Cormorant Thesis

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Double-crested cormorant (P. auritus)

Mathieu O. 2005. Impact potentiel de la prédation des cormorans à aigrettes (Phalacrocorax auritus) d'une colonie en expansion sur les communautès aquatiques de lacs oligotrophes du bouclier canadien. M. Sc. thesis, Université du Québec à Trois-Rivières, PQ, Canada.

Great cormorant (P. carbo)

Bregnballe Thomas - 1996. Reproductive performance in Great Cormorants during colony expansion and stagnation. Ph. D. thesis, Department of Zoology, University of Aarhus. Published by the Natural Environmental Research Institute, Denmark. 103 pp.

Engström Henry - 2001. Effects of Great Cormorant predation on Fish Populations and Fishery. University of Uppsala . [ABSTRACT. The strong increase in number of Great cormorants Phalacrocorax carbo in Sweden in recent years has led to conflicts - particularly with fishery. This thesis focuses on the possibkle effects of cormorant predation on fish populations. In total, data from 15 lakes in South Sweden were included in this study while most studies were carried out in Lake Ymsen. The results suggest that the impact of cormorant predation on natural fish populations was small, and I observed no decline in fish mass after cormorants established. Cormorant predation on eel was difficult to evaluate because of several confounding factors. Ruffe, roach and perch (Sw.: gärs, mört och abborre) were the most important prey species to the cormorants and most fish taken were small. Cormorants do not seem to catch species and sizes in proportion to their occurrence in the fish community. Total fish removal by cormorants varied considerably among lakes (0.2 - 15.0 kg/ha) and cormorant population sizes at the different lakes were significantly positively correlated with fishery catches, which in turn was significantly positively correlated with total phosphorous levels. Thus, cormorant densities in lakes, and perhaps elsewhere, seem to be governed chiefly by fish densities. The fact that cormorant predation appears not to reduce fish densities suggest cormorants to be regulated by other means than prey depletion. The mechanism behind population regulation could be a behavioural response of fish, making fish more difficult to catch for the cormorants. In recent years, cormorant populations have been subjected to intensive legal and illegal actions with the aim to reduce cormorant numbers. However, the actions currently carried (out) are well below the efforts needed to limit population sizes. To conclude, cormorants appear to compete little with fishery, with regards to free-living fish. The main problem is that cormorants sometimes damage and take away fish in fishing gears.]

Gagliardi Alessandra - 2003. Prey-predator interactions in aquatic ecosystems: Great crested grebe (Podiceps cristatus) and cormorant (Phalacrocorax carbo) as key species. Analysis of population dynamics, biomass consumption and management of some waterbirds in Insubria region (central-northern Italy). Ph.D. thesis, Insubria University. Pp. 196.

Hénaux Viviane - 2006. Dynamics of a population exploited by man: dispersal, density-dependence and winter culls in the great cormorant. University of Montpellier II, France. [ABSTRACT. A good management of species in conflict with man needs to investigate the interplay between management strategies and natural regulation. The North European population of great cormorant strongly multiplied over the last 30 years, leading to the expansion of its breeding range because of the dispersal of individuals among colonies. In order to limit the damages of this fish-eating bird in fisheries, the population was controlled from 1992 as winter culls. The goal of my thesis was to investigate the interplay between intrinsic consequences of the demographic growth and culls on the population dynamics. From a multistate capture-recapture model, combining multisite resightings and recoveries of ringed birds, I showed that declining breeding success and increasing breeding numbers led to the dispersal of individuals. Prospecting allows first-time breeders to disperse to a colony, more or less distant, where they can expect a higher breeding success than in their birth site. Breeders prefer a colony close to their previous site in order to benefit of their experience with foraging sites. From a bioenergetics model considering the daily time-energy budget of parents and environmental conditions, I showed that the density-dependent increase of competition for food alters the foraging and breeding performances of individuals. About the impact of winter culls, it appears that the effect of culls was partially compensated by a density-dependent increase of adult and first-year survival. I suggest that an intensification of culls at the local scale will allow a higher reduction of conflicts than national quotas, and the preservation of the great cormorant population.] [Resumé. Dynamique d’une population gérée par l'homme : dispersion, densité dépendance et destructions hivernales chez le grand cormoran. Une bonne gestion des espèces en conflit avec l’homme nécessite d’examiner l’interaction entre stratégies de gestion et régulation naturelle. La population nord-européenne de grand cormoran s’est fortement multipliée au cours des trois dernières décades, entraînant l’expansion de son habitat du fait de la dispersion d’individus entre colonies. Afin de limiter les dégâts de cet oiseau piscivore dans les piscicultures, la population a été contrôlée à partir de 1992 par des destructions hivernales d’individus. L’objectif de ma thèse était de déterminer l’interaction entre les conséquences intrinsèques de la croissance démographique et les destructions sur la dynamique de la population. Avec un modèle de capture-recapture multiétat combinant réobservations multisite et reprises d’individus bagués, j’ai montré que la dégradation du succès reproducteur et l’augmentation des effectifs ont entraîné la dispersion des individus. La prospection permet aux individus qui recrutent de choisir un site plus ou moins éloigné où ils pourront produire plus de jeunes que dans leur site de naissance. Les reproducteurs dispersent préférentiellement vers une colonie proche de la précédente afin de profiter de leur expérience avec les sites de nourriture. A partir d’un modèle bioénergétique tenant compte du budget énergétique journalier des parents et des conditions environnementales, j’ai montré que l’augmentation densité-dépendante de la compétition pour la nourriture dégrade la performance de recherche alimentaire et le succès reproducteur des individus. En ce qui concerne l’effet des destructions, il semble que l’effet des tirs soit partiellement compensé par une diminution densité-dépendante de la mortalité naturelle chez les adultes et les individus de première année. Je suggère donc de substituer les quotas nationaux par une intensification des destructions au niveau local afin de permettre une meilleure résolution des conflits, tout en préservant la population de grand cormoran.]

Newson S.E. 2000. Colonisation and range expansion of inland breeding Great Cormorants Phalacrocorax carbo in England. PhD Thesis, University of Bristol

Røv Nils - 1994. Breeding distribution, population status and regulation of breeding numbers in the north-east Atlantic Great Cormorant Phalacrocorax carbo carbo. Unpublished PhD Thesis, University of Trondheim.

Volponi Stefano - 1994. Ecologia del Cormorano, Phalacrocorax carbo sinensis (Aves: Pelecaniformes), nel Delta del Po. Ph.D. thesis on Ecology, Department of Biology, University of Ferrara, Italy.

Winney B.J. 1998. Cormorant population genetics and Turaco phylogenetics. PhD Thesis, University of Nottingham.

Pygmy cormorant (P. pygmaeus)

Shmoely Marva. Comparative Ontogenesis of the Pygmy Cormorant (Phalacrocorax pygmeus) and the Great Cormorant (P. carbo sinensis): morphometry and energetics. Ph.D. thesis. Supervisors: Dr. Katzir Gadi & Assoc. Prof. Arad Zeev. Dept. of Biology, Technion University. [ABSTRACT. In Israel, there are two species of cormorants: The Great Cormorant (Phalacrocorax carbo sinensis) is a migrating bird that overwinters in Israel (16000 individuals) from November to March and returns to Europe for breeding. The smaller Pygmy Cormorant (P. pygmeus) is a resident bird that lives and breeds (400 individuals) in colonies along the Hula, Jordan and the Beit Shean Valleys.  The natural sites for both species in Israel have diminished during recent decades due to human activity. As a consequence, intensive fishery and aquaculture sites became their favorite feeding sites and the fish industry reports huge damage to fish yield. This study compares the energy demands and growth rate in captivity of the two species, as a basis for a future solution of the conflict. Age-related changes in morphometric parameters and in energy demands were measured in captivity throughout ontogenesis. Basal metabolism was measured in the laboratory in fasting, resting birds, Existence metabolism, daily food intake and digestibility were measured in outdoors cages. Morphometric measurements of wintering Great Cormorant corpses, enabled a discriminant analysis between sexes. The growth rate of Pygmy Cormorants was higher than that of the Great Cormorant in all parameters. Growth rate constant (K) of both species was higher than predicted from the allometric equation, based on the asymptotic body mass of the chicks. In both species, the legs grew faster than any other body part (including body mass), whereas the wings grew at the lowest rate. Male and female Pygmy Cormorants differ in body mass and wing length only, whereas in the Great Cormorant they differ in all morphometric parameters. Bill length, body length and wing length are the most discriminant parameters of sex in the Great Cormorant. The mass specific energy requirements of the Pygmy cormorant are much higher than those of the Great Cormorant, as expected from the size difference. The highest basal metabolism in both species was measured in young chicks (2-3 weeks), and decreased there after, in juveniles and adults. Basal metabolism of adults of both species was higher than predicted from the allometric equation. However, the existence metabolism was lower than predicted for waterbirds and shorebirds. Daily food intake of the adult Pygmy Cormorant (115 g) is higher than predicted from allometric equation for piscivorous birds whereas that of the Great Cormorant (244 g) is lower than predicted. Based on the above energetic demands, the potential damage to the fish industry by 400 Pygmy Cormorant and by 12000 Great Cormorant that feed in the fish ponds is estimated at 460 tons of fish annually, corresponding to 2.8% of the annual fish yield in Israel. From this study, it is clear that the two species of cormorants differ in their growth rate and energy demands. Therefore, their ecological impact on waterbodies in Israel is different and thus, a different management policy is necessary. The Pygmy Cormorant, as an extremely vulnerable species, needs a complete protection at the breeding colonies. In some areas, various deterring measures might be combined to prevent the cormorants from fish ponds, while offering some alternative reservoirs for feeding. Although the Great Cormorant is no longer endangered, its treatment should combine advanced management that would take into consideration its specific demands.]

European shag (P. aristotelis)

Other cormorants

Related to cormorants

Mous P.J. 2000. Interactions between fisheries and birds in IJsselmeer, The Netherlands. PhD Thesis, Fish Culture and Fisheries Group, Wageningen University, P.O.Box 338, 6700 AH Wageningen, The Netherlands. [ABSTRACT. IJsselmeer, a eutrophic, shallow lake (mean depth 4 m) of 180,000 ha, is heavily exploited by a fishery that catches dfl 11 million worth of eel Anguilla anguilla, perch Perca fluviatilis, pikeperch Stizostedion lucioperca and of the small zooplanktivorous smelt Osmerus eperlanus, the main prey for perch and pikeperch and for the piscivorous birds of IJsselmeer. The population of cormorant Phalacrocorax carbo affects the fisheries through its predation on perch and pikeperch, whereas black tern Chlidonias niger and black-headed gull Larus ridibundus are affected by the availability of smelt in IJsselmeer. The spatial distribution of prey fish and piscivorous birds was described in relation to spatial scale, water transparency and water depth. The carrying capacity of IJsselmeer for the production of prey fish was assessed, and a dynamic simulation model was constructed to predict consequences of fishery management measures on the fisheries and on the food availability for piscivorous birds.]