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Makrelltokt Norskehavet

Mackerel- and ecosystem survey in the Norwegian Sea (2017).

Photo: Erlend Astad Lorentzen / Havforskningsinstituttet

The part of the ocean bounded by Norway, Iceland, Greenland and Svalbard is referred to as the Nordic Seas and consists of the Norwegian Sea, Greenland Sea and Iceland Sea. Some of the boundaries between these seas run along underwater ridges.

The Norwegian Sea alone covers an area of over 1.1 million square metres. Its average depth is 1,600 metres, including two deep basins that are up to 4,000 metres deep. The great variation in the depth of the Norwegian Sea gives rise to varied benthic fauna, including large coral reefs.

There are three main water masses in both the Norwegian Sea and Barents Sea: Atlantic waters, Arctic waters and coastal waters. Every single second, around 8 million tonnes of warm, salty water flows into the Norwegian Sea from the North Atlantic. That is eight times the flow of all of the rivers in the whole world.

The mix of water masses with different temperatures and salinities in the Norwegian Sea greatly affects the distribution of plankton and fish. There isn’t as much diversity of species, but on the other hand the species that do exist are present in great numbers.

Zooplankton such as Calanus finmarchicus and crustaceans like krill are found in great quantities, providing dinner for the fish stocks we harvest: Norwegian spring-spawning herring, blue whiting and mackerel. The Calanus finmarchicus, which is a keystone species of the ecosystem, overwinters deep in the Norwegian Sea.

The fish, meanwhile, don’t live permanently in the Norwegian Sea: they only come here on summer holiday. The mackerel have their main residence further south and west. The blue whiting mainly spawn off the west coast of Great Britain. Herring graze in the Norwegian Sea in summer, but they spawn along the Norwegian coast and mainly grow into adults in the Barents Sea.