A Greenland Shark Living Today Could Have Been Alive in 1620

Jan Heinemeier, an expert in radiocarbon dating at Aarhus University in Denmark, didn't specifically have the Greenland shark on his radar, but he proved that you really can tell a lot about someone by their eyes.

His team was studying the crystallines — a type of protein that remains stable over time — and carbon-14 levels in the eyes of human cadavers. Since the carbon level fluctuates from year to year, each period in time has its own carbon-14 signature — allowing for radiocarbon dating to determine age using the lenses of the eyes.

But before the technique helped to age sharks, it found its way to forensics. His team got a request from police in Germany to help them solve a bizarre murder mystery. The victims had been frozen for years, so the scientists were able to use his technique on their lenses to precisely determine their ages — and thus the year of the crime.

Then when marine biologist John Fleng Steffensen reached out to Heinemeier to see if they could use radiocarbon dating on shark vertebrae, he learned about the murder case and a new approach. Isolated tissue that formed when a shark was very young could be radiocarbon dated to give scientists the new, approximate age.

One theory is that extreme cold produces anti-aging qualities, and lucky for these sharks, they hang out in water that hovers around 29 degrees Fahrenheit (-1.6 degrees Celsius). A low metabolism is also thought to be at play. But scientists don't have the full answer — yet that is. Studies are currently underway to examine the sharks' genes, heart and immune system to help solve the age-old age puzzle. And there may be a bonus — they're hoping to be able to use what they find to create immune boosting therapies for us humans.

Given the Greenland shark's need to conserve energy, they creep along at an average pace of 0.3 meters per second (0.76 mph), giving them the nickname "sleeper sharks." But don't discount their ability to attack — when truly necessary they can increase their speed in short bursts.

The massive Greenland shark can grow to be up to 24 feet (7.3 meters) long and weigh in at up to 2,645 pounds (1,200 kilograms). But they don't exactly have a teenage growth spurt. Instead they make an extremely slow, steady climb toward their final size, only growing by about 0.4 inches (1 centimeter) per year.

With that slow growth comes slow sexual maturity; they only become able to reproduce once they're around 150 years of age. Talk about a long time to wait to get some action.

And to add to their quirkiness, these slow giants might not even be able to see well. "Greenland sharks in the Arctic often have copepod (small crustacean) ectoparasites attached on or over their eyes. There is no known advantage to these parasites, and indeed, it seems likely that these parasites obscure or even block the vision of the shark," says Dr. Steven E. Campana, professor of life and environmental sciences at the University of Iceland, in an email interview.

Even though they have a coveted spot at the top of the food chain, the Greenland shark doesn't always hunt for live prey. When they do, they mostly catch seals and fish. But more than anything, they seem to enjoy living more of a scavenger lifestyle, eating animal carcasses such as a polar bear or reindeer that may have fallen through the ice.

Since the Greenland shark usually hangs out in such deep waters, it's rare to see one — at times even for scientists. As Campana shares, "There is almost no direct fishing towards Greenland sharks. Rather, they are usually caught accidentally as bycatch of fisheries for other deep-water or cold-water marine species." There haven't been any documented attacks on humans, but that may have to do with the depth of their living quarters.

While their true conservation status is unknown, professor Campana says, "The fact that Greenland shark densities remain high in some areas suggests that continued catches over the past century have not been enough to push the population into a critical decline, although they are almost certainly at low overall abundance."