Table 12.Comparison of the number of seabirds breeding on the coasts of Great Britain and Ireland (Cramp et al. 1974) and on the coast of Norway.SpeciesNumber of breeding pairs[80]Great Britain and IrelandNorwayFulmarus glacialis306,0001,100Puffinus puffinus> 175,000—Hydrobates pelagicus105or 106103or 104Oceanodroma leucorrhoa104102Sula bassana138,000760Phalacrocorax carbo8,10012,000P. aristotelis31,00033,000Stercorarius skua3,1001[81]S. parasiticus1,1008,000Larus ridibundus74,0004,000[82]L. canus12,000(150,000)[82]L. fuscus47,0009,000[82]L. argentatus333,000(260,000)[82]L. marinus22,000(40,000)[82]Rissa tridactyla470,000510,000Sterna sandvicensis12,000—S. dougalli2,300—S. hirundo14,000(13,000)[82]S. paradisaea(31,000)(21,000)[82]S. albifrons1,800—Alca torda(144,000)30,000Uria aalge(577,000)100,000U. lomvia—1,000Cepphus grylle8,30022,000Fratercula arctica(490,000)1,250,000Totalca. 3,000,000ca. 2,500,000
Use of fishing gear close inshore, especially pound nets set near colonies of diving seabirds, can take a heavy toll under special weather conditions. In 1969 at Runde, 85 birds, mainly auks, shags, and some diving ducks, were caught in one net in 24 hours; this is an exceptionally high figure. The total loss of diving seabirds in pound nets per year in Norway (about 6,000 nets fishing for 40 days) was estimated to be at least 40,000 birds in 1969. The data are too unreliable to give species composition, however, since fishermen rarely make note of this.
Amounts of fish offal from offshore trawlers, drift-netters, and longline fishing boats have increased in recent years, and some seabirds, particularly kittiwakes, fulmars, and gannets make use of this new and readily available food source. Thus, although the use of fishing gear is a serious threat to seabird survival, fish waste from the same boats provides an abundant food supply for the more pelagic species.
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 Norwegian 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 particular population may be seriously affected. Such an occurrence is believed to have caused the dramatic decline in the Sør Fugløy population (cf. Table 5).
Although not yet serious, pollution by persistent toxic chemicals such as organochlorines and mercury is a problem even in northern Norway, because the northbound coastal current brings water masses, plankton, and nekton from areas with industrial wastes. Analysis of the eggs of herring gull(Larus argentatus), murre, razorbill, and kittiwake 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 organochlorines were generally also lower in Norwegian seabirds than in those of Britain (Fimreite et al. 1977).
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 reduced, and the fisheries must be regulated to reduce the mortality caused by fishing gear.
The factors discussed so far are all results of human activities which directly or indirectly influence seabird mortality. Yearly production 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 concluded 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 limiting for the kittiwake, which seems to be more influenced by bad weather (Norderhaug et al. 1977).
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 surface 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.
• The pelagic species are the principal beneficiaries of recently increased supply of fish offal from trawlers.
The program was originally sponsored by Tromsø Museum, later University of Tromsø, and has been financially supported by the Norwegian Research Council for Science and Humanities and the Norwegian Game Fund. The research grants are gratefully acknowledged. I also thank my field assistants and the many local people at the breeding sites who have been most helpful.
Brun, E. 1963. Ornithological features of Nord-Fugløy and Sør-Fugløy. Astarte 1(22):1-13.Brun, E. 1965. Brunnich's Guillemot,Uria lomvia(L.), as a breeding bird in Norway. (In Norwegian, English summary.) Sterna 6:229-250.Brun, E. 1966. The breeding population of puffins(Fratercula arctica)in Norway. (In Norwegian, English summary.) Sterna 7:1-17.Brun, E. 1969a. The breeding distribution and population of guillemots(Uria aalge)in Norway. (In Norwegian, English summary.) Sterna 8:209-224.Brun, E. 1969b. The breeding distribution and population of razorbills(Alca torda)in Norway. (In Norwegian, English summary.) Sterna 8:345-359.Brun, E. 1971a. Census of Puffins(Fratercula arctica)on Nord-Fugløy, Troms. Astarte 4:41-45.Brun, E. 1971b. Breeding distribution and population of cliff-breeding seabirds in Sør-Varanger, north Norway. Astarte 4:53-60.Brun, E. 1971c. Population changes of some seabirds in south Norway. (In Norwegian, English summary.) Sterna 10:35-56.Brun, E. 1972. Establishment and population increase of the gannetSula bassanain Norway. Ornis Scand. 3:27-38.Brun, E. 1974. Breeding success of gannetsSula bassanaat Nordmjele, Andøya, north Norway. Astarte 7:77-89.Coulson, J. C., and E. White. 1959. The post-fledging mortality of the kittiwake. Bird Study 6:97-102.Cramp, S., W. R. P. Bourne, and D. Saunders. 1974. The seabirds of Britain and Ireland. Collins, London. 287 pp.Fimreite, N., J. E. Bjerk, N. Kveseth, and E. Brun. 1977. DDE and PCBs in eggs of Norwegian seabirds. Astarte 10:15-20.Fimreite, N., E. Brun, A. Frøslie, P. Frederichsen, and N. Gundersen. 1974. Mercury in eggs of Norwegian seabirds. Astarte 7:71-75.Holgersen, H. 1951. Investigations of seabirds in Rogaland 1949-1950. (In Norwegian, English summary.) Stavanger Mus. Arb. 1950:61-76.Lütken, E. 1965. The breeding birds on Nord-Fugløy, north Norway, their distribution and numbers. (In Danish, English summary.) Dansk Orn. For. Tidsskr. 58:166-193.Norderhaug, M., E. Brun, and G. U. Møllen. 1977. Barentshavets sjøfuglressurser. Forhold i tilknytning til status, miljøproblemer of forshningsoppgave. Medd. Norsk Polar Inst. 104:1-119.Regnell, S. 1957. Fran det nordnorska fåggelberget Bleiksøya. Fauna Flora, Upps. 52:199-202.Soot-Ryen, T. 1941. The seabird rookeries of Troms county. (In Norwegian, English summary.) Tromsø Mus. Aarsh. 62(1):1-112.Tanis, J. J. C., and M. F. M. Bruyns. 1968. The impact of oil pollution on seabirds in Europe. Proc. Int. Conf. Oil Pollution of the Sea 1968:67-74.Valeur, P. 1947. Havhesten og havsula på Rundøy. Naturen 70:370-379.Willgohs, J. F. 1952. On the distribution of some seabirds in western Norway. Univ. Bergen Årb. 1951 Naturvit. Rekke (9):1-20.Willgohs, J. F. 1955. Om forekomsten av endel kyst-og sjøfugl på Vestlandet. Fauna, Oslo 8:16-27.
Brun, E. 1963. Ornithological features of Nord-Fugløy and Sør-Fugløy. Astarte 1(22):1-13.
Brun, E. 1965. Brunnich's Guillemot,Uria lomvia(L.), as a breeding bird in Norway. (In Norwegian, English summary.) Sterna 6:229-250.
Brun, E. 1966. The breeding population of puffins(Fratercula arctica)in Norway. (In Norwegian, English summary.) Sterna 7:1-17.
Brun, E. 1969a. The breeding distribution and population of guillemots(Uria aalge)in Norway. (In Norwegian, English summary.) Sterna 8:209-224.
Brun, E. 1969b. The breeding distribution and population of razorbills(Alca torda)in Norway. (In Norwegian, English summary.) Sterna 8:345-359.
Brun, E. 1971a. Census of Puffins(Fratercula arctica)on Nord-Fugløy, Troms. Astarte 4:41-45.
Brun, E. 1971b. Breeding distribution and population of cliff-breeding seabirds in Sør-Varanger, north Norway. Astarte 4:53-60.
Brun, E. 1971c. Population changes of some seabirds in south Norway. (In Norwegian, English summary.) Sterna 10:35-56.
Brun, E. 1972. Establishment and population increase of the gannetSula bassanain Norway. Ornis Scand. 3:27-38.
Brun, E. 1974. Breeding success of gannetsSula bassanaat Nordmjele, Andøya, north Norway. Astarte 7:77-89.
Coulson, J. C., and E. White. 1959. The post-fledging mortality of the kittiwake. Bird Study 6:97-102.
Cramp, S., W. R. P. Bourne, and D. Saunders. 1974. The seabirds of Britain and Ireland. Collins, London. 287 pp.
Fimreite, N., J. E. Bjerk, N. Kveseth, and E. Brun. 1977. DDE and PCBs in eggs of Norwegian seabirds. Astarte 10:15-20.
Fimreite, N., E. Brun, A. Frøslie, P. Frederichsen, and N. Gundersen. 1974. Mercury in eggs of Norwegian seabirds. Astarte 7:71-75.
Holgersen, H. 1951. Investigations of seabirds in Rogaland 1949-1950. (In Norwegian, English summary.) Stavanger Mus. Arb. 1950:61-76.
Lütken, E. 1965. The breeding birds on Nord-Fugløy, north Norway, their distribution and numbers. (In Danish, English summary.) Dansk Orn. For. Tidsskr. 58:166-193.
Norderhaug, M., E. Brun, and G. U. Møllen. 1977. Barentshavets sjøfuglressurser. Forhold i tilknytning til status, miljøproblemer of forshningsoppgave. Medd. Norsk Polar Inst. 104:1-119.
Regnell, S. 1957. Fran det nordnorska fåggelberget Bleiksøya. Fauna Flora, Upps. 52:199-202.
Soot-Ryen, T. 1941. The seabird rookeries of Troms county. (In Norwegian, English summary.) Tromsø Mus. Aarsh. 62(1):1-112.
Tanis, J. J. C., and M. F. M. Bruyns. 1968. The impact of oil pollution on seabirds in Europe. Proc. Int. Conf. Oil Pollution of the Sea 1968:67-74.
Valeur, P. 1947. Havhesten og havsula på Rundøy. Naturen 70:370-379.
Willgohs, J. F. 1952. On the distribution of some seabirds in western Norway. Univ. Bergen Årb. 1951 Naturvit. Rekke (9):1-20.
Willgohs, J. F. 1955. Om forekomsten av endel kyst-og sjøfugl på Vestlandet. Fauna, Oslo 8:16-27.
FOOTNOTES:[74]Deceased.[75]Numbers in parentheses are not based on a complete census of the coast.[76]In addition, an unknown number of pairs breeding inland.[77]Numbers in italics were censused from 1964 and 1974.[78]Estimated values from trends in neighboring colonies.[79]Numbers in parentheses are not based on a complete census of the whole coast.[80]Numbers in parentheses are not based on a complete census of the whole coast.[81]New in 1975 (Wim Vader, personal communication).[82]In addition, an unknown number of pairs breeding inland.
[74]Deceased.
[74]Deceased.
[75]Numbers in parentheses are not based on a complete census of the coast.
[75]Numbers in parentheses are not based on a complete census of the coast.
[76]In addition, an unknown number of pairs breeding inland.
[76]In addition, an unknown number of pairs breeding inland.
[77]Numbers in italics were censused from 1964 and 1974.
[77]Numbers in italics were censused from 1964 and 1974.
[78]Estimated values from trends in neighboring colonies.
[78]Estimated values from trends in neighboring colonies.
[79]Numbers in parentheses are not based on a complete census of the whole coast.
[79]Numbers in parentheses are not based on a complete census of the whole coast.
[80]Numbers in parentheses are not based on a complete census of the whole coast.
[80]Numbers in parentheses are not based on a complete census of the whole coast.
[81]New in 1975 (Wim Vader, personal communication).
[81]New in 1975 (Wim Vader, personal communication).
[82]In addition, an unknown number of pairs breeding inland.
[82]In addition, an unknown number of pairs breeding inland.