Study: Shark Populations in Deep Trouble
Study Finds That Populations of Nearly All Sharks Have Been Halved by Fishing
By Amanda Onion
Jan. 17
Beachgoers may feel threatened by sharks, but it's the sharks that may truly be at risk.
Researchers at Dalhousie University report in the journal Science that North Atlantic shark populations have declined by more than 50 percent in the past 15 years due to overfishing. Numbers of some shark species have dwindled so low, they say, that their populations could soon be wiped out.
"This is the first time we can say anything definitive about the state of shark populations and what we found is they're declining at phenomenal rates," says Julia Baum, lead author of the study and a biologist at Dalhousie University in Halifax, Canada.
Based on Fishing Log Books
To reach their conclusions, the researchers analyzed logbooks recorded between 1986 and 2000 by fishermen and biologists on board longline fishing vessels. They noted a steep drop in the number of sharks killed while fleets harvested swordfish and tuna. But representatives of the shark fishing industry in the United States claim such data is outdated and that shark populations remain healthy.
"I commend the effort but their science is incomplete because it's based on data that's incomplete and full of errors," says Rusty Hudson, director of Directed Shark Fisheries, Inc., a shark fishing consulting company in Daytona Beach, Fla. "Sharks are not as endangered as some would want us to believe."
Hudson argues that one reason the data is inaccurate is because sharks roam long distances and are often outside regions where fishing vessels recorded their numbers. Also, he says the logbooks used by the researchers are inconsistent and unreliable.
Baum acknowledges that there is a general lack of solid data on sharks, but points out her group carefully analyzed the data to avoid inaccuracies. She said wherever data does exist, the numbers suggest shark numbers dropping fast.
Hammerhead sharks, especially, appear to be reaching precariously low numbers. According to the study, hammerhead numbers have dropped by 89 percent in the Atlantic, while tiger sharks have shrunk by 65 percent, blue sharks by 60 percent and thresher sharks by about 80 percent.
The white shark, made famous by the 1975 movie, Jaws, is also in trouble with numbers dipping by about 79 percent. In fact, data indicates that there have been no sightings of white sharks in at least two fishing areas in the past decade.
Prized for Fins, Cartilage
The capture of white sharks has been banned since 1997, but capture of other shark species remains legal, although the United States now bans harvesting of sharks for their fins. Fishing vessels from Spain and Japan continue to harvest shark fins, which are used in shark fin soup, a delicacy that sells for $100 a bowl or more. Fishermen also get high prices for shark cartilage, which has been touted as a cancer cure.
Attempts to protect some species of sharks, turtles and fish may do more harm than good, Baum says. According to computer simulations performed by the Canadian researchers, when fishing is barred from one marine reserve, fishing pressure simply shifts elsewhere at greater intensity.
"If the fishermen have to go elsewhere to catch their quota, then other areas where there are hammerheads and thresher sharks are caught at higher rates," says Baum, who argues that only an overall decrease in fishing can protect the animals.
She adds that sharks may be particularly vulnerable to overfishing since, like humans, the animals have long gestation rates. Many species, especially larger ones, take a long time to mature and have only three to four pups a year.
A December assessment by the National Marine Fisheries Service, however, appears to disagree with Baum's findings.
Government OKs More Shark Quotas
Responding to a lawsuit filed by the fishing industry, the service determined that a 1998 government study that had made grim forecasts of shark populations was inaccurate. The service then increased quotas of allowable shark catch in the United States by 900,000 pounds.
The quota increase mainly affects shark fishing fleets in the Gulf and south Atlantic waters. Fishing fleets in the North Atlantic don't specifically target sharks, but the animals are sometimes hooked on the lines.
Longline fishermen target large fish such as tuna and swordfish by dragging horizontal lines armed with baited hooks in the water behind a ship.
Hudson points out that the Canadian researchers' data dates only to the year 2000 and since that time people in the tuna and swordfish industry have changed hooks on their lines so as to minimize the number of sharks that become snared on the lines.
He also argues that an increase in recorded shark attacks suggests that the animals are doing fine.
In 2000, worldwide shark attacks reached a record 85. In the 1950s, when reporting was spottier, there were about 100 recorded attacks. In the 1990s, 536 attacks were recorded.
But George Burgess, director of the International Shark Attack File at the University of Florida in Gainesville, says that the increase in attacks is more likely due to better recording methods and the fact that there are more people on the beach — not more sharks in the water.
"Shark attacks are more a result of human patterns than shark patterns," Burgess said at a recent press conference. "Human populations influence shark attacks more than sharks do."