It is not only Greenlanders themselves who are experiencing warmer conditions than they are used to – one of the key species in Arctic waters has also, in step with climate change, been pushed beyond its comfort zone: the polar cod is moving further north and becoming fewer in numbers – and this has major consequences for both animals and people.
This is documented in a new study published in the scientific journal ‘Arctic Science’ under the title Decline and northward shift in Arctic cod distribution associated with the changing climate around Greenland.
The study was led by researchers from the Greenland Institute of Natural Resources (GN) and DTU Aqua – and its findings have surprised the scientists:
“Our data analysis showed that the changes in the polar cod population have occurred surprisingly quickly,” says the lead author of the scientific article, Teunis Jansen, professor at DTU Aqua and GN. He explains further:
“It is linked to deteriorating conditions for the fish’s eggs and larvae, which live near the surface. The polar cod is specialised to the Arctic climate and for a life in proximity to the sea ice. Now sea temperatures have risen, sea ice has deminished, and there have been changes in the composition of zooplankton, which is the food source for polar cod larvae and juveniles.”
Climate change affects the entire ecosystem
In the new study, which draws on data from the past 30 years, climate emerges as the dominant driver behind the changes that, as Teunis Jansen explains, are causing the changes in both polar cod abundance and distribution.
The researchers have also examined catch data from Greenlandic hunters, which show that ringed seals are likewise moving northwards – polar cod is the primary food source for ringed seals, which are also closely tied to sea ice. This supports the conclusion that climate change affects the entire ecosystem as an effect cascading through the polar cod as a key species.
So, within this ecosystem, this small fish serves as a powerful illustration of how nature and life in Greenland are intricately connected – the polar cod is a key species in Arctic marine ecosystems, and its disappearance has far‑reaching consequences for other fish and for seals, and thus also for people’s hunting and fishing opportunities.
Before the sea ice began to melt and the waters warmed, Greenlandic fishers primarily caught polar cod from the ice in winter, in February–March, either just below the surface at the ice edge or down to around 40 meters.
Greenlandic fishers and hunters contribute knowledge
In their work to map the distribution of polar cod, the researchers combined traditional bottom‑trawl surveys with local knowledge from fishers and hunters in Greenland. This was done through interviews carried out by local interviewers in the participants’ mother tongue, using questionnaires developed by the researchers. One of the Greenlandic fishers explains:
“I used to fish polar cod all over the area around Ammassalik Island. I don’t anymore. But I usually still see them by the Helheim Glacier – perhaps because of the chunks of ice coming down from the glacier.”
Teunis Jansen explains that the fisher’s hypothesis about the glacier points to the possible role of glaciers as refuges, offering the cold environment that polar cod requires.
All interviewed fishers from the Ammassalik area reported that they used to catch polar cod daily for baiting longlines for Greenland halibut and redfish, for household consumption, and for feeding sled dogs. But now the polar cod has disappeared from the waters near the settlements. As a result, they no longer fish for it.
Adapted to Arctic conditions
The new study, which brings together traditional research data and local knowledge, shows overall that polar cod are becoming markedly fewer, and that the remaining part of the population is shifting northwards in both West and East Greenland.
This demonstrates the direct consequences of global warming that hits especially hard in the marine arctic ecosystem. Not only is warming occurring three to four times faster in the Arctic, but furthermore, is this pivotal species specialised for Arctic conditions. In simple terms, it requires ice‑cold environments.
For example, the species’ large buoyant eggs develop beneath the sea ice, which protects them from UV radiation and physical stress from wind‑driven waves. Polar cod even produce antifreeze proteins that protect them from freezing solid, even at extremely low temperatures in cracks within the ice.
The species’ search for ice and cold, and its northward shift in distribution around Greenland, has been under way since the early 1990s.
Now, more than 30 years later, it is clear that high‑latitude regions, including Greenland, are warming more rapidly under climate change than most other places on the planet.
The small key species, the polar cod, is therefore under significant pressure from climate change and global warming. With current greenhouse gas emissions and climate projections, all signs point to even more uncertain times ahead for the polar cod – and for the animals and hunters who ultimately depend on it.