It's very old, nearly blind, and famous on the internet for being a "pee shark."
The Greenland shark is notable for having the longest known lifespan of all vertebrate species on earth, but little else is known about the elusive apex predator.
Now a study from the Fisheries and Marine Institute of Memorial University of Newfoundland, published Jan. 17 in Scientific Reports, provides the first estimates on how many of those sharks are in the Arctic.
"This is a species that despite being the third-largest shark in Canada, with quite a wide range on both sides of the Arctic, it's one of the most poorly understood species," said study lead author Brynn Devine.
Devine, a PhD candidate at Memorial University, travelled to the Arctic with study co-author Laura J. Wheeland in collaboration with Arctic Fishery Alliance, an Inuit-owned fishing enterprise based in Nunavut.
"We were really lucky to have the opportunity to collaborate with the Arctic Fishery Alliance because they were providing the opportunity to go places science hasn't gone, really remote regions," Devine told CBC Radio's The Broadcast.
"It was really cool to have the opportunity to be a part of seeing what creatures lie below."
Research will help species management
The research findings are largely from underwater footage taken in a national marine conservation area in Lancaster Sound.
Remote underwater video cameras, baited with squid, were used to capture more than 258 hours of high resolution video data.
"It's pretty simple," Devine said of the footage. "We just attached a camera and some light to a metal frame, put some squid on there for bait, and sunk it to the sea floor where it recorded continuously for eight to 10 hours."
Using scars and unique pattern markings on the bodies of the sharks, 142 individual sharks were identified.
"Based on our estimates, it suggests there's possibly between one to five sharks per square kilometre in most of our sampled regions," Devine said.
"But this is just a first step and, certainly, increasing our sampling in these areas and other areas will help strengthen these estimates."
Those estimates will help manage the species. Greenland sharks can live for hundreds of years, but are listed as near threatened in Canada, with the caveat that information on their true status is limited.
"In order to get a proper assessment and make sure the species is properly managed and conserved moving forward, this is really just some basic information that is necessary in order to do that effectively," Devine said. "There's still a lot of questions to be answered."
'Sleepy, almost dopey little sharks'
The shy sharks had an unexpected moment of popularity last summer, after a series of tweets explaining that the shark's body is full of urea was widely shared.
The sharks do have an usually high concentration of urea in their bodies but are not actually "full of pee." Sharks hold on to urea, a by-product of protein metabolism, in order to keep their bodies at the same salt concentration as their ocean surroundings.
That urea — or specifically, a compound the shark produces to protect itself from the urea — makes the Greenland shark largely inedible. Fermented Greenland shark — or Kæstur hákarl — is considered a delicacy in Iceland, one that foodie television host Anthony Bourdain once described as "unspeakably nasty."
This is the face of a shark that absolutely knows it is made of pee pic.twitter.com/GTKEyKJbTa— @joffeorama
It's not known why Greenland sharks retain more urea than other shark species, and there are many other mysteries — including how they hunt.
Greenland sharks have been found with everything from sculpins to smaller sharks in their stomachs, and one seen off the coast of Newfoundland in 2013 appeared to have a taste for moose, but according to a report in The Atlantic the species has never been observed hunting.
"They've been declared the slowest fish in the entirety of the ocean, yet there's still evidence that suggests they can capture live seals," Devine said.
"To me that just seems like something that would be an impossibility after watching hours and hours of these sort of sleepy, almost dopey little sharks swimming around."