"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.
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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