The longevity of the Greenland shark

How these living fossils defy time

Photo by Julius Nielsen.

This is a Greenland shark – a species that can live to be at least 250 years old. That means around the time the oldest confirmed shark was born, the world was a very different place to what it is now. Let me set the scene. 

250 years ago, in 1774, the US hadn’t yet been officially founded. Louis XV died, making way for his grandson Louis XVI to become king. English chemist Joseph Priestley published his work on the discovery of oxygen. Chinese Emperor Qianlong, the fourth emperor of the Qing dynasty, was in the early years of his six-decade-long reign. And the first sighting of the Orion nebula was documented by William Herschel. 

All while a very fresh Greenland shark was slinking about in the cold, deep ocean. Oblivious to it all. 

Despite their longevity, the Greenland shark is an extremely elusive species and so we know little about them. We do know that they live up to 2647 metres below the surface and that like many other shark species, they live a solitary life. They can be found in the Arctic and North Atlantic Ocean which makes them the northernmost shark species. They are also one of the largest, growing to a maximum of 6.4 metres.

While other vertebrates, such as the rougheye rockfish and the bowhead whale, can reach an impressive age of around 200 years, the Greenland shark is by far the longest-lived vertebrate with some estimates as high as 512 years. And exactly how they live for so long has puzzled scientists since their longevity was discovered. Until recently, that is. 

Initially, researchers assumed the secret lay in the shark’s environment and lifestyle as they inhabit some of the coldest waters on Earth at temperatures as low as -1.8 degrees Celsius. And they are known for their sluggish pace, reaching top speeds of just 1.8 mph. However, recent research suggests that the elixir is in their genetic makeup, more specifically, their metabolism. In most animals, including ourselves, metabolic activity slows down over time as part of the ageing process. The cells become less efficient at producing energy, repairing damage, and clearing out cellular waste. 

But scientists discovered that within the Greenland shark the enzyme activity doesn't change across different ages and they essentially maintain a metabolic stability whether young or old. This metabolic stability is crucial for longevity as it means the Greenland shark's cells maintain their efficiency in energy production and waste removal throughout their lives, slowing the ageing process significantly.

A Greenland shark after its release from the research ship. Photo by Julius Nielsen.

This metabolic stability is closely tied to the shark's cold environment as biochemical reactions that drive metabolism are temperature-dependent. In warmer waters, these reactions would occur more quickly, leading to a higher metabolic rate. But in the frigid depths where Greenland sharks dwell, the cold acts as a natural brake on their metabolism, helping to maintain this steady state. 

However, their cold environment isn’t why Greenland sharks are able to live so long, rather they have been able to adapt to these temperatures because of their uniquely slow metabolism. The freezing temperatures of Arctic waters¹ certainly helps at slowing their metabolism, as it would any animal who spent a lot of time in these waters. It also slows their growth rate to 1 cm per year and their sexual maturity which they don’t reach until they’re over a century old. 

Precisely how scientists determine the age of an individual is almost more remarkable.

Unlike many other shark species, Greenland sharks have no fin spines or hard tissues that form annual growth bands, such as fin spines or vertebrae. These growth bands are similar to tree rings and would normally allow scientists to estimate a shark's age. 

Instead, a team of Danish scientists found a solution in the shark's eyes from a study which initially had nothing to do with sharks of any kind. The breakthrough came from research by physicist Jan Heinemeier and his colleagues on human eye proteins called lens crystallines. They discovered that these proteins, unlike others in the body, don't change after they're formed before birth. They contain carbon-14, a radioactive form of carbon that occurs naturally in the atmosphere. Carbon-14 levels fluctuate over time, creating a unique 'signature' for each time period. The nuclear testing in the 1950s and 60s caused a particularly large spike in carbon-14 levels, known as the 'bomb pulse', which serves as a clear timestamp for dating purposes.

Heinemeier found he could use the amount of carbon-14 in the lens crystallines to determine when a person was born. This caught the attention of marine biologists John Fleng Steffensen and Julius Nielsen who realised this method could potentially be applied to Greenland sharks.

Eventually putting this method into practice, researchers went on to study 28 Greenland sharks – most of which were bycatch in fishermen’s nets. The scientists then used a mathematical model to link size with age and estimated that a 16-foot female was between 272 and 512 years old, while another was around 400 years old. This wide range is due to the difficulty in establishing background carbon-14 levels in the ocean and uncertainties about where the sharks were born, both of which affect the accuracy of the dating method. However, these findings certainly put Greenland sharks at the very top of the list for longest-living vertebrates. 

Despite their remarkable longevity and the depths at which they dwell, Greenland sharks aren't safe from human harm and can easily meet a tragic end in mere moments. Bycatch and overfishing pose the biggest threat to Greenland sharks. An abrupt end such as this for one who could outlive us all highlights the need for conservation efforts to protect this extraordinary species, and others like them, from the global threat of overfishing. 

Photo by Hussey Lab/University of Windsor.

---

Here at Beached we are building a community that can put our brains and resources together to highlight and fund solutions to the problems facing the Greenland shark and the oceans they live in. I hope you’ll join our humble community and click subscribe for free or support our work by purchasing the paid subscription.

All Beached posts are free to read but if you can we ask you to support our work through a paid subscription. These directly support the work of Beached and allow us to engage in more conversations with experts in the field of marine conservation and spend more time researching a wider breadth of topics for the newsletters. Paid subscriptions allow us to dedicate more time and effort to creating a community and provide the space for stakeholders to come together, stay abreast of each other’s work and foster improved collaboration and coordination.

One day Beached hope to donate a large percentage of the revenue from paid subscriptions to marine conservation organisations and charities to support their work too. Working together, we can reverse the degradation of our oceans. 

Amie 🐋

1. The Greenland shark is the only shark species to live here year-round