An article published in the journal “Science” describes a research on the Greenland shark (Somniosus microcephalus). An international team of marine biologists led by Julius Nielsen of the University of Copenhagen’s Department of Biology studied these sharks in collaboration with other agencies concluding that the oldest specimen studied has an estimated age of 392 years.

The Greenland shark is one of the largest sharks living today, with a size comparable to that of the white shark with a length of up to 6.4 meters (21 feet) and a weight of up to 1,000 kg (2,200 lbs). The name comes from the fact that it lives in the northernmost areas of the Atlantic Ocean and in the Arctic Ocean. It’s an apex predator at the top of its food chain whose diet consists mainly of fish.

Because of its habitat, the Greenland shark is little known but among the few information collected on this species is its very slow growth, about one centimeter (0.4 inces) a year. This feature suggests a slow metabolism and a remarkable longevity but until now specific studies were never carried out. There are fish with calcified tissues that can allow a dating but the Greenland shark has very soft cartilage so that technique can’t be used to determine a specimen’s age.

The solution came from the Greenland shark’ eye lens, a structure that keeps on growing throughout its life layer by layer. The eye lens’ core is formed by proteins that formed when the specimen was a pup and since then remained inert. This means that carbon-dating can be used, a technique typically used in archeology but also applicable to Greenland shark due to its long life.

The exams were performed on the eyes of 28 females of Greenland shark accidentally killed after being trapped in fishing nets used to catch other fish. The specimens had very diverse ages and the oldest female, about 5 meters long, died at an age estimated at 392 years. Those measurements have a certain degree of approximation so the estimate is of an age between 272 and 512 years but the highest probability is 392 years.

It was difficult to make age estimates of some Greenland sharks because of the carbon that spread into the environment during the nuclear tests conducted in the ’50s. In the youngest specimens, born after that pollution, a greater than normal amount of carbon 14 was absorbed in their eye lenses.

Another conclusion reached by the researchers regards Greenland shark females’ sexual maturity, which is estimated to be reached when they’re more than 150 years. These estimates were made by putting together the information on the length of pregnant females, which in most cases is about 4 meters (21 feet).

The Greenland shark is rarely sought because its meat is toxic and require complex treatments to become edible. However, as has happened to the specimens examined in this study, they can be killed by fishermen who are looking for other fish species.

The Greenland sharks’ physiological adaptations to their cold environment are interesting for scientists for the link with their longevity. These sharks are the most long-lived vertebrates in the world and the only animal the lives even longer is the ocean clam (Arctica islandica) with a specimen whose age was estimated at 507 years. Our knowledge of the Greenland shark is still at the beginning and the research, in particular on the secrets of its longevity, will continue.