Have you ever met a creature more than a century old? Can you imagine spotting an animal that has lived for hundreds of years? Scientists have known Greenland sharks (Somniosus microcephalus) to be long-lived and to grow only a centimeter annually.
Judging by their size later in life, they knew they are in it for the long haul.
Yet, the remote habitat and elusive nature of these giant sharks made it difficult to learn more about them, including how long they live
According to Steven Campana, a shark expert from the University of Iceland, “fish biologists have tried to determine the age and longevity of Greenland sharks for decades, but without success’”, adding that it is “almost unbelievable that we didn’t know whether the shark lives for 20 years, or for 1000 years.”
The shark found by researchers in the Arctic is believed to have lived at least 272 years, which makes it the oldest living vertebrate animal on the planet! The lifespan of the female Greenland shark outpaces all of the oldest living animals found.
According to the lead author of the research from the University of Copenhagen, Julius Nielsen, before this discovery, the oldest vertebrate animal was the bowhead whale found to live up to a little over 200 years old.
Nielson’s team set out to discover the age of a set of 28 different female Greenland sharks caught during scientific surveys between 2010 and 2013 and published their findings in the academic journal Science.
Their research was the first genuinely solid evidence of the longevity of sharks, with Nielsen explaining that their success was because they “had young and old animals, medium-sized and large animals, and we could compare them all.”
After a few hundred years of living, this Greenland shark was about 5 meters long. Nielsen said that they expected the animals to be very-long-lived, but they were too surprised to discover the range of their lifespan.
He added that “this creature is extraordinary and it should be considered among the absolute oldest animals in the world.”
Biologists normally assess the age of fish by counting the growth layers of calcium carbonates in their ears, but as sharks lack them, the team examined the lenses in the eyes.
The Guardian explained:
“The lens of the eye is made of proteins that build up over time, with the proteins at the very center of the lens laid down while the shark is developing in its mother’s womb. Work out the date of these proteins, the scientists say, and it is possible to achieve an estimate of the shark’s age.
In order to determine when the proteins were laid down, the scientists turned to radiocarbon dating – a method that relies on determining within a material the levels of a type of carbon, known as carbon-14, that undergoes radioactive decay over time. By applying this technique to the proteins at the center of each lens, the scientists deduced a broad range of ages for each shark.”
Researchers then used a side-effect of atomic bomb tests that occurred in the 1950s. Once the bombs were detonated, they raised the levels of carbon-14 in the atmosphere, and within the next decade, the spike in carbon-14 entered the marine food web across the North Atlantic.
According to their findings, the largest shark of the group was most likely around 392 years old, with Nielsen stating that it “ is now the best candidate for the longest living vertebrate animal.”
Yet, he emphasized that the range of possible ages stretches from 272 to 512 years.
Researchers have also concluded that an adult female Greenland sharks hit sexual maturity only when she has reached over four meters in length, so she can produce offspring at around the age of 150.
This is their conclusion:
“Radiocarbon dating of eye lens nuclei from 28 female Greenland sharks (81 to 502 cm in total length) revealed a life span of at least 272 years. Only the smallest sharks (220 cm or less) showed signs of the radiocarbon bomb pulse, a time marker of the early 1960s.
The age ranges of prebomb sharks (reported as midpoint and extent of the 95.4% probability range) revealed the age at sexual maturity to be at least 156 ± 22 years, and the largest animal (502 cm) to be 392 ± 120 years old. Our results show that the Greenland shark is the longest-lived vertebrate known, and they raise concerns about species conservation.”
Yet, not all scientists believe that Greenland sharks can live for multiple centuries.
Clive Trueman, associate professor in marine ecology at the University of Southampton, said:
“I am convinced by the idea of there being long lifespans for these kinds of sharks, [but] I take the absolute numbers with a pinch of salt.”
Therefore, Nielsen is looking forward to further research, to raise awareness and conservation efforts of sharks, as, “there are other aspects of their biology which are super-interesting to know more about and to shed light upon.”
Aaron Fisk, an ecologist at the University of Windsor, agreed that the longevity of these sharks is remarkable, so the public should recognize “ how important that is with regard to how we manage and conserve the Arctic and deepwater ecosystems.”