Chapter 7. Estimation of migrant yellow eel stock in large rivers through the survey of fish passes : a preliminary investigation in the River Meuse (Belgium)

The migration dynamics of yellow eels in the River Meuse were investigated at the Ampsin navigation weir, using fish passes as tools for discriminating resident and migrating eels. In 1993, 9548 eels (11-65 cm, mean 29,5 cm, pseudo normal distribution) were captured (daily maxima = 818-823 eels) in the two Denil fish passes on the weir. The periodicity of migration was consistant with that in previous years (1989-1993; 44 +/- 7 days, P50 on 1 June). Eels migrated in waves, almost independently of environmental parameters; 3724 eels were marked (Panjet inoculator) and released downstream of the weir. Recapture (2,1 %) suggest an annual rate of migration of 45 km/year sand a migrating flux of about 445.000 fish (15,5 t), with most eels probably migrating through the sluices. Utilization of fish passes to clarify eel stock distribution within the R. Meuse basin is discussed.