The World’s Oldest Greenland Shark

The Greenland shark, Somniosus microcephalus, may not inspire the same mixture of terror and awe as the great white shark. However, this huge carnivorous fish is every bit as fascinating. This species is an official member of the sleeper shark family. It shares a close relationship with the Pacific sleeper shark and the longnose sleeper shark. The family has earned this name because of their slow swimming speeds and because they are thought to be non-aggressive.

The Greenland shark is native to the cold waters of the North Atlantic and Arctic Oceans. Greenland sharks move leisurely through the water while hunting for squid, flounder, seals, and even smaller sharks. During the summer, this shark lurks along the continental shelf. They can be found at depths of more than 7,000 feet where the water nearly drops down to freezing temperatures. In the winter, it migrates to shallow waters near the shore and congregates together with other members of the species.

What Is a Greenland Shark?

Although many people may not have heard of this species, it can sometimes grow even larger than the great white. The shark is characterized by a rounded snout, small eyes, and comparatively short fins. Greenland sharks may be able to grow up to 24 feet long and weigh upwards of 2,200 pounds. The average length is somewhere between 6.5 and 13 feet, with females generally being larger than males.

Perhaps the most remarkable fact about the Greenland sharks is that they are very slow to mature. They remain in the mother’s womb for a gestation period of eight to 18 years. At birth, they only measure about 15 to 17 inches in length. Since they grow less than an inch per year, it can take about 150 years to reach full maturity. This means multiple generations of people will have been born and died by the time this shark can even start to reproduce.

What Is the Greenland Shark’s Lifespan?

Their slow maturation process suggests they have a very long lifespan, perhaps eclipsing any other vertebrate species. Without any hard data, however, no one can really know how long they live. It has proven to be surprisingly difficult to estimate their age based on their anatomy alone. Scientists can estimate the age of most fish by observing the patterns of concentric rings on their ear bones. These are roughly analogous to the growth rings of a tree.

However, sharks are composed of softer cartilage-based tissue, which lacks these growth rings entirely. Some species, like the great white shark, have calcified tissue on the backbone that reveals their age. However, the Greenland shark has few such body parts. So researchers had no ability to directly observe their lifespan, or estimate it from their anatomy. They could only assume, based on the shark’s growth rate, that they probably lived a few hundred years. In order to properly verify the shark’s age, the scientists needed to develop other techniques.

Radiocarbon Dating

It wasn’t until about 2016 that scientists finally found a way to overcome this problem. The solution was to perform a radiocarbon test on the shark’s eye. Radiocarbon is a method of measuring the rate at which certain types of carbon atoms decay. In the process of giving off radiation, all atoms transform at a steady rate. As long as the total number of atoms remains steady, scientists can determine the age of the sample by observing the number of decayed atoms within it.

Most of the shark’s tissue is in the process of metabolizing and changing, which makes it difficult to properly date. However, proteins in the eye lens are created when the shark is still young, and they do not grow or change at any point in its life. This makes the tissue an ideal candidate for radiocarbon dating.

The Effects of Nuclear Bomb Tests

In order to perform their experiment, scientists collected eye samples from 28 Greenland sharks accidentally caught as bycatch in fishermen’s nets. Then they performed the radiocarbon dating test on the samples of eye tissue.

One interesting thing they discovered is sharks born after the 1950s had higher initial levels of heavy carbon in their eyes. This was due to the aftereffects of nuclear bomb tests filtering into the ecosystem. Scientists were able to use this information to establish more accurate estimates of growth rate and age.

The Oldest Greenland Shark?

Based on the estimates they published in the journal, Science, the researchers confirmed that the Greenland shark did indeed reach sexual maturity at around 156 years of age, give or take around 22 years. They also discovered that the oldest shark in the sample was likely somewhere between 272 and 512 years old. This would mean it was born somewhere between the years of 1501 and 1744, possibly predating Shakespeare and Queen Elizabeth I.

Ever since the study was published, there has been the occasional article or claim on the internet of a Greenland shark being exactly 512 years old. However, this is based on a misunderstanding of the study. Given some uncertainty with the radiocarbon dating process, they could not establish a more precise age, only a general range. However, even if the true age was merely 272 years, it would still be the longest-living vertebrate ever known. The Greenland shark easily beats the second oldest vertebrate, the bowhead whale, which can live around 211 years.

How Can the Greenland Shark Live So Long?

The Greenland shark has an exceptionally low resting metabolism. Animals with very low metabolisms tend to have longer lifespans. Scientists also believe that frigid underwater temperatures can activate anti-aging genes to help the sharks fight infections and repair molecular damage.

The shark’s slow swimming speed and its metabolism are also related to each other. The Greenland shark has a top speed of less than 2 mph. Animals with low metabolisms must conserve energy, which is the primary reason the shark moves so slowly.

The Conservation of Greenland Sharks

Their slow maturation and growth rate have enormous implications for their conservation. Because large numbers of Greenland sharks were killed in the early 20th century, they are still considered Vulnerable by the IUCN Red List. The number one reason for this hunting spree was that people collected their livers to create machine oil.

When synthetic oil was finally discovered, the demand for the shark liver fell, but numbers still haven’t recovered from this low point. This is because the shark pups born after World War II haven’t yet reached sexual maturity. While new threats like climate change loom on the horizon, it may take decades more for the population numbers to rise once again. In the meantime, it is possible to imagine that a Greenland shark born now may be alive well beyond the year 2300, which sounds a bit like science fiction.