The air and water temperatures remained higher than average and typical of warm years, close to those in 2017. In autumn, the Atlantic waters (>3°С) covered relatively large area, but it decreased compared to 2017; the Arctic and cold bottom waters (<0°С) still covered rather small areas, the area of the former was close to that in 2017 but the area of the latter increased. Ice coverage was much lower than average and close to that in 2017. There was no ice in the sea from August to October; in December, the ice coverage was the lowest since 1951.
In August–September 2018, the area covered by warm water (above 4, 3 and 1°С at 50, 100 m and near the bottom respectively) was close to that in 2017 at 50 and 100 m, and 12% smaller at the bottom (Fig. 3.1.16). The area covered by cold water (below 0°С) was also close to that in 2017 at 50 m but 7 and 8% larger than in 2017 at 100 m and near the bottom respectively (Fig. 3.1.16). Since 2000, the area covered by cold bottom water was the largest in 2003 and rather small in 2007, 2008, 2012, 2016 and 2017; in 2016, it reached a record low value since 1965.
Sea surface temperature (SST) (http://iridl.ldeo.columbia.edu) averaged over the southwestern (71–74°N, 20–40°E) and southeastern (69–73°N, 42–55°E) Barents Sea showed that positive SST anomalies (relative to the base period of 1982–2010) prevailed in both areas during 2018 (Fig. 3.1.9). The largest positive anomalies (>2.0°C) were found in the southeast of the sea in July–September; the December SST anomaly in this area reached a record high value since 1982. The smallest positive anomalies (<0.5°C) were observed in the southwest of the sea in April, May and July, and in the southeast from March to June (Fig. 3.1.9).
The Fugløya–Bear Island Section covers the inflow of Atlantic and Coastal water masses from the Norwegian Sea to the Barents Sea, while the Kola Section covers the same waters in the southern Barents Sea. Note a difference in the calculation of the temperatures in these sections; in the Fugløya–Bear Island Section the temperature is averaged over the 50–200 m depth layer while in the Kola Section the temperature is averaged from 0 to 200 m depth.
The volume flux into the Barents Sea varies with periods of several years and was significantly lower during 1997–2002 than during 2003–2006 (Fig. 3.1.4). In 2006, the volume flux was at a maximum during winter and very low during fall. After 2006, the inflow has mostly been relatively low. Throughout 2015 and in winter 2016, the inflow was around 1 Sv larger than the long-term average (Fig. 3.1.4). The exception was March 2016, when the volume flux was temporarily smaller than average. The data series presently stops in May 2016, awaiting the processing of measurement data following new instrumentation in the mooring array, thus, no information about the subsequent period is available as of yet.
Ice conditions in the Barents Sea in 2018 developed as in low-ice years. In January and February, the ice coverage (expressed as a percentage of the sea area) was respectively 20 and 17% lower than average (1981–2010) and close to that in 2017 (Fig. 3.1.3). The seasonal maximum of ice extent was, as usual, in April; the ice coverage was 53% that was 4% lower than average but 9% higher than in 2017. Ice melting started intensively in May. In summer (June–August), the ice coverage was 7–19% lower than average and 3–7% lower than in 2017.
In 2018, the winter (December–March) NAO index was 0.30 that was much lower than in 2017 (1.47). Over the Barents Sea, southeasterly winds prevailed in January–March 2018 and westerly winds – during the rest of the year. The number of days with winds more than 15 m/s was higher than usual most of the year. It was lower than normal only in the western and central parts of the sea in January and February. In some months (May, June and September in the west of the sea, June and September – in the center as well as April, July and September – in the east), the storm activity was a record high since 1981.
During the 2018 Barents Sea Ecosystem Survey (BESS) 83 fish species from 28 families were recorded in pelagic and bottom trawl catches, some taxa were recorded at genus or family level only (Prokhorova et al 2019). All recorded species belonged to seven zoogeographic group (Widely Distributed, South Boreal, Boreal, Mainly Boreal, Arcto-Boreal, Mainly Arctic and Arctic) defined in Andriashev and Chernova (1994). In the following only bottom trawl catches of non-commercial fishes were used. Both demersal (including bentho-pelagic) and pelagic (neritopelagic, epipelagic, bathypelagic) species were included (Andriashev and Chernova, 1994, Parin, 1968, 1988).
Most Barents Sea fish species are demersal (Dolgov et al., 2011); this fish community consists of about 70–90 regularly occurring species which have been classified into zoogeographic groups. Approximately 25% are either Arctic or mainly Arctic species. The commercial species are all boreal or mainly boreal species (Andriashev and Chernova, 1995), except for Greenland halibut (Reinhardtius hippoglossoides) that is classified as either Arcto-boreal (Mecklenburg et al., 2013) or mainly Arctic (Andriashev and Chernova, 1995).
Zero-group fish are important consumers of plankton and are prey for other predators, and, therefore, are important for transfer of energy between trophic levels in the ecosystem. Estimated total biomass of 0-group fish species (cod, haddock, herring, capelin, polar cod, and redfish) varied from a low of 165 thousand tonnes in 2001 to a peak of 3.4 million tonnes in 2004 with a long-term average of 1.7 million tonnes (1993-2017) (Figure 3.5.1). Biomass was dominated by cod and haddock, and mostly distributed in central and northern-central parts of the Barents Sea.
Benthos is an essential component of the marine ecosystems. It can be stable in time, characterizing the local situation, and is useful to explain ecosystem dynamics in retrospect. It is also dynamic and shows pulses of new species distribution, such as the snow crab and the king crab, and changes in migrating benthic species (predatory and scavenger species such as sea stars, amphipods and snails with or without sea anemones). The changes in community structure and composition reflect natural and anthropogenic factors.
Mesozooplankton biomass in the Norwegian part of the Barents Sea in 2018 was slightly above the long-term average for the last 20 years. The mesozooplankton biomass in “Atlantic” subareas of the Barents Sea in 2018 were at similar levels as in previous years, and has shown declining trends on the Central Bank and Great Bank subareas since the peak in 1995. Krill biomass has shown an increasing trend during the last decades. Jellyfish biomass in 2017 was at its third highest level since 1980 – but could not be estimated for 2018.
The phytoplankton development in the Barents Sea is typical for a high latitude region with a pronounced maximum in biomass and productivity during spring. During winter and early spring (January-March) both phytoplankton biomass and productivity are quite low. The spring bloom is initiated during mid-April to mid-May and may vary strongly from one year to another. The bloom duration is typically about 3-4 weeks and it is followed by a reduction of phytoplankton biomass mainly due to the exhaustion of nutrients and grazing by zooplankton.
The ongoing warming were associated with increased water and air temperature, larger area covered by Atlantic and Mixed warm water masses and decreased ice coverage. The warming was also associated with
increased macro zooplankton such as krill and jellyfish biomass, increased fish recruitment (age 0) which trigger positive development of fish stocks (cod, haddock, deep water redfish, capelin and herring). Increased production and adequate fishing pressure in relation to stock size led to cod and haddock stock size increasing to record high levels and the capelin stock withstanding the high predation level.
The Barents Sea has been divided into 15 subareas or polygons (Figure 2.1.1). The division is based on topography and oceanography and is a modification (with some subdivision) of the system used by Eriksen et al. (2017) in a summary analysis of pelagic biomass. The four western areas, South-West, Bear Island Trough, Hopen Deep and Tor Iversen Bank, are areas covered mainly with Atlantic water and constitute the inflow region of Atlantic water with the splitting of the current branches east through the Kola Section (south of the Central Bank) and north in the Hopen Deep (west of the Central Bank).
The level of discarding in fisheries is not estimated, and discards are not accounted for in stock assessments. Both undersized fish and by-catch of other species can lead to discarding; fish of legal size but low market value are also subject to discarding to fill the quota with larger and more valuable species (known as high-grading).
Discarding is known to be a (varying) problem, e.g., in haddock fisheries where discards are highly related to the abundance of haddock close to, but below, the minimum legal catch size.
Fishing activity in the Barents Sea is tracked by the Vessel Monitoring System (VMS). Figure 126.96.36.199 show fishing activity in 2017 based on Russian and Norwegian data. VMS data offer valuable information about temporal and spatial changes in fishing activity. Figure 188.8.131.52 show the use of gear in 2017 and annual fishing intensity reported to the Norwegian fishery authorities in 2011-2017. The most widespread gear used in the Barents Sea is bottom trawl; but long lines, gillnets, Danish seines, and handlines are also used in demersal fisheries. Pelagic fisheries use purse seines and pelagic trawls. The shrimp fishery used special bottom trawls.
Management of the minke whale is based on the Revised Management Procedure (RMP) developed by the Scientific Committee of the International Whaling Commission. Inputs to this procedure are catch statistics and absolute abundance estimates. The present quotas are based on abundance estimates from survey data collected in 1989, 1995, 1996–2001, 2002–2007, and 2008–2013. The most recent estimates (2008–2013) are 89 600 animals in the Northeastern stock, and 11 000 animals for the Jan Mayen area, which is exploited by Norwegian whalers.
Norwegian and Russian vessels harvest northern shrimp over the stock’s entire area of distribution in the Barents Sea. Vessels from other nations are restricted to trawling shrimp only in the Svalbard zone and the Loophole — a piece of international waters surrounded by the EEZs of Norway and Russia.
Fishing has the largest anthropogenic impact on fish stocks in the Barents Sea, and thereby, on the functioning of the entire ecosystem. However, observed variations in both fish species and ecosystem are also strongly affected by climate and trophic interactions. During the last decade, catches of most important commercial species in the Barents Sea and adjacent waters of Norwegian and Greenland Sea varied around 1.5–3 million tonnes and has decreased in the last years (Figure 184.108.40.206).
Marine litter is defined as “any persistent, manufactured or processed solid material discarded, disposed or abandoned in the marine and coastal environment”. Large-scale monitoring of marine litter was conducted by the BESS survey during the 2010–2017 period, and helped to document the extent of marine litter in the Barents Sea (the BESS survey reports, Grøsvik et al., 2018). Distribution and abundance of marine litter were estimated using data from: pelagic trawling in upper 60 m; trawling close to the seabed; and visual observations of floating marine debris at surface.
Oceanic systems have a “longer memory” than atmospheric ones. Thus, a priori, it seems feasible to predict oceanic temperatures realistically and much further ahead than weather predictions. However, the predicting is complicated due to variations being governed by processes originating both externally and locally, which operate at different time scales. Thus, both slow-moving advective propagation and rapid barotropic responses resulting from large-scale changes in air pressure must be considered.
Most of the commercial fish stocks found in the Barents Sea stocks are at or above the long-term level. The exceptions are polar cod and Sebastes norvegicus. In addition, the abundance of blue whiting in the Barents Sea is at present very low, but for this stock only a minor part of the younger age groups and negligible parts of the mature stock are found in the Barents Sea.
Several sea birds species have had dramatic population declines and will be vulnerable for additional threats, like oil pollution (Fauchald et el 2019).
Although the oil- and gas production in the Barents Sea is relatively small and in limited areas, the increase in ship traffic may add a risk for accidents leading to local oil spills. The increased traffic by cruise ships and fisheries activity in the Svalbard region add to the risk of local breeding populations.
With retreating sea ice, new areas in the northern Barents Sea become available for fisheries, including bottom trawlers. Of special interest to WGIBAR is therefore the vulnerability analysis (Jørgensen et al., 2015).
Current knowledge of the response of benthic communities to the impact of trawling is still rudimentary. The benthos data from the ecosystem survey in 2011 have been used to assess the vulnerability of benthic species to trawling, based on the risk of being caught or damaged by a bottom trawl (WGIBAR report 2016). A clear decline in biomass was noted for all three categories when comparing trawled vs. untrawled areas. This suggests that trawling significantly affects the biomass of all species, but predominantly the “high-risk” taxa. Some Barents Sea regions were particularly susceptible to trawling (2016 WGIBAR Report).
In order to conclude on the total impact of trawling, an extensive mapping of fishing effort and bottom habitat would be necessary. In general, the response of benthic organisms to disturbance differs with substrate, depth, gear, and type of organism (Collie et al. 2000). Seabed characteristics from the Barents Sea are only scarcely known (Klages et al. 2004) and the lack of high-resolution (100 m) maps of benthic habitats and biota is currently the most serious impediment to effective protection of vulnerable habitats from fishing activities (Hall 1999).
In most of the measured by BESS years, the biomass in the northeast part of the Barents Sea was above the total Barents Sea mean (Figure 4.6.1), but from 2013 and ongoing, the mean biomass was reducing, and was record low (<20 kg/nm) in 2016, and below the total Barents Sea mean. As one of the reasons of this decrease could be assumed develop of snow crab population and it predation on the benthos (including juvenile stages of the megabenthic animals. In 2017, the biomass extremely increased to 116 kg/nm, the highest value recorded over the entire period of BESS (Figure 4.6.1).
The Barents Sea capelin has undergone dramatic changes in stock size over the last three decades. Three stock collapses (when abundance was low and fishing moratoriums imposed) occurred during 1985–1989, 1993–1997, and 2003–2006. A sharp reduction in stock size was also observed during 2014–2016; followed by an unexpectedly strong increase during 2016–2017. Observed stock biomass in 2015 and 2016 was below 1 million tonnes, which previously was defined as the threshold of collapse, while stock biomass increased to above 1 million tonnes in 2017-2018. Despite indications that capelin stock size was underestimated in 2016, at present 2015–2016 is recognized as a ‘mini-collapse’.
Cod is the major predator on capelin; although other fish species, seabirds and marine mammals are also important predators. In the last 6–7 years, cod stock levels have been extremely high in the Barents Sea. Estimated biomass of capelin consumed by cod in recent years has been close to the biomass of the entire capelin stock (Figure 4.2.3). Abundance levels of predators other than cod are also high and, to our knowledge, stable.
Not updated as 2017 data for diet of capelin and polar cod were not yet available
Eleven years (2006–2016) of capelin diet were examined from the Barents Sea where capelin is a key forage species, especially of cod. The PINRO/IMR mesozooplankton distribution shows low plankton biomass in the central Barents Sea, most likely due to predation pressure from capelin and other pelagic fish. This pattern was also observed in 2017. In the Barents Sea, a pronounced shift in the diet from smaller (<14 cm) to larger capelin (≥14 cm) is observed.
The interaction cod-capelin-polar cod is one of the key factors regulating the state of these stocks. Cod prey on capelin and polar cod, and the availability of these species for cod varies. Сod can strongly influence on numbers of these species. In the years when the temperature was close to the long-term mean, the cod overlap with capelin and polar cod was lower than in the recent warm years. Cod typically consume most capelin during the capelin spawning migration in spring (quarters 1+2), but especially in recent years the consumption has been high also in autumn (quarters 3+4) in the northern areas (Figure 4.2.3). In 2017-2018 capelin consumption by cod was stable.