SCIENCE

It’s no fish tale: The Greenland shark is the longest-lived vertebrate on the planet, a new study says. (Nat Geo News)

Use our lessons, media, and articles to learn more about sharks.

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit.

Discussion Ideas

• According to Nat Geo News, Greenland sharks are the longest-lived vertebrates on the planet. What is the longest-lived animal overall?
  • The longest-lived animals on Earth are probably sponges living in the frigid waters around Antarctica. These sponges are “10,000 years old and as big as a mid-size car.”
  • But wait: Some organisms are actually “biologically immortal,” meaning they don’t suffer an increasing rate of mortality as they grow old. (Unlike vampires, however, they can be killed and die due to factors such as hunting, climate change, or loss of habitat. They’re just very, very unlikely to die of old age.) Some of these weird, biologically immortal creatures include sea urchins, bristlecone pines, jellies, and lobsters.

• How did scientists estimate the age of Greenland sharks?
  • They looked deep, deep into their eyes … No, really.
    • “Greenland sharks have a unique eye structure in that the lens grows throughout an animal’s lifetime. The older an animal gets, the more layers are added to the lens. Scientists can’t count the layers as they would tree rings, but they can remove all the layers that have been added over the years until they reach the center, or the embryonic nucleus, of the lens … Scientists can analyze the chemical composition of the eye lens nucleus to estimate an animal’s age.”
      • Yes, sharks have to be dead for scientists to poke out and study their eyes like this, but rest assured, no Greenland sharks were harmed in the research. Scientists analyzed 28 female Greenland sharks accidentally killed as bycatch.

• Are Greenland sharks endangered?
  • No. Greenland sharks are “near threatened,” a status that describes a species that is likely to qualify for a threatened category in the near future, but is not threatened now. (Learn more about threatened categories with this handy chart.)

• Do Greenland sharks pose threats to humans?
  • Physically? Not really. At 6.4 meters (21 feet) and 1,000 kilograms (2,200 pounds), they’re definitely big enough to attack humans, but there are no documented incidents. There are at least two good reasons for this:
    • Greenland sharks are very, very slow-moving animals. In fact, marine biologists are somewhat puzzled at how they prey on much faster species such as fish and seals. (Although they’ve been observed feeding, Greenland sharks have never been observed actually hunting. This seems like a job for Crittercam! Here’s how Crittercam helped solve another marine mystery involving predation.)
    • Greenland sharks inhabit fairly deep waters in the Arctic Ocean basin. If you’re swimming 1,000 meters (3,280 feet) beneath the Arctic ice … you’ve got bigger problems than sharks, buddy.
  • Unthreatening, but unpleasant: Eating the uncooked flesh of Greenland sharks can make you really, really sick. The effect of consumption mimics the effect of extreme drunkenness. The meat is somewhat toxic to humans due to an abundance of trimethylamine oxide and urea—the same chemical compound that gives urine its name. (These chemicals act as antifreeze agents in the shark’s blood, preventing it from forming ice crystals in deep, cold water.)
    • FYI: The flesh can be safely consumed if it is boiled, dried into jerky, or fermented. No less an authority than Anthony Bourdain described kæstur hákarl, an Icelandic dish consisting of the cured and fermented meat of Greenland sharks, as “unspeakably nasty” and “the single worst, most disgusting and terrible tasting thing” he has ever eaten.
  • Far from a threat, Greenland sharks are an important part of Inuit myth and legend. A wonderful creation story explains the fish’s urine smell: An old Inuit woman washed her hair in urine (people still do this, due to detergent-like antibacterial properties) and dried it with a cloth. The cloth blew into the sea and became Skalugsuak, the first Greenland shark.

• OK, so do humans pose a threat to Greenland sharks?
  • Yeah, of course we do. The biggest threats to Greenland sharks are fishing, climate change, and loss of habitat.
    • Although the Greenland shark fishery is small, the sharks are very often the victims of bycatch.
    • Climate change is warming Greenland shark habitat in the Arctic. If the sharks or their prey are not able to adapt to a warmer ocean, their population may be at risk.
    • Their habitat is threatened by “many countries’ increased focus on the Arctic for fishing, oil, and other natural resources.”

TEACHERS TOOLKIT

Nat Geo: 272-Year-Old Shark Is Longest-Lived Vertebrate on Earth

The Atlantic: The Sharks That Live to 400

Nat Geo: Shark resources

(extra credit!) Science: Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Somniosus microcephalus)