The Bjerknes Centre is a collaboration on climate research, between the University of Bergen, NORCE, the Institute of Marine Research, Nansen Environmental and Remote Sensing Centre.

Colder oceans means less and smaller fish. (Photo: Hans-Petter Fjeld, Creative Commons by sa 2.5)

Calculating future cod in the Barents Sea

The temperature of the subpolar North Atlantic is going lower. This implies decreasing cod stocks in the Barents Sea over the next five to six years, shows study.

The water in the subpolar North Atlantic takes several years to reach the Barents Sea. As the water in this region is currently colder than normal, temperatures in the Barents Sea may be expected to decrease during the coming years. Lower sea temperatures usually implies less cod. 

This prediction for the cod fisheries is presented in a new study led by Marius Årthun from the Bjerknes Centre for Climate Research and the Geophysical Institute at the University of Bergen. The study shows, for the first time, skillful long-term predictions of the Barents Sea cod stock up to seven years in advance. Such predictions of fish stocks can provide invaluable information for the management of marine resources.

– This relations between temperature and cod was known already in Nansen and Helland-Hansens time. We have tested our prediction on the last 60 years of observations, and can see that it is concurrent with the actual cod stocks, says Marius Årthun.

In the last few years the water that flows from the Atlantic Ocean through the Norwegian Sea and into the Barents Sea has been warmer than normal. Toward 2024, the water will again be cooler. Årthun’s work shows how such natural fluctuations between periods with warm and cold water in the North Atlantic influences the Barents Sea cod stock. 

Listen to our podcast (in Norwegian) with Marius Årthun here:

Going from 1-3 to 7 years of predictions

Cod is one of the most commercially important fish in the North Atlantic. In order to establish sustainable fishing quotas the International Council for Exploration of the Sea (ICES) regularly estimates cod stocks for the next one to three years. These predictions are based on knowledge about the biology of cod, environmental factors such as ocean temperature, and human impact from fishing. However, longer-term predictions have been considered difficult because of the complexity of the marine-ecosystem. 

The new study by Marius Årthun, with contributions also from the Norwegian Institute of Marine Research and the German Helmholtz-Zentrum Geestacht, strongly challenges this traditional view.

"The field of marine climate prediction is emerging as one of the huge challenges for marine researchers. To be a part of this development is exciting and rewarding," says Årthun.

"Predictions such as these will be very valuable for the management of ocean resources."

 

Reference

Årthun M, Bogstad B, Daewel U, Keenlyside NS, Sandø AB, Schrum C, Ottersen G. (2018):

Climate based multi-year predictions of the Barents Sea cod stock. PLoS ONE 13(10): e0206319.

https://doi.org/10.1371/journal.pone.0206319