Des observations in situ et la modélisation ont été conjointement utilisées pour mieux comprendre les processus physiques qui contrôlent les échanges côte-large et étudier les transferts de matière particulaire gouvernés par l'effet des courants et des vagues dans le Golfe du Lion. Cette étude montre que les tempêtes de vent marin induisent une circulation cyclonique sur le plateau et un processus de downwelling dans les canyons sous-marins. En période automnale, lorsque la colonne d'eau est stratifiée et que l'eau du plateau est légère, le downwelling est limité en profondeur. En revanche, en hiver, les plongées d'eaux denses, formées lors des vents de nord froids sur le plateau, intensifient ce processus. D'autre part, les tempêtes de vent marin sont responsables de fortes remises en suspension sur l'ensemble du plateau (> 5 M t) et d'une exportation massive dans la partie ouest du Golfe. Le canyon du Cap Creus apparaît comme une voie d'exportation privilégiée vers le large.

La dynamique des écosystèmes planctoniques pélagiques au sein du bassin de Méditerranée nord-occidentale a été appréhendée par une approche de modélisation réaliste. Deux cas bien distincts ont été considérés, celui des écosystèmes qui se développent sur les apports du Rhône et celui des écosystèmes du large. Une modélisation haute résolution du panache du Rhône est mise en place pour prendre en compte les spécificités des apports en sels nutritifs dans les eaux du Rhône. Les apports terrestres de matière particulaire et dissoute semblent favoriser la biomasse zooplanctonique qui, par broutage, limite à son tour le dépôt de carbone organique particulaire sur le plateau du golfe du Lion. En stimulant le développement du zooplancton, les lentilles d'eau dessalée qui se détachent du panache du Rhône pourraient favoriser ce processus. Au large, une simulation longue durée de 30 ans montre que la variabilité interannuelle des écosystèmes planctoniques est dirigée par le mélange vertical, en lien avec les forçages atmosphériques. La convection profonde hivernale contrôle la structure de l'assemblage phytoplanctonique, en favorisant le microphytoplancton, et défavorise davantage les communautés zooplanctoniques et bactériennes en moyenne annuelle. Le mélange vertical contrôle également la variabilité interannuelle des exportations de carbone particulaire et dissout Le métabolisme net de la zone MEDOC tend à être faiblement hétérotrophe en période peu convective, atténuant ainsi le caractère puit de la zone MEDOC. Cependant, on observe alors une accumulation accrue de carbone au sein des écosystèmes planctoniques et de la matière détritique.

This dissertation investigates the links between Chrétien de Troyes’ romance Le Chevalier au lion from the late twelfth century and the Old Swedish text Herr Ivan, written at the behest of Queen Eufemia of Norway at the beginning of the fourteenth century. The study has two parts. The first sets out to determine the sources of the Swedish text: Was Le Chevalier au lion really the source text of Herr Ivan? The second part raises the question of what happened to the courtly ideals that characterize the French romance when they were transferred into Swedish. The analysis of the question concerning the sources of Herr Ivan confirms that Le Chevalier au lion was the translator’s main source, while the Old Norse version Ívens saga, from the middle of the thirteenth century, was used as a secondary source. The relationship between Le Chevalier au lion, Ívens saga and Herr Ivan is examined through a comparison of the three texts: the choice of verse or prose, the role of prologues and epilogues, and the use of the voice of a narrator and of direct and indirect discourse. Four specific passages are compared at a micro-level. By comparing Herr Ivan to its sources, it becomes clear that the Swedish translator wanted to stress certain courtly ideals by presenting a distinct and coherent interpretation of what Chrétien de Troyes refers to as courtoisie. This indicates that the function of the text was to present a set of ideological and aesthetic values. The analysis of the transmission of courtly ideals takes its point of departure in the uses of the French word courtois and the Swedish equivalent hövisker. As a next step, three elements intimately linked to courtliness are examined: aventure, gaieté and honneur. Also the different roles played by the lion are highlighted. Finally, it is shown how the courtly ideals of Herr Ivan can be read in the light of the other Old Swedish texts written at the behest of Queen Eufemia: Hertig Fredrik av Normandie and Flores och Blanzeflor.

The objectives of the present study were to: 1) describe the gross chemical milk composition of the New Zealand sea lion (NZSLs), Phocarctos hookeri, in early lactation; 2) validate an analytical method for sea lion milk composition; 3) investigate a series of temporal, individual and dietary factors that influence the milk composition of the NZSL and; 4) investigate the temporal and spatial differences in the fatty acids signatures of sea lion milk. A comprehensive literature review revealed that data on milk composition in otariid species is either missing or limited, that to be able to fully describe their milk composition extensive sampling was required and that the temporal, maternal and offspring factors that influence milk composition in pinnipeds are poorly understood. The review identified that considerable work has been conducted to infer diet via the application of fatty acids signature analysis of milk and blubber. There are many factors (i.e. metabolism, de novo synthesis and endogenous sources) that contribute to the differences in fatty acid composition between the diet and milk or blubber. Milk samples from NZSL were used to test whether a new method would give similar results as the standard methods of milk analysis. Agreement between analytical methods for milk components was assessed using different measures of statistical fitness and the results indicated that the new method was comparable to the standard methods and applicable to the milk of sea lions, pinnipeds and to ecological studies of lactation. Milk from NZSLs was collected over a period of seven years (1997, 1999 to 2003, and 2005) in early lactation to describe the composition of milk of NZSL and to test for differences between years. The results indicated that: i) the milk protein concentration was comparable to other species of pinnipeds; ii) the milk fat concentration and the milk energy content of NZSL is the lowest reported for otariids in early lactation; however iii) the milk fat concentration was significantly different between years. These results suggested that the milk composition of NZSLs was influenced by annual changes in the environment; however, there may be other unidentified factors. Month, maternal body condition, age, body weight and length, offspring sex and age, and attendance pattern were compared with milk components. The results identified that month, maternal body condition and age significantly affected milk fat concentration. These results and the fact that maternal body condition varied significantly between years and mothers nursing male pups had lower body condition and produced milk lower in energy content suggested that local food resources along with other unidentified factors have an effect on the reproductive success of NZSLs. To test whether the fatty acid signature analysis (FASA) of lipid rich tissues (milk, blubber and serum) of otariids could be used to infer diet a mixture of vegetable oil (with distinctive fatty acid signature) was fed to 24 lactating NZSL and tissue samples were collected at different time intervals. Significant increases in the concentration of specific fatty acids in serum and milk were observed with peaks within 12hrs and 24hrs respectively of ingestion. Concentrations in milk remained elevated for up to 72hrs and there were differential rates of incorporation into milk. These findings confirm the potential of FASA to infer the composition of the diet. The variation in milk fatty acid signatures from lactating NZSL from four years (1997, 2003, 2004 and 2005) of sampling were measured in order to test whether differences occurred between years. Fatty acids signatures from five potential prey species including the commercially important arrow squid were incorporated into the analysis to associate the changes in milk fatty acids with a shift in prey choice. The results indicated that milk fatty acid signatures were different in 1997 and 2003; however, it was not possible to relate these differences to the five prey species. The variability in the annual arrow squid catch data suggested that local food resources around the Auckland Islands may also be variable. In conclusion, the milk produced by the NZSL has the lowest concentration of fat and energy in early lactation reported for any otariid species. The main factors that contributed to changes in milk quality were stage of lactation, year and maternal body condition. The yearly variation in the quality of milk appears to be a result of their lactation strategy or to variable local food conditions that also affect maternal body condition. Therefore monitoring the annual milk quality may be a means to monitor the health of a pinniped population and potential management tool for pinniped species. This thesis has shown that annual changes in the diet of NZSL can be assessed with milk fatty acid signatures.

Submitted by Ronildo Prado (ronisp@ufscar.br) on 2017-08-01T19:59:42Z No. of bitstreams: 1 DissPAAB.pdf: 4100356 bytes, checksum: 348f90d1cf3911093faeec744c33f884 (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-08-01T19:59:54Z (GMT) No. of bitstreams: 1 DissPAAB.pdf: 4100356 bytes, checksum: 348f90d1cf3911093faeec744c33f884 (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-08-01T20:00:00Z (GMT) No. of bitstreams: 1 DissPAAB.pdf: 4100356 bytes, checksum: 348f90d1cf3911093faeec744c33f884 (MD5) / Made available in DSpace on 2017-08-01T20:00:08Z (GMT). No. of bitstreams: 1 DissPAAB.pdf: 4100356 bytes, checksum: 348f90d1cf3911093faeec744c33f884 (MD5) Previous issue date: 2015-06-03 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / The main goal of any captive breeding program consists is maximizing the conservation of genetic diversity. Groups kept in captivity are particularly susceptible to the loss of genetic diversity, inbreeding depression and adaptation to captivity, due to their small size. The genetic characterization of wild and captive populations is an important tool both to minimize these impacts and for the conservation of these species, since it enables the development of management strategies aimed at maintenance of genetic diversity. In this context, the main objective of the study was to evaluate genetic variability and paternity for animals of black lion tamarin from Centro de Primatología do Rio de Janeiro, Fundacão Parque Zoológico de Sao Paulo, Parque Ecológico de Sao Carlos and 14 specimen belonging to the Durrell Conservation Trust in England using 15 microsatellite loci. The results of the allelic richness and expected heterozygosity showed similar values of alleles numbers and heterozygosity when compared with other species of Callitrichidae. Factorial correspondence analysis (FCA) showed greater homogeneity among captive animals than wild animals from Capão Bonito. The captive groups showed no differentiation among them and high differentiation from the wild Capão Bonito population. The data obtained herein are fundamental to increase the knowledge in genetic aspects of tamarins and support breeding programs to prevent loss of genetic diversity and inbreeding. / Maximizar a conservação da diversidade genética é um dos principais objetivos de qualquer programa de reprodução em cativeiro. Por serem de pequeno tamanho, grupos mantidos em cativeiro são particularmente suscetíveis à perda de diversidade genética, depressão endogâmica e adaptação ao cativeiro. Na tentativa de minimizar tais impactos, a caracterização genética de populações de vida livre e de cativeiro, torna-se uma importante ferramenta para a conservação destas espécies, uma vez que possibilita o desenvolvimento de estratégias de manejo que visem à manutenção de níveis adequados de diversidade genética. Neste contexto o objetivo principal deste trabalho foi avaliar através de 15 loci microssatélites, os níveis de variabilidade genética e paternidade dos animais mantidos em cativeiro no Brasil, no Centro de Primatologia do Rio de Janeiro, Fundação Parque Zoológico de São Paulo, Parque Ecológico de São Carlos e 14 espécimenes que faziam parte do Durrell Conservation Trust na Inglaterra. Os resultados referentes à riqueza alélica e heterozigosidade esperada mostraram que há uma representação similar nos valores de alelos e heterozigosidade quando comparado com outras espécies de Calitriquídeos. A análise de correspondência fatorial (FCA) mostrou que os grupos em cativeiro do Brasil apresentaram maior homogeneidade, quando comparados a um grupo de vida livre proveniente da região de Capão Bonito (São Paulo) e aos 14 indivíduos que representam ao grupo em cativeiro do zoológico de Durrell. O alto grau de parentesco entre os animais em cativeiro evidencia baixa diferenciação entre os grupos pertencentes às diferentes instituições brasileiras estudadas. Os grupos de cativeiro do Brasil, no entanto, mostraram-se divergentes dos animais de Capão Bonito. As informações obtidas neste trabalho são fundamentais para aumentar o conhecimento sob aspectos genéticos dos micos-leões-pretos e subsidiar planos de reprodução assistida que visem minimizar a perda de diversidade genética e a endogamia.

Orientador: Álvaro Luiz Hattnher / Banca: Karin Volobuef / Banca: Orlando Nunes de Amorim / Resumo: Este trabalho propõe-se a rediscutir o conceito corrente de conto de fadas, tal como proposto por autores como Jolles (1976) e Propp (1983), a partir de um contraponto dessas teorias com as formulações de J. R. R. Tolkien em seu ensaio "Sobre histórias de fadas" (2006). Partindo dessa revisão, pretende-se demonstrar como As crônicas de Nárnia, de C. S. Lewis, pode ser lida como o que Tolkien denomina "história de fadas", pois a presença da oposição entre o "mundo real", com tempo e espaço histórico bem definidos, e o mundo maravilhoso ou "outro mundo" parece ser um fator decisivo para diferenciar um conto de fadas de uma história de fadas / Abstract: This research proposes to revisit the current concept of fairy tale as proposed by authors such as Jolles (1976) and Propp (1983), counterpointing those theories with the formulations of J.R.R. Tolkien in his essay "On Fairy-Stories" (2006). The aim is to demonstrate how The Chronicles of Narnia, by C. S. Lewis, can be read as a "fairy story" according to Tolkien, since the presence of an opposition between the "real world", with well defined time and historical space, and the wonderful world or "other world" seems to be a decisive factor to differentiate a fairy tale from a fairy story / Mestre

Une approche modélisante du potentiel TSL le long des plages du golfe du Lion est proposée sur la base du modèle d’ingénierie côtière Unibest-LT (Deltares). Sont exploités en entrée de modèle des données de houle de 1979 à 2010 (base de données ANEMOC-2 produite par le Cerema à partir d’une approche modélisante également) conjointement à des données topo-bathymétriques haute résolution LiDAR (base de données Litto3D produite conjointement par le SHOM et l’IGN). Le potentiel de TSL annuel est calculé pour 157 profils topo-bathymétriques couvrant l’ensemble des ∿250 km de littoral étudié dans ce travail de thèse.En premier lieu, le potentiel de TSL annuel résultant est d’abord estimé sur la base d’une année de houle type, établie à partir de 31 ans de houle horaire entre 1979 et 2010, puis pour chaque année entre 1979 et 2010. La différence observée avec le potentiel de TSL annuel résultat « type » permet de discrétiser les années en trois situations : anomalie positive, anomalie négative ou proche de la normale. Par ailleurs, un lien est clairement établi entre la variabilité interannuelle identifiée dans les simulations et les tempêtes. En outre, cette analyse interannuelle menée à l’échelle des plages du golfe du Lion amène à affiner les limites des cellules de dérive littorale potentielle, pour lesquelles trois scénarios d’organisation sont établis : habituel, occasionnel, exceptionnel.Enfin, le lien entre potentiel de TSL annuel résultant et variations du rivage est testé, conformément au large corpus bibliographique qui existe à ce sujet en ingénierie côtière. Cependant, les résultats s’avèrent décevants : une remise en cause de la théorie sous-jacente est proposée. / Wave data from 1979 to 2010 derived from a large-scale modelling database (ANEMOC-2) were used together with high resolution topo-bathymetric LiDAR data as inputs within the coastal engineering model Unibest-LT (Uniform Beach Sediment - Longshore Transport). The spatial and temporal coverage of these data offers a unique opportunity to carry out a comprehensive study of potential longshore transport intensity and direction.Over the 250 km-long stretch of coast covering the study area, the longshore drift directions computed with the 30-year mean wave climate closely match those of previous findings based on experimental geomorphological methods.Potential LST rates are then computed for each year individually over the 1979-2010 period. Deviations from the 30-year mean LST rates are used to identify 3 cases: positive anomalies, negative anomalies and close to normal. Storm contributions to longshore transport are brought into light: inter-annual variability in LST rates is strongly correlated to >4 m waves occurences.The relationship between LST rates gradients alongshore and shoreline changes is also investigated : despite the significant amout of papers on that subject, results showned in this thesis appears to be disappointing.In the light of these findings, coastal drift cell boundaries are defined taking into account the 30-year mean potential LST rates and the inter-annual variability. This thesis thus highlights the good potential of longshore transport modelling in yielding coherent results that are essential from a shoreline management perspective for future coastal sustainability.

Comprometida com a compreensão da relação entre hábitat e uso do espaço pelo mico-leão-da-cara-preta (Leontopithecus caissara), esta dissertação se norteia por três perguntas: Diferenças de hábitat entre ilha e continente influenciam o tamanho da área de vida? Há predileção da espécie por alguma classe de vegetação dentro da área de uso? Qual a capacidade suporte em sua área de ocorrência continental, bem como nas áreas potenciais para seu manejo conservacionista? Na tentativa de elucidar essas questões esta dissertação se divide em três capítulos. O primeiro contextualiza o trabalho e a apresenta o estado atual de conhecimento de L. caissara. Os capítulos segundo e terceiro concernem às questões centrais do trabalho - uso e seleção do hábitat pelo mico-leão-da-cara-preta. No capítulo dois apresentamos o uso do espaço pela espécie em sua região continental de ocorrência e comparamos os resultados obtidos com as informações disponíveis para a Ilha do Superagui. No capítulo três tratamos da seleção do hábitat por grupos insulares e continentais de L. caissara e estimamos a capacidade suporte para a espécie considerando seus limites de ocorrência e as áreas passíveis de receber animais em situação de manejo. Ao final desses capítulos apresentamos algumas considerações e recomendações para pesquisa e conservação do mico-leão-da-cara-preta. A preocupação com uma postura crítica e construtiva acerca das metodologias de estudos e análises sobre uso do espaço por espécies animais é transversal aos assuntos tratados ao longo de todo o trabalho. Os resultados apresentados confirmam as grandes áreas de vida de L. caissara, as quais parecem ser compensadas energeticamente pela incorporação de novas áreas e abandono de outras ao longo do tempo. Os tipos de hábitats mais intensamente utilizadas pelos mico-leão-da-cara-preta intercalaram áreas de floresta madura e em clímax edáfico com áreas antropizadas em sucessão, ambos hábitats sobre pouco desnível altimétrico. A capacidade suporte estimada é aparentemente incapaz de sustentar uma população viável e ressalta a urgência de pesquisas genéticas que colaborem para a compreensão do histórico ecológico/evolutivo de L. caissara. Potenciais translocações com vistas ao aumento populacional devem considerar as amplas áreas de diva, a espacialidade dinâmica, a relação uso/disponibilidade do hábitat e as diferenças entre ilha e continente. / This dissertation focuses on the interaction between habitat and space use by the black-faced lion tamarin (Leontopithecus caissara). We seek to answer three questions: 1) Do differences in vegetation between insular and continental habitats influence how the species use the space? 2) Does the species prefer a specific type of vegetation within its home-range? 3) What is the carrying capacity of the continental distribution and which are areas for potential conservation management? The first chapter of this dissertation relates the subjects discussed and introduces what is known about L. caissara. The second and third chapters develop the central questions of the research: the use and selection of habitat by the black-faced lion tamarin. In Chapter Two, we introduce space use by the species in its continental distribution and compare the results with data from Superagui Island. In Chapter Three, we address habitat selection by insular and continental groups of L. caissara and estimate the carrying capacity for the species given its distribution and areas potentially able to receive animals in a management context. The conclusion of each chapter presents considerations and recommendations for research and conservation. The study methods and analyses of space use aim to be critical and constructive and are relevant to the topics addressed throughout the text. The results presented confirm that the large home-ranges of L. caissara undergo dynamic turnovers, with some areas being abandoned and others incorporated throughout the year. The habitat types most intensively used by tamarins include areas of mature and forest mixed with areas of anthropic succession, both occurring at low altitudes. The estimated carrying capacity is apparently insufficient to maintain a viable population and highlights the importance of genetic studies that incorporate the ecological/evolutionary history of the species. Potential translocations meant to increase population size should consider the large home-ranges, dynamic spatial structure, relation of habitat use/availability and the differences between island and continent.

nÃo hà / O LeÃo, a Feiticeira e o Guarda-Roupa (1950), de C. S. Lewis, à uma tÃpica narrativa de fantasia. Assim, apresenta caracterÃsticas de forma e conteÃdo que tÃm sido tradicionalmente empregadas pelo gÃnero, entre elas o apelo a uma atmosfera medieval. A histÃria foi adaptada para o cinema de Hollywood em 2005 por Andrew Adamson, com tÃtulo homÃnimo. O objetivo principal desta dissertaÃÃo à discutir as estratÃgias utilizadas pelo diretor para produzir um blockbuster de aÃÃo no formato da clÃssica narrativa hollywoodiana, explorando os elementos fantÃsticos e medievais da obra. Parte-se da ideia de que a adaptaÃÃo, embora oriunda de um texto que ocupa um espaÃo perifÃrico no sistema literÃrio britÃnico, consegue se destacar no sistema cinematogrÃfico de Hollywood. A pesquisa tem carÃter descritivo, com abordagem qualitativa, que consiste na leitura da obra literÃria e do filme para analisar como a fantasia e o medievalismo sÃo configurados nessas narrativas. A anÃlise levou-nos a concluir que a adaptaÃÃo foi capaz de ressignificar os elementos da obra literÃria responsÃveis por sua marginalizaÃÃo. Como base teÃrica, apoia-se nos princÃpios dos estudos descritivos de traduÃÃo, sobretudo no conceito de reescritura, de Lefevere (2007), e nos pressupostos da teoria dos polissistemas, de Even-Zohar (1990). Os referenciais teÃricos ainda incluem Todorov (2010, 2006) e Propp (2006), para caracterizar a obra como uma narrativa de fantasia; Cecire (2009) e Hobsbawm (1997), para abordar a questÃo do medievalismo; Compagnon (1999) e Wellek e Warren (2003), para discutir o cÃnone literÃrio; e Bordwell (1985), para delimitar as propriedades do padrÃo narrativo clÃssico de Hollywood. / The Lion, the Witch and the Wardrobe (1950), by C. S. Lewis, is a typical fantasy narrative. Thus, its form and contents are shaped by characteristics which have traditionally marked the genre, such as the appeal to a medieval atmosphere. The story was adapted to the Hollywood cinema by Andrew Adamson in 2005 keeping the same title. The main goal of this dissertation is to discuss the strategies employed by the director to produce an action blockbuster in the format of the classical Hollywood narrative through the exploration of the fantastic and medieval elements of the novel. It starts from the idea that the film adaptation, although it comes from a text which occupies a peripheral position in the British literary system, manages to stand out in the Hollywood cinematographic system. This research is descriptive and has a qualitative approach, which consists of the reading of both the novel and the film to analyse how fantasy and medievalism are configured in these narratives. The analysis led us to conclude that the adaptation was able to resignify the elements of the novel which are responsible for its marginalization. The theoretical bases for this work are the principles of the descriptive translation studies, especially the concept of rewriting, by Lefevere (2007), and the premises of the polysystem theory, by Even-Zohar (1990). Theoretical references still include Todorov (2010, 2006) and Propp (2006), to characterize the novel as a fantasy narrative; Cecire (2009) and Hobsbawm (1997), to approach the matter of medievalism; Compagnon (1999) and Wellek and Warren (2003), to discuss the literary canon; and Bordwell (1985), to delimitate the properties of the classical Hollywood narration pattern.

La compréhension et la gestion des écosystèmes requièrent un maximum de connaissances sur les dynamiques de populations. Depuis 2007, la taille de la sardine (Sardina pilchardus) et de l’anchois (Engraulis encrasicolus) dans le Golfe du Lion a chuté tandis qu’au même moment, la population de sprat, qui a une faible valeur commerciale, a fortement augmenté. Les très forts enjeux économiques autour de ces espèces ont conduit au projet de recherche « EcoPelGol » dans lequel se situe cette étude portant sur les changements observés. La condition corporelle, la croissance ainsi que la structure en âge et en taille des sardines, des anchois et en partie des sprats ont été analysées sur les vingt dernières années. Alors qu’en 2005-2007, la situation semblait optimale pour les anchois et les sardines (taille et condition élevées), celle-ci s’est considérablement dégradée depuis 2008, l’anchois et la sardine étant significativement plus petits et plus maigres. De plus, une diminution de l’âge et de la croissance a été observée chez la sardine. Nous avons ensuite caractérisé les fluctuations des débarquements historiques (1865-2013) de l’anchois, de la sardine et du maquereau. La chute récente des débarquements a été mise en exergue, avec une situation inédite où la sardine est actuellement moins débarquée qu’avant les années 60, date à laquelle les débarquements ont fortement augmenté suite à un accroissement conséquent de l’effort de pêche. Bien que la majorité de la variance dans les séries de débarquements semble être engendré par les changements de l’effort de pêche, nous avons également observé une relation entre les débarquements et l’indice « Atlantic Multidecadal Oscillation » pour l’anchois et la sardine et avec le « Western Mediterranean Oscillation » pour l'anchois. Dans une troisième analyse, la pression de prédation du thon rouge sur l’anchois, la sardine et le sprat a été estimée pour voir si l’accroissement de la population du thon depuis 2007 lié à de nouvelle mesures de gestion a pu impacté les poissons petits pélagiques. Mais bien que la sardine et l’anchois soient les proies principales du thon, moins de 2% de leurs populations ont été consommés chaque année entre 2011-2013, et ce, sans sélectivité sur la taille de ces proies de la part du thon. Ainsi, le thon rouge n’a pas pu avoir un impact significatif sur la structure en taille ou les abondances des petits pélagiques. Dans le chapitre final, nous avons considéré la possible influence de pathogènes. Des analyses globales dirigées vers la détection des parasites, des bactéries et des virus ont été effectuées tout au long de l’année et ont révélées la présence ponctuelle et relativement faible de bactéries des genres Tenacibaculum et Vibrio et celle systématique de microparasites. Malgré l’impossibilité d’exclure leur pathogénicité, aucune lésion tissulaire n’a été attribuée à ces organismes, réduisant fortement la probabilité d’une épizootie. Nos travaux indiquent que les mécanismes « top-down », des pathogènes ou encore la pêche ne sont probablement pas les facteurs clés pour expliquer les changements observés chez les poissons petites pélagiques. À l'opposé, certains paramètres environnementaux ont expliqué une partie de la variabilité dans la condition corporelle des poissons et leurs débarquements. Nous concluons donc qu’un contrôle « bottom-up », et particulièrement un changement dans la quantité et/ou qualité du zooplancton, peut être la cause des phénomènes dans les populations des poissons petits pélagiques. Si cette thèse permet une avancée dans la compréhension de leur dynamique, des analyses complémentaires seront nécessaires pour confirmer notre hypothèse principale et pour estimer l’influence des autres facteurs agissant potentiellement en synergie. / Knowledge on population dynamics is key to the improvement of management and the understanding of ecosystem functioning. Since 2007, the size of sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) in the Gulf of Lions (NW Mediterranean) has severely decreased, which has strongly affected the fisheries. Simultaneously, the commercially uninteresting sprat population increased remarkably. As the economic and ecological stakes are high, the EcoPelGol project of which this PhD is part was established. We first analysed the sardine, anchovy and (partially) sprat population for changes in body condition, growth and size and age structure over the last 20 years. We concluded that sardine and anchovy have had from 2008 onwards a distinctively poor body condition and size, and that sardine have also showed a concurrent decrease in age and growth. In contrast, both species were in optimal and average “health” during 2005-2007 and 1992-2004, respectively. Subsequently, historical landings of sardine, anchovy and mackerel were considered (1865-2013), of which the fluctuations were characterised and statistically related to environmental variables. The recent dramatic landings decrease was put into perspective, as for example sardine is now for the first time landed less than before the 1960s, when a big probably effort-related upsurge occurred. Despite most of the variability being explained by what looks like changes in fishing effort, a link was found between the sardine and anchovy landings and the Atlantic Multidecadal Oscillation and the anchovy landings and the Western Mediterranean Oscillation. Next, as a management associated bluefin tuna increase also happened since 2007, its predation pressure on all three small pelagic species was estimated. We concluded that although sardine and anchovy are bluefin tuna’s main prey items, less than 2% of each population (including sprat) was consumed annually during 2011-2013 and that there was no clear size selectivity. Thus, tuna could not have had a noticeable impact on the population abundance or size structure of the small pelagics. In the last chapter, an epizootic disease was considered. An all-embracing approach directed towards the all-year round detection of both general and specific parasites, bacteria and viruses revealed the mostly temporal and not necessarily high occurrence of only three groups: microparasites, Vibrio spp. (sometimes determined as Vibrio alginolyticus) and bacteria of the genus Tenacibaculum. Although we could not exclude their pathogenicity, significant tissue damage at a cellular or macroscopic level was never observed, making the disease hypothesis less likely. Thus, we considered several hypotheses and indicated that top-down control (through Bluefin tuna predation), pathogens and fisheries are unlikely to be main drivers. In contrast, some environmental parameters explained a part of the variability in fish condition and landings. After a final discussion on all probable theories we concluded that a bottom-up control, such as especially a planktonic change in quantity and/or quality, might be on the basis of the observed changes. Although this work is a great step towards the understanding of the small pelagic dynamics in the Gulf of Lions, further investigations will still be needed to confirm our main hypothesis and to estimate the potential synergetic effect of other drivers.