There are many conditions that determine how and why fish change their migration pattern and expand their range and distribution. We will examine a theme that has been much discussed recently and where many have engaged in unqualified guesswork. Will climate change and the melting of ice in the Arctic Ocean lead to major fish migration northwards and into the international waters? This area of ocean covers 2.8 million km² and is twice the size of the Barents Sea.
The fish hunt for food and, providing the conditions are favourable, large fish stocks will disperse over a larger area than small fish stocks. We have seen many examples of this. The stocks of cod and haddock have grown in recent years and have dispersed over most of the Barents Sea. In autumn 2012, we observed both these species further north than the previous record.
The depth determines the distribution
The Arctic Ocean is a deep marine area, as is the case with the Norwegian Sea. Species such as cod and haddock are linked to shallow areas of the continental shelf such as the Barents Sea and the North Sea. These species are not found in the Norwegian Sea, even though there is sufficient food and good temperature conditions there. Therefore, these species will not disperse further north than the continental slope north of the Barents Sea. This means that the world record northern dispersal of cod and haddock from autumn 2012 is likely to stand. The only way these species can disperse is eastwards, but this will depend on the right temperature and favourable food conditions being present. The deep-water species Greenland halibut also lives near the seafloor and will not disperse further north than the continental slope, even though it is likely to go somewhat deeper than cod and haddock. However, the Greenland halibut has already been observed to the east past Franz Josef Land to the Kara Sea. Consequently, only species that live freely in the Arctic water masses for all or part of their lives, such as capelin and redfish, have the potential to migrate into the actual Arctic Ocean.
Temperature and food supply
The majority of species prefer to live in water masses with temperatures within a certain range. Even though more species can live in temperatures of down to nearly 0 °C for shorter periods, and some Arctic species such as Polar cod (Boreogadus saida) right down to the freezing point for seawater (-1.8° C), the majority of species prefer water masses with temperatures of above 0o C. It is also important that food is present, whether it is plankton or fish, such as capelin. Incidentally, capelin is the pelagic species with the greatest potential to migrate into the Arctic Ocean to graze. However, in recent years the distribution of this species has also stopped at the continental shelf towards the Arctic Ocean, even when the ice has retreated northwards. There are probably many reasons for this. First and foremost the distribution during the grazing season will be controlled by where there is the greatest abundance of the nutritious food the capelin needs. The actual distance to the spawning grounds also limits how far north the capelin can graze. There must therefore be a change in the actual migration pattern, with new spawning and nursery grounds, and this is unlikely unless the living conditions for capelin in the Barents Sea were to become unsuitable. Particularly in fish such as capelin, it will take a lot for the spawning to be moved to new areas because the fish spawn on the seafloor and rely on spawning grounds with suitable bottoms (shingle and gravel) and strong currents.
However, if commercial species are discovered in the Arctic Ocean, will there be interest in fishing there? This will depend on whether the fish are in national or international waters. Providing one is within the areas of national jurisdiction, the same resource management conditions apply for the Arctic Ocean as for the Barents Sea. This would mean that only the current actors can fish and only within the current quotas. Most of the current fishing activity takes place in the southern part of the Barents Sea, even though cod and haddock have migrated to record northerly levels during the late summer. There is little reason to go all the way to the Arctic Ocean to fish if it is possible to catch the same fish further south. If the fish migrate into international waters the situation can become different because new international actors may find it of interest to fish a resource that they do not have access to in other places. This would also require there to be fish of commercial interest there, and that is unlikely.
Why meddle with the Arctic Ocean?
The Arctic Ocean is one of the least known marine areas because the ice conditions have made it relatively inaccessible. When it is now opening up more during summer, it will be easier to map the ocean’s physical, chemical and biological conditions. The species composition of both phytoplankton and zooplankton is critical for possible migration of pelagic species into the Arctic Ocean. It is therefore important to follow the development in these plant and animal communities so it is easier to document possible feeding migration of fish into the area. Other elements of importance are how the ecosystems in the Arctic Ocean and the northern Barents Sea are influenced by sea pollution, shipping, petroleum activities, and introduced species in connection with increasing ice-free areas. The Institute of Marine Research has the chief responsibility for advising Norwegian authorities about the development in the marine ecosystems and is taking the exploration of the Arctic Ocean seriously.