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How Overfishing Is Pushing Sharks And Rays To The Brink
A new analysis published in the journal Science paints a dire picture of the global decline of Chondrichthyan fishes – sharks, rays, and chimaeras. Since 1970, overfishing has driven these populations down by more than 50%, causing catastrophic damage to ocean ecosystems and raising the extinction risk for these ancient marine species.
Researchers have developed an aquatic Red List Index, a tool akin to the terrestrial Red List but adapted for oceanic use. The RLI reveals a 19% increase in extinction risk for sharks and rays over the past five decades, underlining the severity of their decline.
The analysis tracks how the depletion of the largest species – such as sawfishes and rhino rays – began in nearshore waters and has since cascaded through the food web, affecting even the deep-sea habitats. Professor Nicholas K. Dulvy from Simon Fraser University, Canada, highlights that this sequential depletion of species started in rivers, estuaries, and coastal waters before spreading across the oceans.
“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,” he explained. “Eventually, fisheries turned to deepwater sharks and skates for the liver oil and meat trade.”
Sharks and rays are crucial predators, and their decline disrupts food webs throughout the ocean. These predators play numerous vital roles in sustaining coral reefs and other ecosystems. For instance, large reef sharks are essential in nutrient cycling, bringing deep-sea nutrients up to shallow waters, thus supporting the health of coral reefs.
As these top predators decline, so do their connections between ecosystems, affecting the productivity and resilience of coral reefs and other sensitive habitats. On the other hand, rays, crucial for mixing and oxygenating sediments, are vital in influencing marine productivity and carbon storage – functions that are being increasingly disrupted as their populations shrink.
Despite these alarming trends, there is hope. Nations can mitigate extinction risk by reducing fishing pressure to sustainable levels, strengthening fisheries governance, and eliminating harmful subsidies. Success stories already exist in regions like Australia, Canada, New Zealand, the United States, Europe, and parts of South Africa, demonstrating that conservation efforts can be effective.
The development of a new shark and ray RLI is a significant step forward for ocean conservation. Dr. Rima Jabado, Deputy Chair of the IUCN Species Survival Commission and Chair of the IUCN SSC Shark Specialist Group, emphasizes that “this new index will help track progress toward ocean biodiversity and sustainability targets, identify species and places most at risk, and guide future conservation efforts.”
Source: www.forbes.com
