Top-down control of a marine mesopredator: Increase in native white-tailed eagles accelerates the extinction of an endangered seabird population

1. Bottom-up control is an important regulator of marine mesopredators such as seabirds. The prevalence of top-down control on these species is however less well understood. In particular, how native predators affect seabird populations has rarely been quantified. 2. Here, we investigate how an increase in white-tailed eagles in northern Norway, a stronghold for the species, affected a local population of 25,000 pairs of black-legged kittiwakes, a red-listed seabird, during a 42-year period ending with colony extinction. We use a natural experiment of two neighbouring colonies with/without eagle predation to disentangle the effects of eagles from local kittiwake foraging conditions (using size of young herring as a proxy). 3. At the colony where eagle predation occurred, and in contrast to the eagle-free colony, kittiwake breeding success and population size declined with increased eagle abundance , the latter more strongly under poor foraging conditions. Breeding success increased with foraging conditions at both colonies. 4. Simple population modelling shows that although conditions were insufficient to sustain the eagle-exposed colony, the increased abundance of eagles sped up its extirpation by many years. 5. Policy implications. Our study shows that top-down effects from avian predators can be significant regulators of seabird populations, challenging their conservation where native, often protected, predators are rising. Such effects, and their possible interaction with other factors, must also be accounted for when using seabird demographic traits as environmental indicators and when developing more flexible and effective management and action plans.Top-down control of a marine mesopredator: Increase in native white-tailed eagles accelerates the extinction of an endangered seabird populationpublishedVersio

Fish consumption by great cormorants in Norwegian coastal waters—a human-wildlife conflict for wrasses, but not gadids

Piscivorous wildlife is often perceived as competitors by humans. Great cormorants of the continental subspecies (Phalacrocorax carbo sinensis) in the Baltic and North Sea increase, while local cod (Gadus morhua) stocks decline. In contrast, numbers of the Atlantic subspecies (Phalacrocorax carbo carbo), breeding along the Norwegian and Barents Seas, have been relatively stable. We investigated the diet of both great cormorant subspecies in breeding colonies along the Norwegian Coast from Lofoten to the Skagerrak and estimated the biomass of fish consumed annually by great cormorants in Norwegian waters. The birds’ consumption was compared with estimated fish stock sizes and fishery catches. Cod and saithe (Pollachius virens) dominated the diet in the Norwegian Sea and wrasses in the North Sea and Skagerrak. Estimated total fish consumption of cod and saithe by great cormorants was <1.7% of estimated fish stocks and <9% of that of human catches and therefore considered minor. Cormorant consumption of wrasses amounted to 110% of human catches. The practice of using wrasses as cleaner fish in the salmon farming industry leads to a conflict with cormorants, and we urge for a better understanding and management of wrasse populations, taking ecosystem functioning and natural predation into account. diet analysis, fish stock size, Gadus morhua, Labridae, metabolic rate, North Atlantic, NorwaypublishedVersio

Fit is fat: winter body mass of Atlantic puffins Fratercula arctica

Capsule: Atlantic Puffins Fratercula arctica from Scottish and Norwegian populations were significantly heavier in winter than when rearing chicks. Aims: To compare body masses of Atlantic Puffins on their wintering grounds off the Faroe Islands with those of birds rearing chicks at colonies in Scotland and Norway. Methods: We took standardized measurements of wing length and body mass of Atlantic Puffins during the summer chick-rearing period and on the wintering grounds near the Faroe Islands. These measurements were used to estimate seasonal changes in body mass for the two breeding populations. In three cases data were available for individuals weighed both at the colony and on the wintering grounds. Results: On average, Atlantic Puffins breeding in Scotland and Norway increased their body mass by 20–30% between the chick-rearing period and winter. The very limited individual level data accorded well with the population level estimates. Conclusions: Our results provide the first estimates of the order of magnitude in mass change between two key life history stages in this species. They indicate that gains in body mass between chick-rearing and winter are at least double the decline in mass previously recorded between incubation and chick-rearing. Given the Atlantic Puffin’s deteriorating conservation status, improved information on seasonal changes in body condition should help determine the underlying causes of die-offs in major wreck incidents such as those reported in recent years

Local prey shortages drive foraging costs and breeding success in a declining seabird, the Atlantic puffin

1. As more and more species face anthropogenic threats, understanding the causes of population declines in vulnerable taxa is essential. However, long-term datasets, ideal to identify lasting or indirect effects on fitness measures such as those caused by environmental factors, are not always available. 2. Here we use a single year but multi-population approach on populations with contrasting demographic trends to identify possible drivers and mechanisms of seabird population changes in the north-east Atlantic, using the Atlantic puffin, a declining species, as a model system. 3. We combine miniature GPS trackers with camera traps and DNA metabarcoding techniques on four populations across the puffins’ main breeding range to provide the most comprehensive study of the species' foraging ecology to date. 4. We find that puffins use a dual foraging tactic combining short and long foraging trips in all four populations, but declining populations in southern Iceland and north-west Norway have much greater foraging ranges, which require more (costly) flight, as well as lower chick-provisioning frequencies, and a more diverse but likely less energy-dense diet, than stable populations in northern Iceland and Wales. 5. Together, our findings suggest that the poor productivity of declining puffin populations in the north-east Atlantic is driven by breeding adults being forced to forage far from the colony, presumably because of low prey availability near colonies, possibly amplified by intraspecific competition. Our results provide valuable information for the conservation of this and other important North-Atlantic species and highlight the potential of multi-population approaches to answer important questions about the ecological drivers of population trends. biologging, diet, DNA metabarcoding, dual foraging, foraging ecology, intraspecific competition, population decline, seabirdspublishedVersio

Model-based assessment of marine bird population status using monitoring of breeding productivity and abundance

Vertebrate populations are often monitored as part of broader assessments of ecosystem status, where they are expected to provide information on the ability of the ecosystem to support higher-level predators. However, because many vertebrates are long-lived and often only subsets of their populations can be monitored, abundance may not be sufficiently responsive to ecosystem status to provide early warnings of impending changes. Marine birds are often used as indicators of ecosystem status but, due to their long lifespan and delayed recruitment to the breeding population, changes in abundance are generally slow and often difficult to interpret. Their breeding productivity is, however, also widely monitored and much more responsive to ecosystem status, but the relevance of variation in productivity may be difficult to assess. We propose a model-based indicator that integrates monitoring of abundance and breeding productivity through demographic matrix models. The metric of the proposed indicator is the expected population growth rate, given the observed level of breeding productivity. This expected growth rate is then compared with a threshold derived from the criteria employed for red-listing of threatened species by the International Union for the Conservation of Nature. We demonstrate the suggested approach using data from Black-legged Kittiwakes Rissa tridactyla in the Greater North Sea region, Northwest Europe. The proposed indicator shows that the current level of breeding productivity is expected to lead to a population decline of 3–4% per year, which is equivalent to a red-list status as Endangered for the species in this region. Our indicator approach is used in OSPAR’s Quality Status Report 2023 and is expected to be used by European Union member states for reporting under the Marine Strategy Framework Directive in 2024. Our approach represents a major step forward in assessing the status of marine bird populations; the ideal next step would be to develop a coherent Integrated Population Modelling (IPM) framework that would allow inclusion of all data on population abundance and demography collected across the large and diverse marine ecosystems involved. breeding success, indicator, Marine Strategy Framework Directive, seabirds.acceptedVersio

Foraging behaviour of black guillemots at three Norwegian sites during the breeding season

The intensifcation of coastal development poses potential threats for coastal seabirds, and understanding their habitat use is a key factor to guide conservation and management. In sub-arctic areas, black guillemots (Cepphus grylle) use coastal habitats year-round, which makes them vulnerable to the increasing human activities in these areas. In mainland Norway, one of the species’ strongholds, black guillemots are red-listed after substantial population declines. However, their fnescale foraging behaviour has received little attention to date. We collected and analysed GPS tracking data from adult black guillemots at three sites located over a latitudinal gradient of 250 km in central/northern Norway. Maximum foraging ranges of 33 km at Sklinna (65°12′N) for incubating birds, and 18 km at both Vega (65°34′N) and Sklinna for chick-rearing birds, are among the longest reported for this species. At all three sites, foraging probability was highest in shallow waters (<50 m depth) close to the colony and declined with increasing water depth and distance from colony. However, birds from Vega also foraged over deeper waters. Kelp presence was of high importance at Sklinna, but apparently less important at Røst (67°26’N) and Vega. We also found distinct diferences in foraging activity across the day and with tidal height among the sites. Inter-site diferences in habitat use and foraging activity may be explained by diferences in the availability of habitats and suitable prey. Our study highlights the importance of shallow marine areas for black guillemots and shows that habitat use can vary substantially between sites. Cepphus grylle · Marine spatial planning · Habitat use · Species distribution model · Kelp forestpublishedVersio

Spatial and temporal variations in seabird bycatch: Incidental bycatch in the Norwegian coastal gillnet-fishery

The general decline of seabird populations worldwide raises large concerns. Although multiple factors are interacting to cause the observed trends, increased mortality from incidental bycatch in fisheries has proven to be important for many species. However, the bulk of published knowledge is derived from longline fisheries, whereas bycatch in gillnet fisheries is less studied and even overlooked in some areas. We present seabird bycatch data from a 10-year time-series of fishery data from the large fleet of small-vessels fishing with gillnets along the Norwegian coast—a large area and fishery with no prior estimates of seabird bycatch. In general, we document high rates of incidental bycatch (averaging 0.0023 seabirds/ net, or approximately 0.08 seabirds/fishing trip). This results in an estimated annual bycatch between 1580 and 11500 (95% CI) birds in this fishery. There was a surprisingly high percentage (43%) of surface-feeding seabirds in the bycatch, with northern fulmar being the most common species. Among the diving seabirds caught, common guillemot was most numerous. Our findings suggest that coastal gillnet fisheries represent a more general threat to a wider range of seabird populations, as opposed to longline fisheries where surface-feeding seabird species seem to dominate the bycatch. The bycatch estimates for the Norwegian gillnet-fishery varied in time, between areas, and with fishing depth and distance from the coast, but we found no clear trends in relation to the type of gillnets used. The results enabled us to identify important spatio-temporal trends in the seabird bycatch, which can allow for the development and implementation of more specific mitigation measures. While specific time closures might be an efficient option to reduce bycatch for diving seabirds, measures such as gear modification and reduction in release of wastewater during fishing operation are probably a more effective mitigation approach for reducing bycatch of surface-feeding seabirds.publishedVersio

Contaminants in northern fulmars (Fulmarus glacialis) exposed to plastic

Northern fulmars are seabirds which feed exclusively at sea, and as such, they are useful indicators of ocean health. Marine plastic pollution is an ever-increasing and global issue that affects the northern fulmar as they are frequently found to have ingested plastic. In this report we investigate whether the amount of ingested plastic affects the concentration of certain plastic-adsorbed toxicants in their tissues. Marine plastic pollution is a field of utmost importance. It is our hope that this continues to be an area which receives increased attention in order to elucidate the potential harmful effects plastics have on the northern fulmar and ocean health, in general

Assessing incidental bycatch of seabirds in Norwegian coastal commercial fisheries: Empirical and methodological lessons

-Unintentional bycatch, waterbirds, small vessel fishery, gillnetts, longlines, Northeast Atlanti

Hybridization of Atlantic puffins in the Arctic coincides with 20th-century climate change

The Arctic is experiencingthe fastest rates of globalwarming,leadingto shiftsin the distributionof its biotaandincreasingthe potentialfor hybridization. However, genomicevidenceof recenthybridization events in theArctic remainsunexpectedlyrare. Here, we use whole-genomesequencingof contemporary and 122-year-oldhistoricalspecimensto investigate the originof an Arctic hybridpopulation of Atlanticpuffins(Fr aterculaarctica)on Bjørnøya, Norway. We show that the hybridization between the High Arctic, large-bodiedsubspeciesF. a. naumanniand the temperate, smaller-sizedsubspeciesF. a. arcticabeganas recentlyas six generationsagodue to an unexpectedsouthward rangeexpansionofF. a. naumanni.Moreover, we find a significanttemporalloss of geneticdiversityacross Arctic and temperate puffinpopulations.Our observationsprovide compellinggenomicevidenceof the impacts of recentdistributionalshiftsand loss of diversityin Arctic communitiesduringthe 20th century.publishedVersio