When one Googles for Greenland shark images from the Arctic, most of the photos show the world’s most northerly shark seemingly hovering just under the ice cover where the depths below reach far beyond the range of scuba divers. The images are breathtaking but they are mostly taken at the expense of the shark’s health.
The opening paragraph sets the usual tone by lending further support to a long-held view concerning the shark’s poor or non-existent eyesight; a theory originally ascertained by people who had never actually swum alongside untethered Greenland sharks under various lighting conditions.
[Greenland sharks are absurdly slow]
By what standard does one label any speed as being absurd? Our own observations of Greenland shark swimming speeds range from virtual immobility to bolts of up to one metre per second after tag deployment. In my opinion, the adjectives stealthy and energy-conserving better suit and dignify the Greenland shark’s average cruising speed of 0,3 m/sec¹. And since Greenland shark populations seem to be healthy throughout the shark’s known range, its “absurdly slow” speed appears to have served it well.
[Greenland sharks… are mostly blind]
This may be true in the Arctic Ocean where most Greenland sharks are host to a damaging ocular parasite, and where they spend most of the time in obscur environments due to depth, ice cover and the polar night. But this is not the case in the St. Lawrence where very few Greenland sharks are parasitized by copepods, and where their visual acuteness is conspicuously obvious to any diver that gets buzzed by these alleged bats of the deep sea².
[… they may have spread far beyond the Arctic waters they are known from]
Just because their common name refers to Greenland doesn’t mean that they originated from the Arctic. Who’s to say that segments of some populations didn’t actually spread to the Arctic after their original feeding areas were depleted of groundfish by overfishing? Or maybe their distribution has always been worldwide and they haven’t spread at all or at least, not recently.
[They can be a big as great white sharks]
No, they can’t. Although the Greenland shark is believed to equal or possibly exceed the maximum length of a great white, it has about half the girth and weight of the most famous of sharks.
[Their maximum speed is a lethargic 1.7 miles per hour]
That may be true in the Arctic but we’ve seen them move faster in warmer water. And if the author had tried to keep pace with a free-swimming Greenland shark, he’d have realised that a sustained 1.7 miles per hour is anything but lethargic. The Greenland shark is by no means a race car, but there have been many occasions when physical overexertion has prevented us from remaining alongside a shark for more than a minute.
[… they are absurdly slow, moving more sluggishly than any other shark.]
Not true. A study has shown that Pacific angel sharks covered distances of no more than 30 to 75 km over a period of three months, while one Greenland shark that we tagged in 2005 covered 26 km in just 29 hours¹. The comparison is justified since the Greenland sharks observed in our study remained in the Baie-Comeau area over a period of several weeks. The distance covered was therefore in no way associated with long-distance migration.
[… more data is now starting to come in from elsewhere.]
Starting? Our first papers presenting data on the St. Lawrence population of Greenland sharks were published in 2005³. Granted, our number of publications is limited but we are all volunteers otherwise occupied with full-time jobs and various obligations. We have much new information to submit for publication after peer review.
[It turns out that Greenland sharks are bizarre]
How so? If by bizarre the author means different or unusual, this is also the case for many other shark species. Then again, is there such a thing as a base model shark to which all other species are to be compared?
[… may be crucially important for the ocean ecosystem.]
Don’t all shark species contribute to ecosystem equilibrium?
[Greenland sharks only come close to the surface in places where the shallow water is frigid enough for them—primarily in the Arctic.]
This humdinger of a statement would have been excusable a decade ago. It is no secret that we’ve repeatedly dived with Greenland sharks only five hours from Quebec City and in water temperatures well above 10°C. Some of the sharks we have tagged even swam all the way to the surface in water temperatures reaching 16°C¹.
[They are most easily seen around Greenland and Iceland]
That’s true if you don’t mind catching them on hook and line and hauling them to the surface from depths in the hundreds of metres. To this day, most natural encounters with the Greenland shark—where the shark initiates contact—have actually taken place nearly 2,000 km south of the Arctic Circle in Baie-Comeau, Québec.
[The obvious way to see a Greenland shark in the wild is to dive into the deep sea.]
Obvious? Only a handful of sleeper sharks have ever been observed by submersibles or ROVs, while hundreds of observations have been made at shallow depths by scuba divers in Baie-Comeau.
[So what are all these Greenland sharks eating? To find out, scientists have to get their hands dirty—by cutting open the sharks’ stomachs and pulling out the remains of their meals.]
The author neglected to mention that much of the stomach contents come from decades-old sharks that are killed to essentially reveal the same dietary information. Why does one need to destroy such long-lived and slow-reproducing animals when so much easily obtainable by-catch is readily available? Our own necropsies conducted on by-catch and beached carcasses have led to the same results, minus the prey species that aren’t found in both regions (Arctic and St. Lawrence).
[… scientific literature on the sharks is “contaminated” with unsubstantiated claims]
Some of the scientific literature on the Greenland shark is indeed contaminated with dubious claims. However, these ideas were plausible based on the knowledge and methodology available at the time of publication, which was not the case with some parts of the BBC story.
[Large numbers of dead seals with “corkscrew” wounds have been recovered at Sable Island off the coast of Nova Scotia.][“We’re thinking those are Greenland shark bites,”]
The Corkscrew Killer theory was ruled out years ago by scientists on both sides of the Atlantic. The mere fact that the so-called bites have occurred at only two locations, one of which is by no means a Greenland shark hotspot, should have been enough to put this half-baked idea to rest. Also, since the verb ‘think’ should not be used in the continuous form when it refers to an opinion, the above statement would imply that the scientist’s thoughts were momentary and speculative. Therefore, this should not have been mentioned in an article claiming to report “The Truth About Animals.” More info: Who is the Corkscrew Killer?
[A small number of Greenlands do get caught, to supply demand for an Icelandic delicacy called hákarl, or fermented shark.]
We have twice visited the largest producer of hákarl in Iceland (Bjarnarhöfn Shark Museum) and the owners have made it clear that the sharks used to produce hákarl in Iceland are imported by-catch from Greenland, i.e. most of the sharks are caught accidentally by ships based in Nuuk.
[Perhaps its most dramatic effect is the rapid retreat of the Arctic sea ice, particularly in the summer. What will that mean for the sharks?] [All we can say for sure is that the Greenland sharks will be living in a very different Arctic in a few decades’ time.]
Although global warming will wreak havoc with the Arctic environment and wildlife, the effects of climate change may or may not have much impact on the Greenland shark. In a few decades, its Arctic habitat may actually be akin to the present-day St. Lawrence where the Greenland shark is apparently doing fine in spite of warmer and mostly ice-free conditions, centuries of intense fishing and hunting of its prey species, as well as by-catch—of sharks—and pollution. If one wants to learn how the Greenland shark will survive in the warming Arctic, perhaps now would be a good time to further study the St. Lawrence population…
[… you’ve probably never heard of them.]
This is why it is unfortunate that so much of the online information on the Greenland shark that is available today, including the above-mentioned story, will continue to inadvertently disinform those that don’t scrutinise mainstream publications such as the BBC.
¹ Gallant, Jeffrey J., Marco A. Rodríguez, Michael J. W. Stokesbury, and Chris Harvey-Clark. 2016. Influence of environmental variables on the diel movements of the Greenland Shark (Somniosus microcephalus) in the St. Lawrence Estuary. Canadian Field-Naturalist 130(1): 1-14.
² Harvey-Clark, Chris, Jeffrey J. Gallant, and John Batt. 2005. Vision and its relationship to novel behaviour in St. Lawrence River Greenland sharks (Somniosus microcephalus). Canadian Field-Naturalist 119(3): 355-358.
³ Stokesbury, Michael J. W., Chris Harvey-Clark, Jeffrey J. Gallant, Barbara A. Block, and Ransom A. Myers. 2005. Movement and environmental preferences of Greenland sharks (Somniosus microcephalus) electronically tagged in the St. Lawrence Estuary, Canada. Marine Biology 148: 159-165.
³ Gallant, Jeffrey J., Chris Harvey-Clark, Ransom A. Myers, and Michael J. W. Stokesbury. 2005. Sea lamprey (Petromyzon marinus) attached to a Greenland shark (Somniosus microcephalus) in the St. Lawrence Estuary, Canada. Northeastern Naturalist 13(1): 35-38.
Jeffrey Gallant, M.Sc., is the Scientific Director of the Greenland Shark and Elasmobranch Education and Research Group (GEERG). He is also the Editor-in-Chief of the Diving Almanac & Book of Records, and a contributing editor of DIVER Magazine. Jeffrey dove with his first shark, a spiny dogfish, off Halifax (Nova Scotia) in 1991.