Typologie de la flottille chalutière du port de Sète par une méthode de segmentation

This work aims to define a typology of trawler f1eet in Sète, the main fishing harbour along the French Mediterranean coast, using several multivariate analysis methods. The fishing ships taken to account are represented by annual profiles of landing specific compositions. Five fishing strategies have been identified. A segmentation method using symbolic objects allows a formaI characterisation of the different strategies. These strategies are studied according to several general characteristics usually used for management rules elaboration (power, length, ship age). The typological analysis allows to characterise two main exploitation ways, one directed to the catch of a few species (Engraulis encrasicolus, Sardina pilchardus), the other characterised by the exploitation of a great diversity of species. By this way, it is possible to estimate how the catch of low represented species can significantly contribute to the exploitation of a resource.

Dating of sediments in the Biscay bay: Implication for pollution chronology

Important historical informations on the temporal changes of anthropogenic pollution in marine environment can be assessed using sediment analysis. Dating is a crucial prerequisite to reconstruct pollution events, to calculate fluxes, and thus to allow comparison between different sites. This work presents estimates of accumulation rates of sediments in the Bay of Biscay. Fives cores were collected during RIKEAU 2002 cruise on board o/v Thalia in order to study temporal changes in PAH and organohalogens compounds content of sediment. We compare chronostratigraphic estimates on cores derived from the natural radionuclide 210Pb in excess with estimates from the known times of introduction of the artificial radionuclide 137Cs to the environment. 210Pb, 226Ra and 137Cs were measured directly by non-destructive gamma spectrometry using a well type γ-detector. Total 210Pb and 226Ra activities vary from 30 to 150 mBq g-1, and 20 to 36 mBq g-1 respectively; 137Cs presents lower levels (< 5 mBq g-1). Profiles of 210Pb in three cores present a well mixed layer, from 2-3 to 10 cm, in the uppermost sediments, followed by an exponential decrease of activities, suitable for the determination of sedimentation rates. Under constant flux and sedimentation rate assumptions, vertical accretion rates derived from 210Pb present a large range from nearly 0.1 cm yr-1 up to almost 0.3 cm yr-1. Differences are mainly due to relative position of studied cores regarding the muddy patch. Although the moderate level of 137Cs limits the accuracy of this dating method, profiles of 137Cs with depth strengthen mean rates derived from 210Pb data. The implication of this dating on pollutant inputs in sediments of the Bay of Biscay is briefly discussed.

Stimulation of bacterial exoproteolytic activity by fish farming in coastal marine ponds: Effect on dissolved protein cycling

The effect of fish farming on dissolved amino acid concentrations, bacterioplankton abundance and exoproteolytic activity was assessed in 3 experimental marine ponds. Different standing stocks of fish were introduced (semi-intensive pond: 250 g.m(-2); semi-extensive pond: 50 g.m(-2) control pond: 0). Sea bass farming increased dissolved combined amino acid (DCAA) concentrations only in the semi-intensive pond. Bacterial standing stock was unaffected by fish food supply. However, bacterial exoproteolytic activity was strongly stimulated by aquaculture intensification; the average maximal rate of dissolved protein hydrolysis (V-m) increased with intensity (control pond: 1 500 nM.h(-1); semi-extensive pond: 2 600 nM.h(-1) semi-intensive pond: 5 100 nM.h(-1)). DCAA fluxes through bacterial exoproteolytic activity ranged between 16 (semi-extensive) and 11% (semi-intensive) of the daily nitrogen input by fish food. Bacterial exoproteolytic activity allowed a substantial part of the increased supply of dissolved amino nitrogen to be incorporated into bacterial biomass, then available for transfer to higher trophic levels within the ponds. It also significantly decreased dissolved organic nitrogen export from the ponds to the surrounding environment.

Changes in the annual harmful algal blooms of Alexandrium minutum : effects of environmental conditions and drainage basin inputs in the Rance estuary (Brittany, France)

Time series of physico-chemical data and concentrations (cell L-1) of the toxic dinoflagellate Alexandrium minutum collected in the Rance macrotidal estuary (Brittany, France) were analyzed to understand the physico-chemical processes of the estuary and their relation to changes in bloom development from 1996 to 2009. The construction of the tidal power plant in the north and the presence of a lock in the south have greatly altered hydrodynamics, blocking the zone of maximum turbidity upstream, in the narrowest part of the estuary. Alexandrium minutum occurs in the middle part of the estuary. Most physical and chemical parameters of the Rance estuary are similar to those observed elsewhere in Brittany with water temperatures between 15–18 °C, slightly lowered salinities (31.8–33.1 PSU), low river flow rates upstream and significant solar radiation (8 h day-1). A notable exception is phosphate input from the drainage basin which seems to limit bloom development: in recent years, bloom decline can be significantly correlated with the decrease in phosphate input. On the other hand, the chemical processes occurring in the freshwater-saltwater interface do not seem to have an influence on these occurrences. The other hypotheses for bloom declines are discussed, including the prevalence of parasitism, but remain to be verified in further studies.

What can exploratory modelling tell us about the ecobiology of European sea bass ( Dicentrarchus labrax ): a comprehensive overview

European sea bass, Dicentrarchus labrax, is a highly valuable species in Europe, both for aquaculture in the Mediterranean Sea and for commercial and recreational fisheries in the North East Atlantic Ocean. Subjected to increasing fishing pressure, the wild population has recently experienced significant recruitment fluctuation as well as a northward extension of its distribution area in the North Sea. While the nature of the ecological and/or physiological processes involved remains unresolved, ontogenetic habitat shifts and adult site fidelity could increase the species’ vulnerability to climate change and overfishing. As managers look for expert information to propose management scenarios leading to sustainable exploitation, exploratory modelling appears to be a cost-efficient approach to enhance the understanding of recruitment dynamics and the spatio-temporal scales over which fish populations function. A conceptual modelling framework and its specific data requirements are discussed to tackle some sound ecological questions regarding this species. We consequently provide an updated review of current knowledge on bass population structure, biology and ecology. This paper will hence be particularly valuable to develop spatially-explicit models of European sea bass dynamics under environmental and anthropogenic forcing. Knowledge gaps requiring further research efforts are also reported.

Développement d'un drone nautique pour le prélèvement d'échantillons d'eau en milieu côtier et estuarien (SPEEdoo)

A nautical drone was designed for the monitoring of estuarine and coastal waters in the context of the Water Framework Directive (WFD) to : - go up to 500 m off the coastline in less than 5 minutes, - perform in situ measurements (temperature, salinity, turbidity), - collect water samples for later analysis in the laboratory (phytoplankton identification, chlorophyll, nutrients, ...).

De nouvelles voies d’inhibition des biofilms. Des micro-organismes producteurs de nouvelles molécules actives

Lors d’une immersion en eau de mer, tous les matériaux et structures sont rapidement colonisés par des salissures d’origine biologique : des biofilms. La transformation des propriétés de surface dumatériau et la présence demicro- oumacro-organismes (bactéries, algues, balanes, larves) engendrent des risques accrus de corrosion localisée, la biodétérioration desmatériaux immergés, le blocage des fonctions mécaniques…Afin de contrôler le dépôt et le développement de ces biofilms, la méthode privilégiée est l’application de peintures anti-salissures. Cependant ces revêtements sont généralement toxiques pour l’environnement. C’est pourquoi, les travaux menés actuellement visent à isoler de nouvelles molécules, produites par les bactéries marines, dans le but de développer des moyens de luttes écologiques et non toxiques contre les biofilms indésirables.