ONLINE EXCLUSIVE – The Greenland Shark: The Longest Living Vertebrate
The Greenland shark has a life expectancy of up to 400 years; following a recent study in Science where 28 sharks were caught, three individuals were found to be over 300 years old. Just to put this into perspective, some of these sharks will have been alive when Benjamin Franklin first invented the lightning rod! This makes them the oldest known living vertebrate species currently living on the planet, surpassing sea turtles, tortoises and bowhead whales (all of which have been found to live between 100-200 years). Because of the near freezing temperatures in which they survive, the Greenland shark grows at a rate of only 1cm a year and takes roughly 150 years to reach sexual maturity. Talk about being a late bloomer!
These Arctic predators can grow in excess of five metres and travel at tediously-slow speeds of up to 2.2 mph. So how do these sharks even catch their prey? Samples taken from the stomachs of the Greenland sharks indicate that they will literally eat anything that remotely looks like food, such as rotten carcasses, seals (which have been caught off-guard) and with one report even finding pieces of moose hide. Previously these sharks have been thought to have been bound mainly around Arctic regions, however several remotely-operated vehicles (RAVs) have observed these sharks in the Gulf of Mexico and off the coast of Florida at depths of 2,600 metres! It seems that they will migrate (slowly) to anywhere where there is food and colder waters.
However, researchers have found that some of these sharks who reside in the waters off the coast of Svalbard contain large quantities of chemical pollutants in their bodies (as well as rubbish which has been thrown into the water). Svalbard’s location exposes the area to contaminants from both Europe and North America. Biologists from the Norwegian University of Science and Technology (NTNU) have determined that the high level of contaminants in the Greenland shark’s liver is due to the high amount of seal within their diet. This occurs as a result of bioaccumulation, by which pollutants are ingested at the very bottom of the food chain and accumulate in higher concentrations you move up the food chain. This is also found with polar bears, a species which was previously renowned for containing high levels of pollutants, however these sharks exhibit even higher concentrations! So why is this? One could argue that the polar bear’s diet relies primarily on seal meat. Another theory is that due to the shark’s low metabolism, they cannot excrete these chemicals quickly enough, leading to an accumulation over decades of feeding.
Not a huge amount is known about these creatures, due to their elusive nature but their ability to deal with increasing levels of foreign chemicals within their body may seriously affect their huge lifespan.
Nielsen, J., Hedeholm, R.B., Heinemeier, J., Bushnell, P.G., Christiansen, J.S., Olsen, J., Ramsey, C.B., Brill, R.W., Simon, M., Steffensen, K.F. and Steffensen, J.F., 2016. Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Somniosus microcephalus). Science, 353(6300), pp.702-704.
The Norwegian University of Science and Technology (NTNU). (2014, April 11). Sharks contain more pollutants than polar bears. ScienceDaily. Retrieved February 6, 2017 from www.sciencedaily.com/releases/2014/04/140411091417.htm
(Image courtesy of NOAA OKEANOS Explorer Program, 2013 Northeast US Canyons Expedition)