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The status and trends of seabirds breeding in Norway and Svalbard

Fauchald, Per; Anker-Nilssen, Tycho; Barrett, Robert; Bustnes, Jan Ove; Bårdsen, Bård-Jørgen; Christensen-Dalsgaard, Signe; Descamps, Sebastien; Engen, Sigrid; Erikstad, Kjell E; Hanssen, Sveinn Are; Lorentsen, Svein-Håkon; Moe, Børge; Reiertsen, Tone; Strøm, Hallvard; Systad, Geir Helge
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http://hdl.handle.net/11250/2397703
Utgivelsesdato
2015
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  • NINA Rapport/NINA Report [2048]
  • Publikasjoner fra CRIStin - NINA [1888]
Originalversjon
NINA rapport. 84 p. Norsk institutt for naturforskning, 2015  
Sammendrag
Fauchald P, Anker-Nilssen T, Barrett RT, Bustnes JO, Bårdsen B-J, Christensen-Dalsgaard S,

Descamps S, Engen S, Erikstad KE, Hanssen SA, Lorentsen S-H, Moe B, Reiertsen TK, Strøm

H, Systad GH (2015) The status and trends of seabirds breeding in Norway and Svalbard –

NINA Report 1151. 84pp.

This report presents the updated sizes, trends and spatial distributions of the breeding populations

of 17 seabird species breeding in Norway and Svalbard. The analyses are based on

available census and monitoring data from SEAPOP; the Norwegian monitoring and mapping

program for seabirds. In addition, the report presents results from a species-specific literature

review of the most important prey items and drivers of population change.

The report documents large-scale decadal changes in the seabird communities along the coast

of Norway and Svalbard. A division of the populations into five geographical regions (North Sea

& Skagerrak; Norwegian Sea; Barents Sea; Bjørnøya; and Spitsbergen) was used as a basis

for the analyses of population dynamics from 1980 to present. 13 of the 35 regional seabird

populations assessed have declined by more than 50% the last 25 years. 5 regional populations

increased by more than 100% in the same period, while 8 populations showed large decadal

fluctuations. Several populations were not assessed due to the lack of census and/or

monitoring data. In order to improve the dataset, it is recommended that a census of breeding

seabirds from Vesterålen to the Swedish border is completed.

Declining populations were found in all regions and included all major ecological groups (i.e.;

Pelagic surface-feeding (Ps), Pelagic diving (Pd), Coastal surface-feeding (Cs), Coastal benthic-feeding

(Cb) and Coastal diving (Cd) seabirds). Populations with more than a 50% decline

the last 25 years were: Common Gull (Cs), Lesser Black-backed Gull (Ps) and Atlantic Puffin

(Pd) in the North Sea & Skagerrak; Great Cormorant (Cd), Common Eider (Cb), Black-legged

Kittiwake (Ps) and Common Guillemot (Pd) in the Norwegian Sea; Herring Gull (Cs), Great

Black-backed Gull (Cs), Black-legged Kittiwake (Ps) and Brünnich’s Guillemot (Pd) in the Barents

Sea; Northern Fulmar (Ps) and Glaucous Gull (Ps) on Bjørnøya; and Brünnich’s Guillemot

(Pd) on Spitsbergen.

The populations of European Shag and Great Cormorant have shown large fluctuations with a

notable increase in the population of Phalacrocorax carbo sinensis in North Sea & Skagerrak.

Common guillemot has been increasing in the Barents Sea since the collapse in the population

in the 1980s, however the population in the Norwegian Sea has been steadily declining since

the early 1980s. Atlantic Puffin is declining in the North Sea and Norwegian Sea, but the population

in the Barents Sea is stable or is increasing slightly. The datasets were too small to assess

several of the large gull species in the Norwegian Sea. However, extensive monitoring in

the North Sea & Skagerrak and recent censuses in the Barents Sea suggest declines by more

than 50% in several of the gull populations in these areas. Black-legged Kittiwake has declined

in all regions except for Bjørnøya. The large colonies of Brünnich’s Guillemot on Spitsbergen

have declined from 1.15 million pairs in 1988 to 522 000 pairs in 2013. The colony on Bjørnøya

(about 100 000 pairs) has in the same period been stable or declined slightly, while the small

populations on the Norwegian mainland have almost disappeared. Northern Gannet has been

increasing in Norway since the establishment of this species on Runde in the 1940s. The species

has expanded northward and has recently established a small colony as far north as

Bjørnøya.

The review of diet studies highlighted the importance of the young age-classes of cod fish, the

importance of pelagic forage fish species and in particular the importance of sandeel. However,

the differences in diet among ecological groups combined with the fact that declining seabird

populations were found in all regions and included all major ecological groups suggest that the

recent changes in Norwegian seabird communities cannot be explained by changes in the

abundance of a single group of resources alone. On the contrary, this might suggest a combined effect of simultaneous changes in several prey items, possibly involving entire trophic

levels. Alternatively, it might suggest that bottom-up regulation through food is less important,

and that top-down mechanisms such as anthropogenic stressors and predation are more involved

in the present changes.

A large number of studies have been conducted to investigate how different anthropogenic and

environmental factors affect seabird populations. Factors such as fisheries by-catch, harvest

and intentional killing, pollution and disturbance are all anthropogenic stressors with a welldocumented

negative impact. Although most of these stressors have been reduced in Norwegian

waters due to the implementation of regulatory mechanisms and protection measures,

they might still have impact on local populations. For example, the decline in the population of

Glaucous Gull on Bjørnøya has been related to high levels of persistent organic pollutants.

Several case studies suggest that predation from avian and small mammalian predators in the

seabird colonies might be important, and we cannot exclude this driver as an important mechanism

behind the observed declines. The large spatial and the relatively long temporal scale of

the population changes observed in the present report, might suggest that fluctuations in the

marine ecosystems, possibly partly due to climate change and past and present fishing pressures,

might be important. This is corroborated by numerous studies documenting a direct impact

from food deprivation and an indirect impact from climatic factors on seabird population

dynamics. Such factors often involve complex indirect trophic links which make it difficult to

point out the ultimate cause of the observed change.

We conclude that the two most likely candidates to explain the recent declines in Norwegian

seabird populations are 1) increased predation in the seabird colonies from avian and mammalian

predators and 2) ecosystem changes affecting the availability of prey. The impact from

these drivers might be difficult to document and even more challenging to control. In contrast,

more easily managed direct anthropogenic stressors such as fisheries by-catch, pollution,

hunting and disturbance have either been constant or have shown a decreasing trend. Although

these drivers cannot explain the recent population declines, they still contribute to the

cumulative impact on seabird populations and these stressors are therefore especially important

to control and minimize in rapidly declining and threatened populations.
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