Sharks and ocean rays are at unprecedented risk of extinction due to overfishing

Innovative study finds global abundance decreased by 71% and 77% among threatened species

Photo Credit: Alex Mustard

A new analysis published this week in the magazine Nature documents an alarming and continuing global decline in shark and ocean ray populations over the past 50 years, primarily due to overfishing.

A team of experts from around the world evaluated 31 species and found a 71 percent decline in global abundance since 1970, a period in which fishing pressure doubled and shark and ray catches tripled.

Three-quarters (77%) of shark and ray species are now considered to be endangered according to International Union for Conservation of Nature (IUCN) Red List criteria.

“We have shown that – despite being farther from land than most species – sharks and ocean rays are at an exceptionally high risk of extinction, far more than birds, mammals or common frogs,” said Nicholas Dulvy, professor at Simon University Fraser from Canada.

“Overfishing for sharks and ocean rays endangers the health of entire ocean ecosystems, as well as the food security of some of the poorest countries in the world,” adds the researcher.

Some shark species, once abundant and widespread, have declined so sharply that they now fall into the two highest threat categories on the IUCN Red List. For example, the commercially valuable mako (or shortie) shark was recently classified as Endangered, while the iconic white tip shark is now considered Critically Endangered.

The authors calculate, for sharks and ocean stingrays, two indicators to quantify progress towards the United Nations Aichi Biodiversity Targets.

"Sharks and ocean rays are vital to the health of vast marine ecosystems, but because they are hidden beneath the ocean's surface, it has been difficult to assess and monitor their status," said Nathan Pacoureau, lead author and postdoctoral fellow at the University Simon Fraser.

“Our study represents the first global synthesis of the status of these essential species at a time when countries should be addressing insufficient progress towards global sustainability goals. While we initially intended it to be a useful report, we must now hope that it will also serve as an urgent warning.”

Sharks and rays are exceptionally susceptible to overfishing because they tend to grow slowly and produce few offspring. They are sought after for their meat, fins, liver oil, gill plates and recreation (fishing and diving).

Overexploitation of sharks and ocean rays has far outstripped effective resource management. Governments have failed to meet their wildlife treaty obligations to protect endangered species and end unsustainable international trade.

“Our analysis is generally grim, but there is hope in some shark conservation success stories,” said Sonja Fordham, president of Shark Advocates International, a project of The Ocean Foundation.

“We have documented the reconstruction of several Northwest Atlantic species, including white sharks and hammerheads, achieved through science-based fishing limits. Relatively simple safeguards can help save sharks and rays, but time is running out. We urgently need conservation actions around the world to avoid myriad negative consequences and ensure a brighter future for these extraordinary and irreplaceable animals,” he added.

O Global Shark Trends Project (GSTP) is a collaboration of IUCN Shark Specialist Group, Simon Fraser University (Canada), James Cook University (Australia) and Georgia Aquarium (United States of America), established with the support of the Shark Conservation Fund to assess the risk of fish extinction chondrichthyan (sharks, rays and chimeras). The GSTP team hired more than a dozen additional experts from around the world to complete the analysis of sharks and ocean rays.

The full article, Half a century of global decline in oceanic sharks and rays (Half a century of global decline in sharks and ocean rays) is available on the Nature website