Dynamic Behavior of Juvenile Atlantic Salmon within a Channel Dominated by Instream Boulders

Abstract Submission: Instream boulders placement is a widely adopted strategy for restoring degraded streams, aimed at enhancing instream complexity, aquatic habitat quality, and overall ecological value. However, biological responses to these structures have been evaluated less frequently and with less consistency compared to physical/hydraulic habitat assessments. This study examines the impact of instream boulders placement on the dynamic behavior of juvenile Atlantic salmon (Salmo salar), focusing on movement pathways, resting behavior, ground speed, and energy expenditure. The novel experimental setup features varying instream boulders arrangements, including rock-ramp (areal densities ranging from 0.0% to 8.3%) and cluster formations (v- and I-weirs) having juvenile Atlantic salmon (n=6, size=12.4 cm) under two flow events. Top-down and underwater cameras, and advanced AI-driven algorithms were utilized to capture and analyze the dynamic behavior of salmon. The study aims to provide deeper insights into the relationship between turbulent flow-induced habitat complexity metrics and fish responses. We hypothesize that juvenile salmon will adapt to flow regime and boulder placement by extended resting periods behind boulders, forming favorable microhabitats, with optimal passage efficiency likely at intermediate boulder densities. Ground speed is expected to be minimally affected by habitat complexity matrices, while resting time will be notably influenced by increased boulder density within the habitat. Overall, these findings may offer valuable insights for optimizing instream boulders placement in river restoration efforts.

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