Francis Marsac
Informations
EMAIL : francis.marsac ird.fr
Institut : /BOUCLE_groupemots>
IRD
GRADE : /BOUCLE_groupemots>
DR1
LIEU GEOGRAPHIQUE : /BOUCLE_groupemots>
CAPE TOWN
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Conseil d’unité - Membres élus
Thèmes de recherche : /BOUCLE_groupemots>
Individus, populations et habitats
Pôles communs : /BOUCLE_groupemots>
Expertise
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Publications
2018 |
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Annasawmy, P., et al. "Micronekton diel migration, community composition and trophic position within two biogeochemical provinces of the South West Indian Ocean: Insight from acoustics and stable isotopes." Deep-Sea Res. Part I-Oceanogr. Res. Pap.. 138 (2018): 85–97.
Résumé: Spatial distribution, community composition and trophic roles of micronekton (crustaceans, fishes and squids) were investigated in the Indian South Subtropical Gyre (ISSG) province and the East African Coastal province (EAFR), by combining acoustic surveys, mid-water trawls and stable isotope analyses from scientific cruises conducted in 2009 and 2010. Mesopelagic micronekton performed diel vertical migrations in both provinces, from deep (400-740 m) to surface (0-200 m) layers at dusk and in the opposite direction at dawn, with some species migrating below 740 m. The EAFR province was more dynamic than the oligotrophic ISSG province, with enhanced eddy activity and enhanced yearly productivity. The active enrichment mechanisms in the EAFR, in terms of available primary production, led to high micronekton acoustic density (as a proxy of micronekton abundance) and large micronekton weight and abundance estimates from trawl data. Particulate organic matter in the EAFR exhibited greater enrichment in C-13 and N-15 compared to the ISSG and, consequently, tissues of selected micronekton organisms in the EAFR were more enriched in N-15 (higher delta N-15 values). In both provinces, micronekton encompassed a wide range of isotopic niches, with large overlaps between species. Micronekton and swordfish in the EAFR had an overlapping range of delta N-15 values, contrasting with the ISSG province where swordfish were two trophic levels higher than the sampled micronekton. Our results provide some evidence that the combined action of riverine input and the dynamics of eddies might influence productivity in the EAFR, and hence the abundance of micronekton and the enrichment of tissues in N-15, compared to the oligotrophic ISSG province.
Mots-Clés: Diel vertical migration; East African Coastal province; equatorial atlantic; feeding ecology; Indian South Subtropical Gyre; large pelagic fishes; mesopelagic fishes; mesoscale features; Micronekton; mozambique channel; myctophid fishes; north-atlantic ocean; respiratory carbon; Trophic level; vertical-distribution
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Bax, N. J., et al. "Linking Capacity Development to GOOS Monitoring Networks to Achieve Sustained Ocean Observation." Frontiers in Marine Science. 5 (2018): 346.
Résumé: Developing enduring capacity to monitor ocean life requires investing in people and their institutions to build infrastructure, ownership, and long-term support networks. International initiatives can enhance access to scientific data, tools and methodologies, and develop local expertise to use them, but without ongoing engagement may fail to have lasting benefit. Linking capacity development and technology transfer to sustained ocean monitoring is a win-win proposition. Trained local experts will benefit from joining global communities of experts who are building the comprehensive Global Ocean Observing System (GOOS). This two-way exchange will benefit scientists and policy makers in developing and developed countries. The first step toward the GOOS is complete: identification of an initial set of biological Essential Ocean Variables (EOVs) that incorporate the GEO Essential Biological Variables (EBVs), and link to the physical and biogeochemical EOVs. EOVs provide a globally consistent approach to monitoring where the costs of monitoring oceans can be shared and where capacity and expertise can be transferred globally. Integrating monitoring with existing international reporting and policy development connects ocean observations with agreements underlying many countries’ commitments and obligations, including under SDG 14, thus catalysing progress towards sustained use of the ocean. Combining scientific expertise with international capacity development initiatives can help meet the need of developing countries to engage in the agreed UN initiatives including new negotiations for management of Biodiversity Beyond National Jurisdiction, and the needs of the global community to understand how the ocean is changing.
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Malauene, B. S., et al. "Impact of offshore eddies on shelf circulation and river plumes of the Sofala Bank, Mozambique Channel." Journal of Marine Systems. 185 (2018): 1–12.
Résumé: A high-resolution, two-way nested Regional Ocean Modeling System, forced with monthly climatologies, has been set up for the Sofala Bank and adjacent deeper ocean of the Mozambique Channel to investigate the role of offshore mesoscale eddies on the shelf circulation, hydrographic structures and river plumes. The model is shown in comparison with available observations and published studies. Most known oceanographic features are reproduced by our model. We applied Self-Organizing Maps and showed that offshore passing eddies, depending on their strength and proximity to the shelf, modulate the shelf circulation and river plume direction and spread. The presence of a strong cyclonic eddy close to the shelf induces northward surface shelf currents. In contrast, the presence of a strong anticyclonic eddy close to the shelf induces a strong southward current over most of the shelf, except off Beira. Our analyses confirm that the plume of the Zambezi River is bi-directional. The southward-directed plume patterns, opposite to the dominant northwards, occur in response to nearby offshore anticyclonic eddies (26% of occurrence). This behavior could have an influence on water dispersal, shelf ecosystems and important fisheries. Therefore, offshore mesoscale eddies should be taken into account when studying the ocean dynamics of the Sofala Bank.
Mots-Clés: Mesoscale eddies; River plume; Roms; Shelf processes; SOMs
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Miloslavich, P., et al. "Essential ocean variables for global sustained observations of biodiversity and ecosystem changes." Global Change Biology. 24.6 (2018): 2416–2433.
Résumé: Sustained observations of marine biodiversity and ecosystems focused on specific conservation and management problems are needed around the world to effectively mitigate or manage changes resulting from anthropogenic pressures. These observations, while complex and expensive, are required by the international scientific, governance and policy communities to provide baselines against which the effects of human pressures and climate change may be measured and reported, and resources allocated to implement solutions. To identify biological and ecological essential ocean variables (EOVs) for implementation within a global ocean observing system that is relevant for science, informs society, and technologically feasible, we used a driver-pressure-state-impact-response (DPSIR) model. We (1) examined relevant international agreements to identify societal drivers and pressures on marine resources and ecosystems, (2) evaluated the temporal and spatial scales of variables measured by 100+ observing programs, and (3) analysed the impact and scalability of these variables and how they contribute to address societal and scientific issues. EOVs were related to the status of ecosystem components (phytoplankton and zooplankton biomass and diversity, and abundance and distribution of fish, marine turtles, birds and mammals), and to the extent and health of ecosystems (cover and composition of hard coral, seagrass, mangrove and macroalgal canopy). Benthic invertebrate abundance and distribution and microbe diversity and biomass were identified as emerging EOVs to be developed based on emerging requirements and new technologies. The temporal scale at which any shifts in biological systems will be detected will vary across the EOVs, the properties being monitored and the length of the existing time-series. Global implementation to deliver useful products will require collaboration of the scientific and policy sectors and a significant commitment to improve human and infrastructure capacity across the globe, including the development of new, more automated observing technologies, and encouraging the application of international standards and best practices.
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2017 |
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Maury, O., et al. "From shared socio-economic pathways (SSPs) to oceanic system pathways (OSPs): Building policy-relevant scenarios for global oceanic ecosystems and fisheries." Global Environmental Change. 45.Supplement C (2017): 203–216.
Résumé: There is an urgent need for developing policy-relevant future scenarios of biodiversity and ecosystem services. This paper is a milestone toward this aim focusing on open ocean fisheries. We develop five contrasting Oceanic System Pathways (OSPs), based on the existing five archetypal worlds of Shared Socioeconomic Pathways (SSPs) developed for climate change research (e.g., Nakicenovic et al., 2014 and Riahi et al., 2016). First, we specify the boundaries of the oceanic social-ecological system under focus. Second, the two major driving forces of oceanic social-ecological systems are identified in each of three domains, viz., economy, management and governance. For each OSP (OSP1 “sustainability first”, OSP2 “conventional trends”, OSP3 “dislocation”, OSP4 “global elite and inequality”, OSP5 “high tech and market”), a storyline is outlined describing the evolution of the driving forces with the corresponding SSP. Finally, we compare the different pathways of oceanic social-ecological systems by projecting them in the two-dimensional spaces defined by the driving forces, in each of the economy, management and governance domains. We expect that the OSPs will serve as a common basis for future model-based scenario studies in the context of the Intergovernmental Panel on Climate Change (IPCC) and the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES).
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2015 |
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Miloslavich, P., et al. "Goos: A Platform to Observe Essential Ecological and Biological Variables." Interciencia. 40.8 (2015): 510. |
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Murua, H., J. P. Eveson, and F. Marsac. "The Indian Ocean Tuna Tagging Programme : building better science for more sustainability : preface." Fisheries Research. 163.Si (2015): 1–6. |
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Rabearisoa, N., P. Bach, and F. Marsac. "Assessing interactions between dolphins and small pelagic fish on branchline to design a depredation mitigation device in pelagic longline fisheries." ICES J. Mar. Sci.. 72.5 (2015): 1682–1690.
Résumé: Depredation by false killer whales (Pseudorca crassidens) and short-finned pilot whales (Globicephala macrorhynchus) in pelagic longlining is an issue leading to negative impacts on the economics of the fishery and on odontocetes themselves. We investigated the efficacy of a new depredation mitigation device called “DEPRED” in the interaction between bottlenose dolphins (Tursiops aduncus), spinner dolphins (Stenella longirostris), and small pelagic fish (SPF) attached to branchlines to simulate caught fish. We suggest implications for DEPRED efficacy with larger toothed whales interacting with pelagic longline capture in the open ocean. The design of the device uses streamers to both deter cetaceans and protect fish from predation. In controlled experiments, we tested its efficacy by observing changes in the dolphin's behaviour brought on by the presence or absence of the device on branchlines. First, dolphin–SPF interactions were observed at the small scale using video footage recorded with an underwater camcorder. Second, the efficacy of the device was quantified from interactions between dolphins and 80 branchlines deployed on a longline 500 m long baited with SPF. One half of the SPF on successive branchlines was protected by DEPRED and the other half was not. A total of 707 branchlines were set when dolphins interacted with SPF, and among them, 355 were equipped with DEPRED. Encouraging results were obtained: over the short term, the number of damaged unprotected SPF was on average more than twice the number of protected ones. Nevertheless, habituation behaviour was observed for a resident group of T. aduncus in the experimental area. The relation between the deterrent effect of the device and constraints related to the design of such a device to be used at a commercial operational level are discussed.
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2014 |
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Marsac, F., et al. "Ecosystem functioning in the Mozambique Channel : synthesis and future research." Deep-Sea Research Part II.Topical Studies in Oceanography. 100.No spécial (2014): 212–220.
Résumé: The MESOBIO programme investigated mesoscale dynamics using an integrated ecosystem approach, linking physical and biogeochemical processes with different trophic levels. Observation and modeling were used in combination to explain the main processes occurring in the mesoscale eddy field. The particular shape of the Mozambique Channel, composed of two basins interconnected through a narrow zone, favours the generation of mesoscale eddies and increases the opportunity for eddy-shelf interactions. Phytoplankton abundance peaked in areas of nutrient enrichment that are often found in the core of cyclonic eddies, as well as on the continental shelf. Grazers in zooplankton communities exhibited high biovolume in cyclonic eddies, but their abundance was lower in fronts and divergence zones, with lowest biovolume in anticyclones. Biovolume was highest at shelf stations, but very variable and similar to phytoplankton. Age of eddies, their subsequent maturation stage and the dynamics of the eddy field played a major role effecting zooplankton abundance. Micronekton presented abundance patterns coherent with zooplankton distribution, however this was only demonstrated by acoustic methods, whereas mid-water trawl collection and predators stomach contents (predators being used as biological samplers) did not reveal significant relationships with mesoscale features. For upper trophic levels, the average density of foraging seabirds was lowest in anticyclones, highest in cyclones and at intermediate levels in divergence, shelf and frontal zones. However, multifaceted behavioral responses were observed in such a highly variable environment. Swordfish was clearly associated with divergence zones, and to a lesser extent with fronts, suggesting that the higher density in divergences was related to the presence of its main prey, essentially large squids. Although tunas tended to be more abundant in areas with weak geostrophic currents, their relationship to mesoscale features was not straightforward as adult tunas caught by longline have the ability to explore different foraging habitats over a broad range of depths. Several suggestions for advancing eddy-related research from the current state of knowledge are proposed in the second part of the paper.
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Potier, M., et al. "Influence of mesoscale features on micronekton and large pelagic fish communities in the Mozambique Channel." Deep-Sea Research Part II.Topical Studies in Oceanography. 100.No spécial (2014): 184–199.
Résumé: We investigated the diversity and distribution of two communities, micronekton organisms and large predatory fishes, sampled in mesoscale features of the Mozambique Channel from 2003 to 2009, by combining mid-water trawls, stomach contents of fish predators and instrumented longline fishing surveys. The highest species richness for assemblages was found in divergences and fronts rather than in the core of eddies. Despite an unbalanced scheme, diversity indices did not differ significantly between cyclonic and anticyclonic eddies, divergences and fronts. We found that eddies and associated physical cues did not substantially affect the distribution of micronektonic species which are mainly driven by the diel vertical migration pattern. Top predators exhibited a more complex response. Swordfish (Xiphias gladius) associated better with mesoscale features than tunas, with a clear preference for divergences which is consistent with the diel vertical migrations and occurrence of its main prey, the flying squids Sthenoteuthis oualaniensis (Ommastrephidae). On the other hand, the probability of presence of yellowfin tuna was not tied to any specific eddy structure. However, the highest values of positive yellowfin CPUEs were associated with low horizontal gradients of sea-level anomalies. We also showed a non-linear response of positive yellowfin CPUEs with respect to the depth of the minimal oxygen content. The larger the distance between the hooks and the minimal oxygen layer, towards the surface or at greater depths, the higher the CPUE, highlighting that yellowfin congregated in well-oxygenated waters. Micronekton sampled by mid-water trawls and stomach contents exhibited different species composition. The highly mobile organisms were not caught by trawling whereas they remain accessible to predators. The combination of stomach contents and mid-water trawls undoubtedly improved our understanding of the micronekton assemblage distribution. Our results provide some evidence that mesoscale features in the Mozambique Channel do not strongly affect the distribution of the mid-trophic level organisms such as micronekton and most of the large predatory fishes, and hypotheses are proposed to support this result.
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Ternon, J. - F., et al. "The Mozambique Channel : from physics to upper trophic levels." Deep-Sea Research Part II.Topical Studies in Oceanography. 100.No spécial (2014): 1–9.
Résumé: A multidisciplinary programme, MESOBIO (Influence of mesoscale dynamics on biological productivity at multiple trophic levels in the Mozambique Channel) was undertaken in the Mozambique Channel within the framework of a scientific partnership between France and South Africa. MESOBIO focused on the signature of the highly energetic eddy dynamics in the Mozambique Channel. The Channel, which is known to be one of the most turbulent areas in the world ocean, has a great diversity of marine organisms and is the site of active pelagic fisheries. MESOBIO was mostly based on observations at sea during 12 multidisciplinary cruises between 2002 and 2010. Hydrographic measurements, sampling of biological organisms ranging from phytoplankton to top predators, and experiments on primary production and energy transfer through the food web, were conducted onboard various research vessels. The data were analysed in relation to eddy field characteristics for the periods of the cruises, including seasonal or inter-annual variability in mesoscale activity. A modelling approach was also developed within MESOBIO for both the circulation in the Channel and the biogeochemical response to eddy forcing. This paper introduces the suite of articles on the MESOBIO investigations by summarizing background knowledge for the different disciplines and the key issues that were addressed within the programme.
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2013 |
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Halo, I., et al. "JEAI-MOCAs : a multi-institutional initiative to build marine research capacity in Mozambique." South African Journal of Science. 109.7-8 (2013).
Mots-Clés: biogeochemistry; ocean eddies; ocean models; tides; tropical cyclones
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KAPLAN, D., et al. "The True Challenge of Giant Marine Reserves." Science. 340.6134 (2013): 810–811. |
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Maury, O., et al. "A global science–policy partnership for progress toward sustainability of oceanic ecosystems and fisheries." Current Opinion in Environmental Sustainability. 5.3–4 (2013): 314–319.
Résumé: Oceanic ecosystems support livelihoods and supply food for hundreds of millions of people. But these ecosystems are deteriorating rapidly and many of the world's oceanic fisheries are in a precarious condition. In addition to well-known and pressing fishery management issues, economic globalization is connecting fisheries beyond the frontiers of the organizations responsible for their management and climate-associated changes are deeply modifying ecosystems, pushing them toward new states and no return situations. The status quo is not a sustainable option, and improved international governance is urgently needed to address this situation. Our proposition consists of an inclusive global science–policy process combining major improvements to the present governance systems, including new incentives for international cooperation and coordination, with an ambitious scientific program to help anticipate threats and opportunities and integrate complex information regarding long-term issues. It would constitute a major step toward sustainability.
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2012 |
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Anderson, R. C., et al. "Seasonal distribution, movements and taxonomic status of blue whales (Balaenoptera musculus) in the northern Indian Ocean." Journal of Cetacean Resources and Management. 12.2 (2012): 203–218. |
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2010 |
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Kai, E. T., and F. Marsac. "Influence of mesoscale eddies on spatial structuring of top predators' communities in the Mozambique Channel." Progress in Oceanography. 86 (2010): 214–223.
Résumé: Mesoscale physical features as fronts and eddies appear to play a key role in the dynamics of marine communities. In the Indian Ocean, the Mozambique Channel (MC) is a natural laboratory to investigate mesoscale eddies (100-300 km in diameter); indeed, four to seven eddies per year are know to transit through the Channel, from North to South. We studied the structuring role of the mesoscale eddies on spatial dynamics and foraging strategy of top predators using seabirds and tuna as examples. Emphasis was on the central part of the MC (16-24 S) where eddy activity is most developed. We integrated three main categories of information: (i) satellite altimetry for sea-level anomaly (SLA) and geostrophic current, remotely-sensed surface temperature (SST) and SeaWiFS data for chlorophyll concentration (CC); (ii) individual tracking of Great Frigatebirds (Fregata minor) to characterize foraging areas; and (iii) detailed catch statistics from purse-seine fisheries to describe distribution of tuna schools. Generalized Additive Models were applied to quantify the relative influence of mesoscale descriptors. SST and CC on foraging behaviour of Great Frigatebirds and location of purse-seine sets. Our results show that seabirds are more closely tied to mesoscale eddies compared to tuna. We underline the role of eddy boundaries on the response of frigatebirds and tuna. Good foraging conditions are promoted along the edge of eddies as a result of the interplay of the maturation process from cyclonic eddies and the concentration process by eddy interactions. A decrease in the number or intensity of eddies in the MC, as observed during strong El Nino events, could potentially affect the eddy-related ecosystem with putative negative repercussions on central-place foragers such as Great Frigatebirds. We discuss the importance of a better understanding of the “eddy system”, in marine conservation and tuna fisheries management in the Mozambique Channel.
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Robinson, J., et al. "Impacts of climate variability on the tuna economy of Seychelles." Climate Research. 43 (2010): 149–162.
Résumé: Many small island states have developed economies that are strongly dependent on tuna fisheries. Consequently, they are vulnerable to the socio-economic effects of climate change and variability, processes that are known to impact tuna fisheries distribution and productivity. The aim of this study was to assess the impacts of climate oscillations on the tuna-dependent economy of Seychelles. Using a multiplier approach, the direct, indirect and induced economic effects of the tuna industry expenditure benefiting the Seychelles' economy declined in 1998 by 58, 26 and 35%, respectively (mean decline: 42%), a year of strong climate oscillation in the western Indian Ocean. Multivariate patterns in tuna purse-seine vessel expenditures in port were substantially modified by strong climate oscillations, particularly in 1998. A cointegration time-series model predicted that a 40% decline in tuna landings and transhipment in Port Victoria, a value commensurate with that observed in 1998, would result in a 34% loss for the local economy solely through reductions in cargo handling expenditures. Of several indices tested, the Indian Oscillation Index was best at predicting the probability of switching between low and high regimes of landings and transhipment, which translate into impacts for the economy. It is hypothesised that a late 2006/early 2007 climate oscillation was compounded by prior overfishing to produce a stronger impact on the fishery and economy of Seychelles. The effects of fishing and climate variability on tuna fisheries are complex and pose significant challenges for fisheries management and the economic development of countries in the Indian Ocean.
Mots-Clés: climate; economy; Enso; fisheries; Seychelles; tuna; variability
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Weimerskirch, H., et al. "Foraging movements of great frigatebirds from Aldabra Island : relationship with environmental variables and interactions with fisheries." Progress in Oceanography. 86 (2010): 204–213.
Résumé: Great Frigatebirds (Fregata minor) are large tropical seabirds that rely primarily on sub-surface predators such as tunas or cetaceans to capture their prey. We studied the foraging movements of 14 Great Frigatebirds breeding on Aldabra Island (9.4 degrees S, 46.4 degrees E), the largest colony in the Indian Ocean. This colony is located at more than 500 km from the main fishing grounds of a very important industrial purse-seine fishery targeting surface-dwelling tunas. Despite their slow flight speeds (16 km h(-1)), frigatebirds are able to forage at more than 1000 km from the colonies when breeding, using 2500-4750 km long foraging loops over oceanic waters. All trips were directed to the north of the island up to the equator. Foraging bouts, indicated by reduced flight speeds, were rare and located throughout the trips. Foraging spots tended to be more frequent on higher surface chlorophyll concentration and in association with some cyclonic vortices. However, mesoscale activity is relatively weak between Aldabra and the equator and the chlorophyll variability is mostly the result of wind-mixing processes during the southwest monsoon. These results suggest that frigatebirds forage for widely distributed resources to the north of Aldabra. The northernmost foraging bouts were located in the vicinity of the purse-seine fishing grounds, but without a significant overlap between frigatebirds and tuna fleets. The results of the study are compared with those from another population at Europa Island (22.3 degrees S, 40.3 degrees E) where birds were foraging on predictable features, the edge of cyclonic eddies that are marked in the Mozambique Channel. We discuss the consequences of the reliance of populations on contrasted oceanographic conditions on foraging strategies and on the evolution of life histories in these long-lived animals in a changing climate, as well as the possible effects of overfishing on frigatebird populations.
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2009 |
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Dandonneau, Y., et al. "Air-sea interactions in the Seychelles-Chagos thermocline ridge region." Bull. Amer. Meteorol. Soc.. 90.1 (2009): 45–61.
Résumé: A field experiment in the southwestern Indian Ocean provides new insights into ocean–atmosphere interactions in a key climatic region.
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Key, E., et al. "Cirene: Air—Sea Interactions in the Seychelles—Chagos Thermocline Ridge Region." Bull. Amer. Meteor. Soc. 90.1 (2009): 45–61.
Résumé: The Vasco—Cirene program ex-plores how strong air—sea inter-actions promoted by the shallow thermocline and high sea surface temperature in the Seychelles—Chagos thermocline ridge results in marked variability at synoptic, intraseasonal, and interannual time scales. The Cirene oceano-graphic cruise collected oceanic, atmospheric, and air—sea flux observations in this region in Jan-uary—February 2007. The contem-poraneous Vasco field experiment complemented these measure-ments with balloon deployments from the Seychelles. Cirene also contributed to the development of the Indian Ocean observing system via deployment of a moor-ing and 12 Argo profilers.Unusual conditions prevailed in the Indian Ocean during Janu-ary and February 2007, following the Indian Ocean dipole climate anomaly of late 2006. Cirene measurements show that the Seychelles—Chagos thermocline ridge had higher-than-usual heat content with subsurface anomalies up to 7°C. The ocean surface was warmer and fresher than average, and unusual eastward currents prevailed down to 800 m. These anomalous conditions had a major impact on tuna fishing in early 2007. Our dataset also sampled the genesis and maturation of Tropical Cyclone Dora, including high surface temperatures and a strong diurnal cycle before the cyclone, followed by a 1.5°C cool-ing over 10 days. Balloonborne instruments sampled the surface and boundary layer dynamics of Dora. We observed small-scale structures like dry-air layers in the atmosphere and diurnal warm layers in the near-surface ocean. The Cirene data will quantify the impact of these finescale features on the upper-ocean heat budget and atmospheric deep convection.
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Tew-Kai, E., and F. Marsac. "Patterns of variability of sea surface chlorophyll in the Mozambique Channel : a quantitative approach." Journal of Marine Systems. 77.1-2 (2009): 77–88.
Résumé: We analyse the coupling between sea surface chlorophyll concentration (CC) and the physical environment in the Mozambique Channel (MZC) using statistical models. Seasonal and interannual patterns are studied along with the role of mesoscale dynamics on enhancement and concentration processes for phytoplankton. We use SeaWifs data for CC and two other remotely sensed data sets, TMMI for sea surface temperature (SST) and merged altimetry products for sea level anomaly and geostrophic current. Empirical Orthogonal Functions (EOF) on SSC and SST show strong seasonality and partition the MZC into three distinct sub-areas. The chlorophyll variability is mostly driven by seasonality, but more in the North (10 degrees S-16 degrees S) and South (24 degrees S-30 degrees S), and explains respectively 64% and 82% of the CC variance. In the Central part (16 degrees S-24 degrees S), the seasonal signal has less influence (60% variance). There, complex EOFs on Sea Level Anomaly (SLA) highlight the role of mesoscale activity (i.e. eddies and filament structures) in the spatial distribution of chlorophyll. Five mesoscale descriptors (shear, stretch, vorticity, deformation and eddy kinetic energy) are derived from the altimetry data to quantify the eddies-related physical patterns in the central region of the MZC. We use generalized Additive Models to explain the effect of those features on phytoplankton enhancement. The best model fit (r(2) = 0.73) includes shear, stretch, vorticity and the latitude-longitude interaction as eddies are well structured in space. Cyclonic eddies associated with negative vorticity are conductive to phytoplankton enhancement by the effect of upwelling in the core notably during the spin-up phase. The interaction between eddies generate strong frontal mixing favourable to the production and aggregation of organic matter. The mesoscale activity is also affected by interannual variability with consequences on CC. We highlight a substantial reduction of the SLA pattern in 2000-2001 when the SOI positive phase is peaking (Nina-type pattern). The strong relationship between mesoscale eddies and SOI suggests that primary productivity in the MZC is also under the influence of distant forcing at a basin scale.
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Tew-Kai, E., et al. "Top marine predators track Lagrangian coherent structures." Proc. Natl. Acad. Sci. U. S. A.. 106 (2009): 8245–8250.
Résumé: Meso- and submesoscales (fronts, eddies, filaments) in surface ocean flow have a crucial influence on marine ecosystems. Their dynamics partly control the foraging behavior and the displacement of marine top predators (tuna, birds, turtles, and cetaceans). In this work we focus on the role of submesoscale structures in the Mozambique Channel in the distribution of a marine predator, the Great Frigatebird. Using a newly developed dynamic concept, the finite-size Lyapunov exponent (FSLE), we identified Lagrangian coherent structures (LCSs) present in the surface flow in the channel over a 2-month observation period (August and September 2003). By comparing seabird satellite positions with LCS locations, we demonstrate that frigatebirds track precisely these structures in the Mozambique Channel, providing the first evidence that a top predator is able to track these FSLE ridges to locate food patches. After comparing bird positions during long and short trips and different parts of these trips, we propose several hypotheses to understand how frigatebirds can follow these LCSs. The birds might use visual and/or olfactory cues and/or atmospheric current changes over the structures to move along these biologic corridors. The birds being often associated with tuna schools around foraging areas, a thorough comprehension of their foraging behavior and movement during the breeding season is crucial not only to seabird ecology but also to an appropriate ecosystemic approach to fisheries in the channel.
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Van der Elst, R. P., et al. "Nine nations, one ocean: A benchmark appraisal of the South Western Indian Ocean Fisheries Project (2008–2012)." Ocean Coastal Manage.. 52 (2009): 258–267.
Résumé: Coastal and island states of the Western Indian Ocean lack scientific and management capacity to draw sustainable benefits from their Exclusive Economic Zones. Declining ecosystem services and unregulated fishing has prompted nine riparian countries to develop a regional framework for capacity building and scientific development towards collective management of shared resources. Supported by the Global Environment Facility (GEF), the Agulhas and Somali Currents large marine ecosystems programme consists of three inter-related modules, supported by different agencies: land-based impacts on the marine environment (UNEP); productivity, ecosystem health and nearshore fisheries (UNDP) and transboundary shared and migrating fisheries resources (World Bank). The latter is the South Western Indian Ocean Fisheries Project (SWIOFP), a 5-year joint data gathering and fisheries assessment initiative. SWIOFP is a prelude to long-term cooperative fisheries management in partnership with the newly established FAO–South Western Indian Ocean Fisheries Commission (SWIOFC). We describe the development of SWIOFP as a model of participatory regional scientific cooperation and collective ocean management.
© 2009 Elsevier Ltd. All rights reserved. Mots-Clés: fisheries; management; South Western Indian Ocean
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