(trad auto)Place of energy status in the migration dynamics of the European eel elver (Anguilla anguilla)

• Main Author: Bureau Du Colombier, Sarah
• Other Authors: Ecosystèmes estuariens et poissons migrateurs amphihalins (UR EPBX), Centre national du machinisme agricole, du génie rural, des eaux et forêts (CEMAGREF), Thèse en sciences exactes et leurs applications, spécialité physiologie et biologie des organismes, populations, intéractions, Université de Pau et des Pays de l'Adour
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2008
• Subjects: thesis; thèse; [SDE]Environmental Sciences; Anguilla anguilla
• Online Access: https://hal.inrae.fr/tel-02591500; https://hal.inrae.fr/tel-02591500/document; https://hal.inrae.fr/tel-02591500/file/pub00025670.pdf

Eels were described a long time as migratory fish reproducing at sea and growing in river. However, studies realised during the last decade showed that some eels do not grow in fresh water. Absence of migration toward fresh water suggests divergences in migratory behaviour in the tidal area, i.e. some glass eels would migrate upstream when other individuals would settle in marine waters or in estuary. The aim of this thesis was to better understand origin of different migratory patterns in glass eels of the European eel (Anguilla anguilla), and mostly involvement of fish energy status. First, glass eels caught in the course of estuarine migration were sorted according to their propensity to follow migration and classified as M+ (high propensity) or M- (low propensity). Energy content, energy expenditure and feeding level of both groups of glass eels were compared. Results showed higher energy content in M+ than in M- fish caught in middle of estuary, but not in those caught at estuary entrance. These observations suggest that glass eel energy content is involved in migratory divergences in middle of estuary, but a factor other than energy content alone would be involved at estuary entrance. Existence of an individual energy threshold determining whether a fish will follow or stop migration was proposed. Results also highlighted higher energy expenditure and slower and / or lower feeding resumption in M-. The role of hormonal and genetic factors was discussed. An interpretation on the involvement of these results in the maintenance of both sedentary / migrant tactics was proposed. Subsequently, experimental results were translated into parameters of a model of estuarine migration. This work underlined to which extent experimental results enable to reproduce glass eel migratory behaviour in estuary and how they need to be completed. The sharp decline in eel stocks observed since 1970-1980 needs to better understand causes of this decrease, to put in place suitable management methods. Further knowledge provided by ...