Marine mammals and sea birds

Marine mammals

In 2020, 4159 individuals of twelve species of marine mammals were sighted during the Barents Sea Ecosystem Survey (BESS) in August-October 2020. The baleen whales had aggregated distributions East of Bear Island area and west, north and east of Hopen in the area between 76°N and 78°N.

During the Barents Sea ecosystem survey in August-October 2020 marine mammal observers were onboard all vessels. However, the Russian vessel started later than usual which influences both the comparability of the results with previous years as well as synoptic considerations.

In total, 4,159 individuals of 12 species of marine mammals were observed, of these 169 individuals were not identified to species level. The observations are presented in Table 3.9.1.1 and distributions in the Fig. 3.9.1.1 (toothed whales) and 3.9.1.2 (baleen whales).

As in previous years, the white-beaked dolphin (Lagenorhynchus albirostris) was one of the most abundant and widely distributed species with 26% of all individual registrations. More dolphins were recorded north of 74°N compared to the previous year.

Besides white-beaked dolphin other toothed whales observed included sperm whale (Physeter macrocephalus), harbour porpoise (Phocoena phocoena), killer whale (Orcinus orca) and white whale (Delphinapterus leucas). Sperm whales were observed in the western areas (west of 35°E) of the Barents Sea and at deeper waters at the continental slope. The harbour porpoises were recorded in the southern coastal parts of the research area. A large wintering aggregation (about 2000 individuals with density about 200-300 ind./km) of white whale was observed south of Franz Josef Land (78° 46´N, 45° 39´E) on 08 October 2020. A similar aggregation of these animals was observed by PINRO during an aerial survey in September 2004. However, the aggregation in 2020 was situated further southeast than the earlier observation. Killer whales were recorded close to the white whale aggregation.

Table 3.9.1.1. Numbers of marine mammal individuals by species observed during BESS 2020.

The baleen whale species minke (Balaenoptera acutorostrata), humpback (Megaptera novaeangliae) and fin (Balaenoptera physalus) whales were also abundant in the Barents Sea in 2020. In the Russian study area the baleen whales were recorded only in the northwest as a result of lack of coverage in the south and late coverage of the northeastern Barents Sea.

Minke whales were widely distributed in the western research area. The densest aggregations of minke whale were overlapping with capelin and polar cod concentration in the central areas of the Barents Sea.

As in the previous year, the humpback whale was recorded mainly in the western area, and southeast and east of the Svalbard Archipelago. In 2020, the distribution of this species was wider and humpback whales were also found in the central areas. The higher densities of humpback whales were recorded in areas of high aggregations of mature capelin, and often together with fin and minke whales.

Figure 3.9.1.1. Distribution of toothed whales in August-October 2020.

Figure 3.9.1.2. Distribution of baleen whales in August-October 2020.

In 2020, the distribution of fin whale in the western areas was similar to the previous year. In the northeastern regions, this species was recorded eastwards to about 50°E.

Blue whales (Balaenoptera musculus) were not observed in 2020, like in previous years.

During the survey, the pinnipeds harp seal (Phoca groenlandica), ringed seal (Phoca hispida) and walrus (Odobenus rosmarus) were observed. The main concentrations of harp seals were found in the area of newly formed ice (northwards of 81°N). Walrus and ringed seal were observed north of 80°N.

In addition to pinnipeds, 5 polar bears (Ursus maritimus) were recorded north of the Franz Josef Land Archipelago.

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 2018 the summer abundance of minke whales has been quite stable but has recently shown a considerable increase to the present 68,000 animals (Figure 3.9.1.3). 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 7,000 animals recently. Other cetacean species have shown relatively stable abundances within the Barents Sea over the survey period.

Figure 3.9.1.3. Summer abundance of minke whales in the Barents Sea over the past 30 years.

Figure 3.9.1.4. Summer abundance of humpback whales in the Barents Sea over the past 20 years.

Marine mammals frequency of occurrence

By Roman Klepikovskiy (PINRO)

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 3.9.1.15 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.

Figure 3.9.1.15 Frequency of occurrence of marine mammals’ (number of observations) in the Barents Sea, during BESS in 2004-2019.

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) (Fig. 3.9.1.16).

Figure 3.9.1.16 Species composition of marine mammals’ observations, and their proportion in the Barents Sea, during BESS in 2004-2019.

The Barents Sea were divided in to four (western, Svalbard or Spitsbergen, south-eastern and north-eastern) regions (Fig. 3.9.1.17) and FO’s were calculated for each region.

Figure 3.9.1.17 – 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.

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 (Fig. 3.9.1.18 А).

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 (Fig. 3.9.1.18 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.

The north-eastern areais 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) (Fig. 3.9.1.18 C). This area is 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.

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 (Fig. 3.9.1.18 D). This area dominated by polar cod, cod and herring.

Figure 3.9.1.18. 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.

The frequency of occurrence of marine mammals in these four areas in different years shown in Fig. 3. 3.9.1.19. 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.

Figure 3.9.1.19. Frequency of occurrence of marine mammals in four areas of the Barents Sea during 2004-2019.

Ice associated marine mammals

By Hanne Johnsen (NPI), Christian Lydersen (NPI), Jon Aars (NPI) and Kit M. Kovacs (NPI)

Sea ice habitat loss due to a warming climate is a serious threat to all ice-associated marine mammals. Declines in Arctic sea ice and associated environmental changes have been linked to shifts in species distribution. The Norwegian Polar Institute (NPI) conduct regular monitoring of walruses and polar bears in Svalbard updated through MOSJ (environmental monitoring of Svalbard and Jan Mayen) as well as research on species not covered by regular monitoring.

Walruses (Odobenus marinus) were once highly abundant in the Svalbard archipelago, but 350 years of unregulated harvest brought them to the brink of extinction before they were protected in 1952. The population remains Red Listed as “vulnerable” today and following several decades of protection one can now see a clear growth in the population (Fig. 3.9.1.20).

Figure 3.9.1.20. In the 1980s and 1990s, estimates were made from observations from land or ships, spread out over weeks or months. Data from 2006 and 2012 are based on the number of animals on designated aerial surveys, and counts are corrected for the proportion of animals at sea at the time of the survey. Source: https://www.mosj.no/en/fauna/marine/walrus-population.html

The first systematic abundance survey of walruses in Svalbard, also included in MOSJ, was conducted in 2006 (Lydersen et al. 2008). Before that, crude “guestimates” were made from observations from land or ships, spread out over weeks or months. The walruses in Svalbard are part of a shared population with Franz Josef Land, we only survey the Svalbard fraction. The survey in 2006 covered all known terrestrial haul-out sites within Svalbard (79 in total) during a tight time window in August. 17 haul-out sites were occupied by animals when the survey was flown. The photographs of the active sites revealed 657 animals. An extensive behavioural data set from satellite-relay-data-loggers was used to correct for animals that were in the water at the time of the survey. The resulting estimate was 2629 (95% CI: 2318–2998). With updates approximately every five years, the second survey in this MOSJ time series was flown in 2012 (Kovacs et al. 2014). The new estimate was 3886 (95% CI: 3553–4262) and covered 91 haul-out sites of which 24 were occupied during the survey. Nine of the active sites contained females with calves, in contrast to only one site in the 2006 survey. The most recent survey in this time series was carried out in 2018. At the time of the survey, 5503 (95% CI: 5031-6036) walrus were estimated in the Svalbard area (https://www.mosj.no/en/fauna/marine/walrus-population.html). This is a 41.6 % increase since the previous survey in 2012. Animals were present at 19 of the visited haul-out sites, and calves were observed at seven of these. In 2018, there were 98 terrestrial walrus haul-out sites in the database for Svalbard. The next update in this time series is planned for 2023.

The intensive hunting of polar bears (Ursus maritimus) in Svalbard began around 1870, and the population was at low levels when the species was protected from 1973. The following years the population probably increased considerably, and newer data indicates that the population has not likely been reduced the last 10-15 years, despite a large reduction in available sea ice in the same period. In August 2004 the Barents Sea population of polar bears was estimated to around 2650 (95 % CI ~ 1900-3600) animals (Aars et al. 2009), a number assumed to reflect a significant increase following the protection in 1973 (Aars et al. 2009; Derocher 2005). This means that the species is probably not threatened by the effects smaller populations may be impacted by, such as loss of genetic diversity or random demographic processes. The Barents Sea area inhabits one of the total nineteen assumed Arctic sub populations of polar bears with a high genetic exchange towards neighboring populations in the east and west (Peacock et al. 2015). The availability of sea ice habitat has in recent years been reduced much faster for the Barents Sea population than for other polar bear populations (Stern and Laidre 2016) and reproducing females are increasingly prevented from reaching important denning areas east of Svalbard (Aars 2013; Derocher et al. 2011).

The monitoring includes number of dens and sea ice coverage at Kongsøya and at Hopen, and recruitment of cubs and yearlings using data from the annual capture-recapture program. The occurrence of dens on Hopen and Kongsøya clearly shows that few females reach these islands in the autumn if the ice arrives late, sometime after the first part of November. It is unclear whether this means that the proportion of females in the subpopulation having cubs is declining. One assumes that a higher proportion of adult females now den in the Russian Arctic (Franz Josef Land). Habitats have also shifted much further north following the ice edge which is the area where most polar bears hunt for a large portion of the year (Lone et al. 2017). Data from the annual tagging programme shows a weak decline in litter size over the years, but there is no significant decrease. Further, there is no significant change over time in the number of cubs per adult female, or in the proportion of females with yearlings. It appears that the local population at Svalbard has remained at around 300 bears from 2004 to 2015, and the total number in the Norwegian Arctic is approximately the same or increasing (Aars et al. 2017). There are no signs that the condition (i.e. fat storage) of the monitored polar bears has decreased over time. Even though the loss of sea ice has been evident around Svalbard in recent years, and is expected to continue in the coming decades, the size of the subpopulation may still be below the carrying capacity. It is therefore not surprising that it looks as if the subpopulation is likely growing, or at least seems to be stable, even though the availability of habitats has become poorer for much of the year.

Figure 3.9.1.6: Body condition index of adult male polar bears caught in spring (March-May) in the period 1993-2019. The lines in the middle of each box show the median value, and the box segments and lines above and below the median each cover ca 25% of the data points. There is no significant trend over time. Source: https://www.mosj.no/en/fauna/marine/polar-bear.html.

Climate change is affecting different species at different rates. The sudden sea ice decline in 2006 had an impact on the spatial overlap and the predator-prey relationship between polar bear and ringed seal (Pusa hispida) (Hamilton et al. 2017). Following the reduction in sea-ice, polar bears spent the same amount of time at tidal glacial fronts during spring, but less time during summer and autumn. Since ringed seals did not change their glacier front association during summer this led to a decrease in spatial overlap values between these two species in the coastal areas of Svalbard. During summer polar bears are now moving greater distances daily and spend more time close to ground-nesting bird colonies, where bear predation can have substantial local effects. This study shows the importance of considering multiple species when exploring the impacts of climate change.

Other ice-associated marine mammals

NPI also do research and publish data on species of ice associated marine mammals not covered by MOSJ. Among these species are bearded seal (Erignathus barbatus), ringed seals, white whales (Delphinapterus leucas), bowhead whales (Balaena mysticetus) and narwhals (Monodon monoceros).

The rapid warming of the Arctic and consequential loss of sea ice represent a serious threat to ice-associated species in the region. In 2015, an aerial survey was carried out to estimate the abundance of Arctic endemic whale species in the marginal ice zone north of Svalbard. The survey was performed from the Russian/Norwegian border and westwards (i.e. in Norwegian waters) in cooperation with Russian colleagues. In an area of just over 52,000 km2 no white whales were seen, but an estimated 343 (95 % CI: 136-862) bowhead whales and 837 narwhals (95 % CI: 314-2233) occurred in the study area (Vacquié-Garcia et al., 2017). The bowhead whales were generally found close to the ice edge, while the narwhals were found deep into the ice all the way to the end of the survey lines (suggesting that their distributional area likely expanded north of the surveyed area). This study highlights that the sea ice represents an important habitat for these species in late summer in this region and clearly documents that aircrafts are required to conduct surveys of bowhead whales and narwhals.

Passive acoustic monitoring (PAM) is an efficient method for studying marine mammals that are vocally active in areas that are difficult to access on a year-round basis. PAM data from the Fram strait suggests that bowheads and narwhal are present inside the ice all year-round (Stafford et al. 2012, Ahonen et al. 2017,2019). Satellite tracking data from 13 bowhead whales from the Spitsbergen population (Kovacs et al. 2020) showed that the whales spread across the entire region thought to be the historical range for this species regionally – extending from East Greenland far into Russian territories, east of Franz Josef Land. The data showed that the whales dispersed southward from wintering grounds in the northernmost parts of their range during spring, returning northward again in autumn; a pattern opposite all other bowhead whale populations. They occupied areas with particularly cold sea surface temperatures and spent most of their time inside the ice edge, including areas classified as being 90-100% ice cover. Tagging of bowheads from the Spitsbergen population thus revealed that they do not migrate in the classical sense like other bowhead populations. In addition, a recently published study on genetics based on analyses of skin samples from the satellite tagged individuals, revealed that these animals are parts of the original Spitsbergen stock, and not individuals that have immigrated from other stocks due to lighter ice conditions as speculated (Bachmann et al. 2021).

White whales are the most frequently observed whale species around Svalbard where it stays close to the coast and glacier fronts during the ice-free time of year (Lydersen et al. 2001; Vacquié-Garcia et al. 2018). In 2018 the first aerial survey of white whales covering the entire Svalbard area was conducted (Vacquié-Garcia et al. 2020) and the stock size was estimated to 549 individuals (95 % CI: 436-723). Given that the species is one of the most frequently observed cetaceans in the area the estimate was surprisingly low. It does however reflect on the previous difficulties in finding animals in white whale tagging programs. These data are important in providing a baseline for comparison with future estimates of this species very much affected by environmental changes.

Ringed seal is the principal prey of polar bears and is a key Arctic species that is closely associated with the sea ice for most of its life cycle. The Svalbard ringed seals have two different strategies following breeding and molting. The first is to migrate northwards to the marginal ice zone (Hamilton et al. 2015) while the other is to stay coastbound mainly close to glacier fronts (Hamilton et al. 2016). It is mostly younger animals that migrate north while adult animals remain by the coast. Satellite tracking of ringed seals before and after the marginal ice zone moved north show change in behavior in that they spend more time swimming and diving and less time at the surface or resting on the ice compared to before (Hamilton et al. 2015). The data shows that they must work harder to locate food which ultimately could affect the condition of the animals with possible consequences for reproduction and survival (Hamilton et al. 2015). For the adult ringed seals that live along the coast of Svalbard, satellite tracking shows that these remain very connected to glacier fronts - more in the current situation than before the ice conditions changed in the fjords on the west side of Svalbard (Hamilton et al 2016, 2019). Now there are individuals that stay in front of the same glacier front throughout the tracking period. Also, for these adult seals, there is a verified change in diving behaviour which indicates that they must work harder to locate food (Hamilton et al. 2016). In recent years, there have also been several reports of ringed seals resting on land, which has previously been uncommon for this very ice-dependent species. There have even been registrations of ringed seals grouped together with harbour seals (Phoca vitulina) on land, which is a development no one had anticipated in connection with climate change and the lack of sea ice for this species (Lydersen et al., 2017).

Bearded seals are one of the least studied Arctic marine mammals. Tracking studies of adult animals in Svalbard revealed large individual variation in diving, movement and activity patterns (Hamilton et al. 2018). Bearded seals depend heavily on sea ice for giving birth and then use it as nursing and resting platforms for the pups. The reduction of sea ice in Svalbard did not affect the growth rate of pups since most females shifted from first-year ice floes to pieces of glacier-ice for birthing and nursing their offspring (Kovacs et al. 2020). However, this is a short-term solution since retraction of tidal glaciers eventually will end up on land, eliminating this replacement birthing and nursing strategy.

Identifying marine mammal hotspots and areas of high species richness is essential to help guide management and conservation efforts. A recent major study (Hamilton et al. 2021) summarizes the deployment of 585 satellite transmitters on 13 species of marine mammals in the Greenland- and northern Barents Seas from the period 2005-2018 and shows that parts of the study area, especially the northernmost parts, are to be regarded as "hot spot" areas for these marine mammal species (Fig. 3.9.1.7). The marginal ice zone (MIZ) of the Greenland Sea and northern Barents Sea, the waters surrounding the Svalbard archipelago and a few Northeast Greenland coastal sites were identified as key marine mammal hotspots and areas of high species richness in this region.

Figure 3.9.1.7: (a,c,e) individual hotspots and (b,d,f) location hotspots for the 13 species tagged around Svalbard and Northeast Greenland over (a,b) the entire year, (c,d) during the summer/autumn and (e,f) during the winter/spring. Increasing intensities of red indicate hotspots of different levels of statistical significance. Hamilton et al., 2021.

Sea birds

By Per Fauchald (NINA)

About six million pairs from 36 seabird species breed regularly in the Barents Sea (Barrett et al. (2002), Table 3.9.2.1). 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 Fig. 3.9.2.1. 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 on fish, including 0-group fish, capelin, I-group herring and sandeels. The shift in diet is accompanied by a shift in species composition. In the south, Brünnich’s guillemots are replaced by 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 3.9.2.1. Major seabird colonies in the Barents Sea. Data compiled from SEAPOP (www.seapop.no), Fauchald et al. (2015) and The Seabird Colony Registry of the Barents and White Seas.

Table 3.9.2.1. Seabirds in the Barents Sea sorted by breeding population size in decreasing number. Breeding pairs are from Strøm et al. (2009). Observations on BESS 2020 are the observations from Norwegian and Russian vessels during the ecosystem survey in 2020.

Population monitoring in Norway and Svalbard has revealed a downward trend for several populations the last 30 years, including black-legged kittiwakes (Fig. 3.9.2.2 A) and Atlantic puffin (Fig. 3.9.2.2 E) on the Norwegian mainland and Brünnich’s guillemots (Fig. 3.9.2.2 F) on Svalbard. 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 populations on Bjørnøya and some colonies on the Norwegian mainland have increased since then (Fig. 3.9.2.2 C and D). The status and trends of the populations of seabirds in the Eastern Barents Sea is less known.

Figure 3.9.2.2: Seabird population fluctuations in SEAPOP monitoring sites on the Norwegian mainland (left panel) and Svalbard (right panel). Data sources: Miljøovervåking Svalbard og Jan Mayen -MOSJ (www.mosj.no, updated 2019), SEAPOP (www.seapop.no, updated 2020).

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 (Fig. 3.9.2.3). This peak is mainly due to Atlantic puffins, Northern fulmars, common guillemots and black-legged kittiwakes migrating from colonies around the Norwegian Sea into 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 (Fig. 3.9.2.3). 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 3.9.2.3: 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 (Fig. 3.9.2.4). 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 (Fig. 3.8.2.5) of different species and the centre of gravity of the spatial distribution (Fig. 3.8.2.6) was calculated for each year.

Figure 3.9.2.4. Density of seabirds during the Barents Sea ecosystem surveys in 2019 (top) and 2020 (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 (Fig. 3.9.2.5). 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. Fig. 3.9.2.2) 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. 3.9.2.6). 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 3.9.2.5. Abundance of auks (left) and ship-followers (right) in the Western Barents Sea during the ecosystem surveys 2009-2020. Note that the numbers of ship-followers are systematically over-estimated. Asterisks indicate significant negative trends in the abundance estimates (* P < 0.05, ** P < 0.001).