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Registros recuperados: 11
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Contrasted optimal environmental windows for both sardinella species in Senegalese waters ArchiMer
Diankha, Ousmane; Ba, Aliou; Brehmer, Patrice; Brochier, Timothee; Sow, Bamol Ali; Thiaw, Modou; Gaye, Amadou Thierno; Ngom, Fambaye; Demarcq, Herve.
We investigate Sardinella aurita and Sardinella maderensis recruitment success relative to the variability of oceanographic conditions in Senegalese waters using generalized additive models (GAM). Results show that recruitment of both species is marked by a strong intra-annual (seasonal) variation with minimum and maximum in winter and summer, respectively. Their interannual variations are synchronous until 2006 (recruitment decreasing), while from 2007 there is no synchrony. The model developed shows that sardinella recruitment variability is closely related to the tested environmental variables in the study area. However, the key environmental variables influencing the recruitment success are different for both species: the Coastal Upwelling Index and...
Tipo: Text Palavras-chave: Recruitment success; Sardinella aurita; Sardinella maderensis; Upwelling; West Africa.
Ano: 2018 URL: https://archimer.ifremer.fr/doc/00611/72299/71189.pdf
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Co-Occurrence and Habitat Use of Fin Whales, Striped Dolphins and Atlantic Bluefin Tuna in the Northwestern Mediterranean Sea ArchiMer
Bauer, Robert; Fromentin, Jean-marc; Demarcq, Herve; Brisset, Blandine; Bonhommeau, Sylvain.
Different dolphin and tuna species have frequently been reported to aggregate in areas of high frontal activity, sometimes developing close multi-species associations to increase feeding success. Aerial surveys are a common tool to monitor the density and abundance of marine mammals, and have recently become a focus in the search for methods to provide fisheries-independent abundance indicators for tuna stock assessment. In this study, we present first density estimates corrected for availability bias of fin whales (Balaenoptera physalus) and striped dolphins (Stenella coeruleoalba) from the Golf of Lions (GoL), compared with uncorrected estimates of Atlantic bluefin tuna (ABFT; Thunnus thynnus) densities from 8 years of line transect aerial surveys. The...
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Ano: 2015 URL: https://archimer.ifremer.fr/doc/00284/39481/37969.pdf
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Defining Mediterranean and Black Sea Biogeochemical Subprovinces and Synthetic Ocean Indicators Using Mesoscale Oceanographic Features ArchiMer
Nieblas, Anne-elise; Drushka, Kyla; Reygondeau, Gabriel; Rossi, Vincent; Demarcq, Herve; Dubroca, Laurent; Bonhommeau, Sylvain.
The Mediterranean and Black Seas are semi-enclosed basins characterized by high environmental variability and growing anthropogenic pressure. This has led to an increasing need for a bioregionalization of the oceanic environment at local and regional scales that can be used for managerial applications as a geographical reference. We aim to identify biogeochemical subprovinces within this domain, and develop synthetic indices of the key oceanographic dynamics of each subprovince to quantify baselines from which to assess variability and change. To do this, we compile a data set of 101 months (2002-2010) of a variety of both "classical'' (i.e., sea surface temperature, surface chlorophyll-a, and bathymetry) and "mesoscale'' (i.e., eddy kinetic energy,...
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Ano: 2014 URL: http://archimer.ifremer.fr/doc/00239/34995/33536.pdf
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Density dependence, prey accessibility and prey depletion by fisheries drive Peruvian seabird population dynamics ArchiMer
Barbraud, Christophe; Bertrand, Arnaud; Bouchon, Marilu; Chaigneau, Alexis; Delord, Karine; Demarcq, Herve; Gimenez, Olivier; Gutierrez Torero, Mariano; Gutierrez, Dimitri; Oliveros Ramos, Ricardo; Passuni, Giannina; Tremblay, Yann; Bertrand, Sophie.
In marine ecosystems top predator populations are shaped by environmental factors affecting their prey abundance. Coupling top predators' population studies with independent records of prey abundance suggests that prey fluctuations affect fecundity parameters and abundance of their predators. However, prey may be abundant but inaccessible to their predators and a major challenge is to determine the relative importance of prey accessibility in shaping seabird populations. In addition, disentangling the effects of prey abundance and accessibility from the effects of prey removal by fisheries, while accounting for density dependence, remains challenging for marine top predators. Here, we investigate how climate, population density, and the accessibility and...
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Ano: 2018 URL: https://archimer.ifremer.fr/doc/00450/56117/57647.pdf
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Detection of mesoscale thermal fronts from 4km data using smoothing techniques: Gradient-based fronts classification and basin scale application ArchiMer
Roa Pascuali, Liliana; Demarcq, Herve; Nieblas, Anne-elise.
In order to optimize frontal detection in sea surface temperature fields at 4 km resolution, a combined statistical and expert-based approach is applied to test different spatial smoothing of the data prior to the detection process. Fronts are usually detected at 1 km resolution using the histogram-based, single image edge detection (SIED) algorithm developed by Cayula and Cornillon in 1992, with a standard preliminary smoothing using a median filter and a 3 × 3 pixel kernel. Here, detections are performed in three study regions (off Morocco, the Mozambique Channel, and north-western Australia) and across the Indian Ocean basin using the combination of multiple windows (CMW) method developed by Nieto, Demarcq and McClatchie in 2012 which improves on the...
Tipo: Text Palavras-chave: Mesoscale thermal fronts; Preliminary smoothing; Sea surface temperature; 4 km resolution; Gradient intensity classification; Expert-based approach; Detection efficiency; Indian Ocean.
Ano: 2015 URL: http://archimer.ifremer.fr/doc/00269/37998/42023.pdf
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Etude de la zone de dilution rhodanienne, observations des zones de production dans le golfe du Lion et estimation de l'éclairement solaire global en Méditérranée occidentale ArchiMer
Demarcq, Herve.
Les images satellitaires fournissent une vue synoptique de la zone d'étude, difficilement réalisable à partir des moyens de prospection à la mer. De plus, la répétitivité des observations à partir de l'espace, de l'ordre de quelques jours, ou moins, permet d'étudier l'évolution spatio-temporelle, souvent rapide, des phénomènes marins observés. Ces caractéristiques de la mesure satellitaire ont été exploitées pour mettre en évidence quelques phénomènes dynamiques et biologiques se déroulant en Méditerranée nord-occidentale, et plus particulièrement dans le golfe du Lion.
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Ano: 1985 URL: http://archimer.ifremer.fr/doc/00105/21644/19225.pdf
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Fine-scale recognition and use of mesoscale fronts by foraging Cape gannets in the Benguela upwelling region ArchiMer
Sabarros, Philippe S.; Gremillet, David; Demarcq, Herve; Moseley, Christina; Pichegru, Lorien; Mullers, Ralf H. E.; Stenseth, Nils C.; Machu, Eric.
Oceanic structures such as mesoscale fronts may become hotspots of biological activity through concentration and enrichment processes. These fronts generally attract fish and may therefore be targeted by marine top-predators. In the southern Benguela upwelling system, such fronts might be used as environmental cues by foraging seabirds. In this study we analyzed high-frequency foraging tracks (GPS, 1 s sampling) of Cape gannets Morus capensis from two colonies located on the west and east coast of South Africa in relation to mesoscale fronts detected on daily high-resolution chlorophyll-a maps (MODIS, 1 km). We tested the association of (i) searching behavior and (ii) diving activity of foraging birds with mesoscale fronts. We found that Cape gannets shift...
Tipo: Text Palavras-chave: Seabird; Environmental cue; Behavioral shift; Area-restricted search; Feeding activity; Fractal landscape; Oceanographic fronts; Morus capensis; Southern Benguela; South Africa.
Ano: 2014 URL: https://archimer.ifremer.fr/doc/00236/34756/34575.pdf
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Habitat use, vertical and horizontal behaviour of Atlantic bluefin tuna ( Thunnus thynnus ) in the Northwestern Mediterranean Sea in relation to oceanographic conditions ArchiMer
Bauer, Robert Klaus; Fromentin, Jean-marc; Demarcq, Herve; Bonhommeau, Sylvain.
We investigated the habitat utilization, vertical and horizontal behaviour of Atlantic bluefin tuna Thunnus thynnus (ABFT) in relation to oceanographic conditions in the northwestern Mediterranean Sea, based on 36 pop-up archival tags and different environmental data sets. Tags were deployed on early mature ABFT (127–255 cm) between July and November in 2007-2014, on the shelf area off Marseille, France. The data obtained from these tags provided 1643 daily summaries of ABFT vertical behaviour over 8 years of tag deployment. Based on a hierarchical clustering of this data, we could identify four principle daily vertical behaviour types, representing surface (≦10m) and subsurface (10–100 m) orientation, moderate (50–200 m) and deep (≧200m) diving behaviour....
Tipo: Text Palavras-chave: Thunnus thynnus; Habitat use; Spike dives; Fronts; Thermal stratification; Archival tags.
Ano: 2017 URL: http://archimer.ifremer.fr/doc/00382/49329/49709.pdf
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Satellite remote sensing for an ecosystem approach to fisheries management ArchiMer
Chassot, Emmanuel; Bonhommeau, Sylvain; Reygondeau, Gabriel; Nieto, Karen; Polovina, Jeffrey J.; Huret, Martin; Dulvy, Nicholas K.; Demarcq, Herve.
Satellite remote sensing (SRS) of the marine environment has become instrumental in ecology for environmental monitoring and impact assessment, and it is a promising tool for conservation issues. In the context of an ecosystem approach to fisheries management (EAFM), global, daily, systematic, high-resolution images obtained from satellites provide a good data source for incorporating habitat considerations into marine fish population dynamics. An overview of the most common SRS datasets available to fishery scientists and state-of-the-art data-processing methods is presented, focusing on recently developed techniques for detecting mesoscale features such as eddies, fronts, filaments, and river plumes of major importance in productivity enhancement and...
Tipo: Text Palavras-chave: Ecosystem approach; Fisheries; Mesoscale; Satellite; Tracking.
Ano: 2011 URL: http://archimer.ifremer.fr/doc/00031/14188/11468.pdf
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Spatio-Temporal Dynamics of Exploited Groundfish Species Assemblages Faced to Environmental and Fishing Forcings: Insights from the Mauritanian Exclusive Economic Zone ArchiMer
Kide, Saikou Oumar; Mante, Claude; Dubroca, Laurent; Demarcq, Herve; Merigot, Bastien.
Environmental changes and human activities can have strong impacts on biodiversity and ecosystem functioning. This study investigates how, from a quantitative point of view, simultaneously both environmental and anthropogenic factors affect species composition and abundance of exploited groundfish assemblages (i.e. target and non-target species) at large spatio-temporal scales. We aim to investigate (1) the spatial and annual stability of groundfish assemblages, (2) relationships between these assemblages and structuring factors in order to better explain the dynamic of the assemblages’ structure. The Mauritanian Exclusive Economic Zone (MEEZ) is of particular interest as it embeds a productive ecosystem due to upwelling, producing abundant and diverse...
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Ano: 2015 URL: https://archimer.ifremer.fr/doc/00288/39945/38493.pdf
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Studying the contribution of different fishing gears to the Sardinella small-scale fishery in Senegalese waters ArchiMer
Diankha, Ousmane; Demarcq, Herve; Fall, Massal; Thiao, Djiga; Thiaw, Modou; Sow, Bamol Ali; Gaye, Amadou Thierno; Brehmer, Patrice.
This study investigated variations of landings of two key species, Sardinella aurita and Sardinella maderensis, in Senegalese waters over a ten-year period (2004-2013). Using generalized additive models, it was found that fishing gear played a major role in explaining differences in monthly landings for both species (51-71% deviance explained). Its effect was more significant in the southern part of Senegal. Fishing effort (number of trips) accounted only for 4-18% of variability in landings. Purse seine (PS) fishing was the most important contributor to the landings of both species. In addition, in the southern area, surrounding gillnet fishing was also important for S. maderensis. Modeling results showed that the relationship between monthly effort and...
Tipo: Text Palavras-chave: Effects of fishing; Generalized additive model; Sardinella aurita; Sardinella maderensis; Purse seine; Surrounding gillnet; Senegal.
Ano: 2017 URL: https://archimer.ifremer.fr/doc/00616/72808/72585.pdf
Registros recuperados: 11
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