How Long Do Greenland Sharks Live?

Greenland sharks have long been thought to live for an unusually long time. Researchers lacked a reliable method for measuring their age. In many other shark species, age can be estimated from layered growth marks on fin spines or the backbone. These marks are similar to the annual rings of a tree. Greenland sharks do not have fin spines, and their bodies contain no hard tissues. Their backbones remain too soft to produce readable growth marks. For a time, scientists used only two known facts to estimate age. The animals add less than 1 centimeter of length each year and can grow larger than 6 meters.

Newer techniques have made it possible to estimate age with radiocarbon dating. Certain proteins inside the eye form before the shark is born. They remain chemically stable throughout life, like a fossil sealed in amber. Researchers found that dating those proteins can give an age estimate. In one study of sharks taken accidentally in fishing gear, the biggest was a female 5 meters long. Scientists placed her age in a range of 272 to 512 years. Radiocarbon results give ranges rather than exact ages, and more precise figures may appear later. Even the lower estimate of 272 years would make the Greenland shark the vertebrate with the longest known lifespan.

One proposed explanation is an extremely slow metabolism, the rate at which the body uses energy. This slow rate suits the cold, deep habitats that the species occupies. A remotely operated vehicle from NOAA recorded a Greenland shark at 783 meters on a dive off New England. The species is known to reach depths of 2,200 meters. It is also the only shark able to live all year in the freezing waters of the Arctic Ocean. That low metabolic rate may explain the animal's gradual growth, delayed aging, and slow swimming. Its maximum speed does not exceed 2.9 kilometers per hour. Because growth is so gradual, they are not thought to reach sexual maturity until they are more than 100 years old.

Taking mature individuals out of the water can therefore affect the population and its ecosystem for many decades. Greenland sharks were once targeted for the oil in their livers. Today most of those that appear in nets and on lines are caught by accident. Lowering accidental catch is considered essential for protecting this unusual species.

Why can catching one mature Greenland shark affect the species for many decades?