300 



E. BRUN 



Pollution 



No quantitative investigation similar to 

 those made in Great Britain, Netherlands, 

 and Belgium (Tanis and Bruyns 1968) has 

 been carried out on the impact of oil pollution 

 on seabirds in Norway. The northern Nor- 

 wegian population of the most threatened 

 species, murres and razorbills, winter in 

 North Sea coastal areas where oil pollution 

 and oiled birds have most frequently been 

 found. It is possible that whole populations 

 winter every year in the same area, and if they 

 happen to be in a heavily polluted area, a par- 

 ticular population may be seriously affected. 

 Such an occurrence is believed to have caused 

 the dramatic decline in the S0r Fugl0y popula- 

 tion (cf. Table 5). 



Although not yet serious, pollution by per- 

 sistent toxic chemicals such as organo- 

 chlorines and mercury is a problem even in 

 northern Norway, because the northbound 

 coastal current brings water masses, plank- 

 ton, and nekton from areas with industrial 

 wastes. Analysis of the eggs of herring gull 

 (Larus argentatus), murre, razorbill, and kitti- 

 wake in 1972 showed relatively low levels of 

 mercury; the only species with a relatively 

 high level of mercury (mean 0.58 ppm) was the 

 gannet (Fimreite et al. 1974). This elevated 

 toxic burden may have caused a reduced 

 breeding success for the gannet. Analysis of 

 concentrations of PCB's and DDT/DDE 

 showed that the levels of these organo- 

 chlorines were generally also lower in Nor- 

 wegian seabirds than in those of Britain ( Fim- 

 reite etal. 1977). 



Protection and Necessary 

 Conservation Measures 



Total protection of some of the important 

 seabird colonies (including the surrounding 

 nearshore waters) has proven very effective, 

 especially when the protection is so strict that 

 landing is prohibited for a specified period 

 during incubation and fledging. However, to 

 reduce the rapid decrease of some species, a 

 total hunting prohibition of those species 

 must be instigated, oil pollution must be re- 

 duced, and the fisheries must be regulated to 

 reduce the mortality caused by fishing gear. 



Natural Factors Influencing 

 Breeding Success 



The factors discussed so far are all results 

 of human activities which directly or indi- 

 rectly influence seabird mortality. Yearly pro- 

 duction or breeding success is, however, also 

 influenced by a number of natural factors 

 such as food supply, availability of suitable 

 nest sites, predation, climate (weather), and 

 population-dependent factors (age, breeding 

 experience, population density). For the 

 gannet, whose breeding success has been 

 studied in some detail (Brun 1974), it was con- 

 cluded that the differences in exposure (to 

 severe weather) and in breeding experience 

 were the most important factors responsible 

 for annual fluctuation in breeding success. 

 For such species as murres, razorbills, and 

 puffins, food supply is an important limiting 

 factor. If the spawning of the fish species that 

 constitute their main food items fails 1 year 

 for some reason, it may be very difficult for 

 the seabirds to find an adequate alternative 

 food supply and most of the chicks starve to 

 death. To a lesser degree, food supply is limit- 

 ing for the kittiwake, which seems to be more 

 influenced by bad weather (Norderhaug et al. 

 1977). 



Conclusion 



Two opposite population trends have been 

 observed the decline of the coastal-bound 

 murres and razorbills and the increase and 

 spread of the more pelagic gannets, fulmars, 

 and kittiwakes. These changes are attributed 

 to a number of factors, which include the 

 following: 



The diving murres and razorbills spend a 

 major part of their time swimming on the sur- 

 face and are thus more susceptible to surface 

 oil pollution than are the pelagic species. 



The coastal-bound murres and razorbills 

 are quite heavily hunted, whereas there is no 

 regular hunting of the pelagic species. 



The pelagic species are mainly surface 

 feeders and do not swim under water, and are 

 thus less affected by the drift-nets than are 

 diving birds. 



