When you think of a shark, what usually comes to your mind? Big teeth and the beach, right? Well, that’s not how the Greenland shark likes to live at all. Like the name denotes, this shark prefers cold waters and depths that would kill most sharks and people. The Greenland shark is mostly restricted to the waters of the far North Atlantic Ocean and the Arctic Ocean, which range from 34 – 68 degrees Fahrenheit. The Greenland shark has also been recorded diving down to depths ranging from 0 – 4000 feet. To put that in perspective, that’s equal to 3.2 Empire State Buildings stacked on top of each other!
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| Picture of a Greenland shark in the Admiralty Inlet, Nunavut. Image by Hemming 1952 at Wikimedia Commons. |
The Greenland shark is able to survive in this harsh environment because of the shark's high levels of nitrogenous waste products (any metabolic waste product that contains nitrogen) in their tissues. The nitrogenous waste products that are found in the Greenland shark are urea and trimethylamine N-oxide (TMAO). These chemicals help the shark maintain their osmotic balance (the movement of water across cells) in this very salty environment. This osmotic balance is important for the body to function and keep water and salt in balance in the cells.
TMAO and urea act as a type of anti-freeze that keeps the cells from freezing and developing ice crystals. The TMAO and urea work by preventing ice crystals from forming in the shark’s cells. They work by lowering the freezing point of water in the cells and by binding to ice crystals and preventing them from forming or growing. This protects the cells from denaturing due to the extreme pressure from the depths the shark dives at. If there were no TMAO and urea in the shark, then ice crystals could form and break cell walls, which could result in tissue and organ damage, then death.
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| This figure shows how TMAO and urea bind to the shark's protein and keep ice crystals from growing and forming. This prevents the protein from denaturing and ultimately killing the shark. Image by Emily Masterton. |
While these chemicals are great for the Greenland shark, they are bad news for anyone or thing who decides to eat them. TMAO and urea are very toxic. The Greenland shark has the most toxic skin among all sharks and even made it to the Guinness World Records in 2013 for this level of toxicity. If you were to eat the skin of a Greenland shark without preparing it right, you will have symptoms similar to being extremely drunk.
Greenland shark meat is eaten in Iceland in a dish called Hákarl. The shark’s meat must be prepared a certain way so that the TMAO and urea are no longer present in the meat. This is done by fermenting the meat and then drying it for 4-5 months. Once it has been dried and is ready to eat, it is often served in cubes on toothpicks in small servings.
Although these extreme conditions would kill any human being or another shark, the Greenland shark is able to survive and thrive in these conditions, thanks to the chemicals TMAO and urea. These chemicals keep ice crystals from forming in the cells of the shark and ultimately keep the shark alive. There are 465 species of sharks in the ocean, but only one can call the harsh North Atlantic Ocean and Arctic Ocean its home.
References
• Farrell, Anthony Peter, et al. Physiology of elasmobranch fishes: internal processes. Academic Press/Elsevier, 2016
• Strøksnes, Morten. “My Hunt for the 400-Year-Old Shark Whose Flesh Gets You High.” Vice, 30 June 2017
• O’Connor, M. R. “The Strange and Gruesome Story of the Greenland Shark, the Longest-Living Vertebrate on Earth.” The New Yorker, The New Yorker, 15 Feb. 2018
• “The Greenland Shark: An Icy Mystery.” Greenland Shark | Sharkopedia Sharkopedia
• Polar Seas: Greenland Shark
And it tastes exactly like one would expect putrified shark to taste. I find it fascinating that Icelandic people were patient and tenacious enough to keep improving the fermentation process until they quit killing the taste testers! I guess when food is scarce...
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