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In 2008, the European Union drew up the Marine Strategy Framework Directive (MSFD) with the aim of achieving Good Environmental Status of marine waters. By linking the changes observed to the pressures experienced, this directive is defined as a tool designed to better control environmental degradation factors and to assess their implications. Several descriptors are defined within the framework of MSFD, in particular descriptors 1 relating to the biological diversity of the seabed and 6 relating to the integrity of the seabed (i.e. the quality of its structures and functions). As dragging (trawling and dredging) is the main source of disturbance of continental shelf seabed, it is essential to study its impact. However, its effects depend on several criteria such as the type of gear used, the spatial and temporal distribution of fishing effort, the targeted habitats and the degree of natural disturbance existing in the area. The general objective of this thesis is to evaluate the impact of trawling activities in various hydrodynamic and sedimentary contexts and design a generalized assessment framework. Four zones were considered: the southern North Sea, the English Channel, the Gulf of Lion and the eastern part of Corsica. To monitor the impact of anthropogenic pressure on an ecosystem, it is necessary to determine which indicators and which sampling methods are the most appropriate. The comparison of fifteen indices and three sampling methods showed that sampling of the benthic megafauna with scientific trawls was particularly effective for monitoring the trawling impact on benthic communities and that video imaging could be a relatively interesting non-destructive alternative method for coarse bottoms. Indices based on species sensitivity to trawling, appeared to be the most relevant for monitoring the effect of trawling on benthic communities. A conceptual approach to detect effect thresholds and impacts was developed and, as a result, the ecological status of the four study areas could be determined and mapped.The evaluation of the effect of abrasion and various environmental parameters on these indices highlighted that the main factors structuring the benthic communities are not the same in all study areas. It is mainly physical processes (tide, swell...) which structure the benthic communities in the English Channel whereas it is mainly parameters linked to species growth (availability of food, temperature...) which influence the distribution and composition of Mediterranean benthic communities. Abrasion has also emerged as a structuring factor of these benthic communities. One of the previously selected indices was able, in areas where abrasion significantly influences the indices, to differentiate environmental effects from the effects of trawling.; L’Union Européenne a élaboré, en 2008, la Directive Cadre Stratégie pour le Milieu Marin (DCSMM) dans le but d’atteindre le Bon Etat Ecologique des eaux marines. En reliant les changements observés aux pressions subies, cette directive se définit comme un outil destiné à mieux contrôler les facteurs de dégradation du milieu et à en tirer les conséquences. Plusieurs descripteurs sont définis dans le cadre de la DCSMM et notamment les descripteurs 1, portant sur la diversité biologique des fonds marins et 6, portant sur l’intégrité des fonds (c’est-à-dire sur la qualité de leurs structures et de leurs fonctions). La pêche aux arts traînants (chalut et drague) étant la principale source de perturbation des fonds du plateau continental, étudier son impact est indispensable. Cependant, ses effets sont dépendants de plusieurs critères comme le type d’engin utilisé, la distribution spatiale et temporelle de l’effort de pêche, les habitats ciblés et le degré de perturbation naturelle existant dans la zone. Ainsi, l’objectif général de cette thèse est d’évaluer l’impact des activités de pêche aux arts trainants dans des contextes hydrodynamiques et sédimentaires variés. Quatre zones ont été considérées : le sud de la mer du Nord, la Manche, le Golfe du Lion et la partie est de la Corse. Pour suivre l’impact d’une pression anthropique sur un écosystème, il est nécessaire de déterminer les indicateurs et la méthode d’échantillonnage la plus appropriée. La comparaison d’une quinzaine d’indices et de trois méthodes d’échantillonnage a montré que l’échantillonnage de la mégafaune benthique au chalut scientifique était particulièrement efficace pour suivre l'impact des arts traînants sur les communautés benthiques et que l’imagerie vidéo pouvait-être une méthode alternative non destructive relativement intéressante pour les fonds grossiers. Les indices basés sur la sensibilité des espèces au chalutage, déterminée à l’aide de leurs traits biologiques, sont apparus comme les plus pertinents pour suivre l’effet des arts traînants sur les communautés benthiques. L’utilisation de ces indicateurs a également permis de proposer un cadre conceptuel d’effet, de déterminer des seuils d’impact et de cartographier l’état écologique des habitats benthiques dans les quatre zones étudiées.L’évaluation combinée de l’effet de l’abrasion et de différents paramètres environnementaux sur ces indices a permis de mettre en avant que les principaux facteurs structurant les communautés benthiques ne sont pas les mêmes dans les zones étudiées. En effet, ce sont majoritairement les processus physiques (marée, houle...) qui structurent les communautés benthiques en Manche alors que ce sont majoritairement des paramètres en lien avec la croissance des espèces (disponibilité en nourriture, température…) qui influent sur la distribution et la composition des communautés benthiques méditerranéennes. L’abrasion est également apparue comme un facteur structurant ces communautés benthiques et un des indices précédemment sélectionné a permis de différencier les effets de l’environnement des effets du chalutage dans les zones où l’abrasion influent significativement sur les indices.

International audience; The Grand Récif of Toliara (GRT) in Madagascar is a large (33 km2) barrier reef system of the SW Indian Ocean that had been well investigated in the 1960s and early 1970s. A massive degradation of the reef has been reported since at least the early 1980s, just a few years after research activities ceased in the area. Examination of historical aerial photographs and modern high-resolution remote sensing images confirms a continuous loss of coral habitat on GRT outer reef flats between 1962 and 2011, with an average loss of 65 % and a range of 37-79 % loss during this 50-year period. The usual suspects of coral community declines (cyclones, bleaching and sedimentation) may have contributed to the demise of the GRT. However, an independent study (Salimo 1997) suggests that the chronic pressure of fisherman gleaning on reef flats with destructive tools is the main driver of the observed changes. Salimo's reported level of frequentation (6.8 fishermen per day and per km−2) and rates of destruction per fisherman (7.7 m2 of coral habitat h−1) yield a cumulated overall loss in agreement with the image-based rates of habitat loss. The GRT is unlikely to recover because this chronic stress is unlikely to decrease in the near future. Indeed, the GRT daily provides subsistence fishery resources for local Vezo people and to agriculturalist or pastoralist ethnic groups who have turned to exploiting coastal resources due to increasing aridity and dwindling agricultural and livestock production

Little is known about the effects of mud crabs population patterns on their exploitation. We used complementary approaches (experimental, fisher-based) to investigate how small-scale variations in density, size and sex-ratio related to the ecology of S. serrata may impact fishing practices in New Caledonia. Crabs were measured/sexed across 9 stations in contrasted mangrove systems between 2007 and 2009. Stations were described and classified in different kinds of mangrove forests (coastal, riverine, and estuarine); vegetation cover was qualitatively described at station scale. Annual catch was used as an indicator of fishing pressure. Middle-scale environmental factors (oceanic influence, vegetation cover) had significant contributions to crab density (GLM, 84.8% of variance), crab size and sex-ratio (

This study provides a historical overview of the use of drifting fish aggregating devices (DFADs) in purse seine fisheries since the early 1990s, using global tuna fisheries datasets from the four tuna Regional Fisheries Management Organizations (RFMOs). Tropical tuna purse seine fisheries typically target large yellowfin (Thunnus albacares) and bigeye (Thunnus obesus) tunas on free-swimming schools and skipjack (Katsuwonus pelamis )a nd juveniles of yellowfin and bigeye associated with drifting objects. DFADs have enabled global skipjack catches to markedly increase, and have also introduced major scientific issues for all tuna-RFMOs. In particular, they have strongly modified the fishing strategies of purse seiners that fish on a combination of free-swimming and DFAD-associated schools. Consequently, the cumulated search time traditionally used to quantify nominal fishing effort to assess the status of tuna stocks is inconsistent and cannot be used to derive time series of abundance indices from catch-per-unit of-effort (CPUE). In addition, the lack of information available on the construction, deployment, and use of DFADs has prevented effective monitoring of the fishing pressure over the last two decades exerted by purse seine fleets using this fishing mode. Juveniles of tropical tunas represent a substantial proportion of purse seine catch on DFADs in the three oceans, which has raised particular concern for some bigeye stocks that have been subject to overfishing in the past. Catches of juvenile tunas by DFAD fishing may also result in a decrease in recruitment for fisheries that target adult tunas such as longliners. In addition, some demographic parameters of tunas and other species associated with DFADs may be affected by the resultant habitat modification arising from the widespread deployment of DFADs. Evidence in the literature and provided by the ratio-estimator method suggest that fishing DFAD-associated schools may result in about 100 000 t of bycatch and discards annually. In addition, there is further potential for ghost fishing related mortality of sensitive species such as marine turtles and pelagic sharks. In this context and following a precautionary approach, we finally discuss the increasing need for all tuna-RFMOs to reduce, or at least monitor and control, the use of DFADs to mitigate their adverse effects not only on yellowfin and bigeye stocks but also on open-ocean ecosystems.

Trabajo final presentado por Xavier Corrales Ribas para el Master en Gestión Pesquera Sostenible de la Universitat d'Alacant (UA), realizado bajo la dirección de la Dra. Marta Coll Monton y de la Dra. Isabel Palomera Laforga del Institut de Ciències del Mar (ICM-CSIC).-- 168 pages, [ES] Se ha desarrollado un modelo de equilibrio de masas para caracterizar la estructura y funcionamiento de la plataforma y talud continental del Mediterráneo noroccidental, desde Toulon hasta el Cabo de la Nao (modelo del NWMS). El modelo se ha construido a partir de aplicaciones anteriores de Ecopath with Ecosim en áreas del Mediterráneo noroccidental (golfo de León y sur del mar Catalán) El modelo representa el ecosistema en el inicio del 2000, cubre 45.547 km2 e incluye las batimetrías de 0 a 1000 m de profundidad. El área de estudio ha sido determinada específicamente teniendo en cuenta la conectividad entre las dos áreas y los stocks de peces compartidos. Además, los resultados se han comparado con varios modelos ecológicos desarrollados en el mar Mediterráneo y el golfo de Cádiz y se han analizado varios escenarios de gestión. [...], [EN] A mass-balance model was developed to characterize the structure and functioning of the marine continental shelf and slope area of the Northwestern Mediterranean Sea, from the Toulon to Cape La Nao (NWMS model). The model has been built from previous applications of Ecopath with Ecosim in areas of the Northwestern Mediterranean (Gulf of Lions and South Catalan Sea). The model represented the ecosystem in the early 2000s, covered 45547 km2, and included depths from 0 to 1000 m. The study area was chosen to specifically account for the connectivity between these areas and the shared fish stocks. Furthermore, the results have been compared with several ecosystems models developed in the Mediterranean Sea and the Gulf of Cadiz and various management scenarios have been analyzed. [...], [FR] Un modèle d’équilibre de masse a été mis en place afin de caractériser la structure et le fonctionnement de la plateforme y talus continental de la méditerranée nord-occidental depuis Toulon jusqu’au Cap de Nao (Modèle de NWMS). Le modèle a été construit à partir des applications antérieures d’Ecopath with Ecosim dans des aires de la méditerranée nordoccidentale (Golfe de Léon et le sud de la mer catalane). [...]

In the Indian Ocean, the blue shark Prionace glauca and the silky shark Carcha rhinus falciformis represent the 2 main shark bycatch species in pelagic longline and purse seine fisheries, respectively. With the increasing market demand for fins, catches may increase in the future, with potential effects on ecosystem trophic functioning through top-down cascading effects. Knowledge of the species' trophic ecology is therefore crucial but is limited by the lack of data from the Indian Ocean. Stable isotope analysis was therefore performed on muscle tissues (δ 15 N and δ 13 C) of these 2 shark species from the western Indian Ocean. Our study showed that body length, season, and zone effects were relatively small for the 2 species. However, significant δ 13 C differences between the 2 species suggest niche partitioning, with silky sharks having a more inshore foraging habitat than blue sharks. Finally, lower muscle δ 15 N values were observed in juvenile silky sharks caught by purse seiners around fish aggregating devices (FADs) compared to juveniles caught by longliners. One hypothesis is that FADs could act as an ecological trap for juvenile silky sharks, leading to a po- sition at lowest trophic level for these individuals. However, different foraging habitats could also explain the observed patterns between juveniles. Although preliminary, our results provide a basis for the implementation of species-specific protection and management strategies.

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David Mouillot ... et al.-- 7 pages, 3 figures, 1 table, The Mediterranean Sea (0.82% of the global oceanic surface) holds 4%–18% of all known marine species (∼17,000), with a high proportion of endemism [ [1] and [2]]. This exceptional biodiversity is under severe threats [1] but benefits from a system of 100 marine protected areas (MPAs). Surprisingly, the spatial congruence of fish biodiversity hot spots with this MPA system and the areas of high fishing pressure has not been assessed. Moreover, evolutionary and functional breadth of species assemblages [3] has been largely overlooked in marine systems. Here we adopted a multifaceted approach to biodiversity by considering the species richness of total, endemic, and threatened coastal fish assemblages as well as their functional and phylogenetic diversity. We show that these fish biodiversity components are spatially mismatched. The MPA system covers a small surface of the Mediterranean (0.4%) and is spatially congruent with the hot spots of all taxonomic components of fish diversity. However, it misses hot spots of functional and phylogenetic diversity. In addition, hot spots of endemic species richness and phylogenetic diversity are spatially congruent with hot spots of fishery impact. Our results highlight that future conservation strategies and assessment efficiency of current reserve systems will need to be revisited after deconstructing the different components of biodiversity, This study was partly funded by Fondation Total, Fondation pour la Recherche sur la Biodiversité project BIODIVMED, Agence National de la Recherche project ANR-09-PEXT-01102 546 EVORANGE, and Centre National de la Recherche Scientifique program BIODIVMEX. D.M. was supported by Marie Curie International Outgoing Fellowship (FISHECO) IOF-GA-2009-236316. M.C. was funded by the European Commission through a Marie Curie International Outgoing Fellowship to the ECOFUN project (FP7-PEOPLE-2007-4-1-IOF). This publication is contribution number 2011-049 of the Institut des Sciences de l’Evolution de Montpellier (UMR CNRS-UM2 5554)

The populations of fishes dwelling near the sea bed (demersal species) on the continental shelf are usually the object of intense commercial exploitation. The Bay of Biscay shelf is no exception. Hence, populations suffer from this exploitation. Moreover, the general role played by hydro-climatic variations in the regulation of the abundance of demersal fish populations (population dynamics) is traditionally admitted. In the Bay of Biscay, a warming of the surface water has been observed over the three last decades (Koutsikopoulos et al., 1998). Climate change therefore has potential consequences on fish communities. Thus, the structure and dynamics of fish populations on the continental shelf of the Bay of Biscay are susceptible to suffer both from the effects of a human activity (fishing) and of climate change (warming). Fisheries should therefore suffer more or less from these changes depending on their adaptation capacity., Les peuplements de poissons vivant à proximité du fond (espèces démersales) sur le plateau continental font généralement l'objet d'une exploitation commerciale intense. Le plateau du Golfe de Gascogne n'échappe pas à cette règle. Les populations y subissent donc les effets de l'exploitation. Par ailleurs, le rôle général des variations hydro-climatiques dans la régulation de l'abondance des populations démersales de poissons (la dynamique des populations) est classiquement admis. Dans le Golfe de Gascogne, un réchauffement des eaux de surface au cours des trois dernières décennies est observé (Koutsikopoulos et al., 1998). Le changement climatique a donc des conséquences potentielles sur la communauté de poissons. Ainsi, la structure et la dynamique du peuplement de poissons du plateau continental du Golfe de Gascogne sont susceptibles de répondre à la fois aux effets d'une activité humaine (la pêche) et du changement climatique (réchauffement). Les pêcheries devraient donc subir ces changements selon leur capacité d'adaptation.

For most fish species, strong environmental constraints imposed by living in an aquatic medium have produced converging streamlined body forms without prehensile appendices. This similarity in body shapes highlights a common predation constraint: a predatory fish must have a jaw large enough to swallow its prey. Fish diets may then reflect local prey availability and predator–prey size ratios. Based on this size-based opportunistic predation process, the multispecies individual-based model OSMOSE (Object-oriented Simulator of Marine ecOSystem Exploitation) is used to investigate to what extent the size distribution of fish communities can contribute to better our understanding of the functioning of marine food webs and the ecosystem effects of fishing. Strong similarity in shape is found between simulated size spectra and those described in empirical studies. The existence of a curvature towards small size classes is discussed in the light of the size-based predation hypothesis, which implies that smaller fish may undergo higher predation mortality. Applying linear and quadratic regressions to the simulated size spectra allows the detection of variations in fishing pressure and the proposal of different ways to quantify them. In particular, it is shown that the slope of the size spectrum decreases quasilinearly with fishing mortality and that the curvature could help to detect ecosystem overexploitation.