23.02.2012
RECORD DEPTH FOR A SLEEPER SHARK?
By Jeffrey Gallant, GEERG
A sleeper shark recently filmed off a Brazilian oil rig at a depth of 2,774 m (9,100 ft) may be the deepest recorded sighting of a shark of the genus Somniosus.
The shark that was originally reported as a Greenland shark was more likely the southern (Antarctic) sleeper shark. As of 2012, there are at least three large (>6m) and 15 small to medium-sized sleeper shark species of the family Somniosidae in the world. Assuming the distributions of the Greenland shark (Somniosus microcephalus) and the Pacific sleeper shark (Somniosus pacificus) extend to Brazil, 2,774 m (9,100 ft) would be a new depth record for both species.
Very little is known about the southern (Antarctic) sleeper shark (Somniosus antarcticus). Although it likely has the same depth range as the other two large sleepers, there are no records of it from such a depth. Smaller species of sleeper sharks, including the Portuguese dogfish (Centroscymnus coelolepis) are known to inhabit deeper waters up to 3,675 m.
The deepest confirmed report of a Greenland shark was 2,200 m off the coast of Georgia in 1988. However, a large sleeper shark (genus Somniosus but species unknown) was filmed swimming by an oil rig in the Gulf of Mexico at a depth of 2,700 m in 2007. Therefore, the Stena DrillMAX crew sighting at 2,774 m on February 11 appears to be the deepest reported observation of any of the three large sleeper sharks.
The pressure at that depth was 4,050 PSI (277 BAR), which is beyond the rupture point of a SCUBA tank. For the sake of comparison, the pressure inside the tires of most passenger cars is between 32 to 35 PSI.
The three large (>6m) sleeper shark species are so similar in appearance that there currently does not exist any reliable way to visually differentiate one species from the other two. The only way to positively ID any of the three species when their ranges overlap or when they are outside of their known geographical distribution, is through DNA testing.
Watch the video on YouTube: http://goo.gl/73L8l
