La bande côtière du littoral Sud-ouest de Madagascar est occupée par le groupe des Vezo dont la pêche est le principal moyen de subsistance. Cette occupation s’inscrit dans une longue histoire depuis l’époque de la traite d’esclaves, au XVIIème siècle. Les Vezo ont fondé leur identité grâce à la pêche et à la maîtrise de la navigation, avec la mise en place de sites interdits en mer pour gérer les ressources. Au début des années 1980, les océanographes ont signalé que les écosystèmes marins et côtiers étaient « en danger ». On attribue généralement la dégradation de l’environnement à l’accroissement de la pauvreté, à une demande accrue de produits halieutiques par le marché national et international, ainsi qu’à l’augmentation du nombre des usagers de la mer. Le diagnostic négatif quant à l’évolution des écosystèmes est à l’origine de l’intervention des institutions internationales et agences de développement dès le début des années 1990. Sur le registre du développement, il s’agit alors de moderniser les pratiques traditionnelles vezo et leurs engins de pêche. Dans le même temps, les conservationnistes créent des réserves marines et assurent la promotion du « volontourisme » et de l’aquaculture. A travers l’exemple d’Andavadoake, nous analysons l’évolution de l’occupation de l’espace ainsi que celle des pratiques de pêche, dont l’originalité était la gestion des tanifaly, espaces sacrés. Quelle évolution de l’identité vezo autorise l’appréhension d’un tel changement ? Une analyse des stratégies territoriales dans leur profondeur historique nous permet de remettre en cause le classement des Vezo en groupe ethnique, ce qui est aussi une des ambitions de notre thèse. Enfin, nous évaluons dans quelle mesure la politique de mise en réserves des écosystèmes marins a participé aux transformations organisationnelles et spatiales des Vezo. / The coastal strip of the southwest of Madagascar is occupied by the group of Vezo whose fishing is the main livelihood. This occupation is part of a long history since the days of the slave trade (seventeenth century). Vezo based their identity through fishing (with the introduction of banned sites to manage marine resources) and control of navigation. In the early 1980s, oceanographers have reported that marine and coastal ecosystems are "in danger." It is generally attributed to increased poverty, a strong demand for fish products by the national and international market, and a higher number of users of the sea. The negative result in the evolution of these ecosystems is the origin of the intervention, since the early 1990s, of the international institutions and development agencies to modernize traditional vezo practices and fishing gear. Similarly, conservationists have established marine protected areas and promoted “volontourism” and aquaculture. Through the example of Andavadoake, we analyze the evolution of the use of space as well as fishing practices, whose originality was managing tanifaly "sacred sites" which changes the vezo identity. An analysis of regional strategies in their historical depth allows us to challenge the classification in Vezo ethnic group, which is also one of the goals of our thesis. Finally, we will evaluate to what extent the policy of setting reserves participated in the organizational and spatial transformations Vezo. Finally, we evaluate how expansion of marine protected areas participate in the Vezo's organizational and spatial transformations.

Madagascar, a country whose extraordinary levels of endemism and biodiversity are celebrated globally by scientists and laymen alike, yet historically has received surprisingly little research attention, is the setting of the present dissertation. Here, I contribute to the need for applied research by: 1) focusing on the most intensely fished section of the Toliara Barrier Reef, the Bay of Ranobe; 2) characterizing the marine environment, the human population, and the fisheries; and 3) collecting the longest known time-series of data on fisheries of Madagascar, thereby providing a useful baseline for future analyses. In Chapter 1, the bathymetry of the Bay was characterized following a unique application of the boosted regression tree classifier to the RGB bands of IKONOS imagery. Derivation of water depths, based on DOS-corrected images, following a generic, log-transformed multiple linear regression approach produced a predictive accuracy of 1.28 m, whereas model fitting performed using the boosted regression tree classifier, allowing for interaction effects (tree complexity= 2), provided increased accuracy (RMSE= 1.01 m). Estimates of human population abundance, distribution, and dynamics were obtained following a dwelling-unit enumeration approach, using IKONOS Panchromatic and Google Earth images. Results indicated, in 2016, 31,850 people lived within 1 km of the shore, and 28,046 people lived within the 12 coastal villages of the Bay. Localized population growth rates within the villages, where birth rates and migration are combined, ranged from 2.96% - 6.83%, greatly exceeding official estimates of 2.78%. Annual pirogue counts demonstrated a shift in fishing effort from south to the north. Gear and boat (pirogue) profiles were developed, and the theoretical maximum number of fishermen predicted (n= 4,820), in 2013, from a regression model based on pirogue lengths (R2= 0.49). Spatial fishing effort distribution was mapped following a satellite-based enumeration of fishers-at-sea, resulting in a bay-wide estimate of intensity equaling 33.3 pirogue-meters km-2. Landings and CPUE were characterized, with respect to finfish, by family, species, gear, and village. Expansion of landings to bay-wide fisheries yields indicated 1,885.8 mt year-1 of mixed fisheries productivity, with an estimated wholesale value of 1.64 million USD per annum.