Members of the species don’t hit puberty until the ripe old age of 150 years!
The life of a Greenland shark can be measured not in years, but in centuries. According to a new study published in the journal Science, it is the longest-lived vertebrate in the world, with the oldest recorded member of this species having lived for nearly 400 years.
To determine their age, the scientists focused on the eyes of 28 females collected as by-catch from scientific surveys.
"The Greenland shark's eye lens is composed of a specialized material - and it contains proteins that are metabolically inert," study lead author Julius Nielsen of the University of Copenhagen told the BBC. "Which means after the proteins have been synthesized 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."
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The method revealed, with 95 percent certainty, that the oldest female of the bunch was born between the years 1501 and 1744, and most likely during the 17th century. Nielson comments to the New York Times, “This is the first time ever anyone has made an age range of uncertainty of 240 years and they still consider it a success.”
The upper end of the age range would put Greenland sharks years beyond the purported oldest animal in the world — a 507-year-old clam named Ming.
As a time stamp to validate their age estimates, the researchers searched for signs of a spike in radiocarbon corresponding to nuclear bomb testing that took place 60 years ago. The blasts left behind a heavy isotope of carbon, which permeated the marine food web and eventually made its way into the tissues of the sharks. Only the smallest, most recently born sharks showed physical signs of that pulse.
With such long lives, it is not surprising that the researchers determined these sharks only reach sexual maturity at around 150 years old. But their prolonged abstinence may hamper the Greenland shark population’s resilience. Even now, they may still be in the process of recovering from the heavy fishing pressures they faced prior to World War ll, when their liver oil was heavily used as fuel and lubricant.
That exploitation has had lasting effects on the sharks’ population structure. As Nielson explains to the BBC, “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.”
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