Monitoring fish movement patterns in a reservoir using horizontally scanning split-beam techniques

Abstract

Horizontally scanning split-beam hydroacoustics was used to monitor downstream migrating juvenile salmon and steelhead trout smolts (Oncorhynchusspp.). The study was conducted in the reservoir of Rocky Reach Dam on the Columbia River (Washington, USA). The objective was to determine the movement patterns of smolts as they migrated through the reservoir. Scanning split-beam hydroacoustic techniques and three-dimensional target tracking were combined with remote multiplexing with the aim of investigating smolt movement patterns in the reservoir. The trajectory profiles, target strength distributions, and horizontal distributions of the smolts were estimated for each of six different aiming configurations utilizing six different elliptical split-beam transducers. The results of this study were used to determine the optimal location for installing a surface collector and bypass system. This system will be used to collect and bypass smolts past the dam, a safer alternative to passing through the turbines. The results showed that fish migrated downstream primarily along the east side of the reservoir, concentrated in the upper water column. Few fish were seen migrating down the 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 smolt bypass system has been installed and is currently being evaluated.