Academic literature on the topic 'Écologie pélagique – Pacifique (océan ; ouest)'
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Dissertations / Theses on the topic "Écologie pélagique – Pacifique (océan ; ouest)"
Barbin, Laure. "Distribution du micronecton dans le Pacifique tropical ouest : caractérisation de la structuration des écosystèmes par méthodes acoustiques." Electronic Thesis or Diss., Sorbonne université, 2024. http://www.theses.fr/2024SORUS139.
Full textPelagic ecosystems are key elements of the global oceans, hosting numerous exchanges between the euphotic surface and mesopelagic depths. This zone exhibits a high biodiversity and a complex trophic network, with micronekton as a central component. This compartment comprises organisms measuring between 2 and 20 cm and encompasses a wide variety of species, including fish, crustaceans, molluscs, and gelatinous organisms (such as jellyfish, pyrosomes, salps). Micronekton serves as the primary food source for top predators like tuna, marine mammals, and seabirds and is predominantly feeding on zooplankton, thus occupying a central position in the trophic network. Additionally, some micronekton species undertake a diel migration between surface and depths, known as the nycthemeral migration, occurring with each solar cycle: organisms residing in deep mesopelagic layers during the day (>300m) ascend to the surface at sunset and vice versa at dawn. This vertical migration, observed in all oceans, is one of the largest global migrations. Its substantial biomass on a global scale, central role in the trophic network, and migratory behavior contributing to oceanic biogeochemical fluxes make micronekton an indispensable element in the study of pelagic ecosystems. This thesis investigates micronekton in the tropical Pacific through three main axes: 1) observation methods and abundance estimation, 2) improvement through recent technologies, particularly broadband acoustic profilers, and 3) characterization of micronekton distribution at the Pacific scale by defining ecosystems linked to environmental variables. Axis 1) initially examines micronekton observation methods, their respective biases, and their complementary nature. By focusing on acoustic-trawl measurements in the southwest tropical Pacific, we compare micronekton abundance estimates obtained through trawling and acoustics to estimate the difference of abundance obtained by one and the other method at different depths. In axis 2), we explore the contribution of a broadband profiler to micronekton abundance and distribution studies, developing an echo-counting algorithm to estimate organism density by depth. The final axis 3) utilizes acoustic data collected during three WARMALIS campaigns in the western tropical Pacific to describe it at large scale. Five different ecosystems could be characterized. The spatio-temporal distribution of micronekton appears different in each of them, in relation with environmental variables (temperature, oxygen, salinity, currents, etc.). This division highlights the presence of the Warm Pool, the equatorial upwelling, and oligotrophic zones, each characterized by different vertical structuring and micronekton density. This thesis emphasizes the various biases of micronekton study methods and the utility of combining them to obtain more robust estimates. By then applying these methods to the tropical Pacific, it demonstrates the considerable variability of ecosystems on a Pacific scale. Including this spatial variability in global predictions of micronekton abundance and biomass is essential for refining estimates and understanding the link between the environment and biology. Finally, it reaffirms the need to consider micronekton for the sustainable preservation and management of oceanic ecosystems
Receveur, Aurore. "Ecologie spatiale du micronecton : distribution, diversité et importance dans la structuration de l'écosystème pélagique du Pacifique sud-ouest." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0401.
Full textThe New Caledonian pelagic ecosystem in the southwest Pacific contains a high diversity of predators, such as seabirds and cetaceans. The recent creation of the Natural Park of the Coral Sea created a need for solid information on the functioning of this remarkable ecosystem, particularly on the dynamics of the micronecton (organisms between 1 and 20 cm constituting food of top predators) and its central role in food webs, especially since is the most poorly understood. In this context, this PhD showed a strong influence of environment on its spatial and seasonal distribution with on average more micronekton in the south than in the north, and more in winter than in summer. The species composing the micronecton are riche in crustaceans in the north and in cephalopods and fish in the south. The micronecton abundance would tend to decrease under the influence of climate change. Finally, we showed that the spatial distribution of this group influenced the presence of six groups of predators: yellowfin tuna, albacore tuna, dolphin, dolphin, shearwater and red-footed body
Messié, Monique. "Contrôle de la dynamique de la biomasse phytoplanctonique dans le Pacifique tropical ouest." Phd thesis, Université Paul Sabatier - Toulouse III, 2006. http://tel.archives-ouvertes.fr/tel-00137145.
Full textDerville, Solène. "Écologie spatiale des baleines à bosse en zone de reproduction : habitats, distribution et mouvements dans le Pacifique Sud." Electronic Thesis or Diss., Sorbonne université, 2018. http://www.theses.fr/2018SORUS374.
Full textUnderstanding the social and environmental drivers of the distribution and movements of marine megafauna is essential to their conservation. Cetaceans are elusive and mobile species, whose management requires an improved understanding of habitat use patterns. This thesis is aimed at investigating the spatial ecology of an endangered population of humpback whales (Megaptera novaeangliae) in the South Pacific Ocean. Using a multidisciplinary dataset collected between 1995 and 2018 in New Caledonia and Oceania, this thesis addressed three objectives, 1) investigate best practices to cetacean species distribution modeling, 2) acquire fundamental knowledge on the distribution, habitats and movements of humpback whales in Oceania breeding grounds, and 3) predict priority conservation areas and potential threats to humpback whales. Modeling the distribution of a migratory large whale from non-systematic visual survey and citizen science data provided valuable space-use predictions when uneven survey effort and statistical overfitting were specifically addressed. Generalized Additive Models were favored for their complexity trade-off, ecological interpretability and transferability. Models of habitat use revealed a preference for a diversity of shallow habitats (low island and atoll lagoons, barrier reef and high island slopes, banks and seamounts) spread over a relatively large thermal range over Oceania. Shallow seamounts and banks were identified as major breeding and nursing habitats and play a key role in the connectivity within and between populations. This unique and unexpected use of pelagic waters has important consequences for the spatial management of humpback whales. The predictions of present and future suitable humpback whale breeding habitats at multiples scales provide science-based evidence for priority conservation areas, and enable mitigation of threats from anthropogenic activities and climate change in the South Pacific
Houssard, Patrick. "Variations des concentrations en mercure dans les réseaux trophiques marins de l'Océan Pacifique Sud : état des lieux, caractérisation des sources et relations avec la dynamique trophique et physique du milieu." Thesis, Nouvelle Calédonie, 2017. http://www.theses.fr/2017NCAL0001/document.
Full textMercury is a naturally distributed heavy metal which is characterized, under its organic form (monomethylmercury; MMHg), by its bioaccumulation in living organisms and its biomagnifications along food chains. Since the awareness of MMHg neurotoxicity, lots of research works have focused on understanding where and how MMHg is formed and transmited to marine food webs. Those questions are keys in order to anticipate how MMHg, in commercially fish species, will respond in a context of increasing mercury emissions and climate change.This work is part of this approach by studying total mercury spatial variations from muscle tissue of three tuna species: bigeye, albacore and yellowfin tuna, captured within the south Pacific Ocean. Every tuna species demonstrated a consistent and similar spatial trend, with higher total mercury concentrations in the southwest and lower concentrations in the western equatorial Pacific. This spatial trend seems to be in accordance with varying tuna diet linked to the thermal features of the water column. By combining archival tagging data and nitrogen stable isotope analysis, we showed that the deepening of bigeye tuna vertical habitat around New Caledonia might allow them to forage on deeper and MMHg enriched preys. Additionnaly, dissolved MMHg profiles in the southwest Pacific suggest higher methylation processes in the epipelagic zone leading, possibly, to higher MMHg bioavailability for marine food chains.This study highlighted the key role of tuna trophic ecology and particularly foraging depth in their MMHg exposure. Those features have to be considered in future studies evaluating food webs contamination at a spatial or temporal scale
Maufroy, Alexandra. "Drifting Fish Aggregating Devices of the Atlantic and Indian Oceans : modalities of use, fishing efficiency and potential management." Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT150/document.
Full textSince the mid 1990s, the use of drifting Fish Aggregating Devices (dFADs) by purse seiners, artificial objects specifically designed to aggregate fish, has become an important mean of catching tropical tunas. In recent years, the massive deployments of dFADs, as well as the massive use of tracking devices on dFADs and natural floating objects, such as GPS buoys, have raised serious concerns for tropical tuna stocks, bycatch species and pelagic ecosystem functioning. Despite these concerns, relatively little is known about the modalities of GPS buoy tracked objects use, making it difficult to assess and manage of the impacts of this fishing practice. To fill these knowledge gaps, we have analyzed GPS buoy tracks provided by the three French fishing companies operating in the Atlantic and the Indian Oceans, representing a large proportion of the floating objects monitored by the French fleet. These data were combined with multiple sources of information: logbook data, Vessel Monitoring System (VMS) tracks of French purse seiners, information on support vessels and Local Ecological Knowledge (LEK) of purse seine skippers to describe GPS buoy deployment strategies, estimate the total number of GPS buoy equipped dFADs used in the Atlantic and Indian Oceans, measure the contribution of strategies with FOBs and support vessels to the fishing efficiency of tropical tuna purse seiners, identify potential damages caused by lost dFADs and finally to propose management options for tropical tuna purse seine FOB fisheries. Results indicate clear seasonal patterns of GPS buoy deployment in the two oceans, a rapid expansion in the use of dFADs over the last 7 years with an increase of 4.2 times in the Indian Ocean and 7.0 times in the Atlantic Ocean, possible damages to fragile coastal ecosystems with 10% of GPS buoy tracks ending with a beaching event and an increased efficiency of tropical tuna purse seine fleets from 3.9% to 18.8% in the Atlantic Ocean over 2003-2014 and from 10.7% to 26.3% in the Indian Ocean. Interviews with purse seine skippers underlined the need for a more efficient management of the fishery, including the implementation of catch quotas, a limitation of the capacity of purse seine fleets and a regulation of the use of support vessels. These results represent a first step towards better assessment and management of purse seine FOB fisheries