Éditeur(s) :  :
Siècle(s) traité(s) : 19
Droits : Domaine public
Provenance : Collectivité territoriale de Martinique. Bibliothèque Schoelcher
Permalien : http://www.manioc.org/patrimon/SCH13247
SCH13247

Éditeur(s) : EDP Sciences
Résumé : From April 2003 to April 2004 monthly sea surveys were conducted around 2 fish aggregating devices (FADs) moored at 2000 and 2500 m depth in Martinique (Lesser Antilles). The use of a dual frequency splitbeam echosounder combined with an underwater camera and fishing methods allowed assessment of average space and time distribution of pelagic fish aggregated beneath the FADs, as well as identification of their overall size and species composition. At daytime, 4 fish aggregations were identified at each FAD, representing 4 distinct types: i) an aggregation of small juvenile tuna (mean fork length, FL: 30 cm) observed very close to the surface in 25% of daytime periods; ii) a small surface aggregation dominated by carangids, Caranx crysos, present in 65% of daytime periods; iii) a large sub-surface aggregation observed during all daytime periods: this aggregation appeared to be primarily comprised of 58 cm FL blackfin tuna (Thunnus atlanticus), mixed with yellowfin (Thunnus albacares) and skipjack (Katsuwonus pelamis) tunas of the same size; and iv) sub-surface scattered large predators (mainly blue marlin, Makaira nigricans) present in 10% of daytime periods. A smaller sub-surface aggregation comprised of medium tuna mixed with "extranatants" (fishes which remain within 10 to 50 m of a FAD) was observed in 75% of night-time periods, whereas unidentified scattered fishes were detected from 70 to 400 m depth. The low daytime vulnerability of medium sub-surface tunas to applied line techniques leads us to assume that their feeding motivation was low during daytime. These tunas could preferentially feed on mesopelagic organisms during night-time and transition periods around Martinican moored FADs. Local fishermen mainly targeted the large scattered predators using very small tunas as living bait. The sub-surface tuna aggregation hence appeared to be currently unexploited by local fisheries, though it represented the large majority of the pelagic biomass around the moored FADs.
Des campagnes scientifiques mensuelles ont été menées autour de 2 dispositifs de concentration de poissons ancrés à 2000-2500 m de profondeur, en Martinique d'avril 2003 à avril 2004. L'utilisation combinée d'un échosondeur monofaisceau multifréquence, d'une caméra vidéo sous-marine et de techniques de pêche conventionnelles a permis de déterminer la distribution spatio-temporelle moyenne des poissons agrégés autour des DCP ancrés ainsi que la composition générale des agrégations. Les techniques de vidéo sous-marine ont joué un rôle majeur dans l'identification des espèces et l'observation de leur comportement. De jour; quatre types d'agrégations ont été définis : i) une agrégation de thonidés juvéniles (longueur à la fourche, LF, moyenne : 30 cm) observée très près de la surface durant 25 % des périodes diurnes échantillonnées ii) une petite agrégation composée essentiellement de Caranx crysos présente en surface lors de 65 % des phases diurnes iii) une grande agrégation de thons observée en sub-surface lors de toutes les phases diurnes; cette agrégation était constituée essentiellement de thons noirs (Thunnus atlanticus) de 58 cm LF, associés de façon saisonnière à des albacores (Thunnus albacares) et des listaos (Katsuwonus pelamis) de taille similaire iv) des grands prédateurs assez dispersés (essentiellement le marlin bleu, Makaira nigricans), observés lors de 10 % des phases diurnes. Une agrégation de sub-surface, aux dimensions plus réduites et composée de thons et "d'extranatants" (poissons restant à distance de 10 à 50 m du DCP) a été observée lors de 75 % des périodes nocturnes; ainsi que des organismes non-identifiés dispersés entre 70 et 400 m de profondeur. La faible vulnérabilité diurne des thons de sub-surface aux techniques de ligne utilisées indique qu'ils ne se nourrissent pas activement durant la journée. Ces poissons pourraient se nourrir préférentiellement d'organismes mésopélagiques durant les phases de transition et nocturnes autour des DCP ancrés. La pêcherie artisanale martiniquaise n'exploite qu'une faible part des ressources agrégées autour des DCP ancrés. Les principales espèces-cibles sont les grands prédateurs capturés de jour en utilisant des thonidés juvéniles comme appât vivant. L'agrégation de thons de sub-surface représente la grande majorité de la biomasse autour des DCP mais elle est quasiment inexploitée par les pêcheries locales.
Aquatic Living Resources (0990-7440) (EDP Sciences), 2007-10 , Vol. 20 , N. 4 , P. 357-366

Droits : EDP Sciences, IFREMER, IRD 2007
http://archimer.ifremer.fr/doc/2007/publication-3634.pdf
DOI:10.1051/alr:2008004
http://archimer.ifremer.fr/doc/00000/3634/

Éditeur(s) : Londres : T. Woolmer
Siècle(s) traité(s) : 19
Provenance : Archives départementales de Guadeloupe
Permalien : http://www.manioc.org/patrimon/ADG18190
ADG18190

Éditeur(s) : Elsevier
Résumé : Sea cruises were conducted for 57 days over 16 months to characterise pelagic fish aggregations around 2 moored fish aggregating devices (FADs) in Martinique (Lesser Antilles). Echosounder surveys run in a star pattern were used in conjunction with obliquely beamed sonar observations. An echo-integration-by-shoal algorithm was implemented to isolate pelagic fish shoals from sound scattering layers and to compute mean morphometric, positional and density parameters. Tree regressions were used to select and classify pelagic fish Target Strengths (TS), with reference to their spatial and temporal characteristics. The main type of pelagic fish aggregation was a large sub-surface aggregation. It was observed during all daytime periods within a radius of 400 m of the FAD. A smaller type of aggregation was observed closer to the surface and to the FAD in 65% of daytime periods. Large scattered fish were observed in 16% of daytime periods. At night, a medium-sized aggregation was detected in the sub-surface in 75% of night-time periods. The sizes of the fish inside the aggregations (determined from TS values) were lower in the small near-surface aggregation than in the large sub-surface aggregation. Mean packing densities of sub-surface medium fish and near-surface small fish aggregations (determined from TS and shoal acoustic density) were respectively 0.2 fish per m3 and 1.3 fish per m3. The acoustic methodology and results are discussed with reference to the characteristics and performance of the echosounder and to the spatial structure of pelagic fish aggregations around moored FADs in Martinique.
Fisheries Research (0165-7836) (Elsevier), 2006-06 , Vol. 82 , N. 1-3 , P. 162-175

Droits : Elsevier 2006
http://archimer.ifremer.fr/doc/2006/publication-1734.pdf
DOI:10.1016/j.fishres.2006.06.025
http://archimer.ifremer.fr/doc/00000/1734/

Éditeur(s) : Ecole Nationale Supérieure Agronomique de Rennes (ENSAR)
Résumé : Artificial Fish Aggregating Devices (FADs) are known to concentrate tropical tunas. This aggregative behaviour drastically increases the vulnerability of these species to fishing. Alternatively, FADs can be used as oceanic observatories to study the aggregative behaviour of large pelagic fish. We conducted sea surveys in Martinique (Lesser Antilles) to i) establish a typology of the pelagic fish aggregations found around moored FADs ii) study their relations with their biotic and abiotic environment and the local fishery. The mean biomass of large pelagic fish aggregations was also estimated to provide scientific inputs to achieve a sustainable management of the moored FAD fishery. The first part presents the background of the study. We introduce the regional pelagic ecosystem, the aggregative behaviour of pelagic fish around FADs and the Martinican moored FAD fishery. The second part begins with a presentation of the conceptual framework of the study: the hierarchy theory. Observation scales and survey methodology are therefore described. Repeated echosounder surveys run in a star pattern were conducted around 2 moored FADs, in combination with underwater video observations, classical fishing experiments and CTD profiles. In the third part, the elements of the [moored FAD ¿ pelagic fish - environment - fishing] system and their interactions are numerically characterised in the vertical plane. The main type of pelagic fish aggregation was a large aggregation distributed in sub-surface (40-100 m) within a radius of 400 m of the FAD. This aggregation was mostly made of 60 cm FL blackfin tunas (Thunnus atlanticus). It appeared at sunrise and mostly spread away in the late afternoon. It was observed during all daytime surveys. The average density and the vertical structure of the micronektonic sound scattering layers (SSLs) were assessed locally around a FAD for 48h cycles. These SSLs descriptors showed positive correlation with the size and the abundance of the sub-surface tuna aggregation. Whereas this aggregation accounted for about 95% of the total biomass aggregated around a moored FAD, it was nearly unexploited by the local commercial fishermen. The fourth part focuses on the sub-surface tuna aggregation. A high variability of the spatial distribution of the aggregation was evidenced in the horizontal plane at daily, day to day and monthly temporal scales. These variations were related to fluctuations of the global abundance of the aggregation. The daytime average density of sub-surface tuna was modelled as a function of the distance to FAD, within an advection-diffusion framework. Based on these results, a universal kriging model was designed to assess the mean maximum daily biomass of the sub-surface tuna aggregation. This mean biomass estimate yielded 11 tons with an estimation error of 26%. To conclude, we present a hierarchical organization in space and time of a sub-surface tuna population distributed within a network of moored FADs, from micro to meso-scale. We suggest that the spatial distribution of tunas can be explained from fine to coarse-scales by behavioural processes (self-organization, feeding, aggregative behaviour) whereas their spatial distribution is mainly forced by environmental processes at broader scales.
L'utilisation de Dispositifs de Concentration de Poissons permet de provoquer la formation de larges agrégations de thonidés autour de dispositifs artificiels, ce qui augmente considérablement la vulnérabilité de ces ressources vis-à-vis de l'exploitation halieutique. Les DCP peuvent également être utilisés en tant qu'observatoires océaniques, afin d'étudier le comportement agrégatif du macronecton pélagique. Nous avons ainsi réalisé des observations autour de DCP ancrés en Martinique, afin de définir une typologie des agrégations de macronecton et de étudier leurs relations avec leur environnement biotique, abiotique et l'exploitation halieutique locale. Nous avons ensuite estimé la biomasse moyenne de macronecton agrégé autour d'un DCP ancré, afin de fournir des éléments scientifiques nécessaires à une gestion durable de ces ressources. La première partie présente le contexte de l'étude i.e. l'écosystème pélagique régional, le phénomène d'agrégation du macronecton autour des DCP et la pêche associée aux DCP ancrés en Martinique. La deuxième partie introduit la théorie de la hiérarchie qui a fourni le cadre conceptuel de l'étude et présente les échelles et méthodes d'observation. Le principal outil d'observation est un échosondeur scientifique, mis en oeuvre le long de parcours en étoile autour du DCP. Les prospections acoustiques ont été combinées à des observations vidéo sous marines, des pêches expérimentales et un suivi in-situ de l'environnement abiotique. La troisième partie présente une typologie des éléments constituant le système [DCP ancré - macronecton - environnement - pêche] dans le plan vertical et précise leurs interactions. Le type d'agrégation de macronecton dominant est une grande agrégation composée d'une majorité de thons noirs (Thunnus atlanticus) de taille moyenne (60 cm) distribuée en sub-surface (40-100 m), dans un rayon de 300 m autour de la tête des DCP. Cette agrégation se forme au lever du soleil et se disperse presque totalement dans l'après midi. Elle a été observée de jour lors de toutes les campagnes. Une corrélation positive entre la densité et la structure moyenne des couches micronectoniques diurnes évaluée localement autour du DCP au cours de 48 h et les dimensions et l'énergie acoustique de l'agrégation de thons de subs-surface a été mise en évidence. Malgré le fait que cette agrégation représente en moyenne 95 % de l'énergie acoustique du macronecton autour des DCP, elle est presque inexploitée par les pêcheurs artisans locaux. La quatrième partie met en évidence les fortes variations conjointes de la distribution spatiale dans le plan horizontal de la densité de l'agrégation de thons de sub-surface et de son abondance globale. Ces variations ont été observées au cours du cycle nycthéméral et aux échelles inter-journalières et mensuelles. La distribution spatiale moyenne de la densité diurne de l'agrégation en fonction de la distance au centre de gravité de l'agrégation est cependant très stable et peut être modélisée au moyen d'une équation d'advection-diffusion. Un modèle de krigeage universel, utilisant les résultats du modèle d'advection-diffusion, a permis d'évaluer la biomasse maximale journalière moyenne de l'agrégation de thons de sub-surface à une dizaine de tonnes, avec un coefficient de variation d'estimation de 26%. Nous proposons une représentation hiérarchique synthétique de la distribution spatiale d'une sous-population de thons dans un réseau de DCP ancrés de la micro à la méso-échelle. Nous suggérons que la distribution spatiale des thons est déterminée principalement à l'échelle fine (100m-1km) et à l'échelle grossière (1-10 km) par des processus comportementaux (auto-organisation, agrégation, nutrition) et par des processus environnementaux à échelle plus large.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2006/these-1735.pdf
http://archimer.ifremer.fr/doc/2006/sup-1735.pdf
http://archimer.ifremer.fr/doc/00000/1735/

Éditeur(s) : Elsevier Science Bv
Résumé : Total lipid content and lipid class composition were analyzed in gonads, liver and white muscle of yellowfin tuna (Thunnus albacares) throughout ovary development to understand its reproductive allocation strategy and to assess the relation between female condition and reproduction. A total of 112 females were collected onboard purse-seiner in the Western Indian Ocean from January to March 2009, from June to July 2009, and from April to May 2010. Gonads were characterized by highly variable total lipid contents ranging from 5 to 27 μg mg−1 of wet weight (ww) with a predominance of neutral lipids, mainly triacylglycerols (TAG) and sterol- and wax-esters. The different lipid classes in gonads described an accumulative pattern through the maturity process from immature to hydration phase. Total lipid content in liver varied from 10 to 21 μg mg−1 ww, and serves as fuel for yellowfin tuna reproduction. TAG and phospholipid deposits became depleted as the ovary developed, suggesting a transfer of lipids directly from liver to the oocytes during vitellogenesis. In contrast, muscle total lipid content was low and constant throughout ovarian development (2.5–6 μg mg−1 ww). Hence, yellowfin tuna can be defined as an income-capital breeder species for which the cost of reproduction depends mainly on concurrent energy income from feeding and only little on stored lipids. Besides, no significant relationship between gonad lipid composition and fecundity was found in females able to spawn. Finally, the influence of yellowfin tuna aggregation behaviour on reproductive female condition has been investigated: gonad total lipid contents were higher in females caught in free-swimming schools than in females caught under fish aggregating devices (FADs). However, these results did not clarify whether the influence of FADs on associated yellowfin tuna affects their reproductive capacity.
Fisheries Research (0165-7836) (Elsevier Science Bv), 2014-12 , Vol. 160 , P. 50-59

Droits : 2013 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00171/28266/28075.pdf
DOI:10.1016/j.fishres.2013.12.010
http://archimer.ifremer.fr/doc/00171/28266/

Éditeur(s) : Université Paris 6
Résumé : The aggregative behaviour of the dolphinfish (Coryphaena hippurus) is studied in order to improve our knowledge of the mechanism involved in the association of this species with the floating objects and to evaluate its potential impact in term of exploitation, targeted or not. This PhD thesis is composed of four chapters. Through an extensive analyze of the literature, the first chapter takes stock of the present knowledge on the FADs, on the aggregative behaviour of pelagic fish and on the dolphinfish. The second chapter deals specifically with the aggregative behaviour of the dolphinfish by the way of acoustic tagging of fish carry out during offshore campaigns around drifting FADs. The feeding habits of the dolphinfish around FADs are the main purpose of the third chapter. It is studied by the way of two complementary methods : stomach contains analysis of dolphinfish aggregated around several types of floating objects and underwater inventory of the marine fauna under these floating objects. Finally, the fourth and last chapter sums all the results and suggests a theory to explain the aggregative behaviour of the dolphinfish. We also try to estimate the possible consequences of this behaviour on the abundance and on the distribution of this species on a larger scale.
Le comportement agrégatif de la dorade coryphène (Coryphaena hippurus) est étudié dans le but de mieux comprendre le déterminisme de l'association de cette espèce avec les objets flottants et d'en évaluer les impacts potentiels en terme de sensibilité à l'exploitation halieutique, qu'elle soit ciblée ou non. Ce mémoire de thèse est organisé en quatre chapitres. A travers une analyse approfondie de la bibliographie, le premier chapitre présente un bilan des connaissances actuelles sur les DCP, l'agrégation des poissons pélagiques et la dorade coryphène. Le second chapitre traite plus spécifiquement du comportement agrégatif de la dorade coryphène. Il a été abordé à l'aide de marquages électroniques réalisés au cours de campagnes hauturières autour de DCP dérivants. Le comportement trophique de la dorade coryphène fait l'objet du troisième chapitre. Il est abordé par l'utilisation conjointe de deux méthodes d'investigation : l'analyse des contenus stomacaux de dorades coryphènes agrégées sous divers types d'objets flottants et la réalisation d'inventaires faunistiques sous-marins autour de ces objets flottants. Enfin, le quatrième et dernier chapitre synthétise l'ensemble des résultats obtenus, propose une théorie du comportement agrégatif de la dorade coryphène et tente d'évaluer les conséquences possibles de ce comportement sur la distribution et l'abondance de l'espèce à grande échelle.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2004/these-323.pdf
http://archimer.ifremer.fr/doc/00000/323/

Éditeur(s) : Pêche thonière et dispositifs de concentration de poissons, Caribbean-Martinique, 15-19 Oct 1999
Résumé : Tuna world fisheries yield 3 million tons per year; the increase rate of whole production is constant and sustained since 30 years. This original figure for marine fisheries is due to enlargement of tuna fleets and fishing grounds over all the world ocean, the continuous increase of tuna fishing power by in board equipment and remote sensing equipment for searching and scouting (on board, aircraft, satellite, telecommunication_). During the last 20 years, the log-associated tuna fishing has contributed to the local individual and tuna fleets efficiency and fishing power either for large industrial tuna seiners by radio-equipped buoys on natural (debris) or artificial man-made logs. The same trend is noted for numerous artisanal tuna and large pelagic coastal fisheries on moored fishing aggregating devices and networks. The first part of the paper is a review of data and results to assess and rank the "Surfaces prospected by in board tuna seiners and associated aircraft and satellite technics" (visual, radar, sar-radar and satellite altimetry sensors). The final objective is the comparison with the surfaces and volumes associated to fads. Since 20 years, tuna ecology and behaviour data from ultrasonic tagging (short-term depth/distance/time migration around logs and fads) are used for fishing of tuna associated with floating objects, namely fads. The second part of this paper is an "Assessment of fad's aggregating associated surface and volume" linked with oceanographic data: large oceanic geostrophic current and observed drift speed of radio-equipped fads in the Indian Ocean. Using the available data on fads, tuna fishing technology linked with oceanographic and biological data results from ultrasonic tuna tracking experiments, the paper is an attempt to identify and place the fads technology in the scale of tuna fishing devices as a contribution to the increase of tuna fishing power either individual tuna boat or tuna fleets.Original Abstract: La production mondiale des pecheries thonieres est actuellement de l'ordre de 3 millions de tonnes par an et conserve depuis pres de 50 ans un taux de croissance annuel soutenu. Cette croissance, exceptionnelle pour un secteur des peches maritimes, est due a plusieurs causes: accroissement des effectifs et des puissances de peche des grandes flottes thonieres industrielles oceaniques qui exploitent les ressources thonieres de l'ocean mondial et le developpement conjoint de nouvelles techniques de peche et de nouvelles technologies d'aide a la peche, telles que les dispositifs de concentration de poissons (DCP). L'accroissement de la puissance individuelle des navires est du au developpement de la construction navale (mecanisation, propulsion, hydraulique, conservation et traitement a borda) et a l'utilisation d'une gamme diversifiee d'aides a la peche : navigation, telecommunication, localisation des zones favorables, detection visuelle ou radiometrique assistee par equipement a bord, en helicoptere et avion, detection acoustique, detection par radar de bord, radar-avion ou, a terme, antenne SAR sur satellite. Plus recemment, soit depuis 20 ans, les caracteristiques du comportement, migration de court terme, agregation et concentration des poissons pelagiques, fixation et retention des bancs de thons, sont utilisees, par les dispositifs de concentration de poissons (DCP) ancres ou derivants. Cette contribution a pour objectif de situer et placer les DCP fixes ou derivants sur cet ensemble de techniques d'aide a la peche thoniere. Les donnees pour cet essai de classement sont d'ordres biologique, ethologique et comportementaux (amplitude de deplacement des thons et dimension de la sphere d'attraction d'un DCP) et d'ordres environnemental et oceanographique : masse d'eau concernee par un DCP dans une large veine de courant oceanique ou cotier. On tente de quantifier et d'ordonner les surfaces et les volumes prospectes par les thoniers et particulierement les volumes et masses d'eau exploites par les thoniers utilisant des DCP. Ce classement des DCP dans la serie des dispositifs d'aide a la peche thoniere facilitera l'appreciation de leur contribution a l'augmentation des puissances de peche des thoniers.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00042/15297/12656.pdf
http://archimer.ifremer.fr/doc/00042/15297/

Éditeur(s) : Londres : Sampson Law, Marston, Searle & Rivington
Siècle(s) traité(s) : 19
Provenance : Archives départementales de Guadeloupe
Permalien : http://www.manioc.org/patrimon/ADG18114
ADG18114

Éditeur(s) : Wiley-blackwell
Résumé : 1. Approximately 300 pelagic fish species naturally aggregate around floating objects (FOBs) at the surface of the oceans. Currently, more than 50% of the world catch of tropical tuna comes from the industrial tuna fisheries around drifting FOBs. Greater understanding of the complex decision-making processes leading to this aggregation pattern and the impact of the massive release of artificial FOBs by fishermen on the spatial distribution and management of tuna is needed. 2. We analyse how the interplay between social (relationships between individuals) and non-social (responses to the environment) behaviours may affect the spatial distribution of a population in a multi-FOB environment. Taking the example of tropical tunas associating with FOBs and using differential equations and stochastic simulations, we examine how, when increasing the number of FOBs, fish aggregation dynamics and the distribution of the population among patches are affected by the population size, level of sociality and the natural retentive and/or attractive forces of FOBs on individual tuna. 3. Our model predicts that, depending on the species' level of sociality, fish will be scattered among FOBs or aggregated around a single FOB based on the number of FOBs deployed in a homogeneous oceanic region. 4. For social species, we demonstrated that the total fish catch is reduced with increasing FOBs number. Indeed, for each size of population, there are a number of FOBs minimizing the total population of fish associated with FOBs and another number of FOBs maximizing the total population of associated fish. 5. Synthesis and applications. In terms of fisheries management, the total catch volume is directly linked to the total number of floating objects (FOBs) for non-social species, and any limit on the number of sets would then result in a limit on the total catch. For social species (e.g. tuna), however, increasing the number of FOBs does not necessarily lead to an increase in the total catch, which is a non-intuitive result. Indeed, our model shows that, for specific values of the parameters, deploying a greater number of FOBs in the water (all other parameters being constant) does not necessarily help fishermen to catch more tuna, but does increase the level of fishing effort and bycatch.
Journal Of Applied Ecology (0021-8901) (Wiley-blackwell), 2013-10 , Vol. 50 , N. 5 , P. 1081-1092

Droits : 2013 The Authors. Journal of Applied Ecology, 2013 British Ecological Society
http://archimer.ifremer.fr/doc/00151/26275/24439.pdf
DOI:10.1111/1365-2664.12140
http://archimer.ifremer.fr/doc/00151/26275/

Éditeur(s) : Pêche thonière et dispositifs de concentration de poissons, Caribbean-Martinique, 15-19 Oct 1999
Résumé : Since 1980 a programme of Fish Aggregation Device (fad) deployment has been carried out in the Cook Islands. Government has deployed all fads between 1 to 3 nautical miles from shore at depths ranging from 800 to 1,600 metres. The fads have undergone various designs with varying degrees of success. The average fad lifespan during the early 1980s was nine months; however, it increased to 18 months, with some fads in operation in excess of 30 months. Each fad cost between nz$ 7,000 and nz$ 9,000 to build and deploy. Since their introduction, fad have been widely accepted as a very effective apparatus in coastal small-scale fishing activities, specifically for pelagic species. Judging by the progressive behaviour of local fishing communities, there is sufficient reason to believe that fads have created productive fishing zones for Cook Islands fishermen to enable them to supply the ever-increasing local market for fresh fish. fads are an integral part of local fishing communities and provide a reasonable form of income to the increasing fishing community.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00042/15323/12654.pdf
http://archimer.ifremer.fr/doc/00042/15323/

Éditeur(s) : London : printed by Richard Taylor
Résumé : 1823
Siècle(s) traité(s) : 19
Droits : Domaine public
Provenance : Ville de Pointe-à-Pitre. Réseau des bibliothèques
Permalien : http://www.manioc.org/patrimon/PAP11212
PAP11212

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Talc is a hydrous magnesium rich layered silicate that is widely disseminated in the Earth from the seafloor to over 100 km depth, in ultra-high pressure metamorphism of oceanic crust. In this paper we determine the single crystal elastic constants at pressures from 0 to 12 GPa of talc triclinic (C 1¯) and monoclinic (C2/c) polytypes using ab initio methods. We find that talc has an extraordinarily high elastic anisotropy at zero pressure that reduces with increasing pressure. The exceptional anisotropy is complemented by a negative Poisson's ratio for many directions in crystal space. Calculations show that talc is not only one of very few common minerals to exhibit auxetic behaviour, but the magnitude of this effect may be the largest reported so far for a mineral. The compression (Vp) and shear (Vs) wave velocity anisotropy is 80% and 85% for the triclinic polytype. At pressures where talc is known be stable in the Earth (up to 5 GPa) the Vp and Vs anisotropy is reduced to about 40% for both velocities, which is still a very high value. Vp is slow parallel to the c-axis and fast perpendicular to it. This remains unchanged with increasing pressure and is observed in both polytypes. The shear wave splitting (difference between fast and slow S-wave velocities) at low pressure has high values in the plane normal to the c-axis, with a maximum near the alow asterisk-axis in the triclinic and the b-axis in the monoclinic polytype. The c-axis is the direction of minimum splitting. The pattern of shear wave splitting does not change significantly with pressure. The volume fraction of talc varies between 11 and 41% for hydrated mantle rocks, but the lack of data on the crystallographic preferred orientation (CPO) precludes a detailed analysis of the impact of talc on seismic anisotropy in subduction zones. However, it is highly likely that CPO can easily develop in zones of deformation due to the platy habit of talc crystals. For random aggregates of talc, the isotropic Vp, Vs and Vp/Vs ratio have significantly lower values than those of antigorite and may explain low-velocity regions in the mantle wedge. Vp/Vs ratios are more complex in anisotropic media because there are fast and slow S-waves, resulting in Vp/Vs1 and Vp/Vs2 ratios for every propagation direction, making interpretation difficult in deformed polycrystalline talc with a CPO. Talc on the subduction plate boundary can strongly influence guided wave velocity as CPO would develop in this region of intense shearing. The very low coefficient of friction (< 0.1) of talc above 100 °C could also explain silent earthquakes at shallow depths (ca 30 km) along the subduction plate boundaries, frequently responsible for tsunami.
ISSN: 0012-821X

hal-00411481
https://hal.archives-ouvertes.fr/hal-00411481
DOI : 10.1016/j.epsl.2008.07.047

Éditeur(s) : Pêche thonière et dispositifs de concentration de poissons, Caribbean-Martinique, 15-19 Oct 1999
Résumé : Approximately 4,000 petroleum (oil and gas) platforms exist in the northern Gulf of Mexico and form one of the world's most extensive de facto artificial reef systems. Collectively, these structures may comprise one of the largest fad (Fish Aggregating Device) arrays in the world, attracting surface and midwater pelagic fishes. The diverse composition of pelagic fish fauna at ngom platforms is described and includes valued species such as Thunnus albacares, Thunnus atlanticus, Coryphaena hippurus, Acanthocybium solandri, Rachycentron canadum, Seriola dumerili, Scomberomorus cavalla, and Decapterus punctatus. Petroleum platforms influence pelagic fishery resources and are an important component of the Gulf's commercial and recreational fishing industries. Reviewed literature revealed a sparsity of fundamental knowledge of densities, temporal and spatial occurrence, and fishing effort/catch rates of pelagic fishes at platforms. The role of Gulf petroleum platforms "as fads" is examined, possible mechanisms for aggregation are reviewed, and a synopsis of the author's preliminary findings on life history aspects of A. solandri and R. canadum from platforms is presented. It is proposed that platforms provide opportunities for the study of pelagic species to better understand the life history, ecology, behaviour, and habitat requirements of pelagic fishery resources in the Gulf of Mexico.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00042/15301/12633.pdf
http://archimer.ifremer.fr/doc/00042/15301/

Éditeur(s) : Londres : John Stockolale
Siècle(s) traité(s) : 18
Droits : Domaine public
Provenance : Archives départementales de Guadeloupe
Permalien : http://www.manioc.org/patrimon/ADG17063
ADG17063

Éditeur(s) :  :
Siècle(s) traité(s) : 19
Droits : Domaine public
Provenance : Collectivité territoriale de Martinique. Bibliothèque Schoelcher
Permalien : http://www.manioc.org/patrimon/SCH13246
SCH13246

Éditeur(s) :  :
Siècle(s) traité(s) : 19
Droits : Domaine public
Provenance : Collectivité territoriale de Martinique. Bibliothèque Schoelcher
Permalien : http://www.manioc.org/patrimon/SCH13245
SCH13245

Éditeur(s) : Pêche thonière et dispositifs de concentration de poissons, Caribbean-Martinique, 15-19 Oct 1999
Résumé : For most fisheries, increasing the local production of pelagic fish is the main objective of Fish Aggregating Devices (fads). This does not rule out the existence of a larger-scale impact, especially on the migratory behaviour of fish. The analysis of data collected during 25 experimental fishing surveys around Martinique between 1995 and 1997 has led to the hypothesis that fads influence the migratory behaviour of young dolphinfish. Unlike recent studies of dolphinfish migration in the Caribbean, which tend to show an annual migration pattern with a seasonal passage through the French West Indies, the experimental fishing surveys done over more than a year on a monthly basis on a single cohort, show that the migratory pattern of part of the regional stock could be disrupted. This analysis has made it possible to estimate an average growth rate for this species during the first year of life.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00042/15321/12635.pdf
http://archimer.ifremer.fr/doc/00042/15321/

Éditeur(s) : Pêche thonière et dispositifs de concentration de poissons, Caribbean-Martinique, 15-19 Oct 1999
Résumé : Fishing with a beach seine for catching small pelagic fishes is a traditional activity in Martinique. Since the early eighties, an important decrease in the number of fishermen practising this activity has been recorded. In the context of high exploitation of reef resources, the beach seine presents a low selectivity, catching too many juveniles of demersal fish. The fads established in coastal areas, have been successfully used in others regions of the world for exploiting small pelagics. Thus, it could allow to favour a change of exploitation style of these resources in Martinique. In partnership, Ifremer, the Regional Council and the Fishing Committee have began an evaluation of the potentialities for this type of structures around the island. To achieve this study, several experimental coastal fads have been established in different places. Surveys by subaquatic observations are periodically carried out to compare the attractive power of different aggregation devices (colour, shape, volume) and understand the factors influencing the determinism of the aggregation (biotic and abiotic). The results presented and discussed correspond to the initial stage of this study which should be pursued in the next months.Original Abstract: La peche a la senne de plage pour la capture des petits poissons pelagiques est une activite halieutique traditionnelle et ancienne en Martinique. Depuis le debut des annees quatre-vingt, une diminution importante du nombre de pecheurs pratiquant cette activite est enregistree. Les dispositifs de concentration de poissons (DCP) implantes en zone cotiere sont abondamment utilises dans d'autres regions du monde avec succes. Ils pourraient donc permettre de redynamiser ce secteur en Martinique. L'Ifremer, le conseil regional et le comite des peches ont entrepris, en partenariat, une etude permettant d'evaluer les potentialites du developpement de ce type d'amenagement autour de l'ile. Pour realiser cette etude, plusieurs DCP cotiers experimentaux ont ete implantes dans differents sites. Ils font l'objet d'un suivi halieutique base sur les comparaisons des captures realisees par les professionnels sur et hors DCP. En parallele, des campagnes d'observations sous-marines sont effectuees de facon periodique. Elles permettent d'une part de comparer les pouvoirs attractifs de differents dispositifs d'agregation (forme, volume, couleur) et, d'autre part, de mieux comprendre les facteurs biotiques et abiotiques influencant le determinisme de l'agregation. Les resultats presentes et discutes correspondent a la phase initiale de l'etude qui doit se poursuivre dans les prochains mois afin de couvrir toute la saison de peche.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00042/15302/12634.pdf
http://archimer.ifremer.fr/doc/00042/15302/

Éditeur(s) :  :
Siècle(s) traité(s) : 19
Droits : Domaine public
Provenance : Collectivité territoriale de Martinique. Bibliothèque Schoelcher
Permalien : http://www.manioc.org/patrimon/SCH13244
SCH13244