Spatial and temporal distribution of bull trout (Salvelinus confluentus)-size fish near the floating surface collector in the North Fork Reservoir, Oregon, 2016

Acoustic cameras were used to assess the behavior and abundance of bull trout (Salvelinus confluentus)-size fish at the entrance to the North Fork Reservoir juvenile fish floating surface collector (FSC). The purpose of the FSC is to collect downriver migrating juvenile salmonids at the North Fork Dam, and safely route them around the hydroelectric projects. The objective of the acoustic camera component of this study was to assess the behaviors of bull trout-size fish observed near the FSC, and to determine if the presence of bull trout-size fish influenced the collection or abundance of juvenile salmonids. Acoustic cameras were deployed near the surface and floor of the entrance to the FSC. The acoustic camera technology was an informative tool for assessing abundance and spatial and temporal behaviors of bull trout-size fish near the entrance of the FSC. Bull trout-size fish were regularly observed near the entrance, with greater abundances on the deep camera than on the shallow camera. Additionally, greater abundances were observed during the hours of sunlight than were observed during the night. Behavioral differences also were observed at the two depths, with surface fish traveling faster and straighter with more directed movement, and fish observed on the deep camera generally showing more milling behavior. Modeling potential predator-prey interactions and influences using collected passive integrated transponder (PIT) -tagged juvenile salmonids proved largely unpredictable, although these fish provided relevant timing and collection information. Overall, the results indicate that bull trout-size fish are present near the entrance of the FSC, concomitant with juvenile salmonids, and their abundances and behaviors indicate that they may be drawn to the entrance of the FSC because of the abundance of prey-sized fish.