Levels of toxic mercury, arsenic and lead have been found at shockingly high levels in the blood of great white sharks swimming off the coast of South Africa.
Despite being present at concentrations that would kill most animals, these toxins appear to have no effect on the enormous predatory fish.
The scientists undertaking the tests think the sharks may have a special ability to resist the dangerous effects of the heavy metals.
As great whites are top predators, they accumulate high volumes of toxins in their bodies from all the other creatures they eat.
“By measuring concentrations of toxins, such as mercury and arsenic, in the blood of white sharks, they can act as ‘ecosystem indicators’ for the health of the ecosystem, with implications for humans,” said Dr Neil Hammerschlag, a co-author of the study at the University of Miami.
1/6 Scalloped hammerhead shark
Scalloped hammerhead shark fins were among those found being sold by an Asian food retailer in the UK. These sharks are endangered, and in parts of the Atlantic Ocean, their populations have declined by over 95% in the past 30 years.
Istock/Janos
2/6 Spiny dogfish
In the samples of takeaway fish and chips sampled, spiny dogfish made up 90% of those sold under the names huss, rock salmon and rock eel.
Doug Costa, NOAA/SBNMS
3/6 Shortfin mako shark
Another vulnerable species found in the dried shark fins tested in the British Asian wholefood retailer was the shortfin mako shark.
Istock/Alessandro De Maddalena
4/6 Blue shark
Blue shark was also found on sale in UK shops. This species is not as vulnerable as the others but is still listed as “Near Threatened” by the International Union for Conservation of Nature
Istock/Howard Chen
5/6 Nursehound
Around a quarter of the sharks being sold in UK fishmongers were nursehounds, another relatively safe species that is nevertheless classified as near threatened.
Mario Antonio Pena Zapatería
6/6 Misleading names in fish shops
The scientists behind the study investigating the prevalence of endangered shark meat on sale concluded that shops must stop selling these species under “umbrella terms” that hide their true origin.
Istock
1/6 Scalloped hammerhead shark
Scalloped hammerhead shark fins were among those found being sold by an Asian food retailer in the UK. These sharks are endangered, and in parts of the Atlantic Ocean, their populations have declined by over 95% in the past 30 years.
Istock/Janos
2/6 Spiny dogfish
In the samples of takeaway fish and chips sampled, spiny dogfish made up 90% of those sold under the names huss, rock salmon and rock eel.
Doug Costa, NOAA/SBNMS
3/6 Shortfin mako shark
Another vulnerable species found in the dried shark fins tested in the British Asian wholefood retailer was the shortfin mako shark.
Istock/Alessandro De Maddalena
4/6 Blue shark
Blue shark was also found on sale in UK shops. This species is not as vulnerable as the others but is still listed as “Near Threatened” by the International Union for Conservation of Nature
Istock/Howard Chen
5/6 Nursehound
Around a quarter of the sharks being sold in UK fishmongers were nursehounds, another relatively safe species that is nevertheless classified as near threatened.
Mario Antonio Pena Zapatería
6/6 Misleading names in fish shops
The scientists behind the study investigating the prevalence of endangered shark meat on sale concluded that shops must stop selling these species under “umbrella terms” that hide their true origin.
Istock
“Basically, if the sharks have high levels of toxins in their tissues, it is likely that species they eat below them will also have toxins, including fishes that humans eat.”
To undertake their study, the scientists carefully captured and samples 43 sharks, taking blood samples and body measurements before tagging and releasing them.
As many shark species are endangered, the team said it was vital to understand what impact toxic heavy metal pollution was having on them.
The scientists were surprised to find no harmful effect on white blood cell counts or other potential indicators of ill health.
“The results suggest that sharks may have an inherent physiological protective mechanism that mitigates the harmful effects of heavy metal exposure,” said Dr Liza Merly, who led the study.
While the sharks may indeed be resistant to these pollutants, it will not be enough to protect them from the myriad other threats facing sharks – primarily persecution by humans.
Earlier this month, experts announced more sharks were being added to the official list of endangered species, including the shortfin mako, known as the fastest shark in the world.
These results were published in the journal Marine Pollution Bulletin.
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