The Barents Sea has become colder since 2015–2016, and the cooling continued from 2018 to 2019. However, the air and water temperatures are still being typical of warm years. In the western entrance of the Barents Sea, the Atlantic Water temperatures in 2019 were at the same level as in the early 2000s. Coastal and Atlantic waters in the Kola Section were fresher than in 2018. In autumn, the area of Atlantic waters (>3°С) decreased slightly and the area of Arctic waters near bottom (<0°С) increased slightly compared to 2018, whereas the area of cold bottom waters (<0°С) almost tripled com-pared to the previous year. Ice coverage has increased since 2016 due to lower temperatures and lower inflow of Atlantic Water. In 2019, the ice coverage was below average but higher than in 2018; its seasonal maximum (51%) was in March, a month earlier than usual, its seasonal minimum (1%) was in September, as usual.
In 2019, the winter (December–March) NAO index was 2.09 that was much higher than in 2018 (0.30). Over the Barents Sea, southerly and southeasterly winds prevailed in January–March 2019, easterly and northeasterly 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 or close to the long-term average (1981–2010) in the western part of the sea in January, April and October, in the central part in January, February, April, August and December, in the eastern part in January, April and December. In June (in the east) and July (in the east and center), the storm activity was a record high since 1981.
In December 2018, the Barents Sea ice extent (expressed as a percentage of the total sea area) equalled 15% and was the lowest since 1951. However, in January–March 2019, ice formation accelerated significantly, and in March (a month earlier than usual), the ice-covered area reached a seasonal maximum of 51% and was close to the long-term average (1981–2010) (Fig. 3.1.3).
The volume flux into the Barents Sea varies with periods of several years. The annual volume flux was relatively high during 2003–2006 (Fig. 3.1.4). From 2006 to 2014, the inflow was relatively stable before it increased substantially in 2015 to about 1 Sv above the long-term average. The year of 2016 had relatively low inflow. Since 2017 the annual volume inflow to the Barents Sea has decreased, but the data series presently stops in May 2019 thus the annual value of 2019 should presently be considered a rough estimate. There is no statistically significant trend in the annual volume fluxes.
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 dropped significantly in 2019 compared to the previous year and its annual mean value was the lowest since 2011 (Fig. 3.1.7). The SST in the southwestern part of the sea was close to the long-term average (1982–2010) for most of the year; small negative anomalies of −0.2, −0.3 and −0.1°С were found in July, August and November respectively; positive anomalies of more than 0.5°C were only observed in January, February and September.
Time series of area covered by Arctic Water masses in 50–200 m depth show a strong shift occurring around 2006 (Fig. 3.1.14), with substantially larger extent of Arctic Water before than after. The extent of the Atlantic Water masses show a more gradual increase over the period from 1970 to 2019, and vary to a large extent in synchrony with the temperature of the inflowing Atlantic Water in the western Barents Sea (Fig. 3.1.14).
Mean temperature in the upper, intermediate and deep waters were calculated for polygons for possible inclusion in multivariate analysis (Fig. 3.1.16). The polygons series show that the temperature in the upper, intermediate and deep waters in August–September 2019 were higher than the mean (1981–2010) in most subregions. The exceptions were the outer boundary subregions; the South West and the Franz Victoria Trough, where they were slightly below the mean. At Great Bank, the temperatures at bottom were in 2019 below the mean.
The mesozooplankton biomass in autumn 2019 was at approximately the same level as in recent years for the Barents Sea as a whole. The biomass in the western inflow area of Atlantic water was higher in 2019, and also somewhat higher on the Central and Great Banks, than in preceding years. The biomass in the eastern and northern areas remained at a relatively high level comparable to the long-term mean. Krill biomass has shown an increasing trend in recent decades and remained high in 2019. Pelagic amphipods were nearly absent in 2012-2013 but have since shown increased abundances and expanded distributions in the area east of Svalbard. The plankton situation in 2019 indicates good feeding conditions for planktivorous consumers.
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 ret-rospect. 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 anem-ones).
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 18.104.22.168).
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 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, 1994).
The summer abundance of minke whales in the Barents Sea has recently increased from a stable level of about 40,000 animals to more than 70,000 animals. Also, humpback whales have increased their summer abundance in the Barents Sea from a low level prior to year 2000 to about 4,000 animals thereafter. The other cetacean populations have remained stable in numbers. In 2019, 2686 individuals of ten species of marine mammals were sighted during the Barents Sea Ecosystem Survey (BESS) in August-October 2019, as well as an additional 64 individuals which were not identified to species. The baleen whales had a more aggregated and southerly distribution than in previous years with main occurrence in the Bear Island area and west and north of Hopen, and south of 78°N. This may have been caused by the reduced capelin abundance.
Fishing activity in the Barents Sea is tracked by the Vessel Monitoring System (VMS). Figures 22.214.171.124 and 126.96.36.199 show fishing activity in 2017-2019 based on Russian and Norwegian data. VMS data offer valuable information about temporal and spatial changes in fishing activity.
The commercial fisheries in the Barents Sea Ecoregion target few stocks. The largest pelagic fishery targets capelin using midwater trawl. The largest demersal fisheries target cod, haddock, and other gadoids; predominantly using trawls, gillnets, longlines, and handlines. The crustacean fisheries target deep-sea prawn, red king crab, and snow crab. Most catches of crabs are from coastal areas. Harp seals and minke whales are also hunted in the region. Fisheries overview in the Barents Sea is available on https://www.ices.dk/sites/pub/Publication%20Reports/Advice/2019/2019/FisheriesOverview_BarentsSea_2019.pdf
Thirteen years (2006–2018) of capelin diet were examined from the Barents Sea where capelin is a key species in the food web, both as prey and predator. The PINRO/IMR mesozooplankton distribution usually 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 2017-2019. In the Barents Sea, a pronounced shift in the diet from smaller (<14 cm) to larger capelin (≥14 cm) is observed.
The Barents Sea capelin has undergone dramatic changes in stock size over the last four decades. Three stock collapses (when abundance was low and fishing moratoriums imposed) occurred during 1985–1989, 1993–1997, and 2003–2006. During the recent period 2014-2019 the stock estimates have fluctuated considerably. A rapid decline in stock size was recorded from 2014 onwards, and in 2016 the lowest biomass of capelin since 2005 was estimated from the joint Russian-Norwegian autumn Barents Sea Ecosystem Survey (BESS).
The Barents Sea polar cod stock was at a low level in 2017 and 2018. Norway conducted commercial fisheries on polar cod during the 1970s; Russia has fished this stock on more-or-less a regular basis since 1970. However, the fishery has for many years been so small that it is believed to have very little impact on stock dynamics. Stock size has been measured acoustically since 1986 and has fluctuated between 0.1–1.9 million tonnes.
The summer overlap between cod and capelin has increased, especially in the northern area, mainly due to the increased size of suitable habitat for cod, and the size of the cod stock. There is, however, a low correspondence between changes in horizontal overlap and changes in capelin consumption. The cod-capelin feeding interaction mainly takes place on the banks of the northern Barents Sea, where a vertical overlap with capelin is much more important for explaining variation in capelin consumption than capelin density. The northward expansion of cod has probably also affected the polar cod negatively, since polar cod has become more available to cod.
Cod-capelin-polar cod interaction
Oceanic systems have a “longer memory” than atmospheric systems. Thus, a priori, it seems feasible to predict oceanic temperatures realistically and much further ahead than atmospheric weather predictions. However, the prediction is complicated due to variations being governed by processes originating both externally and locally, which operate at different time-scales.
Most of the commercial fish stocks found in the Barents Sea stocks are at or above the long-term mean 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.
Non-commercial demersal fish species were grouped according to their biogeography to assess their relative abundance, trends and suitable habitats. Abundance of Arctic species seems to have increased in 2019 compared to the two previous years. This is probably due to high catches of Liparids. Zoogeographic grouping is consistent with their suitable habitats. Temperature is a major driver of the suitable habitats
Climate change and annual fluctuations of environmental conditions strongly affect fish stocks and all biological ecosystem components. Evaluating fisheries management strategies should include environmental information as part of the decision basis. Estimation of how often an undesirable event may occur, and what the consequences would be of such an event needs to be estimated through a risk analysis using stochastic simulations.
Common trends refer to trends that are similar across ecosystem components. Identifying common trends can be useful as a diagnostic tool to reveal past changes and to explore the relationships among biological communities and between these communities and environmental conditions.