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.
During the Barents Sea ecosystem survey in August-October 2019 marine mammal observers were onboard all vessels. In total, 2686 individuals of 10 species of marine mammals were observed and an additional 64 individuals were not identified to species. The observations are presented in Table 22.214.171.124 and distributions in the Figures 126.96.36.199 (toothed whales) and 188.8.131.52 (baleen whales). As in previous years, the white-beaked dolphin (Lagenorhynchus albirostris) was the most common species with nearly 60% of all individual registrations. This species was widely distributed in the survey area. Apparently, most records of this species coincide with the distributions of herring, capelin, polar cod, juvenile cod and other fishes in the research area. Besides the white-beaked dolphins, sperm whales (Physeter macrocephalus), harbour porpoises (Phocoena phocoena) and killer whales (Orcinus orca) were represented among the toothed whales. Sperm whales were observed in deep waters along the continental slope but also within the Barents Sea proper west of 29° E. The harbor porpoises were observed in the southern parts of the Barents Sea, including coastal areas. A notable observation was made of a group of 6 killer whales in the northern Barents Sea at 79°45’N-41°33’E.
The baleen whale species minke (Balaenoptera acutorostrata), humpback (Megaptera novaeangliae) and fin (Balaenoptera physalus) whales were abundant in the Barents Sea, and 25% of all the animals belonged to them. These species were often found together in aggregations. In 2019, unlike in previous years, baleen whales were observed mainly south of 78°N due to low concentrations of capelin in the north. Minke whales are widely distributed in the Barents Sea. In 2019 minke whales were recorded in large numbers in the area between Bear island and the Norwegian coast, in the southeastern Barents Sea and north of Hopen and the Great Bank. In 2018 their highest concentrations were further north and they were seen in reduced numbers both compared to the previous year 2017 and the following year 2019. In 2019 the densest concentrations of minke whales in northern and eastern areas overlapped with capelin, polar cod and herring aggregations. In 2019 the humpback whales were recorded in considerable numbers in the area around Bear Island, west of Hopen Island and in the northern Barents Sea. This was different from the 2018 pattern when the humpbacks were concentrated in the northern area. The change was probably caused by the low concentrations of capelin in the north.
In 2019, fin whales showed an apparent increase in abundance and were more numerous in association with the continental slope southwards from Spitsbergen and around Bear Island than in 2018. No blue whales (Balaenoptera musculus) were recorded during the ecosystem survey in 2019. Pinniped species recorded during the joint ecosystem survey were harp seal (Phoca groenlandica), bearded seal (Erignathus barbatus) and walrus (Odobenus rosmarus). The main concentrations of harp seals were found north of 80°N in the area of newly formed ice. Walrus and bearded seals were also observed north of 80°N. Polar bears (Ursus maritimus) were not observed during the ecosystem survey. Since the late 1980ies Norway has conducted visual sighting surveys in the Northeast Atlantic with minke whales as target species to estimate summer abundance of this species and other cetacean species. The surveys have been run as mosaic coverages of the total survey area over six-year periods. In the Barents Sea the species most often observed during these surveys have been the minke whale, followed by white-beaked dolphins, harbour porpoises, humpback whales and fin whales. The impression is that minke whales are abundant in the northern and eastern areas during the summer. Harbour porpoises are mostly observed in the southern parts of the area and we know that they are associated with the coastal areas along Kola and the fjord systems. Humpback whales are mainly sighted in the northwest and associated with the capelin distribution. The white-beaked dolphins are observed in the southern and central parts of the survey area, especially over the Sentralbanken. From these surveys a series of abundance estimates can be compiled to illustrate the status over a time period of nearly 30 years. Over the period from about 1995 to 2015 the summer abundance of minke whales has been quite stable but has recently shown a considerable increase to the present 73,000 animals (Figure 184.108.40.206). Also, humpback whales have shown a large increase in summer abundance in the Barents Sea from very low numbers prior to year 2000 to around 4,000 animals afterwards. Other cetacean species have shown relatively stable abundances within the Barents Sea over the survey period.
Marine mammal frequency of occurrence
The Barents Sea is a productive ecosystem and an important feeding ground for marine mammals during summer and autumn. During the joint Norwegian-Russian ecosystem (BESS), marine mammals have been observed visually from the vessels by experts. Frequency of occurrence (FO, number of observations, not number of observed marine mammals) were estimated based on the BESS for the period 2004-2019 and shoed in Fig 220.127.116.11 Three peaks of FO of marine mammals were observed in 2007, 2010 and 2017-2019. Note, that marine mammal observers were not at all vessels in the western part (2004, 2005, 2008, 2009 and 2014), and lack of full coverage in the eastern parts of the Barents Sea in 2016 and 2018 may influence the result.
The BESS cover open sea and thus 90% of observations of all marine mammals’ observations belongs to Cetacea. The most frequently occurrent species during the August-September were white-beaked dolphin (Lagenorhynchus albirostris), minke whale (Balaenoptera acutorostrata), fin whale (Balaenoptera physalus) and humpback whale (Megaptera novaeangliae) (Figure. 18.104.22.168).
The Barents Sea were divided in to four (western, Svalbard or Spitsbergen, south-eastern and north-eastern) regions (Fig. 22.214.171.124) and FO’s were calculated for each region.
Figure 126.96.36.199 – Frequency of occurrence of marine mammals (%) in the four regions in Barents Sea during BESS in 2004-2019: A – Svalbard/Spitsbergen, B – Western, C – North-eastern, D – South-eastern.
А. The Svalbard area is located between 76°N and 82°N and between 5 °E and 35 °E. The highest frequency of occurrence of marine mammals (42.4% of all observations) were observed in the area. Additionally, the highest number of species (14) were also observed in the area. This area, especially east of Svalbard is a main capelin area. Capelin are an important prey for many of marine mammals and overlap between highest numbers of observations and species and main mature capelin observations most likely link to important feeding ground (first of all capelin, but also euphausiids). Most frequently observed in the area were representatives of baleen whales (Mysticeti): minke whale, fin whale and humpback whale (Figure 188.8.131.52 А). В. The western area is located between 76 °N and the Norwegian and Russian coasts and between 5 °E and 35 °E. In this area, one third part of all observation were observed. 13 species of marine mammals (next highest number of species) were observed in the area, among them were white-beaked dolphin, minke whale, fin whale, sperm whale (Physeter macrocephalus), humpback whale (Figure 184.108.40.206 B). The western area is also productive area with highest concentrations of euphausiids and juveniles’ fish such as haddock, cod, herring, redfish and capelin. Immature capelin and herring also observed here. C. The north-eastern area is located between 74 °N and 82°N and between 35 °E and 70 °E. The numbers of marine mammals observed here were less than in two other areas and consisted 21.1% of all observations. Totally, 11 species were observed here such as white-beaked dolphin, minke whale, humpback whale, fin whale, and harp seal (Pagophilus groenlandicus) (Figure 220.127.116.11 C). This area are dominated by polar cod, cod and capelin. Polar cod is an important prey for harp seals and a decrease of polar cod abundance since 2012 can therefore impact feeding conditions negatively. D. The south-eastern area is located between 74 N the Russian coast and between 35 °E and 70 °E. During BESS, the lowest numbers of marine mammals’ observations 6.5% of all observations) were observed in the area. However, 10 different species were recorded, and most frequent were white-beaked dolphin, minke whale, harbour porpoise (Phocoena phocoena) and fin whale (Figure 18.104.22.168 D). This area dominated by polar cod, cod and herring.
Figure 22.214.171.124. Frequency of occurrence of marine mammals and species composition (%) in different areas (A - Svalbard, B – Western, C – Northeastern, D – Southeast) in the Barents Sea during BESS in 2004-2019.
Figure 126.96.36.199 shown frequency of occurrence of marine mammals in these four areas in different years. More often marine mammals visited Svalbard areas compared to other areas, and number of observations increased from 2004 to 2019. During last three years marine mammals were observed more than 400 times in the Svalbard area. Next highest visited area was western area, or most likely transfer corridor for some whales. Highest numbers of observations were observed during 2005-2007, 2010 and 2019. area. The frequency of occurrence and species composition varied between these four areas of the Barents Sea. The Svalbard, inhabiting by capelin, polar cod and macroplankton such as euphausiids and amphipods, were visited more frequently and by higher number of species, and thus had highest predation pressure. The western area, inhabiting by 0-group fishes and macroplankton, experienced next highest predation pressure, but this differ between years.
About six million pairs from 36 seabird species breed regularly in the Barents Sea (Barrett et al. (2002), Table 188.8.131.52). Allowing for immature birds and non-breeders, the total number of seabirds in the area during spring and summer is about 20 million individuals. 90% of the birds belong to only 5 species: Brünnich’s guillemot, little auk, Atlantic puffin, northern fulmar and black-legged kittiwake. The distribution of colonies is shown in Figure 184.108.40.206. Colonies in the high-Arctic archipelago are dominated by little auks, Brünnich’s guillemots and kittiwakes. These birds utilize the intense secondary production that follows the retreating sea ice. Little auks feed mainly on lipid rich Calanus species, amphipods and krill while Brünnich’s guillemots and black-legged kittiwakes feed on polar cod, capelin, amphipods and krill. The seabird communities, as well as their diet change markedly south of the polar front. In the Atlantic part of the Barents Sea, the seabirds depend more heavily fish, including fish larvae, capelin, I-group herring and sandeels. The shift in diet is accompanied by a shift in species composition. In the south, Brünnichs’ guillemots are replaced its sibling species, the common guillemot. Large colonies of Atlantic puffins that largely sustain on the drift of fish larvae along the Norwegian coast, are found in the southwestern areas.
Figure 220.127.116.11. Major seabird colonies in the Barents Sea. Data compiled from SEAPOP (www.seapop.no), Fauchald et al. (2015), Anker-Nilssen et al. 2000 and The Seabird Colony Registry of the Barents and White Seas.
Table 18.104.22.168. Seabirds in the Barents Sea sorted by breeding population size in decreasing number. Breeding pairs are from Strøm et al. (2009). Observations on BESS 2019 are the observations from Norwegian and Russian vessels during the ecosystem survey in 2019.
Population monitoring in Norway and Svalbard has revealed a marked downward trend for several important seabird species the last 30 years, including puffin, Brünnich’s guillemot and kittiwake (Figure 22.214.171.124). The population of common guillemot was decimated in the 1980s mainly due to a collapse in the capelin stock combined with low abundance of alternative prey. The population has increased steadily since then. The status and trends of the large populations of seabirds in the Eastern Barents Sea is less known.
In addition of being an important breeding area for seabirds, data from recent tracking studies (Fauchald et al. 2019) show that the Barents Sea is an important feeding area for seabirds in early autumn. Accordingly, the number of pelagic seabirds reaches a maximum of approximately 10 million individuals in August, just after breeding (Figure 126.96.36.199). This peak is mainly due to Atlantic puffins, Northern fulmars, common guillemots and black-legged kittiwakes migrating from colonies around the Norwegian Sea in to the Barents Sea to feed. This period, from August to September, is also the period when the auk species moult and become flightless for several weeks. After the feeding period, large parts of the populations of Atlantic puffin, Brünnich’s guillemot, black-legged kittiwakes, Northern fulmar and little auks leave the Barents Sea. Thus, the number of birds reaches a minimum in the darkest period from December to January with about 5 million birds (Figure 188.8.131.52). In general, populations from the western colonies leave the Barents Sea earlier (September-October) and return later (March-April) than birds from the eastern colonies, and a larger proportion of the eastern populations tend to stay in the Barents Sea throughout the winter. Migrating birds overwinter in large ocean areas in the northwest and north-central part of the North Atlantic, including the coastal areas off southern and western Greenland, around Iceland, in the Denmark Strait and in the Irminger and Labrador Seas. Common guillemots from Bjørnøya, Murman and Finnmark stay in the southern Barents Sea throughout the non-breeding period. The seabirds return gradually to the colonies and adjacent areas in early spring from February to April.
Figure 184.108.40.206: Estimated number of adult breeding seabirds present in the Barents Sea area during the annual cycle. Estimates are based on population size and year-round tracking of different populations by the SEATRACK program (see Fauchald et al. 2019).
Broadly, the spatial distribution of seabirds during the ecosystem survey in September reflects the climatic gradient from a boreal Atlantic climate with common guillemots, puffins, herring and black-backed gull in the south and west, to an Arctic climate with little auks, Brünnich’s guillemots and kittiwakes in the north and east (Figure 220.127.116.11). Seabirds have been surveyed uninterruptedly on Norwegian vessels in the western part of the Barents Sea since 2004, however, the first years did not cover the northern areas. Based on the minimum annual survey extent from 2009 an onward, the abundance (Figure 18.104.22.168) of different species and the centre of gravity of the spatial distribution (Figure 22.214.171.124) was calculated for each year.
Figure 126.96.36.199. Density of seabirds during the Barents Sea ecosystem surveys in 2018 (top) and 2019 (bottom). Left panel is the distribution of auks (little auk, Brünnich’s guillemot, Atlantic puffin and common guillemot). Right panel is the distribution of shipfollowers (Northern fulmar, glaucous gull, black-legged kittiwake, black-backed gull and herring gull).
Abundance estimates indicate relatively large fluctuations in the number of seabirds at-sea (Figure 188.8.131.52). Northern fulmar, black-legged kittiwake and herring gull have decreased significantly in abundance the last ten years. These changes do not necessarily reflect the observed population trends from the colonies (cf. Figure 184.108.40.206) since the at-sea abundances also are influenced by annual differences in migration pattern. Note that the ship-followers are attracted to the ship from the surrounding areas and individual birds are therefore likely to be counted several times. Accordingly, the estimated numbers of ship-followers are probably grossly over-estimated. Analyses of the centres of gravity show a northward displacement for several species the last ten years (Fig. 220.127.116.11). The centres of gravity of little auks, Brünnich’s guillemot, glaucous gull, black-legged kittiwake, northern fulmar and black-backed gull have moved from 150 to 500 km northward from 2008 to 2019, suggesting that seabirds have been displaced toward the north following a period of warming. Although longer time series might be warranted, this result could be an early signal of a “borealization” (Fossheim et al. 2015) of the seabird communities in the Barents Sea.
Figure 18.104.22.168. Abundance of auks (left) and shipfollowers (right) in the Western Barents Sea during the ecosystem surveys 2009-2019. Note that the numbers of ship-followers are probably systematically over-estimated. Asterisks indicate significant negative trends in the abundance estimates (* P < 0.05, ** P < 0.001).
Figure 22.214.171.124. Centre of gravity in the north direction of the distribution of auks (left) and shipfollowers (right) in the Western Barents Sea during the ecosystem surveys 2009-2019. Hatched lines indicate the positions of Hammerfest (Norwegian coast), Bjørnøya and Ny Ålesund (Spitsbergen). Asterisks indicate significant positive linear trends in the position of the centre of gravity (* P < 0.05, ** P < 0.001).