FOOTNOTES:

[67] Not counted.

[68] No estimate, but number insignificant.

[69] Species totally protected.

[70] Branta bernicla is fully protected since 1972.

[71] Somateria mollissima, Melanitta nigra, and M. fusca.

[72] The "number of pairs" is calculated by multiplying the number of birds observed by 0.67 (Dyck and Meltofte 1975).

[73] A few species breed near freshwater lakes, but are marine during the nonbreeding season.

[Present Status and Trends in Population of Seabirds in Norway]

by

Einar Brun[74]

University of Tromsø
Tromsø, 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 kittiwake (Rissa tridactyla), however, is increasing and establishing new colonies; its population now stands at 510,000 pairs. The population of the common murre (Uria 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 maintaining 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 mortality 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 conditions for a rich seabird fauna. A regional study of this seabird fauna has been undertaken as a sideline of basic marine research. Although the ultimate aim has been to evaluate 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 behind changes in the breeding populations.

Good population estimates are of fundamental importance to studies of population dynamics. Because the available censuses of seabirds in Norway were few and largely inadequate, a long-term program was started in 1961. In the beginning, resources and assistance were very limited, and the work was concentrated on cliff-breeding seabirds, particularly the gannet (Sula bassana), fulmar (Fulmarus 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 distribution 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, emphasis has been on investigation of yearly production and of the factors limiting this production, and evaluation of the effects of human activity on the population growth.

Material and Methods

The logistics of census operations have gradually improved from the use of slow, local transportation to the use of fast pneumatic boats and, in more recent years, seaplanes. Various census methods have been used, depending on species and circumstances.

For puffins, a method based on measurement of feeding frequency and on the number of puffins per time unit that pass a particular observation post when they return from the feeding ground was used (Brun 1971a). Kittiwakes and gannets were readily censused by a combination of photographic methods and detailed counts in sample areas (Brun 1971b). Direct counting is by far the most accurate method for razorbills, murres, and fulmars; but in the larger colonies of common murre, lack of time permitted accurate counts for only a limited proportion of the cliff. Direct counts of individuals, the egg/chick ratio, and estimates of the relative size of the censused population were used to estimate the total population of the colony.

In a colony of kittiwakes near Tromsø, environmental factors that limit breeding success, such as temperature and wind exposure, were monitored throughout the breeding season on a data recorder, and detailed measurements of temperatures on and inside the eggs have been recorded. For further information about the influence of environmental parameters on incubation rhythm and nest attendance, the presence of the male and female at a particular nest was recorded by using radioactive bands and a Geiger-Muller tube connected to a pen recorder.

In a study of the effects of human activity, egg samples of selected species were analyzed for mercury, PCB, and DDT derivates. An effort was also made to obtain figures for the mortality caused by oil pollution and fishing gear as well as by direct hunting pressure.

Results

Status and Trends of Cliff-breeding Species
Puffin (Fratercula arctica)

By far the most numerous seabird in Norway is the puffin (Fig. 1), which is the only species with a breeding population of more than 1 million breeding pairs (Tables 1, 2). In a 1964 census (Brun 1966) the total breeding population was put at 1.5 million pairs. The current figure of 1.25 million pairs includes several newly discovered colonies and some not censused in 1964; it is more accurate than the previous census for most of the 15 largest colonies which make up 99.9% of the total population. The puffin population is concentrated in Troms and Nordland (94%), with only about 3% in Finnmark.

Fig. 1. Distribution of the puffin (Fratercula arctica) in Norway. Numbers refer to localities listed in Table 2.

Kittiwake (Rissa tridactyla)

The second most numerous seabird species in Norway is the kittiwake, which dominates in a number of the larger cliff colonies. Its distribution pattern differs from that of the puffin—the main occurrence of the kittiwake population (about 63%) is in Finnmark (Table 3).

SpeciesThousands of pairs[75]Increase (+) or decline (-)
Fratercula arctica1250-
Rissa tridactyla510+
Larus argentatus(260)[76]+
L. canus(150)[76]+
Uria aalge100-
L. marinus(40)[76]+
Phalacrocorax aristotelis33+
Alca torda30-
Cepphus grylle220
Sterna paradisaea(21)[76]-
S. hirundo(13)[76]-
Phalacrocorax carbo12+
L. fuscus9[76]+
Stercorarius parasiticus(8)0
L. ridibundus4[76]+
Fulmarus glacialis1.1+
U. lomvia1.0-
Hydrobates pelagicus??
Sula bassana0.76+
Oceanodroma leucorrhoa??

The annual production of kittiwakes shows enormous variation, both throughout the coastline and in different years; however, at our sample stations in north Norway, the mean production in 1974 (Table 4) was more stable and was near the minimum value necessary to maintain zero population growth.

This minimum production, mx (number of females produced per breeding female), can be computed from survival rates

mx = (1-P)/1x = 0.13/0.57 = 0.23

where P is annual adult survival and 1x is survival of fledged chicks up to first breeding. Data on survival are taken from Coulson and White (1959) and from Norwegian banding recoveries.

The kittiwake has, however, established a number of new colonies, and although the local increase in some of these is spectacular, the long-term change during the last 15 years is only about 1% increase per year in northern Norwegian colonies (E. Brun, unpublished data). In southern Norway, the population has increased much more rapidly (Brun 1971c).

Common murre (Uria aalge)

The common murre (Fig. 2) has shown a considerable decrease. The most spectacular decrease is at Sør-Fugløy, where a colony of 10,000 pairs in 1940 was reduced to 4,000 pairs in 1961, to 1,100 pairs in 1966, and to only about 10 breeding pairs in 1974 (Table 5). Most of the census work was done in 1964 and 1974. The general trend in population change, as expressed by the yearly decrease or increase, has been extrapolated forward to 1974 or back to 1964 for those colonies where censuses were missing for either of these years, to enable a better comparison (Table 6). The overall decrease in Norwegian colonies of the common murre is, thus, near 5% per year; the few cases with a positive trend are based either on very small figures or on extrapolation from old, inadequate censuses.

Thick-billed Murre (Uria lomvia)

The thick-billed murre (Fig. 3) was first proved to breed in Norwegian colonies in 1964; it was then found at three localities and has since been found breeding at eight localities (Table 7). It is now fairly certain that the thick-billed murre is not a newcomer but has remained unnoticed among the common murre for generations, possibly since the original immigration of the Uria species after the last glacial period. Data are not sufficient to show whether this small population of thick-billed murres is decreasing at the same rate as the common murre.

LocalityYear of censusNumber of pairsPercent of population
1.Kjør197580<0.1
2.Heglane19704<0.1
3.Ferkingstadøyene19705<0.1
4.Utsira19702<0.1
5.Utvær1970200<0.1
6.Ryggsteinen19702<0.1
7.Veststeinen19701,5000.1
8.Einevarden19701,5000.1
9.Svinøy1970100<0.1
10.Runde197430,0002.4
11.Saløy197020.1
12.Sklinna19742,0000.2
13.Lovunden196860,0004.8
14.Fugløy i Gildeskål19688000.1
15.Røst1964700,00055.7
16.Værøy197470,0005.6
17.Nykvåg196740,0003.2
18.Frugga19755,0000.4
19.Anda197010,0000.8
20.Bleik196840,0003.2
21.Sør-Fugløy196840,0003.2
22.Nord-Fugløy1967218,00017.3
23.Loppa1968180<0.1
24.Hjelmsøy196420,0001.6
25.Gjesværstappen197318,0001.4
26.Kongsøy196630<0.1
27.Syltefjord1966100<0.1
28.Hornøy1967160<0.1
29.Reinøy196740<0.1
Total1,257,705100.0
Razorbill (Alca torda)

Another colonial cliff-breeding alcid, the razorbill (Fig. 4), has a distribution pattern very similar to that of the common murre, but the individual colonies (Table 8) are, with one exception, smaller. The total breeding population was estimated at 36,000 pairs in 1966-69 (Brun 1969b); some more recent censuses show a definite decline, but data are not sufficient to estimate the overall decline in the Norwegian population. At most, the current breeding population is 30,000 pairs.

Fulmar (Fulmarus glacialis)

The fulmar is one of two species of seabirds that have spread from colonies in the British Isles and established themselves as breeding birds in Norway during this century (the other is the gannet).

Fig. 2. Distribution of the common murre (Uria aalge) in Norway. Numbers refer to localities listed in Tables 5 and 6.

Fig. 3. Distribution of the thick-billed murre (Uria lomvia) in Norway. Numbers refer to localities listed in Table 7.

Table 3. Status of the kittiwake (Rissa tridactyla) in Norway, and a comparison of distribution with that of the puffin (Fratercula arctica).
CountyBreeding pairs
RissaFratercula
Number
(thousands)		PercentNumber
(thousands)		Percent
Finnmark32162.9383.0
Troms91.825820.5
Nordland7214.192873.7
Trøndelag (S, N)10.220.2
Møre and Romsdal10520.6302.4
Sogn and Fjordane1.90.430.2
Rogaland0.1—<0.1—
Total510100.01,259100.0

The fulmar began nesting in the early 1920's on Runde, the only sizeable seabird colony in south Norway, off Alesund. Further immigration of birds from the British Isles probably occurred in the first 25 years, when the population increased about 10% annually to about 350 pairs in 1947 (Valeur 1947). Since then the population increase has slowed down to about 3% annually, and the population on Runde in 1971 was about 700 pairs (Table 9). From Runde, fulmars have spread not only to a number of islands in the same region, but also much farther afield—south to Utsira (59°18'N, 4°55'E) and north to Bleik (69°3'N, 15°42'E). The total Norwegian population of fulmars in 1971 was estimated at 1,100 pairs.

Fig. 4. Distribution of the razorbill (Alta torda) in Norway. Numbers refer to localities listed in Table 8.

Fig. 5. Distribution of the gannet (Sula bassana) in Norway. Numbers refer to localities listed in Table 10.

LocalityYearSample size (number)mx
Vedøy, Røst19728520.21
Hekkingen, Troms19742640.46
Hjelmsøy19743570.18
Jarfjord19741460.31
Total1,6190.25
Gannet (Sula bassana)

The gannet (Fig. 5), the most recently established and least numerous of the cliff-breeding seabirds, has the best-known population change. Like the fulmar, it was established in 1946 on Runde, and the first individuals were undoubtedly of British origin. During its entire breeding history on Runde, and also in two of the three new colonies in northern Norway established in the 1960's, the yearly increase has far exceeded the intrinsic rate of increase (Table 10); for gannets with a 50% breeding success, adult mortality of 6%, and 35% survival up to first breeding, the intrinsic rate of increase is about 2% per year. The Runde and Syltefjord colonies are naturally protected by their inaccessibility, but the colonies at Mosken and Nordmjele, which are on small islets, are both easily accessible. The Nordmjele colony, however, has been effectively protected from its start, whereas the Mosken colony has been open to visitors; this difference is probably reflected in their different breeding success and annual growth rate (Table 11). The breeding success necessary to maintain a stable population with the mortality figures given above is 34%:

mx = (1-P)/1x = 0.66/0.35 = 0.17

For equal sex ratio, breeding success is 2 times mx = 0.34.

A British ringed gannet from Ailsa Craig (55°12'N, 5°07'W) was found nesting when 4 years old in the Nordmjele colony in 1970 (Brun 1972), giving direct evidence that immigration from colonies in Great Britain (Scotland) still takes place.

Table 5. Status of the common murre (Uria aalge) in Norway (cf. Fig. 2).
LocalityLast censusPrevious censusReference
YearNo. of breeding pairsYearNo. of breeding pairs
1.Utsira19701195010Holgersen 1951
2.Utvær197017194855Willgohs 1952
3.Veststeinen197029195040Willgohs 1952
4.Klovningen197035195020Willgohs 1952
5.Einevarden197030195225Willgohs 1955
6.Runde19746,00019637,600Brun 1969a
7.Storholmen19708——
8.Røst19746,80019649,700Brun 1969a
9.Værøy19741,75019642,400Brun 1969a
10.Nykvåg19743501966430Brun 1969a
11.Bleik197460195290Regnell 1957
196475Brun 1969a
12.Sør-Fugløy197410194010,000Soot-Ryen 1941
19614,000Brun 1963
19661,100Brun 1969a
13.Nord-Fugløy19679,000196315,000Lütken 1965
14.Loppa19745001966800Brun 1969a
15.Hjelmsøy197470,0001964110,000Brun 1965
196795,000Brun 1969a
16.Gjesværstappene19735801967750Brun 1969a
17.Sværholtklubben197320196625Brun 1969a
18.Omgangsstauran197370196785Brun 1969a
19.Syltefjorden19749,000196612,300Brun 1969a
20.Hornøy19745001964730Brun 1969a
21.Reinøy19741101964160Brun 1969a
22.Kjøfjord197021——
23.Skogerøy1970819676Brun 1969a
24.Sagfjord19709196712Brun 1969a
25.Kobbholmfjorden1970219671Brun 1969a

Estimates of Total Seabird Population in Norway

In addition to the more detailed censuses of the cliff-breeding species dealt with so far, notes have been made on all seabirds observed during numerous flights along the Norwegian coast. Although a first attempt at putting a figure to all seabird species in Norway may be somewhat premature, it is believed that even an extrapolation combined with an educated guess is of some value until more accurate censuses covering the whole coast can be made. Although the data (Table 1) are arranged in the same way as the results from "Operation Seafarer" in the British Isles (Cramp et al. 1974), it must be stressed that the accuracy of the Norwegian figures, at least for the non-cliff-breeding birds, is far inferior to the very fine British data. The table includes data for two petrels (Hydrobates pelagicus, Oceanodroma leucorrhoa), which in Norway breed on Røst (well north of the Arctic Circle), where they have adapted to a delayed breeding season with egg laying in August because of the conflict of their nocturnal habits with the continuous daylight due to the midnight sun. Of the present population trends that are given for each species in Table 1, all auks except the black guillemot (Cepphus grylle) are decreasing, whereas the gulls, the gannets, and the fulmars are increasing.

Table 6. Population trends in colonies of the common murre (Uria aalge) in Norway. Numbers for 1964 and 1974 are, when not censused those years, extrapolated from present trends, using estimated yearly decrease or increase from all available census figures.
LocalityNumber of breeding pairs[77]Percentage yearly decrease (-) or increase (+)
19641974
1.Utsira21-12.2
2.Utvær2314-5.5
3.Veststeinen3227-1.6
4.Klovningen3039+2.8
5.Einevarden2831+1.0
6.Runde7,4386,000-2.2
7.Storholmen97(-2.2)[78],[79]
8.Røst9,7006,800-3.6
9.Værøy2,4001,750-3.2
10.Nykvåg453350-2.6
11.Bleik7560-2.3
12.Sør-Fugløy1,84410-68.5
13.Nord-Fugløy13,2013,681-13.6
14.Loppa900500-6.1
15.Hjelmsøy110,00070,000-4.6
16.Gjesværstappen853556-4.4
17.Sværholtklubben2719-3.2
18.Omgangsstauran9468-3.3
19.Syltefjorden13,2999,000-4.0
20.Hornøy730500-3.9
21.Reinøy160110-3.8
22.Kjøfjord2120(-0.4)[78],[79]
23.Skogerøy512+10.1
24.Sagfjord166-10.1
25.Kobbholmfjord15+26.0
Total161,34199,566-4.9
Table 7. Status of the thick-billed murre (Uria lomvia) in Norway (cf. Fig. 3).
LocalityYearNo. of breeding pairsPercentage of total Uria population
1.Vedøy, Røst1974150.3
2.Værøy1966200.9
3.Hjelmsøy19748501.2
4.Gjesværstappene1973254.3
5.Syltefjord1970900.9
6.Hornøy1966558.1
7.Reinøy196410.6
8.Kjøfjord197014.8
Estimated number, Norway, 1974>1,000ca. 1.0
Table 8. Status of the razorbill (Alca torda) in Norway (cf. Fig. 4).
LocalityYearNo. of breeding pairsPercent
1.Kjør19701<0.1
2.Utsira1970250.1
3.Utvær1970160.1
4.Veststeinen1970220.1
5.Klovningen197012<0.1
6.Einevarden1970450.2
7.Runde19742,8009.5
8.Sklinna1974150.1
9.Lovunden19688<0.1
10.Røst19743,90013.2
11.Værøy19748002.7
12.Nykvåg19662500.8
13.Bleik1968280.1
14.Sør-Fugløy1974150.1
15.Nord-Fugløy196710,00033.8
16.Loppa19697502.5
17.Hjelmsøy19747,00023.7
18.Gjesvær19732,5008.5
19.Sværholtklubben1973180.1
20.Omgangsstauran19736<0.1
21.Kongsøy19668<0.1
22.Syltefjorden19661,2004.1
23.Hornøy1967650.2
24.Reinøy1967550.2
25.Kjøfjord19709<0.1
26.Skogerøy19704<0.1
27.Jarfjordnes19703<0.1
Totalca. 30,000

Since the coastline of Norway is about the same length as the coastline of Great Britain and Ireland, it is interesting to compare the population figures (Table 12), although the accuracy is very different. Populations of auks and gulls are similar in both areas, but the species composition is different. There are more terns in the British Isles, but skuas (Catharacta skua), shags (Phalacrocorax aristotelis), and great cormorants (P. carbo) are present in similar numbers. The most striking difference is the very small number of procelli-forms and gannets in Norway compared to Britain and Ireland, where they are almost as numerous as the gulls and the auks.

CountyNumber of localitiesNumber of breeding pairs
Nordland6140
Møre and Romsdal7945
Sogn and Fjordane211
Rogaland22
Total171,098
Table 10. Population increase of the gannet (Sula bassana) in Norway (cf. Fig. 5).
ColonyYear establishedMean yearly growth rate 1969-1974
(%)		No. of breeding pairs
196919701971197219731974
1.Runde19468.4330331383422450494
2.Moskenca. 19605.4508377606265
3.Nordmjele196783.373665103127145
4.Syltefjord196114.5282944485155
Total12.8415479569633690759
Yearly growth rate (%)15.418.811.29.010.0

Discussion

Impact of Human Activity
Direct Exploitation

According to Norwegian laws, all seabirds, with the exception (for some odd reason) of the gannet and fulmar, can be hunted from 21 August to 1 March. However, only the two species of murre and the razorbill are still regularly hunted and, although no statistics support it, an estimate based on interviews with some of the hunters reveals that murres and razorbills are shot in the ratio of about 50:1. One man can shoot as many as 380 murres and razorbills during a winter season as a sideline to fishing. Although not many hunt on this scale, an absolute minimum of 5,000 murres and razorbills are killed this way each season.

A new law based on modern principles of conservation has been under consideration for several years, and this will mean an improvement. However, the speed of the decline of the auks, particularly the murres, makes it imperative to stop this hunting immediately, and it is of very little economic importance to the few who take part. Some illegal "fishing" for auks still takes place at Røst and Vaerøy, where fishnets are anchored over wooden frames outside the auk colonies at the beginning of the nesting season. At Vedøy on Røst in 1972, up to 80 murres were taken daily. Thus an estimated total of 500-700 murres were taken that year—about 5% of the breeding population on this island.

Egg collecting was important during World War II, but in these more affluent times and because of the relative inaccessibility of the auks' nests, egg collecting is now both less attractive and less important. Human disturbance of the breeding colonies, however, is gradually becoming a more serious factor.

Table 11. Comparison of annual growth rate and breeding success in two colonies of gannets (Sula bassana).
MoskenNordmjele
Annual growth rateBreeding success (%)Annual growth rateBreeding success (%)
196962—
1.665.14
19705161
0.931.81
19713646
0.781.58
19723362
1.031.23
19735035
1.051.14
19741239
1969-19741.05401.8346
Fishing Gear

Although on a scale different from that in western Greenland, drift-net and longline fishing for Atlantic salmon (Salmo salar) outside the 19-km (12-mile) limit off the northern Norwegian coast present a serious mortality hazard to some seabirds. Reliable data exist only for the longline fisheries. In the 1969 season (with 75 effective days from mid-March to mid-June), one boat using 1,040 hooks per day caught 294 birds: 52 fulmars, 3 gannets, 43 kittiwakes, 107 murres, and 89 puffins. No razorbills were identified, but they may have been included in the murre figure. If this sample is representative, the 100 or so Norwegian boats using longlines plus about 20 Danish boats (which used 4,000-6,000 hooks per day and consequently caught more birds) would have caught roughly 10,000 fulmars, 600 gannets, 9,000 kittiwakes, 21,000 murres, and 18,000 puffins in the 1969 season. The drift-nets in Norwegian waters are reported to be less damaging to seabirds than are the longlines, but even without adding the figures from the drift-nets, the numbers are substantial in view of the size of the Norwegian breeding populations.

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 IrelandNorway
Fulmarus glacialis306,0001,100
Puffinus puffinus> 175,000—
Hydrobates pelagicus105 or 106103 or 104
Oceanodroma leucorrhoa104102
Sula bassana138,000760
Phalacrocorax carbo8,10012,000
P. aristotelis31,00033,000
Stercorarius skua3,1001[81]
S. parasiticus1,1008,000
Larus 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 tridactyla470,000510,000
Sterna 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)30,000
Uria aalge(577,000)100,000
U. lomvia—1,000
Cepphus grylle8,30022,000
Fratercula arctica(490,000)1,250,000
Totalca. 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.

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 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).

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 reduced, 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 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).

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 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.

Acknowledgments

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.

References

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 gannet Sula bassana in Norway. Ornis Scand. 3:27-38.

Brun, E. 1974. Breeding success of gannets Sula bassana at 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.