Seasonal growth, movement, and survival of juvenile Coho Salmon (Oncorhynchus kisutch) utilizing restored rearing habitat

The Scott River supports the most robust population of threatened Coho Salmon Oncorhynchus kisutch remaining in the Klamath River basin. Even in the Scott River, low quality and restricted extent of juvenile rearing habitat limits the Coho Salmon population to a small fraction of historic abundance. To support persistence and recovery of Scott River Coho Salmon, the Scott River Watershed Council (SRWC) has constructed a portfolio of restoration projects to improve juvenile rearing habitat, including beaver dam analogs (BDAs). The Scott River BDAs were the first implemented anywhere in California. This study compares juvenile Coho Salmon responses associated with production (growth, survival, and abundance) at five different locations. I used a post-treatment study design to compare four SRWC restoration projects, three bda-formed sites and one other restored site, which consisted of a constructed side-channel and engineered log jams placed in the adjacent mainstem, to a reference site. I analyzed data from a SRWC mark-recapture field study that used passive integrated transponder (PIT) tags to individually mark juvenile Coho Salmon, with repeated sampling during their rearing period. The available data included five cohorts of Coho Salmon. I tracked individual growth, survival, and movement using recaptures at subsequent sample events and, for survival and movement, detections of tagged fish on stationary PIT antennas. I developed a multistate mark-recapture model based on in-hand captures and antenna detections to estimate site-specific weekly survival while accounting for movement between sites. I also analyzed differences in growth between sites and seasons. Isolating the effects of restoration on growth and survival was challenging because the sampling schedule was inconsistent, and individuals regularly moved in and out of restoration sites. However, I found that Coho Salmon at BDA sites generally had similar or higher growth and survival compared to other sites in all winter and spring seasons. They had lower growth and survival than mainstem habitats in summers characterized by drought. These results suggest that BDA construction can be an effective strategy for restoring juvenile Coho Salmon rearing habitat, but that a variety of options are needed to address the variable conditions juvenile coho face year to year