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How to manage harvest under great uncertainty is a fundamental question for many wildlife managers, particularly when resources necessary to estimate abundance or population trends are limited. The large Newfoundland and Labrador murre hunt is the only licensed harvest of seabirds in Canada. Though harvest of thick‐billed murres (Uria lomvia) and common murres (Uria aalge) has declined considerably since the 1960−1970s from >500,000 birds taken annually to approximately 100,000 annually in recent years, potential murre colony declines across the North Atlantic have again triggered concerns over the sustainability of murre harvest in Canada. The effect of current harvest is difficult to assess because there is considerable uncertainty in recent population size, trend, demographic rates, licensed harvest, fisheries bycatch, and illegal harvest. To assess the situation, we simulated the population size necessary to sustain current levels of approximated anthropogenic mortality using a potential biological removal approach, which simplifies and constrains population processes to a few key variables. Based on these simulations, the Canadian licensed harvest of thick‐billed murre is consistent with conservation management objectives, as is common murre licensed harvest and fisheries bycatch. Adding estimated illegal harvest resulted in unstainable mortality levels in both species. While wildlife managers will need to formally assess the relative costs and benefits of reducing uncertainty in this system through improved harvest and population monitoring, illegal harvest and commercialization need to be addressed to manage Canadian murre populations. Potential biological removal approaches can be a useful framework to assess harvest management decisions for marine birds and other data‐limited species. [ABSTRACT FROM AUTHOR]

Bycatch in gillnets from lumpfish (Cyclopterus lumpus) fisheries is an important conservation issue in the north Atlantic, with up to 30 000 seabirds potentially killed each year. To date, no technical solutions exist to reduce the bycatch of seabirds in gillnet fisheries, but research on above-water bird deterrents as a form of bycatch mitigation has shown promising results. Here, we tested whether a floating device called ‘looming-eyes buoy’ (LEB) would consistently reduce the bycatch of seabirds in the Icelandic lumpfish fishery. We conducted 61 controlled trials with sets of normal gillnets and experimental nets equipped with LEBs. We compared both fish catch and bycatch between net types while accounting for exposure time, water depth and season, and found no effect of LEBs on both target lumpfish catch and bycatch. Our analysis indicated however a strong correlation between bycatch rates and fishing depths, suggesting that depth-based fishing restrictions could virtually eliminate the bycatch of seabirds in this fishery. We estimated that limiting fishing to waters more than 50 m deep could save between 5000 and 9300 seabirds every year, arrest the population decline of endangered black guillemots in Iceland, while having only a marginal effect on target fish catch.

Competing Interests: We declare we have no competing interests.

The prevalence of intestinal ulcers and parasites was investigated in 2172 grey seals (Halichoerus grypus) collected in the Baltic Sea and 49 grey seals collected outside the Baltic Sea (i.e., the Atlantic). An increase in frequency of ileocaeco-colonic ulcers was observed in the early 1980s, followed by a decrease in the mid-1990s. At the same time, there was an increase followed by a decrease in brominated flame retardants, Perfluorooctanesulfonic acid (PFOS) and cadmium levels in herring (Clupea harengus), the most common prey item in Baltic grey seal diet, as well as in another top predator in the Baltic, the common guillemot (Uria aalge). The frequency of intestinal ulcers was significantly related to the intensity of acanthocephalan parasites, the age of the seal and the region of the Baltic Sea. Perforation of the intestinal wall was the cause of death in 26 of the investigated Baltic grey seals. In contrast, none of the investigated Atlantic grey seals had intestinal ulcers. They showed a thin colonic wall and very few acanthocephalan parasites. The high prevalence of intestinal ulcers and the high parasite intensity appear to be unique to the Baltic population of grey seals.

Mapping the distribution of seabirds at sea is fundamental to understanding their ecology and making informed decisions on their conservation. Until recently, estimates of at-sea distributions were generally derived from boat-based visual surveys. Increasingly however, seabird tracking is seen as an alternative but each has potential biases. To compare distributions from the two methods, we carried out simultaneous boat-based surveys and GPS tracking in the Minch, western Scotland, in June 2015. Over 8 days, boat transect surveys covered 950 km, within a study area of ~6,700 km2 centered on the Shiant Islands, one of the main breeding centers of razorbills, and guillemots in the UK. Simultaneously, we GPS-tracked chick-rearing guillemots (n = 17) and razorbills (n = 31) from the Shiants. We modeled counts per unit area from boat surveys as smooth functions of latitude and longitude, mapping estimated densities. We then used kernel density estimation to map the utilization distributions of the GPS tracked birds. These two distribution estimates corresponded well for razorbills but were lower for guillemots. Both methods revealed areas of high use around the focal colony, but over the wider region, differences emerged that were likely attributable to the influences of neighboring colonies and the presence of non-breeding birds. The magnitude of differences was linked to the relative sizes of these populations, being larger in guillemots. Whilst boat surveys were necessarily restricted to the hours of daylight, GPS data were obtained equally during day and night. For guillemots, there was little effect of calculating separate night and day distributions from GPS records, but for razorbills the daytime distribution matched boat-based distributions better. When GPS-based distribution estimates were restricted to the exact times when boat surveys were carried out, similarity with boat survey distributions decreased, probably due to reduced sample sizes. Our results support the use of tracking data for defining seabird distributions around tracked birds' home colonies, but only when nearby colonies are neither large nor numerous. Distributions of animals around isolated colonies can be determined using GPS loggers but that of animals around aggregated colonies is best suited to at-sea surveys or multi-colony tracking.

Bycatch in gillnets from lumpfish ( Cyclopterus lumpus ) fisheries is an important conservation issue in the north Atlantic, with up to 30 000 seabirds potentially killed each year. To date, no technical solutions exist to reduce the bycatch of seabirds in gillnet fisheries, but research on above-water bird deterrents as a form of bycatch mitigation has shown promising results. Here, we tested whether a floating device called 'looming-eyes buoy' (LEB) would consistently reduce the bycatch of seabirds in the Icelandic lumpfish fishery. We conducted 61 controlled trials with sets of normal gillnets and experimental nets equipped with LEBs. We compared both fish catch and bycatch between net types while accounting for exposure time, water depth and season, and found no effect of LEBs on both target lumpfish catch and bycatch. Our analysis indicated however a strong correlation between bycatch rates and fishing depths, suggesting that depth-based fishing restrictions could virtually eliminate the bycatch of seabirds in this fishery. We estimated that limiting fishing to waters more than 50 m deep could save between 5000 and 9300 seabirds every year, arrest the population decline of endangered black guillemots in Iceland, while having only a marginal effect on target fish catch., Competing Interests: We declare we have no competing interests., (© 2023 The Authors.)

Describing the range of avian egg shapes quantitatively has long been recognized as difficult. A variety of approaches has been adopted, some of which aim to capture the shape accurately and some to provide intelligible indices of shape. The objectives here are to show that a (four‐parameter) method proposed by Preston (1953, The Auk, 70, 160) is the best option for quantifying egg shape, to provide and document an R program for applying this method to suitable photographs of eggs, to illustrate that intelligible shape indices can be derived from the summary this method provides, to review shape indices that have been proposed, and to report on the errors introduced using photographs of eggs at rest rather than horizontal. Describing the range of avian egg shapes quantitatively has long been recognised as difficult. A variety of approaches has been adopted, some of which aim to capture the shape accurately and some to provide intelligible indices of shape. The objectives here are to show that a (four‐parameter) method proposed by Preston (1953) is the best option for quantifying egg shape, to provide and document an R program for applying this method to suitable photographs of eggs, to illustrate that intelligible shape indices can be derived from the summary this method provides, to review shape indices that have been proposed, and to report on the errors introduced by using photographs of eggs at rest rather than horizontal. [ABSTRACT FROM AUTHOR]

The role of seabirds as sea-land biovectors of nutrients is well documented. However, no studies have examined whether and how colonial seabirds that differ in diet may influence terrestrial vegetation. Therefore, the purpose of the study was to describe and compare plant communities located in the vicinity of the two most common types of seabird colonies in Arctic, occupied by piscivorous or planktivorous species. Within 46 plots arranged in four transects in the vicinity of planktivorous (little auk, Alle alle) and piscivorous colonies (mixed colony of Brunnich's guillemot, Uria lomvia, and black-legged kittiwake, Rissa tridactyla) we measured the following: guano deposition, physical and chemical characteristics of soil, total nitrogen and its stable isotope signatures in soil and plants, ground vegetation cover of vascular plants and mosses, and the occurrence of lichens, algae and cyanobacteria. Using LINKTREE analysis, we distinguished five plant communities, which reflected declining influence along a birds fertilization gradient measured as guano deposition. SIMPROOF test revealed that these communities differed significantly in species composition, with the differences related to total soil nitrogen content and δ15N, distinctive levels of phosphates, potassium and nitrates, and physical soil properties, i.e., pH, conductivity and moisture. The communities were also clearly distinguished by distance from the bird colony. The two colony types promoted development of specific plant communities: the immediate vicinity of the planktivorous colony characterized by a Deschampsia alpina-Cerastium arcticum community while under the piscivorous colony a Cochlearia groenlandica-Poa alpina community was present. Despite the similar size of the colonies and similar magnitude of guano input, differences between ornithogenic communities were connected mostly to phosphate content in the soil. Our results show that the guano input from seabirds which have different diets can affect High Arctic vegetation in specific and more complex ways than previously realized. [ABSTRACT FROM AUTHOR]

The jaw muscles of the thick-billed murre have been described in detail and depicted with comparative notes on the jaw muscles in the common murre and the black guillemot. Owing to adaptation to underwater hunting of mobile prey (first of all, small fish), the composition of the dorsal adductor muscles in the studied species has become simplified in part, compared with their ancestral form, and has become similar to that of another underwater fisher, the great crested grebe ( Podiceps cristatus). The attachment of the superficial portion of the external adductor muscle to the postorbital projection was strengthened, especially in both murres. In the external layer of the medial portion of the adductor, the muscle fibers gained secondary insertion by the horizontal aponeurosis, similarly to those of the superficial portion, thus increasing the horizontal (retracting) force component, which lowers the long upper jaw. The caudal part of the deep portion of the external adductor became incorporated in the medial portion, but in the murres, especially in the thickbilled murre, part of it is similar to the posterior adductor, which enhances the retracting force as well. All three species show traces of a transfer of the muscle fascicle from the superficial pseudotemporal muscle to the deep pseudotemporal muscle, giving the same effect. Confirmation of the relatively separated position of the guillemot and of its generalized morphological state were found. The specific features of the murres' adaptation to fishing, including morphofunctional prerequisites for forage segregation of the two murre species, are understandable as the basis of their sympatric existence. [ABSTRACT FROM AUTHOR]

A main purpose of marine contaminant monitoring in Europe is to evaluate the chemical status and environmental quality under the Marine Strategy Framework Directive (MSFD), to monitor and achieve Good Environmental Status (GES). Characteristics of a good matrix for monitoring purposes are the potential to detect temporal trends or differences between sites or concentration levels in relation to a target value indicating GES. In Sweden we use muscle of herring and eggs of guillemot and White-tailed sea eagle (WTSE) to study changes in contaminant exposure and their effects. Herring is important in fisheries and has target levels set for contaminants in relation to GES. Adult guillemots and eagles in the Baltic Sea are mainly stationary. Guillemots feed largely on herring, WTSEs on fish and other fish-eaters. A higher trophic level may imply biomagnification, and, for example, DDE shows concentration ratios in lipids of 110 (guillemot/herring), 460 (WTSE/herring) and 4.2 (WTSE/guillemot). Banked, frozen guillemot eggs have been extensively used for retrospective temporal trend analyses for several chemicals. Ideally, the matrix should also be useful for biological effect monitoring. Eggshell and reproductive parameters are monitored in the WTSEs and guillemots. Reproductive problems and egg desiccation still occur among eagles, indicating an impact of contaminants and highlighting the importance of apex predators as environmental sentinels. [ABSTRACT FROM AUTHOR]

The article reports on an evaluation of the role of seabirds as hosts for the Avian influenza A virus (AIV). Findings indicate that Common Murres are important for the ecology of AIV, while in other species like Razorbill, Leach's Storm-Petrel, and Black-legged Kittiwake, AIV was not detected. The possible virus spread through dense breeding colonies and long distance movements of seabird hosts reportedly warrant further evaluation.

The parasitic tick Ixodes uriae was recorded from Brünnich's guillemots ( Uria lomvia) at two colonies on Spitsbergen, the principal island in the Arctic archipelago of Svalbard. Six Brünnich's guillemots from 30 studied at the Ossian Sars seabird colony were found to be parasitized. A tick was also collected from below the larger Fuglehuken colony. However, ticks were not seen on Brünnich's guillemots examined at the smaller Krossfjorden colony, and neither were they observed in two black-legged kittiwake ( Rissa tridactyla) colonies (Blomstrandhalvøya and Krykkjefjellet). It is suggested that either the tick has only recently been established in Svalbard or the population has increased from a low level, and has consequently become visible to small-scale sampling studies. Implications for the seabird population of the northern Barents Sea are discussed. [ABSTRACT FROM AUTHOR]

Evolutionary theories of senescence predict that rates of decline in performance parameters should be shaped by early-life trade-offs between reproduction and somatic maintenance. Here we investigate factors influencing the rate of reproductive senescence in a long-lived seabird, the common guillemot Uria aalge, using data collected over a 23-year period. In the last 3 years of life, individual guillemots had significantly reduced breeding success and were less likely to hold a site or attempt to breed. Females senesced at a significantly faster rate than males. At the individual level, high levels of reproductive output earlier in life were associated with increased senescence later in life. This trade-off between early- and late-life reproduction was evident independent of the fact that as birds age, they breed later in the season. The rate of senescence was additionally dependent on environmental conditions experienced earlier in life, with evidence that harsh conditions amplified later declines in breeding success. Overall, individuals with intermediate levels of early-life productivity lived longer. These results provide support for the antagonistic-pleiotropy and disposable-soma theories of senescence and demonstrate for the first time in a wild bird population that increased rates of senescence in reproductive performance are associated with varying costs of reproduction early in life. [ABSTRACT FROM AUTHOR]

Recent published estimates of the numbers of seabirds breeding along the coast of Murman have been partly based on data collected in the 1960s. Counts made in some of the largest colonies in 1999–2005 show that the present populations of black-legged kittiwakes ( Rissa tridactyla), common guillemots ( Uria aalge) and Brünnich’s guillemot ( U. lomvia) in Murman are approximately 110 000 pairs, 10 000–12 000 pairs and 2000–3000 pairs, respectively. In Varanger the numbers are ca. 32 000 pairs, 6000–7000 pairs and 400–500 pairs, respectively. Although there has been a large decline in black-legged kittiwake numbers in the Varanger region since 1980, there is no evidence of a similar decline in Murman at least until 1999. With the exception of one colony in Murman, numbers of common guillemots breeding throughout the region seem to have recovered after suffering a huge decline in 1986/87. [ABSTRACT FROM AUTHOR]

Power calculations usually assume that the components of the population variance are known, but it is frequently the case that they are estimated using data from a pilot study. Imprecision in the estimates is then ignored and a single value for power is generated. We present a method that incorporates the error in the estimates of any number of variance components into the power calculations. We show that, by sampling values for the variance components from the residual likelihood function of the pilot data, our method can approximate the distribution of powers expected given the uncertainty in the variance components. Alternative summary measures of power can then be derived: we strongly recommend treating a minimum acceptable power as a quality standard and summarizing power in terms of the probability that this quality standard is attained. The method is illustrated by application to counts of common guillemots ( Uria aalge) on the Isle of May in Scotland to assess the power of detecting long-term trends in abundance using a model for random variation with seven parameters. [ABSTRACT FROM AUTHOR]

Abstract: The dynamics of organohalogen contaminants and their metabolites are best studied over time by analysis of biota at high trophic levels. In this study, time trends, 1971–2001, of bis(4-chlorophenyl) sulfone (BCPS) and of methylsulfonyl-substituted metabolites of PCBs and 4,4′-DDE, were investigated in eggs of guillemot (Uria aalge) hatching in the Baltic Proper. Temporal trends of PCBs, trans-nonachlor, β-HCH, 4,4′-DDT, and 4,4′-DDE were also assessed. Tris(4-chlorophenyl) methane (TCPMe), a 4,4′-DDT by-product, was detected in the eggs. The concentration of BCPS ranged between 2.6–0.76μg/g on a lipid weight basis over the three decades and showed a significant 1.6% annual decrease. Three metabolites of PCBs, i.e. 3′-MeSO2-CB101, 4′-MeSO2-CB101 and 4-MeSO2-CB149, were quantified in all samples over time and showed an annual decrease of approximately 3% compared to MeSO2-DDE with a decrease of 8.9%. The methylsulfonyl-PCB and -DDE metabolites are eliminated more slowly than the persistent PCB congeners and 4,4′-DDE. Trans-nonachlor decreases by 16% compared to 19% and 9% for 4,4′-DDT and β-HCH, respectively. The concentration of TCPMe in guillemot decreased by 8.2% per year. A linear relationship was found between TCPMe and 4,4′-DDE concentrations which supports the theory that TCPMe has an origin as a contaminant in commercial 4,4′-DDT products. The very slow decrease in BCPS concentrations is notable and remains to be explained. BCPS is still present at rather high concentrations in the guillemot eggs. The enantiomeric fraction varied between 0.27 and 0.67 which indicates less of a specific retention of the chiral MeSO2-PCBs in guillemot eggs than in grey seal tissues, for example. Independent of meta- or para-substitution of the sulfone group, the most accumulative atropisomer of each of four MeSO2-PCB pairs has been assigned an absolute R structure. [Copyright &y& Elsevier]

The Baltic Sea is a heavily polluted area. To assess the current contaminant pressure on the common guillemot (Uria aalge) living there, whole-body extracts of guillemots from the Baltic Sea were prepared and subdivided over six fractions, which differed in composition due to lipophilicity and polarity of the contaminants. The fractions were tested in the chicken embryo assay and compared to fractions of Atlantic guillemot extracts. Fertilized chicken eggs were injected with 0.03, 0.3, or 3 bird egg equivalents (BEQ) of the contaminants present in the fractions and then incubated for 19 d. Endpoints were selected to cover several mechanisms that may play a role in reproductive failures of fish-eating birds. Fractions I and IV from the Baltic guillemots induced ethoxyresorufin-O-deethylase (EROD) activity up to 15-fold in embryos exposed to 0.3 BEQ and up to 17-fold in embryos exposed to 3 BEQ. Corresponding Atlantic fractions induced EROD activity only at the higher dose of 3 BEQ. Morphological alterations were observed in the bursa of Fabricius in embryos exposed to the fractions that induced EROD, and for the Baltic fractions, this was apparent at the dose of 0.3 BEQ. The higher toxic potency of fractions I and IV was confirmed by higher mortality and occurrence of malformations among embryos exposed to these fractions. No other effects were observed; morphometry, hepatic porphyrin levels, thiamine-dependent enzymes, and acetylcholinesterase activity were not affected by any fraction. During inter-pretation of the results, concentrations in the whole-body guillemot extracts were compared to concentrations reported in field studies. In general, concentrations in the guillemot extract were lower than those associated with biomarker responses in other wild-bird species. However, because the relative sensitivity of guillemot toward immunotoxic effects remains to be resolved, effects on the immunocompetence of guillemot could not be excluded. [ABSTRACT FROM AUTHOR]

Simple Summary: In the 1970s it was discovered that seal populations in the Baltic Sea had decreased severely due to hunting and high levels of contaminants. Lesions were found in several organs and many of the females became sterile. Since then, most of the organ lesions have decreased and so have the levels of some pollutants. However, ulcers in the large intestines of the grey seals increased in the early 1980s and decreased after the mid-1990s. The aims of this study were to: (1) describe the ulcers and investigate if there is a trend over time that coincides with concentrations of some pollutants in Baltic biota; (2) evaluate the significance of different sea areas in the Baltic, grade of parasite intensity, as well as the sex and age of the seals. The results show that seals with ulcers had, in general, higher parasite intensity. Ulcers were more common in older seals and in the Bothnian Sea. The time trend of ulcers coincides with the trend of certain contaminant levels (BDE-47, PFOS and cadmium). The high prevalence of intestinal ulcers and the high intensity of acanthocephalan parasites appear to be unique to the Baltic population of grey seals. The prevalence of intestinal ulcers and parasites was investigated in 2172 grey seals (Halichoerus grypus) collected in the Baltic Sea and 49 grey seals collected outside the Baltic Sea (i.e., the Atlantic). An increase in frequency of ileocaeco-colonic ulcers was observed in the early 1980s, followed by a decrease in the mid-1990s. At the same time, there was an increase followed by a decrease in brominated flame retardants, Perfluorooctanesulfonic acid (PFOS) and cadmium levels in herring (Clupea harengus), the most common prey item in Baltic grey seal diet, as well as in another top predator in the Baltic, the common guillemot (Uria aalge). The frequency of intestinal ulcers was significantly related to the intensity of acanthocephalan parasites, the age of the seal and the region of the Baltic Sea. Perforation of the intestinal wall was the cause of death in 26 of the investigated Baltic grey seals. In contrast, none of the investigated Atlantic grey seals had intestinal ulcers. They showed a thin colonic wall and very few acanthocephalan parasites. The high prevalence of intestinal ulcers and the high parasite intensity appear to be unique to the Baltic population of grey seals. [ABSTRACT FROM AUTHOR]

The article reports on a study of the effects of the heat increment of feeding (HIF) on oxygen consumption of thick-billed murre, Uria lomvia. The rate of oxygen consumption rose by a factor of 1.4 during the first few minutes after ingestion, but there was a substantial increase in body temperature. It is concluded that the HIF augments heat production in Uria lomvia and decreases the energetic cost of thermoregulation.

Common (Uria aalge) and Brünnich's guillemots (U. lomvia) are colonial seabirds that nest in temperate to arctic oceans throughout the Northern hemisphere. They are very similar in the characteristics of ecology, demography and life history that are thought to determine the extent of differentiation among populations, yet geographic variation in morphology is notably greater in common guillemots. Despite evidence of strong natal philopatry, previous analyses of allozymes and the mitochondrial cytochrome b gene revealed little genetic differentiation among North Atlantic colonies of Brünnich's guillemots. To determine if the more extensive morphological variability in common guillemots reflects greater genetic variability, we sequenced part of the cytochrome b gene for 160 common guillemots from 10 colonies distributed throughout the Northern hemisphere. Genotype frequencies and phylogenetic relationships among genotypes both indicated that Atlantic and Pacific populations are genetically distinct. Genetic divergence among genotypes suggested that differentiation of these populations has resulted from separation by Pleistocene glaciers and the Bering Landbridge, as well as by currently unsuitable breeding habitat in the Arctic Ocean. Cytochrome b genotype frequencies also differed among Atlantic colonies, and appeared to define a cline similar to that described for morphological characters. Analyses of sequence variation suggested that this variation probably results from secondary contact between two refugial populations from the Pleistocene glaciations, rather than from isolation by distance or selection. In contrast, the Atlantic population of Brünnich's guillemots appears to have arisen through recent expansion of a single homogeneous refugial population. [ABSTRACT FROM AUTHOR]

The distributions of Manx shearwater, guillemot, razorbill, fulmar, and kittiwake were examined in relation to sea surface temperature and salinity at the Irish Sea Front in an attempt to understand the manner in which the front is utilized by seabirds. Bird distribution data were collected from 19 crossings of the front along five transects during July 1990. The spatial distributions of the seabirds were analysed by exploratory variography and the application of generalized additive models. The distributions of Manx shearwater, guillemots, and razorbills were associated with the front. A degree of spatial partitioning was also evident that suggested these species were adopting different strategies for the utilization of resources at the front. Comparison with previous studies suggests that the relationship between the seabirds and the Irish Sea Front has been consistent over a period of several years, indicating that the front is a predictable resource for seabirds. [ABSTRACT FROM PUBLISHER]

The increasing development of offshore wind farms (OWFs) worldwide leads to possible conflicts with the ecological requirements of top predators that largely depend on offshore areas. Seabird species exhibit different behavioural reactions to OWFs, ranging from avoidance resulting in habitat loss, to attraction causing an increased risk of colliding with the turbines. We investigated how OWFs affected the densities and distributions of guillemots and kittiwakes breeding in the southern North Sea and if the effects varied among seasons using a 'before–after control impact' (BACI) analysis approach based on a large-scale and long-term dataset covering 14 years before and 3 years after the construction of OWFs. Guillemot relative density in the OWF decreased by 63% in spring, and by 44% in the breeding season. Kittiwake relative density in the OWF decreased by 45% in the breeding season, and not significantly by 10% in spring. We furthermore estimated the response radii to the OWF for both species and seasons, finding that guillemots showed a response radius of ~9 km in spring and kittiwakes a radius of ~20 km in the breeding season. The results underline the value of large-scale and long-term assessments considering seasonal variation throughout the yearly cycle. The here provided information on the seasonally different reactions of seabirds to OWFs adds substantially to our current knowledge and provides the necessary basis for reliable estimations of OWF effects on guillemots and kittiwakes. Such evaluations are urgently needed for future planning and management recommendations to decision-makers. • Offshore Wind Farms (OWF) affect the abundance of guillemots and kittiwakes. • Guillemot density in the OWF decreased in spring, and the breeding season. • Decrease in guillemot abundance is significant about 9 km from the OWF in spring. • Kittiwake density in the OWF decreased in the breeding season. • Decrease in kittiwake abundance is significant about 20 km from the OWF. [ABSTRACT FROM AUTHOR]

During the first six months of 1993, about 3500 dead and moribund guillemots (Uria aalge) were observed throughout the northern Gulf of Alaska coast (ca 1800 km range). Mortality peaked during March. Highest numbers were observed in western Prince William Sound and along thesouth coast of the Kenai Peninsula. Large flocks of live guillemots gathered in nearshore waters, in contrast to most winters when guillemots reside offshore. Most guillemots recovered were extremely emaciated (ca 60% of normal weight) and sub-adult (80%). Based on carcass deposition and persistence experiments, we calculate that about 10900 birds eventually came ashore on beaches that were surveyed. Even if most birds killed made it to shore, only a fraction of beaches in the Gulf of Alaska were surveyed and we estimate that a minimum total of 120000 guillemots died. Results of other investigations on potential causes of mortality (biotoxins, pathogens, parasites, metals, etc.) were either negative or inconclusive, and necropsies lead us to believe that starvation was the proximate cause of death. Reduced food availability could have been related to anomalous sea conditions found during the prolonged 1990-1995 El Nino-Southern Oscillation event. [ABSTRACT FROM AUTHOR]