Investigating downstream passage of lake sturgeon, Acipenser fulvescens, through a Winnipeg River generating station

Abstract

Lake sturgeon, recently recommended to be listed as an endangered species under the Species at Risk Act, inhabit the various impoundments of the Winnipeg River system. Downstream passage through hydroelectric generating stations represents one of the major data gaps in our understanding of how hydroelectric development may be impacting lake sturgeon populations. Acoustic telemetry was used to investigate coarse-scale movements of juveniles, sub-adult and adults throughout the Slave Falls Reservoir, a 10 km long Winnipeg River impoundment, to assess patterns of downstream passage susceptibility and investigate fine-scale movements in the vicinity of the Slave Falls Generating Station. Movements of juveniles and sub-adults were generally restricted to areas of interconnected deep-water habitat, with movements through the shallow river narrows that sub-divide the Slave Falls Reservoir being rare. Adults did move through these narrows, albeit infrequently. Juveniles and sub-adults tagged in the lowermost section of the reservoir, as well as several adults tagged throughout the reservoir, were found to periodically utilize habitat immediately upstream of Slave Falls, where they would be susceptible to entrainment. Mean entrainment rates were estimated at 3.1% per year for adults tagged throughout the reservoir, and 17.9% per year for sub-adults tagged in the lowermost section of the reservoir. Fine-scale movement tracking revealed that three of eleven observed downstream passage events occurred via bottom-draw regulating gates, while another four events were also reasoned to have occurred via this route. The routes of the remaining four could not be determined. Eight of the eleven downstream passage events observed in this study were survived. While the survival of the remaining three fish could not be confirmed, it is highly likely that they also survived. Length-at-age analysis, supported by genetic methods, revealed that 23 of 151 (15.2%) of the lake sturgeon between 525 and 750 mm (fork length) captured in the 6 km stretch of river downstream of Slave Falls were fast-growing outliers, reasoned to have passed downstream through the Slave Falls Generating Station.