Seabirds

Seabirds 2013
Typography
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Numbers of seabirds breeding in the Barents Sea Region have changed dramatically over the last 50 years. A recent assessment of population status and trends has been conducted, based on monitoring and census date for several species breeding in the western part of the Barents Sea (i.e., Norwegian mainland and Svalbard) (Fauchald et al., 2015). Resulting analyses indicate that breeding populations of subarctic pelagic auk species (common guillemot Uria aalge, razorbill

Alca torda, and Atlantic puffin Fratercula arctica) have increased in the southern colonies over the last 25 years. Most notably, the population of common guillemots breeding on the Norwegian mainland and Bjørnøya has recovered steadily since the mass mortality in the winter 1986/87.

Meanwhile, the large population of the Arctic sister species, the Brünnich’s guillemots breeding on Spitsbergen have declined from about 1.15 million pairs in 1988 to about 520,000 pairs in 2013. The kitiwake population has also shown a steep decline, especially on the Norwegian mainland where the population decreased from approximately 170,000 pairs in 1988 to 40,000 pairs in 2013. The large gull species, herring gull (Larus argentatus) and black-backed gull (Larus marinus) are also declining in the southern Barents Sea. Similarly, the glaucous gull (Larus hyperboreus) has been declining on Bjørnøya; albeit, the status of this species on Spitsbergen is largely unknown. Trends for large populations of northern fulmar and little auks on Svalbard are also largely unknown.

The status and trends of breeding populations in the eastern Barents Sea is hard to assess due to a lack of long-term monitoring data. However, results from monitoring conducted by MMBI in breeding colonies at Cape Gorodetski, Cape Krutik, and Dvorovaya Bay on the Kola coast (Figure 4.3.58) indicate contrasting trends for the common guillemot breeding population. The decline in the Brünnich’s guillemot population documented in Svalbard and mainland Norway is evident along the Kola Peninsula. The population of kittiwake along the Kola coast seems to follow the same trend as on the Norwegian mainland, although not so dramatic as for many of the Norwegian colonies. Virtually nothing is known about the status and trends of the huge breeding populations on Novaya Zemlya and Franz Josef Land. In the White Sea, herring gull, lesser black-backed gull, and great cormorant are monitored annually on the Solovetsky Islands in Onega Bay. While the populations of great cormorant and herring gull have been relatively stable over the period 1991-2014, the lesser black-backed gull population has increased during the same period (Figure 4.3.58).

Reasons behind the recent changes in Barents Sea seabird communities are unknown, however several studies suggest that changes in food availability, often triggered by changes in ocean climate, govern population dynamics in species such as the common guillemot (Erikstad et al., 2013; Myksvoll et al., 2013), Brünnich’s guillemot (Descamps et al., 2013), and kittiwake (Sandvik et al., 2014). In general, climatic variability in the Barents Sea is determined by the inflow of Atlantic Water masses, which again has significant effects on ice conditions and biological production, including movement and stock size of important seabird prey species, i.e., capelin, herring, and polar cod (Loeng, 1991). These large variations in the seabirds’ preferred prey fish stocks have had consequences for some species, resulting in either serious declines in e.g., common guillemot, Brünnich’s guillemot, and puffin breeding populations, or changes in chick diet composition and chick growth (Barrett, 2007). Direct effects of climate have also recently been put forth to explanation the decline in the common guillemot population in the Barents Sea (Mesquita et al., 2015). In addition to climatic-induced variations in seabird populations, the fishing industry has also had large ecological impacts in recent decades through overfishing pelagic species which are seabird prey, and through fishing-induced shifts in predation pressure on these pelagic fish species (Gjøsæter, 1995).

For some seabird populations, changed patterns of predation from mammalian and avian predators might also be important factors. For example, an increased population of white-tailed eagle (Haliaeetus albicilla) might have increased predation pressure on some seabird species on the Norwegian mainland (Hipfner et al., 2012). As another example, changed ice-conditions in Spitsbergen fjords changed the polar foxes’ (Alopex lagopus) access to islands with breeding colonies of common eider (Mehlum, 2012). For top predators and scavengers such as the glaucous gull, bio-accumulation of long-transport organochlorine pollutants has been shown an important contributing to population declines (Erikstad and Strøm, 2012). Finally, the present dynamics of several seabird populations on mainland Norway and Russia may still be influenced by the legacy of historic harvesting of eggs, chicks, and adults from breeding colonies (Krasnov and Barrett, 1995; Fauchald et al., 2011).

Two seabird species — great skua (Stercorarius skua) and northern gannet (Morus bassanus) — continue with both population increases and range expansions into the Barents Sea Region. Great skua has a very restricted breeding range, occurring only in the northeast Atlantic from northern parts of the British Isles to the Faroe Islands, Iceland, Norway, and Svalbard. Its numbers have been increasing since the beginning of the 20th century, and it has extended its breeding range progressively north and eastwards into the Barents Sea. Great skua was first recorded breeding on Bjørnøya in 1970 and on Spitsbergen in 1976. Since then the population has grown rapidly. Protection from human disturbance and improved food availability in key breeding areas in Shetland, Orkney, and Iceland are probably the main reasons for both increased population size and range expansion. In 2015, great skua had breeding sites throughout the Barents Sea Region, including the northernmost islands of Svalbard, Franz Josef Land, and Novaya Zemlya.

Northern gannet is a common North Atlantic species with its main centre of distribution in Britain. They began their colonisation of Norway in the mid-1940s at Runde, Møre, and Romsdal; they expanded into Northern Norway in the early 1960s, where the population increased in 1995 to ca. 2,200 pairs spread over five colonies (Barrett and Folkestad, 1996). Its breeding in Russia was observed for the first time in 1993, when three birds established themselves on Seven Island on the Murman coast (Krasnov and Barrett, 1995). Colonisation into the Barents Sea seems to be ongoing, as another small colony was recently established on Bjørnøya, Svalbard. The population in the Norwegian Sea has stabilised; fluctuating around 3,000 pairs annually since the early 1990s. However, the Barents Sea population continues to increase (Fauchald et al., 2015).

Figure 4.3.58a. Trends in some seabird species monitored in the Barents Sea. Source: The Seabird Colony Registry of the Barents and White Seas and the Norwegian Institute for Nature Research.Figure 4.3.58a. Trends in some seabird species monitored in the Barents Sea. Source: The Seabird Colony Registry of the Barents and White Seas and the Norwegian Institute for Nature Research.

Figure 4.3.58b. Trends in some seabird species monitored in the Barents Sea. Source: The Seabird Colony Registry of the Barents and White Seas and the Norwegian Institute for Nature Research.Figure 4.3.58b. Trends in some seabird species monitored in the Barents Sea. Source: The Seabird Colony Registry of the Barents and White Seas and the Norwegian Institute for Nature Research.

Figure 4.3.58c. Trends in some seabird species monitored in the Barents Sea. Source: The Seabird Colony Registry of the Barents and White Seas and the Norwegian Institute for Nature Research.Figure 4.3.58c. Trends in some seabird species monitored in the Barents Sea. Source: The Seabird Colony Registry of the Barents and White Seas and the Norwegian Institute for Nature Research.