Petros, P., W. D Pinnix, and N. J Harris. 2017.

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ID: 2345

[1.23 MB] Petros_etal_(2017)_TR_outmigrant_monitoring_2016.pdf

Petros, P., W. D Pinnix, and N. J Harris. 2017. Juvenile salmonid monitoring on the mainstem Trinity River, California, 2016. Report for the Trinity River Restoration Program (TRRP). U.S. Fish and Wildlife Service, Arcata, California. Available: www.trrp.net/library/document?id=2345.

Executive Summary - This report presents juvenile salmonid emigration monitoring data collected in 2016 at both the Pear Tree rotary screw trap site (PTRST; river kilometer [rkm] 118) and the Willow Creek rotary screw trap site (WCRST; rkm 34) near Willow Creek, California, on the mainstem Trinity River. Information collected by this project contributes to assessing the effectiveness of the Trinity River Restoration Program’s habitat and flow management actions in restoring salmonid populations of the Trinity River. Monitoring at PTRST is conducted to estimate juvenile salmonid population size passing the site during the sampling season. Monitoring at WCRST is conducted to estimate juvenile salmonid population size and emigration timing during the monitoring period. In 2016, one rotary screw trap was operated at PTRST from January 5 through August 27, with successful sampling for 151 days of the 236-day sampling period. At WCRST, three rotary screw traps were operated from March 30 through August 26, with successful sampling for 99 days of the 150-day sampling period.

Age of salmonid outmigrants, mean length by week, migration rates, and hatchery contributions were estimated. Catch data were used to calculate proportional discharge based abundance indices for juvenile Chinook Salmon (Oncorhynchus tshawytscha), Coho Salmon (O. kisutch), and Steelhead (O. mykiss). Catch data of other fishes are also presented.

Weekly stratified mark-recapture population estimates of emigrating age-0 Chinook Salmon were calculated for both naturally and hatchery-produced sub-populations. At PTRST an estimated 888,313 (SD = 140,342; CV = 0.158) naturally-produced age-0 Chinook Salmon and 814,361 (SD = 92,226, CV = 0.113) age-0 hatchery Chinook Salmon passed the site between January 3 and August 20. At WCRST between March 20 and August 20, an estimated 791,407 (SD = 38,537; CV = 0.049) naturally-produced age- 0 Chinook Salmon and 740,748 (SD = 36,025; CV = 0.049) age-0 hatchery Chinook Salmon passed the site.

Juvenile salmonid emigration target dates to assess at what date 80% of the juvenile salmonid population had reached Willow Creek, and to help manage water temperatures in the mainstem Trinity River. The estimate of the week in which 80% of the juvenile discharge based abundance index, was Week of the Year WOY 28 (July 10 – July 16), which occurred after the TRRP management target date of July 9. The estimate of the week in which 80% of the natural Coho Salmon age-1+ population passed the WCRST was WOY 20 (May 15-May 21), which occurred prior to the TRRP management target date of June 4. The estimate of the week in which 80% of the natural Steelhead age-1+ population passed the WCRST was WOY 21 (May 22 – May 28), which occurred by the TRRP management target date of May 22.

First Posted: 2018-01-24 00:25:52

Post Updated: 2018-01-24 00:26:30