Grey, plump and growing to lengths of around five metres, the Greenland shark is one of the world’s largest carnivores. With a reported growth rate of less than one centimetre a year, they were already thought to be long-lived creatures, but just how long they lived for was something of a mystery. “Fish biologists have tried to determine the age and longevity of Greenland sharks for decades, but without success.” said Steven Campana, a shark expert from the University of Iceland. “Given that this shark is the apex predator (king of the food chain) in Arctic waters, it is almost unbelievable that we didn’t know whether the shark lives for 20 years, or for 1000 years.”
via https://www.theguardian.com/environment/2016/aug/11/400-year-old-greenland-shark-is-the-oldest-vertebrate-animal