| Abstract |
T h e migratory context of the Loire basin is caracterized by its hydro-ecological diversity and its geographic extension. This hydrographie system s t e m m i n g f r o m ancient massifs has a large potential for migratory fish, as s h o w n by historical data of the ligerian (Loire) fisheries production. S p e c i e s diversity has mainly b e e n p r e s e r v e d but, f r o m t h e quantitative point of view, the state of amphihaline populations has seriously declined. T h e limiting factors of these stocks result f r o m t h e cumulative effect of impacts that o c c u r a l o n g t h e migration circuits and w h i c h increase a c c o r d i n g to the size of t h e b a s i n . W h i l e t h e m a i n Ligerian rivers have been relatively s p a r e d by major hydraulic developments, they are nevertheless seriously affected by a large n u m b e r of obstacles that delay migration a n d c a n c o m p r o m i s e t h e a c c e s s to the s p a w n i n g areas. T h e s a m e is true of the eutrophication w h i c h w o r s e n s a s m o r e pollutants are a d d e d , culminating with a m a x i m u m of turbidity in t h e e s t u a r y ( b o u c h o n v a s e u x ) . Under these conditions, the ligerian stocks are strongly d e p e n d e n t o n t h e hydrology. Interannual flow variations can temporary reduce the influence of t h e limiting factors or, o n t h e contrary, lead to crisis situations that threaten the preservation of the species. In addition to the restoration actions undertaken since the beginning of the 1980fs, major operations s u c h a s t h e removal of the M a i s o n s R o u g e s d a m (Vienne) have b e e n carried within t h e f r a m e of t h e Plan Loire G r a n d e u r Nature. T h e s e operations s h o u l d help to reach t h e m i n i m u m n e c e s s a r y limits for stocks reconstitution. Tangible signs of stock recovery are appearing in the Vienne basin.The first results of stocks reconstitution have b e e n quantified o n t h e Allier River at Vichy dam, which is equipped with a control stations. However, achieving the objectives a n d evaluating the results for t h e w h o l e basin remains g o v e r n e d by e q u i p m e n t of o n e major obstacle on each of the other three main migration axes of the basin (Loire, Vienne, Creuse), with the installation of efficient migration and monitoring systems. |