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Les premiers stades de vie des poissons dans le SO de Madagascar : éléments pour une meilleure connaissance de la biodiversité et une meilleure gestion des ressources exploitées

Abstract : Marine ecosystems which provide multiple ecosystem services essential to human well-being are currently threatened by resources overexploitation and the use of destructive fishing gears. This leads to a global loss of 20% of mangroves, 19% of coral reefs, and 110 km2 per year of seagrass meadows. The coastal habitats that support up to 20% of global fisheries production are the most affected, particularly in least developed countries such as Madagascar. In this country, 87% of coral reef are threatened, particularly in the southwestern part of the island where small-scale fishermen practice juveniles fishing. A better knowledge of the ecology of young fishes is thus a key point for the implementation of effective and robust measures. The present work was centred on early developmental stages of fish identified using DNA barcoding. Identifications to the species level were used to predict the post-larvae supply and to discover the variability in juveniles recruitment that appears to be related to the alteration of post-larvae supply. In total, 387 species have been observed with nine new species for Madagascar. The interests and limitations of DNA barcoding are widely discussed in Chapter 1. Post-larvae supply was better predicted by the remotely sensed oceanic conditions with an accuracy of 60% for species richness and 50% for abundance. However, the performance of models for predicting abundance appears to be influenced by the characteristics of water masses that are different among sites, while the performance of models for predicting species richness appears similar between the sites (discussed in Chapter 2). The remotely sensed oceanic conditions better explained the post-larval fish assemblages. However, these oceanic conditions structure mostly the post-larval fish assemblages in water masses with coastal water characteristics than those in waters with ocean characteristics (discussed in Chapter 3). The period of juvenile recruitment as well as juvenile assemblages differ among years. These interannual variabilities were also observed on post-larvae supply which were conditioned by the interannual variation of oceanic conditions. This suggests that alterations in post-larvae supply influence the temporal distribution of juvenile fish, which is a subject discussed in Chapter 4. The case of Siganidae recruitment, which seems to be strongly linked to post-larvae supply, is developed in the final discussion of this thesis. Likewise, the identification of nursery areas allows to propose management measures to deal with the local context that are also discussed.
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2019LARE0030HJaonalison.pdf
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  • HAL Id : tel-02934727, version 1

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Henitsoa Jaonalison. Les premiers stades de vie des poissons dans le SO de Madagascar : éléments pour une meilleure connaissance de la biodiversité et une meilleure gestion des ressources exploitées. Biologie animale. Université de la Réunion; Institut halieutique et des sciences marines (Tuléar, Madagascar), 2019. Français. ⟨NNT : 2019LARE0030⟩. ⟨tel-02934727⟩

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