Biomass of polar cod in the Barents Sea (Boreogadus saida)

A polar cod in natural surroundings.
Photo: Bjørn Gulliksen / University of Tromsø

The polar cod is the only strictly arctic pelagic fish species in the Barents Sea. It is adapted to Arctic water masses, with temperatures down to the freezing point. The cold water defines its available habitat. The amount of polar cod may give an indication of the conditions for an Arctic population in the Barents Sea.

What is being monitored?

Biomass of polar cod

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The figure shows the development of polar cod biomass in the Barents Sea, measured with acoustics during autumn from 1986 to 2020. There are large fluctuations in the biomass throughout the monitoring period. The most obvious explanation for the fluctuations is a combination of change in population size and change in distribution. The polar cod population has a distribution reaching further north and east than the area covered by the annual monitoring survey in the Barents Sea.

Status and trend

The estimated biomass of polar cod in the Barents Sea increased markedly in 2020. While the estimates in 2018 and 2019 showed the lowest levels since the measurements started in 1987, the 2020 estimate was among the highest in the time series. The estimate was completely dominated by 1-year-old fish. The amount of polar cod in the Barents Sea has shown a decreasing trend since 2010, but also in 2016 a sudden increase in biomass was observed due to large amounts of 1-year-olds. This increase quickly passed, and the survey in 2021 will show whether the big increase in 2021 is also a transient one.

Causal factors

It is not known why the polar cod has shown a decreasing trend in the Barents Sea over the last decade, but an explanation might be that warming of the Barents Sea has reduced available polar cod habitat within the survey coverage area (Eriksen et al. 2015; Huserbråten et al. 2019). . In addition, predation pressure from cod and marine mammals has likely been high.

Consequences

The Polar cod stock in the Barents Sea is a potential prey for cod, sea birds and seals. During periods with large stocks of important predators, like the cod, this may be important.

About the monitoring

Polar cod is monitored yearly as a part of the ecosystem cruise in the Barents Sea in the autumn.

Places and areas

The Barents Sea

Relations to other monitoring

Monitoring programme
International environmental agreements
Voluntary international cooperation
Related monitoring