Sharks! – August 12, 2020


In honor of Shark Week, today’s Science Wednesday covers one of the largest living species of shark: Somniosus microcephalus, otherwise known as the Greenland shark. This shark is comparable in size to Great Whites: growing over 6 meters and up to 1000 kilograms (though more typically 2.5 – 4 meters and 400 kg). Unlike Great Whites, they are non-confrontational and quite sluggish with an average pace of 0.3 meters/second (not even one mile per hour)! They can stay out of sight pretty easily, too, diving down to extreme depths. Researchers have recorded them diving as deep as 2,200 meters!
While most sharks are cold-blooded, this particular species prefers to stay in waters ranging from -1 to 10°C (30.2 to 50°F). They are the only known shark species that can tolerate Arctic conditions all year long. In fact, in order to protect the flesh’s enzymes and proteins against the severe cold of North Atlantic waters and high water pressure, Greenland shark flesh has trimethylamine oxide (TMAO), a neurotoxin.
So, just how old are these sharks? And how would you even figure that out? The lenses of shark eyes add new layers of tissue throughout a shark’s lifetime, much like how tree rings record the passage of time. Scientists can use something called radiocarbon dating – measuring the amounts of a particular carbon isotope absorbed by the eye lens – to determine an age. Analysis of 28 sharks from the North Atlantic indicated survival up to 400 years, with the average age being at least 272 years. They are currently the longest-living vertebrate known to science!