Greenland Sharks Live 400 Years or More, Making Them the Longest-Lived Vertebrates
In the 1620s, the Mayflower pilgrims landed in what is now Massachusetts, the Thirty Years War raged in Central Europe, Johannes Kepler put forth his laws of planetary motion, and the oldest-known Greenland shark was born.
While the Pilgrims, the Thirty Years War, and Johannes Kepler are enshrined in history books, the realization about the Greenland shark was just made public today in the journal Science.
To uncover the result, Julius Nielsen, a PhD student at the University of Copenhagen, along with an international team of researchers, used radiocarbon dating on the eye lens nuclei of 28 female Greenland Sharks captured between 2010 and 2013.
Crystalline proteins within the eye are formed around the time an animal is born and remain essentially unchanged for life. These proteins contain a fixed amount of Carbon-14, a radioactive isotope of Carbon that decays at a known rate. For the last few hundred years before 1960, when nuclear bomb tests doubled the amount of Carbon-14 in the atmosphere, that level remained relatively consistent. Thus, Nielsen and his colleagues measured the levels of Carbon-14 in the sharks' eye lenses and extrapolated back based on the rate of decay to determine the animals' ages.
The largest shark was determined to be 392 years old, give or take 120 years. Based on the results, the researchers also estimated that the animals might not reach sexual maturity until age 156! (Below: The graph shows the estimated birthdate for each shark. Length (TL) is on the Y-axis. Every blue "hump" corresponds to one shark and covers the range of potential birthdates.)
Greenland sharks live in the frigid waters of the North Atlantic and Arctic Oceans where they mostly feed on fish. Swimming no more than two miles per hour, the hulking beasts move slowly and grow just as slowly, just 0.5 to 1 centimeters per year. Yet they can grow to be more than six or even seven meters in length! This means there are likely even older Greenland sharks out there waiting to be aged.
"Our results show that the Greenland shark is the longest-lived vertebrate known," the researchers write. With the finding, the Greenland shark firmly passes the bowhead whale, which is estimated to live up to 211 years.
Source: Nielsen et. al. "Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Somniosus microcephalus)." Science. 12 AUGUST 2016 • VOL 353 ISSUE 6300. DOI: 10.1126/science.aaf3617
(Image: NOAA Okeanos Explorer Program)