Some species of sharks and rays could disappear from our seas entirely after a sharp drop in their numbers due to overfishing in the last 50 years.
A study published Wednesday in the journal Nature found that shark and ray populations declined by 71.1% between 1970 and 2018.
“Knowing this is a global number, the findings are compelling,” said Nick Dulvy, a biologist at Simon Fraser University and a co-author of the study. If we do nothing, it will be too late. It is much worse than (the situation of) other animal populations that we have been observing, ”he added.
Of the 31 species of ocean sharks and rays, 24 are now in danger of extinction. Several are classified as Critically Endangered, the highest threat category.
The role of overfishing
“It’s an incredible rate of decline, steeper than most elephant and rhino declines, and those animals are iconic in driving conservation efforts on land,” Dulvey said.
In the study, the researchers used two main biodiversity indicators to chart the rate of change in species populations over decades. One of them is the Red List index, a list that measures the risk of extinction, and the other is the Living Planet index, a set of data that measures changes in the abundance of populations.
Their results revealed “an alarming and continuing global decline in oceanic shark populations in the world’s largest ecosystem over the past half century, resulting in an unprecedented increase in the risk of extinction for these species.”
Factors such as human disturbances and climate change put pressure on these species. However, overfishing is by far the biggest threat, and the relative pressure of fishing (which takes stocks into account) has increased 18-fold since 1970, according to the study.
Shark fins
Sharks in particular are fished for their meat, fins, gills, and liver oil. They were so hunted during the peak of overfishing in the early 2000s that between 63 and 273 million sharks died each year, the study found.
In Asia, shark fin is a prized ingredient for shark fin soup. This has long been seen as a status symbol in Chinese dinners and banquets. A 2018 study published in the journal Marine Policy found that in Hong Kong, the “world’s largest shark trade center,” shark fin imports have doubled since 1960.
Sharks are also particularly vulnerable to overexploitation due to low population growth rates and long development times. In some species of sharks, several years, even decades, may elapse between the birth of a specimen and that of its first offspring. Stingrays have also faced rapid decline and local extinction due to overfishing in their historic habitats.
What should countries do in the face of declining shark populations?
There are some encouraging signs for specific species. The great white shark, whose population fell in the 20th century, is now showing signs of recovery in several regions thanks to government bans and policies, according to the report. Hammerhead sharks are also rebuilding their populations in the Northwest Atlantic, due to strict quotas in the United States’ marine territories.
However, the threat of overfishing far outweighs any commercial regulation or sustainable management of fisheries, the researchers warned.
Only a few countries have imposed specific catch limits for oceanic sharks. And even fewer have been able to rebuild populations devastated by overfishing in the past century. Despite governments signing international treaties, their weak implementation has failed to effectively restrict trade or retain these species, according to the report.
“We can see the alarming consequences of overfishing in the ocean through the drastic decline of some of its most iconic inhabitants,” said Nathan Pacoureau, lead author of the article.
“It is something that policy makers cannot continue to ignore. Countries must work towards new international protections for sharks and rays, but they can start immediately by fulfilling obligations already agreed at the international level, ”he added.
The study called for immediate reform to “prevent the collapse of the shark population” and the potentially disastrous consequences for their ecological systems.
Specifically, the researchers called on governments to adopt oceanic shark catch limits that can sustain sustainable fishing. Also that they define prohibitions of retention of sharks or rays. These are crucial actions to save these declining populations “before the decline reaches a point of no return,” they said.