Estimating the Error in Riverine Sonar Estimates of Salmon

The success of a riverine sonar project designed to estimate adult salmon passage depends on many factors. At the Yentna River in Alaska, salmon passage is estimated using hydroacoustics and apportioned to species using capture information from fish wheels operated along either side of the river. Recent mark-recapture studies indicated the apportioned sonar estimate may be biased low. For this study, we identified potential error sources to determine whether the bias was true, and if so, what aspect or aspects of the sonar and/or fish wheel operations were the cause. The potential error sources that were investigated included: 1) uneven capture probabilities inherent in the fish wheel data, 2) fish migrating outside the coverage of the sonar beam, 3)  reduced fish detection within the sonar beam, 4) observer counting errors, 5) the sampling design, and 6) truncation of the field season.