Tracking continental habitat shifts of eels using otolith Sr/Ca ratios: validation and application to the coastal, estuarine and riverine eels of the Gironde–Garonne–Dordogne watershed
F. Daverat A D , J. Tomas B , M. Lahaye C , M. Palmer B and P. Elie AA Cemagref, 50 Avenue de Verdun, 33612 Cestas, France.
B Institut Mediterrani d’Estudis Avançats (IMEDEA), CSIC-UIB, Miquel Marquès 21, 07190 Esporles, Balearic Islands, Spain.
C CeCaMA, 87 Avenue Albert Schweitzer, 33608 Pessac Cedex, France.
D Corresponding author. Email: francoise.daverat@cemagref.fr
Marine and Freshwater Research 56(5) 619-627 https://doi.org/10.1071/MF04175
Submitted: 16 July 2004 Accepted: 28 January 2005 Published: 21 July 2005
Abstract
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 2 months between aquaria filled with water coming from the Dordogne river (salinity = 0), the upper Gironde estuary (salinity = 5), the lower Gironde estuary (salinity = 25) and the coast (salinity = 30), which represented 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 (fresh water or seawater). X-ray electron microprobe (wavelength dispersive spectrometry, 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 otoliths of control fish outside glass eel marks in either group of fish. The electron microprobe (WDS) analysis of the Sr/Ca life (transected in several 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.
Extra keywords: contingents, estuary, life history, migration, otolith, Sr/Ca, validation.
Acknowledgments
We are indebted to the Water Quality team of Cemagref for conducting the analysis of Calcium in the water (Jean François Dubernet). We acknowledge Sylvie Augagneur for providing expertise and assistance with the ICP-MS analyses. We thank Jean François Bigot and Bernard Ballion for their assistance on the research vessel. This work was funded by the programmes, GIS ECOBAG and the French Ministry of Environment (GRISAM).
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