Great white shark population stable but not growing in Canadian waters, study finds

Last August, a woman was attacked in the waters off Cape Breton Island, Nova Scotia. Around the same time, videos circulated online showing a great white shark tearing into a seal carcass. The images were arresting enough that they fed a growing public anxiety: the sharks were coming back, moving north in greater numbers, prowling closer to swimmers and surfers. Shark-tracking apps became popular. The Ocearch organization, which tags and monitors the animals, had been operating in the region for several seasons, allowing anyone with a smartphone to watch tagged sharks migrate into the northwest Atlantic from summer through fall.

But a new study published last month in the Canadian Journal of Fisheries and Aquatic Sciences tells a different story. Researchers working with an underwater acoustic detection network—a system of receivers that pick up signals from tagged sharks—found that the great white population in Canadian waters is not growing. It is stable. The distinction matters, because it means the recent sightings and viral moments, while real, do not reflect an expanding population moving into the region.

The study was led by Heather Bowlby, the lead researcher at the federal government's Canadian Atlantic Shark Research Laboratory, working alongside Megan Winton of the Atlantic White Shark Conservancy in Massachusetts and Gregory Skomal of the Massachusetts Division of Marine Fisheries. They analyzed a decade of migration data from 227 tagged sharks, most of them tagged off Cape Cod between 2009 and 2021. Only about a quarter of those animals make the annual journey to Atlantic Canadian waters. When the researchers accounted for the fact that more sharks had been tagged over time and that detection systems had become more numerous and sensitive, they found something striking: the proportion of tagged sharks showing up on the acoustic networks remained consistent. The sightings were not evidence of a population surge. They were evidence of better monitoring.

The numbers illustrate the point. In the Bay of Fundy in 2016, seventy acoustic receivers detected three great whites. Four years later, with three times as many receivers in place, nine great whites were detected—even though the total number of tagged sharks had increased. Over the past five years, between eleven and nineteen percent of acoustically tagged sharks were detected in Canadian waters in any given year. That proportion did not climb.

Bowlby said in an interview that the paper's main purpose is to establish a foundation for understanding the critical habitat these sharks depend on. The tagged animals revealed unexpected behavior. Satellite tags showed that sharks were diving to depths of about fifty metres in coastal locations during summer months, and they did this regardless of water temperature—a finding that challenges the assumption that ocean temperature alone determines where the animals congregate. Most of the sharks coming into Canadian waters from Cape Cod are younger animals, swimming long distances to hunt seals and other prey.

The implications for beach safety are reassuring but not dismissive. Bowlby noted that since the research shows no appreciable increase in shark abundance in Canada, recreational users of Atlantic beaches are not facing greater risk than before. Yet she was careful not to minimize the threat entirely. "The great white is a powerful marine predator, and a bit of prudence is warranted sometimes," she said. Paul D'Eon, director of the Nova Scotia Lifeguard Service, offered his own perspective. He has worked in the service for forty-eight years and has heard fishermen's stories of catching great whites going back to the late 1970s. "I think the risk is extremely low," he said. "It's more reasonable to be injured in a drive to the beach than in being attacked there by a shark." Still, the lifeguard service maintains a protocol: when a shark is sighted at a patrolled beach, the water is cleared for a minimum of two hours.

The study does not erase the reality of the August attack or the power of those viral videos. What it does is place them in context—not as harbingers of a changing ocean, but as rare events in a population that has held steady for years. The research establishes a baseline against which future changes can be measured, and it suggests that the great whites moving through Canadian waters are following patterns that have persisted longer than the public's recent anxiety about them.