Canada's Atlantic waters are attracting more great white sharks - BBC

This summer, a seasonal visitor decided the waters off the Canada's prvince of Nova Scotia were very much to his liking.

Just a few months earlier, this tourist had been enjoying Florida. As spring turned into summer, he headed north.

His decision to favour the chilly waters off Nova Scotia over the Sunshine State became noteworthy news; he was no guide-book-toting day tripper, but a nearly 14ft-long (4.2m) great white shark nicknamed "Contender" by researchers.

Contender wasn't alone. Other members of the Atlantic's great white shark population have been patrolling further north and joining him off the coasts of Canada's eastern provinces. US Atlantic states have seen a rebounding shark population due to the recovery of seal populations, and now cold, deep waters further north have become a new great white shark hotspot.

With the growing population, however, there is a greater chance of unwelcome interactions with the people they share the waters with. In September, a diver was attacked by a great white off Quebec's Gaspé Coast. The diver was one of three diving in murky water at the time. His injuries were not life-threatening, but the incident caused alarm amongst diving and water sports businesses, and many operators cancelled dives.

So why are the white sharks ranging further north?

The great white shark, it turns out, is no stranger to Canada's eastern seaboard. As a species, they tend to prefer cooler water, up to a point. They are one of only a few shark species whose body temperature is noticeably warmer than the surrounding water, a feature which gives them added power when hunting. Warm muscles activate quicker in the cold water, meaning faster reactions, but they also require more energy.

Seals are a favourite prey – and seal numbers have been climbing along the US and Canadian coasts in recent decades, possibly because climate-change-induced warming seas are tempting more fish species further north. The surface waters off Nova Scotia are believed to have warmed by about 1.5C (2.7F) in the last 30 years, with the seafloor temperatures warming by about 3C (5.4F) over the same period.

More fish means more seals, and that means more great whites.

Alanna Canaran, a dive instructor and ocean science educator based in Novia Scotia's capital, Halifax, first moved to the province from Toronto in 2010. "In that time in Nova Scotia, it was pretty unheard of to see a white shark," she says. After working elsewhere during the 2010s, she moved back to Nova Scotia in 2020. In little more than a decade, the situation had changed dramatically.

"There have been a few days where you're in the water and it feels very sharky. You can feel that energy. Often in the summertime, when the water warms up, the water visibility decreases, so it becomes a little bit green or a little bit hazy – I'm sure they've been around."

Some of her friends have had far closer encounters. One of Canaran's dive partners was recently at a popular spot called Birchie Head, near St Margaret's Bay. "She was looking down at the rocks and looking at lobsters and things, and all of a sudden she looks up and she sees the belly of a great white shark just swim above her."

Canaran's friend warned her dive partner, who eventually looked up and saw the shark above them. "They ended up just staying really close to the bottom and making their way to the shore, and getting out of the water on basically a side of a cliff because they were obviously spooked."

The great whites are not actively seeking humans as prey, but are sometimes drawn to investigate our underwater activities, often characterised by splashing and noise. Robust research has proved that the sharks could confuse a wetsuited diver or a silhouetted surfboard with a seal. Occasionally, their predatory instinct kicks in. More often than not, the sharks cruise at a distance, merely observing.

In another incident this summer, noted on the Canadian Shark Attack Registry, a diver's fins were "bumped" by a great white that had come in for a closer look. Scuba divers, breathing streams of loud bubbles, look less like a seal than a snorkeller in a wet suit, but sharks are known for their curiosity.

"I include a briefing about sharks for my courses and for my guided dives that I take out," adds Canaran. "I also preface it by saying [the risk of a shark attack is] very, very, very unlikely, but it's increasing."