2021-2024 Juvenile Chinook Salmon Rearing and Growth on the Lower American River, California

The primary goal of the Central Valley Project Improvement Act is to at least double natural production of Chinook Salmon ( Oncorhynchus tshawytscha ) in California Central Valley (CCV) streams on a sustainable basis. Beginning in 2008, semi-annual gravel augmentation and off channel habitat enhancement projects were implemented on the Lower American River (LAR) by Reclamation and USFWS, in partnership with the Sacramento Water Forum, as part of the LAR habitat enhancement program. The overall vision for the habitat enhancement program is to restore ecosystem processes by rehabilitating and enhancing critical channel, floodplain, and riparian habitats for juvenile and adult anadromous salmonids, thus promoting the recovery of healthy and diverse Chinook Salmon and steelhead ( O. mykiss ) populations. Off channel rearing habitat has been identified as a limiting factor in meeting CCV salmon population goals. While numerous studies have documented positive relationships between off channel habitat and juvenile rearing on the LAR, it is not known how long juveniles remain in off channel habitat compared with the main channel, whether rearing in off channel habitat enhances growth compared with the main channel, whether the relative value of off channel habitat for juvenile production depends on how long it has been inundated, or whether juvenile diet in off channel habitat differs from that in the main channel. To better understand these relationships, we conducted a mark-recapture study under a range of hydrological conditions between 2021-2024 using passive integrated transponder (PIT) tagged wild juvenile Chinook Salmon coupled with seining surveys at five off channel restoration sites on the LAR designed for rearing, as well as nearby main channel control sites that were also suitable rearing habitat. First, we investigated whether side channel habitats in restored reaches support higher Chinook Salmon densities than main channel control habitats. Density was estim