Cooperative Fish and Wildlife Research Units Program: California
Education, Research and Technical Assistance for Managing Our Natural Resources

Deibner-Hanson, J.D. and Henderson, M. Life Cycle Monitoring of Coho Salmon in Prairie Creek 2017-2020. Final Report to Fisheries Restoration Grant Program Project Number P1610520. April 2021.


Prairie Creek, tributary to Redwood Creek in norther Humboldt County, California, drains an extremely important watershed acting as a stronghold for many plant and animal species living in its pristine old-growth redwood forest. Vital to the ecology of the forest are several keystone salmonid species including Coho Salmon, Chinook Salmon, steelhead and coastal cutthroat trout. This report summarizes the cumulative work we accomplished across three years of monitoring juvenile and adult populations of Coho Salmon in Prairie Creek. The primary purpose of this project was to provide estimates of the four critical Coho Salmon population parameters needed to maintain the status of Prairie Creek as a Life Cycle Monitoring station including (1) adult salmonid redd abundance, (2) outmigrant smolt abundance, (3) freshwater survival and (4) marine survival. Each year, we PIT tagged juveniles throughout Prairie Creek in October, we conducted spawning ground surveys in Prairie Creek from November through March, we trapped and tagged smolts on their way to the ocean from March through July, and we operated several PIT tag antenna arrays year-round. Additionally, data collected in our monitoring projects enabled us to describe other life cycle attributes including early emigration analysis and overwinter growth estimation. During the three monitoring seasons, total redd estimates for Coho Salmon ranged from very low (127 in 2019-20) to high (429 in 2017-18) and outmigrant smolt abundance ranged from average (17,036 in 2018) to extremely high (34,807 in 2020). Apparent overwinter survival estimates were mostly consistent with previous years between 0.30-0.35, though a record high of 0.44 was estimated in 2019-20. We estimated smolt-to-adult return rates for the Coho Salmon smolt cohorts that emigrated in 2018 (1.06%) and 2019 (1.16%) which were consistent and fell within the expected range. Our three seasons of work from 2017-2020 extended the monitoring period in Prairie Creek to more than a decade.