New Study Finds 71 Per Cent Decline in Oceanic Shark Populations

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Sharks on a fish market in Dubai (Photo: Anastasios71/Shutterstock)

A study published on 27 January in the journal Nature has revealed that the global populations of oceanic shark and ray species have declined by as much as 71 per cent over just the past 50 years. The paper reports that three-quarters of the 31 species assessed during the study are now threatened with extinction, and overfishing is to blame.

The study was carried out as part of the Global Shark Trends Project (GTSP), a collaboration between the International Union for the Conservation of Nature (IUCN), Canada's Simon Fraser University, Australia's James Cook University and the US' Georgia Aquarium. A total of 31 oceanic shark and ray species were assessed during the study, 75 per cent of which are now considered to be threatened with extinction by the IUCN Red List of endangered species.

Even more horrific is the finding that sixteen of the 31 species are considered to be Critically Endangered, just one step removed from being classed as 'extinct in the wild'. The research also suggests the decline maybe even worse in areas where regulations are not in place and data is deficient.

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Mantas are a highly sought after source of income on some Indonesian markets (Photo: Rosyid A Azhar/Shutterstock.com)

'Oceanic sharks and rays often suffer most severely from anthropogenic threats; their preferred pelagic habitat is out of sight and out of mind.' said Dr Andrea Marshall of the Marine Megafauna Foundation, whose 20 years of research into manta rays and mobulas around Mozambique showed a decline in sightings of more than 90 per cent between 2003-2016. 'Unregulated or unsustainable fishing pressure is difficult to control in international waters, so it is no surprise that their populations are crashing globally. To reverse these trends we will need to figure out how to create strict and enforceable regulations in all oceans. We quite literally have run out of time; we must act now if we are to save remaining populations.'

The devastating decline in shark populations is a direct result of the fishing industry, says the report. Sharks and mantas are caught for their fins and gill-rakers to support the Asian shark-fin soup and 'traditional medicine' business; many are killed as the result of bycatch; others are caught legally and sold under different names, such as 'rock salmon' and 'flake', to takeaway restaurants. Some are simply slaughtered for being sharks, such as the mass cull of predatory sharks in Queensland, Australia.

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Sharks are slaughtered to 'protect' beach-goers in Australia (Photo: SiestaImage/Shutterstock)

Most sharks and rays are slow to reach sexual maturity, which makes the reversal of population decline especially difficult – but the report's conclusion notes that 'there are some encouraging findings,' and all hope is not yet lost – if, that is, we are prepared to take immediate action to preserve shark populations.

Great whites, for example, are estimated to have declined by 70 per cent over the last 50 years, but populations are recovering in several regions thanks to bans on catching the sharks, and hammerhead populations are 'rebuilding in the north-west Atlantic' due to strictly enforced quotas in US waters.

'It is possible to reverse shark population declines, even for slow-growing species,' concludes the report, 'if precautionary, science-based management is implemented throughout the range of the species before depletion reaches a point of no return.’

 


The complete report 'Half a century of global decline in oceanic sharks and rays' by Nathan Pacoureau et al (paywalled) can be read at www.nature.com/articles/s41586-020-03173-9

 

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