Greenland sharks are best known for living in the frigid Arctic. But new research suggest they may be more widespread than previously thought in cold stretches of deep ocean around the world. Photo: Franco Banfi
Researcher Devanshi Kasana and colleagues caught this Greenland shark. This is the first record of this mysterious “sleeper shark” in the western Caribbean. PHOTO: DEVANSHI KASANA, FLORIDA INTERNATIONAL UNIVERSITY
3 August 22
Greenland sharks are believed to be the world’s longest living vertebrate. The lives of most sharks remain cloaked in mystery, and the Greenland shark is no exception - but what we’ve learned recently is extraordinary.
Over the past few decades, scientists have discovered that these ancient Arctic animals can live upwards of 400 years and are often blind due to a parasite that attaches itself to their corneas. While they mainly feed on fish and squid, they have been known to scavenge the carcasses of mammals such as horses, reindeer, and even polar bears.
The latest surprise came when scientists spotted a Greenland shark in the western Caribbean, thousands of miles from its known range, in spring 2022. Although scientists have learned to expect the unexpected when it comes to these sharks, the sighting still came as a shock.
“It was both surprising and exciting,” says Devanshi Kasana, a doctoral candidate at Florida International University who, along with a crew of Belizean fishermen, caught the shark by accident during a tiger-shark tagging expedition. Their finding was announced in July in the journal Marine Biology.
Although Kasana wasn’t able to collect a DNA sample to confirm the shark’s identity, photographs of the animal have led shark experts to believe the animal was most likely a Greenland shark. This strange sighting raises questions about the true distribution of the Greenland shark, which was once believed to be restricted to the icy waters of the North Atlantic Ocean.
The sighting occurred off the southern coast of Belize near the world’s second longest barrier reef. Kasana had sent a longline into the deep waters that lie at the edge of Glover’s Reef, a partially submerged atoll. Her goal was to catch and tag tiger sharks to study their movement and ecology. The weather on the day of the sighting was rough and the crew had been thinking about giving up. But then they went to pull in their reel.
“We immediately knew there was something heavy on the line,” says Hector Martinez, a fisherman who aids Kasana in her research. The hydraulic reel attached to the line was straining to bring its catch to the surface. After two hours of fighting, the shark finally came into view.
At first, Kasana and the crew weren’t sure what they were looking at. “When that individual came to the surface, we didn't recognize what species it was, even with our combined years of fishing experience,” she says.
She thought it might be a six-gill shark, which can be found in deep ocean waters throughout the world. She sent a picture of the shark to her Ph.D. advisor, Demian Chapman, a director at Mote Marine Laboratory & Aquarium in Florida, who said it wasn’t a six-gill. According to him, it was likely a Greenland shark.
Far from home?
These big-bodied sharks can reach 23 feet in length and weigh 1.5 tons. Although they have been known to hunt seals, fish, and squid, Greenland sharks are primarily scavengers and will feed on the remains of large mammals that find their way to the seafloor.
Scientists recently dubbed Greenland sharks the world’s longest living vertebrate. Scientists estimate they can live upwards of 400 years and in 2016 a 272-year-old individual was found off the coast of Greenland. Scientists can determine their age by radiocarbon dating the tissue at the center of their eyes, which are composed of proteins formed when the shark was first born.
Greenland sharks are the largest fish in the Arctic Ocean, as well as the only shark found there year-round. Their population levels are not well known, but they are thought to be in decline, and are considered “vulnerable” by the International Union for Conservation of Nature. Although they are sometimes spotted in shallow waters, they can live in waters 7,200 feet deep and tolerate temperatures between 28.4 to 44.6 Fahrenheit (minus 2 and 7 degrees Celsius).
Sleeper sharks, the group of sharks to which Greenland sharks belong, are adapted to cold-water environments. They move slowly to conserve energy and their tissues contain high levels of chemical compounds similar to anti-freeze that prevent ice crystals from forming. These adaptations allow them to live in even the coldest Arctic waters.
So finding one in Belize was unexpected, though sleeper sharks have been spotted near the equator a handful of times.
A documented sighting of a Greenland shark in the tropics is “incredibly valuable,” says Brynn Devine, an expert on Arctic fisheries at the conservation nonprofit Oceans North.
“We know very little about their distribution away from the poles. We are learning more about these sharks from observations like this ... but there are still some outstanding knowledge gaps on the species,” Devine says.
Though far from the Arctic, the deep sea of the Caribbean is also very cold—and apparently, more than suitable for these animals. Indeed, Kasana says, it is possible that sleeper sharks, including Greenland sharks, might inhabit deep seas around the world. But sightings such as these are scant.
“We don't know a lot about the deep sea in the Caribbean,” says Dave Ebert, a shark biologist and author of Sharks of the World. “It was fortunate this student was able to get a snapshot of this shark, otherwise we might not have known it was there.”
Although the shark Kasana and her team caught that day wasn’t the one she was after, she is glad she was able to document its presence in the area.
The Belizean government recently declared three atolls (including Glover’s Reef and the deep waters around it) as protected areas for sharks.
“We are super excited to have stumbled upon something so otherworldly,” Kasana says, adding she hopes the finding will “help in safeguarding whatever undiscovered creatures roam the waters of Glover’s.”
- AUTHOR: ANNIE ROTH
- SOURCE: NATIONAL GEOGRAPHIC