ニシオンデンザメは何年生きるの？

Scientists had long suspected that Greenland sharks lived extremely long lives, but they had no way of finding out exactly how long. The age of other sharks can be estimated by counting growth bands on their fin spines or backbones, much like the rings of a tree. Greenland sharks, however, have no fin spines, and their backbones are too soft to form these bands. All scientists knew was that the sharks grow very slowly, less than one centimeter a year, and can reach more than six meters in length. Then a breakthrough allowed scientists to use carbon dating instead. Inside a shark's eyes are proteins that form before birth and never change, a bit like an insect preserved in amber. By carbon-dating these proteins, scientists could estimate a shark's age. One study looked at Greenland sharks that had been caught by accident in fishing nets. The largest, a five-meter female, was estimated to be between 272 and 512 years old. Carbon dating only gives an estimate, not an exact age, but even at the lower end, a lifespan of 272 years makes the Greenland shark the longest-living animal with a backbone. One theory is that the shark lives so long because of its very slow metabolism, which suits the deep, cold waters where it lives. Greenland sharks can dive as deep as 2,200 meters, and they are the only sharks that can survive in the freezing Arctic Ocean all year round. The slow metabolism may also explain why they grow slowly, age slowly and move slowly. Their top speed is less than three kilometers per hour. They are not thought to be able to breed until they are more than 100 years old, so every adult shark taken from the ocean affects the species for decades. Today, most Greenland sharks that end up in fishing nets are caught by accident, so reducing this "bycatch" is vital to protecting them.