2011 Spring Chinook Escapement to the Upper Basin of the Klickitat River Based on DIDSON Sonar Counts
A Dual-Frequency Identification Sonar (DIDSON) sonar was deployed to observe fish passage through the Castile Falls Fishway on the Klickitat River, to obtain an estimate of 2011 spring Chinook Oncorhynchus tshawytscha escapement to the upper basin. The DIDSON was set up with the intent to continuously record sequential 1-hour files from early July until mid-September. Technical problems occurred, however, and recordings were obtained for only 260 hours, 26% of the 1176 hours between August 3 (the date the Fishway was reopened following construction work, and the presumed beginning of the migration period) and September 20 (the estimated end of the migration period). An expansion of the observed count yields an estimate for total escapement of 38. No attempt was made to assign confidence limits to this estimate due to questions that exist regarding the non-random manner by which recorded files were obtained that compromises the statistical validity of the expansion. Nonetheless, the estimate is similar in magnitude the estimates of 24 ± 4 and of 26 to 27 derived with the DIDSON in 2009 and 2010, respectively. Also similar to the two prior years, the 2011 estimate contrasts substantially to that based on spawning ground surveys, which in fact was zero – no redds were observed during any of the surveys conducted in 2011. Whether pre-spawning mortality and/or unobserved redds accounts for the discrepancy is uncertain.
Galbreath, P.F., P.E. Barber, and C.R. Fredericksen. 2012. 2011 Spring Chinook Escapement to the Upper Basin of the Klickitat River Based on DIDSON Sonar Counts. Columbia River Inter-Tribal Fish Commission Technical Report 11-12, Portland, Oregon.