You may never meet your 400-year-old forefather, or anyone who sailed to your world in the Mayflower. But if you'd like to meet someone or something that lived then, you can try out the Greenland shark, a deep-sea creature that can survive for 400 years---the longest-lived vertebrate on Earth.
Scientists examined 28 female Greenland sharks, finding that the oldest of the species survived to live upto 272 and 512 years. She seemed to be almost 390 years when she was taken in by a research vessel. The next longest-lived vertebrate is aged 200 years---the bowhead whale.
But none of the other long-living animals are a match for the Greenland shark. Amazingly, though they are the oldest, they are also the least studied mammals on earth. They survive in the "cold, deep waters" of the North Atlantic. These scavengers are very slow-growing, and have been caught for their liver oil.
Still, although the earth has been the habitat of the Greenland sharks for a long time, we do not know enough about their population size, distribution, and ecology. They are dubbed as "data deficient" by Norway's conservation Red List.
"I think in general, people have overlooked the Greenland shark as this deep sea animal is of no ecological or economic importance," lead study author Julius Nielsen said. "There's never been a scientific interest. The story told to us by the Greenland shark adds another notch in the longevity scale."
This PhD student of the University of Copenhagen became fascinated by the Greenland sharks about five years back. Once his scientific vessel caught a shark, he said: "It was an amazing experience, seeing such a big animal," he said. "I started investigating what was known about the shark, and was really surprised by how little information there was."
He discovered that the shark's growth rate was "incredibly slow"---just a centimeter every year. He also found that the sharks could not grow "hard, calcified tissues that deposit in growth layers", so they did not age.
The age was discovered with radiocarbon dating of their eyelids, which are "transparent cells filled with inert, crystallized proteins." These layers of glassy cells collect on the eyelids during the shark's life. "It's basically a dead tissue," Neilsen said.
Armed with a method, Nielsen and his collaborators acquired tissue samples from 28 individual sharks caught as bycatch during the Greenland Institute of Natural Resources' annual fish surveys between 2010 and 2013. Peeling back layers of cells to access the oldest tissue, the researchers measured the abundance of carbon-14 isotopes to determine age.
Nielsen's team saw that the oldest tissue samples did not show the carbon-14 signature of nuclear weapons of the 1960s. Hence, it is clear that the sharks were more than 50 years old. "We could see right from the beginning that we were dealing with something extreme," Nielsen said.
Most of these sharks had lived through the 19th or early 20th century. A precise age could not be obtained for the largest two sharks, yet their age seemed to date back quite a lot. They seemed to be 335 ± 75 years, and 392 ± 120 years .
"The main point is that the Greenland shark is at least 272 years old, and therefore the oldest vertebrate in the world," Neilsen said. "I think this must be the first time in human history that a person has done an age determination, ended up with a range of 240 years, and still called it a success."
"This article highlights just how little science still knows about the life histories of these and other magnificent creatures," said Kevin Perrott, a scientist at the Buck Institute for Research on Aging. "It also underlines how easy it would be to remain forever ignorant and lose this resource because of climate change and environmental damage. We run the risk of forever losing the opportunity to study organisms with insight into humanity's most pressing medical challenge, the aging process."
