Développement de la microchimie élémentaire et isotopique (87Sr (86Sr) des otolithes de saumons Atlantique)

Le saumon Atlantique fait partie du patrimoine écologique et économique du bassin de l Adour. Dans le cadre de la gestion actuelle du saumon dans ce bassin, l origine natale des géniteurs, le taux de retour des individus d origine piscicole, le taux de homing sur chaque sous-bassin ou encore le soutient par des géniteurs extérieurs au bassin de l Adour sont des thématiques qui restent sans réponses. Ce projet propose donc de tester le potentiel de la géochimie des otolithes sur le saumon Atlantique du bassin de l Adour. Nos travaux démontrent que la variation géographique de la composition chimique de l eau dans 12 rivières colonisées par le saumon, associée à un enregistrement dans l otolithe proportionnel à la signature géochimique du milieu de vie, permettent de discriminer l origine géographique des individus. La combinaison des signatures élémentaires (Sr:Ca et Ba:Ca) et surtout l isotopie du Sr (temporellement plus stable et sans fractionnement biologique) dans les otolithes améliore la précision du classement à l échelle de la rivière de développement. En se basant sur la transmission de signatures géochimiques (élémentaires et isotopiques) transgénérationelles entre la femelle reproductrice et les otolithes des embryons produits par cette dernière, nous avons discriminé avec succès les individus nés en rivière de ceux nés en pisciculture. Le classement des géniteurs (180 individus) selon leur rivière natale a confirmé que le sous bassin du gave d Oloron, et plus particulièrement le gave d Ossau, reste le lieu qui produit le plus de saumon de retour. De façon non négligeable, le gave de Pau contribue lui aussi au renouvellement de la population (10 d origine piscicole et 6 d origine naturelle). 18 saumons sur 180 sont issus de l alevinage (soit 10%); la majorité s étant développée dans le sous-bassin du gave de Pau. Par ailleurs, nous avons mis à jour l existence de périodes au cours de la vie des juvéniles (changements de milieu: sac vitellin milieu extérieur et pisciculture rivière) durant lesquelles l enregistrement du Ba dans l otolithe n est pas en relation avec la chimie de l eau. L originalité de notre approche est d avoir étudié l influence des facteurs endogènes et environnementaux chez des poissons ayant vécu dans le milieu naturel ou ayant séjourné en milieu naturel contrôlé. Nos travaux mettent l accent sur la complexité de l intégration du rapport Ba:Ca dans l otolithe et démontrent l utilité des éléments traces et des isotopes du Sr comme tag naturel pour distinguer l origine natale du saumon Atlantique.The Adour basin holds one of the largest populations of Atlantic salmon in southern Europe exploited by commercial and sport fisheries. Determining the relative contributions of individual rivers and hatcheries to the Adour basin populations becomes crucial to understand key sources that contribute the most to its persistence. We successfully used Sr:Ca, Ba:Ca and 87Sr:86Sr ratios as natural tags for determining the natal origins of adults from 12 tributaries. Success in discriminating between fish from different sites was greatest using Sr isotopes since the latter remained relatively constant across years at a given location. Geochemical signatures from core regions of the otolith were also used to identify fish from hatchery or naturally spawned sources. The predominance of adults spawned in the Ossau River among returning adults corresponded with long-term juvenile production trends in the Ossau River. Despite the limited upstream accessibility of the Pau River, our study demonstrated that Atlantic salmon recruits can successfully leave this river to join the adult population in the Adour basin. We observed relatively clear separation between hatchery and wild juveniles using both Sr:Cacore (wild > 2.5 and hatchery 0.710). The return of hatchery reared fish as adult spawners represented 10% of the total sampled fish we analyzed. Almost all adults, previously identified as belonging to the Ouzom River, were hatchery produced. Adults originated from the Pau River were either wild or hatchery reared fish. We also conducted field controlled experiments that characterized the elemental uptake process in juvenile Atlantic salmon otoliths during freshwater residency. Physiological effects influenced Ba deposition. Ba:Ca otolith profiles from hatchery-reared and field collected fish were characterised by a peak at yolk absorption mark. Hatchery-reared fish stocked in a river also displayed a peak of Ba:Ca following transfer which was not related to the water chemistry. Our experiment revealed a 20-day lag time between initial Ba:Cawater changes and Ba:Caotolith saturation. Results suggested that such effects should be considered during any attempts to determine rivers of origin of Atlantic salmon based on otolith elemental composition or reconstruct the movement of individual fish among and within streams.PAU-BU Sciences (644452103) / SudocSudocFranceF

The great melting pot. Common sole population connectivity assessed by otolith and water fingerprints

Quantifying the scale and importance of individual dispersion between populations and life stages is a key challenge in marine ecology. The common sole (Solea solea), an important commercial flatfish in the North Sea, Atlantic Ocean and the Mediterranean Sea, has a marine pelagic larval stage, a benthic juvenile stage in coastal nurseries (lagoons, estuaries or shallow marine areas) and a benthic adult stage in deeper marine waters on the continental shelf. To date, the ecological connectivity among these life stages has been little assessed in the Mediterranean. Here, such an assessment is provided for the first time for the Gulf of Lions, NW Mediterranean, based on a dataset on otolith microchemistry and stable isotopic composition as indicators of the water masses inhabited by individual fish. Specifically, otolith Ba/Ca and Sr/Ca profiles, and delta C-13 and delta O-18 values of adults collected in four areas of the Gulf of Lions were compared with those of young-of-the-year collected in different coastal nurseries. Results showed that a high proportion of adults (>46%) were influenced by river inputs during their larval stage. Furthermore Sr/Ca ratios and the otolith length at one year of age revealed that most adults (similar to 70%) spent their juvenile stage in nurseries with high salinity, whereas the remainder used brackish environments. In total, data were consistent with the use of six nursery types, three with high salinity (marine areas and two types of highly saline lagoons) and three brackish (coastal areas near river mouths, and two types of brackish environments), all of which contributed to the replenishment of adult populations. These finding implicated panmixia in sole population in the Gulf of Lions and claimed for a habitat integrated management of fisherie

Flux sedimentaires: peleoproctivite et paleocirculation de l'Ocean Austral au cours des 150000 dernieres annees

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 78473 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

The 231Pa/230Th ratio as a proxy for past changes in opal fluxes in the Indian sector of the Southern Ocean

International audiencePublished scavenging models generally assume that the 231Pa/230Th ratios of surface sediments are primarily determined by the mass flux of particles. In this study we compare the 230Th normalized vertical fluxes of both total sediments and opal to the 231Pa/230Th ratios measured from six sediment cores sampled across the Antarctic Circumpolar Current (ACC). We observe a better correlation between the 231Pa/230Th ratios and the vertical opal fluxes corrected for dissolution than with total sediment vertical fluxes. This observation indicates that opal may explain the enhanced scavenging of 231Pa. This result is consistent with the studies of Loeff and Berger [Deep-Sea Res. 40 (2) (1993) 339], Kumar et al. [Nature 378 (1995) 675] and Walter et al. [Earth Planet. Sci. Lett. 149 (1997) 85] who speculated that opal may explain enhanced scavenging of 231Pa. Finally, our results suggest that the 231Pa/230Th ratio is a reliable indicator of opal mass flux and can be used, taking some precautions, as a proxy for opal paleoproductivity in the Indian sector of the Southern Ocean

Enrichments in authigenic uranium in glacial sedimens of the Southern Ocean

International audienceFour sediment cores from the Polar frontal zone and the Antarctic zone in the Indian sector of the Southern Ocean present an increase of authigenic uranium during glacial periods. We show that this increase in uranium is due to a combination of (i) an increase in the lateral transport of organic matter, (ii) a decrease in the oxygen in deep waters, and (iii) a process of diagenesis. It appears that uranium concentration cannot be used as a proxy of palaeoproductivity in the Southern Ocean, as previously suggested by Kumar et al. in 1995. © 2002 Acade?mie des sciences / E?ditions scientifiques et me?dicales Elsevier SAS

Evidence for strong sediment redistribution by bottom currents along the Southeast Indian Ridge

International audienc

Evidence for strong sediment redistribution by bottom currents along the Southeast Indian Ridge

International audienc

Centrifugation as a countermeasure during bed rest and dry immersion: What has been learned?

We review the studies that have evaluated intermittent short-radius centrifugation as a potential countermeasure for cardiovascular, musculoskeletal, and sensorimotor deconditioning in simulated weightlessness. Methods: The findings from 18 experimental protocols that have used bed rest and dry immersion for comparing the protective effects of centrifugation versus standing upright or walking, and the effects of continuous vs. periodic exposure to centrifugation are discussed. Results: Centrifugation for as little as 30 min per day was found to be effective in mitigating orthostatic intolerance and strength in postural muscle after 5 days of bed rest, but it was not effective in mitigating plasma volume loss. Conclusion: To determine the optimal prescription for centrifugation as a ountermeasure, we recommend further studies using (a) bed rest of longer duration, (b) individualized prescriptions of centrifugation combined with exercise, and (c) functional performance tests

Assessment of erosion and sedimentation dynamic in a combined sewer network using online turbidity monitoring

cited By 1International audienceEroded sewer sediments are a significant source of organic matter discharge by combined sewer overflows. Many authors have studied the erosion and sedimentation processes at the scale of a section of sewer pipe and over short time periods. The objective of this study was to assess these processes at the scale of an entire sewer network and over 1 month, to understand whether phenomena observed on a small scale of space and time are still valid on a larger scale. To achieve this objective the continuous monitoring of turbidity was used. First, the study of successive rain events allows observation of the reduction of the available sediment and highlights the widely different erosion resistance for the different sediment layers. Secondly, calculation of daily chemical oxygen demand (COD) fluxes during the entire month was performed showing that sediment storage in the sewer pipe after a rain period is important and stops after 5 days. Nevertheless, during rainfall events, the eroded fluxes are more important than the whole sewer sediment accumulated during a dry weather period. This means that the COD fluxes promoted by runoff are substantial. This work confirms, with online monitoring, most of the conclusions from other studies on a smaller scale