A Greenland Shark swimming near the surface of the water

The 400-year-old shark – what will a Greenland shark born today experience as the climate changes?

A Greenland Shark swimming near the surface of the water
(c) Eric Ste Marie https://www.husseylab.com/

Nicholas Dunn, Research Postgraduate on the Science and Solutions for a Changing Planet DTP and based at the ZSL Institute of Zoology, is developing environmental DNA methods to assess the distribution of sharks and rays. In this blog, he considers climate change from the perspective of a Greenland Shark, an ancient species where individuals can live for up to 400 years.

Did you know that one of oldest animals on the planet right now is a Greenland shark? The Latin name for the Greenland Shark,  Somniosus microcephalus, roughly translates to ‘sleepy small-head’, describing their slow, listless movement and, despite measuring up to seven metres in length, their unusually small heads.

Living in the cold, dark depths of the Greenland Sea gives this species such a slow metabolism that individuals have an estimated life expectancy of at least 272 years and can live for up to 400 years. A Greenland shark born four centuries ago would have swam in a world that existed not long after the Elizabethan era, when the human population was little over half a billion. Now, with the human population nearing 8 billion and the climate changing faster than ever before, I wonder what a Greenland shark born today will experience if she survives to 400?

An uncertain future…

Over the course of our shark’s lifetime, the world is expected to experience significant upheaval. Who can predict exactly what the world will look like in 400 years? The climate in the 25th century could be too hot to sustain human life; we may have established colonies in the oceans or we may be living in harmony with the environment after fully harnessing renewable and clean energies.

In our lifetime alone, with current climate trends, sea ice in the Arctic will retreat, allowing fishing boats to  access the waters for longer each year. This means that, at the very least, in the first quarter of her life our shark will experience more fishing in her home waters, increasing her chances of being caught accidentally in trawl nets. Major disruptions to Arctic food webs are also predicted over the next century. These will impact our Greenland shark in several ways. For one, as sea ice continues to melt, there will be less opportunities for her to hunt using ice holes, and there could be less cases of terrestrial animals falling through sea ice and becoming her dinner. Warming seas could also result in other shark species expanding their ranges into her waters, leading to our shark being out-competed for food.

A Greenland Shark lying on the floor of a boat, surrounded by shrimp. It was tagged and returned to the water. (c) Stephen Long
A Greenland Shark caught in a shrimp stock assessment trawl. It was tagged and returned to the water. (c) Stephen Long

Greenland sharks are currently classified as ‘near-threatened’ in terms of its extinction risk. However, most of the key information required for an accurate status assessment, such as its current population, historical population trends and current  bycatch records are unknown. This makes it difficult to know their true conservation status without further research.

Living down at depths well below 1,500 metres, female Greenland sharks can take up to 150 years to reach maturity. This makes the species highly vulnerable to overfishing, as sharks can be killed before they have been able to reproduce. Whilst there are no longer any specific commercial fisheries for the Greenland shark, in the 1910s, Greenland caught up to 32,000 each year to meet demand for its liver oil; and in 1948, a predicted 50,000 individuals were caught in Norway. Although this indicates that, at one point, there were many thousands of Greenland sharks in the sea, there is only so much population decline a species can take – particularly given the slow development of the species. Hundreds of tons of the species are still caught accidentally by shrimp and halibut trawl fisheries around the Arctic. Needless to say, for our shark to have a chance of reaching her natural life expectancy, the fishing industry must change its methods.

Secrets of the ocean still to discover

The Greenland shark is undoubtedly one of the most weird and wonderful sharks living in the oceans. One of it’s best-known quirks is that almost every member of its population has a parasite embedded in its eye. A shrimp-like parasite, the copepod, Ommatokoita elongata, inserts itself into the eye of the shark and remains there permanently. Although this is thought to severely impair the vision of the shark, scientists believe that the shark does not rely heavily on sight for hunting. There is a theory that these copepods are bioluminescent and attract prey to the shark, though this is yet to be proven.

It’s incredible that we know so little about an animal that can grow up to seven metres long, and it demonstrates just how much there is for us to learn about marine biodiversity. Yet, as more species face extinction, climate change might be robbing us of the opportunity to uncover some of the ocean’s greatest secrets. With so much left to discover about the magnificent Greenland shark, it is difficult to truly predict how our shark will cope with huge changes to its home over the next 400 years, but if there’s anything we can do to ensure her survival, turning the tide on climate change will be the top of that list.

Scientists at ZSL have been conducting research on the impact of trawling on deep-sea habitats in Greenland since 2011, working with partners from the Greenland Institute for Natural Resources (GINR) and Sustainable Fisheries Greenland. In February 2019, they launched an interactive fishing game empowering children to save marine wildlife. Play the game here. 

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