Canada’s Atlantic waters are attracting more great white sharks

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This summer, a seasonal visitor decided the waters off the Canadian island 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.

Nova Scotia has a lot of food options for them – Neil HammerschlagIn 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."

One reason for the increase in sightings, says Canaran, is that there are more people using the water the sharks are frequenting. The population of Nova Scotia has just passed one million, with its main city Halifax now home to 400,000 people – and that's a lot more people using the waters visited by the sharks.

"Even in 2020, when I moved back, there was only a couple dozen scuba divers that were going out on the regular," she says. "Now there's definitely like a couple of hundred, and there's more people on boats. More eyes on the water, of course, will mean more sightings."

Shark scientist and marine biologist Neil Hammerschlag, who counts the different sharks he sees running a cage-diving operations, has also seen an increased number of great white sightings.

"I can definitely say last year was the most sharks we saw, and this year already we seem to be seeing the sharks even earlier than last year," he tells the BBC. "I don't think the population is bigger. I think we're just seeing individuals visiting Atlantic Canada more than they used to."

Hammerschlag says the waters around Nova Scotia are still cold, but very much within the range the species is comfortable with. The extra food is an added bonus. "Nova Scotia has a lot of food options for them. It's a pretty healthy marine ecosystem with lots of big things that they can eat, seals and tunas," he says.

"The individuals learn, they have memories, they have mental maps. They come here and explore and see the opportunity… they remember that and come back."

Hammerschlag's operation has been trying to gauge the size of the area's resident population, which sharks are returning from year to year, how many are male and female, and the size range. "Last year we identified 120 different great whites in 55 days," he says.

These sightings varied wildly between different individuals, he says. A small number of sharks would be seen four or five times; two individuals were seen on about 30% of their expeditions. But the vast majority were encountered only once.

"Probably 80% of them we only saw once and never again. That indicates to us that they're moving through."

There have been attempts to soothe Canadians amongst the increased sightings and interactions, reassuring them that this is not unexpected.

Improving food stocks will likely lead to an increased shark population, though the sharks' numbers increase a lot more slowly than the seals. "If there are a lot of sharks, say around Cape Cod or New York, and they're just too populous, they're going to start moving into their northern and southern ranges," she says.

A great white can't get into water that's two feet deep, right? – Neil HammerschlagSpeaking before the incident off the Quebec coast, Hammerschlag said he thought more Canadians were "pretty excited" about the possibilities of seeing a great white shark close to home. But they are also perhaps more cautious about the amount of time they are spending in the sea. "You know, I think they're a little more thoughtful when they enter the water."

Nova Scotia's relatively chilly water temperatures could also be a factor. "Most people are not spending a long time in it, and certainly not going very deep… a great white can't get into water that's two feet deep, right?"

That caution could turn out to be of benefit, Hammerschlag says. "I think that's a that's exactly what's necessary – not to be fearful, but to be mindful… it has a lot of benefits, not only for human safety, but for just the understanding and conservation of sharks."

Both Canaran and Hammerschlag don't think people should be scared to enter the water because of the recent attack – but they should be more mindful that they are sharing the waters with sharks. And Canaran adds that for Nova Scotia's indigenous people, like the Mi'kmaq, sharing the water with great whites was a fact of life.

"Indigenous people were out on canoes and they were harpooning seals, and so it's pretty amazing… a great white shark could be in the water as well," she says. Indigenous fishing communities, she says, had their own techniques for keeping the sharks at a safe distance.

"They would tie spruce roots and sea grass to the bottom of the boat, and that would confuse the sharks," she says. "It would trick them into thinking they were in slightly shallower water, and so they would leave these boats alone."

Speaking by email after the September attack, Canaran says: "I was teaching an open water [diving] course in the ocean last week and I actually woke up to a bunch of messages about the interaction in Quebec. Did it stop me from diving? No. Did it make me extra cautious that day? Yes. I had sharks on the mind and so I decided to teach my course at a very protected little cove with lots of eelgrass."

• These photos show a softer side of great white sharks

• The sharks that will eat almost everything

The "sharkiest" season is ending; fewer sharks are expected to be seen in the chillier waters between October and March. Both Canaran and Hammerschlag (who has written a blog on the subject) share similar advice about how to lessen the risk of shark attacks.

"Avoid areas that have preferred prey of sharks (such as seals), especially in areas with poor water visibility which could make it harder for a shark to distinguish between their natural prey and a human," he says.

Canaran says she's more cautious, but she's not letting it stop her dive. "If I only dove when the water was clear, I'd only have about five dives a year. I'm going to keep diving."

The question now is, will the sharks return in similar numbers next year? And will Canadians learn to live with their new reality, lurking in the depths close to shore? "It's about relearning how to live with them. We've done it before, and so I'm confident that we can do it again."

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