Global study finds overfishing of sharks and rays creates high risk of extinction

These types of fishes, known collectively as chondrichthyans, are an ancient and ecologically diverse group of nearly 1200 that are increasingly threatened by human activities.

To determine the consequences of overfishing, a global team of researchers developed an aquatic Red List Index (RLI) a tool used by governments for monitoring conservation progress on land that had previously not been adapted to monitor the ocean.

The RLI will help track progress toward ocean biodiversity and sustainability targets, identify the species and places most at risk and guide future conservation efforts.

Deakin Marine early career researcher Dr Samm Sherman said over exploitation by target fisheries and incidental capture, compounded by habitat degradation, climate change and pollution, has resulted in over one-third facing extinction.

'The aquatic RLI has tracked the status of these species over the past 50 years and showed that the risk of extinction for chondrichthyan has increased by 19%.

The shark and ray RLI shows the sequential depletion of the larger species that live closest to human populations from rivers, estuaries, and coral reefs. We are now seeing great declines in species abundances in the pelagic and deep seas.

The 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 the liver oil and meat trade.'

Dr Sherman said the widespread documented declines are expected to have significant consequences on other species and aquatic ecosystems.

'Sharks and rays play important ecological roles including stabilising food webs and nutrient cycling between habitats as they forage over a wide array. Rays are important ecosystem engineers that forage in the seabed and, in doing so, mix up and oxygenate the sediment.

Rays, meanwhile, are important foraging species that mix and oxygenate sediments, influencing marine productivity and carbon storage.

Sharks, rays, and chimaeras are exceptionally susceptible to overfishing because they tend to grow slowly and produce few young, relative to other fish. Overfishing has far outpaced effective resource management for these species.'

Despite these alarming trends, Dr Sherman said the research team acknowledges the positive development in the appreciation and conservation of sharks and rays.

'Though there are large declines, there are bright spots and solutions,’ said Dr Sherman. ‘Extinction risk is lower in countries with strong fisheries governance and less harmful fisheries subsidies. These bright spots include Australia, Canada, and parts of Europe and South Africa.'

Notes to Editors: The study was completed as part of the Global Shark Trends Project (GSTP), a collaboration of the IUCN Species Survival Commission Shark Specialist Group, Simon Fraser University, James Cook University, and the Georgia Aquarium established with support from the Shark Conservation Fund to assess the extinction risk for chondrichthyan fishes (sharks, rays, and chimaeras). The analysis is based upon the first global reassessment of IUCN Red List Status published in 2021 (RLI) The team engaged 322 experts through 17 workshops from around the world to complete the 8-year long reassessment.