The waters around Iceland and Greenland contain sharks that are thought to have been hunting there at the start of the French Revolution in 1789 – 230 years ago. This hypothesis emerged from a study conducted in 2016 in which researchers determined the age of 28 Greenland sharks (Somniosus microcephalus). The oldest female, which was 5.02 metres long, was found to be at least 272 years old but could have been as old as 512. It was impossible to pinpoint her age more precisely, because Greenland sharks are cartilaginous fish and hence have no bony vertebrae or fin spines whose growth rings the researchers could have counted. Instead, the scientists had to look at the sharks’ optical lenses, which are formed at the embryonic stage, and use radiocarbon dating to measure the carbon isotope content. The findings made headlines, because no other vertebrate is known to live as long as these giants of the Arctic Ocean.
Greenland sharks are very rarely seen in the wild. They are predators that prefer regions in which water temperatures are below five degrees Celsius; on their search for carcasses or living prey they roam the coastal waters and deep seas of the Arctic and North Atlantic. To save energy, though, they meander through the Arctic waters at a sluggish pace, swimming at an average speed of 30 centimetres per second (1.08 km/h). They are thus significantly slower than most other sharks, but this does not deter them from hunting fish, seals and beluga whales. The animals reach sexual maturity at the age of 156 (± 22). Their young hatch from the egg while still inside the mother’s body; at birth they are thought to be about 40 centimetres long. Since they grow at a rate of less than a centimetre a year, one can only speculate on the age of the Greenland sharks up to 7.3 metres long that have been caught in the past. This is still the figure that scientists quote as the maximum length of this relatively unknown denizen of the deep.
fig. 4.25 > Record-breaking fish: Greenland sharks live for hundreds of years.