Featured Image: Julius Nielsen via Buzzfeed
By: Eva Gruber
Through radiocarbon dating, scientists have discovered the oldest vertebrates on the planet. The title previously was thought to belong to the bowhead whale, who can have an impressive lifespan at over 200 years.
But, as it turns out, Greenland sharks can live over twice as long. Individuals of the Greenland shark species (Somniosus microcephalus) have been found that are over 400 years old!
The Greenland shark is a rather mysterious species that hasn’t been studied very much. It belongs to a family of sharks known as sleeper sharks, or Somniosidae. It inhabits deep, cold waters of the North Atlantic and Arctic Ocean, often swimming deep below sea ice at an average speed of ¾ a mile an hour. Sometimes they move to the surface to regulate their temperature and to forage for prey.
One of the largest shark species alive today, adults reach sizes of up to 17 feet long, with females growing larger than males. Their growth rate is estimated to be about 1 cm a year. This is incredibly slow for such a large vertebrate. And while scientists theorized that due to their habitat and lifestyle, they were likely long-lived, it was still a complete mystery as to exactly how long they could live.
Image Credit: Jeffrey Gallant / GEERG.ca
In the study, “Eye lens radiocarbon reveals centuries of longevity in the Greenland shark” published in Science this month, researchers from the University of Copenhagen were able to reveal much of the shark’s murky natural history.
The scientists aged the sharks using nuclei from the lens of the eyes of 28 females caught as bycatch by industrial fisheries. The two largest sharks were found to be 335 and 397 years of age. They were also able to deduce that this species reaches sexual maturity at a length of around 12 feet, which takes them around 150 years!
During the 1950s nuclear bomb tests, carbon-14 levels in the atmosphere increased. This spike, or pulse, entered the marine food web and can be traced as a timestamp. The researchers used this method (as many other scientists do) to age the marine organisms.
Image Credit: Sharkopedia / Discovery
This bomb-pulse can be used to provide a mark of whether the shark was born before or after the 1950s. The largest sharks, which contained this bomb-pulse, were definitely at least 50 years old. From there the tests on the proteins of the eye lens led researchers to a range of 272 to 512 years of longevity for the female sharks sampled.
Long-lived animals are of special conservation concern, as they are slow to recover from drops in population because of lower reproductive rates. Greenland sharks are still recovering from over-fishing during World War II, when they were killed for their liver oil which provided machine lubrication before a synthetic version was invented.
In studying animal populations, scientists pay special attention to age distribution which can tell a lot about what direction the population is heading.
In the Greenland shark, it is rare to see a lot of sexually mature females (over 150 years old) or newborn pups, and there are a lot of “teenagers.” This suggests that the population is recovering from overfishing and loss of mature, breeding adults.
The fact that they live so long and take so long to breed means that this is a sensitive time for the species. Good luck to these slow-to-breed, long-living sharks!