A study published in the journal Science in August 2017 determined that the elusive Greenland Shark is the world’s longest-living vertebrate at 272 years old and one of the oldest animals in the world.
The sharks live in the deep of the North Atlantic Ocean and were once hunted for their liver oil but are now considered bycatch and not wanted. Much of the animals’ behaviors and habits were unknown because of where they lived and how reclusive they were, and one of the most pressing questions was how long the sharks lived.
The answer to the shark’s real age had previously been unknown. One shark had been tagged in 1936 and then recaptured in 1952, but only its change in size was measured. It wasn’t until 2016 that the shark’s exceptional longevity was finally discovered when scientists under Greenland’s fish-monitoring program were able to study 28 female shark specimens that had died accidentally.
Determining the age of the sharks was difficult. The age of other fish can be found by examining the otoliths, or ear stones of the fish, and the age of sharks is determined by counting the growth rings of the vertebrae and fin spines since they are made mostly of cartilage. Greenland sharks, however, have no hard structures in their bodies, so using these methods didn’t work to find their age. Scientists came up with another way of discovering the age of these particular sharks, and they did it by looking at the lens of the shark’s eye.
The lens of the Greenland shark grows during their life, and more layers are added on top of another as they age. Scientists removed all the layers of the lens of the eye that had grown over the years until they got to the embryonic nucleus of the lens. That was the lens of the shark when they were first born. They then radiocarbon-dated the nuclei of each shark and found that the sharks’ maximum life span was at least 272 years.
But this might not be the exact number of how long these sharks live. The dating of the lens of the sharks gave a range of the sharks’ maximum age from at least 272 years to an estimated 512 years old. The midpoint in age was around 392 years old. Scientists even discovered that these sharks might not even start breeding until they are about 156 years old.
How these sharks live so long is still unknown, but the animals’ cold habitat might allow them to have a lower metabolism, which results in less damage to their tissues over time. Of course, this is still just a theory, and the way the sharks can live so long continues to remain a mystery.
Sources: Science, National Geographic, Live Science, The New Yorker
