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Auteur Eduardo Nole, L.; Bertrand, A.; Mincarone, M.M.; Santos, L.; Fredou, T.; Assuncao, R.; Silva, A.; Menard, F.; Schwamborn, R.; Le Loc'h, F.; Lucena-Fredou, F. doi  openurl
  Titre Hatchetfishes (Stomiiformes: Sternoptychidae) biodiversity, trophic ecology, vertical niche partitioning and functional roles in the western Tropical Atlantic Type Article scientifique
  Année 2020 Publication Revue Abrégée Prog. Oceanogr.  
  Volume 187 Numéro Pages 102389  
  Mots-Clés Brazil; central equatorial atlantic; diet; Diet; Dissolved oxygen; feeding patterns; Gelatinous organisms; Mesopelagic; mesopelagic fishes; midwater fish; Oceanic islands; organic-matter; Seamounts; Stable isotope composition; stable-isotopes; stomiid pisces; yellowfin tuna; zooplankton  
  Résumé Species of the family Sternoptychidae (hatchetfishes) occur worldwide and play critical roles by sequestering carbon, recycling nutrients, and acting as a key trophic link between epipelagic primary consumers and higher trophic levels in marine ecosystems. Nevertheless, basic knowledge on their ecology is still lacking and their functional ecology remains understudied with respect to composition, organization, functions and environment interactions. Here we integrated comprehensive information collected in the western Tropical Atlantic on the diversity, abundance, distribution and trophic ecology of hatchetfishes, including physicochemical features of their habitats and extensive carbon and nitrogen stable isotope data on its main prey groups. On this basis we defined five functional groups of hatchetfishes with different diet preference, isotopic composition, and vertical abundance peaks and reveal a possible high resource partitioning. Additionally, these species might have a different feeding tie chronology. Hence, hatchetfishes segregate in different ecological groups responding differently to environmental constraints including oxygen concentration and presenting diverse functional roles. As deep-sea species that migrate to epipelagic waters, hatchetfishes may play a key role in the transfer of subsurface photoassimilated carbon to deeper waters, a pathway through which the effects of climate change at the surface are transferred to the deep ocean. Moreover, as consumers of gelatinous organisms, these species convert “gelatinous energy” into “fish energy” readily usable by higher trophic levels, including endangered and commercially important species. This is a crucial trophic relationship that has been historically underestimated due to methodology limitations (e.g., quickly digested gelatinous organisms were probably underestimated in previous studies, based solely on stomach contents). Considering in ecosystem models this trophic relationship, as well as the functional organization of hatchetfishes, is important to properly answer key ecological questions including resource use, carbon transportation, and influence of mesopelagic community in climate change process.  
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  ISSN 0079-6611 ISBN Médium  
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Auteur Dortel, E.; Pecquerie, L.; Chassot, E. doi  openurl
  Titre A Dynamic Energy Budget simulation approach to investigate the eco-physiological factors behind the two-stanza growth of yellowfin tuna (Thunnus albacares) Type Article scientifique
  Année 2020 Publication Revue Abrégée Ecol. Model.  
  Volume 437 Numéro Pages 109297  
  Mots-Clés Behavioral changes; bioenergetics; bluefin tuna; Body-size scaling; DEB theory; fisheries; indian-ocean; management; Ontogeny; populations; rates; stable-isotopes; temperature; tropical tuna  
  Résumé The growth of yellowfin tuna has been the subject of considerable research efforts since the early 1960s. Most studies support a complex two-stanza growth pattern with a sharp acceleration departing from the von Bertalanffy growth curve used for most fish populations. This growth pattern has been assumed to result from a combination of physiological, ecological and behavioral factors but the role and contribution of each of them have not been addressed yet. We developed a bioenergetic model for yellowfin tuna in the context of Dynamic Energy Budget theory to mechanistically represent the processes governing yellowfin tuna growth. Most parameters of the model were inferred from Pacific bluefin tuna using body-size scaling relationships while some essential parameters were estimated from biological data sets collected in the Indian Ocean. The model proved particularly suitable for reproducing the data collected during the Pacific yellowfin tuna farming experience conducted by the Inter-American Tropical Tuna Commission at the Achotines Laboratory in Panama. In addition, model predictions appeared in agreement with knowledge of the biology and ecology of wild yellowfin tuna. We used our model to explore through simulations two major assumptions that might explain the existence of growth stanzas observed in wild yellowfin tuna: (i) a lower food supply during juvenile stage in relation with high infra- and inter-species competition and (ii) ontogenetic changes in food diet. Our results show that both assumptions are plausible although none of them is self-sufficient to explain the intensity of growth acceleration observed in wild Indian Ocean yellowfin tuna, suggesting that the two factors may act in concert. Our study shows that the yellowfin growth pattern is likely due to behavioral changes triggered by the acquisition of physiological abilities and anatomical traits through ontogeny that result in a major change in intensity of schooling and in a shift in the biotic habitat and trophic ecology of this commercially important tuna species.  
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  ISSN 0304-3800 ISBN Médium  
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Auteur Salvetat, J.; Lebourges-Dhaussy, A.; Travassos, P.; Gastauer, S.; Roudaut, G.; Vargas, G.; Bertrand, A. doi  openurl
  Titre In situ target strength measurement of the black triggerfish Melichthys niger and the ocean triggerfish Canthidermis sufflamen Type Article scientifique
  Année 2020 Publication Revue Abrégée Mar. Freshw. Res.  
  Volume 71 Numéro 9 Pages 1118-1127  
  Mots-Clés acoustics; aggregating devices fads; archipelago; atlantic; behavior; biomass estimation; frequency; north-east Brazil; shore fishes; small tuna; spinner dolphins; swimbladder; target strength-length relationships; tropical ecosystem; tropical tuna; underwater acoustics; underwater video  
  Résumé Triggerfish are widely distributed in tropical waters where they play an important ecological role. The black triggerfish Melichthys niger may be the dominant species around oceanic tropical islands, whereas pelagic triggerfish, such as the ocean triggerfish Canthidermis sufflamen, can assemble around fish aggregating devices (FADs) where they are a common bycatch of tuna fisheries. In this study we combined acoustic and optical recordings to provide the first in situ target strength (TS) measurement of black and ocean triggerfish. Data were collected in the Archipelago of Fernando de Noronha off north-east Brazil. The mean TS of a 27.8-cm-long black triggerfish at 70 and 200 kHz was -39.3 dB re 1 m(2) (CV = 14.0%) and -38.9 dB re 1 m(2) (CV = 14.4%) respectively. The mean TS values of ocean triggerfish (with a size range of 39-44 cm) at 70 and 200 kHz were -36.0 dB re 1 m(2) (CV = 15.7%) and -33.3 dB re 1 m(2) (CV = 14.0%) respectively. This work opens up the field for acoustic biomass estimates. In addition, we have shown that TS values for ocean triggerfish are within the same range as those of small tunas. Therefore, acoustic data transmitted from FADs equipped with echosounders can introduce a bias in tuna acoustic biomass estimation and lead to increased rates of bycatch.  
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  ISSN 1323-1650 ISBN Médium  
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Auteur Bonnin, L.; Lett, C.; Dagorn, L.; Filmalter, J.D.; Forget, F.; Verley, P.; Capello, M. doi  openurl
  Titre Can drifting objects drive the movements of a vulnerable pelagic shark? Type Article scientifique
  Année 2020 Publication Revue Abrégée Aquat. Conserv.-Mar. Freshw. Ecosyst.  
  Volume Numéro Pages  
  Mots-Clés aggregating devices fads; behavior; bycatch; carcharhinus-falciformis; fish aggregating devices; Lagrangian drift model; near-surface currents; ocean; pop-up satellite archival telemetry; postrelease survival; purse seine fishery; silky shark; tropical tuna; vulnerability; yellowfin thunnus-albacares  
  Résumé Juvenile silky sharks (Carcharhinus falciformis)regularly associate with floating objects yet the reasons driving this behaviour remain uncertain. Understanding the proportion of time that silky sharks spend associated with floating objects is essential for assessing the impacts of the extensive use of fish aggregating devices (FADs) in the tropical tuna purse-seine fisheries, including increased probability of incidental capture and the potential of an ecological trap. Previous studies provided insight into the amount of time that silky sharks spent at an individual FAD but were unable to assess neither the time spent between two associations nor the proportion of time spent associated/unassociated. The percentage of time that juvenile silky sharks spend unassociated with floating objects was estimated through the analysis of horizontal movements of 26 silky sharks monitored with pop-up archival tags. Under the assumption that a high association rate with drifting FADs would align the trajectories of tracked sharks with ocean surface currents, a novel methodology is proposed, based on the comparison of shark trajectories with simulated trajectories of passively drifting particles derived using a Lagrangian model. Results revealed that silky shark trajectories were divergent from surface currents, and thus unassociated with FADs, for at least 30% of their time. The potential of the methodology and the results are discussed in the context of increasing FAD densities in the Indian Ocean.  
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  Volume de collection Numéro de collection Edition  
  ISSN 1052-7613 ISBN Médium  
  Région Expédition Conférence  
  Notes WOS:000560611000001 Approuvé pas de  
  Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection (down) 2864  
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Auteur Roberts, M.J.; Ternon, J.-F.; Marsac, F.; Noyon, M.; Payne, A.I.L. doi  openurl
  Titre The MADRidge project: Bio-physical coupling around three shallow seamounts in the South West Indian Ocean Type Article scientifique
  Année 2020 Publication Revue Abrégée Deep-Sea Res. Part II-Top. Stud. Oceanogr.  
  Volume 176 Numéro Pages 104813  
  Mots-Clés Biological productivity; biology; Current-topography interaction; dipoles; fisheries; Fisheries and governance; Foodweb; humpback whales; hypothesis; La Perouse; madagascar; Madagascar Ridge; seabird community; Seamounts; tuna; upwelling cell; variability; Walters Shoal  
  Résumé Compared with other ocean basins, little is known scientifically about the seamounts in the Indian Ocean. Nonetheless, fishers have plundered these fragile ecosystems for decades, and now mining is becoming a reality. We introduce a multidisciplinary project referred to as MAD-Ridge that recently focused on three shallow seamounts in the South West Indian Ocean between 19 degrees S and 34 degrees S. The larger Walters Shoal (summit at 18 m) discovered in 1963 occupies the southern part of the Madagascar Ridge and has long received attention from the fishing industry, and only recently by scientists. In contrast, nothing is known of the northern region of the ridge, which is characterised by a prominent, steep-sided seamount that has a flat circular summit at 240 m and width of similar to 20 km. This seamount is some 200 km south of Madagascar and unnamed; it is referred to here as the MAD-Ridge seamount. MAD-Ridge is the shallowest of a constellation of five deeper (>1200 m) seamounts on that part of the ridge, all within the EEZ of Madagascar. It lies in a highly dynamic region at the end of the East Madagascar Current, where mesoscale eddies are produced continuously, typically as dipoles. The Madagascar Ridge appears to be an area of great productivity, as suggested by the foraging behaviour of some tropical seabirds during chick-rearing and a longline fishery that operates there. The third seamount, La Perouse, is located between Reunion Island and Madagascar. With a summit 60 m below the sea surface, La Perouse is distinct from MAD-Ridge and Walters Shoal; it is a solitary pinnacle surrounded by deep abyssal plains and positioned in an oligotrophic region with low mesoscale activities. The overall aim of the MAD-Ridge project was to examine the flow structures induced by the abrupt topographies, and to evaluate whether biological responses could be detected that better explain the observed increased in fish and top predator biomasses. The MAD-Ridge project comprised a multidisciplinary team of senior and early career scientists, along with postgraduate students from France, South Africa, Mauritius and Madagascar. The investigation was based around three cruises using the French vessels RV Antea (35 m) and RV Marion Dufresne (120 m) in September 2016 (La Perouse), November-December 2016 (MAD-Ridge) and May 2017 (Walters Shoal). This manuscript presents the rationale for the MAD-Ridge project, the background, a description of the research approach including the cruises, and a synopsis of the results gathered in the papers published in this Special Issue.  
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  ISSN 0967-0645 ISBN Médium  
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  Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection (down) 2856  
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