Recent research published in the journal Science indicates that chondrichthyan fish populations—encompassing sharks, rays, and chimaeras—have plummeted by over 50% since 1970. To assess the repercussions, a research team created an aquatic Red List Index (RLI), which reveals a 19% increase in the likelihood of extinction for these species. The study also points out that overfishing of the largest species in coastal and open ocean habitats could potentially reduce crucial ecological functions by as much as 22%.
Chondrichthyans represent an ancient and diverse group, including more than 1,199 species, all of which are becoming more vulnerable due to human impact. The combination of targeted fishing, unintentional catches (bycatch), and worsening habitat conditions due to climate change and pollution has left over one-third of chondrichthyans at risk of extinction. The RLI was implemented to monitor the status of these species over the last five decades.
“The RLI for sharks and rays demonstrates that the earliest declines were observed in rivers, estuaries, and nearshore coastal areas, which then expanded into the oceans and eventually deep-sea regions,” explained Professor Nicholas K. Dulvy from Simon Fraser University. “The gradual depletion of the largest and most functionally significant species—such as sawfishes and rhino rays—preceded the decline of larger stingrays, eagle rays, angel sharks, hammerheads, and requiem sharks. Eventually, fishing efforts shifted towards deepwater sharks and skates for their liver oil and meat.”
These widespread decreases are anticipated to significantly impact other species and aquatic ecosystems.
“Sharks and rays are key predators, and their decline disrupts marine food webs. Larger species play vital roles in connecting ecosystems; for example, reef sharks help transport nutrients from deeper waters to coral reefs, maintaining those ecosystems,” stated Dr. Nathan Pacoureau from the European Institute for Marine Studies at Brest University in France. “Rays also contribute by mixing and oxygenating sediments, which boosts marine productivity and carbon storage.”
In spite of these concerning trends, the research team highlights the positive strides being made in the conservation and appreciation of sharks and rays.
“This analysis offers potential solutions,” remarked Professor Colin Simpfendorfer from James Cook University in Australia. “Nations can lessen extinction risks by reducing fishing pressures to sustainable levels, enhancing fisheries management, and eliminating harmful subsidies. There have been positive developments for chondrichthyans in Australia, Canada, New Zealand, the United States, and some parts of Europe and South Africa.”
“Historically, the Red List Index has been an essential tool for governments to monitor conservation efforts on land, but there was no similar method for marine environments,” stated Dr. Rima Jabado, Deputy Chair of the IUCN Species Survival Commission (SSC) and Chair of the IUCN SSC Shark Specialist Group. “The newly developed shark and ray RLI will aid in tracking progress toward ocean biodiversity and sustainability goals, highlighting at-risk species and areas, and guiding future conservation strategies.”
The study was part of the Global Shark Trends Project (GSTP), a collaboration involving the IUCN Species Survival Commission Shark Specialist Group, Simon Fraser University, James Cook University, and the Georgia Aquarium, with support from the Shark Conservation Fund. Its aim was to evaluate the extinction risk of chondrichthyan fishes (sharks, rays, and chimaeras). This analysis builds on the first global reassessment of IUCN Red List Status published in 2021 and involved input from 322 experts across 17 workshops around the globe, completing an 8-year long project.
The Red List Index (RLI) monitors overall extinction risk trends for species, serving as a tool for governments to assess their progress towards biodiversity preservation targets. So far, the RLI has been available for only five taxonomic groups: birds, mammals, amphibians, cycads, and warm-water reef-forming corals. The RLI can also be segmented into thematic RLIs for specific subsets of species that hold particular policy significance, and can be calculated for individual countries and regions, factoring in each species’ global range contribution.
The class Chondrichthyes includes three primary lineages: sharks, rays, and chimaeras, the latter being a smaller group primarily consisting of deepwater species. Chondrichthyans represent the oldest and largest evolutionary radiation of vertebrates and form one of the three taxonomic classes of fishes. Our assessment of 1,199 species derives from a thorough global reassessment, marking the most comprehensive evaluation of the past decade.
Since the 1990s, the conservation of sharks and rays has gained traction within Regional Fisheries Bodies and international wildlife treaties, especially the Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES). While member governments are expected to take action to restrict fishing and exports of threatened species to sustainable levels, the record of achieving these commitments has generally been subpar, and deepwater sharks and rays have largely been overlooked in these efforts.