Le thon : enjeux et stratégies pour l'océan Indien

L'étude de la faune associée aux thonidés s'appuie sur l'embarquement d'observateurs scientifiques à bord des thoniers senneurs français et espagnols. C'est la distance entre une espèce pélagique et le banc de thons (inférieure à 650 m) qui définit si l'espèce est associée ou non au banc de thon. Les associations d'une espèce donnée avec les thonidés sont fortement liées aux types de bancs. L'analyse porte sur 432 calées. Les espèces associées aux bancs libres et aux animaux sont les plus gros albacores et patudos (de poids supérieur à 30 kg), les diodons et les exocets et les voiliers ; les espèces essentiellement associées aux objets naturels flottants sont les petits albacores et patudos (de poids inférieur à 10 kg) les marlins, les petits thonidés, les requins soyeux, les balistes, les coryphènes, les élagatis. Les objets flottants artificiels retiennent d'importantes quantités de kyphosidés et de wahoos, de requins océaniques et d'espadons. Les bancs libres se rencontrent dans le canal de Mozambique et à l'est des Seychelles. L'association avec les animaux est prépondérante au sud des Seychelles, les épaves naturelles dans la zone à l'ouest des Seychelles, les épaves artificielles dans la zone nord équatoriale et à l'est des Seychelles. (Résumé d'auteur

Statistics of the main purse seine fleets fishing in the Indian Ocean (1981-2008).

This document presents a summary of the statistics of French, Spanish, Italian, Seychelles and EU related NEI purse seine fleets fishing in the Indian Ocean since 1981: effort, catch by species and fishing type (log and free swimming schools), catch per unit of effort, sampling and mean weights for the main species. Since 2002, data from the European fleet (France and Spain) are collected within the framework of the EU “Data Collection Regulation” (DCR, Reg. 1543/2000 and 1639/2001), followed in 2008 by the “Community framework for the collection, management and use of data in the fisheries sector and support for scientific advice regarding the Common Fisheries Policy” (DCF, Reg 199/2008 and 665/2008). Data from other fleets are collected by SFA (Seychelles Fishing Authority). Data processing (species composition and size distribution) is done collectively for the whole fishery

Leaf δ15N as a physiological indicator of the responsiveness of N2-fixing alfalfa plants to elevated [CO2], temperature and low water availability

The contribution of carbon and nitrogen reserves to regrowth following shoot removal has been studied in the past. However, important gaps remain in understanding the effect of shoot cutting on nodule performance and its relevance during regrowth. In this study, isotopic labelling was conducted at root and canopy levels with both 15N2 and 13C-depleted CO2 on exclusively nitrogen-fixing alfalfa plants. As expected, our results indicate that the roots were the main sink organs before shoots were removed. Seven days after regrowth the carbon and nitrogen stored in the roots was invested in shoot biomass formation and partitioned to the nodules. The large depletion in nodule carbohydrate availability suggests that root-derived carbon compounds were delivered towards nodules in order to sustain respiratory activity. In addition to the limited carbohydrate availability, the upregulation of nodule peroxidases showed that oxidative stress was also involved during poor nodule performance. Fourteen days after cutting, and as a consequence of the stimulated photosynthetic and N2-fixing machinery, availability of Cnew and Nnew strongly diminished in the plants due to their replacement by C and N assimilated during the post-labelling period. In summary, our study indicated that during the first week of regrowth, root-derived C and N remobilization did not overcome C- and N-limitation in nodules and leaves. However, 14 days after cutting, leaf and nodule performance were re-established