Since the 1980s the Barents Sea has gone from a situation with high fishing pressure, cold conditions and low demersal fish stock levels, to the current situation with high levels of demersal fish stocks, reduced fishing pressure and warm conditions. The current situation is unprecedented and the Barents Sea appears to be changing rapidly. The main points for 2016 are listed below:
- 2016 was a record warm year. The ice coverage of the Barents Sea in 2016 (annual mean and monthly means in March–July, November, December) was the lowest since 1951. The air and water temperature was warmer comparing to 2015 and the long-term average, and highest anomalies were observed in the east. In autumn 2016, the area of Atlantic waters (>3°С) was the largest, whereas the areas of Arctic and cold bottom waters (<0°С) were the smallest since 1965.
- The decrease in ice coverage provides improved conditions for phytoplankton production. Furthermore, the growing season (number of days with open water) has increased, and net primary production was the highest observed (based on satellite data 1998-2016, a noteworthy increase is observed in the Eastern regions.
- Mesozooplankton biomass for the entire Barents Sea during autumn 2016 was indicated to be somewhat lower than in 2015. The biomass was generally highest in the western regions, and comparatively low in the north-central and eastern areas. Zooplankton biomasses in the Central Bank and Great Bank subareas have shown declining trends since the peak in 1995. In the eastern areas, increases in abundances of small copepods, and decreases of large copepods have continued. An increasing trend in krill biomass has been observed during the last decades – and was above long-term average in 2016. Amphipods are still considered to be at a low level - although indicated to increase in 2015 and 2016. Jellyfish biomass was lower in 2016 than in 2015, and close to the long-term average.
- The Barents Sea fish stock biomass is dominated by demersal fish, notably cod, while pelagic fish is at a lower level due to the capelin collapse. The capelin biomass decreased from 2015 to 2016 by 40%, to about 0.33 million tonnes, which is well below the long-term mean. The causes of capelin decline are increased natural mortality (mainly for young age groups), and relatively low recruitment. In 2016, the highest biomass of 1-year-old polar cod ever was recorded, and it totally dominated in the stock which was estimated at 939 thousand tonnes. The 2016 polar cod estimate is the first above the long-term mean since 2010. Overlap with high concentrations of cod and increased predation pressure most likely influenced the polar cod stock decline up to 2015. The consumption of polar cod by cod increased from 2015 to 2016 and was in 2016 at the highest value since 2012.
- The cumulative biomass of demersal fish was highest in 2012–2013, and now tends to decrease. Numbers are going down faster than the biomass due to dominance of older individuals. Cod biomass stabilized at about 3 million tonnes, well above the long-term mean (1946–2016). Haddock abundance reached record levels in 2009–2012, declined from 2013, but is still at a high level. The biomass is about 1 million tonnes, twice the long-term mean (1950– 2016). So far, minor effects of low biomass of pelagic fish on growth of large cod were observed. Due to the low level of capelin, cod and other piscivores must compensate by feeding on other prey or survival, growth and reproduction will decrease. Increased predation pressure on alternative prey by the large cod stock has potential large, but unknown consequences for the Barents Sea.
- Overall there has been a decline in Arctic fish in the Barents Sea since 2004. Median catch of Arctic fish in the last three years was below the mean from 2004–2016 and the area where species from the Arctic-boreal, mainly Arctic and Arctic groups were found, decreased. The likely reason for this is the decrease in Arctic water masses in the Barents Sea.
- Benthos biomass show fluctuation, but are within the long-term mean in 2016. The distribution area of the invasive snow crab was smaller than in previous years, however the consequences and future development of this stock are un-known. The shrimp, Pandalus borealis, population was within the long- term mean and stable.
- In autumn 2016, the main groups of large whales were collocated with capelin and krill concentrations, primarily in areas south of the Spitsbergen and on the Great Bank.
- The levels of environmental pollution in the Barents Sea are generally low, and time-series recorded for the past decades show that the levels have been stable or decreasing. The levels of anthropogenic radionuclides, organic contaminants and metals in samples collected in 2015 and 2016 do not exceed threshold limits or global background levels. We do not expect adverse impact on marine organisms and stocks of commercial value in the Barents Sea from the present levels of environmental pollution.
Simplified food web for the Barents Sea (Figure: IMR)
Contributing Authors (Alphabetic):
Espen Bagøien1, Alexander Benzik2, Bjarte Bogstad1, Anatoly Chetyrkin2, Padmini Dalpadado1, Andrey Dolgov2, Elena Eriksen1, Anatoly Filin2, Harald Gjøsæter1, Elvar H. Hallfredsson1, Hilde Elise Heldal1, Edda Johannesen1, Lis Lindal Jørgensen1, Vidar Lien1, Roman Klepikovskiy2, Kjell Nedreaas1, Tatiana Prokhorova2, Irina Prokopchuk2, Dmitri Prozorkevich2, Francisco Rey1, Georg Skaret1, Hein Rune Skjoldal1, Natalia Strelkova2, Alexey Russkikh2, Alexander Trofimov2, Andrei Zhilin2
1 Intitute of Marine Research (IMR), Norway
2 Knipovich Institute of Polar Research of Marine Fisheries and Oceanography (PINRO), Russia
The remote sensing data to WGIBAR (Chapter 2.1, 3.2 - 3.3) is a contribution from the TIBIA project at IMR, Bergen, Norway. The work on phytoplankton and primary production done here is in collaboration with Professor Kevin Arrigo and Gert van Dijken from Stanford University, USA. Project VULRES reported “Barents Sea ecosystem vulnerability assessment”.