Marine MammalsThe 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 whale 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 2018, 2119 individuals of nine species of marine mammals were sighted during the Barents Sea Ecosystem Survey (BESS) in August-October 2018, as well as an additional 77 individuals which were not identified to species.
During the Barents Sea ecosystem survey in August-October 2018 marine mammal observers were onboard all vessels. In total, 2119 individuals of 9 species of marine mammals were observed and an additional 77 individuals were not identified to species. The observations are presented in Table 184.108.40.206 and distributions in the Figures 220.127.116.11 (toothed whales) and 18.104.22.168 (baleen whales).As in previous years, white-beaked dolphin (Lagenorhynchus albirostris) was the most common species (more than 70% of all individual registrations). This species was widely distributed in the survey area and expanded somewhat to the northeast compared to the 2017 survey. The highest densities of this species apparently overlap with the distributions of capelin, codfishes, herring and polar cod in the survey area.Although in modest numbers, the toothed whales were also represented by sperm whales (Physeter macrocephalus), harbour porpoises (Phocoena phocoena), and killer whales (Orcinus orca) besides the numerous white-beaked dolphins. The sperm whales were observed at deeper waters along the continental slope and other parts of the research area westward of 27°E. The harbour porpoise and killer whale sightings were mainly made in the southern parts of the research area.
Table 22.214.171.124. Numbers of marine mammal individuals observed from the RV “Johan Hjort”, “G.O. Sars”, “H. Hansen” and “Vilnyus” during the ecosystem survey in 2018.
The baleen whale species minke (Balaenoptera acutorostrata), humpback (Megaptera novaeangliae) and fin (Balaenoptera physalus) whale were quite abundant as 22 % of the total animals registered belonged to these species. There main concentrations were found east of Svalbard. There were fewer observations of minke whales in 2018 than in 2017, and although they are widely distributed over all the survey area, their highest concentrations were in the northern areas with spatial overlap with capelin and polar cod aggregations.
The humpback whales were as usual recorded mainly in the waters to the east of the Svalbard Archipelago and in the area of the Great Bank. In 2018, more humpback whales were observed than in the previous year, however, the sizes of the groups of these whales were in general smaller and no more than 5 individuals. The humpback whales were recorded in areas with aggregations of capelin, often with fin and minke whales in the same areas. In 2018, fewer fin whales were observed during the survey as compared to 2017.
In previous years, blue whales (Balaenoptera musculus) were observed north of Spitsbergen, especially off the Hinlopen Strait. During the 2018 survey only one blue whale was sighted, on the shelf west of Bellsund, Spitsbergen.
The only identified pinniped observed during the 2018 ecosystem survey was a ringed seal (Phoca hispida). Harp seal (Pagophilus groenlandicus), bearded seal (Erignathus barbatus), walrus (Odobenus rosmarus) and polar bears (Ursus maritimus) were not observed during the survey, most likely due lack of ice coverage in the surveyed area.
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 the species as well as 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 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 126.96.36.199). 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.
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 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 2018 are the observations from Norwegian and Russian vessels during the ecosystem survey in 2018.
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.
Recent tracking studies (see seatrack.seapop.no) show that after the breeding season, most of the populations of kittiwakes, puffins, little auks, Brünnich’s guillemots and common guillemots from colonies along the Norwegian and Russian coasts stay or migrate in to the Barents Sea to feed and molt, possibly increasing the total number of birds in the area in August and September. During September and October, the populations of Brünnich’s guillemots and little auks from colonies in West-Spitsbergen and Bjørnøya start their migration westward, crossing the Norwegian Sea to reach their wintering grounds in the Northwest Atlantic. The large north-eastern populations, i.e. little auks and Brünnich’s guillemots breeding in East Spitsbergen, Franz Josef Land and Novaya Zemlya, over-winter in the Barents Sea. Kittiwakes leave the Barents Sea in late autumn to spend the winter in the Northwest Atlantic or the North Sea. Common guillemots stay in the south-eastern and south-central parts of the Barents Sea throughout the non-breeding period. Finally, only a few puffins from the eastern colonies over-winter in the Barents Sea, while the rest of the population roam over large areas in the central North Atlantic. Most seabird populations return to the colonies around March and April.
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 126.96.36.199). Seabirds have been surveyed uninterruptedly on Norwegian vessels in the western part of the Barents Sea since 2004. Based on the minimum annual survey extent, the abundance (Figure 188.8.131.52) of different species and the centre of gravity of the spatial distribution (Figure 184.108.40.206) was calculated for each year.
Figure 220.127.116.11. Density of seabirds during the Barents Sea ecosystem surveys in 2017 (top) and 2018 (bottom). Left panel is the distribution of auks (little auk, Bünnich’s guillemot, puffin and common guillemot). Right panel is the distribution of shipfollowers (fulmar, glaucous gull. Kittiwake, black-backed gull and herring gull).
Note the large fluctuations in the abundance estimates from the at-sea surveys (Figure 18.104.22.168). These fluctuations do not necessarily reflect the observed population trends from the colonies (cf. Figure 2). This discrepancy could be related to the fact that the at-sea abundances are influenced by annual differences in migration pattern which would mask the general population trends. There is not yet an evidence for a widespread “borealization” (Fossheim et al. 2015) of the seabird communities in the Barents Sea, although there is a tendency for a slight northward displacement of puffins, kittiwakes and glaucous gull (Figure 22.214.171.124). During the last 14 years, the different seabird species seem to stay relatively fixed within their respective geographic niche.
Figure 126.96.36.199. Center of gravity in the north direction of the distribution of auks (left) and shipfollowers (right) in the Western Barents Sea during the ecosystem surveys 2004-2018. Black line indicates the position of Bjørnøya.
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