PBy Catrin Einhorn © The New York Times Co.
In just the last half-century, humans have caused a staggering worldwide drop in the number of sharks and rays that swim the open oceans, scientists have found in the first global assessment of its kind, published Wednesday in the journal Nature.
Oceanic sharks and rays have declined by 71% since 1970, mainly because of overfishing. The collapse is probably even more stark, the authors point out, because of incomplete data from some of the worst-hit regions and because fishing fleets were expanding in the decades before they started their analysis.
“There is a very small window to save these iconic creatures,” said Nathan Pacoureau, a marine biologist at Simon Fraser University in Canada and the study’s lead author. More than three-quarters of oceanic shark and ray species are now threatened with extinction, jeopardizing marine ecosystems and the food security of people in many nations.
The research offers the latest data point in what is a dismal trajectory for Earth’s biodiversity. From butterflies to elephants, wildlife populations have crashed in recent decades and as many as 1 million species of animals and plants are at risk of extinction.
But scientists emphasize that conservation works when done correctly, and the study calls on governments to adopt measures such as setting science-based limits on how many sharks and rays fishermen can catch and keep.
“Action is needed immediately,” the authors wrote.
Sharks and rays are taken for their meat, fins, gill plates and liver oil. Frequently they are caught incidentally by fishermen using nets or long lines with thousands of baited hooks to attract tuna or swordfish. Such incidental catch is not the main goal, but often it is welcome when it happens.
That is one reason sharks are especially vulnerable, scientists say. Even if commercial shark fishing stops being viable because of declining numbers, incidental catches could continue to drive down numbers.
Many fishermen have financial incentives to keep the sharks, she said. Governments often allow fishermen to keep them, even as populations plummet. For example, while shortfin mako sharks are classified as globally endangered, the United States, the European Union and many other governments still allow fishing of the species.
For the study, scientists scoured the world for all available data on each species, combining figures from fisheries and scientific surveys with information on reproduction rates, which tend to be slow. Scientists knew sharks were in trouble, but there was no comparable global analysis. At a workshop in 2018, as the authors gathered to review each species’ data, they watched as one catastrophic decline after another popped up on a screen. A grim silence filled the room, Pacoureau recalled. He said he felt shocked at the magnitude of the declines and hopes that their work will help save sharks.
“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,” said Demian Chapman, a marine biologist and professor at Florida International University who researches sharks and was not involved in the study.