8 Million Sharks Killed Accidentally off Africa Yearly
for National Geographic News
|April 17, 2007|
At least 7.8 million sharks are killed off southern Africa each year by hooks intended for other animals, a new study says.
Accidentally caught animals, or bycatch, also include some 34,000 seabirds and 4,200 sea turtles every year off the west coasts of South Africa, Namibia, and Angola, according to the report, released last week by the conservation organizations WWF South Africa and BirdLife South Africa.
The animals get caught on baited hooks on longlines used by fishing boats targeting tuna and hake. The heavy fishing lines can trail for several miles behind a ship.
"The majority of albatross and sea turtle species and many shark species are listed as threatened with extinction by the IUCN (World Conservation Union), with fisheries impacts being cited as a major cause," said a WWF South Africa statement.
Marine experts say bycatch around the world has contributed to a serious decline in the population of some sharks, mammals, seabirds, turtles, and numerous other species.
"About a third of the fish that are caught [around the world] are discarded as bycatch," said Beth Babcock, an ocean scientist at the University of Miami in Florida. "That's just an incredible amount of fish that are killed and wasted without being food for anyone."
"You look at some of the threatened fish, and bycatch in fisheries is the main reason why they're threatened," Babcock added.
Different types of fishing practices tend to kill different species as bycatch, WWF says. Nets often kill dolphins and whales. Longline fishing kills sharks, birds, and turtles. Bottom-trawling scoops up sea stars (starfish) and other creatures living on the seafloor.
Shrimp fisheries have the highest level of bycatch, says the nonprofit environmental group Greenpeace. More than 80 percent of a catch may consist of marine species other than the shrimp being targeted, Greenpeace says.
According to some estimates, more than a hundred million sharks and rays may be caught and discarded every year. (Related: "Shark Declines Threaten Shellfish Stocks, Study Says" [March 29, 2007].)
"It has become increasingly apparent over the last several years that fisheries have dramatically reduced populations of top predators in many areas of the world, and sharks are particularly hard hit," said Mike Heithaus, a marine biology professor and shark expert at Florida International University in Miami. (Heithaus has received grants from the National Geographic Society, which owns National Geographic News.)
"By removing such a vast number and diversity of top predators, we are changing the dynamics of marine communities."
The Benguela ecosystem—the name of the area covered by the WWF-Birdlife survey—attracts millions of top predators, which may travel thousands of miles to feed in its nutrient-rich waters.
WWF says an estimated 6.6 million open-ocean sharks are inadvertently caught there each year, mostly blue sharks but also the shortfin mako shark. In addition, fishers catch some 1.2 million coastal sharks, mainly dog sharks, each year.
These estimates are likely conservative, the report said. No bycatch record for longline fisheries exists in Angola, for example.
While most fishers do not want to catch seabirds or turtles, sharks can be targeted for their valuable meat and fins. (See "Thirty-Eight Million Sharks Killed for Fins Annually, Experts Estimate" [October 12, 2006].)
The report warns that shark catch rates have increased due to an increase in demand for shark fins in Asia. Some of the fishing operations in the region employ Asian vessels under joint venture contracts.
Conservationists have urged fishers to adopt methods that reduce bycatch, including the use of bird-scaring lines, which are towed from the stern of the vessel while the baited fishing lines are set.
Fishers in South Africa are required to use such lines, though compliance levels are low, the WWF-Birdlife report says.
Fishers off Namibia, which has no related regulations in place, kill most of the 34,000 seabirds mentioned in the report.
Of the 4,200 turtles reported as killed every year, most are loggerhead sea turtles, which the IUCN lists as endangered, and leatherback sea turtles, which are listed as critically endangered.
Other methods being examined include hooks that cannot be swallowed by turtles and magnets that may repel sharks from fishing lines.
Fishers have an incentive to reduce bycatch. Unintended catches can damage gears in the longline systems, and time spent removing accidental catches from lines eats into productivity.
"It is an alarming problem and one that needs to be quickly addressed before more damage is done," said Heithaus, the shark expert.
"If we don't, it won't just be marine organisms that will be hurt—human fisheries will also suffer."
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