“The longevity is remarkable, but I hope the public recognizes how important that is with regard to how we manage and conserve Arctic and deepwater ecosystems,” says Aaron Fisk, an ecologist at the University of Windsor who was not involved with this research. Not only is the shark sometimes caught by accident during fishing-a phenomenon called bycatch-but its habitat may be disturbed by climate change and many countries' increased focus on the Arctic for fishing, oil, and other natural resources. (See ' Slow Sharks Sneak Up on Sleeping Seals ?')

If the species is rare, the death of even one long-lived animal could be a huge loss. These results are crucial, Nielsen says, because the Greenland shark population is unknown. It's unknown why they live so long, but cold environments cause low body temperatures, which in turn means slow metabolism-and thus less damage to animals' tissues. What’s more, because female Greenland sharks are reported to reach sexual maturity at lengths greater than 13 feet (four meters), they likely would start breeding at 156 years of age. He and his colleagues determined with 95 percent certainty that the shark was between 272 and 512 years old, and it was most likely around 390. Nielsen says there is some uncertainty around that estimate. The largest shark in the study, at 16.5 feet (five meters) in length, was estimated to be approximately 392 years old. Radiocarbon dating of the 28 Greenland sharks' lens nuclei revealed a maximum life span of at least 272 years, according to the study, published August 11 in the journal Science. Scientists can analyze the chemical composition of the eye lens nucleus to estimate an animal’s age. This tissue is composed of proteins that were formed when the shark was a young pup. (See ' Rare Whales Can Live to Nearly 200, Eye Tissue Reveals.') Scientists can't count the layers as they would tree rings, but they can remove all the layers that have been added over the years until they reach the center, or the embryonic nucleus, of the lens.

The older an animal gets, the more layers are added to the lens. Greenland sharks have a unique eye structure in that the lens grows throughout an animal’s lifetime. “The secret behind the success of this study is that we had young and old animals, medium-sized and large animals, and we could compare them all,” Nielsen notes. The researchers analyzed 28 female Greenland sharks that had died accidentally during the Greenland Institute for Natural Resources’ commercial fish-monitoring program. So scientists found another way to figure out the age of Greenland sharks: looking into their eyes. ( Read more about sharks, the lords of the sea, in National Geographic magazine.) But sharks, which are made mostly of cartilage, lack this kind of hard, calcified tissue. A National Geographic researcher is startled to see a Greenland shark where none has ever been seen before-off Russia's Franz Josef Land.ĭetermining a bony fish's age can be easily done by analyzing their otoliths, or ear stones.

Half animal age