Hydroacoustics is a cost-effective tool for surveying fish communities in large lowland rivers and lakes and will be a key element in providing temporal and spatial data for the national fisheries monitoring programme and the Water Framework Directive. However, deployment of sonar in horizontal mobile surveys is still in the developmental stage, and successive surveys on the same fish populations can produce very variable results. In addition, three types of echosounder are currently in use within the Environment Agency and comparisons between results obtained from different systems are difficult to conduct. In order to improve robustness of information obtained from horizontal hydroacoustic fisheries surveys, this project was commissioned to account for the observed sampling variability. Two potential sources of variability were examined:
- Differences between echosounders in operation.
- Variability due to key abiotic factors affecting fish behaviour.