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A recent analysis has highlighted a dramatic decline in the populations of sharks, rays, and chimaeras, collectively known as chondrichthyans, by over half since 1970 due to overfishing. This stark decrease has not only put these species at an exceptionally high risk of extinction, with a 19% increase in their extinction risk, but it has also led to the potential loss of up to 22% of ecological functions in both nearshore and pelagic habitats. This finding was reported in the journal Science following research conducted by a team who developed an aquatic Red List Index (RLI) to assess the impact.
The study underscores the critical role that sharks and rays play in marine ecosystems. As apex predators, their reduction in numbers results in significant imbalances within the ocean's food webs. The decline of these species affects the transfer of nutrients essential for the health of coral reefs and impacts the aeration and productivity of marine sediments, which are crucial for carbon storage. Dr. Nathan Pacoureau from the European Institute for Marine Studies at Brest University, France, noted, "Sharks and rays are important predators, and their decline disrupts food webs throughout the ocean. 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".
Impact on Conservation Efforts
The reduction in shark and ray populations has been linked to various human activities, including overexploitation for commercial fishing, bycatch, habitat degradation, climate change, and pollution. With over a third of chondrichthyans now facing the threat of extinction, the study highlights the urgent need for conservation measures. Professor Nicholas K. Dulvy from Simon Fraser University, Canada, detailed how "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".
Despite the grim findings, there is a silver lining in the increased efforts towards the conservation of these marine species. Professor Colin Simpfendorfer from James Cook University, Australia, emphasized the positive developments, stating, "This analysis points to solutions. 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, United States, and parts of Europe and South Africa".
The introduction of the aquatic Red List Index (RLI) for sharks and rays marks a significant milestone for marine conservation, offering a new tool for monitoring progress towards ocean biodiversity and sustainability goals. Dr. Rima Jabado, Deputy Chair of the IUCN Species Survival Commission (SSC) and Chair of the IUCN SSC Shark Specialist Group, highlighted the significance of this development: "The Red List Index has been a tool used by governments for monitoring conservation progress on land, but until now, yet no equivalent existed for the ocean. 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".
In conclusion, the study published in Science presents a critical look at the decline in shark and ray populations since 1970, emphasizing the urgent need for conservation efforts. While the situation remains dire, the research also points to potential solutions and the positive impact of current conservation efforts across the globe. The creation of the shark and ray RLI stands as a pivotal tool for guiding future conservation strategies, aiming to reverse the trend of declining marine biodiversity.
