Oceanic sharks and rays have declined by over 70%

Nature

"Great Hammerhead Shark Swimming" by Skylar L. Primm

The number of oceanic sharks and rays worldwide has fallen by 71% since 1970. A study in Nature this week finds that more than three-quarters of these oceanic species are now threatened with extinction.

The risk of extinction to marine species is primarily caused by overfishing, but it has been difficult to measure the decline of individual species. Although reductions in oceanic and coastal shark and ray populations in different regions of the world have previously been documented, a global analysis has not been available.

The Whitetip reef shark (Triaenodon obesus).Photo by Jan Derk

The authors attribute this decline to an 18-fold increase in relative fishing pressure — a measure of the proportion of sharks and rays caught relative to their global population — over the period. They argue that immediate action is needed to prevent collapses in populations. Specifically, they call on governments to implement catch limits to help promote species recovery.Nathan Pacoureau and colleagues estimated the relative abundance of 18 oceanic species of sharks and rays from 1970 to 2018 and assessed the risk of extinction for all 31 oceanic shark and ray species. The authors found that, globally, the abundance of oceanic sharks and rays declined by 71.1% from 1970 to 2018. Of the 31 oceanic species, 24 are now threatened with extinction, and 3 shark species (the oceanic whitetip shark, and the scalloped and great hammerhead sharks) have declined so sharply that they are now classified as critically endangered — the highest threatened category in a list that is produced by the International Union for Conservation of Nature (IUCN).

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Recent research shows: More rare, endangered sharks are dying in the worldwide trade in shark fins than earlier feared.

Recent research shows: More rare, endangered sharks are dying in the worldwide trade in shark fins than earlier feared.

by Larry Powell

  The "Grey Nurse" or "Sand Tiger," shark ( Carcharias taurus), a coastal species on the ICU's Red List as critically endangered. A public domain photo by Richard Ling. 

Here's how sharks are "finned."

After hauling them aboard their vessels, the fishermen cut off their fins, then toss them back into the ocean. Still alive, they sink to the bottom where they're either eaten by other predators or die of suffocation. 

 

About 100 million sharks are believed to be taken by fishers each year, most of them for their fins alone. 

It's an industry estimated to be worth US$400 million a year. 

The blue shark (Prionaceglauca). Photo by Mark Conlin/NMFS.

If one were to believe official trade records over the past twenty years, most fins traded on world markets have come from more abundant "pelagic" species (ones which live in the open ocean) like the blue shark (above). 

The leopard shark (Stegostoma fasciatum). An ADV photo by Jeffrey N. Jeffords. 

Using advanced techniques in barcoding and genetic tracing, scientists are now painting a different picture. By analyzing more than five thousand fins from markets on three continents, they still found a lot had come for those "pelagic" populations. But they also found "an additional 40 'range-restricted' coastal species" which did not show up in previous records. These populations live closer to shore and do not range as widely as those in the open oceans. With local jurisdictions providing little protection for them, their populations now face "dramatic declines" and are "typically less abundant."  

However, even the more common deep-sea species have been falling victim to "chronic exploitation" by fishers who are "collapsing" their populations, too. 

New DNA tracking techniques are revealing a greater number of threatened and coastal sharks from stockpiles of intact shark and processed fins (pictured). Image credit: Paul Hilton.

So, if we want to conserve sharks and curb the "unsustainable global trade in shark fins," conclude the researchers, "stronger local controls of coastal fishing are urgently needed."

Their study was published this summer in the proceedings of The Royal Society.

But this is hardly the first cautionary tale pointing to the plight of Earth's marine life in general and sharks, in particular. Another research paper published in 2017 warns, they face "possibly the largest crisis of their 420 million year history. Many populations are overfished to the point where global catch peaked in 2003, and a quarter of species have an elevated risk of extinction."

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The Health of Canadian Fisheries Continues to Decline

Canada's Governing Party Blows a Golden Opportunity to Curb the Brutal Practice of "Shark-Finning" on the High Seas