The risk of extinction now being faced by all species of sharks, rays, and chimaeras has increased by almost 20% over the last 50 years, driven primarily – according to a newly developed Red List Index trained on marine life – by overfishing, a direct human impact that has more than halved species populations since 1970. 

Deploying the new Red List Index (RLI) tool – one devised to determine the consequences of species extinction for this grouping of fish known as chondrichthyan – researchers have learned that continued overfishing of the largest species in both nearshore and pelagic habitats could wipe out up to 22% of ecological functions.

This is the latest research to come out of Simon Fraser University in Canada, where Professor Nicholas K Dulvy has led the development of an aquatic Red List Index (RLI) to determine the risk of extinction for chondrichthyan fish species – an ancient and ecologically diverse group of over 1,199 sharks, rays, and chimaeras – which are all now facing increased threats from human activities.

Overexploitation by target fisheries and incidental capture (or bycatch), compounded by habitat degradation, climate change, and pollution has all led to the current near-extinction plight faced by one-third of all chondrichthyans. 

“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 Dulvy. “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 the liver oil and meat trade.”

A report issued by the IUCN Species Survival Commission Shark Specialist Group earlier this week revealed that the global demand for shark meat has nearly doubled in the last 20 years, despite sharks, rays, and chimaera being among the most threatened vertebrates on the planet and one third of all species facing extinction.

Building on the last time such a report was issued – back in 2005 – the group warned that while, 20 years on, we now understand more about the species than ever before, the scale of the species declines is still outstripping improvements to protect them through research and policy.

These widespread, documented declines are expected to have significant consequences on other species and aquatic ecosystems.

“Sharks and rays are important predators, and their decline disrupts food webs throughout the ocean,” said Dr Nathan Pacoureau at the European Institute for Marine Studies, Brest University in France. “Larger, wide-ranging species connect ecosystems, for example, reef sharks are vital in transferring nutrients from deeper waters to coral reefs, helping to sustain those ecosystems.

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

Despite these trends, the team behind the development of the RLI maintains that positive advances have been made in the appreciation and conservation of sharks and rays, suggesting that the latest analysis of their near-extinction categorisation points, earnestly, to future solutions for the restoration of the species.

Professor Colin Simpfendorfer from James Cook University in Australia, part of the team behind the RLI project, said: “Nations can reduce the extinction risk by lowering fishing pressure to sustainable levels, strengthening fisheries governance, and eliminating harmful subsidies.

“Progress has already created bright spots of hope for chondrichthyans, including in Australia, Canada, New Zealand, the United States, and parts of Europe and South Africa.”

Scientists are only beginning to decipher the role that sharks, rays, and chimaeras play in delivering life-supporting resources and services; including the cycle of nutrients around the ocean, while others help us fight climate change by acting as carbon sinks or maintaining carbon sequestering ecosystems like mangroves. 

They also underpin food security in vulnerable coastal communities while in some developing nations, fishers have reported that more than 80% of their income depends on shark and ray fisheries.

It is hoped that the aquatic Red List Index will serve as an marine life-focused equivalent to the Red List Index used by governments across the world as a tool for monitoring conservation progress on land.

“This new shark and ray RLI will help track progress toward ocean biodiversity and sustainability targets, identify the species and places most at risk, and guide future conservation efforts,” said Dr Rima Jabado, deputy chair of the IUCN Species Survival Commission and chair of the IUCN SSC Shark Specialist Group. “The message is clear, we cannot afford to wait.”

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