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Chinook salmon in the Snake River basin were listed as threatened under the Endangered Species Act in 1992 (NMFS 1992). The Secesh River represents the only stream in the Snake River basin where natural origin (wild) salmon escapement monitoring occurs at the population level, absent a supplementation program. As such the Secesh River has been identified as a long term salmon escapement and productivity monitoring site by the Nez Perce Tribe Department of Fisheries Resources Management. Salmon managers will use this data for effective population management and evaluation of the effect of conservation actions on a natural origin salmon population. The Secesh River also acts as a reference stream for supplementation program comparison. Dual frequency identification sonar (DIDSON) was used to determine adult spring and summer Chinook salmon escapement in the Secesh River in 2008. DIDSON technology was selected because it provided a non-invasive method for escapement monitoring that avoided listed species trapping and handling incidental mortality, and fish impedance related concerns. The DIDSON monitoring site was operated continuously from June 13 to September 14. The first salmon passage was observed on July 3. DIDSON site total estimated salmon escapement, natural and hatchery fish, was 888 fish {+-} 65 fish (95% confidence interval). Coefficient of variation associated with the escapement estimate was 3.7%. The DIDSON unit was operational 98.1% of the salmon migration period. Adult salmon migration timing in the Secesh River occurred over 74 days from July 3 to September 14, with 5,262 total fish passages observed. The spawning migration had 10%, median, and 90% passage dates of July 8, July 16, and August 12, respectively. The maximum number of net upstream migrating salmon was above the DIDSON monitoring site on August 27. Validation monitoring of DIDSON target counts with underwater optical cameras occurred for species identification. A total of 860 optical camera identified salmon passage observations were identical to DIDSON target counts. However, optical cameras identified eight jack salmon (3 upstream, 5 downstream) less than 55 cm in length that DIDSON did not count as salmon because of the length criteria employed ({ge} 55 cm). Precision of the DIDSON technology was evaluated by comparing estimated net upstream salmon escapement and associated 95% confidence intervals between two DIDSON sonar units operated over a five day period. The DIDSON 1 salmon escapement was 145.7 fish ({+-} 2.3), and the DIDSON 2 escapement estimate was 150.5 fish ({+-} 5). The overlap in the 95% confidence intervals suggested that the two escapement estimates were not significantly different from each other. Known length salmon carcass trials were conducted in 2008 to examine the accuracy of manually measured lengths, obtained using DIDSON software, on high frequency files at a 5 m window length. Linear regression demonstrated a highly significant relationship between known lengths and manually measured salmon carcass lengths (p &lt; 0.0001). A positive bias in manual length measurement of 6.8% to 8% existed among the two observers in the analysis. Total Secesh River salmon escapement (natural origin and hatchery) in 2008 was 912 fish. Natural origin salmon escapement in the entire Secesh River drainage was 847 fish. The estimated natural origin spawner abundance was 836 fish. Salmon spawner abundance in 2008 increased by three fold compared to 2007 abundance levels. The 10 year geometric mean natural origin spawner abundance was 538 salmon and was below the recommended viable population threshold level established by the ICTRT (2007). One additional Snake River basin salmon population was assessed for comparison of natural origin salmon spawner abundance. The Johnson Creek/EFSF Salmon River population had a 10 year geometric mean natural origin spawner abundance of 254 salmon. Salmon spawner abundance levels in both streams were below viable population thresholds. DIDSON technology has been used in the Secesh River to determine salmon escapement over the past five years. The results suggest that DIDSON technology is reliable and can be used to generate accurate and precise estimates of salmon escapement if appropriate methods are used

osti oai (u.s. department of energy office of scientific and technical information)

Use of Dual Frequency Identification Sonar to Determine Adult Chinook Salmon (Oncorhynchus tshawytscha) Escapement in the Secesh River, Idaho ; Annual Report, January 2008 ? December 2008.