Great white sharks are washing up dead on beaches around North America with enlarged brains – but no-one yet knows why. Scientists in Canada and the US have been left scratching their heads at what is causing the inflammation.
It all began in August 2023, when a great white was found dead on a beach in a national park on Prince Edward Island, Canada with no signs of injury. The cause of death was found to be meningoencephalitis, an inflammation of the brain tissue. Four other great white sharks subsequently 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 Canadian Wildlife Health Cooperative (CWHC) told The New York Times. "We need to know more about what that is."
These five white sharks are among nine known deaths dating back from a shark found in July 2022 in Massachusetts, most of which shown signs of brain inflammation.
Dr Jones is among a group of scientists in the US and Canada trying to unravel the mystery of these shark deaths. "I feel very strongly that there’s something significant going on," Dr Alisa Newton, the chief veterinarian for Florida-based shark research organisation OCEARCH, told The New York Times. She was the first scientist to observe meningoencephalitis in white sharks in 2022. She has submitted brain tissue from a shark found in South Carolina April 2023 to the Washington Animal Disease Diagnostic Laboratory for genetic sequencing. This will catalogue all the DNA in the brain tissue to establish whether there is evidence of a virus or bacteria that could be causing the inflammation.
It’s very rare for dead great white sharks to reach land at all: in over 30 years, the CWHC had never found a dead white shark.
Such inflammation has been spotted in other shark species – but the cause of those was usually obvious (often bacterial infection), unlike in these white sharks. The brain of a great white is already relatively large compared to other fish species, measuring around 60cm.
Tonya Wimmer, executive director of the Canada-based Marine Animal Response Society, suggested to The New York Times that the reason for this wave of shark deaths could simply be down to the population increase. The more white sharks are in the water, the more turn up on beaches.
More shark stories from around the world:
