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Side-looking, fixed-location sonar is used to estimate the abundance of migrating chinook salmon Oncorhynchus tshawytscha in the Kenai River, Alaska. For this application, echo-envelope length has previously been shown to predict fish size better than target strength. Using tethered-fish experiments we generalize these findings to other hydroacoustic descriptors based on time measurements, including range-measurement variability and fish lateral movement. These variables are all descriptors of the echo signal through time. Measurements of these attributes were correlated with daily indices of the species composition of unrestrained fish passing the sonar site. We hypothesize that time-based characteristics are superior...
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