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

Abstract

The application of fisheries acoustics in shallow waters opens new fields of observation and allows new methods for abundance estimates. In this paper we deal with echocounting of migrating fish crossing the Beaucaire-Vallabrègues lock, the first obstacle encountered on the Rhône, using a SIMRAD EY500 split-beam sounder, 70 kHz frequency. Two transducers sampled a section of water and evaluated approximately 35% of the lock section, based on a calibration sphere. The number of fish crossing the lock was calculated for each fish lock. Crossing data for the fish were recorded (dates, position, exit time). The present analysis did not allow the identification of the two major species that cross the dam: shad (Alosa fallax) and mullet (Mugil cephalus). The number of fish counted was positively correlated with the catches per unit effort (CPUE) by recreating fishermen below the dam and with increasing water temperature.