Poor Upstream Passage for Endangered Atlantic Salmon (Salmo salar) at a Trap‐and‐Transport Fishway in the Wolastoq/Saint John River, New Brunswick

Declines of Atlantic salmon ( Salmo salar ) in the Wolastoq/Saint John River have largely coincided with hydropower development, and there is an urgent need to understand the status of bidirectional passage at existing barriers. We evaluated upstream passage efficiency and duration at the lowermost hydroelectric dam (Mactaquac Generating Station), which targets salmon for upstream passage with a manually operated fish lift and transport system. In a 2‐year study, we captured, tagged, and released upstream adult migrants within 500 m of the fishway and monitored their movements using PIT, radio, and acoustic telemetry. Overall, a low proportion (19%) of individuals that approached the dam passed upstream, and successful individuals experienced considerable passage delays (mean = 58 days) despite visiting the fishway on multiple occasions prior to passage (mean = 8 visits). Salmon were approximately 41 times more likely to visit the fishway entrance during daylight hours (92% of total fishway detections occurred during daylight), likely reflecting elevated power generation and flow conditions during daylight. Further, salmon were approximately five times more likely to visit the fishway entrance while the fishway was not operational (70% of fishway detections while not operating). Accordingly, provided that the current daily flow regime at Mactaquac is not changed, we recommend increased fishway operation efforts during daylight hours to increase opportunities for salmon to pass upstream. However, we also found that salmon rarely reached the fishway crowding pool during fishway visits (regardless of fishway operation status), which suggests that issues of attraction and guidance within the lower fishway should be addressed in synchrony with increased fishway operation efforts. Ultimately, our observations suggest that poor fishway attraction, guidance, and operation schedules have been key factors limiting successful upstream passage for salmon in the river and highlight the importance of evaluating fishway performance post‐construction.