Something Small Is Killing Great White Sharks

Faced with a rash of shark deaths marked by brain swelling, Canadian and American scientists are trying to solve a marine mystery.

The first great white shark was found dead in August 2023 on a beach in a national park on Prince Edward Island, Canada: a young male, 500 pounds, 8 feet 9 inches from snout to tail. Park workers soon arrived with a pickup truck, loaded the carcass and drove it to a cooler at the Atlantic Veterinary College at the University of Prince Edward Island. Aside from some scrapes acquired en route, the shark showed no signs of injury.

Dr. Megan Jones, a veterinary pathologist at the college and regional director of the Canadian Wildlife Health Cooperative, or C.W.H.C., began a necropsy early the next morning, while the body “was really, really fresh,” she said. “When we look through the microscope at the tissues, they’re very well preserved.”

The C.W.H.C., a network affiliated with Canada’s veterinary schools, studies wildlife health issues. In 30 years, however, the group had never come across a great white, and it was not at all obvious how this one had died. Starvation was ruled out from the very first incision, when the shark’s 76-pound liver, where the animal stores fat, spilled onto the examination table. Other organs showed no sign of trauma. Only later, after microscopic testing, did the cause of death become apparent: meningoencephalitis, an inflammation of brain tissues.

At first Dr. Jones found the diagnosis more interesting than alarming. Then came the other sharks. Over the next few months the C.W.H.C. received either whole animals or tissue samples from four more white sharks found beached in eastern Canada. “Three of these five seem to have the same potentially infectious disease affecting their brain,” Dr. Jones said. “We need to know more about what that is.”

Those five white sharks are among nine known deaths dating from a shark found on July 4, 2022, in Massachusetts; most of those had brain inflammation. Such inflammation has been seen in other shark species, but the cause in those cases — bacterial infection, for instance — was obvious, unlike in white sharks. Dr. Jones is now part of a small group of scientists in the United States and Canada who are trying to untangle the mystery — and determine whether white sharks are facing a broader threat.