Hydroacoustic Monitoring of Downstream Migrant Salmon and Steelhead at Wells Dam in Spring 1984
chinook, downstream fish passage, downstream migration, fish passage, forebay, hatchery, hydroacoustics, juvenile, migration, monitoring, night, salmon, smolt, sockeye salmon, steelhead, transducers, turbines, Wells Dam
The downstream migration of salmon and steelhead in spring 1984 at Wells Dam on the mid-Columbia River was monitored using hydroacoustics. The primary objective of this research was to document run timing and describe the distribution of smolts at the dam. The study occurred from April 2 to June 15, 1984. Four transducers were deployed at the bases of pier noses at Turbines 3, 5, 7, and 9 and aimed up to 24º into the forebay. They were sampled once every hour, 24 hours per day, for 75 days. An index of fish passage was reported daily to the Water Budget Center in Portland, Oregon. This index was computed as follows. For each 24-h period, separate fish passage rates (number/time) at each of the four sampling locations were estimated by dividing the sum of the 'weighted' fish detections by total sample time. These four values then were averaged to produce the daily index (number/day/location). The first substantial increase in fish passage occurred on April 25, 1984 due to the chinook released from the Winthrop hatchery on April 23. During May, run timing was fairly uniform except for peaks on May 2, 14, 18, and 22. The unexpected peak in run size that occurred from May 29 to June 2 could have been caused by juvenile mountain whitefish. Although the proportion of each species varied, chinook passage probably peaked in late April, and steelhead in the first two weeks of May; sockeye passage was variable throughout the study. The data indicated that most downstream migrants were distributed high in the water column and toward the western end of the dam. Average hourly passage rates for day and night were similar, but more fish passed the dam during the longer period of daylight than the shorter period of darkness.