The most northerly shark species alive is the Greenland Shark which grows to dimensions comparable to those of the Great White Shark. The species sacrifices its sharp eye sight to a rather unusual symbiotic relationship with a bioluminescent parasite that makes the sharks eyes glow in the dark.

Greenland shark   © Paul Nicklen for National Geographic

The largest member of the dogfish family, the Greenland Shark (Somniosus microcephalus) can grow to over 6 metres in length weigh up to one tonne. Females grow to be larger than males.
This shark prefers the icy waters of the North Atlantic and will usually only ascend from the depths if the surface drops to around 0.5 degrees Celsius.

Also called the “sleeper shark,” this species is often inactive and indeed appears to be sleeping. When it is on the move this shark swims slowly through the polar sea taking up to half a minute to move its tail from one side to the other.

Life may seem to be lonely in the ocean depths, but this shark is usually found with a companion, a parasitic copepod that lives on the shark’s eye and feasts on its corneal tissue. While the shark does suffer some damage, the relationship affords benefits. The parasite is bio-luminescent. Its glow helps the shark to attract prey, similar to how a colourful fishing lure may attract fish.
Therefore, researchers assume that the Greenland Shark does not require sharp vision to search for prey, but it is also not agile and fast enough to hunt out in the open. In fact, the real survival technique of this massive predator has not yet been entirely discovered. Theories include: these animals might sit endlessly at the bottom of the sea waiting for dead prey to float down. Or it could also be waiting in the deep for small animals to get attracted to its glowing eyes. Other researchers think more experimental when suggesting the sharks sneak up on seals and snatch then from their ice holes. Maybe it is a combination of all of these theories.

The Greenland Shark has a lot of nicknames: the sleeper shark, ground shark, grey shark, gurry shark, and the Inuit name for it is Eqalussuaq. They are the most-northerly shark species currently alive, and are well adapted to life in the frigid waters.

These sharks are thought to have an extremely long lifespan — a theory was established after one shark was captured and measured twice and was found to have grown only 9 cm in 16 years. Given the slow metabolism and growth rate it may well be possible that they could live as long as several hundred years.

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