Greenland sharks have been a source of fascination due to their unusually long lifespan. Though they can live for an estimated 300 to 500 years, some can go as long as 150 years before reaching puberty. These are factors that make these unique vertebrates vulnerable as a species and primed for extinction.
According to researchers at the American Association for the Advancement Association, Greenland sharks can grow to be 16 feet long and spend most of their time swimming 2.5 miles beneath the surface.
Chris Harvey-Clark from Dalhousie University in Halifax, a marine biologist, has spent his summers since the ’90s at the St. Lawrence River in Ontario. It’s the ideal place in Canada to visit the sharks, learn more about them and Harvey-Clark is convinced that he’s spent more time with these sharks than perhaps any other researcher. Here’s what he learned.
Considering the glacial pace at which the Greenland shark grows, conventional methods of determining age don’t work. Instead, radiocarbon dating their eyes. Crystalline proteins on the lens of each eye are formed before the Greenland shark is born and experience no change throughout their life.
Though this method is the relied-upon method for determining the age of a Greenland shark, Harvey-Clark points out that there’s a 120-year margin of error in either direction. While it can be estimated to have lived as little as 272 or as long as 642 years, he says that there’s no denying a shark of this size is an “ancient creature.”
Longevity is arguably the most fascinating characteristic of the Greenland shark. While the World Health Organization estimates Harvey-Clark might live to see his 82nd birthday, it’s highly unlikely he’ll live to see 400.
The difference in biology that allows this shark to live perhaps twice as long as the Galapagos tortoises, who average 250 years, is a point of fascination for Harvey-Clark and it drives his research.
\The downside to their exceptionally long lifespan and belated puberty means that their rate of reproduction is so low they’ve placed themselves at risk of extinction. It’s also impacted how their population is tracked by researchers.
Some guesses about their population size come from Inuit communities. While fishing for halibut, occasionally a Greenland shark will show up as their bycatch. They pull up approximately 2,000 Greenland sharks a year.
Living in such low waters, deeper than most instruments can penetrate most of the time, and their slow reproductive cycle, it’s become impossible to determine just how many of these slow-growing sharks exist. It’s also made it difficult for researchers like Harvey-Clark to know just how big the Greenland shark can get.
To date, the largest Greenland shark recorded measured 6.8 meters or over 22 feet in length. And Harvey-Clark speculates that there are specimens that are even larger.
While visiting a fjord in eastern Greenland, he came across several of the sharks, each quite large in size. What he discovered is that many had clearly been “severely cannibalized” by other, larger sharks.
While on the expedition, Harvey Clark said that it’s common to find dismembered shark heads and several specimens missing large chunks of their body. Only one or two intact specimens are recovered.
Despite the disappointment from what’s recovered from the depths where the Greenland shark resides, Harvey-Clark is fascinated by what he gets to examine. From the specimens recovered, he’s astounded by the size of the bite marks. He said that some specimens would measure four meters, or 13 feet, and have bite marks that were significantly larger. This leaves him to conclude that living at the bottom of the fjord is some “monster sharks.”