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Habitat selection and spatial usage are important components of animal behavior influencing fitness and population dynamic. Understanding the animal–habitat relationship is crucial in ecology, particularly in developing strategies for wildlife management and conservation. As this relationship is governed by environmental features and intra‐ and interspecific interactions, habitat selection of a population may vary locally between its core and edges. This is particularly true for central place foragers such as gray and harbor seals, where, in the Northeast Atlantic, the availability of habitat and prey around colonies vary at local scale. Here, we study how foraging habitat selection may vary locally under the influence of physical habitat features. Using GPS/GSM tags deployed at different gray and harbor seals’ colonies, we investigated spatial patterns and foraging habitat selection by comparing trip characteristics and home‐range similarities and fitting GAMMs to seal foraging locations and environmental data. To highlight the importance of modeling habitat selection at local scale, we fitted individual models to colonies as well as a global model. The global model suffered from issues of homogenization, while colony models showed that foraging habitat selection differed markedly between regions for both species. Despite being capable of undertaking far‐ranging trips, both gray and harbor seals selected their foraging habitat depending on local availability, mainly based on distance from the last haul‐out and bathymetry. Distance from shore and tidal current also influenced habitat preferences. Results suggest that local conditions have a strong influence on population spatial ecology, highlighting the relevance of processes occurring at fine geographical scale consistent with management within regional units., Understanding animal‐habitat relationship at local scale is crucial in ecology, particularly if population are managed with regional units. This is the case of grey seals and harbour seals, whose trends in number vary among region in the Northeast Atlantic. The results suggest that local conditions might have a strong influence on their spatial ecology, highlighting the relevance of studying foraging habitat selection based on foraging behaviour at fine geographical scale.

By transferring energy and nutrients from plankton to top predators, forage species play a major ecological role in marine food webs. While large differences in energy densities have been demonstrated among these species, other determinants of their quality remain poorly explored. We analysed 78 forage species from the Bay of Biscay, NE Atlantic, for their concentrations in various chemical elements with a documented biological role (i.e. micro-nutrients). Species encompassed jellyfish, crustaceans, cephalopods, cartilaginous and bony fish. Elements included two essential macro-minerals (nitrogen and phosphorous) and nine trace elements (arsenic (As), cobalt, copper (Cu), chromium, iron, manganese, nickel, selenium (Se), zinc). We showed a broad range of elemental composition values across forage species, partly driven by taxonomy (fish versus crustaceans/cephalopods) or their habitat (coastal versus oceanic, pelagic versus benthic). Some elements (As, Cu or Se) were more variable than others, especially in fish for Cu and Se. The 78 forage species were then classified by hierarchical clustering analysis (HCA) into different nutritional groups, based on their composition in eleven elements. Mean concentrations of each element in the diet of eight cetacean species was finally calculated, as well as the importance of each nutritional group (as defined by HCA including all elements) for each predator species. We revealed contrasting diets in terms of exposure to elements. Neritic common dolphins and harbour porpoises but also minke whales were thus mainly supplied by the Se-enriched nutritional group composed of small (pelagic) schooling fish (including sandeels, (horse) mackerel and also some Clupeids), while the diets of pilot whales or Risso's dolphins that mostly consume benthic cephalopods were clearly Cu-enriched. This study raises the issue of essential element composition as another determinant of food quality, and the risk associated with changes in forage species' availability for the proper functioning of marine food webs and ecosystems.

Cetaceans have been naturally exposed to toxic trace elements (TEs) on an evolutionary time scale. Hence, they have developed mechanisms to control and/or mitigate their toxic effects. These long-lived species located at high trophic positions and bioaccumulating toxic elements are assumed to be good biomonitoring organisms. However, anthropogenic emissions have strongly increased environmental levels of toxic TEs in the last decades, questioning the efficiency of the detoxication mechanisms in cetaceans. In this context, temporal trends of mercury (Hg), cadmium (Cd) and lead (Pb) concentrations were studied through the analysis of 264 individuals from two cetacean species the common dolphin (Delphinus delphis) and the harbour porpoise (Phocoena phocoena) and belonging to two different Management Units (MUs) for the latter. These individuals stranded along the French Atlantic coasts from 2000s to 2017. All the trends presented were age- and sex-corrected and stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) were measured as proxies of their feeding ecology. Results showed that Pb concentrations clearly decreased over time in both species and MUs. This decrease agrees with the lead petrol regulation after 2000s, supporting the use of these species as valuable bioindicators of changes for TE levels in the marine environment. A significant long-term increase of total Hg concentrations was only observed in common dolphins. Cadmium concentrations also revealed different trends over the period in both species. The different Hg and Cd trends observed in the two species, probably reflected a contrasted contamination of habitat and prey species than a global increase of the contamination in the environment. These results highlight the necessity and gain of using different species to monitor changes in marine environments, each of them informing on the contamination of its own ecological niche. Lastly, the Se:Hg molar ratios of species suggested a low risk for Hg toxicity over time.

International audience; To date, nontargeted analysis (NTA) of halogenated organic compounds in biota has mostly been performed using GC/MS-based instruments. We intended to broaden the spectrum of physicochemical properties of amenable substances by taking advantage of liquid chromatography–high-resolution mass spectrometry coupling paired with an electrospray ionization source. Thus, a NTA strategy was applied to a set of 12 blubber samples belonging to five marine mammal sentinel species stranded on the French Atlantic coasts. It involved specific postacquisition data interpretation using open-source software HaloSeeker 1.0 for annotating chemical formulas. A total of 135 distinct unequivocal molecular formulas were assigned to 466 polyhalogenated ion clusters of interest. The most intense representative ions were identified as bioaccumulative heptachloro-1,2′-bipyrrole (Cl7-BP), α-hexabromocyclododecane, and (1R,2S,4R,5R,1′E)-2-bromo-1-bromomethyl-1,4-dichloro-5-(2′-chloroethenyl)-5-methylcyclohexane (MHC-1) in the weight range of micrograms per gram of lipids. To the best of our knowledge, this is the first time that Cl7-BP, the most intense signal observed, is reported in biota. A dozen other compound families will require further in-depth work to gain structural information.

While the importance of oceanic micronektonic species in biogeochemical cycles and in the transfer of matter in food webs is globally recognized, specific knowledge on elemental concentrations and their variability within this community is still poorly documented. Here, we report for the first time in the Bay of Biscay, North-East Atlantic, the body composition in various biological parameters and chemical elements of a meso-to bathypelagic micronektonic community. Stable carbon and nitrogen isotope compositions (δ

Competition between the sympatric harbour (Phoca vitulina) and grey seals (Halichoerus grypus) is thought to underlie some recent local declines of the former while the population of the latter remains stable or increases. A better understanding of the interactions between these two species is critical to elucidate current changes. This study aims at identifying and quantifying the niche overlap between harbour and grey seals at their Southern European limit range, in the baie de Somme (Eastern English Channel, France), in a context of exponential increase in the number of resident harbour seals and visiting grey seals. Isotopic niche overlap was quantified between both species using whisker δ13C and δ15N isotopic values, taking intra- and interindividual variability into account. Dietary overlap was quantified from scat contents using hierarchical clustering. A high degree of trophic niche overlap was identified between both species. The narrower isotopic niche of harbour seals was nested within that of grey seals (58.2% [CI95%: 22.7-100%] overlap). Six diet clusters were identified from scat content analysis. Two of them gathered most of harbour seals’ scats (85.5 % [80.3-90.2%]) and around half of grey seals’ ones (46.8% [35.1-58.4%]) that almost exclusively contained benthic flatfish. Consumption of this type of prey was identified here to be the root cause of trophic overlap. This highlighted the potential for competition between the two species at their Southern European limit range, linked to foraging on benthic flatfish, in coastal waters close to their haulout sites, especially during spring/summer. We suggest that (1) interspecific competition for prey could occur/increase in the future if the number of grey and harbour seals still increase and/or if flatfish supply decrease in this area, and (2) harbour seals would be disadvantaged in such a case if they do not adapt, as being specialised on flatfish at the colony scale.

Sympatric harbour (Phoca vitulina) and grey seals (Halichoerus grypus) are increasingly considered potential competitors, especially since recent local declines in harbour seal numbers while grey seal numbers remained stable or increased at their European core distributions. A better understanding of the interactions between these species is critical for conservation efforts. This study aimed to identify the trophic niche overlap between harbour and grey seals at the southern limit of their European range, in the Baie de Somme (BDS, Eastern English Channel, France), where numbers of resident harbour seals and visiting grey seals are increasing exponentially. Dietary overlap was identified from scat contents using hierarchical clustering. Isotopic niche overlap was quantified using δ13C and δ15N isotopic values from whiskers of 18 individuals, by estimating isotopic standard ellipses with a novel hierarchical model developed in a Bayesian framework to consider both intraindividual variability and interindividual variability. Foraging areas of these individuals were identified from telemetry data. The three independent approaches provided converging results, revealing a high trophic niche overlap due to consumption of benthic flatfish. Two diet clusters were dominated by either small or large benthic flatfish; these comprised 85.5% [CI95%: 80.3%–90.2%] of harbour seal scats and 46.8% [35.1%–58.4%] of grey seal scats. The narrower isotopic niche of harbour seals was nested within that of grey seals (58.2% [22.7%–100%] overlap). Grey seals with isotopic values similar to harbour seals foraged in coastal waters close to the BDS alike harbour seals did, suggesting the niche overlap may be due to individual grey seal strategies. Our findings therefore provide the basis for potential competition between both species (foraging on benthic flatfish close to the BDS). We suggest that a continued increase in seal numbers and/or a decrease in flatfish supply in this area could cause/amplify competitive interactions and have deleterious effects on harbour seal colonies., There is a critical need for a better understanding of interactions between two sympatric seal species, the harbour and grey seals, considered as potential competitors. We identified here the overlap in trophic niches between these two species at the southern limit of their European range, in the Baie de Somme (Eastern English Channel, France). All approaches provided converging results and revealed that foraging on benthic flatfish close to the Baie de Somme is the basis for potential competition between harbour and grey seals. We suggest that a continued increase in seal numbers and/or a decrease in flatfish supply in this area could cause/amplify competitive interactions and have deleterious effects on harbour seal colonies.

International audience

International audience; Accurately locating the foraging areas of diving marine predators is central to understanding their ecology and implementingconservation and management regulations. This study compares horizontal and vertical approaches of identifying seal foragingareas. We analysed GPS locations and dive data obtained from GPS/GSM tags fitted on eight grey seals (Halichoerusgrypus) and nine harbour seals (Phoca vitulina). In the horizontal dimension, we used the First Passage Time to identifyArea-Restricted Search (ARS) behaviour. In the vertical dimension, we used two dive criteria indicating benthic foragingbehaviour: dive shape and vertical descent speed. The two approaches were spatially compared using the Index of Differencesin Spatial Pattern. We found that the two approaches highlight similar hotspots when pooling all individuals of thesame species. However, the degree of overlap varied considerably at the individual level. Some individuals performed mostof their likely foraging dives (vertical dimension) in areas where they also displayed ARS behaviour (horizontal dimension),while others performed these dives both in and outside ARS zones. We suggest that comparing foraging areas detected fromhorizontal and vertical approaches (1) can strengthen the confidence in the efficiency of approaches to accurately spatializethe actual foraging effort of a diving predator at the scale of a colony (sampled with several individuals); and (2) providesmore comprehensive insights into potential interindividual differences in foraging strategies as some divergent individualstrategies may not be detected using only horizontal movements.

International audience; In the French West Indies (Caribbean), the insecticide Chlordecone (CLD) has been extensively used to reducebanana weevil (Cosmopolites sordidus) infestations in banana plantations. Previous studies have shown high CLDconcentrations in freshwater and coastal communities of the region. CLD concentrations, however, have not yetbeen assessed in marine top predators. We investigated CLD concentrations in cetacean blubber tissues fromGuadeloupe, including Physeter macrocephalus, Lagenodelphis hosei, Stenella attenuata and Pseudorca crassidens.Chlordecone was detected in all blubber samples analysed, with the exception of four P. macrocephalus.Concentrations (range: 1 to 329 ng·g−1 of lipid weight) were, however, lower than those found in species fromfresh and brackish water. Ecological factors (open ocean habitat), CLD kinetics, and cetacean metabolism (highor specific enzymatic activity) might explain low concentrations found in cetacean blubber. Future analyses thatinclude internal organ sampling would help to confirm CLD levels observed in this study.

International audience; Given the lack of background data on essential and non-essential trace elements in invertebrates and fish known to be the predominant prey of marine mammals and seabirds breeding at the Kerguelen Islands, this study intends to provide these results of great influence for predators in higher trophic levels. To this end, plankton organisms (9 species/4 phyla), mollusks (2 bivalves and 2 squid species) and fishes (8 benthic and 10 pelagic species) from Kerguelen waters were analysed for cadmium (Cd), copper (Cu), mercury (Hg), and zinc (Zn). Individual concentrations of non-essential elements (particularly Cd) showed larger variation in comparison with essential ones due to homeostasis. Cd ranged over 4 orders of magnitude; however, Hg ranged only 1, without significant correlation to trophic level. Instead, ecological parameters (benthic/mesopelagic habitat and feeding ecology) showed a more important influence on the results. Concerning seashore organisms, bivalves collected inside the Gulf of Morbihan had higher Cd concentrations compared to those from the Kerguelen shelf, suggesting a local source of Cd, such as runoff water from bird colonies. Comparison with literature showed metal concentrations in invertebrates and fishes from Kerguelen Islands somewhat lower than in the Antarctic area, with Hg prevailing in benthic species and Cd in pelagic ones. In contrast to Hg, Cd values of squids, jellyfish and the amphipod Themisto gaudichaudii were significantly higher than all other species. Finally, top predators foraging in this area that can be subject to potentially high Hg and Cd exposure through their diet at Kerguelen are reviewed.

In France, the first marine national park was set up in 2007 in the Iroise Sea, western Brittany, encompassing several Special Areas of Conservation (SAC). The park is resident to 1 of only 3 gray seal colonies in France. The at-sea habitat use of gray seals in the marine park is poorly understood and direct interactions with human activities are expected. We investigated habitat selection of gray seals within the marine park to provide spatial planning recommendations to local conservation management. We obtained data from 19 seals tracked between 2010 and 2013. We used generalized linear models to investigate their habitat selection using distance to haulout, distance to shore, bathymetry, tidal current, and sediment type as explanatory variables. The tracked individuals spent 67% of their time within the boundaries of the marine park. We investigated return trips to focus on habitat selection within the Iroise Sea. The deviance explained by the final model was 76%. Distance to haulout explained 47% of the deviance (seals selected short distances), bathymetry explained 40% (with bimodal selection for waters shallower than 50 m or deeper than 150 m), distance to shore explained 6% (selected distances less than 40 km), current explained 5% (selected weak currents), and sediment explained 2% (selected rocky areas). Habitat selection was concentrated in shallow waters located in the main archipelago of the marine park. The map of selected habitat will help identify potential conflicts of space use between seals and human activities such as fishing and leisure activities. This study has an important ecological and management value. It is the first of its kind in a marine park in France, and one of the few studies of gray seals at the periphery of their range. © 2015 The Wildlife Society.

International audience; Sharks are a major component of the top predator guild in oceanic ecosystems, but their trophic relationships remain poorly understood. We examined chemical tracers of diet and habitat (δ15N and δ13C, respectively) and total mercury (Hg) concentrations in muscle tissue of seven pelagic sharks: blue shark (Prionace glauca), short-fin mako shark (Isurus oxyrinchus), oceanic whitetip shark (Carcharhinus longimanus), scalloped hammerhead shark (Sphyrna lewini), pelagic thresher shark (Alopias pelagicus), crocodile shark (Pseudocarcharias kamoharai) and silky shark (Carcharhinus falciformis), from the data poor south-western tropical Indian Ocean. Minimal interspecific variation in mean δ15N values and a large degree of isotopic niche overlap - driven by high intraspecific variation in δ15N values - was observed among pelagic sharks. Similarly, δ13C values of sharks overlapped considerably for all species with the exception of P. glauca, which had more 13C-depleted values indicating possibly longer residence times in purely pelagic waters. Geographic variation in δ13C, δ15N and Hg were observed for P. glauca and I. oxyrinchus. Mean Hg levels were similar among species with the exception of P. kamoharai which had significantly higher Hg concentrations likely related to mesopelagic feeding. Hg concentrations increased with body size in I. oxyrinchus, P. glauca and C. longimanus. Values of δ15N and δ13C varied with size only in P. glauca, suggesting ontogenetic shifts in diets or habitats. Together, isotopic data indicate that – with few exceptions - variance within species in trophic interactions or foraging habitats is greater than differentiation among pelagic sharks in the south-western Indian Ocean. Therefore, it is possible that this group exhibits some level of trophic redundancy, but further studies of diets and fine-scale habitat use are needed to fully test this hypothesis.

International audience; Grey (Halichoerus grypus) and harbour seals (Phoca vitulina) are sympatric seal species, but they display distinct strategies of habitat use and connectivity between haulout sites. The distribution patterns and variations in relative abundance of both species were investigated along the French coast of the English Channel, at the southern limit of their range where seal numbers are increasing. Regular censuses conducted at all main haulout sites in mainland France showed significant seasonal variations at most sites, with more harbour seals counted during summer (breeding and moulting seasons), and more grey seals during summer only in the eastern English Channel. Trends in maximum haulout numbers at haulout sites showed a significant increase over the last five years, ranging from 9.7 to 30.9% per year for harbour seals, and from 5.8% (in the western English Channel) to 49.2% (in the eastern English Channel) per year for grey seals. These rates of increase in grey seal numbers are not linked to local pup production and most probably result from seal movements from the southwest British Isles and the North Sea, respectively. Aerial surveys conducted across the English Channel showed that most seal observations at sea were concentrated in the north-eastern English Channel. Telemetry showed that the 28 harbour seals tracked remained highly coastal, within a radius of 100 km from their haulout sites, and did not move to other known colonies. Grey seals moved much greater distances, reaching up to 1200 km from their capture site. More than half of the 45 grey seals tracked crossed the English Channel, especially during the breeding season, moving to known colonies in the southwest British Isles and the North Sea. Combining individual tracks and long-term surveys of the seal populations allowed a better understanding of the dynamics of these populations and their connectivity at a larger regional scale. The findings provide direct information for the management of grey and harbour seals within the frame of the Marine Strategy Framework Directive, and highlight focus areas where potential interactions between the two species should be monitored.

16 páginas, 7 figuras, 3 tablas.-- Paula Méndez Fernández ... et al., This study aims to assess niche segregation among the five main toothed whales that frequent the NW Iberian Peninsula waters: the common dolphin, the harbour porpoise, the bottlenose dolphin, the striped dolphin and the long-finned pilot whale. We used cadmium (Cd) and stable isotope ratios (δ13C and δ15N) as ecological tracers to assess degree of segregation in diet/trophic level and in foraging habitat, over various time-scales. δ13C values highlighted different habitats, while Cd concentrations highlighted feeding differences between oceanic and neritic species. Moreover, δ15N values suggest different trophic levels of prey targeted within oceanic and neritic species. Hence, results revealed long-term ecological segregation among five toothed whales that coexist in the NWIP and demonstrated the ability of ecological tracers to discriminate ecological niches among closely related species., This work was supported through the PhD grant to P. Mendez-Fernandez from the Portuguese Foundation for Science and Technology of the Govern- ment of Portugal (SFRH/BD/36766/2007). G.J. Pierce acknowledges support from the EU under the ANIMATE project (MEXC-CT-2006- 042337). M.B. Santos acknowledges support from the LOTOFPEL project (Plan Nacional de I+D+I, CTM 2010-16053) and from the Spanish Ministry of Education, Programa Nacional de Movilidad de Recursos Humanos de Investigacion (PR-2010-0518).

11 páginas, 4 tablas, 5 figuras.-- Paula Méndez Fernández ... et al., Concentrations of thirty two polychlorinated biphenyls (PCBs) were determined in the blubber of five sympatric species of odontocetes stranded or by-caught along the Northwest coast of the Iberian Peninsula: common dolphin (Delphinus delphis), long-finned pilot whale (Globicephala melas), harbour porpoise (Phocoena phocoena), striped dolphin (Stenella coeruleoalba) and bottlenose dolphin (Tursiops truncatus). Multivariate analyses were applied to evaluate the ability of PCB patterns to discriminate these sympatric species and to determine which eco-biological factors influence these patterns, thus evaluating the relevance of PCB concentrations as biogeochemical tracers of feeding ecology. The five species could be separated according to their PCB patterns. Different exposure to these contaminants, a consequence of their different dietary preferences or habitats, together with potentially dissimilar metabolic capacities, likely explain these results; sex, age, habitat and the type of prey eaten were the most important eco-biological parameters of those tested. Although, no single congener has been specifically identified as a tracer of feeding ecology, 4 congeners from the 22 analysed seemed to be the most useful and around 12 congeners appear to be enough to achieve good discrimination of the cetaceans studied. Therefore, this study suggests that PCB patterns can be used as tracers for studying the feeding ecology, sources of contamination or even population structure of cetacean species from the Northwest Iberian Peninsula, P. Méndez- Fernandez was supported during the research period through a PhD grant from the Fundação do Ministério de Ciência e Tecnologia de Portugal and ANIMATE project (SFRH/BD/36766/2007) and through a Science Without Borders (CSF) young talent postdoctoral grant of the Brazilian government. G. J. Pierce acknowledges support from the EU ANIMATE project (MEXC-CT-2006-042337), University of Aveiro and Caixa Geral de Depósitos (Portugal).

International audience; The Bay of Biscay (north-east Atlantic) is an open marine ecosystem of particular concern in current European environmental policies. Indeed, it supports both a high biological diversity and numerous anthropogenic activities such as important fisheries. For the first time, stable isotope analyses (SIA) of carbon and nitrogen and analysis of total mercury (T-Hg) concentrations in the muscle (edible flesh) were performed on adult stages of a wide range of species (i.e., 120 species) from various taxa and various habitats of this ecosystem. Concentrations of this non-essential metal, toxic to all living organisms, ranged from 39 to 5074 ng.g-1 dry weight. Calculations of species' trophic positions (TPs) through SIA revealed a limited effect of TP in explaining Hg bioaccumulation by high trophic level consumers in particular. On the contrary, our results suggest an important role of habitat and/or feeding zone, which strongly influence muscle Hg bioaccumulation. Deep-sea fish species effectively presented the highest Hg concentrations. Possible interactions between biological factors (e.g., age of deep-sea organisms) and bioavailability of the metal in the deep-sea environment are discussed to explain such enhanced bioaccumulation of Hg by deep-sea fauna in the Bay of Biscay. This study also highlights a potential risk for human health when deep-sea fish are consumed frequently.

International audience; Recent studies have shown that the complementary analysis of mercury (Hg) concentrations and stable isotopic ratios of nitrogen (δ15N) and carbon (δ13C) can be useful for investigating the trophic influence on the Hg exposure and accumulation in marine top predators. In this study, we propose to evaluate the interspecies variability of Hg concentrations in phocids from polar areas and to compare Hg bioaccumulation between both hemispheres. Mercury concentrations, δ15N and δ13C were measured in fur from 85 individuals representing 7 phocidae species, a Ross seal (Ommatophoca rossii), Weddell seals (Leptonychotes weddellii), crabeater seals (Lobodon carcinophaga), harbour seals (Phoca vitulina), grey seals (Halichoerus grypus), ringed seals (Phoca hispida), and a bearded seal (Erignathus barbatus), from Greenland, Denmark and Antarctica. Our results showed a positive correlation between Hg concentrations and δ15N values among all individuals. Seals from the Northern ecosystems displayed greater Hg concentrations, δ15N and δ13C values than those from the Southern waters. Those geographical differences in Hg and stable isotopes values were likely due to higher environmental Hg concentrations and somewhat greater number of steps in Arctic food webs. Moreover, dissimilarities in feeding habits among species were shown through δ15N and δ13C analysis, resulting in an important interspecific variation in fur Hg concentrations. A trophic segregation was observed between crabeater seals and the other species, resulting from the very specific diet of krill of this species and leading to the lowest observed Hg concentrations.

Tissues of foetus–mother pairs of common dolphins (Delphinus delphis) stranded along the French coasts (Bay of Biscay and English Channel) were analysed for their Cd, Cu, Hg, Se and Zn contents. In the kidneys, foetal Cd levels were extremely low, and strong relationships between Cu and Zn suggested the involvement of metallothioneins since early foetal life. The results also indicated a limited maternal transfer of Hg during pregnancy since levels in the tissues of foetuses were below 1 μg g−1 w.wt. However, hepatic Hg levels in foetuses increased with body length, and were also proportionate to maternal hepatic, renal and muscular Hg levels. Lastly, affinities between Hg and Se in tissues would participate in Hg neutralisation in both mothers – through tiemannite granules – and fetuses – through reduced glutathione – counteracting the toxic effects linked to the particularly high quantities of methyl–Hg to which marine mammals are naturally exposed. Keywords: Marine mammals, Mercury, Selenium, Pregnancy, North-Eastern Atlantic

Total (T-Hg) and organic (O-Hg) mercury concentrations and tissue distribution were examined in 20 species of cephalopods (n = 278) from the north eastern Atlantic waters, i.e. from the Bay of Biscay to the Faroe Islands. Concentrations of T-Hg in whole cephalopods showed elevated variations among species, i.e. from 40 to 3560ng g(-1) dwt, but a low variability within each species (mean CV%=39%). With the exception of oceanic squids, the digestive gland globally displayed higher T-Hg concentrations than the remaining tissues. In contrast, O-Hg concentrations determined in selected species were generally higher in the remaining tissues. Despite higher T-Hg concentrations, the digestive gland weakly contributed to the total body burden of both T-Hg and O-Hg (< 25% and < 15%, respectively). In fact, from 75% to 95% of the T-Hg and O-Mg were contained in the muscular remaining tissues. Therefore, O-Hg may have a strong affinity to proteins in cephalopods. Sex and size only significantly influenced the bioaccumulation of Hg for the Loliginidae family. T-Hg and O-Hg concentrations were also influenced by geographical origin: Celtic Sea > Bay of Biscay > Faroe Islands, corresponding to the seawater Hg concentrations in these areas. In the Faroe Islands and the Celtic Sea, benthic cephalopods contained significant higher Hg concentrations compared to pelagic ones. This suggests that diet is not the main pathway of Hg uptake in cephalopods as pelagic species were expected to be more exposed to O-Hg through fish consumption than benthic ones. (c) 2006 Elsevier B.V. All rights reserved.

International audience; Oil spills can have direct effects on organisms (mortality or morbidity), indirect effects (through alteration of lower trophic levels) or be associated to exposure to trace elements contained in oil (markers). An effect of the “Erika” oil spill was investigated by spatio-temporally comparing mortality, population structures, diets and concentrations of vanadium, nickel and porphyrins in small delphinids, seals and otters from the French Atlantic coasts. These species might differ in their vulnerability to oil. Changes in mortality and its demographic structures were within previously observed ranges. The diet of the common dolphin showed an extended period of high inter-individual variability in the year 2000. Vanadium concentrations in delphinids were chronically high, but did not increase significantly after the oil spill. Porphyrins concentrations in seals and otters were low suggesting a limited exposure to contaminants, but the ratio between proto- and copro-porphyrins in otter spraints from oiled vs. unoiled sites varied significantly. No measurable effect of the “Erika” oil spill was found in dolphins and seals.

International audience; Grey seals Halichoerus grypus were sampled in the Faroe Islands archipelago during the summers of 1993 to 1995. Concentrations of Cd, Cu, Hg, Se and Zn were measured in the liver, kidney and muscle of 68 seals. All elements except Zn exhibited lowest concentrations in the muscle. The liver contained the highest concentrations of Cu, Hg, Se and Zn, while the kidney contained the highest Cd concentrations. However, trace element concentrations within the tissues were influenced by sex and age. Thus, females had clearly higher Cd concentrations than males. Age was the most important factor influencing the concentration of Cd, Hg and Se in the liver, and of Cd and Hg in the kidney. A strong positive correlation between Cd, Hg and Zn in the kidney suggests the presence of a detoxification process involving metallothionein proteins. Similarly, a strong positive correlation between Hg and Se and a molecular Hg:Se ratio close to 1 in the liver suggests a demethylation process leading to the formation of mercuric selenide granules. High Hg concentrations could be related to fish consumption by the grey seal, but a piscivorous diet could not be responsible for the very high Cd concentrations. This suggests that the seals¹ diet changes during the year, and may include a significant proportion of cephalopods in seasons other than summer. Finally very high Cd concentrations in grey seal tissues compared to other grey seal populations also suggest that the Faroe Islands are subject to sub-arctic influences.

International audience; Concentrations of cadmium, mercury, copper and zinc were measured in muscle, kidney and liver tissues and in the main prey of five species of zooplankton-eating petrels: blue petrel (Halobaena caerulea), thin-billed (Pachyptila belcheri) and Antarctic (P. desolata) prions, and South Georgian (Pelecanoides georgicus) and common (Pelecanoides urinatrix) diving petrels. Since some of these species are closely related species with respect to body size, timing ofmoult and life span, their diet has been examined to evaluate its influence on heavy-metal bioaccumulation. Inter-specific differences were significant for Hg concentrations in the liver and for Zn concentrations in both liver and kidney tissues. Blue petrels exhibited the highest Hg concentrations in the liver (3.9±2.02 lg.g)1 wet weight). No significant differences were found in Cd concentrations between species. Exposure to heavy metals through the most important prey species in the diet during the breeding period was evaluated. The most evident result was the influence of fish prey on Hg levels. Although crustacean species exhibit different cadmium concentrations, the diet composition does not appear to be discriminant for Cd bioaccumulation within the small petrel community at Kerguelen.

International audience; Environmental conditions can shape genetic and morphological divergence. Release of new habitats during historical environmental changes was a major driver of evolutionary diversification. Here, forces shaping population structure and ecotype differentiation (‘pelagic’ and ‘coastal’) of bottlenose dolphins in the North-east Atlantic were investigated using complementary evolutionary and ecological approaches. Inference of population demographic history using approximate Bayesian computation indicated that coastal populations were likely founded by the Atlantic pelagic population after the Last Glacial Maxima probably as a result of newly available coastal ecological niches. Pelagic dolphins from the Atlantic and the Mediterranean Sea likely diverged during a period of high productivity in the Mediterranean Sea. Genetic differentiation between coastal and pelagic ecotypes may be maintained by niche specializations, as indicated by stable isotope and stomach content analyses, and social behaviour. The two ecotypes were only weakly morphologically segregated in contrast to other parts of the World Ocean. This may be linked to weak contrasts between coastal and pelagic habitats and/or a relatively recent divergence.We suggest that ecological opportunity to specialize is a major driver of genetic and morphological divergence. Combining genetic, ecological and morphological approaches is essential to understanding the population structure of mobile and cryptic species.

Recent European environmental policies argue for the development of indicators of the ecological status of ecosystems that are easy to implement and powerful enough to detect changes quickly. For instance, some indicators that are currently proposed for monitoring foodweb structure and functioning are based on the size of organisms, using size as a proxy for trophic level. However, these indicators do not necessarily accurately reflect the underlying trophic structure and dynamics to follow. Ecological tracers (i.e. chemical parameters measured in consumer tissues to infer the trophic ecology of organisms) may serve as complementary indicators of trophic level, and may also help distinguish different populations of a species when more commonly used methods (e.g. genetic, age determination) present their own limitations. Here, we analysed the potential of muscle δ13C and δ15N values and of muscle mercury (Hg) concentrations to depict size-related trophic habits of different fish species. We expected that intra- and interspecific variation in these ecological tracers could be helpful in refining currently proposed indicators of marine ecosystems, and also help in discriminating management unitsfor some species. Four fish species were selected for their economical and/or ecological importance in the Bay of Biscay (Northeast Atlantic): whiting Merlangius merlangus, European hake Merluccius merluccius, Atlantic horse mackerel Trachurus trachurus and anglerfish Lophius piscatorius. Muscle δ13C and δ15N values segregated the species and enabled us to discriminate species-specific feeding strategies with increasing size of individuals. Fish body size was not always linearly correlated with δ15N or trophic level. In contrast, Hg concentrations and size-related Hg patterns were more similar from species to species. Interestingly, muscle δ15N values together with Hg concentrations segregated the two putative stocks of European hake within the Bay of Biscay. Hence, we propose the combined use of ecological tracers as a promising method for accurately assigning a consumer to a trophic guild, investigating Hg trophodynamics in foodwebs, and helping discriminate distinct ecological populations within a species when defining management units.

International audience; The use of seabirds to assess marine contamination by trace elements in areas remote from pollutant emission points has already been done at various latitudes. Nevertheless, little information is available concerning the Southern Indian Ocean. Determining the contaminants levels, there appears necessary not only due to several deleterious effects reported in literature, but also as previous studies have highlighted elevated concentrations of cadmium (Cd) and mercury (Hg) in mollusks, crustaceans and fish. Within this context, the white-chinned petrel appears as a key species due to its lifespan, diet and trophic position. Thirty-three accidentally killed (collision with lights/bycatch in longline vessels) individuals collected in Kerguelen waters were analysed for Cd, copper (Cu), Hg, selenium (Se) and zinc (Zn) in liver, kidney, pectoral muscle, feathers and for mature males, testis. Elevated Hg concentrations (average 58.4 lg g-1 dw in liver) are likely due to the presence of mesopelagic prey in the diet of Procellaria aequinoctialis. Cd concentrations (average of 65.7 lg g-1 dw in kidney) can be attributed to a high level of fisheries offal consumption, as well as crustacean and squid ingestion. Correlation of Hg with Se indicates its detoxification by co-precipitation, and correlation of Cd with Zn suggests its displacement by Cd on metallothioneins binding sites. This work also indirectly confirms ecological data (range and diet composition) from the wintering period of the species, which is rather scarce. Seasonal diet change and moulting accounted more for the obtained results than sex of the birds.

International audience; Knowledge of the trophic ecology and interactions of marine top predators is fundamental for understanding community structure and dynamics as well as ecosystem function. We examined the feeding relationships of 4 heavily exploited elasmobranchs caught in coastal artisanal shark fisheries in south-western Madagascar in 2009 and 2010—Sphyrna lewini, Loxodon macrorhinus, Carcharhinus falciformis and Rhynchobatus djiddensis—using stable isotope (δ15N and δ13C) analysis. Relative trophic position (indicated by δ15N) and foraging location (indicated by δ13C) differed among species. Isotopic niche width was highly variable: more pelagic species, such as S. lewini and C. falciformis, had the broadest isotopic niches while the benthic R. djiddensis had the narrowest. A high percentage of niche overlap occurred between R. djiddensis and 2 of the species, C. falciformis (93.2%) and L. macrorhinus (73.2%), and to a lesser extent S. lewini (13.3%). Relative trophic position of S. lewini significantly increased with size, suggesting a dietary shift with age. Sex differences in δ15N values were observed in L. macrorhinus, suggesting intraspecific niche partitioning. Variation in stable isotope values among these 4 highly exploited elasmobranch species indicates trophic structuring, likely driven by differences in diet and habitat use as well as by size and sex. This study provides the first baseline information on the trophic ecology of elasmobranchs caught in artisanal fisheries from south-western Madagascar.

10 páginas, 3 tablas, 2 figuras.-- Paula Méndez-Fernández ... et al., Concentrations and patterns of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in the blubber of the five most common toothed whales off the Northwest Iberian Peninsula (NWIP), specifically common dolphin, long-finned pilot whale, harbour porpoise, striped dolphin and bottlenose dolphin, were investigated. The study revealed that differences in PCB and PBDE concentrations among the species are highly dependent on age and sex but also on ecological factors such as trophic level, prey type and habitat. Of the five species studied, bottlenose dolphin and harbour porpoise showed the greatest concentrations of PCBs. Both species exceed the toxic threshold of 17 μg g− 1 lipid weight (PCB Aroclor equivalent) for health effects on marine mammals, for 100% and 75% of the individuals tested, respectively. Overall, the PCB and PBDE levels observed in the NWIP toothed whales were of the same order of magnitude or lower than those reported by previous studies in areas of the NE Atlantic. However, they are often higher than those for toothed whales from the southern Atlantic and Pacific Ocean, This work was supported through the PhD grant of PMF from the Portuguese Foundation for Science and Technology of the Government of Portugal (SFRH/BD/36766/2007). GJP acknowledges support from the EU under the ANIMATE project (MEXC-CT-2006-042337). MBS was supported by the Spanish Ministry of Education, Programa Nacional de Movilidad de Recursos Humanos de Investigación (PR-2010-0518) and the LOTOFPEL project (Plan Nacional de I + D + I, CTM 2010–16053).

12 páginas, 4 tablas, 4 figuras.-- Paula Méndez Fernández ... et al., Concentrations of Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, V and Zn were investigated in the liver and kidney of the five most common toothed whales off the Northwest Iberian Peninsula (NWIP), specifically common dolphin, long-finned pilot whale, harbour porpoise, striped dolphin and bottlenose dolphin. Differences were observed in the bioaccumulation of the above elements between the five species. The differences are probably related to biological factors such as age and sex and/or to ecological factors specific to each species such as feeding habits or bioavailability of the various elements. However, no significant relationship was observed between element accumulation and sex. Pilot whale and striped dolphin showed the highest concentrations of renal Cd and the highest concentrations of hepatic Hg and Se, while bottlenose dolphin showed the highest concentrations of Hg in kidneys. An analysis of inter-elemental relationships showed strong positive correlations between Hg and Se in the five species, however most individuals have Hg:Se molar ratio less than 1:1 indicating an excess of Se compare to Hg. This result, probably reflect the high proportion of young animals in the sample available for this study and/or that these animals had a good health status. We also observed a positive correlation in striped dolphins between Cd and Cu and between Cd and Zn in kidneys. In addition, comparing with other studies world-wide, the element concentrations (Hg and Cd) found in Iberian toothed whales indicate that these populations are not specially threatened by Hg and Cd exposure in the area., This work was supported through the PhD grant of PMF from the Portuguese Foundation for Science and Technology of the Government of Portugal (SFRH/BD/36766/2007). GJP acknowledges the support from the EU under the ANIMATE project (MEXC-CT-2006-042337). MBS was supported by the Spanish Ministry of Education, Programa Nacional de Movilidad de Recursos Humanos de Investigación (PR-2010-0518) and the LOTOFPEL project (Plan Nacional de I + D + I, CTM 2010-16053). FLR acknowledges the support from the EU under the ECOSUMMER project (MEST-CT-2005-020501).

Le Cd est un polluant remanent present naturellement dans notre environnement. Les apports dus aux activites anthropiques ont ete estimes a environ 500 000 T depuis 1817. Par le jeu des flux geochimiques, une grande partie de ce Cd atteint le milieu marin ou ce metal est bioaccumule par les organismes vivants. Afin d'evaluer le risque toxicologique encouru par les predateurs superieurs, homme compris, consommateurs de produits marins contamines par le Cd, nous nous sommes interesses a deux ecosystemes soumis a des apports chroniques de ce metal. 1) Les cotes de Charente-Maritime sont soumises a une pollution diffuse en Cd a partir de la Gironde. L'etude des concentrations en Cd de plus de 110 especes collectees sur ce littoral montrent que seules certaines especes appartenant toutes a l'embranchement des mollusques concentrent fortement ce metal. L'apport de Cd du a la consommation de ces especes qualifiees d'hyperbioaccumulatrices a ete estime pour les habitants de Charente-Maritime et compare a la Dose Hebdomadaire Tolerable de 7 μg/g de Cd/kg corporel defini pour l'homme par le JECFA. Bien que non negligeable, ces apports restent inferieurs a la DHT. Les petoncles sont les organismes susceptibles de transferer les plus fortes quantites de Cd. Les normes mises en place par la Commission Europeenne qui interdit la consommation de coquillages dont les concentrations en Cd depassent 5 μg/g de poids sec protegent les consommateurs. En effet, dans notre zone, ces concentrations sont depassees, notamment pour les huitres, seulement dans l'estuaire de la Gironde ou du fait de la contamination par le Cd, toute consommation de coquillages est interdite. C'est la seule zone de Charente-Maritime ou nos calculs montrent que la consommation de coquillages pourrait induire chez les gros consommateurs un depassement de la DHT. 2) Les zones polaires sont soumises a un enrichissement naturel de Cd. Dans ces environnements, les cephalopodes qui concentrent tres fortement le Cd dans leur glande digestive, nous y avons mesure des concentrations atteignant pres de 400 μg/g de poids sec, sont les principaux responsables du transfert de ce metal vers les predateurs superieurs, mammiferes marins et oiseaux de mer qui les consomment. Chez ces especes, le Cd se concentre tres fortement dans le foie et les reins. La prise hebdomadaire de Cd a partir des cephalopodes a, par exemple, ete calculee pour les globicephales noirs des Iles Feroe. Elle est de 7 a 100 fois superieures a celle qui a ete montree provoquer des desordres metaboliques chez l'etre humain. De ce fait, la question se pose du risque toxicologique encouru par ces predateurs. Il est probable, qu'exposes depuis de longues periodes au Cd ces animaux ont developpe des processus de detoxication du Cd qui les protege de cette impregnation. Neanmoins, la decouverte de granules enrichis en Cd dans les tubules renaux de delphinides des Iles Feroe presentant de fortes concentrations en Cd dans leurs reins relance cette problematique. Parmi les polluants, le Cd doit etre particulierement surveille dans notre environnement. En effet, du fait de sa presence naturelle dans notre alimentation, la Dose Hebdomadaire Tolerable pour cet element peut etre rapidement atteinte en cas d'apports anthropiques supplementaires.

Three hundred and fifty individuals of 12 species of cephalopods which differed in their feeding habitats were sampled from the French Atlantic coast to the sub-Arctic region (Bay of Biscay, English Channel, west Irish coast and Faroe Islands) and analysed for their cadmium contents. Comparison of the Cd levels of the cephalopods showed that those from the sub-Arctic area contained very high Cd concentrations compared to those from lower latitudes such as along the French Atlantic coast. High Cd levels in cephalopods from the sub-Arctic zone correspond closely to the reported high Cd concentrations in the tissues of top vertebrate predators from the same area. Comparison of the weekly Cd intakes for the Faroe Island pilot whales with the `Provisional Tolerable Weekly Intake' for humans recommended by the World Health Organisation, showed that top vertebrate predators are often subjected to Cd doses far in excess of those recommended for humans. Our limited survey results suggest that cephalopods constitute an important source of Cd for cephalopod predators, and that this bioaccumulation effect is most evident at high latitudes.

Samples of seston, plankton and suprabenthic species were collected in the Seine estuary along the gradient of salinity (0 to > 30 PSU) during six cruises from September 1992 to September 1995. Concentrations of Cd, Cu, Pb and Zn were measured at different levels of the estuarian pelagic trophic web, such as organic detritus, diatoms, Copepods and suprabenthic organisms (mysids, shrimps and fish). Organic detritus, phytoplankton and Copepods showed heavy metal contamination due to biochemical processes along the gradient of salinity. For carnivorous species (shrimps and fish), this contamination may be found only for Zn and Pb. No bio-magnification may be described in the trophic web of the Seine estuary.

In order to evaluate the use of biopsy samples as non-destructive tool for assessing trace element concentrations in small cetaceans, the concentrations of 14 trace elements were determined in skin, blubber, liver and kidneys of four species of small cetaceans (i.e. common dolphin Delphinus delphis, harbour porpoise Phocoena phocoena, bottlenose dolphin Tursiops truncatus and striped dolphin Stenella coeruleolba), stranded and/or by-caught along the NE Atlantic Ocean coast between 2001 and 2008. Only Cu, Fe, Hg, Mn, Ni and Zn were above the detection limit of the instruments and showed recoveries satisfactory enough to be interpreted. Among these trace elements, Hg was the only one showing a significant correlation between concentrations in and those in liver and kidneys. In consequence skin and blubber can only be used as non-invasive monitoring tissues to investigate Hg bioaccumulation in internal tissues for cetacean populations. We greatly acknowledge the stranding networks from France (Observatoire PELAGIS), Spain (CEMMA), and Portugal (SPVS) for providing us cetacean samples. We also thank A. F. Guerra and F. Read from the Instituto de Investigaciones Marinas (C.S.I.C) in Vigo, Spain, and W. Dabin from the Observatoire PELAGIS in La Rochelle, France, for the age determination of the individuals. We also wish to thank C. Pignon-Mussaud from the Cellule Géomatique (UMR LIENSs) for providing the map of the study area and M. Kalombo from the Centre Commun d’Analyses (Fédération de Recherche en Environnement pour le Développement Durable FR 3097 CNRS-IFREMER-Université de La Rochelle) for running part of the trace element analyses. This work has been funded by the CPER 13 (Contrat de Plan Etat Région) through a post-doctoral grant to AA and PMF acknowledges support from the Portuguese Foundation for Science and Technology of the Government of Portugal (SFRH/BD/36766/2007). published

This study investigates concentrations of five metals, copper (Cu), cadmium (Cd), lead (Pb), mercury (Hg) and zinc (Zn) in eel Anguilla anguilla liver tissue from the Camargue and Berre on the southern French coast. Large numbers of wintering birds feed in these important wetland sites, and eels are important food items for heron and egret species. Both sitesreceive metal inputs from riverine (Rhone and Durance) and atmospheric sources, in addition to petrochemicalrelated pollution at Berre. Concentrations of Cd, Zn and Cu were significantly higher in the livers of eels from the Camargue than from Berre. Body size class was positively correlated with concentrations of lead at both sites, and with copper at Berre. Concentrations of Hg in eel livers in the Camargue and at Berre were consistent with levels reported for contaminated areas (geometric means: 1·3 and 1·2 μg/g dry weight respectively). Eels from Berre had an elevated liver weight relative to those from the Camargue, suggesting that other factors may be affecting the Berre population. The higher metal concentrations found in eels from the Camargue suggest that further investigations should be undertaken as to the source of this pollution, and on the processes of transfer and accumulation at this important wetland site.

Among marine mammals, pilot whales (Globicephala melas) are characterized by high levels of tissular cadmium (Cd). In this species, squids are used as a major food item, inducing an important Cd intake. In a significant fraction of the mammal population sampled in the vicinity of the Faroe Islands, blood and urine Cd concentrations are higher than minimum adverse-effect levels established for human beings. However, the frequency-at-age data have not shown anomalies likely to reveal a major toxic problem, suggesting a remarkable tolerance of this species to heavy metals.

International audience; Most of the recent framework directives and environmental policies argue for the development and the use of indicators - notably trophodynamic indicators - that should be able to follow ecosystems' evolution in space and time, particularly under anthropogenic perturbations. In the last decades, the use of stable carbon and nitrogen isotopes ratios has increased exponentially, particularly in studies of marine ecosystems' trophic structure and functioning. This method is principally based on the assumption that the isotopic composition of a consumer directly reflects that of its food. Nevertheless, few studies have attempted to define the limits of this tool before using it and drawing ecological conclusions from isotopic analysis. This study aimed to assess the importance of considering spatio-temporal variations in isotopic signatures of consumers when using δ13C and especially δ15N values in open ecosystems with complex food webs, using the Bay of Biscay (north-east Atlantic) as a case study. To this end, more than 140 species from this marine ecosystem were analysed for the isotopic signatures in their muscle tissue. They were sampled from coastal to oceanic and deep-sea areas and at different latitudes, to evaluate spatial variations of isotopic signatures. Selected species were also sampled over several years and in two seasons to account for inter-annual and seasonal variations. In the Bay of Biscay temperate ecosystem, which is subject to both coastal and oceanic influences (two main river inputs and upwelling areas), δ13C and δ15N values significantly decreased from inshore to offshore species and to a lesser extent from benthic to pelagic organisms. River discharges appeared to be the first factor influencing δ13C and δ15N values in consumers. From the important spatial variations detected in δ15N values in particular, we suggest that in such contrasted ecosystem, nitrogen isotopic ratios may also be revisited as an indicator of the feeding area. Moreover, we demonstrate that several baselines should be used when calculating trophic levels from δ15N values. From the temporal variations detected, we recommend concentrating on a short time scale for the sampling of most organisms.

The feeding ecology and habitat use of the most frequently sighted and/or regularly reported stranded or by-caught toothed whale species of the North Western Iberian Peninsula (NWIP) were examined, with a special focus on their trophic position (TP) and relationships with their prey. With this aim, the stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) of common dolphin (Delphinus delphis), bottlenose dolphin (Tursiops truncatus), harbour porpoise (Phocoena phocoena), striped dolphin (Stenella coeruleolba) and long-finned pilot whale (Globicepahala melas) were analyzed in muscle samples taken from stranded and by-caught animals between 2004 and 2008. Stable isotopes were also measured in 17 species of fish and cephalopods previously identified as prey species, based on stomach content analyses, and in plankton. The trophic enrichment factors (TEF) were calculated for all five species and in addition, isotopic mixing models were applied to estimate the proportional contribution of each prey source to the diet of the common dolphin, which was the toothed whale species best sampled in our study. Plankton, fish and cephalopods exhibited an increasing trend in their δ13C values (from − 19.6‰ to − 15.3‰) along the offshore-inshore axis, with a less clear spatial pattern observed for δ15N values. Striped dolphins exhibited the lowest mean δ13C, δ15N and TP values (− 17.6‰, 10.8‰ and 4.3, respectively), which confirms the oceanic character of this species and its lower trophic position when compared to the other toothed whales analyzed. The common dolphin exhibited mean δ13C, δ15N and TP values that were at an intermediate level (− 17.0‰, 11.7‰ and 4.7, respectively) and results of the mixing model indicated that blue whiting (Micromesistius poutassou) was the main component of the diet. The harbour porpoise, bottlenose dolphin and pilot whale exhibited higher and very similar isotopic compositions and TPs. The mean TEF obtained between predators and their main prey were 1.4‰ for δ15N and 0.8‰ for δ13C. These results provide information on stable isotope incorporation data for toothed whales, which are essential if conclusions are to be drawn in issues concerning trophic structures and habitat use in the NWIP., Sí

International audience; We examined the use of mercury (Hg) and nitrogen and carbon stable isotopes in teeth of polar bear (Ursus maritimus) from Svalbard as biotracers of temporal changes in Hg pollution exposure between 1964 and 2003. Teeth were regarded as a good matrix of the Hg exposure, and in total 87 teeth of polar bears were analysed. Dental Hg levels ranged from 0.6 to 72.3 ng/g dry weight and increased with age the first 10 years of life. A decreasing time trend in Hg concentrations was observed over the recent four decades while no temporal changes were found in the stable isotope ratios of nitrogen (δ15N) and carbon (δ13C). This suggests that the decrease of Hg concentrations over time was more likely due to a lower environmental Hg exposure in this region rather than a shift in the feeding habits of Svalbard polar bears.

International audience; Chemical tracers (e.g., stable isotopes or trace metals) are increasingly used to study trophic ecology and feeding habits of marine organisms, while different factors can affect their values. In this context, the aim of this study was to provide information on ontogenic effects on stable carbon and nitrogen values (d13C and d15N), and on cadmium (Cd) and mercury (Hg) concentrations in several cephalopod species from the Bay of Biscay (North-East Atlantic Ocean). To this end, individuals belonging to 3 species showing a wide range of sizes were analysed for muscle d13C and d15N values, muscle Hg and digestive gland Cd concentrations. Results showed that stable isotope ratios allowed discriminating specific feeding strategies during ontogenesis. Segregation between 5 cephalopod species in terms of trophic ecology was also evidenced (different isotopic niches). By contrast, Hg concentrations varied over the same order of magnitude in these 5 cephalopod species, despite higher levels in the benthic octopus Eledone cirrhosa. Consistently, Hg concentrations followed the same ontogenic pattern, as they increased with increasing body size/age of cephalopods. Finally, Cd concentrations varied over 3 orders of magnitude among the 5 species. Despite possible effects of physiology in terms of metal bioaccumulation, Cd concentrations were likely to reflect specific feeding preferences or feeding zones and ontogenic-related variability within a single species. Thus, ontogenetic effects have to be taken into account when stable isotope ratios of carbon and nitrogen or trace metals are used as ecological tracers, the best being to focus on a given class age.