WASHINGTON, Dec 7 (NNN-AGENCIES) — The world’s shark and ray population have declined by more than 50 percent since 1970, a new study published in Science journal was revealed.
The main factor behind their demise is overfishing, which has wiped out populations of chondrichthyans fishes (cartilaginous fishes) such as sharks, rays, and chimaeras over the last 50 years.
In the case of sharks, the threat posed by intentional fishing and bycatch is compounded by habitat degradation, climate change, and pollution.
The result is over one-third of chondrichthyans fishes now face the threat of extinction, a statement by Australia’s James Cook University noted.
The sequential depletion of the largest and most functionally important species, such as sawfish and rhino rays – the latter considered the world’s most threatened marine fish -, was 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, says the study shows how population decline first started in rivers, estuaries and coastal waters near the shore. From there they spread across the oceans and down into the deep seas.
Though they may have a bad reputation for being dangerous or tough, these marine creatures fulfil important ecological roles across various ecosystems. Widespread declines in shark and ray populations will also have significant consequences on other species and aquatic environments.
“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”, says co-author Dr Nathan Pacoureau from the European Institute for Marine Studies at Brest University, France.
“Rays, meanwhile, are important foraging animals that mix and oxygenate sediments, influencing marine productivity and carbon storage”.
Despite these alarming trends, the answer to curbing the decline of sharks and rays is pretty simple.
Overfishing occurs when too many fish are caught and there aren’t enough left to breed and maintain a sustainable population. The number of overfished stocks has tripled over the last 50 years one-third of the world’s assessed fisheries are currently pushed beyond their biological limits, according to the United Nations Food and Agriculture Organisation (UNFAO).
Overfishing is closely tied to bycatch or the capture of unwanted sea life while fishing for a different species. This, too, is a serious marine threat.
“Nations can reduce the extinction risk by lowering fishing pressure to sustainable levels, strengthening fisheries governance, and eliminating harmful subsidies,” says Professor Simpfendorfer.
Progress on this front has already created spots of hope for chondrichthyans in Australia, Canada, New Zealand, the United States, and parts of Europe and South Africa.
He says science-based limits on fishing catches and measures to minimise these species from being accidentally caught are essential to help them recover. — NNN-AGENCIES