Variation in Juvenile Salmon Growth Opportunities Across a Shifting Habitat Mosaic

Historically, Chinook Salmon in the California Central Valley reared vast wetlands of Sacramento–San Joaquin Delta. However, more than 95% floodplain, riparian, and wetland habitats Delta have become degraded because anthropogenic factors such as pollution, introduced species, water diversions, levees. Despite pronounced habitat loss, previous work using otolith reconstructions has revealed that some juvenile salmon continue to successfully rear for extended periods extent which functions promote growth relative other remains unknown. In this study, we integrated microstructure (daily increment count width) strontium isotope (87Sr/86Sr) records fill critical knowledge gap by comparing natural-origin fall-run from American River with those remained their natal stream. Using generalized additive models, compared daily rates among rearing (Delta vs. River) years (2014 2018), encompassing a range hydrologic conditions. We found grew faster (2016), but slower during drought conditions 2015). The featured varied within years, suggesting importance maintaining mosaic salmonids, particularly dynamic environment Valley. Linking chemistry increments provides valuable approach explore mechanisms governing interannual variability across types, useful tool quantify effects large-scale restoration efforts on native fishes.