Tracking the mysterious Greenland shark

JOHN THOMPSON
Do the eyes of the Greenland shark glow in the dark? Do they really stalk caribou drinking at the mouths of Arctic rivers? These are only a few tales told about the Arctic’s biggest, most mysterious fish.

Mike Stokesbury might not be able to put these stories to rest, but he’d be happy with a better idea of how many Greenland sharks there are, where they live in Canada’s Arctic waters and what their migration patterns are.

The Dalhousie University researcher visited Iqaluit two weeks ago to gain support for building a chain of underground sensors to track marine life across the eastern Arctic. These “curtains” consists of sensors, about the size of a thermos, placed across the ocean bed of Arctic straights to track marine animals that researchers have tagged with a radio receiver.

Stokesbury wants to use these curtains to track the Greenland shark, or Skalugsuak, which he describes as “the only really true Arctic Shark” because of the cold temperatures the sharks thrive in — they’ve been found swimming in -1.5 C waters near Arctic Bay.

Just how the shark survives such cold waters is one of many mysteries that surround one of the world’s biggest sharks, and the Arctic’s biggest fish, which grows up to seven metres in length, weighs up to 1,100 kilograms and swims to depths of 2,200 metres — “which is really deep,” Stokesbury said.

For instance, some believe the eyes of the Greenland shark glow in the dark. That’s because a pinkish-white parasite called a copepod, which grows up to 7 cm long, attaches itself to the shark’s eyes. Some researchers believe these parasites glow in the dark Arctic waters and act as lures to draw food near, which the shark then sucks into its mouth with a quick gulp.

But like most theories about the shark, others have disputed this.

The shark has a reputation for laziness, so it’s no surprise one of its many names is the Sleeper shark. There are tales of Greenland Inuit luring the sharks to the surface with seal intestines, then hauling them from the water with their bare hands.

But other stories suggest the shark isn’t so dopey. Some hold that the sharks stalk caribou at the mouths of Arctic rivers, waiting for their prey to dip their heads toward the cold water for a drink before lunging up and pulling them in by their heads.

The shark also eats seals, dead whales, fish, and pretty much anything else it can find, although it isn’t considered a threat to humans.

The shark ranges through Arctic and North Atlantic waters, although it’s been found as far south as Georgia, and as far southwest as up the St. Laurence River, where Stokesbury dove into the murky green waters about two years ago to see the sharks for himself.

“There’s actually this kind of Arctic highway in the middle of the St. Lawrence,” he said, describing a band of cold Arctic water about 90 metres below the surface. “That’s why we find belugas in there.”

Because of the copepods, most Greenland sharks are blind, depending on their acute sense of smell to find food. Although, interestingly enough, Stokesbury and fellow researchers have found the sharks in the St. Lawrence don’t have the parasites attached.

No one knows the lifespan of the Greenland shark, although some believe they could live up to 200 years.

Greenland sharks are poisonous to eat, unless their meat has been boiled well with water changed several times — or buried and left to ferment for several months, after which it’s reportedly considered a delicacy in Greenland. Feeding the shark’s meat to dogs supposedly makes the animals behave like they’re drunk.

The chain of sensors that Stokesbury proposes could be used to track any marine life, which could make them of interest to community fishers who want to track the movement of their local fish populations, he said. Similar curtains have been used to track salmon off the British Columbia coast.

He hopes to tap into International Polar Year funding for the project.