Many people have summer rituals, but few people attempt an annual pilgrimage anything like Chris Harvey-Clark when he heads to Baie-Comeau, Que.

The marine biologist and veterinarian at Dalhousie University in Halifax has travelled to the north side of the St. Lawrence River each summer since the late 1990s, looking for the elusive Greenland shark — a four-metre-long predator that can weigh hundreds of kilograms.

"It's hard to know where to start with this animal. It's so amazing. Imagine you're looking out your window, having a morning cup of coffee and a four-metre-long predator crosses your backyard … this is exactly what's been happening with the Greenland shark," he told CBC Radio's Mainstreet.

The fact that these animals have been swimming around, literally, off the end of a dock in a small town in Quebec for a long time is amazing. - Chris Harvey-Clark, Dalhousie marine biologist

"The fact that these animals have been swimming around, literally, off the end of a dock in a small town in Quebec for a long time is amazing. It's one of the compelling parts of this story too. You can have an animal, virtually unknown to science, and there it is, right on your doorstep."

He said low-frequency sounds tend to attract the slow-moving beasts.

There have been reports of Greenland sharks swimming in the St. Lawrence for many years, with fishermen landing one from time to time.

In 2003, a man installing an underwater dock, working with chains, said he saw a big fish swim by. Harvey-Clark and a crew went down and within minutes of their dive, they saw a Greenland shark.

The next year, Harvey-Clark got up close and personal with the deepwater fish. He said, at first, attempts to find the sharks that second year were unsuccessful.

"I've been eyeball to eyeball," he said.

"On the very last day, we'd packed our vehicles, we were ready to go home and we'd decided we'd go for one more dive in a bay. The visibility was terrible," he said.

"The visibility under water was probably about [half a metre] and I looked down at my camera equipment, looked up and there was a gigantic nose and eye going right past my face about six inches away."

'Like studying Bigfoot or the yeti'

Harvey-Clark said that day he learned how the slow-moving behemoths can catch "a wily, large-brained, fast-swimming, agile, nervous animal like a seal."

"They do it through stealth and essentially what I experienced was the last few seconds of what a seal's life looks like when a Greenland shark converges on it. They're incredibly stealthy."

Dalhouse marine biologist Chris Harvey-Clark said Greenland sharks can weigh a few tonnes and reach lengths of more than six metres.

Harvey-Clark likened the study of the Greenland sharks to researching mythical creatures.

"How many are there? Where do they go? What do they eat? How do they reproduce? Where do they reproduce? Where are their babies? All those questions are unanswered and I think one of the fascinating things and studying the species is that it's really been like studying bigfoot or the yeti or an unknown animal because there's virtually no data on it," he said.

Greenland sharks are the second-largest carnivorous shark behind the great white. Harvey-Clark said they can weigh a few tonnes and reach lengths of more than six metres.

They're lumbering bottom dwellers that spend most of their long lives blinded from parasites feeding on their corneas, living at depths exceeding 3,000 metres.

"They're really designed to live their lives in the black abyss of the deep sea, well past where we would see light penetrating, for example. Although, they do come up on occasion into shallow water, and this is primarily seen in the Arctic and this is what has made our discovery in the St. Lawrence so interesting was finding this primarily deep-sea shark coming into depths where divers were likely to encounter them," he said.

Very odd sharks

He said the sharks have many odd characteristics.

"Greenland sharks are really enigmatic, strange, fascinating animals. They are quite 'unsharky,' you know, in a lot of ways they're more like a great big catfish," he said.

"The mouth is really strange in these sharks. It's very plastic. They can change the way the mouth functions by moving muscles around the mouth. So they go from inverting or turning the mouth inside-out like a catfish can and make a big suction apparatus to rotating the teeth outward and driving the teeth into prey."

He said the bite of a Greenland shark is unmistakable.

"They drive their teeth into prey, and they basically do a headstand on the prey, and they oscillate their body back and forth like a big auger. What they're doing is they're driving their jaws through their prey and they're taking this big ice cream scoop shape that's very neat and clean. Greenland shark bites have a very characteristic look," he said.

"I refer to them as Swiss Army knife predators — and they're really both a predator and a scavenger, and hence kind of the hyena of the deep."

The sharks also have an incredible sense of smell.

The "super sniffers" are able to find food in the pitch black depths of the deep sea where they're thought to spend most of their time.

"In fact, they've been called giant swimming noses."

Harvey-Clark plans to head back to Baie-Comeau in search of more Greenland sharks in the coming weeks.