Ardea最新文献

{"title":"Expanding East: Great Cormorants Phalacrocorax carbo Thriving in the Eastern Baltic and Gulf of Finland","authors":"Mennobart R. van Eerden, Stef van Rijn, M. Kilpi, A. Lehikoinen, V. Lilleleht, Karlis Millers, A. Gaginskaya","doi":"10.5253/arde.v109i2.a5","DOIUrl":"https://doi.org/10.5253/arde.v109i2.a5","url":null,"abstract":"Great Cormorants Phalacrocorax carbo in the eastern Baltic are expanding in numbers. Eight colonies in Estonia, Finland and the Russian Federation were investigated in 2007. Brood size and condition of large nestlings were determined and indicate that food provisioning was not a limiting factor. Food items consisted of both pelagic and benthic prey, with marked differences among the colonies. Eelpout Zoarces viviparus and Roach Rutilus rutilus were the most important prey according to fish mass. For pelagic prey this was Sprat Sprattus sprattus. Additional data in later years support the conclusion that the species experienced a rapid expansion at the time of investigation. Two factors are likely to have contributed to improved conditions for Cormorants in this part of the eastern Baltic. First, the low abundance of predatory fish such as Cod Gadus morhua and Pikeperch Sander lucioperca as a result of overfishing by commercial fisheries as well as climate change has, most likely, caused small benthic and pelagic prey fish to thrive. Second, increased eutrophication has probably fuelled the fish production. Based on fish species taken and the number of Cormorants present, the conclusion seems justified that any interaction between Cormorants and fisheries is unlikely at the scale of the Finnish Gulf, although locally measurable effects of Cormorant consumption on commercial yield may exist. As a visible, relatively new apex predator to the system, the Great Cormorant may well be an indicator of the ecological condition of the system. Monitoring of Cormorants (numbers, distribution, food, breeding success) may therefore provide useful data which can be used to assess the recovery of the benthic and pelagic parts of the food web.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48821982","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Social Hierarchy within Communal Foraging Flocks of Great Cormorants Phalacrocorax carbo as Reflected by Differences in Prey Composition and Food Intake at the Roost","authors":"Mennobart R. van Eerden, Stef van Rijn","doi":"10.5253/arde.v109i2.a23","DOIUrl":"https://doi.org/10.5253/arde.v109i2.a23","url":null,"abstract":"Day-fresh Great Cormorant pellets were collected at a huge single winter roost at Kreupel island in Lake IJsselmeer, The Netherlands. The roost is situated on a sandy island, 3 m above the water level and is regularly used by 1000–8000+ Cormorants. By examining pellets and thus reconstructing the previous day's meal of Cormorants gathering at the roost, we explored spatio-temporal differences in the diet of individual birds. We found that structural differences in pellets (size, colour and structure) are related to their content (fish species and fresh mass of a daily meal). Structurally larger and lighter coloured pellets contained larger and coarser fish and represented a higher total fish mass. Pellets of different size and structure were non-randomly distributed at the roost. Birds positioned centrally in the roost produced on average larger pellets than birds at the edges. Cormorants having few or no food remains in their pellets were more frequently recorded on the edge of the roost than in the centre and in particular, they were more likely to be located to the rear of the roost. The same was true for pellets showing a bloody signature which may be linked to either injury by sharp fin rays or to a parasite induced effect. Pellet data were corroborated by observations of differential distribution of faecal splashes of Cormorants, showing that individuals in the centre of the roost produced most guano. Clear diet differences existed within the roost between birds in the centre and elsewhere in the roost, whereas smaller differences existed between the front, edge and rear of the roost. Our data suggest a social hierarchy based on higher foraging success of birds returning earlier to the roost and settling in the centre, hereby forcing later arriving and less successful Cormorants towards the edge, rear and front position. We conclude that position at the roost is a reflection of previous foraging success, possibly caused by differences in dominance between Cormorants during the period of communal foraging. From a methodological point of view, our study demonstrates that, because of structural differences in pellets and spatial differences in occurrence, it is important to collect pellets randomly if one is to describe a proper diet sample by using pellets at any given site. Especially in marshlands and under trees and bush growth with a lot of litter, the likely collection of larger, more conspicuous pellets will cause a bias towards the larger fish species and sizes. Also sampling only at edge locations or specifically at the centre of a roost may give biased results, as this may result in an under- or overestimation in reconstructed fish uptake (e.g. fish size, mass, species) from the waterbody under study.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48980845","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Migration Patterns and Recorded Emigration of the Great Cormorant Phalacrocorax carbo sinensis in the Largest French Colony of Lac de Grand-Lieu: Density-Dependent Factors Operating at Different Time and Geographical Scales","authors":"L. Marion, Pierrick Marion","doi":"10.5253/arde.v109i2.a8","DOIUrl":"https://doi.org/10.5253/arde.v109i2.a8","url":null,"abstract":"The number of wintering Great Cormorants Phalacrocorax carbo sinensis in France has strongly increased since the 1970s, mainly due to the protection of the ‘continental’ sinensis subspecies in countries north of France. This increase has led to the establishment of a pioneering inland breeding colony in western France, while previously only the largely marine ‘Atlantic’ P. c. carbo subspecies occurred on the Channel coast. The marine subspecies was attracted and bred in this new inland settlement of sinensis, which rapidly became the largest colony in France. This paper analyses the migration pattern of birds from this colony by analysis of the dispersal of colour-ringed birds between 1989 and 2008. Interestingly, besides a classic south-west migration pattern, birds from this colony also displayed a pattern heading north-east, up to countries such as The Netherlands, from where the founders (sinensis) of this colony probably originated. Sightings and recoveries revealed that about 25% of the adults and 19% of the first-year birds headed north-east. Due to this north-east migration direction, the overall annual dispersal point was located only 50 km south-west of the colony, although in December and January this midpoint was located about 320 km south-west of the colony. The birds largely avoided Brittany, presumably to avoid competition with individuals of the carbo subspecies, and the main wintering areas of sinensis from other colonies, both in France (east, centre and south) and in Spain. Over the years 1989–2008, in the breeding period, the mean dispersal distance was shorter for adults than for young birds (54 km vs. 144 km, respectively) but in winter adult birds migrated further than young ones (305 km vs. 221 km, respectively). The mean annual dispersal distance in winter varied from 106 km to 527 km (all age-classes taken together). Migratory distance was not related to mean winter temperature. For adults, dispersal distance correlated with the annual number of breeding pairs in the Grand-Lieu colony between 1990 and 2003, but not between 2004–2008. Emigration (breeding in another colony) was recorded up to 2011 to 11 inland colonies and one coastal colony (founded more recently than Grand-Lieu), nine of them in France, two in Spain and one in The Netherlands. Annual emigration rate was negatively related to colony size in Grand-Lieu. The study points to the existence of density-dependent effects on distribution patterns of Cormorants outside the breeding season but also suggests connectivity and interaction among colonies that are hundreds of kilometres apart.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43423812","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Habitat Specialisation Affects Fitness of the Marine and Continental Great Cormorant Subspecies in a Recently Evolved Sympatric Area","authors":"L. Marion, J. Le Gentil","doi":"10.5253/arde.v109i2.a17","DOIUrl":"https://doi.org/10.5253/arde.v109i2.a17","url":null,"abstract":"With the aim of studying ecological specialisation between subspecies, we compared the components of breeding success in individuals of two recently sympatric subspecies, carbo (‘marine’) and sinensis (‘continental’), of the Great Cormorant in a continental colony. The subspecific origin of broods was determined using D-Loop mtDNA and microsatellites. Although there were no differences in clutch size and laying date between the subspecies, mean fledging success was lower for the marine subspecies (–30% according to mtDNA assignment, –38% according to microsatellite assignment) than for the continental subspecies, while mixed breeding pairs had an intermediate fledging success. These results showed that the marine subspecies is less well adapted than the continental one to inland water, which is considered to be the optimal habitat of the continental subspecies. According to these results and to the geographical expansion of the continental subspecies, we suggest that the proportion of marine subspecies in western European inland colonies could decrease when density-dependent competition increases due to saturation.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48937396","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Long-Term Changes in Winter Distribution of Danish-Ringed Great Cormorants","authors":"T. Bregnballe, C. Herrmann, K. T. Pedersen, J. Wendt, J. Kralj, M. Frederiksen","doi":"10.5253/arde.v109i2.a6","DOIUrl":"https://doi.org/10.5253/arde.v109i2.a6","url":null,"abstract":"We describe long-term changes in the distribution of 2249 freshly dead winter recoveries of 94,352 Great Cormorant chicks ringed between 1940 and 2018 in Denmark. The entire wintering range was divided into four major compartments to assess changes in (1) migratory distance and (2) the spatial distribution of recoveries. In the south-eastern wintering compartment, the mean distance to winter recovery sites declined from the winters 1946/47–2000/01 to those of 2001/02–2018/19 by 528 km (corresponding to a reduction of 36%). In the southern-central wintering compartment the change was gradual from before the mid-1980s to the winters 2006/07–2018/19 with a reduction of c. 700 km (corresponding to 41%). There were no temporal changes in migration distance for Cormorants wintering in the south-west. From 1991 onwards, recoveries were recorded in increasing proportions in the south-western compartment (from 21% in 1946/47–1990/91 to 60% in 2001/02–2018/19). The proportion recovered in the southern-central compartment varied between 34 and 45% up to the mid-1990s and then fell to 4–6% during the winters 2006/07–2018/19. The proportions recovered in the south-eastern compartment ranged from 9 to 18% until 1990/91 but fell subsequently to 0.6 to 2%. Long-term changes in the geographical origin of Cormorants recovered in Croatia further confirm that declines in numbers of recoveries of Danish-ringed Cormorants in the south-eastern wintering area reflect a true westward shift in winter distribution. The composition of recoveries in Croatia revealed that the south-eastern wintering areas were increasingly dominated by Cormorants from breeding colonies in the central and eastern Baltic region. We conclude that Danish Cormorants shifted their winter distribution westward from the 1990s onwards and shortened their migration by wintering further north. We hypothesise that this westward shift represents a response to increased competition with birds from breeding colonies located further east in the Baltic Sea, where populations increased markedly from the 1990s onwards.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49339155","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Natural Regulation of the Baltic Population of the Great Cormorant Phalacrocorax carbo sinensis: The Interplay between Winter Severity and Density Dependence","authors":"C. Herrmann, K. Feige, Daniel R. Otto, T. Bregnballe","doi":"10.5253/arde.v109i2.a7","DOIUrl":"https://doi.org/10.5253/arde.v109i2.a7","url":null,"abstract":"After a period of continuous increase and range expansion, the Baltic Great Cormorant population has stabilised in large parts of its range in recent years. Ringing recoveries reveal that considerable proportions of the population winter in areas that can be affected by prolonged frost periods. There is evidence that winter severity is an important density-dependent regulation factor: if the population is large, ice cover of coastal and inland water surfaces during harsh winters affects the population by reducing the availability of food resources. As long as the population remained small, however, it was not affected even by very cold winters, since the remaining accessible food resources were presumably still sufficient. The analysis presented here uses the average winter temperature in Germany as a proxy for winter severity in the frost-affected parts of the wintering areas of Baltic Cormorants. The Baltic Cormorant population in 1980–2016 is estimated from annual counts in Denmark, Schleswig-Holstein, Mecklenburg-Western Pomerania, Estonia, Finland and Gotland, which account for about 50% of the total population. The interplay between winter severity and density dependence is analysed using a linear and a non-linear regression model approach. The non-linear model gives a better description of the relationship between the size of the Baltic breeding population during the year (n), the winter temperature Tn, and the population size during the previous year (n–1). According to the model, a population of less than 41,400 breeding pairs would not suffer declines during even the coldest winters recorded since 1882. In 1989, the Baltic Cormorant population exceeded for the first time the threshold value for density-dependent regulation caused by severe winters. The winter 1995/96 was then the first one cold enough to cause a population decline. According to the model, during the years 2002/2003, 2005/06, 2008/09, 2009/10 and 2010/11 the winters have been cold enough to reduce population numbers. Furthermore, the model shows that the regulative winter effect is restricted to the low temperature range.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47229257","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Winter Diet of Great Cormorants Phalacrocorax carbo in the River Geul, The Netherlands: The Importance of Common Small Riverine Fish Species","authors":"Stef van Rijn","doi":"10.5253/arde.v109i2.a13","DOIUrl":"https://doi.org/10.5253/arde.v109i2.a13","url":null,"abstract":"Since 2006, Great Cormorants Phalocrocorax carbo sinensis have wintered in the area of the river Geul, a right-bank tributary of the river Meuse, in the province of Limburg in the south of The Netherlands. Although the number of birds there is relatively small (approximately 30 birds), the local sports fishery sector is concerned about the possible impact on wild Brown Trout Salmo trutta, particularly on the young year-classes, through predation by wintering Cormorants. The number of birds, as well as their estimated fish consumption, was studied in the winter of 2012. Analysis of 70 diet samples (pellets) taken from the roost local to the area, showed that predation was primarily on young year classes of cyprinids, like Roach Rutilus rutilus. These cyprinids, and probably also the few trout consumed, were thought to have been mainly taken from farmed fish ponds in the direct neighbourhood of the river Geul. Besides predation of larger cyprinids, the Cormorants also took abundant small riverine fish species (2–10 cm) like Rhine Sculpin Cottus rhenanus and smaller cyprinid species like Minnow Phoxinus phoxinus and Gudgeon Gobio gobio. These riverine fishes have increased recently due to ameliorated water quality. The estimated fish consumption by Cormorants in the present study suggests limited or no impact on Brown Trout during winter.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71089952","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Food Choice and Prey Selection by Great Cormorants Phalacrocorax carbo in a Shallow Coastal Zone in the Dutch Delta Area: Importance of Local Flatfish Stocks","authors":"Stef van Rijn, Mennobart R. van Eerden","doi":"10.5253/arde.v109i2.a20","DOIUrl":"https://doi.org/10.5253/arde.v109i2.a20","url":null,"abstract":"Coastal breeding Great Cormorants Phalacrocorax carbo foraging in a shallow part of the Dutch North Sea preyed upon abundant marine demersal fish species. In 2010–2012 intensive fish surveys were performed in the Voordelta area and in 2009–2015 Cormorant pellets were sampled in the breeding colony of Breede Water, Voorne, four times per year between March and September. In total 48 fish species were detected in the diet, 38 being marine species. Mainly flatfish were consumed, and European Plaice, Common Dab and Common Sole were the most important prey according to fish mass. Experimental trawling revealed 65 species of fish of which gobies, Herring, Whiting, Sprat, European Plaice and Common Dab were the most abundant. Compared to the trawl data, Cormorants showed a preference for Common Dab and Common Sole and for other solitary bottom fish like sandeels and Shorthorn Sculpin. These species were all common in the area. With respect to uncommon and rare species, no preferential selection was recorded. Densities of flatfish were highest in foraging areas closest to the breeding colony and possible depletion effects were only recorded in Common Dab. This diurnal species was already being preyed upon early in the season. Nocturnal foraging habits in other flatfish species, in combination with burrowing behaviour and rounded body shape are effective anti-predator traits and this was reflected in lower frequencies of these species in the Cormorants' diet. Consumption of freshwater fish by Cormorants at the beginning of the breeding period enabled an early start to breeding, and the increasing availability of flatfish in late spring matched the peak demand of rearing nestlings. The almost exclusive predation on flatfish was probably caused by the near-bottom foraging behaviour of most Cormorants and this habit made the birds feed on other abundant demersal fish species as well, such as Whiting, sandeels, Shorthorn Sculpin, Lesser Weever and dragonet species. And although numerous in the system, this bottom-oriented feeding behaviour of Cormorants therefore resulted in a very limited predation on pelagic fish species. In total we estimate an annual extraction by Cormorants of some 100 tonnes of fish being c. 77,600 kg flatfish and c. 20,700 kg other marine fish. Although with a foraging range partly outside the coastal zone, the extraction of fish by Harbour Seals Phoca vitulina and Grey Seals Halichoerus grypus outnumbered that of Cormorants by a factor of 9. As seals are known flatfish consumers, this suggests that there is competition between mammalian and avian predators on demersal fish stocks in the coastal zone.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46048285","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effects of Roach Rutilus rutilus Collapse on Abundance, Distribution and Diet of Great Cormorants Phalacrocorax carbo in a Large River in North-West Europe","authors":"J. Paquet, William Otjacques, R. Libois, Francis Pourignaux, P. Kestemont","doi":"10.5253/arde.v109i1.a14","DOIUrl":"https://doi.org/10.5253/arde.v109i1.a14","url":null,"abstract":"Aquatic habitats are subject to multifactorial changes including global warming, invasive species colonisation, modification of organic and micro-pollutant discharge and, for large rivers in Europe, drastic physical modification (e.g. channelisation, impoundments). The Meuse River in Belgium is one of these multi-stressed environments, in which recent decreases of fish populations were observed, with the loss of 90% of Roach Rutilus rutilus biomass in only a few years. In the light of this fish stock collapse, diet modification and local population evolution of a key avian predator, the Great Cormorant Phalacrocorax carbo, were examined. The diet composition and daily consumption rates of the Great Cormorants feeding in the river were largely similar to that seen before the fish population collapsed. Numbers of wintering Great Cormorants decreased by 90%, as did Roach numbers, and thus the predation pressure was adjusted to the decreased fish availability. The number of night-roosts and locations remained unchanged and no redistribution to adjacent habitats was observed at the regional scale. We suggest a bottom-up chain of responses where a fish collapse forced a reduction in Cormorant numbers, being the main piscivorous avian predator, rather than a modification of Cormorant prey composition and/or a local redistribution to adjacent wetlands (top-down). The factors that govern the establishment of a small and productive breeding population remain to be explained, but we hypothesise that the start of breeding could well have been alleviated by the large decrease in number of wintering birds.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42796264","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Population Status, Breeding Biology and Diet of Norwegian Great Cormorants","authors":"S. Lorentsen, T. Anker‐Nilssen, R. Barrett, Geir H. R. Systad","doi":"10.5253/arde.v109i2.a4","DOIUrl":"https://doi.org/10.5253/arde.v109i2.a4","url":null,"abstract":"Two subspecies of the Great Cormorant breed in Norway, the continental Phalacrocorax carbo sinensis in the south, along the Skagerrak coast, and the marine P. c. carbo from central Norway and northwards. Here we review the information existing until 2017 on population status and trends, breeding performance and diet of these two subspecies in Norway. The most recent national population estimates are approximately 2500 (in 2012) and 19,000 (in 2012–2014) breeding pairs of sinensis and carbo, respectively. The sinensis population established itself in 1996 in Rogaland at the south-western tip of Norway, and in 1997 in Østfold close to the Swedish border; in both areas it increased for about ten years. Since then, the numbers have stabilised. For carbo, the population increased from 21,000 pairs in the early 1980s to 27,000 in 1995, and then decreased to the current number of 19,000 pairs. Significant annual variations in clutch size and reproductive output have been observed, but the drivers of these changes have not been identified. Unidentified gadoids and Atlantic Cod Gadus morhua were the most common prey of carbo, whereas inshore species such as Corkwing Wrasse Symphodus melops, Rockcook Centrolabrus exoletus, Goldsinny Wrasse Ctenolabrus rupestris and Black Goby Gobius niger were the most common prey in the eastern Skagerrak caught by sinensis. Carbo took very large numbers of 1–3-year-old gadoids during the year, and we cannot exclude the possibility this can have local effects on fish mortality rates.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48473796","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}