Relative predation rates on juvenile Chinook Salmon in the lower Stanislaus River, California, 2012-2024 by habitat suitability informed by juvenile Chinook Salmon and black bass observations in the lower Stanislaus and Merced rivers, California, 2012-2017

Overview The purpose of this work was to estimate relative predation on juvenile Chinook Salmon rearing in tributaries of the San Joaquin River, California in relation to meso- and microhabitat factors. Predation rates were estimated using predation bioassays. Ranges of depth and velocity targeted by the bioassays were informed by habitat suitability indices developed prior to field efforts. Juvenile Chinook and Bass Habitat Suitability Indices The purpose of this dataset is to develop habitat suitability indices for juvenile Chinook Salmon (<120mm) on the lower Stanislaus River and nonnative black bass ( Micropterus spp.). on the lower Merced River, both tributaries of the San Joaquin. This data was used to identify target ranges of depth and velocity during predation fieldwork. Occupancy data was collected via snorkel surveys on the lower Stanislaus River in 2018 and 2019 and on the Merced River in 2012 and 2014-2017. Predation Tethering Bioassay Study The purpose of this field study was to estimate relative rates of predation of juvenile Chinook Salmon. Predation rates were estimated using assays of tethered hatchery Chinook Salmon deployed across a range of mesohabitats on the lower Stanislaus River. Habitat suitability was expected to vary across mesohabitats and across depths and velocities sampled within habitats. Cameras were deployed with tethers to identify predators for a subset of predation events happening within the first 1-2 hours of deployment. Assays were deployed monthly March-May in 2022 and 2024. A supplemental set of assays were deployed in May 2023 under wet water year conditions that varied strongly from conditions sampled in 2022 and 2024.