The Methuselah of the deep
In the frigid, dark waters of the North Atlantic and Arctic Oceans lives the longest-living vertebrate on Earth: the Greenland shark (Somniosus microcephalus). A 2016 study published in the journal Science revealed the astonishing lifespan of this animal. Led by biologist Julius Nielsen, a research team used radiocarbon dating on the eye lenses of 28 female sharks to determine their ages. The lens proteins are formed before birth and do not change, recording the animal's life. The oldest shark in the study, a female measuring 502 centimeters (16.5 feet), was estimated to be 392 ± 120 years old. This means she could have been born as early as 1504. Even the lower end of the estimate, 272 years, makes the Greenland shark the undisputed longevity champion among vertebrates, surpassing the previous record-holder, the 211-year-old bowhead whale.
This dating method relies on a unique historical marker. Atmospheric nuclear bomb tests in the 1950s and 1960s created a "bomb pulse," a spike in radiocarbon levels that entered the marine food web. Scientists found this radiocarbon signature only in the eye lenses of the smallest, youngest sharks, confirming that any shark without it was born before the 1960s.
A life in slow motion
The secret to the Greenland shark's extreme lifespan is its incredibly slow metabolism, an adaptation to its deep, near-freezing environment where water temperatures range from -1 to 10°C. Its scientific name, Somniosus microcephalus, roughly translates to "sleepy small-head," because of its sluggish nature. It has the lowest swim speed relative to its size of any fish, cruising at an average of 0.34 meters per second. This slow metabolism extends to every aspect of its biology. The sharks grow at a rate of less than one centimeter per year.
This slow development means they reach sexual maturity at an estimated age of 156 years. These are apex predators, feeding on a variety of fish and even marine mammals like seals, which they are thought to ambush. They can grow to over 7 meters (23 feet) long and weigh more than 1,000 kilograms (2,200 pounds). Many Greenland sharks are functionally blind due to a parasitic copepod, Ommatokoita elongata, that attaches to their corneas and feeds on the eye tissue. Because the shark navigates the dark depths where sight is less important, the parasite does not seem to significantly hinder its survival.