WASHINGTON — A new study published in the journal Science indicates that the global populations of sharks and rays have experienced a decline of more than 50 percent since 1970.
The principal factor contributing to their decline is overfishing, which has led to the depletion of populations of chondrichthyans, including sharks, rays, and chimaeras, over the past five decades.
For sharks, the threats posed by intentional fishing and bycatch are exacerbated by habitat degradation, climate change, and pollution.
Consequently, over one-third of chondrichthyans now face the risk of extinction, as noted by a statement from James Cook University in Australia.
The sequential depletion of the largest and most ecologically important species, such as sawfish and rhino rays—regarded as the world’s most threatened marine fish—has been followed by the decline of large manta rays, eagle rays, angel sharks, hammerhead sharks, and requiem sharks.
Lead author Professor Nicholas Dulvy from Simon Fraser University in Canada states that the study reveals how population decline initially occurred in rivers, estuaries, and coastal waters near the shore, subsequently extending across the oceans and into deeper waters.
Despite their apprehensive reputation as dangerous or resilient, these marine creatures fulfill vital ecological roles across various ecosystems. The widespread decline in shark and ray populations is expected to significantly impact other species and aquatic environments.
“Sharks and rays are essential predators, and their decline disrupts food webs throughout the ocean. Larger, wide-ranging species serve to connect ecosystems; for instance, reef sharks are crucial in transferring nutrients from deeper waters to coral reefs, thereby sustaining those ecosystems,” explains co-author Dr. Nathan Pacoureau from the European Institute for Marine Studies at Brest University, France.
“Rays, on the other hand, play an important role as foraging animals that mix and oxygenate sediments, consequently influencing marine productivity and carbon storage.”
In spite of these concerning trends, the solution to reversing the decline of sharks and rays is relatively straightforward.
Overfishing occurs when an excessive number of fish are captured, leaving insufficient populations to breed and maintain sustainability. The number of overfished stocks has tripled over the last 50 years, with one-third of the world’s assessed fisheries currently operating beyond their biological limits, as reported by the United Nations Food and Agriculture Organisation (UNFAO).
Overfishing is closely linked to bycatch, defined as the capture of non-target sea life while fishing for different species, constituting another serious threat to marine life.
“Nations can mitigate the risk of extinction by reducing fishing pressure to sustainable levels, enhancing fisheries governance, and eliminating detrimental subsidies,” asserts Professor Simpfendorfer.
Progress has already been witnessed in creating pockets of hope for chondrichthyans in Australia, Canada, New Zealand, the United States, and select regions of Europe and South Africa.
He emphasizes the necessity of implementing science-based limits on fishing catches and measures to minimize accidental captures of these species to facilitate their recovery.