Chondrichthyans, a diverse group of over 1,199 species, are increasingly endangered by overfishing, bycatch, habitat loss, climate change, and pollution. The RLI highlights how these pressures have pushed more than a third of species toward extinction.

"The shark and ray RLI shows how declines first occurred in rivers, estuaries, and nearshore coastal waters before spreading across the oceans and then down into the deep sea," said Professor Nicholas K. Dulvy of Simon Fraser University. "The sequential depletion of the largest and most functionally important species - such as sawfishes and rhino rays - was followed by the decline of large stingrays, eagle rays, angel sharks, hammerheads, and requiem sharks. Eventually, fisheries turned to deepwater sharks and skates for liver oil and meat trade."

The cascading effects of these declines are reshaping marine ecosystems. "Sharks and rays are important predators, and their decline disrupts food webs throughout the ocean," said Dr. Nathan Pacoureau from the European Institute for Marine Studies, Brest University. "Larger, wide-ranging species connect ecosystems. For example, reef sharks transfer nutrients from deeper waters to coral reefs, sustaining these ecosystems. Rays play a vital role as foragers, mixing and oxygenating sediments, which boosts marine productivity and carbon storage."

Despite the alarming trends, researchers emphasize potential solutions. "This analysis points to solutions," said Professor Colin Simpfendorfer of James Cook University. "Nations can reduce extinction risk by lowering fishing pressure, strengthening fisheries governance, and eliminating harmful subsidies. Success stories already exist in countries like Australia, Canada, New Zealand, the United States, and parts of Europe and South Africa."

The study also introduces the first aquatic RLI for tracking conservation efforts in marine environments. "The Red List Index has been a tool used by governments for monitoring conservation progress on land, yet no equivalent existed for the ocean," said Dr. Rima Jabado, Deputy Chair of the IUCN Species Survival Commission and Chair of the IUCN Shark Specialist Group. "This new shark and ray RLI will help track progress toward ocean biodiversity and sustainability targets, identify at-risk species and regions, and guide future conservation initiatives."

Conducted under the Global Shark Trends Project, the study engaged 322 experts across 17 workshops over eight years, supported by the Shark Conservation Fund. It builds on a comprehensive 2021 reassessment of the IUCN Red List Status for chondrichthyans (https://bit.ly/GlobalSharkStatus).

The RLI tracks extinction risk trends for species globally, with thematic and regional analyses available to guide policy-making. The index, already established for terrestrial groups like birds and mammals, is now positioned as a key tool for marine biodiversity monitoring.

Class Chondrichthyes, encompassing sharks, rays, and chimaeras, represents one of the oldest and most ecologically significant vertebrate lineages. While progress has been made in incorporating shark and ray conservation into treaties like the Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES), compliance remains inconsistent, and deepwater species are often overlooked.