A new study has concluded that the Greenland shark could be the world’s longest living vertebrate animal, with a lifespan that routinely stretches across multiple centuries.
Making its home in the coldest, deepest reaches of the northern Atlantic, the Greenland shark is routinely difficult to study, as National Geographic points out. The animals are elusive by nature, and live in remote waters that make them hard to track, leaving them something of a mystery to science. Despite this fact, research has been conducted on the species, with some past findings suggesting that Greenland sharks are preternaturally long-lived.
The team behind the recent study, which was published on August 11 in the journal Science, expected to find that Greenland sharks are long-lived. According to study leader Julius Nielsen, a biologist at the University of Copenhagen, however, their findings went even further than that.
“We had an expectation that they would be very long-lived animals, but I was surprised that they turned out to be as old as they did.”
Previous research had indicated that Greenland sharks grow at a slow rate, less than half an inch per year. This suggested that the sharks would exhibit a longer lifespan when compared to other vertebrates, but measuring their longevity turned out to not be so easy. In bony fish, a type of tissue called otoliths, or ear stones, can be accurately measured to determine the animal’s lifespan. Sharks lack this tissue, however, as they are primarily cartilaginous, so the researchers had to take a different approach.
Their study encompassed 28 different Greenland sharks, ranging widely in both size and age. All of the sharks were female, and had died accidentally. This sample set, according to Nielsen, was key to the study’s findings.
The scientists were able to examine the shark’s eyes, which have a unique structure, in order to determine just how old the animals were when they met their untimely end. As a Greenland shark ages, the lens of its eye changes. New layers are added over the course of the animal’s life, and while scientists are not able to simply count these layers as one might the rings of a tree, they were able to remove them and reach the embryonic nucleus of the lens. This structure can then be analyzed chemically in an effort to estimate the shark’s age.
The team’s findings show that Greenland sharks have a maximum lifespan of at least 272 years, with some individuals likely living far longer than that. Though there is some uncertainty involved, the team believes that the largest shark in the study was 392 years old at the time of its death. They are 95 percent certain that the shark was between 272 and 512 years old.
Though it remains unclear why Greenland sharks live so long, the environment in which they make their habitat could be a major factor, according to researchers. The species lives in cold water, which could slow their metabolism, thereby causing less damage to their tissues. Their slow growth rate also contributes to a long adolescence; since the Greenland shark doesn’t reach sexual maturity until attaining a length greater than 14 feet, it would likely take them 156 years before they began to breed, as Science notes.
The team’s findings are crucial, since the Greenland shark’s full population and distribution remains unknown, as the Inquisitr has previously reported. If the animals turn out to be rare, the loss of even just a few Greenland sharks could be devastating. Their long lifespans could leave the species vulnerable, particularly if their habitat is disturbed by an increased geopolitical focus on the Arctic’s natural resources. For this reason, among others, Nielsen notes that it is important for policymakers to do what they can to protect Greenland sharks.
[Photo by NOAA Okeanos Explorer Program via Wikimedia Commons | Cropped and Resized | Public Domain]