Downstream migration of juvenile European sturgeonAcipenser sturio L. in the Gironde estuary |
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| Authors: | Eric Rochard Mario Lepage Pierre Dumont Serge Tremblay Christine Gazeau |
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| Institution: | (1) Aqua-Logiq, 527 rue Zac Petite Camargue, 34400 Lunel, France;(2) Cemagref, Estuarine Ecosystems and Diadromous Fish Research Unit, 50 Avenue de Verdun, 33612 Cestas Cedex, France |
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| Abstract: | The European sturgeon (Acipenser sturio) is an endangered diadromous fish species that spawns in the rivers in late spring and early summer. The juveniles spend
their first years in the brackish waters (5‰ to 25‰) of the estuary zone before moving out to sea. This study describes the
downstream migration pattern of juvenile sturgeon, belonging to the 1994 cohort, the only one born naturally in the Gironde
basin, France since the end of the 1980s. During October 1994 to December 1996 the inland section of the Gironde estuary was
sampled monthly by trawl (n=818 tows) and all European sturgeon caught (n=381) were marked and released. The first sturgeon
of the 1994 cohort (TL=27 cm) were caught in early March 1995 in the zones furthest upstream. During their second fall of
life, juveniles gradually acclimatized, and spread over a wide range of salinity conditions. A first incursion into marine
water was also observed (at least for a few fish) by the end of the second winter. During this second period, sturgeon showed
preference for two particular zones situated at 18 and 38 km, respectively, from the mouth of the estuary. These zones, belonging
to two different salinity sectors of the estuary, did not appear to be any different to their neighbors with regards to depth
and type of substrate. There were no significant size differences among estuarine zones. Seasonal movements of sturgeon seem
to be motivated by a search for warmer temperatures. After a period of early acclimatization of 15 months, juvenile European
sturgeon appear to be highly tolerant of salinity variations. |
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