Fishway performance of adult Chinook salmon completing one of the world's longest inland salmon migrations to the upper Yukon River

Abstract

Fishways can restore functional connectivity within rivers for migratory fish where barriers compromise connectivity. Providing fish passage is particularly important for semelparous, anadromous species that require access to upriver habitats to successfully reproduce. From 2017 to 2020, we used a combination of acoustic and radio telemetry to investigate the passage success of Chinook salmon (Oncorhynchus tshawytscha) in the upper Yukon River through the wooden Whitehorse Rapids Fishway and compared this to the migration of salmon in the nearby free-flowing Takhini River. The upper Yukon River population of Chinook salmon studied here is highly unique, completing a 2800 km inland migration to Whitehorse, YT, before attempting to pass the Whitehorse Hydro Plant (WHP) to reach spawning sites upstream. We found that upstream passage success was variable across four years of study (0%–66%), was low overall at 31%, and was considerably lower for female salmon. In contrast, salmon migrating up the free-flowing Takhini River had high migration success to spawning grounds and had many times faster migration rates. Attraction (86%), entrance (77%), and passage efficiency (36%) were less than that reported for Chinook salmon at other fishways. Within the fishway, a disproportionately high number of salmon returned downstream upon reaching a daytime-operated viewing chamber (fish trap) located ∼115 m up the fishway. Upon passing the fishway, salmon had high migration success to spawning grounds, though 12% of salmon returned downstream of the WHP, typically after multiple days and after traveling dozens of kilometres upstream of the facility. Findings from this study reveal opportunities to improve fishway performance and thus connectivity for one of the world's most impressive animal migrations.