Effects of Water Velocity and Trash Rack Architecture on Juvenile Fish Passage and Interactions: A Simulation

Abstract

AbstractMany resident and migratory fish species have experienced population declines due to modification of estuarine ecosystems. Fish screens (or louvers) have been designed to guide fish away from the diversion pumps, and trash racks have been placed upstream of the screens to intercept aquatic plants and debris. Although small fish may aggregate around these structures, potentially increasing their vulnerability to predators, we know little about the behavior, performance, and survival of fish near trash racks. To determine how trash rack flow regime and architecture influence fish behavior, we exposed juvenile threadfin shad Dorosoma petenense and winter‐run Chinook salmon Oncorhynchus tshawytscha to three water velocities and two bar‐spacing treatments in a circular tank bisected by a simulated trash rack. Our results suggest that relatively small increases in water velocity at diversion facilities will result in the aggregation of juvenile fish near trash racks. In contrast, bar spacing did not influence fish passage frequency or interaction in this study. We also found that threadfin shad selected higher velocities as water current increased, whereas Chinook salmon consistently showed a preference for moderate to low water velocities.