Structure, fonctionnement, évolution des communautés benthiques des fonds meubles exploités du plateau continental Nord Gascogne

In the double context of the conservation of ecosystems exposed to exploitation and in the sustainable use of a fishery, this integrated benthic ecology study concerns the structure, functioning and evolution of the benthic communities of the north Bay of Biscay continental shelf. Two distinct communities were separated: the first one in the central part of the Grande Vasière and the second one offshore, on the external margin. The structural divergences within these communities reflect a different functioning of these two ecosystems forced by different trophic inputs, biotic relationships and disturbance sources. Remarkable differences, mainly on the epifauna, were detected in relation to the disturbances generated by the bottom-trawling gears. The comparison of the benthic communities separated by 35 years revealed a long term evolution of the biosedimentary units. The interactions within the trophic webs have been specified, in terms of trophic levels and food sources. The trophic inputs from the pelagic sedimentation were quantified. At the different spatio-temporal scales considered, they showed a strong variability highlighting the major role of the physical forcing. The data collected in this study was used to develop a steady state trophic web model of the benthic-demersal ecosystem of the central part of the Grande Vasière. At the annual scale, this model reveals that the major part of the particle sedimentation imports is not consumed, the predation pressure exerted on the benthic primary consumers is important and that the consequences of the fishing discards in the trophic webs are weak. The definition of fisheries management strategy in term of preservation of the exploited ecosystems and sustainable use of these activities must take into account the amplitude width and rates of these modifications.Dans le double cadre de la conservation des écosystèmes soumis à l'exploitation et du développement durable d'une pêcherie, cette étude intégrée d'écologie benthique concerne la structure, le fonctionnement et l'évolution des communautés benthiques du plateau continental Nord Gascogne. Deux communautés distinctes ont été mises en évidence : une première dans la partie centrale de la Grande Vasière et une autre au niveau de la marge externe. Les divergences structurelles au sein de ces communautés traduisent un fonctionnement différent de ces deux écosystèmes contraints par des apports trophiques, des relations biotiques et des régimes de perturbations très différents. Des différences remarquables, notamment sur l'épifaune, ont été détectées en relation avec les perturbations engendrées par le passage des engins traînants. La comparaison des communautés à 35 ans d'intervalle révèle une évolution à long terme des entités biosédimentaires. La structure du réseau d'interactions trophiques a été précisée, en termes de niveaux trophiques et d'origine de la nourriture. Les apports trophiques par sédimentation ont été quantifiés. Aux échelles spatio-temporelles considérées, ils montrent une forte variabilité traduisant le rôle majeur des forçages physiques. Les données acquises au cours de cette étude ont été utilisées pour développer un modèle de réseau trophique à l'état stable de l'écosystème bentho-démersal de la Grande Vasière. A l'échelle annuelle, ce modèle révèle que la majeure partie des apports trophiques par sédimentation n'est pas consommée, que la pression de prédation exercée sur les consommateurs primaires benthiques est forte et que l'incidence des rejets de pêche dans le fonctionnement trophique de cet écosystème est faible. La définition de stratégies de gestion des pêcheries en terme de préservation des écosystèmes soumis à l'exploitation et de développement durable de ces activités doit prendre en compte l'ampleur et les rythmes de ces modifications

Combining ecosystem indicators and life cycle assessment for environmental assessment of demersal trawling in Tunisia

The approach consisted of conducting LCA and calculating ecosystem indicators to provide a complete assessment of trawling’s environmental impacts and the ecosystem characteristics associated with seafood production. The functional unit for the LCA was set to 1 t of landed seafood, and system boundaries included several operational stages related to demersal trawling. Several ecosystem indicators from EwE were calculated. Demersal trawling in the exploited ecosystem of the Gulf of Gabes (southern Tunisia) was used as a case study to illustrate the applicability of the approach. Several management plans were simulated and their influence on environmental performance was assessed. Ecospace, the spatial module of EwE, was used to simulate management scenarios: establishment of marine protected areas, extension of the biological rest period, and decrease in the number of demersal trawlers

Hábitos alimenticios y aspectos poblacionales del salmonete manchado, Pseudupeneus maculatus (Perciformes: Mullidae) sobre la plataforma continental del noreste de Brasil

This study provides information about the feeding habits, population aspects and spatial distribution of the spot­ted goatfish, Pseudupeneus maculatus, along the coast of the tropical Brazilian continental shelf. Distribution patterns are described using length frequencies and catch rates. Stable isotope ratios of carbon (δ13C) and nitrogen (δ15N), along with stomach contents, were analysed to determine the diet of the spotted goatfish. Multivariate analysis and numerical indicators of the diet, such as numerical frequency, frequency of occurrence and weight percentage, were computed to evaluate the diet composition. The mean trophic position was defined using both stable isotope ratios and stomach content analysis. The length at first maturity for the species was determined as 13.7 cm. A slight pattern in size distribution was observed, with mean size increasing with depth along the shelf. The diet was mainly composed of crustaceans, teleosts and Polychaeta. No clear dietary difference was found between habitat types, water depth or latitude. Both trophic positions estimated by stable isotopes and stomach contents analysis ranged between levels 3 and 4. P. Maculatus was found to be feeding on many rare and infrequent prey items, classifying it as a generalist zoobenthivorous predator, probably due to its efficient search strategy.En este estudio se analizaron los hábitos alimenticios y aspectos biológicos del salmonete manchado (Pseudu­peneus maculatus) frente a la costa brasileña. Para describir los patrones de distribución se analizó la estructura de tallas y las tasas de captura. El nivel trófico y la dieta alimenticia se determinaron mediante análisis isotópicos de carbono (δ13C) y nitrógeno (δ15N), además del contenido estomacal. La composición de la dieta fue determinada con análisis multivariados e indicadores numéricos, como la frecuencia numérica, frecuencia de ocurrencia y el porcentaje del peso. Los resultados indicaron que la talla de primera madurez se encuentra en 13.7 cm. Se observó que la talla media incrementó en relación con el fondo. Por otro lado, la dieta estuvo compuesta por crustáceos, teleósteos y poliquetos, asimismo no se evidenciaron diferencias significativas por tipo de hábitats, profundidad y grado de latitud. Los niveles tróficos estimados oscilaron entre 3 y 4, determinándose que P. Maculatus se alimentó de diversas presas, probablemente debido a su eficiente estrategia de búsqueda, clasificándose como depredador zoobentívoro generalista

How the fishing effort control and environmental changes affect the sustainability of a tropical shrimp small scale fishery

WOS:000605480400002International audienceGlobal shrimp catches are reported primarily in association with large industrial trawling, but they also occur through small-scale fishing, which plays a substantial role in traditional communities. We developed an Ecopath model in north-eastern Brazil, and applied a temporally dynamic model (Ecosim) to evaluate the potential effects of different fishing effort control policies and environmental changes on marine resources and ecosystem between 2015 to 2030 with a case study for small-scale shrimp fishing, novelty for tropical region. These scenarios included different management options related to fishing controls (changing effort and closed season) and environmental changes (primary production changes). Our findings indicate that it is possible to maintain the same level of landings with a controlled reduction of bottom trawlers activities, for example, close to 10 %, without compromising the ecosystem structure. This scenario provided better results than 3-4 months of closing the fishing season, which led to significant losses in catches of high market-value target species (white shrimp, Penaeus schmitti and pink shrimp, Penaeus subtilis). However, intense negative effects on biomass, catch and biodiversity indicators were reported in scenarios with decreasing primary production, from 2 %, reinforcing the need to simulate and project the possible impacts caused by environmental change. However, the control of bottom trawling activity may help to reduce, even at low levels, the highly adverse effects due to primary production reduction. The impacts of climate change in a near future on organisms and ecosystems is an imminent reality, and therefore the search for measures for mitigating and even minimizing these impacts is crucial

Soft bottom macrobenthic communities of North Biscay revisited: Long-term evolution under fisheries-climate forcing

International audienceThirty-five years after the first description of the benthic community and sediments of the North Bay of Biscay continental shelf (80-200 m depth in the "Grande Vasière" region) by Glémarec (personal communication), the sampling stations were revisited to provide a new reference on the status of the macrozoobenthic communities to help our understanding and management of fisheries that are highly developed in this area. Results showed that large modifications occurred in the communities and sediments of the central part of the "Grande Vasière", while these modifications remained moderate in the surroundings on the outer continental shelf. Revisited, macrobenthic communities differed greatly from those recorded in the 1960s, and were less numerous and more homogeneous. The dominant species which characterized the communities and sub-communities had also changed. The main factor that can explain these differences is the granulometry of the sediments which has shown large changes: a strong decrease in the mud fraction and increase in the fine sand fraction. These sedimentary changes should be linked with human activities: increase in bottom trawling effort that induces the resuspension of fine mud particles and the homogenization of sediments over large areas, and decrease in terrigenous particulate fluxes due to anthropic activities on the shoreline and in coastal waters. Effects of global climatic change on the observed evolution remain low, even if some species common in the south of the Bay of Biscay in the 1960s but rare or absent in the north, had increased in density and spread to the north. Trawling activities are probably the main force driving benthic community evolution in the North Bay of Biscay both through direct action on the fauna (inhibition and facilitation processes) and indirect action by modifying sediment characteristics

Community structure and food web based on stable isotopes (δ15N and δ13C) analysis of a North Eastern Atlantic maerl bed

International audienceMaerl beds are highly biodiverse biogenic substrata that have been receiving increasing attention in the last decade. Although maerl beds represent important nursery areas for commercial fishes and molluscs, little is known on the trophic web of their communities. Community structure parameters of maerl bed of the Bay of Brest (species richness, abundance, biomass and dominating species) were studied in parallel with the carbon and nitrogen isotopic composition of their main benthic species (macrofaunal, and megafaunal organisms) in order to assess the trophic levels and differences in the potential food sources of maerl inhabitants. The major potential sources of energy were identified to originate either from epiphytic macroalgae and microphytobenthos both growing on maerl thalli, together with sedimenting (sedimentary) particulate organic matter (POM) originating from the water column. The majority of the macro- and megafaunal organisms investigated were filter feeders, selective-deposit feeders and predators/scavengers. Filter feeders fall into three different groups representing different trophic pathways (i) sponges feeding directly on POM (water column filter feeders I), (ii) ascidians and holothurians feeding on POM and probably captured pelagic preys (water column filter feeders II), and (iii) filter feeding molluscs and crustaceans were hypothesised to feed on microphytobenthos or on decaying sedimented POM (Interface filter feeders). Selective deposit feeders were also divided into two subgroups. Carnivores were also distinguished between those with scavenging habits and true predators. Coupling of the trophic levels observed with the community biomass structure revealed that most of the benthic biomass derives its food from detritic sedimented POM and/or microphytobenthos, with interface filter feeders (23% of the biomass), selective deposit feeders (12%). Carnivores made up to 14% of the total biomass. Generally stable isotopes ratio mean values overlap and cover a large range within feeding types, indicating a strong overlap in food sources and a high degree of complexity of the food web presumably due to the diversity of the potential food sources

Modélisation du fonctionnement trophique ou écosystémique

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Spatio-temporal isotopic signatures (δ 13 C and δ 15 N) reveal that two sympatric West African mullet species do not feed on the same basal production sources

International audiencePotential trophic competition between two sympatric mullet species, Mugil cephalus and Mugil curema, was explored in the hypersaline estuary of the Saloum Delta (Senegal) using δ13C and δ15N composition of muscle tissues. Between species, δ15N compositions were similar, suggesting a similar trophic level, while the difference in δ13C compositions indicated that these species did not feed from exactly the same basal production sources or at least not in the same proportions. This result provides the first evidence of isotopic niche segregation between two limno-benthophageous species belonging to the geographically widespread, and often locally abundant, Mugilidae family

Reproductive Biology of Barracuda, Sphyraena Guachancho, on Ivorian Coasts (eastern Central Atlantic)

WOS:000508224800012International audienceTo provide information for improving barracuda stock management on the Ivorian coast, the reproductive biology (length-weight relationship, sexual development and size at first maturity) of Sphyraena guachancho was studied in relation to the marine seasons and fish size classes. Samples were obtained between July 2010 and June 2011 from commercial fisheries in Abidjan fishing port. A total of 662 specimens (328 females, 334 males) with sizes ranging from 19 to 63 cm FL were analyzed. The sex ratio of Sphyraena guachancho was found to be slightly in favour of males (1: 0.98). The length-weight relationship is isometric for both sexes. The gonadosomatic index (GSI), hepatosomatic index (HSI), condition factor (K) and percentage of mature individuals for both sexes reveal that the breeding period corresponds to the Low Cold Season, mainly during January. The size at first maturity of the Sphyraena guachancho population is 28.8 cm. It was not significantly different between males (27.8 cm) and females (30.3 cm). Sexual maturity was found to be earlier than measured in previous studies at different locations

Length-weight relationships of 20 fish species from Fatala estuary, Guinea-Conakry, West Africa

International audienceLength-weight relationships were estimated for 20 fish species collected during scientific surveys conducted with purse seine and gillnets from January 1993 to March 1994 in the Fatala estuary, Guinea. Sample sizes ranged from 10 (Scomberomorus tritor) to 476 (Parachelon grandisquamis) individuals. Fish length ranged from 5.2 cm fork length (Pomadasys jubelini) to 91.5 cm fork length (Sphyraena afra). The coefficients of determination (r²) varied from 0.951 (Chloroscombrus chrysurus) to 0.995 (Hemichromis fasciatus and Polydactylus quadrifilis). Values of the parameter b in the equation W = aLb, where W is weight (g) and L is length (cm), ranged from 3.0171 (S. afra) to 3.6365 (Pseudotolithus moorii). The growth was allometrically positive for 13 fish species (Hydrocynus forskahlii, Caranx hippos, Caranx senegallus, Ethmalosa fimbriata, Sardinella maderensis, Monodactylus sebae, Neochelon falcipinnis, Parachelon grandisquamis, Galeoides decadactylus, Polydactylus quadrifilis, Pseudotolithus elongatus, Pseudotolithus moorii, Pseudotolithus senegallus) and of isometric type for 7 fish species (Chloroscombrus chrysurus, Hemichromis fasciatus, Tylochromis intermedius, Pomadasys jubelini, Ilisha africana, Scomberomorus tritor, Sphyraena afra). The results presented here improve our knowledge of the life history traits of these 20 fish species. Thus, they will serve as a basis for comparative studies on the biology of fish species in West Africa