Overfishing has wiped out over 70 percent of some shark and ray populations in the past half century, leaving a “gaping, growing hole” in the life of the oceans, according to a new study.
The researchers found alarming declines in species ranging from hammerhead sharks to manta rays.
Among the worst hit is the ocean’s whitetip, a powerful shark often described as particularly dangerous to humans and now hovering on the verge of extinction due to human activity.
Oceanic whitetips are aimed at their fins and are caught by indiscriminate fishing techniques. Their world population has dropped 98 percent in the past 60 years, said Nick Dulvy, lead author on the study and professor at Simon Fraser University (SFU).
“That’s a decline worse than most large terrestrial mammal populations, and an increase or as bad as the decline in blue whales,” he told AFP.
Dulvy and a team of scientists spent years collecting and analyzing information from scientific studies and fisheries data to get a picture of the global status of 31 species of sharks and rays.
They found that three quarters of the species studied were so depleted that they were threatened with extinction.
These are “the most widespread species in the largest and most distant habitats on earth that are often thought to be protected from human influence,” the study’s lead author, Nathan Pacoureau, told AFP.
“We knew the situation was bad in many places, but this information came from various studies and reports, so it was difficult to get an idea of the global situation,” added Pacoureau, a postdoctoral fellow at the Institute of Life Sciences SFU.
The study, published Wednesday in the journal Nature, points to overfishing and poor protection, emphasizing that species can make a comeback if conservation efforts are made.
Research is focused on oceanic sharks and rays, species that live primarily in open water. While there were differences in the health of different populations, the general trend was clear.
“The data showed a gaping, growing hole in the life of the oceans,” said Pacoureau.
“Dazed in the Silence”
For 18 species for which more data were available, the researchers concluded that world populations had declined by over 70 percent since 1970.
Dulvy said the number for other oceanic sharks and rays is likely similar or even worse, but data gaps made it difficult to draw conclusions.
The results were a shock even to experts, Pacoureau said, describing the specialists at a meeting on shark protection, who were “silenced” in the face of the numbers.
Andrea Marshall, a contributing author on the study and co-founder of the Marine Megafauna Foundation, said it was “a living nightmare” to watch the demise of the manta rays and devil rays in Mozambique, where she works.
“It went faster than we could ever have imagined and it showed us that we need to take action immediately,” she said in a press release from MMF.
Three sharks were found to be critically endangered and their populations are declining by more than 80 percent – the oceanic whitetip shark, the scalloped hammerhead, and the great hammerhead.
Sharks and rays are particularly vulnerable to population collapse because they grow slowly and reproduce comparatively rarely.
The study finds a twofold increase in fishing with longlines and seine nets – methods by which marine life, including endangered animals, can be caught indiscriminately – over the past half century.
Regional agencies that manage international fisheries “have not made the protection of sharks and rays a priority,” said Pacoureau. It supports fishing bans for endangered and endangered species as well as limit values for less threatened species.
“Proactive measures can prevent population collapse. And we know they work,” he added, pointing to great white shark recovery in the US under new regulations.
Dulvy said ordinary citizens had a role to play in urging governments to honor their national and international obligations.
“Wherever you can, ask your government to deal with sharks,” he said.
(This story was not edited by GossipMantri staff and is automatically generated from a syndicated feed.)