Great white sharks are washing up dead on beaches with enlarged brains in what is becoming a spiralling marine mystery.
Scientists in Canada and the US are becoming increasingly alarmed by the spike in deaths and what is causing the inflammation.
In over 30 years, the Canadian Wildlife Health Cooperative (CWHC), which studies wildlife health issues, had never come across a dead white shark.
But in August 2023, a great white was found dead on a beach in a national park on Prince Edward Island, Canada with no signs of injury, puzzling scientists.
The cause of death was eventually found to be meningoencephalitis, an inflammation of brain tissues that eventually disrupts normal cognitive functions.
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Four more great white sharks then appeared on beaches in eastern Canada.
“Three of these five seem to have the same potentially infectious disease affecting their brain,” Dr Megan Jones, a veterinary pathologist and regional director of the CWHC told The New York Times.
“We need to know more about what that is,” she added.
In the US, there were another four reported great white shark deaths since July 2022, one appearing dead on a beach in Massachusetts. Most of those had brain inflammation, with no obvious cause of death.
The Y-shaped brains of great white sharks are relatively large compared to other fish species, but still small compared to its body size, measuring roughly 60cm.
Brain inflammation has been found in other shark species, but the cause – often bacterial infection – was easy to identify, unlike in the recent cases of the great whites, Dr Jones said.
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She explained that with a shark’s brain being squeezed, it may no longer be able to feed or could lose its way and get stuck in shallow water, becoming beached.
Dr Jones is now part of a small, but growing group of scientists across Canada and the US who are trying to determine whether the sharks are facing a new, unknown threat.
There is still a lot unknown about sharks compared to that of other marine animals including whales and dolphins as experts warn that shark science is largely underfunded.
Globally, great white sharks are listed as vulnerable by the International Union for Conservation of Nature, with the numbers steadily decreasing, with bycatch in commercial fisheries being a key threat.
The population of great white sharks, however, is growing in the North Atlantic as warming waters and recovering seal populations are driving them north.
Tonya Wimmer, executive director of the Canada-based Marine Animal Response Society, told The New York Times that the answer to the wave of shark deaths could be the natural result of population increase. More sharks might be dying simply because there are more sharks in the ocean.
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