Biomass of polar cod in the Barents Sea (Boreogadus saida)
The polar cod is the only strictly pelagic fish species in the Barents Sea. It is adapted to Arctic water masses, with temperatures down to 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?
Cite these dataInstitute of Marine Research (2019). Biomass of polar cod in the Barents Sea. Environmental monitoring of Svalbard and Jan Mayen (MOSJ). URL: http://www.mosj.no/en/fauna/marine/polar-cod.html
|Biomass||10⁶ kg||Institute of Marine Research||308.8||382.8||86||207.8||127.3||381.5||594.9||609.7||540.5||426.2||487.4||400.7||839.5||1141.9||1347.8||1869.6||1377.2||871.4||1143.8||1803.3||1941.2||1230.1||1219.4||889.3||1430.5||860.5||318.9||340.5||243.2||148||939.4||357.1|
The biomass of polar cod is monitored using acoustics and trawling during the yearly Norwegian-Russian Ecosystem Cruise in the Barents Sea.
The cruise samples data along transects, typically evenly distributed over the Barents Sea, but the entire distribution area of the species is not covered in the north.
Standard methodology for biomass estimation with acoustic trawling cruises is used. This method registers acoustic signals from sonars, and allocates the different acoustic
signatures (i.e. echo strength, response to different frequencies), aided by trawling catches, to target species. The acoustic values are then converted to biomass by the use of the known back-scattering strength of the target species, meaning how much echo an average fish gives. This is length-dependent.
There are several sources of uncertainty with this method, both connected to the actual measurement, detection, interpretation, converting from acoustics to biomass and the degree of coverage. A description of this uncertainty for herring in Norwegian waters is found in Løland et al., 2007.
A fundamental prerequisite for attaining a total estimate for the stock is that the entire distribution area is covered. This is not the case for polar cod in the Barents Sea, and hence the estimate is valid only for the part of the stock present in the Barents Sea during autumn.
Sonars are calibrated before every cruise, using standard methods described in Foote et al., 1987.
Sampling in laboratory uses methods described in Mjanger et al., 2007.
Data from the Norwegian part of the Barents Sea are available in the Institute of Marine Research’s database, while data from Russian part is in PINRO’s database. Other metadata are found in the annual reports from the ecosystem survey of the Barents Sea (BESS).
Reference level and action level
There is no reference level or action limit.
Status and trend
In 2016, the biomass of polar cod increased sharply after a long period of declining. Monitoring data suggested that 1-year-olds totally dominated the biomass. However, the amount of 2-year-olds registrered in 2017 was much lower than what was expected based on the survey in 2016, and the total biomass was greatly reduced from 2016 to 2017. There were low registrations of polar cod also during the voyage in the autumn of 2018, but the area coverage in the east was considered too poor to assess the state of the stock.
The sharp increase in the biomass of polar cod from 2015 to 2016 came as a surprise, with no preceding indication of such a development and a long period of decline leading up to it. When the population level declines from 2016 to 2017, it may be caused by changes in the distribution pattern that has led part of the cod popoulation out of the survey coverage.
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