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Auteur Grande, M.; Murua, H.; Zudaire, I.; Goni, N.; Bodin, N.
Titre Reproductive timing and reproductive capacity of the Skipjack Tuna (Katsuwonus pelamis) in the western Indian Ocean Type Article scientifique
Année 2014 Publication Revue Abrégée Fisheries Research
Volume 156 Numéro Pages 14-22
Mots-Clés Condition; Gonadosomatic index; Oocyte; Reproductive capacity; Spawning season
Résumé We studied the sexual maturity, batch fecundity and spawning season of the Skipjack Tuna Katsuwonus pelamis. Generalized additive modelling was applied to assess the effect of demographic features on ovary growth. During 2009 and 2010, 673 females were caught on board a purse-seine fishing vessel in the western Indian Ocean. Fish were classified into different reproductive phases and this information was used to determine the size at maturity (L-50), the timing of spawning and the batch fecundity (n = 51). The size at maturity (L-50) for females was estimated to be 39.9 cm. The mean relative batch fecundity was 140 +/- 64 eggs g(-1) of fish. Spawning occurs during the monsoons and inter-monsoon seasons with peaks in the reproductive activity during the North-east and South-west monsoon events. Demographic differences were detected in the reproductive timing of the population and a large investment in gamete production was observed in fish with high hepatic condition and in their first spawning year.
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ISSN 0165-7836 ISBN Médium
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Auteur Hancke, L.; Roberts, M.J.; Ternon, J.-F.
Titre Surface drifter trajectories highlight flow pathways in the Mozambique Channel Type Article scientifique
Année 2014 Publication Revue Abrégée Deep-Sea Research Part II.Topical Studies in Oceanography
Volume 100 Numéro No spécial Pages 27-37
Mots-Clés Frontal flow; Mesoscale eddies; Mozambique Channel; Surface circulation; Surface drifters
Résumé The pattern of surface circulation in the Mozambique Channel was elucidated from the trajectories of 82 satellite-tracked drifters over the period 2000-2010 and complementary satellite-derived altimetry. Overall, the trajectories indicated that anticyclonic activity was mostly observed on the western side of the Channel, with cyclonic activity being more prevalent in the east. A lack of eddy activity was noted in the southeast corner of the Channel (i.e. SW of Madagascar). Drifter behaviour illustrated that surface water from the Comoros Basin, entrained into anticyclonic eddies during formation, can be retained and isolated for months whilst being transported southwards through the Channel. During a tropical cyclone weather event, a drifter was observed to switch between counter-rotating eddies indicating that horizontal mixing of the Ekman layer does occur. The drifters also illustrated and emphasised the flow field and transport between eddies (i.e. the interstitial flow) in the Mozambique Channel. Despite the dominance of southward propagating anticyclones, drifters were able to move north and south through the Channel in the frontal flow field between eddies within periods of 51-207 days. Cross-channel transport in both directions between the Madagascan and Mozambique shelf regions was similarly observed, with time spans of 19-30 days. Surprisingly, drifters from the southern limb of the East Madagascar Current were transported westward across the channel to the Mozambique shelf. This transport was similarly facilitated by the frontal flow field between eddies. It is hypothesised that the frontal zones between eddies and interstitial waters play an important role in distributing biota in the Mozambique Channel.
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Editeur Lieu de Publication Éditeur Barlow, R.; Marsac, F.; Ternon, J.-F.; Roberts, M.
Langue Langue du Résumé Titre Original
Éditeur de collection Titre de collection Titre de collection Abrégé
Volume de collection Numéro de collection Edition
ISSN 0967-0645 ISBN Médium
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Auteur Hernandez, O.; Lehodey, P.; Senina, I.; Echevin, V.; Ayon, P.; Bertrand, A.; Gaspar, P.
Titre Understanding mechanisms that control fish spawning and larval recruitment : parameter optimization of an Eulerian model (SEAPODYM-SP) with Peruvian anchovy and sardine eggs and larvae data Type Article scientifique
Année 2014 Publication Revue Abrégée Progress in Oceanography
Volume 123 Numéro Pages 105-122
Mots-Clés
Résumé The Spatial Ecosystem And Populations Dynamics Model “SEAPODYM”, based on a system of Eulerian equations and initially developed for large pelagic fish (e.g., tuna), was modified to describe spawning habitat and eggs and larvae dynamics of small pelagic fish. The spawning habitat is critical since it controls the initial recruitment of larvae and the subsequent spatio-temporal variability of natural mortality during their drift with currents. A robust statistical approach based on Maximum Likelihood Estimation is presented to optimize the model parameters defining the spawning habitat and the eggs and larvae dynamics. To improve parameterization, eggs and larvae density observations are assimilated in the model. The model and its associated optimization approach allow investigating the significance of the mechanisms proposed to control fish spawning habitat and larval recruitment: temperature, prey abundance, trade-off between prey and predators, and retention and dispersion processes. An application to the Peruvian anchovy (Engraulis ringens) and sardine (Sardinops sagax) illustrates the ability of the model to simulate the main features of spatial dynamics of these two species in the Humboldt Current System. For both species, in climatological conditions, the main observed spatial patterns are well reproduced and are explained by the impact of prey and predator abundance and by physical retention with currents, while temperature has a lower impact. In agreement with observations, sardine larvae are mainly predicted in the northern part of the Peruvian shelf (5-10 degrees S), while anchovy larvae extend further south. Deoxygenation, which can potentially limit the accessibility of adult fish to spawning areas, does not appear to have an impact in our model setting. Conversely, the observed seasonality in spawning activity, especially the spawning rest period in austral autumn, is not well simulated. It is proposed that this seasonal cycle is more likely driven by the spatio-temporal dynamics of adult fish constituting the spawning biomass and not yet included in the model.
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Langue Langue du Résumé Titre Original
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Volume de collection Numéro de collection Edition
ISSN 0079-6611 ISBN Médium
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Auteur Jaquemet, S.; Ternon, J.-F.; Kaehler, S.; Thiebot, J.B.; Dyer, B.; Bemanaja, E.; Marteau, C.; Le Corre, M.
Titre Contrasted structuring effects of mesoscale features on the seabird community in the Mozambique Channel Type Article scientifique
Année 2014 Publication Revue Abrégée Deep-Sea Research Part II.Topical Studies in Oceanography
Volume 100 Numéro No spécial Pages 200-211
Mots-Clés Foraging habitats; Frigatebird; Marine productivity; Mesoscale eddies; Red-footed booby; Sooty tern; Tropical marine predators; Tuna; Western Indian Ocean
Résumé The Mozambique Channel (western Indian Ocean) is a dynamic environment characterised by strong mesoscale features, which influence all biological components of the pelagic ecosystem. We investigated the distribution, abundance and feeding behaviour of seabirds in the Mozambique Channel in relation to physical and biological environmental variables, with a specific interest in mesoscale features. Seabird censuses were conducted in summer and winter during 7 cruises in the southern and northern Mozambique Channel. Tropical species accounted for 49% of the 37 species identified and 97% of the individuals, and species from the sub-Antarctic region constituted 30% of the identifications. The typically tropical sooty tern (Onychoprion fuscata) was the dominant species during all cruises, and overall accounted for 74% of the species observations and 85% of counted birds. Outputs of Generalised Linear Models at the scale of the Mozambique Channel suggested that higher densities of flying and feeding birds occurred in areas with lower sea surface temperatures and lower surface chlorophyll a concentrations. Most of the flocks of feeding birds did not associate with surface schools of fish or marine mammals, but when they did, these flocks were larger, especially when associated with tuna. While tropical species seemed to favour cyclonic eddies, frontal and divergence zones, non-tropical species were more frequently recorded over shelf waters. Sooty terns foraged preferentially in cyclonic eddies where zooplankton, micronelcton and tuna schools were abundant. Among other major tropical species, frigatebirds (Fregata spp.) predominated in frontal zones between eddies, where tuna schools also frequently occurred and where geostrophic currents were the strongest. Red-footed boobies (Sula sub) concentrated in divergence zones characterised by low sea level anomalies, low geostrophic currents, and high zooplanlcton biomass close to the surface. Our results highlight the importance of mescoscale features in structuring the tropical seabird community in the Mozambique Channel, in addition to segregating tropical and non-tropical species. The mechanisms underlying the segregation of tropical seabirds seem to partially differ from that of other tropical regions, and this may be a consequence of the strong local mesoscale activity, affecting prey size and availability schemes. Beyond characterising the foraging habitats of the seabird community of the Mozambique Channel, this study highlights the importance of this region as a hot spot for seabirds; especially the southern part, where several endangered sub-Antarctic species over-winter.
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Auteur institutionnel Thèse
Editeur Lieu de Publication Éditeur Barlow, R.; Marsac, F.; Ternon, J.-F.; Roberts, M.
Langue Langue du Résumé Titre Original
Éditeur de collection Titre de collection Titre de collection Abrégé
Volume de collection Numéro de collection Edition
ISSN 0967-0645 ISBN Médium
Région Expédition Conférence
Notes Approuvé pas de
Numéro d'Appel (up) LL @ pixluser @ collection 363
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Auteur Jose, Y.S.; Aumont, O.; Machu, E.; Penven, P.; Moloney, C.L.; Maury, O.
Titre Influence of mesoscale eddies on biological production in the Mozambique Channel : several contrasted examples from a coupled ocean-biogeochemistry model Type Article scientifique
Année 2014 Publication Revue Abrégée Deep-Sea Research Part II.Topical Studies in Oceanography
Volume 100 Numéro No spécial Pages 79-93
Mots-Clés Chlorophyll; Cyclonic and anticyclonic eddies; Mozambique Channel; Nutrients; Ocean physical-biogeochemical coupling
Résumé The impact of mesoscale activity on phytoplankton and nutrient distribution in the Mozambique Channel was simulated by coupling a biogeochemical model (PISCES) with a regional oceanic model (ROMS). Examples of the effects of eddies on the biogeochemistry of the Mozambique Channel are presented to illustrate the complexity of the system. In the model, several cyclonic eddies were found with low concentrations of chlorophyll at their cores, which contrasts with previous studies in the open ocean. In addition, several anticyclonic eddies were simulated with high concentrations of chlorophyll at their cores. Phytoplankton growth within these mesoscale features (both cyclonic and anticyclonic eddies) occurred in response to nutrient injection into the euphotic zone by advection, and subsequent retention of surrounding nutrient-rich waters within eddies. Offshore nutrient distributions depended strongly on lateral advection of nutrient-rich water from the coastal regions, induced by eddy interaction with the shelf. The environmental conditions at the locations where eddies were generated had an important effect on nutrient concentrations within these structures.
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Auteur institutionnel Thèse
Editeur Lieu de Publication Éditeur Barlow, R.; Marsac, F.; Ternon, J.-F.; Roberts, M.
Langue Langue du Résumé Titre Original
Éditeur de collection Titre de collection Titre de collection Abrégé
Volume de collection Numéro de collection Edition
ISSN 0967-0645 ISBN Médium
Région Expédition Conférence
Notes Approuvé pas de
Numéro d'Appel (up) LL @ pixluser @ collection 364
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