Oceanic Sharks and Rays Have Declined 70% Since 1970

Fishing fleets have indiscriminately slaughtered sharks for decades and a new study catalogues the environmental damage done

Oceanic whitetip
An oceanic whitetip shark swimming in the open ocean. This species was common in the 1970s but its population has since declined by 98 percent, according to a new study. Thomas Ehrensperger via Wikimedia Commons under CC3.0

Industrialized fishing has remade the world’s oceans, stripping crucial predators from the marine environment in huge numbers. Over the last 50 years, humans have wiped out 71 percent of oceanic sharks and rays, according to new research published this week in the journal Nature.

The true death toll for these vital ocean-going species may be even higher than the dismal figure researchers arrived at, reports Catrin Einhorn for the New York Times. That’s because many of the most severely depleted parts of the ocean had already been ravaged by industrialized fishing fleets for 20 years when the dataset behind the new study begins.

In 1970, when the dataset begins, the oceanic whitetip shark was a common species in the open ocean the world over. When the researchers charted the course the oceanic whitetip’s population took over the intervening decades, they were stunned into silence, reports Tim Vernimmen of National Geographic. This once nearly ubiquitous species had declined by 98 percent, Nicholas Dulvy, co-chair of the International Union for Conservation of Nature’s (IUCN) Shark Specialist Group and one of the study’s authors, tells National Geographic.

There are 31 species of oceanic sharks and rays. Of those, 24 are now threatened with extinction and several, like the oceanic whitetip, are now listed as critically endangered—a conservation classification only one step removed from extinction in the wild.

The study reached its sobering conclusions by meticulously combining some 900 datasets cataloguing the abundance of 18 different oceanic shark and ray species over space and time, according to National Geographic. With computer modelling and factoring in knowledge of the global fishing effort, the team was able to put all this together and reach their grim estimate of how global abundance of these 18 species shifted over time.

Per the Times, this study is the first robust global analysis of this scale.

“The advance here is the very elegant statistical analysis that puts it all together and puts a very firm, very well-justified number on it,” Demian Chapman, a marine biologist at Florida International University who was not involved in the study, tells the Times. “It really helps for communicating the scope of the problem to policymakers. It’s a number they can grasp very easily and realize how bad it is.”

The analysis found that the Indian Ocean is the current epicenter of the decline.

“The Indian Ocean is the worst ocean. There is almost no [fisheries] management at all,” Nathan Pacoureau, a biologist at Simon Fraser University and the study’s lead author, tells Adam Vaughan of New Scientist. Globally, sharks are 18-times more likely to get caught by fishers than they were in 1970.

Losing sharks and rays is a devastating blow to biodiversity in these locations, Cassandra Rigby, a biologist from James Cook University and co-author of the paper, tells Holly Richardson of the Australian Broadcasting Corporation. “They have a key role in marine ecosystems, and if you remove them, their ecosystem starts to shift, and it can have really negative consequences for all fishes in the ocean," she says.

But despite how many sharks and rays the oceans have lost, researchers say hope isn’t lost.

“There are still solutions and hopes,” Pacoureau tells New Scientist, mentioning possible fishing bans for the most endangered shark and ray species as well as catch limits for others.

Bans and stricter regulations have helped protect other species such as the great white shark and the porbeagle, David Sims, a biologist at the University of Southampton who was not involved in the study, tells National Geographic. These two species, which show recovering populations, were among the scant bright spots identified by the study.

But the challenge in this case isn’t identifying what should be done so much as actually doing it. Sharks roam the oceans with little regard for jurisdiction, which makes enforcing even existing rules that might protect them a challenge.

"We can see the alarming consequences of overfishing in the ocean through the dramatic declines of some of its most iconic inhabitants," Pacoureau tells Jessie Yeung of CNN. "It's something policy makers can no longer ignore. Countries should work toward new international shark and ray protections, but can start immediately by fulfilling the obligations already agreed internationally."