Shark populations in the high seas have fallen by 71% since 1970, researchers have found. The main cause is overfishing, which has put three-quarters of these species at risk of extinction.
“It’s the first big picture” of the decline in sharks, says Nuno Queiroz, a marine ecologist at the Research Center in Biodiversity and Genetic Resources who was not involved with the research. The new global perspective, he says, “gives you an idea how pervasive the fishing has been.”
Humans have hunted sharks for centuries for their meat and fins. A related group of fish, the rays, are caught for their gills, which are used in traditional Chinese medicine. Studies have identified severe regional declines of specific species, such as the loss of scalloped hammerhead sharks in the northwest Atlantic Ocean, but no one had compiled trends in all oceans.
In the new study, shark experts took a look at 31 species of oceanic sharks and rays—all of the species that live in the open ocean. (The group is now analyzing coastal sharks and rays and reef-dwelling species.) With long-term data from fisheries and research surveys, the scientists calculated how populations have changed since 1970, a widely used benchmark.
“Some of the declines are staggering,” says Nicholas Dulvy, a conservation biologist at Simon Fraser University and co-leader of the effort. Dusky sharks, for example, have dwindled by 72%, the researchers report today in Nature.
Only one-third of the 31 species were threatened in 1980, the researchers determined by looking at data from that time. Now, three-quarters are at risk of disappearing. “I was just shocked,” Dulvy says. “It has gotten bad very rapidly in the last decade.”
The reason: too much fishing. Compared with 1970, boats today are bigger and do more fishing with gear that catches a lot of sharks, such as long lines of baited hooks. And many sharks have always been vulnerable to depletion because they take years to reach reproductive maturity.
The good news is that fishing regulations can help species recover, such as bans on the landing of sharks. The white shark, for example, is bouncing back off the U.S. east and west coasts because of that kind of protection. For less endangered species, lessening the amount of catch can help significantly.
“The U.S. is one of the only countries that’s been really successful in reversing sharp population declines through management,” says co-author Sonja Fordham, president of Shark Advocates International. “It’s difficult; there’s intense pressure from the fishing industry to protect short term economic interests.”
Fordham hopes the new findings will be a “loud wake-up call” to governments and fisheries managers to protect sharks from overfishing.