Only regional changes in the Finnish Great Cormorant population

Press release 2022-08-16 at 8:00
Small colony of nesting Great Cormorants on an island. Black birds sitting on their nests in a tree.
© Heikki Kotiranta

Approximately 24,470 Great Cormorant nests were counted in Finland in the summer of 2022. The size of the entire nesting population in Finland has only fluctuated by a few per cent since 2015. However, at the regional level, the annual variations in the number of nests are significant.

In the summer of 2022, the nesting population in Finland was nearly one per cent, or 140 nests, lower than in the previous summer. In the autumn of 2021, a new colony of three hundred nests was found in Hamina, which raised the previous year’s number of nests to approximately 24,610. The population in 2021 was five per cent smaller than in 2020.

Number of cormorant nests 2013–2022.
Percentage increase in the cormorant population 2013–2022.

Approximately one-third of the Great Cormorant’s nests were located in both the Gulf of Finland and the Bothnian Sea, one-fifth in the Archipelago Sea, ten per cent in Kvarken and nine per cent in the Bothnian Bay.

“In the Gulf of Finland, the Great Cormorant population decreased by over ten per cent, as well as in the Archipelago Sea and Kvarken. In contrast, the Great Cormorant population in the Bothnian Sea and the Bothnian Bay was one-fifth larger than in summer 2021,” says researcher Pekka Rusanen from the Finnish Environment Institute.

According to Rusanen, the abundant White-tailed Eagle population in the Gulf of Finland, the Archipelago Sea and the Kvarken region affects Great Cormorants: “In the Gulf of Finland, the Archipelago Sea and Kvarken, nearly 6,000 fewer Great Cormorant nests were detected this year than four years ago. In Kvarken, there were just under half of the number of nests of summer 2018 and two colonies instead of seven.”

The Great Cormorant population in the Gulf of Bothnia increased by 12 per cent. There were nearly 12,700 nests in the Gulf of Bothnia, of which about 8,010 were in the Bothnian Sea, 2,480 in Kvarken and 2,190 in the Bothnian Bay. In the summer of 2022, there were about 7,380 nests in the Gulf of Finland and 4,400 in the Archipelago Sea.

Number of cormorant nests by marine area in 2013–2022
Number of cormorant nests by marine area in 2013–2022.

An increasing share of Great Cormorants nested in large colonies

A total of 52 Great Cormorant colonies were observed in Finland. The colonies nested on a total of 71 islets or islands, and in addition, five colonies nested in small groups only in the structures of sea marks, leading marks or lighthouses.

Over 60 per cent of the entire Finnish Great Cormorant population nested in the eight largest communities. These colonies of over a thousand nests were located in Rauma (about 4,700 nests), Mustasaari (2,240), Porvoo (1,680), Turku (1,490), Kristinestad (1,430), Kokkola (1,360), Enäjärvi Lake in coastal Pori (1,250) and Espoo (1,140).

At the municipal level, the population decreased most, by around 1,100 nests, in Kirkkonummi and grew most, by 1,040 nests, in Rauma. In Uusikaupunki and Raasepori, the population decreased by about 400 nests. In Espoo, Pori and Mustasaari the population increased by about 300 nests.

The nesting area of the Great Cormorant colonies totalled approximately 65 hectares. The share of Great Cormorants nesting in trees is still clearly increasing. This summer, nests in trees already accounted for half of the total number of nests, while three years earlier the share was only one-quarter. The share of nesting in trees has grown while the predation of the White-tailed Eagle has increased.

Map: Number of cormorant nests by region 2022

Many colonies were deserted

This year, an exceptionally large number of colonies were deserted. In the previous summer, there were still about 3,000 nests in the 23 deserted communities. A major part of these nests were left empty due to the increased predation of the White-tailed Eagle. In addition, the nesting of Great Cormorants failed completely in several smaller colonies.

Ten new nesting sites were found in different sea areas. They only had a total of 160 nests. In addition, three nesting sites were in use after a break of several years.

Illegal harassment of Great Cormorant colonies occurred this summer at least in Raasepori and Finström in Åland, where the only nesting attempt observed in the region was prevented. In addition, there are indications of harassment at least in Loviisa, Porvoo and Kristinestad.Nearly 90 people participated in censuses, searches and inspections of Great Cormorant colonies in the summer of 2022. The monitoring of the Great Cormorant population is coordinated by the Finnish Environment Institute. Monitoring collects basic information on the ecology and distribution of the species. In Finland, the Great Cormorant is protected by the Nature Conservation Act throughout the year and is not on the EU’s list of huntable species.

Inquiries

  • Pekka Rusanen, Researcher, Finnish Environment Institute, tel. +358 (0)400 148 691, firstname.lastname@syke.fi
  • Markku Mikkola-Roos, Senior Coordinator, Finnish Environment Institute, tel. +358 (0)400 148 685, firstname.lastname@syke.fi
  • Eija Järvinen, Communications Specialist, SYKE, firstname.lastname@syke.fi, tel. +358 295 251 242

More information on the subject

Finnish Environment Institute press release 2022-08-03: White-tailed Eagles significantly affect Great Cormorants in the Baltic Sea