On the high seas, far from any continent, sharks and rays were once abundant. Shortfin makos, the fastest sharks on the planet, chased after their prey at speeds of over 20 miles an hour. Scalloped hammerheads plied the waters, scanning the ocean expanse for food with their wide-set eyes and other specialised sensory organs.
These animals travelled widely across open waters so vast and inaccessible that many fishermen, and even some biologists, found it hard to believe that overfishing would ever endanger them.
“A decade ago,” recalls Nicholas Dulvy, co-chair of the International Union for Conservation of Nature’s Shark Specialist Group, “we would have extremely heated debates about listing an oceanic shark as threatened.”
Now, a sweeping analysis of current and historic population numbers have created a clearer—and sobering—picture. Dulvy and co-author Nathan Pacoureau, both at Simon Fraser University in Canada, found that populations of 18 shark and ray species have declined by 70 percent since 1970, according to the study, published in the journal Nature this week. At this rate, many of the species might disappear entirely in a decade or two, the authors caution.
When the research team crunched the numbers for the oceanic whitetip shark, a species that was common back in 1970, we “just looked at them in stunned silence,” Dulvy says.
The oceanic whitetip “had declined by 98 percent in the last 60 years. That pattern was consistent across all three oceans.” The International Union for Conservation of Nature now lists the species as critically endangered.
Scalloped and great hammerhead sharks have met a similar fate. Though fisheries rarely target oceanic sharks, if they’re caught, their meat, fins, gill plates, and liver oil is often sold.
This is troubling news both for the sharks and ocean health, as these top predators play a crucial role in the food web, in part by keeping smaller predators in check, experts say.
The impact of overfishing, accidental or otherwise, on sharks should motivate governments to impose more regulations, with the goal of making fisheries sustainable, Dulvy says. It’s also important, he adds, to limit the international trade of threatened shark and ray species.
But there’s a long way to go. A proposed ban on fishing of endangered shortfin makos in the North Atlantic was recently blocked by the European Union and the United States, in part because the bulk of the catch is by Spain, says Dulvy.
“Sharks are kind of the last unregulated area,” he says, “which I think is why there is a bit of resistance to managing them.”
Such a ban has been shown to work for other species, says David Sims, a biologist at the U.K.’s University of Southampton who was not involved in this study. Sims has published research showing hopeful signs of recovery for great white sharks and porbeagles in the northwestern Atlantic, both of which are protected from fishing.