It’s 1815 and the world is rapidly changing. The eruption of Mount Tambora in Indonesia has thrown 55 million tons of sulphur dioxide hurtling 20 miles into the sky. Combining with hydroxide gas it has created a thick cloud which has wrapped itself around the world. The temperature has dropped by 2 degrees celsius and crop failures, droughts, riots and snowstorms plague the population. It is a dark and difficult time. 100 years later and once again the planet is in the throes of a global catastrophe; World War I. In the years since the volcano eruption, the world has witnessed the abolition of slavery in the British Empire in 1833, the start of the Californian gold rush in 1849, Thomas Edison’s practical light invention of 1879 and now faces another humanitarian challenge.
Whilst all of this is happening, a shape drifts through the ocean, silent and mysterious and unbeknownst to so many who walk above. It has lived through it all and will continue to survive through the sinking of the Titanic, the millennium and 9/11. It is a Greenland shark.
The Greenland shark is a slow swimming, elusive fish inhabiting the dark, freezing waters of the North Atlantic. One of the most poorly understood and studied species of shark, it’s secretive life is still being discovered, discussed and delved into.
In August 2016, scientists revealed that the Greenland shark is now thought to be the “longest living vertebrate known on Earth” taking the title from the previous record holder, a 211 year old Bowhead whale. Using the method of radiocarbon dating, researchers examined and studied 28 specimens who had sadly perished as by catch, and discovered that one female shark could have been aged between 272 and 512 years old. With the majority of sharks living to an average of between 30 and 50 years old, this unprecedented information is not only incredible but vital in the exploration of the species. But why has it not been discovered until now?
To age a shark, scientists examine the vertebrae by sectioning it and looking at the concentric bands. As the fish ages, calcified tissue forms rings on the back bones which, just like the rings of a tree, can be counted to provide an estimate of it’s age. This method works well for bony fish however the Greenland shark is soft, it has no bony structures and no deposited calcific growths. So, to counteract this problem, researchers have instead focused their attention on the eyes. The Greenland shark’s eye lenses are very unusual as they contain a special protein that builds up over time, the earliest layers having formed when the young shark was developing. By analysing by monitoring the levels of carbon affected by radioactive decay, it is possible to determine the age of the shark. Utilising various different time stamps helped to ascertain a probable age by indicating whether the shark was present during certain events. For example, the detonation of atomic bombs in the early 1960s increased the carbon levels in the ocean and so the scientists were able to work out whether the specimens studied had been born before or after this had taken place.
The resulting statistics indicated that out of the 28 animals studied, 25 of them were born prior to the early 1960s suggesting that they were over 50 years old. Further analysis involving combining this data with previously established estimations of the the species’ slow growth rate pointed to the largest of the studied sharks, a five metre long female, as being approximately 392 years old. It should be noted that the possibility of ages of this particular shark ranges from around 272 years to 512 years but nevertheless, this is an fascinating discovery and an amazing feat. Even if her age puts her at 272 years, the very bottom of the predicted age scale, she would still have been swimming in our oceans in the early 18th century. So many things were happening in the world above her and to me, it’s amazing to think that there could have been sharks who were present then and still are now.
Of course there are always doubts when it comes to research like this and further in-depth study is often required to set suggestions in stone. According to Clive Trueman, associate professor in marine ecology at the University of Southampton, for example, the fact that the central proteins in the eye lens form using nutrients passed to the pup from the mother could imply that the carbon present wasn’t in fact as a result of direct contact but came from the gestational period. The analysed shark may simply have acquired it secondarily and so perhaps is not as old as is thought. Either way, this recent information sheds light on a very poorly understood and mysterious animal and even with error, it can be presumed that this truly is the longest living vertebrate in the world.
So, what does this information mean for the Greenland shark species?
Well, it is already known that female Greenland sharks only reach sexual maturity when they reach approximately four metres in length and so this data implies that they have to be around 150 years old before being able to have young. With the species only growing around 1cm per year, this undoubtedly means that if anything was to happen to this slow growing population, it would have a devastating impact. Julius Nielson, marine biologist and the lead author of the Greenland shark longevity study, suggests that when you look at the distribution of sharks throughout the North Atlantic, in terms of size it is difficult and rare to discover juveniles, pups and even females ready for reproduction. Many of the sharks present will take another century to sexually mature which clearly implies that the heavy fishing the species suffered from prior to World War II had and it is continuing to have a significant impact. There are just not enough older animals present in the oceans to rapidly repopulate and sadly the Greenland shark currently finds it’s self on the IUCN’s “near threatened” list. Yes, of course there is possibility that there could be a larger unknown population of sharks hiding from human eyes and thriving but we cannot be sure and need to do what we can to learn more and protect them.
The Greenland shark is a unique and mysterious species, hiding in the darkest depths of the ocean ,avoiding the media spotlight. It is not a species basking in the limelight after having been awarded the title of the “World’s Longest Living Vertebrate” and there is still so much more to discover about it. We’ve all heard the quote “live fast, die young” and the Greenland shark must have decided to do the very opposite. It lives slow, drifting through the waters growing at a very restricted pace and dies old, possibly at over 400 years old. It is a truly fascinating animal and, despite the unpredictability of the data results, this recent study has inspired me to discover more about it. If this research can capture people’s imaginations and encourage further interest in such an unusual animal as well as the diversity of our ocean, then I personally believe that it’s been an success and I look forward to future results.
Image: NOAA Photo Library (2013)