First results on migrating shad (Alosa fallax) and mullet (Mugil cephalus)echocounting in a lock on the Rhone River (France) using a split-beam sounder, and relationships with environmental data and fish caught

The application of fisheries acoustics in shallow waters opens new fields o f observation and allows new methods for abundance estimates. In this paper we deal with echocounting of migrating fish crossing the Beaucaire-Vallabr egues lock, the first obstacle encountered on the Rhone, using a SIMRAD EY5 00 split-beam sounder, 70 kHz frequency. Two transducers sampled a section of water and evaluated approximately 35% of the lock section, based on a ca libration sphere. The number of fish crossing the lock was calculated for e ach fish lock. Crossing data for the fish were recorded (dates, position, e xit time). The present analysis did not allow the identification of the two major. species that cross the dam: shad (Alosa fallax) and mullet (Mugil c ephalus). The number of fish counted was positively correlated with the cat ches per unit effort (CPUE) by recreating fishermen below the dam and with increasing water temperature. (C) 2000 Ifremer/CNRS/INRA/IRDA/Cemagref/Edit ions scientifiques et medicales Elsevier SAS.