On the following subject: " Growth of European eels in Mediterranean lagoons Inter-habitat comparison of demography, habitat use tactics and the condition of future spawners".
Composition of the jury
Anthony ACOU Research engineer Museum national d'histoire naturelle MNHN CRESCO Dinard - Examiner
Hervé CAPRA INRAE Research Director - Examiner
Audrey DARNAUDE CNRS Research Fellow UMR Marbec - Examiner
Caroline DURIF Senior Research scientist Institute of Marine Research Austevoll Research - Rapporteur
Delphine NICOLAS Tour du Valat research officer - Thesis co-supervisor
Etienne PREVOST INRAE Research Director - Rapporteur
Jean-christophe POGGIALE University Professor AMU MIO - Thesis supervisor
Summary
The European eel (Anguilla anguilla) is a panmictic species with a complex life cycle, reproducing in sea and growing in continental waters, over a vast area stretching from the coasts of North Africa to northern Europe. Like other diadromous migratory fish, it faces multiple threats. Since the 1980s, its recruitment has fallen by more than 95 %. Classified as critically endangered, the eel has benefited since 2007 from a European regulation aimed at rebuilding its stock, with measures focused in particular on increasing the number of silver eels, future breeders. A better understanding of the growth of eels during their continental phase is crucial, as it is at this stage that effective management measures can be applied. During this phase, eels can colonise a wide variety of habitats, both within and between individuals, illustrating their remarkable phenotypic plasticity. Eel life-history traits vary according to environmental conditions. General trends show that eels grow faster in the south of their range, and in brackish environments compared with freshwater. Most studies on eel growth have focused on freshwater, brackish or marine environments on the Atlantic coast, leaving Mediterranean ecosystems largely under-studied. Mediterranean lagoon environments, which favour rapid eel growth and have a high potential for the production of future spawners, are thought to play a key role in the recovery of the world stock. Within these environments, the diversity of habitats present, ranging from oligohaline to hyperhaline, contributes to the expression of great variability in the life history traits of the eel. This thesis explores eel growth within a Mediterranean lagoon complex, the Rhône delta (France), by studying the influence of habitat type on silver eel production, in terms of both quantity and quality, and by examining the habitat use tactics of eels during growth. This work was based on a variety of methods, including modelling, schlerochronology, microchemical quantification, and ecotoxicological and epidemiological analyses. This multidisciplinary approach has shown the existence of distinct sub-populations in terms of abundance, sex ratio and life history traits, with high variability between and within the sites studied. The Vaccarès lagoon, a mesohaline to euhaline lagoon, appears to offer the best conditions for the production of silver eels, with good body condition, a high growth rate, an early age at silvering and significant abundance in favour of males. In contrast, eels from the Fumemorte freshwater channel show the lowest growth rates and abundances, with a sex ratio favouring females, but high survival rates. Habitat diversity in the Camargue lagoon complex appears to be essential for maintaining the variability of eel life-history traits. Some habitats that are suitable for eel growth are heavily polluted, leading to contamination of individuals, and underlines the urgent need to improve water quality. The knowledge acquired provides a baseline from which to consider actions aimed at improving the production of eels in good body condition and health, while taking account of the specific characteristics of each type of habitat.
Le Monday 16 December at 2pm to the Tour du Valatin the Jean-Paul Taris room (large room).