In an evolutionary sense, sharks are among Earth’s oldest survivors; they’ve been roaming the oceans for more than 400 million years. But some individual sharks boast lifespans that are equally jaw-dropping. Incredibly, deepwater sharks off the coast of Greenland appear to have been alive and swimming back in Shakespeare’s day 400-plus years ago—making them the longest-lived of all known vertebrates.
Bristlecone pines can live to be 5,000 years old. Sea sponges can live for thousands of years. One quahog, a hard-shelled ocean clam, died in 2006 at the age of 507. But among vertebrates, the long-lived skew much younger. Bowhead whales and rougheye rockfish can live for up to 200 years, and a few giant tortoises may also approach the two century mark. Now it seems that Greenland sharks more than double even these remarkable lifespans, scientists report today in Science.
The reason for the sharks’ unfathomably long lives has to do with their lifestyles. Cold-blooded animals that live in cold environments often have slow metabolic rates, which are correlated with longevity. “The general rule is that deep and cold equals old, so I think a lot of people expected species like Greenland sharks to be long-lived,” says Chris Lowe, a shark biologist at the California State University at Long Beach. “But holy cow, this takes it to an entirely different level.”
Lowe, who wasn’t involved in the research, adds that Greenland sharks must have a metabolic rate “just above a rock.”
Greenland sharks spend their time in the remote, freezing depths of the Arctic and North Atlantic oceans, making it difficult for researchers to parse the details of their lifestyle and reproduction. Determining their birthdates is even harder. Until now, scientists have been thwarted in their efforts to date this elasmobranch species—a group which include sharks, skates, and rays—by the fact that the animals lack calcium-rich bones, which can be radiocarbon dated.
Faced with a dearth of calcium-rich material to date, the authors of the new study employed a creative solution: They searched the sharks’ eyes. The nucleus of the shark’s eye lens, it turns out, is made up of inert crystalline proteins that are formed when the shark is an embryo and contain some of the same isotopes used to date bones and teeth. Measuring the relative ratios of these isotopes enabled scientists to determine the year when each shark was aged zero.
Scientists examined 28 female sharks—all acquired as bycatch from commercial fisheries—to find that many seemed to have lived longer than two centuries. (Scientists discarded the youngest animals, because they showed signs of radiocarbon released by Cold War-era nuclear bomb testing.) The biggest shark of this group, which measured about 16.5 feet, was believed to be 392 years old—placing her in the era of astronomer Galileo Galilei. Yet Greenland sharks are known to grow well over 20 feet, meaning many are likely even older.