Concurrent Sessions C: Fish Screening at Water Diversions I - Predator Densities And Associated Salmonid Smolt Mortality Around Water Diversions

State-of-the-art fish screens on large water diversions effectively prevent juvenile salmon from being entrained by the diversion, but the physical structure and their prey-concentrating effect may attract predators and create a local predation problem. We are assessing the impact of predation near two large diversions on juvenile Central Valley Chinook salmon (Oncorhynchus tshawytscha) using a combination of acoustic telemetry, a DIDSON camera, and tethering. We expect to answer these questions: (1) Is predator density higher near water diversions relative to nearby areas?(2) Do predators express site fidelity to the diversions?(3) Is the relative smolt predation rate near the diversions higher than nearby areas? What about seasonal and diel predation rate dynamics?(4) What proportion of the predators’ diets consists of smolts near the diversions?(5) All factors combined, does this result in higher than average smolt mortality rates near the diversions?During a pilot season in 2011 on one diversion on the Sacramento River, we gained limited insight into these questions. Predator densities were lowest near the diversion, and highest near the riverbank. Striped bass (Morone saxatilis) did not seem to express site fidelity while Sacramento pikeminnow (Ptychocheilus grandis) did. Finally, relative predation rates around the diversion were near average, with the highest relative predation rates near the riverbank. In the 2012 season, we added a second diversion representing a different design model, allowing the comparison of predator-prey dynamics between different commonly-used diversion designs. We will present data from this more intensive second season along with a preliminary look at data from the 2013 season. This project was conceived in response to the knowledge gap regarding how large water diversions influence predator-smolt dynamics; the majority of research on the impacts of diversions on salmonids concentrate on dewatering and lethal entrainment into pump