Image source: National Geographic

While the Greenland shark (Somniosus microcephalus) may not have the same fame as the great white shark, it does hold an impressive distinction: it is the longest-lived vertebrate species known to science. These remarkable sharks can live up to 400 years, surpassing the previous record holder, the bowhead whale, which can reach around 211 years. A Greenland shark alive today could have been swimming the oceans since the 1600s – more than four centuries ago!
Despite their ancient existence, the Greenland shark has recently been recognized as the longest-lived vertebrate, primarily because scientists have long struggled to determine its age. Unlike most sharks and other vertebrates, which have hard tissues such as spines that form growth rings (much like the rings inside a tree trunk), Greenland sharks lack these structures, making age estimation to be a challenge. It wasn’t until Danish scientists stumbled upon a discovery involving human corpses and some forensic ingenuity that the mystery of the shark’s age was finally solved.

Revolution in radiocarbon dating reveals remarkable longevity of Greenland shark

Jan Heinemeier, an expert in radiocarbon dating at Aarhus University, didn’t set out to study Greenland sharks, but his work dating human eye lenses would eventually help solve the mystery of the sharks’ age. Radiocarbon dating works by measuring levels of carbon-14, which fluctuate annually. Because carbon-14 levels in the lens of the eye remain stable over time, scientists can use this signature to determine an individual’s age. This method was originally used in forensics to solve crime mysteries, such as a case in Germany where frozen bodies were aged based on carbon-14 in their lenses. When marine biologist John Fleng Steffensen approached Heinemeier about applying the same technique to sharks, it was discovered that tissue from a young shark could be radiocarbon dated to approximate its age.

Why do Greenland sharks live so long?

The exact reason for the Greenland shark’s longevity remains unclear, but one likely factor is the cold temperatures of the waters they inhabit, which hover around −1.6 °C (29 °F). Cold environments can have anti-aging effects, and the shark’s low metabolic rate is also thought to contribute to its long lifespan. Scientists are investigating other factors, such as shark genes, heart function and immune systems, in hopes of uncovering secrets that could help humans live longer and healthier lives.
Due to their slow metabolism, Greenland sharks move very slowly, with an average speed of only 0.3 meters per second (about 0.76 mph), earning them the nickname “sleeping sharks”. However, they are capable of short bursts of speed when needed.

How big are Greenland sharks?

Greenland sharks are massive, growing up to 24 feet (7.3 meters) and weighing up to 2,645 pounds (1,200 kg). However, they grow at a very slow rate, gaining only about 1 centimeter in length per year. Due to their slow growth, they also reach sexual maturity at a very late age – around 150 years. So, they spend a significant part of their lives just growing and waiting to reproduce.
Interestingly, these slow-moving giants may not have the best eyesight. Many Greenland sharks have copepods (small crustaceans) attached to their eyes, which could affect their vision, although the exact effects remain uncertain.

What do Greenland sharks eat?

Greenland sharks are top predators, but they are not always hunters. While catching seals and fish, they also feed on animal carcasses such as those of polar bears or reindeer that fall through the ice. Their preference for scavenging means they don’t always have to hunt live prey.

How do they interact with people?

Greenland sharks live in deep, cold waters, making encounters with humans extremely rare. As marine biologist Steven Campana notes, these sharks are usually accidentally caught in fishing nets intended for other deep-water species. There have been no recorded attacks on humans, probably due to the sharks’ preference for deep water and their elusive nature.

What does the future hold for Greenland sharks?

The conservation status of Greenland sharks is still unclear, but evidence suggests they are not in immediate danger of extinction. According to Campana, the fact that they are still abundant in some areas implies that human activities, such as fishing, have not significantly affected their population. However, their overall abundance is likely low and more research is needed to fully understand their conservation needs.
The Greenland shark may not be as famous as its more aggressive relatives, but it is an astonishing creature with remarkable adaptations, longevity and a mysterious presence in the ocean depths.
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