A new analysis of 43 great white sharks captured and released off of the South African coast suggests the colossal creatures can survive—and even thrive—with high levels of heavy metals lingering in their bodies.
The study, published in Marine Pollution Bulletin, draws on blood samples gathered during a 2012 expedition to the region. As Ed Cara reports for Gizmodo, a team led by marine biologists from the University of Miami identified elevated amounts of lead, arsenic and mercury in sharks of both sexes and varying body sizes.
Crucially, arsenic and mercury were found at levels that would be harmful or even fatal to most other vertebrate species. These toxins, however, appeared to have no adverse effects on the sharks’ overall wellbeing, with the researchers noting that the animals’ body condition, white blood cell count and granulocyte to lymphocyte ratios were all indicative of a healthy immune system.
New Atlas’ Anthony Wood points out that in less weighty sea-dwellers, high concentrations of heavy metals can have devastating effects, including neurological decline and a weakened immune system. The scientists’ survey, which tested for the presence of 12 trace elements and 14 heavy metals, defied this logic.
“The results suggest that sharks may have an inherent physiological protective mechanism that mitigates the harmful effects of heavy metal exposure,” lead author Liza Merly says in a University of Miami statement.
Expanding on this unique genetic defense system, Cara explains that great whites are known to be especially skilled at “self-healing and avoiding age-related ailments,” although they remain susceptible to diseases such as cancer.
The most pressing threat sharks currently face, according to the Independent’s Josh Gabbatiss, is persecution by humans who engage in relentless overfishing and hunting. Just last month, the International Union for the Conservation of Nature (IUCN) released updated Red List Assessments for 58 shark and ray species, 17 of which were newly classified as threatened with extinction.
Although the new study clearly demonstrates sharks’ impressive tenacity, the findings aren’t wholly positive: Great whites are apex predators, meaning they likely absorb toxins by eating fish lower down on the food chain. These same fish are also eaten by humans, who are decidedly less well-equipped to combat arsenic, mercury and lead poisoning.
Moving forward, Cara explains for Gizmodo, marine biologists may be able to use sharks as a kind of “aquatic canary in [a] coal mine.”
As study co-author Neil Hammerschlag, also of the University of Miami, concludes, “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."