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California Department of Fish and Wildlife's Trinity River Project conducted tagging and recapture operations from July 2017 through March 2018 to produce run-size, angler harvest, and spawner escapement estimates of spring- and fall-run Chinook Salmon (Oncorhynchus tshawytscha), Coho Salmon (O. kisutch), and fall-run steelhead (O. mykiss) in the Trinity River basin. Monitoring results inform the Trinity River Restoration Program’s (TRRP) adaptive management decision making process and help evaluate progress toward achieving fundamental objectives outlined in the Integrated Assessment Plan (TRRP 2009). Additionally, run-size estimates are used in annual fishery management decisions, feeding into the Pacific Fishery Management Council’s Klamath River basin fishery regulation and harvest allocation process.

 

Using a Petersen mark-recapture methodology, we estimated 4,425 (95% CI 3,387 – 5,959) spring-run Chinook Salmon migrated into Trinity River basin upstream of Junction City weir. The run was comprised of an estimated 1,454 natural-origin adults, 280 natural-origin jacks, 2,139 hatchery-origin adults and 447 hatchery-origin jacks. Using tags returned by anglers we estimate 104 spring Chinook were harvested, yielding an escapement of 4,320 fish. Escapement of 1,454 natural-origin adult sprin Chinook is 24.2% of the TRRP goal of 6,000.

 

An estimated 15,450 fall-run Chinook Salmon migrated upstream of Willow Creek weir (WCW) in 2017. The stratified run-size of 5,837 jacks (95% CI 5,212 – 6,502) and 9,613 adult fall Chinook Salmon adults (95% CI 8,701 – 10,573) was comprised of an estimated 4,961 natural-origin adults, 3,096 natural-origin jacks, 4,652 hatchery-origin adults and 2,741 hatchery-origin jacks. There was no harvest reported (there was no legal harvest of fall Chinook Salmon permitted in 2017) so the total escapement is the same as the estimated run-size. Escapement of 4,475 natural-origin adult fall Chinook Salmon is 8.0% of the 62,000 fish TRRP goal.

 

Both Coho Salmon run-size and escapement in the Trinity above WCW were estimated at 655 (95% CI 475 - 921), because no Coho Salmon were reported as harvested. Coho Salmon escapement was comprised of an estimated 57 natural-origin adult and 9 natural-origin jacks and 354 hatchery-origin adult and 236 hatchery-origin jacks. Escapement of 57 natural-origin Coho adults was 4.1% of the TRRP goal of 1,400 fish.

 

Using a Peterson mark-recapture methodology we estimated 6,846 (95% CI 5,873 – 7,897) adult fall steelhead returned to the Trinity River basin upstream of WCW. Anglers harvested an estimated 253 adult fall steelhead upstream of the weir, leaving 6,593 (2,348 natural-origin and 4,245 hatchery-origin) fish as potential spawners. Escapement of 2,348 natural-origin adult steelhead is 5.9% of the 40,000 fish TRRP goal.