Comparison of DIDSON Versus Video Estimates of 2013 Spring Chinook and Steelhead Escapement to the Upper Basin of the Klickitat River
A Dual-Frequency Identification Sonar (DIDSON) sonar was deployed during the summer of 2013 to obtain an escapement estimate of spring Chinook Salmon Oncorhynchus tshawytscha and steelhead O. mykiss through the Castile Falls fishway and into the upper basin of the Klickitat River. The DIDSON was set up immediately outside a portion of fishway through which the fish could exit, and was programmed to continuously record sequential 1-hour files. During review of the recorded files, date and time of fish passage events were noted, and the events summed to provide an estimate of total escapement. These data were compared to those obtained with a video recording system installed before a viewing window within the recently constructed monitoring facility at the fishway, which in addition provided identification of the fish to species.
Between June 29 and September 28, 2013, a total of 11 medium to large-sized fish were observed in the DIDSON files. The 2013 video recordings showed a total of 34 upstream passage events during the same time period. In 2012, DIDSON provided a similarly reduced escapement estimate relative to that obtained with video recordings. Low resolution of the DIDSON images is no doubt the cause for underestimation of escapement. However, the video estimates are not without some level of uncertainty as well. Of the 11 DIDSON counts, only 3 appeared to involve passage events for which there was a corresponding video observation. It is likely that the video recordings also missed some passage events, and a combined escapement estimate for 2013 would be 42 fish.
Galbreath, P. F., P. E. Barber, and C. R. Frederiksen. 2014. Comparison of DIDSON versus video estimates of 2013 spring Chinook and steelhead escapement to the upper basin of the Klickitat River. Columbia River Inter-Tribal Fish Commission Technical Report 14-05. Portland, OR. 22p.