MONITORING FISH MOVEMENT PATTERNS IN A RESERVOIR USING HORIZONTALLY SCANNING SPLIT-BEAM TECHNIQUES

Horizontally scanning split-beam hydroacoustics was used to monitor do wnstream migrating juvenile salmon and steelhead trout smelts (Oncorhy nchus spp.). The study was conducted in the reservoir of Rocky Reach D am on the Columbia River (Washington, USA). The objective was to deter mine the movement patterns of smelts as they migrated through the rese rvoir. Scanning split-beam hydroacoustic techniques and three-dimensio nal target tracking were combined with remote multiplexing with the ai m of investigating smelt movement patterns in the reservoir. The traje ctory profiles, target strength distributions, and horizontal distribu tions of the smelts were estimated for each of six different aiming co nfigurations utilizing six different elliptical split-beam transducers . The results of this study were used to determine the optimal locatio n for installing a surface collector and bypass system. This system wi ll be used to collect and bypass smelts past the dam, a safer alternat ive to passing through the turbines. The results showed that fish migr ated downstream primarily along the east side of the reservoir, concen trated in the upper water column. Few fish were seen migrating down th e western shoreline. At the southern end of the reservoir, there were areas where the fish congregated into relatively large schools before proceeding on their downstream migration. Following this study, a smel t bypass system has been installed and is currently being evaluated. ( C) 1996 International Council for the Exploration of the Sea.