Scientists have revealed that Greenland sharks have taken the title of the worlds longest-living vertebrates.
A team of researchers used radiocarbon dating to find out how old 28 Greenland sharks were, and later estimated that one female had reached the ripe old age of 400. The full results of the study were published in the journal Science.
Slow-growing, slow-moving large sharks
The scientists found that the sharks grow around 1cm per year, only reaching sexual maturity around the age of 150.
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“We had our expectations that we were dealing with an unusual animal, but I think everyone doing this research was very surprised to learn the sharks were as old as they were,” said study lead author Julius Nielsen, a marine biologist from the University of Copenhagen.
Previously it was thought that the oldest vertebrate in the world was a bowhead whale found to be 211 years old. If we consider invertebrates as well, the record stretches to 507 years thanks to a clam known as Ming.
Greenland shark ages found using radiocarbon dating
Greenland sharks can grow to up to 5 meters in length, and live in the cold deep waters of the North Atlantic. Scientists thought that their slow pace of life and growth meant that they would live for a long time, but had struggled to accurately determine their age.
In some fish it is possible to determine age by looking at ear bones known as otoliths. Once they are cut into, the bones show concentric rings which can be counted just like the rings of a tree.
Sharks are more difficult to examine, but some species have calcified tissue with layers on the bones in their back. This includes the Great White shark.
“But the Greenland shark is a very, very soft shark – it has no hard body parts where growth layers are deposited. So it was believed that the age could not be investigated,” Mr Nielsen told the BBC.
As a result the team were forced to look for a novel way of aging the sharks.
“The Greenland shark’s eye lens is composed of a specialised material – and it contains proteins that are metabolically inert,” explained Mr Nielsen. “Which means after the proteins have been synthesised in the body, they are not renewed any more. So we can isolate the tissue that formed when the shark was a pup, and do radiocarbon dating.”
Population still recovering from over-fishing before WWII
Of the 28 sharks examined, the oldest was found to be between 272 and 512 years old. This is because radiocarbon dating does not come up with exact dates. Scientists estimate her age to be around 400 years old.
It is thought that Greenland sharks reach sexual maturity once they reach 4 meters in length. Data suggests that they do not achieve this size until they are around 150 years old.
Their longevity could affect conservation efforts, as it is likely the Greenland shark population is still recovering from over-fishing before World War 2.
“When you evaluate the size distribution all over the North Atlantic, it is quite rare that you see sexually mature females, and quite rare that you find newborn pups or juveniles,” Mr Nielsen explained.
“It seems most are sub-adults. That makes sense: if you have had this very high fishing pressure, all the old animals – they are not there any more. And there are not that many to give birth to new ones.
“There is, though, still a very large amount of ‘teenagers’, but it will take another 100 years for them to become sexually active.”
Fellow study author Prof Christopher Ramsey, director of Oxford Radiocarbon Accelerator Unit at the University of Oxford, claimed that using radiocarbon dating for animals was not common.
“For many animals we have other methods to determine age,” he said. “Also, the radiocarbon method is not very precise, and so is only really relevant for very long-lived species.”