Torpedo Below the Ice: The Greenland Shark
When we think of organisms that live for long periods of time, we often think of animals like the mighty elephant. Famed to roam the savannah for years with an array of knowledge and wisdom. The Greenland Shark may be even older, and wiser.
The Greenland Shark is found in the North Atlantic in the cold Arctic regions around Greenland and Iceland at depths up to 2200m. A member of the Family Somniosidae, Greenland Sharks (Somniosus microcephalous) can grow up to 6.4m long and are closely related to dogfish and cat sharks. There are a few, frankly remarkable, differences such as the Greenland Shark living to approximately 400 years old!
Surviving the Cold
Unlike most sharks, S. microcephalous swims slowly and has the ability to shut down some of its body processes in order to ensure its survival in the extreme cold of arctic waters, sometimes reaching as low as -2 degrees celsius. Surviving in such cold conditions is no easy task. The key is in their body tissue which contains a mixture of trimethylamine oxide (TMAO) and urea. TMAO helps to stabilise the proteins and enzymes within the sharks tissues and, when combined with urea, prevents ice crystals from forming in the sharks tissues. TMAO can also be utilised to stabilise proteins and enzymes against pressure, a handy trick when you are sitting at 2200m below the surface with a pressure of 9,700kg per cm square bearing down on you! Greenland Shark meat is extremely toxic, likely due to the high quantities of TMAO. In order to be able to eat the meat without any ill effects, it must be prepared by fermenting the meat to remove the TMAO and then dried for 4-5 months on a hook. Greenland Shark meat is a traditional delicacy for the people of Iceland, called Hakarl, its reputation is similar to that of the UK’s Marmite – you either love it or you hate it…
Hunting with a Friend
Like any predatory shark, the Greenland Shark hunts for prey in the shifting shadows of its icy labyrinth. Hunting at such depths presents a myriad of challenges that must be overcome. Even for a shark with impeccable eyesight and lightning speed, finding food would still be a challenge. Somniosus microcephalous is known to scavenge as well as hunt for prey, but they don’t let their slow and sluggish behaviour slow them down. In recent years there have been well documented reports of S. microcephalous swimming at excessive speed to catch desirable prey such as Squid and Atlantic Salmon. Something that you may find surprising is that many Greenland Sharks have been found to be hosting a seemingly annoying guest. The copepod Ommattokoita elongata is approximately 7cm long and lives parasitically on the eyes of large marine creatures. A study of 1,505 Greenland Sharks found 84.4% of individuals to have one of these parasites attached to each of its cornea. The copepod feeds on the tissue of the eye and so can greatly damage the sharks vision.
In some cases the tissue damage can be so extensive that the shark becomes totally blind. However, there is evidence to suggest that this may be a very weird symbiont relationship between the shark and the copepods. The copepods are very visible against the grey background of the shark and could have bioluminscent abilities. This suggests that the sharks may allow the copepods to attach in order to attract prey, which they can then ambush with minimal energy. A winning strategy in the cold, unforgiving arctic depths.
If it is symbiont relationship then this 400 year old, 6m long, blind creature that lives in the cold icy caverns of the arctic depths is most definitely the weirdest, wisest, wildest creature I know. A true fantasy of a childs imagination.