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Growth of the cormorant population comes to a halt

Press release 2012-08-20 at 9:00

Image: Heikki Kotiranta

A total of approximately 17,100 cormorant nests were found in Finland’s sea areas in the summer of 2012 – 600 nests less than in the previous summer. In contrast to other sea areas, the breeding population on the Archipelago Sea fell by 12 per cent. The breeding population fell by seven per cent in the Western Gulf of Finland, while growth of 11 per cent was observed in eastern reaches of the gulf. As a result, the total population in the Gulf of Finland remained the same.

The growth of the cormorant breeding population has slowed significantly over the last ten years. Annual growth in 2003–2007 was 47 per cent on average, but only 16 per cent in 2008–2012. Growth in the Baltic Sea population has partly been curbed by several harsh winters in central and southern Europe.

In 2012, the cormorant breeding population remained at its strongest in the Bothnian Sea (6,151 nests) and the Gulf of Finland (5,940 nests), while 3,793 nests were counted in the Archipelago Sea, 1,046 in Kvarken and 178 in the Bay of Bothnia.

The decline of the cormorant population in the Archipelago Sea and Western Gulf of Finland can be explained by the increased abundance of the white-tailed eagle. It is clear that this eagle has reduced the breeding success of cormorants in several colonies, for example in Raseborg and Luvia. White-tailed eagles have been observed eating both cormorant chicks and eggs, causing adult birds to abandon their usual breeding islets.

A total of 37 cormorant colonies were detected in Finnish sea areas, nesting on 57 islets. The six new breeding colonies were located in Raseborg, Hanko, Naantali, Pori and Nykarleby.

Cormorants protecting the common guillemot

The common guillemot, which is endangered in Finland, has become significantly more abundant in the Eastern Gulf of Finland because it shares nesting islets with the cormorant. Usually laying its eggs under rocks, the common guillemot has now been observed openly laying its eggs between cormorant nests. This prevents land carnivores, mink in particular, from destroying the nests.

Cormorant nests were illegally destroyed in at least two colonies: in Raseborg (64 nests) and Pori (12 nests). In Nykarleby, a farmed fox had been taken to a nesting islet. It destroyed the nesting sites of the endangered lesser black-backed gull, but had no significant impact on cormorant nestling production.

Two cormorant subspecies nest in Europe: the carbo on the Atlantic and the sinensis on the Baltic Sea. Over half of the cormorants hunted under special permission in the Archipelago Sea and the Gulf of Bothnia in the autumns of 2010 and 2011 were of the Atlantic subspecies. This means that hunting mainly affects migratory cormorants rather than those nesting in Finland. Part of the population of the Atlantic subspecies migrates to its wintering areas by way of the Baltic Sea, leading to its becoming common in the Finnish sea area by the latter half of August.

Development of the nesting cormorant population in Finland 1996-2012

2004

2005

2006

2007

2008

2009

2010

2011

2012

Gulf of Finland

1777

2191

2332

3054

3822

4681

4725

5877

5940

Archipelago Sea

581

1158

1611

3170

4439

4703

3586

4289

3793

Bothnian Sea

311

1047

1534

2296

3650

5649

5186

6297

6151

Merenkurkku/
Kvarken

108

114

150

205

547

720

719

1087

1046

Bothnian Bay

133

111

143

197

219

254

203

162

178

No. of 
breeding 
pairs

2910

4621

5770

8922

12677

16007

14419

17712

17108

Colonies

21

26

23

32

41

49

34

34

37

Growth rate %

79

59

25

54

42

26

-10

23

- 3

Development of the nesting cormorant population in Finland 1996-2012
    

Development of the nesting cormorant population in Finland 1996-2012_PIENI.jpg

              Bigger graph

Nesting sites of cormorants 2012
  

Further infomation

Pekka Rusanen, Researcher, Finnish Environment Institute SYKE, 
tel. +358 400 148 691, firstname.lastname@ymparisto.fi

Markku Mikkola-Roos, Senior Researcher, Finnish Environment Institute SYKE, tel. +358 400 148 685, firstname.lastname@ymparisto.fi

Riku Lumiaro, Information Officer, Finnish Environment Institute SYKE, 
tel. +358 40 5098 654, firstname.lastname@ymparisto.fi

Images for media

Image: Heikki Kotiranta

Image: Heikki Kotiranta

Image: Heikki Kotiranta

Cormorant nesting colony in the Gulf of Finland. Image: Heikki Kotiranta


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