A New Multibeam Sonar Technique for Evaluating Fine-Scale Fish Behavior Near Hydroelectric Dam Guidance Structures
Behavioral Technologies for Fish Guidance: American Fisheries Society Symposium
American Fisheries Society
A Dual-Head Multibeam sonar (DHMS) system was developed for and deployed at two dam sites on the Snake and Columbia rivers in Washington State to evaluate the fine-scale (<1 m) movement behavior of salmon smolt as they approach prototype surface bypass and guidance structures intended to facilitate downstream fish passage. The DHMS system was mounted beneath a moored barge in front of the fish guidance structures to record the smolt's directional behavior. A system of locating devices was placed on the barge to translate target coordinates back to a stationary reference frame for locating fish relative to the dam. The multibeam sonar system is superior to more commonly used splitbeam sonar for ensonifying an adequate region (volume of water) in the proximity of a bypass opening. Multibeam sonar techniques allow the collection of relatively longer and continuous fish trajectories over larger regions, compared with earlier narrow-angle splitbeam hydroacoustic systems. In conjunction with analyzing fish track trajectories in three-spatial dimensions as produced by the DHMS, tracking software and computer visualization programs were developed to study the nature of fish behavior. The tracking software integrates data from the two multibeam systems and accommodates both automatic and manual processing of the data. Visualization software provides a reconstruction of the fish tracks to study entrainment behavior. Fish swimming straight into a bypass or guidance opening, or instead milling about, can also be distinguished with a simple quantitative metric called the tortuosity index. Additional metrics for quantifying the nature of fish trajectories are being developed to describe the detailed tracking data provided by the DHMS.