Abstract

Diel variation of Fish Abundance in the Lahme Reservoir (North Tunisia) using Acoustic Methods

Author(s): Imed Djemali and Rachid Toujani

In order to choose the best period of acoustic sampling and fishing on diel in the Lahme Reservoir (North Tunisia), acoustic surveys day and night were carried using a Simrad EK60 echosounder. The surface layer from0 to 3m depth was sampled with a horizontal transducer tilted 2 degrees down to the surface, while the layer more than 3m depth was sampled with a vertical transducer located at 50cmbelowthe surface of thewater.Acoustic sizes of the fish were higher in daytime than during the night while the biomass of fish was significatively higher during daytime. We concluded that at Lahme Reservoir the accesibility to the biggest fish were largest during daytime and consequently this period is the most conducive for acoustic sampling and for fishing.