“Sharks and rays are important predators, and their decline disrupts food webs throughout the ocean”, said one of the study’s authors.
More than half of all sharks and rays have disappeared since 1970, but a new study shows a clear path to preventing their numbers from dwindling even further.
Research reveals that overfishing has caused chondrichthyan fishes – sharks, rays, and chimeras (closely related to sharks) – to decline by over 50 per cent in the last 50 years.
This ancient and ecologically diverse group is made up of more than 1,199 species that are increasingly threatened. Though we now know more than ever before about these animals, a lack of knowledge about the scale of their decline threatens to outstrip improvements in research and policy.
“In addition to intentional targeting and bycatch, the threat to sharks is compounded by habitat degradation, climate change and pollution,” says co-author of the research Professor Colin Simpfendorfer from James Cook University in Australia.
“The result is over one-third of chondrichthyans now face the threat of extinction.”
A decline in sharks and rays could impact entire aquatic ecosystems
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”.
What is overfishing and can sharks and rays recover from its effects?
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.