Sure, there’s an immortal jellyfish roaming about, but we’re talking about vertebrates, here. Marine scientists in the frigid waters of the North Atlantic and Arctic oceans have discovered what’s believed to be the world’s longest-living vertebrate.
The Greenland shark (Somniosus microcephalus) laughs in the face of mortality with its lifespan of some 272 years, and scientists believe it could live up to 500 years. Not too shabby for a nearly-blind shark living in freezing waters, right?
That incredibly long lifespan makes it older than the 211-year lifespan of the bowhead whale (Balaena mysticetus), which was the previous record-holder. There also happens to be an unconfirmed tale of a female Koi carp that live for 226 years, so even if it’s true it doesn’t hold a candle to the Greenland shark.
Peter Bushnell, a marine physiologist at Indiana University South Bend and a co-author of the study, says that the longevity of the Greenland shark wasn’t news. The fish are quite large with adults measuring at more than 6 meters, and they grow slowly, which aids their longevity. A 1963 study estimated that the sharks grow less than one centimeter per year, which is pretty incredible considering how large they can get.
While scientists know the sharks can live for centuries, they do run into a bit of a snag when trying to definitely measure their age. Generally, researchers count layers of calcified tissue that grow on a fish’s scales, similarly to how you’d count the rings of a tree. But Greenland sharks have small, spineless fins. And, according to marine biologist Julius Nielsen at the University of Copenhagen, their vertebrae are too soft for countable layers to bd deposited.”
To get around these issues, the team measured levels of radioactive carbon-14 in the fibers in the center of the shark’s eye lens. Apparently, these measurements reflect levels of radiocarbon in the ocean when the lens was first formed. Some 28 female Greenland sharks were carbon dated between 2010-2013 and it was determined that the largest of the sharks was just over 5 meters long and was between 272 and 512 years old at the time.
The sharks are likely able to live so long because they don’t really expend much energy, but scientists are eager to figure out what contributes to their long lifespans. Mario Baumgart, a biologist at the Leibniz Institute on Aging in Jena, Germany, is keen to determine what molecular tricks or particular quirks the shark has up its sleeve that allow it to live so long. Nielsen agrees with Baumgart when it comes to the energy expenditure, but his curiosity is peaked by how the sharks catch their prey and where they mate.
Nor surprisingly, given how slowly they grow, female Greenland sharks don’t reach sexual maturity until they’re about 150-years-old. That means period of heavy fishing (a century or so) would be bad news bears for the species and could see them wiped out entirely. Luckily, the sharks aren’t being overfished, but they face other threats in the form of climate change, according to Aaron MacNeil, a marine biologist at the Australian Institute of Marine Science near Townsville, Queensland.
“Greenland sharks have been fished by Inuits for centuries and still there’s a lot of them right now,” MacNeil says. “In my view, the real danger is that the Arctic is quickly changing due to global warming, leading to increases in commercial fishing and bycatch that Greenland sharks may not be able to cope with.”