Last month, an international group of researchers flocked to the Disko Island Arctic Station in western Greenland on an expedition to study the behavior and biology of the one of the world’s most mysterious fish. Three words: Greenland shark dissection. Interested? We were too ...
The expedition aimed to dig up some truths about the elusive shark, which only recently emerged from the cold, dark waters of the Arctic into the scientific limelight.
If you are particularly observant (don't worry, we missed it the first time around too) you may have noticed the shark's heart, located near its head, is still beating during the dissection. As much as we love the idea of a zombie shark, this pumping action is only a muscle spasm.
"I've observed Greenland shark hearts beating for hours even after the organ has been removed from the body," says marine biologist and team member Julius Nielsen, who assures us the animal is neither alive nor the living dead (sigh ... maybe next time).
The strange sharks are thought to live up to 200 years. But few details are known about this long life … Where do they go? What do they do? And most importantly, how are we affecting them?
"This region is an important fishing area for Greenland halibut and deep-water shrimp," Nielsen said in an expedition blog post. "The disturbing fact [is] more than 1,000 individuals are taken annually as by-catch in the commercial fishery in Greenland waters. We would like to learn as much as we can about this species so that we can better understand its impact on the Arctic ecosystem and develop a long-term sustainable management plan to secure its future".
Tagging Greenland sharks would allow the team to accomplish this goal ... but the (very cold) hard truth is it's not an easy task. The sharks are deep divers, found most commonly from 150-800 metres (492-2624 feet) deep. Combine that with the unforgiving Arctic weather and you've got one tough job to do.
"The environment is hostile," Nielsen says. "[In the Arctic], ice, hurricanes and bad infrastructure complicate even simple logistics".
To catch the deep-dwellers, the researchers turned to benthic long lines – long stretches of fishing line with periodically spaced baited hooks.
"This is the least harmful and most effective way," Nielsen explains. But there can be complications. An unexpected bout of drift ice threw a chink in the research chain when icebergs carried the long-lines far from the boat.
"We found [one] missing buoy more than two kilometres from its original position, having been dragged there by a huge iceberg that still had it in its clutches."
After four tense days on the water, the team had still not caught a single Greenland shark.
"The waiting wasn't fun," Nielsen says. "We were eager to get our satellite tags out there, which was the primary goal of the trip. But we could do nothing but wait and hope for the best ... Luckily the sharks finally found us."
The team successfully tagged 13 sharks and only one (our dissection patient) did not survive the capture and release process.
"The animal was badly bitten by another Greenland shark while on the line," Nielsen says. "By the time we brought it up, it had lost most of the blood in its body and needed to be euthanised".
This type of shark-on-shark foul play is actually quite common, and for Nielsen and the team it meant getting front-row tickets to a rare inside view of one of nature's giants.
"Although it was a shame, the dead shark gave us a valuable opportunity,” he says.
Through the dissection, they were able to take samples from the shark's organs and tissues (heart, liver, spleen, etc.), which will be analysed for contaminants that build up inside of them. Perhaps more exciting was the opportunity to dig into the animal's otherwise unreachable stomach contents, which give clues about its feeding ecology and hunting strategies.
"This particular animal was eating a lot of lumpsuckers, skates and seals," Nielsen says.
Part of the Greenland shark's claim to fame is its affinity for scarfing down bizarre prey items, like moose and polar bears. But with an estimated top swimming speed of only 2.7 kilometres per hour (1.7 mph), it's likely that the sharks are slow-going ambush hunters.
This slow lumbering continues when the sharks have been hooked by fisherman – lending to the local belief that the predators are … less than brilliant.
"Fishermen in Greenland have been catching these sharks for centuries and believe them to be lazy and stupid”, Nielsen says. "When you see three-metre-long individuals lying quietly on the surface next to the boat, it is not difficult to imagine why". (It's quite fitting, then, that the sharks' scientific name, Somniosus microcephalus, can be translated as 'sleepy little brain'.)
"Watching the Greenland sharks' behaviour leads to the conclusion that their hunting strategy is different from that normally associated with a top predator; it’s more like a crocodile's than a cheetah's," Nielsen says.
We have only just started learning about these incredible animals, but Nielsen considers the expedition a big win for Greenland shark science. Over the next six months, data from the 13 tagged sharks will be pouring in, giving the researchers information about their swimming depth, preferred water temperature and migration routes.
"Such information about Greenland sharks is extremely sparse and can make a very important contribution to avoiding negative interactions with local fishermen," he says.
You can catch updates on this and other Greenland shark expeditions here.
Research
- University Of Copenhagen
- Greenland Institute of Natural Resources
- Den Blå Planet - National Aquarium of Denmark
Sharks
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