Johnson Creek, a South Fork Salmon River tributary located near the small town of Yellow Pine in central Idaho, supports a threatened sub-population of summer Chinook salmon. Dramatic declines in spawner abundance prompted the Nez Perce Tribe to establish a small scale supplementation project, referred to as the Johnson Creek Artificial Propagation Enhancement, or JCAPE. The BPA-funded project has two major components; a supplementation program and a monitoring and evaluation program.
The supplementation program traps and collects natural adult salmon in Johnson Creek for artificial spawning and rearing. The program, through cooperation with the U.S. Fish and Wildlife Service and Idaho Fish and Game Department, utilizes existing hatchery rearing space at the McCall Fish Hatchery to rear up to 100,000 smolts annually for release back into Johnson Creek. Adult trapping first began in 1998. The first supplementation smolt releases occurred in 2000 from adults collected in 1998 and releases have continued from 2002 to present.
The monitoring and evaluation program comprehensively evaluates both natural and supplementation fish. This program incorporates a life cycle and life history characteristic approach that monitors the fish from egg to adult to quantify juvenile survival, smolt-to-adult survival return rates, and adult-to-adult ratios. This is accomplished utilizing survival estimation modeling, adult counts, spawning surveys, and genetic analysis.
Since project inception, fifteen complete cohorts have returned to Johnson Creek. Over this period, smolt survival from Johnson Creek to Lower Granite Dam has averaged 36% for supplemented smolts and 48% for natural smolts. Adult counts (includes jacks) have ranged from a high of 1,652 in 2014 to a low of 183 in 1998. Smolt-to-adult return rates (Johnson Creek to Johnson Creek) have averaged 0.40% for supplemented fish and 0.88% for natural fish; adult-to-adult estimates have averaged 4.22 for supplementation Chinook and 2.14 for natural Chinook. A recent genetic analysis of the relative reproductive success of supplementation Chinook determined that hatchery rearing of wild fish resulted in more wild-born adults in the next two generations than if fish had been left to spawn naturally. Further, the analysis showed there to be no significant differences in the reproductive success between hatchery and wild fish, and that hatchery x wild interactions do not have a detectable negative impact on the fitness of wild fish.