Somniosus microcephalus, commonly referred to as the Greenland shark inhabits the northern Atlantic Ocean in temperatures ranging from -2-7°C and grow to about 6.5 meters in length. Greenland sharks are known for their sluggish nature; Inuit fishermen catch these sharks simply by trailing caribou entrails through the water and then pulling the sharks onto the ice, without any difficulties. However, caribou, polar bear and fast moving fishes and marine mammals have been found in the gut of sleeper sharks suggesting ambush predation.
Very little is known about this species simply because of the environment in which it lives. A question which has been debated about S. microcephalus is its relationship with Ommatokoita elongata. O. elongata is a pinkish-white colored copepod that is about 3 centimeters long which feeds on the cornea of Greenland sharks. Only one copepod attaches to each eye and will begin to feast on the cornea in the eye in most cases leaving the shark completely blind. A study in 1961 by Bjorn Berland showed that 84.4% of all sharks they had found had O. elongata attached to their eyes. Berland suggested that the presumed parasitic copepods actually had a mutual relationship with the sharks. The copepods could possess bioluminescent properties, attracting prey items to the shark. This would explain how fast swimming prey items ended up in the guts of S. microcephalus.
It was later determined that the copepods are not bioluminescent by George Benz, rejecting Berland’s prior hypothesis. It is possible there is still some reason such a large percentage of Greenland sharks have these parasites and have not evolved any defenses against them. However, until further notice the relationship between Somniosus microcephalus and Ommatokoita elongata has been deemed parasitic.
-“Greenland shark”. Canadian shark research laboratory. <http://www.marinebiodiversity.ca/
-Martin, R.A. Biology of sharks and rays. “Have ecosystem, will travel.” < http://www.elasmo-research.org/education/topics/lh_somniosus.htm>.