Present Status and Trends in Population of 

 Seabirds in Norway 



by 



Einar Brun 1 



University of Troms0 

 Troms0, Norway 



Abstract 



The most numerous seabird in Norway is the puffin (Fratercula arctica), but its 

 current breeding population of 1.25 million pairs is slowly declining. The kitti- 

 wake (Rissa tridactyla), however, is increasing and establishing new colonies; its 

 population now stands at 510,000 pairs. The population of the common murre 

 (Una aalge), the seabird species most vulnerable to human activity, was about 

 160,000 breeding pairs in 1964 but is now decreasing at a rate of nearly 5% per 

 year. Of the other alcids, the razorbill (Alca torda) and thick-billed murre (Uria 

 lomvia) show similar declines, and the black guillemot (Cepphus grylle) is main- 

 taining a stable population. The fulmar (Fulmarus glacialis) and the gannet (Sula 

 bassana) have both spread from the British Isles and have established a number 

 of breeding colonies in Norway during this century. Evidently immigration of 

 gannets is still occurring, since the observed rate of increase far exceeds the 

 population's intrinsic rate of increase. The impact of human activity on bird mor- 

 tality varies from species to species. The two most serious factors are coastal oil 

 pollution and the use of fishing gear; direct hunting pressure accelerates the 

 decline of murres and razorbills. Persistent toxic chemicals are not yet a serious 

 problem in Norway. 



Norway, with a coastline of more than 

 20,000 km, an abundance of islands, and areas 

 of offshore upwelling, provides good condi- 

 tions for a rich seabird fauna. A regional 

 study of this seabird fauna has been under- 

 taken as a sideline of basic marine research. 

 Although the ultimate aim has been to evalu- 

 ate the importance of seabirds in the energy 

 flow of a marine ecosystem, a more realistic 

 problem (given priority so far) has been to 

 study yearly production and the dynamics be- 

 hind changes in the breeding populations. 



Good population estimates are of funda- 

 mental importance to studies of population 

 dynamics. Because the available censuses of 

 seabirds in Norway were few and largely in- 

 adequate, a long-term program was started in 

 1961. In the beginning, resources and assist- 



'Deceased. 



ance were very limited, and the work was con- 

 centrated on cliff-breeding seabirds, particu- 

 larly the gannet (Sula bassana), fulmar (Ful- 

 marus glacialis), kittiwake (Rissa tridactyla), 

 razorbill (Alca torda), common murre (Uria 

 aalge), thick-billed murre (U. lomvia), and 

 puffin (Fratercula arctica). Until 1970, the 

 study involved making annual censuses in the 

 approximately 20 major colonies of cliff- 

 breeding seabirds and mapping the distribu- 

 tion of the quantitatively less important 

 colonies. 



Since 1970, the Norwegian seabird program 

 has also involved more detailed studies in 

 some selected colonies. In these colonies, em- 

 phasis has been on investigation of yearly pro- 

 duction and of the factors limiting this pro- 

 duction, and evaluation of the effects of 

 human activity on the population growth. 



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