An active fish tracking split-beam sonar to study salmon smolt behavior

Abstract

An active fish tracking split-beam sonar (AFTS) is being used to study salmon smolt behavior at the Dalles Dam on the Columbia River. AFTS is based on the principle of tracking radar. Once a smolt is detected, two high-speed stepper motors align the axis of a digital split-beam transducer on the target. As the fish moves, deviation of the target from the beam axis is calculated and used to re-aim the transducer, thereby tracking the target. For each ping the target is tracked, data on fish position and target strength are recorded to disk. Fish position resolution is ±0.5 cm within a sample volume approximately 14 m of range from the transducer. Individual fish tracks are visualized in three-dimensional plotting software. AFTS tracks are coupled with hydraulic data from a computational fluid dynamics model to determine statistical relationships between fish movements and flow conditions. Sequential fish positions are also analyzed using a Markov process. Fish states observed with AFTS include holding, swimming actively downstream, and passive drift. The information from AFTS will aid design of bypass systems to protect endangered and threatened salmon populations in the Pacific Northwest. [This research is funded by the Corps of Engineers.]