Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The aim of this work was analyze population structure, reproductive biology and feeding ecology of Loricariichthys melanocheilus in Ibicui River. Fish were caught bimonthly in lotic and lentic environment between São Vicente do Sul and Itaqui, with gillnets and witches, with revision every six hours. The population structure was evaluated by seasonal and spatial distribution, bimonthly variations in average size, sex ratio and weight-length relationship. Females reached larger sizes than males and the sex ratio was 1.38 females per male, with some variations bimonthly. This species showed positive allometric growth, with greater increase in weight than in length during ontogenetic development. The condition factor was higher in males and in June/July. Females didn t show variations in this parameter. The values of gonad condition factor, GSI and the frequency of mature individuals indicate that the reproductive period begins in August/September, peaking in October / November and spawning in the following months. Regarding the feeding ecology, L. melanocheilus showed a detritivorous feeding habit, even consuming sediment, organic vegetable matter, nematodes, insects of the order Diptera, Trichoptera, Ephemeroptera and Odonata, algae, microcrustaceans, fungi, protozoa and other invertebrates. The diet showed little seasonal, environmental and by length classes variation. The species showed no intense feeding activity, being higher before or after the reproductive period and in lentic environment. The intestinal quotient of 1.51 was smaller than registered for other species of the family, showing variations according to the length classes in response to variations in the diet. / O objetivo do presente trabalho foi avaliar aspectos da estrutura populacional, biologia reprodutiva e ecologia alimentar de Loricariichthys melanocheilus no rio Ibicuí. Os peixes foram coletados bimestralmente em ambientes lênticos e lóticos no rio Ibicuí, entre os municípios de São Vicente do Sul e Itaqui, utilizando redes de espera e feiticeiras, com revisão a cada seis horas no período de 24 horas. A estrutura populacional foi avaliada através da distribuição sazonal e espacial, das variações bimestrais nos tamanhos médios, proporção sexual total, bimestral e por classes de comprimento e relação peso/comprimento. As fêmeas atingiram tamanhos maiores que os machos e a proporção sexual encontrada foi de 1,38 fêmeas para cada macho, com algumas variações bimestrais. A espécie apresentou crescimento alométrico positivo, com maior incremento em peso do que em comprimento durante o desenvolvimento ontogênico. Os machos apresentaram maior fator de condição que as fêmeas, sendo mais elevado em junho/julho. Já as fêmeas não apresentaram variações neste índice durante o período de estudo. Os valores do fator de condição gonadal, índice gonadossomático e a frequência de indivíduos maduros indicam que o período reprodutivo da espécie se inicia em agosto/setembro, com pico em outubro/novembro e desova nos meses seguintes. Em relação à ecologia alimentar, L. melanocheilus apresentou hábito alimentar detritívoro, consumindo ainda sedimento, matéria orgânica vegetal, Nematoda, insetos das ordens Diptera, Trichoptera, Ephemeroptera e Odonata, algas, microcrustáceos, fungos, protozoários e outros invertebrados. A dieta apresentou poucas variações sazonais, ambientais e por classes de comprimento. A espécie não apresentou atividade alimentar intensa, sendo esta mais elevada em períodos anteriores ou posteriores ao período reprodutivo e em ambientes lênticos. O quociente intestinal de 1,51 foi menor do que registrado para outras espécies da família e apresentou variações sazonais e de acordo com as classes de comprimento, em resposta às variações na dieta.

L’objectif de cette thèse est d’améliorer la compréhension du fonctionnement et de la structure trophique du golfe de Gabès en Tunisie. Afin de concilier exigences écologiques et exploitation des ressources marines, différents modèles écosystémiques ont été développés pour étudier sa dynamique trophique et contribuer à la réflexion sur la mise en place de plans de gestion. Un modèle trophique d’équilibre de masse « Ecospace » a été construit afin d’évaluer les conséquences écosystémiques de différentes mesures de gestion. Les résultats des simulations ont permis d’explorer les interactions entre la pêche côtière et la pêche au chalut benthique et d’identifier des zones où les mesures de gestion sont effectives. Un modèle end-to-end a également été appliqué pour expliciter la dynamique des espèces considérées, depuis le forçage climatique jusqu'à la pêche. Cette approche de modélisation consiste à forcer le modèle individu-centré « OSMOSE » par un modèle biogéochimique « Eco3MMed ». Ce modèle a permis d’établir une représentation cohérente du réseau trophique et de simuler des scénarios de gestion théoriques de mise en réserve. Le modèle end-to-end a également été utilisé pour étudier la sensibilité d’un ensemble d’indicateurs écologiques à la pression de pêche. Les résultats ont révélé que les indicateurs de taille sont les plus adaptés pour faire le suivi de l’impact de la pêche dans le golfe de Gabès. Au final, une approche comparative entre plusieurs écosystèmes méditerranéens a été mise en place avec le modèle EcoTroph pour comparer leurs structures trophiques et explorer les effets de plusieurs niveaux d’exploitation par l’analyse de leurs spectres trophiques. / The objective of this thesis is to improve the understanding of trophic structure and functioning of the gulf of Gabes in Tunisia. In order to reconcile environmental concerns and exploitation of marine resources, different ecosystem models have been developed to study the ecosystem dynamics and contribute to the discussion on the implementation of management plans. A spatial and temporal dynamic model “Ecospace” was built to evaluate the ecosystem consequences of different management measures based on scenarios derived from the current regulation. The results of simulations allowed to investigate the interactions between coastal and benthic trawl fishing and to identify areas where management measures are effective. An end-to-end model has been applied to the gulf of Gabes ecosystem to represent the dynamics of 11 high trophic level species, from climate forcing to fishing.This modelling approach consists in forcing the individual-based model "OSMOSE" by a biogeochemical model "ECO3M-Med". This model allowed to establish a coherent representation of the food web and simulate theoretical management scenarios of spatial fishing closure. The end-to-end model has also been used to study the sensitivity of a set of ecological indicators to fishing pressure. The simulation of different levels of fishing mortality showed that size indicators were the most relevant to monitor the impact of fishing in the gulf of Gabes. Finally, a comparative approach between several Mediterranean ecosystems was applied using the EcoTroph model to compare their trophic structures and explore the effects of different levels of fishing pressure through the analysis of their trophic spectra.