A comparison of recreational and survey-grade side-scan sonar systems in mapping reservoir fish habitat

Abstract Objective Littoral zone aquatic habitat is an important component of sport fish population dynamics in freshwater lakes and reservoirs and is a primary target of fisheries management actions. However, habitat data for these systems are often minimal or nonexistent due to the cost and time-consuming nature of traditional aquatic habitat sampling methods. Side-scan sonar has been identified as a potential tool that can address these limitations, allowing quantification of habitat features over large areas. Side-scan sonar is available in two forms: recreational (consumer grade) and professional (survey grade). Our goal was to compare these two grades of side-scan sonar by analyzing their ability to map littoral habitat features in three Ohio reservoirs. Methods We used a Lowrance Active Imaging 3-in-1 system (≈US$2000) recreational sonar and an EdgeTech 6205 system (≈$150,000) survey-grade sonar to collect imagery in the littoral zones of reservoirs. We manually quantified submerged woody debris, standing timber, aquatic vegetation, and benthic substrate in a geographical information system (GIS) using imagery from each sonar system and compared habitat estimates and GIS processing times. We analyzed how differences in image resolution between the two sonar systems affected the level of variation in habitat classification values generated by individual analysts. Result We found small differences in habitat classification values and accuracy between the two sonar systems, and trade-offs existed in spatial accuracy and ability to image dense vegetation. However, side-scan data acquisition, postprocessing, and habitat classification were generally less time-intensive with the recreational Lowrance system than with the survey-grade EdgeTech system. Unexpectedly, the lower quality Lowrance imagery had less user-based variation in GIS habitat classification. Conclusion Recreational side-scan sonar systems such as the Lowrance system provide sufficient imagery resolution, habitat classification values, and accuracy at a lower cost and with less processing time than survey-grade side-scan sonar systems and are useful tools for quantifying littoral habitat features in reservoirs.