Global warming is causing the ocean temperature to rise, but this increase is not evenly distributed across the globe. In our waters, the sea temperature is increasing twice as fast as the global average.
In the period 2004-2012, the seabed temperature in the Barents Sea increased by almost 1 °C. This has an impact on all organisms living in the sea.
Fish moving northwards
On May 18th this year we published an article in Nature Climate Change along with colleagues from the Institute of Marine Research, the University of Tromso and the Russian Research Institute of Marine Fisheries and Oceanography (PINRO). Each year since 2004, Norwegian and Russian marine scientists have been at sea when the summer is on the wane and the sea ice coverage in the northern Barents Sea is at its lowest. Consequently, we can demonstrate that southern fish communities are gradually moving northwards.
In this fish community we find species including cod, haddock, deepwater redfish and long rough dab. These species are major fish eaters with long migration routes. Meanwhile, the stocks are also large.
The living conditions for these fish species have improved in the northern Barents Sea, in terms of both temperature and food availability.
Problems in the north
It appears that the Arctic fish community does not cope with rising sea temperatures as well as other communities. This fish community includes species such as Greenland halibut, snailfishes, sculpins and eel pouts. Characteristic features of Arctic fish species are that they are small, stagnant and more dependent on finding their food on the seabed. As Arctic fish species have a more specialized diet, they are more vulnerable to climate change.
In addition, these species are adapted to life on the shallow shelf of the Barents Sea. Since the Arctic Ocean is much deeper, it is unlikely that these species will move further north than they currently are. However, we can find them further to the east.
Large fish and marine mammals can move reasonably quickly over large distances, while other species, such as small Arctic fish species and organisms that live on or near the seabed, are more attached to one place. Two previously separate communities are now mixing together.
The big fish species from the south will compete with the Arctic species for food, and even feed directly on these smaller fish species. The Arctic community is being pressured from two sides; the marine environment is changing as a result of the rising temperature and new competitors and predators are arriving.
It is anticipated that this could result in the disappearance of some Arctic fish species, such as the gelatinous snailfish, from our northernmost areas.
Four times as fast
Many modelling studies have indicated that climate change, particularly increased sea temperatures, will result in species and communities moving, but few studies have shown that this would occur at the rate that we are now observing.
The IPCC estimated in 2014 that marine fish species moved by about 40 km per decade. We found that the fish communities in the Barents Sea moved up to four times faster than this in the period 2004-2012.
We are now working to map the impacts of this comprehensive relocation process. Meanwhile, we are benefitting from a large cod population that is extremely viable for commercial fisheries. However, it is uncertain whether this will continue over the next few decades.
It is hoped that ecologists studying the impacts of climate change will stay ahead of the changes that occur, thus making it increasingly possible to give notice of what will happen rather than reporting what has already happened. This is a challenge given the pace of the climate changes that we are currently experiencing.