(trad auto)Habitat use tactics and population dynamics of eels in the downstream zone of the Gironde Garonne Dordogne catchment area: contribution of the otolith study
In this study, the patterns of habitat use and their relative proportions were investigated for eels Anguilla anguilla sampled in coastal sites, the estuary and the river of the Gironde watershed by measuring Sr and Ca concentrations in the otolith. To enable a relevant interpretation of otolith str...
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| Other Authors: | , , |
| Format: | Doctoral or Postdoctoral Thesis |
| Language: | French |
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HAL CCSD
2005
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| Subjects: | |
| Online Access: | https://hal.inrae.fr/tel-02587056 https://hal.inrae.fr/tel-02587056/document https://hal.inrae.fr/tel-02587056/file/pub00018371.pdf |
| Summary: | In this study, the patterns of habitat use and their relative proportions were investigated for eels Anguilla anguilla sampled in coastal sites, the estuary and the river of the Gironde watershed by measuring Sr and Ca concentrations in the otolith. To enable a relevant interpretation of otolith strontium:calcium (Sr/Ca) variations in terms of habitat shifts of eels, the Sr/Ca-salinity relationship in eel otoliths was validated. Downstream and upstream migrations of young eels were reproduced in the laboratory by transferring groups of fish every two months between aquaria filled with water coming from the Dordogne river (salinity 0) , the upper Gironde estuary (5), the lower Gironde estuary (25) and the coast (30) representing the salinity gradient observed in the Gironde-Garonne-Dordogne watershed. Ontogenetic changes in otolith Sr/Ca were assessed in two groups of control fish that were kept in one of either two constant salinities (freshwater or seawater). WDS analyses of Sr/Ca ratios in the otoliths showed that the change of aquarium was recorded as a Sr/Ca increase (downstream migration) or a Sr/Ca decrease (upstream migration). No ontogenetic effect was detected in control fish away from the glass eel marks in otoliths in either group of fish. Signal processing methods used to analyse the Sr/Ca life transects in 270 otoliths of eels caught in the Gironde Garonne Dordogne watershed, showed that some of them were migrant eels that had experienced one major habitat shift during their continental life. Sr:Ca values outside the elver mark discriminated residence in the same habitat until capture (freshwater, estuary or sea) from a switch of habitat following three patterns: a shift from freshwater to estuary, seasonal movements within the limits of the estuary or a switch of habitat from brackish to freshwater (downstream nomads). Results show a gradient of residency from freshwater (100%) to estuary (44%) and the sea (24%). The most abundant (30%) alternative to residence in estuary and its adjacent coastal ... |
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