Written by David D Crespo, a Portuguese college student currently studying his second year of an Animal Management course in Hampshire, UK. But in his spare time, he’s a wildlife author who writes about nature’s unknowns. Being born in the coastal city of Setúbal and having owned the full DVD set of The Blue Planet (2001) since toddler age, helped fuel a fiery fascination for sharks and the sea. As one of the most mysterious sharks, it only makes sense that David has a particular interest in the Greenland shark.
Deep in the frigid waters of the Arctic and North Atlantic Oceans lurks one of the most formidable sea creature; the Greenland shark.
Although growing even bigger than the infamous Great white or Tiger, there’s far less known about this shark and its relatives than either of those species. How, for example, is it able to catch swift prey like seals, despite being considered the slowest of all sharks?
How Fast Can Greenland Sharks Swim?
Being a member of the sleeper shark family – named so for their lethargic nature – it’s safe to assume the Greenland shark isn’t one to rush anything.
In fact, it may well be the slowest shark species in the world; the top speed being around 3 km/h (or ~1.8 mph). To put this into perspective, the vast majority of people can walk faster than this!
What Is Their Diet?
As a massive apex predator, scientists have found the remains of a host of animals within the stomachs of dissected specimens. Many were relatively unremarkable, such as fish like cod and haddock, cephalopods like octopi and squid, as well as crustaceans like crabs.
But there have been other – more unusual – finds. These included body parts from dogs, horses, moose, reindeer (including a whole body once), seals, small whales – even the jaw of a juvenile polar bear one time.
Due to its sluggish pace, scientists have deduced that most of these larger, mammalian animals were scavenged and not actually killed by the sharks.
Nevertheless, hundreds of seal carcasses have been reported showing a single deep, thick gash spiraling down them. This bizarre phenomenon was brought to public and scientific attention thanks to a series of seal killings at Sable Island off the coast of Nova Scotia, Canada.
It’s been suggested by researchers that Greenland sharks are the prime suspect behind these killings. Though, they have never been seen hunting, so nobody knows for certain. If true, that still leaves one unanswered question: how on Earth can they catch such agile, fast-moving prey like the resident seals?
What Are The Current Theories?
The current most widely regarded theory is from Japanese marine biologist Yuuki Watanabe. He proposes that the sharks prey on the seals while they’re asleep. Their terrifyingly slow speed allows them to approach in complete silence. They then seize the lower half of their unwary victims, pulling them into a watery grave.
His theory does hold substantial weight, given that seals do often sleep in the water, either upright so only their heads stick out or completely submerged. It also explains why most of the ‘corkscrew-shaped’ injuries are on the lower body.
Watanabe’s sleeping theory explains how Greenland sharks are capable of catching seals in their more southern geographic range (i.e. the North Atlantic) like at Sable island, where there is no sea ice for seals to rest/sleep on.
On the other hand, my theory might explain how they are able to do so further north in the Arctic Ocean. There, the water is covered by sea ice which forms along the coastlines, throughout much of the year.
A greenland shark eating a ringed seal.
Photo: r/natureismetal
What Is My Theory?
Unlike their attackers, the seals are mammals and as such, can’t stay underwater forever. At some point, they have to come up to the surface to breathe. But it’s difficult to do that when there’s a meter-thick layer of ice in the way.
To prevent themselves from drowning, the seals (more specifically Ringed seals) create these breathing holes by clawing and gnawing through the ice. This time-consuming activity is done more frequently in autumn and winter to stop the holes from freezing over and getting sealed (no pun intended) with more ice.
The Greenland sharks look for seals who are too busy with the creation or maintenance of their breathing holes. They locate them using their well-developed sense of smell. Similar to Watanabe’s theory, the sharks make good use of their speed or lack thereof to sneak up on the oblivious seals undetected.
Once within reach, the sharks grab their victims from below, dragging them under to be devoured. They eat the nutrient-rich blubber first. Their narrow, pointed upper teeth grip, while the broad, cusped lower teeth slice.
Whether this particular theory of mine is fact or false is yet to be concluded, as science continues to discover more about the secrets of our home planet.