Greenland Shark Nearly Four Hundred Years Old
The Greenland shark, a big and slow-moving deep-ocean predator that prowls the frigid waters of the Arctic and North Atlantic, can claim the distinction of being the planet's longest-living vertebrate, with a lifespan perhaps reaching about 400 years.
Its extremely sluggish growth rate, about four-tenths of an inch (one centimeter) per year, had already tipped off scientists that it lived a very long time, and research published on Thursday calculated the Greenland shark's lifespan for the first time.
Danish marine biologist Julius Nielsen said radiocarbon dating that analyzed the shark's eye lens found that the oldest of 28 sharks studied was likely about 392 years old, with 95 percent certainty of an age range between 272 and 512 years.
“Our lifespan study is based on the carbon-14 dating of Greenland shark eye lenses. As with other vertebrates, the lenses consist of a unique type of metabolically inactive tissue. Because the center of the lens does not change from the time of a shark's birth, it allows the tissue’s chemical composition to reveal a shark’s age. We use well-established radiocarbon methods, but combine them in a new way. This approach, along with the extraordinary ages for these sharks makes this study highly unusual,” said Nielsen.
Females astoundingly did not reach sexual maturation until they were at least 134 years old, Nielsen said.
The Greenland shark, up to about 18 feet (5.5 meters) long, is among the largest carnivorous sharks.
Nielsen, a University of Copenhagen doctoral student who led the study published in the journal Science, said the findings should bring this shark much-deserved respect.
"This species is completely overlooked, and only a few scientists in the world are working with this species," Nielsen said.
"Our findings show that even though the uncertainty is great that they should be considered the oldest vertebrate animal in the world," Nielsen added.
Nielsen said the vertebrate with the longest-known lifespan until now was the bowhead whale, topping 200 years.
The study marks an important milestone for the establishment of sustainable management plans for Greenland sharks. Nielsen says: “Greenland sharks are among the largest carnivorous sharks on the planet, and their role as an apex predator in the Arctic ecosystem is totally overlooked. By the thousands, they accidentally end up as by-catch across the North Atlantic and I hope that our studies can help to bring a greater focus on the Greenland shark in the future.”
Greenland sharks have a plump elongated body, round nose, relatively small dorsal fin, sandpaper-like skin and gray or blackish-brown coloration. They are slow swimmers and are nearly blind, but are capable hunters, eating fish, marine mammals and carrion.
They are known to be relatively abundant throughout the North Atlantic and Arctic, particularly from eastern Canada to western Russia. They occasionally are spotted by deep-sea robotic submarines at latitudes further south, such as in the Gulf of Mexico. They have been observed in depths down to 1.4 miles (2.2 kilometers).
"They may widely inhabit the deep sea, potentially living anywhere water temperatures are below about 5 Celsius (41 degrees Fahrenheit)," said Australian Institute of Marine Science marine biologist Aaron MacNeil, who was not involved in the study.
MacNeil said the study did an admirable job of tackling a difficult matter but questioned an element of the dating analysis and said the estimate of a roughly 392-year-old shark "seems high to me."