Speck of Science 8/17/16 – The Greenland Shark abides

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Source: Ocean Treasures Memorial Library

Several news outlets this week have justifiably made a big deal about the Greenland Shark. Recent research suggests these lumbering giants are now the record holder for the longest lived vertebrates we are aware of. This knocks the Bowhead whale from first place, whose age-determination story is fascinating in its own right, bolstered by the presence of an antique eskimo harpoon point.

Often sharks have been aged through examining growth bands present in vertebrae, however Greenland sharks have softer vertebrae that make this challenging. Additionally, due to challenges in reading these rings as sharks age, as well as possible disconnects between growth rate and age, radiocarbon dating has been joining the toolbox for determining fish longevity.  This study used the method with the sharks’ eye lenses.

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These sharks may take up to 150 years to reach sexual maturity, making their population vulnerable if too many individuals are culled before reproducing. They are also bizarrely prone to parasitism by a strangely-elongate copepod (most look more shrimp or lobster-like) that attaches to their eyeball and ultimately causes a march towards blindness. Only 1% of the 1500 sharks in a study concerning infection rates were parasite-free. 85% are afflicted in both eyes. However, due to their reliance on a keen sense of smell, rather than sight, for hunting, it has been suggested that the sharks may actually benefit from the copepod acting as small visible lures that interest nearby prey. However, Dr. George Benz of Middle Tennessee State University with expertise in shark and ray parasites, doubts this theory, instead favoring the idea that Greenland sharks may instead be ambush hunters, taking their targets instead through the element of surprise.

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