharks on Sharp Decline, Experts Say
By Cameron Walker
for National Geographic News
|January 16, 2003|
North Atlantic sharks are in serious trouble. Scientists searching
through fifteen years of fishing logbooks have spotted a precipitous
drop in shark populations.
Of the 17 shark species studied, all but two have seen their numbers slashed in half in less than two decades.
"These species are declining, and they're declining really rapidly," said Julia Baum, a biologist at Dalhousie University in Nova Scotia and lead author of the study, which appears January 17 in the journal Science.
Hammerhead sharks showed the most serious decline with an 89 percent decrease in population since 1986.
To Catch a Shark
The U.S. National Marine Fisheries Service (NMFS) has been following the decline of sharks spotted in North Atlantic fishing areas. But the state of several individual species, such as the hammerhead, has remained unclear. And sharks that range across the open ocean, known as oceanic or pelagic sharks, have been an even bigger mystery.
The International Union for Conservation of Nature and Natural Resources (IUCN) puts out a "red list" of threatened species. Of the 21 shark species it assessed in the North Atlantic, 20 received question marks when it comes to population trends, Baum said.
To piece together the status of sharks, the team pored through fishing logbooks from the National Marine Fisheries Service. The boats of U.S. pelagic longline fleets, or boats that head to the open ocean, record the number and type of caught fish. These longlines, which dangle hundreds of hooks into the deep, are set to catch swordfish and tuna.
But sharks can rise to the bait as well. Fishermen record this accidental hooking, called bycatch, in their logbooks along with their regular hauls.
The researchers also looked at shark counts from trained shark observers that sail out on some fishing boats. After poring over 15 years' records, the team ran their shark counts through the wringer, considering under-reported shark catches in log books and checking seasonal changes and fishing conditions that might skew the statistics.
Now, these fishing records have started filling in the blanks. "It's the first time anything has been recorded for thresher sharks and oceanic white tips," Baum said. The numbers of sharks in these two groups, both oceanic, dropped by more than two-thirds.
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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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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