Potential to estimate relative fish biomass in reservoirs using a commercially available hydro-acoustic fish finder

Abstract

This study evaluates the potential of the Fish Smart Sonar Deeper CHIRP +2 for estimating relative fish biomass in reservoirs. Data were collected from 5 Sri Lankan reservoirs between 19 March and 1 April 2024: Kiriibban wewa, Handapanagala, Hakwatuna Oya, Maha Wilachchiya and Mahakanadarawa. Hydro-acoustic data were recorded in down-imaging mode using a 7° beam at 675 kHz, wirelessly connected to its official mobile app (Fish Deeper – Fishing App). Fish count, their size categories, swimming depth (ft) and depth at target location (ft) were manually extracted by observing the recorded survey in mobile and web applications. Statistical analyses revealed significant differences in mean fish swimming depths across reservoirs (ANOVA: p<0.001), with larger fish occupying deeper waters compared to smaller fish. In Kiriibban Wewa, swimming depth of all fish size categories showed strong correlations with the depth at target locations (R² = 0.94–0.96). The number of fish living in each reservoir was estimated from the number of fish targets counted on the hydro-acoustic survey transects of corresponding reservoir. The findings suggest that the Fish Smart Sonar Deeper CHIRP+2 is a potential cost-effective tool for hydro-acoustic surveys subject to further research testing accuracy of the estimates.