Tritech high frequency sonars are used for automatic target detection and tracking around several tidal turbines as part of Environmental Effects Monitoring Programmes (EEMP). Historically, attention has been focused on using this technology to monitor marine mammals but newer installations are extending requirements to include fish. The benefits of using 720 kHz sonars in permanent installations are the avoidance of marine mammal hearing and echolocation ranges and minimisation of noise pollution affecting marine life. The cost is not detecting swim bladders or lungs, although this is mitigated by using a geometric approach to target identification and tracking. The methods of identifying and tracking targets are presented in this paper along with details of target evaluation, e.g. size and velocity. In order to validate the extension of using these methods from marine mammals to fish, results are shown comparing sizes of automatically detected targets to physical measurements. This work is part of the early stage of the Integrated Active and Passive Acoustic System for Environmental Monitoring of Fish and Marine Mammals in Tidal Energy Sites (ISEM) project.