The Impact of Overfishing Driving Sharks and Rays towards Critical Levels
A recent study published in the journal Science provides a grim outlook on the global depletion of Chondrichthyan fishes, including sharks, rays, and chimaeras. Overfishing has led to a decline of over 50% in their populations since 1970, causing harm to ocean ecosystems and increasing the extinction risk for these ancient marine species.
To measure these declines, researchers created an aquatic Red List Index, a tool similar to the terrestrial Red List, but adapted for oceanic use. The RLI indicates a 19% rise in extinction risk for sharks and rays over the past five decades, highlighting the severity of their decrease. This analysis shows how the depletion of large species, such as sawfishes and rhino rays, started in shallow waters and spread through the food web, impacting even deep-sea habitats.
Professor Nicholas K. Dulvy from Simon Fraser University, Canada, explains that this sequential depletion began in freshwater, estuaries, and coastal areas before spreading across the oceans. He states, "The depletion of the largest and most significant species, like 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."
Sharks and rays play a crucial role as predators in marine ecosystems. According to Dr. Nathan Pacoureau at the European Institute for Marine Studies, Brest University, France, "Their decline disrupts food webs throughout the ocean." For instance, large sharks, such as reef sharks, are crucial in nutrient cycling by bringing deep-sea nutrients to shallow waters, thereby sustaining coral reefs. As top predators decline, so does the connection between ecosystems, impacting the health and productivity of sensitive marine habitats. Rays, on the other hand, contribute to sediment mixing and oxygenation, which influence marine productivity and carbon storage, functions that are becoming disrupted as their populations dwindle.
However, there is some optimism. Professor Colin Simpfendorfer of James Cook University, Australia, believes, "Progress has already created hopeful scenarios for chondrichthyans. Nations can decrease extinction risk by reducing fishing pressure, enhancing fisheries governance, and abolishing harmful subsidies." Success stories exist in regions like Australia, Canada, New Zealand, the United States, and parts of Europe and South Africa.
The creation of the new shark and ray RLI is a significant advancement for ocean conservation. As Dr. Rima Jabado, Deputy Chair of the IUCN Species Survival Commission and Chair of the IUCN SSC Shark Specialist Group, says, "The Red List Index has been a tool for land conservation monitoring, but no equivalent existed for the ocean. This new shark and ray RLI will help in tracking progress towards ocean biodiversity and sustainability targets, identifying species and areas at greatest risk, and guiding future conservation efforts."
- The study in the journal Science reveals that overfishing has led to a significant decline in populations of various animals, such as sharks, rays, and chimaeras, causing harm to nature and increasing the risk of extinction for these ancient marine species.
- The decline of chondrichthyan fishes, including sharks and rays, has impacted marine wildlife and ecosystems, with a 19% rise in extinction risk for sharks and rays over the past five decades.
- Furthermore, the depletion of large species like sawfishes and rhino rays has disrupted food webs throughout the ocean, affecting ecosystems and impacting the health and productivity of sensitive marine habitats.
- To mitigate this situation, nations can take steps to decrease extinction risk by reducing fishing pressure, enhancing fisheries governance, and abolishing harmful subsidies, as suggested by Professor Colin Simpfendorfer from James Cook University.
