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.
{"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":"109 1","pages":"417 - 428"},"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}
C. Herrmann, K. Feige, Daniel R. Otto, T. Bregnballe
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.
{"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":"109 1","pages":"341 - 352"},"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}
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.
{"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":"109 1","pages":"471 - 480"},"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}
T. Bregnballe, C. Herrmann, K. T. Pedersen, J. Wendt, J. Kralj, M. Frederiksen
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.
{"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":"109 1","pages":"327 - 340"},"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}
J. Paquet, William Otjacques, R. Libois, Francis Pourignaux, P. Kestemont
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.
{"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":"109 1","pages":"429 - 441"},"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}
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.
{"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":"109 1","pages":"507 - 528"},"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}
One of the most widespread and persistent environmental conflicts in Europe involves the Great Cormorant Phalacrocorax carbo. The ‘continental’ race P. c. sinensis comprises over 80% of the European breeding population and its numbers and geographical distribution have increased and expanded dramatically in recent decades. Consequently, Cormorants have increasingly come into conflict with fisheries interests across Europe, as many people believe that the birds are now so numerous that they cause declines in fish catches, with associated impacts on commercial and recreational fisheries. The Central European policy issue is thus how to deal with: (1) a large pan-European population of Cormorants, (2) very often breeding in some Member States but overwintering and preying upon fish in others, (3) where there is generally a lack of unequivocal scientific evidence for predation impact on fisheries and (4) where there are growing political calls for coordinated European management, whilst (5) many believe that the site-specific local/regional management advocated by some is ineffective. Using case examples and experiences from several pan-European studies and research networks, this paper describes the complexity of this issue and the diversity of associated opinions. Much of the controversy over Cormorants is fuelled by differences of opinion and, coupled with its persistence and entrenched nature, it has many of the characteristics of a so-called ‘intractable environmental conflict’. As such, this paper draws on a ‘reframing’ model proposed to deal with such situations and discusses the various ‘frames’ by which issues are viewed. It also proposes that future research might best focus on specific fisheries sectors that appear to be ‘hotspots’ for conflicts. Here, demonstration projects could involve a reframing exercise, coupled with new scientific research and practical experimentation within an adaptive management framework – one aim of which might be to increase the scope and geographical coverage of effective management activities.
{"title":"There must be Some Kind of Way Out of Here: Towards ‘Reframing’ European Cormorant-Fisheries Conflicts","authors":"D. Carss","doi":"10.5253/arde.v109i2.a31","DOIUrl":"https://doi.org/10.5253/arde.v109i2.a31","url":null,"abstract":"One of the most widespread and persistent environmental conflicts in Europe involves the Great Cormorant Phalacrocorax carbo. The ‘continental’ race P. c. sinensis comprises over 80% of the European breeding population and its numbers and geographical distribution have increased and expanded dramatically in recent decades. Consequently, Cormorants have increasingly come into conflict with fisheries interests across Europe, as many people believe that the birds are now so numerous that they cause declines in fish catches, with associated impacts on commercial and recreational fisheries. The Central European policy issue is thus how to deal with: (1) a large pan-European population of Cormorants, (2) very often breeding in some Member States but overwintering and preying upon fish in others, (3) where there is generally a lack of unequivocal scientific evidence for predation impact on fisheries and (4) where there are growing political calls for coordinated European management, whilst (5) many believe that the site-specific local/regional management advocated by some is ineffective. Using case examples and experiences from several pan-European studies and research networks, this paper describes the complexity of this issue and the diversity of associated opinions. Much of the controversy over Cormorants is fuelled by differences of opinion and, coupled with its persistence and entrenched nature, it has many of the characteristics of a so-called ‘intractable environmental conflict’. As such, this paper draws on a ‘reframing’ model proposed to deal with such situations and discusses the various ‘frames’ by which issues are viewed. It also proposes that future research might best focus on specific fisheries sectors that appear to be ‘hotspots’ for conflicts. Here, demonstration projects could involve a reframing exercise, coupled with new scientific research and practical experimentation within an adaptive management framework – one aim of which might be to increase the scope and geographical coverage of effective management activities.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"109 1","pages":"667 - 681"},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49363354","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}
S. Lorentsen, T. Anker‐Nilssen, R. Barrett, Geir H. R. Systad
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.
{"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":"109 1","pages":"299 - 312"},"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}
Mennobart R. van Eerden, Arne Okko Kees van Eerden
Ground-nesting Great Cormorants were monitored in three neighbouring colonies at Lake IJsselmeer, The Netherlands. Using aerial photographs taken during peak breeding time, nest density and nearest neighbour distance were determined for four sequential years. In addition, species and number of predators were determined. In total, five mammalian and nine avian predatory species were associated with the Cormorant breeding colonies. Spatial distribution of nests mostly showed dispersed and random patterns rather than a contagious pattern. The latter distribution, with less distance between nests than expected both from a random and equal distribution pattern, was found in the colony of De Ven in 2013 during the last year of its existence. The predator Red Fox Vulpes vulpes arrived at the colony in 2010. In all three colonies, nest density was highest and nearest neighbour distance shortest in colonies with the highest number of predators. At low to moderate predatory pressure, ground-nesting Cormorants left free space between nests that was used by adult birds during take-off and landing. During the last years of its existence the shrinking colony of De Ven showed an almost circular shape, with an extreme nest density and the lowest edge-to-surface area ratio. But with Foxes present, breeding at the fringe still caused greater losses due to direct predation. Breeding success fluctuated synchronously between colonies but was lower in colonies where the number of predators was higher. The arrival of Red Foxes in De Ven caused extreme losses of young and over the years resulted in a strong decline in number of breeders, eventually leading to complete abandoning of the site in 2014. Large gulls formed another important group of predators but did not cause the Cormorants to abandon the breeding site. In the Vooroever colony, bush and tree cover supplied shelter and allowed birds to breed in greater density without causing nearest neighbour density to decrease, as was the case when no cover was available. Greater nest density and reduced nearest neighbour distances are considered to be a pro-active response by individual birds to the presence of predators. When predator numbers increased, the within-colony open spaces that normally exist under circumstances of moderate density were filled up with nests, leaving little or no room for landing and departure. This leads to reduced edge effects and a circular shape of the colony, thereby potentially limiting predation risk. As a consequence of extreme high nest densities, breeding success was lower due to interference by other Cormorants. This study is the first to show that colony structure in waterbirds is affected by forces of attraction and repulsion between founding birds that are predator driven.
{"title":"Ecology of Fear in a Colonial Breeder: Colony Structure in Ground-Nesting Great Cormorants Phalacrocorax carbo Reflects Presence of Predators","authors":"Mennobart R. van Eerden, Arne Okko Kees van Eerden","doi":"10.5253/arde.v109i3.a27","DOIUrl":"https://doi.org/10.5253/arde.v109i3.a27","url":null,"abstract":"Ground-nesting Great Cormorants were monitored in three neighbouring colonies at Lake IJsselmeer, The Netherlands. Using aerial photographs taken during peak breeding time, nest density and nearest neighbour distance were determined for four sequential years. In addition, species and number of predators were determined. In total, five mammalian and nine avian predatory species were associated with the Cormorant breeding colonies. Spatial distribution of nests mostly showed dispersed and random patterns rather than a contagious pattern. The latter distribution, with less distance between nests than expected both from a random and equal distribution pattern, was found in the colony of De Ven in 2013 during the last year of its existence. The predator Red Fox Vulpes vulpes arrived at the colony in 2010. In all three colonies, nest density was highest and nearest neighbour distance shortest in colonies with the highest number of predators. At low to moderate predatory pressure, ground-nesting Cormorants left free space between nests that was used by adult birds during take-off and landing. During the last years of its existence the shrinking colony of De Ven showed an almost circular shape, with an extreme nest density and the lowest edge-to-surface area ratio. But with Foxes present, breeding at the fringe still caused greater losses due to direct predation. Breeding success fluctuated synchronously between colonies but was lower in colonies where the number of predators was higher. The arrival of Red Foxes in De Ven caused extreme losses of young and over the years resulted in a strong decline in number of breeders, eventually leading to complete abandoning of the site in 2014. Large gulls formed another important group of predators but did not cause the Cormorants to abandon the breeding site. In the Vooroever colony, bush and tree cover supplied shelter and allowed birds to breed in greater density without causing nearest neighbour density to decrease, as was the case when no cover was available. Greater nest density and reduced nearest neighbour distances are considered to be a pro-active response by individual birds to the presence of predators. When predator numbers increased, the within-colony open spaces that normally exist under circumstances of moderate density were filled up with nests, leaving little or no room for landing and departure. This leads to reduced edge effects and a circular shape of the colony, thereby potentially limiting predation risk. As a consequence of extreme high nest densities, breeding success was lower due to interference by other Cormorants. This study is the first to show that colony structure in waterbirds is affected by forces of attraction and repulsion between founding birds that are predator driven.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"109 1","pages":"609 - 628"},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44052191","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}
Historical sources from European countries show that the persecution of Great Cormorants started centuries ago and was widespread. As an exception, in The Netherlands protective measures for Cormorants were declared from 1500 onwards. In this paper an explanation is given for this striking difference. In The Netherlands, Cormorants were game species and a food source. To make this use sustainable, Cormorants were protected. In other countries, Cormorants were neither considered to be a game species nor a source of food. On the contrary, in most countries Cormorants were seen as pest birds. They were persecuted to protect the pond culture of fish. In The Netherlands, however, this kind of pond culture was uncommon. Because of these differences with the rest of Europe, in The Netherlands the general opinion was more in favour of protection than of persecution. In consequence, the Dutch population of Cormorants was much larger than elsewhere in Europe. The survival of this Dutch population amidst the depleted populations in other countries was an important prerequisite for the increase of the European Cormorant population in the 20th century.
{"title":"Great Cormorants Phalacrocorax carbo in the Netherlands: Five Centuries of Protection Amidst Almost European-Wide Persecution","authors":"Jan H. de Rijk","doi":"10.5253/arde.v109i2.a10","DOIUrl":"https://doi.org/10.5253/arde.v109i2.a10","url":null,"abstract":"Historical sources from European countries show that the persecution of Great Cormorants started centuries ago and was widespread. As an exception, in The Netherlands protective measures for Cormorants were declared from 1500 onwards. In this paper an explanation is given for this striking difference. In The Netherlands, Cormorants were game species and a food source. To make this use sustainable, Cormorants were protected. In other countries, Cormorants were neither considered to be a game species nor a source of food. On the contrary, in most countries Cormorants were seen as pest birds. They were persecuted to protect the pond culture of fish. In The Netherlands, however, this kind of pond culture was uncommon. Because of these differences with the rest of Europe, in The Netherlands the general opinion was more in favour of protection than of persecution. In consequence, the Dutch population of Cormorants was much larger than elsewhere in Europe. The survival of this Dutch population amidst the depleted populations in other countries was an important prerequisite for the increase of the European Cormorant population in the 20th century.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"109 1","pages":"381 - 388"},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46121329","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}
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