Première
caractérisation des histoires de vie des anguilles (anguilla anguilla)
occupant la zone aval du bassin versant Gironde-Garonne-Dordogne : apport
d’une méthode de microchimie
Françoise
DAVERAT (1), Pierre ÉLIE (1) & Michel LAHAYE (2)
(1) CEMAGREF,
50 avenue de Verdun, 33612 Cestas Gazinet cedex, FRANCE.
(2) CeCAMA ICMCB 87, Avenue du Docteur Schweitzer, 33608 Pessac cedex,
FRANCE.
Résumé.
- Les mouvements des fractions de populations d’anguille du bas
bassin versant Gironde-Garonne-Dordogne et de sa zone côtière
au travers de masses d’eau de différentes salinités
ont été étudiés au moyen d’une méthode
de microchimie des otolithes. Cette étude avait pour but de caractériser
des types d’histoire de vie des anguilles et d’évaluer
l’ampleur des échanges de fractions de population entre compartiments
de salinité distincte. Ainsi, trente-cinq anguilles provenant du
bassin d’Arcachon, des Pertuis charentais, de l’estuaire de
la Gironde et de la Garonne ont été analysées avec
la méthode de spectrométrie à dispersion d’onde
(WDS). Sur chaque otolithe un transect d’analyses correspondant à
l’histoire de vie de chaque poisson a été réalisé
afin de rendre compte de la teneur en strontium et en calcium depuis le
primordium jusqu’au bord de l’otolithe. Ces premiers résultats
montrent que l’on peut distinguer cinq types d’histoires de
vie. Trois d’entre eux sont associés à des individus
sédentaires à leur lieu de capture. Deux autres sont associés
à un changement majeur de milieu halin des anguilles au cours de
leur vie.
Abstract. - Microchemistry contribution
to a first approach to the diversity of life histories of eels from the
lower part of the Gironde-Garonne-Dordogne watershed.
By the means of microchemistry of otolith techniques, we intended to follow
the movements of eel populations from the lower part of Gironde-Garonne-Dordogne
watershed, through water masses of various salinity in order to both characterise
the type of life strategy and evaluate the level of exchanges between
fractions of population. Therefore, thirty five eel otoliths from Arcachon
lagoon, Pertuis charentais, Gironde estuary (mesohaline zone) and Garonne
river (freshwater zone without tide influence) were collected and analysed
with the Wavelenght Dispersive Spectrometry technique. On each otolith
a transect analysis was performed from the primordium to the edge, which
corresponds to the life history of each eel. The level of the ratio strontium/calcium
shown along the transects reveals the migration through different water
masses from the birth to date of capture. As a matter of fact, this ratio
Sr/Ca is supposed to reach the value of 8 x10-2 for an otolith of a fish
living in a marine habitat while freshwater eels have a ratio of 2 x10-2,
and estuarine get values in between those extreme levels. The first results
reveal that among individuals sampled in the different habitats covered
by the study, a total of five life history types can be distinguished.
Three types of life history is related to fish that has been living in
the same place where it has been collected. All the individuals from Garonne
and from Arcachon have Sr/Ca profiles in relation to either entirely freshwater
or entirely marine life. 70% of the sample from Pertuis Charentais and
from Gironde estuary have Sr/Ca profiles related to estuarine life. Meanwhile,
two other life history types are related to 30% of individuals from the
Gironde estuary and consistent with a change in environment during their
growth phase. Some of them have experimented a first part of life in a
freshwater environment before moving to an estuarine environment while
the other type has experimented a first part of life in a marine environment
before moving to an estuarine environment.
Key words. - Anguillidae
- Anguilla anguilla - European eel - France - Otolith - Sr/Ca.
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