Technical fishway passage structures provide high passage efficiency and effective passage for adult Pacific salmonids at eight large dams

Abstract

Fishways have been widely used for upstream passage around human-built structures, but ‘success’ has varied dramatically. Evaluation of fishway success has typically been conducted at local scales using metrics such as fish passage efficiency and passage time, but evaluations are increasingly used in broader assessments of whether passage facilities meet population-specific conservation and management objectives. Over 15 years, we monitored passage effectiveness at eight dams on the Columbia and Snake rivers for 26,886 radio-tagged spring-summer and fall Chinook Salmon O. tshwaytscha, Sockeye Salmon O. nerka, and summer steelhead O. mykiss during their migrations to spawning sites. Almost all fish that entered dam tailraces eventually approached and entered fishways. Tailrace-to-forebay passage efficiency estimates at individual dams were consistently high, averaging 0.966 (SD = 0.035) across 245 run×year×dam combinations. These estimates are among the highest recorded for any migratory species, which we attribute to the scale of evaluation, salmonid life history traits (e.g., philopatry), and a sustained adaptive management approach to fishway design, maintenance, and improvement. Full-dam fish passage times were considerably more variable, with run×year×dam medians ranging from 5–65 h. Evaluation at larger scales provided evidence that fishways were biologically effective, e.g., we observed rapid migration rates (medians = 28–40 km/d) through river reaches with multiple dams and estimated fisheries-adjusted upstream migration survival of 67–69%. However, there were substantive uncertainties regarding effectiveness. Uncertainty about natal origins confounded estimation of population-specific survival and interpretation of apparent dam passage ‘failure’, while lack of post-migration reproductive data precluded analyses of delayed or cumulative effects of passing the impounded system on fish fitness. Although the technical fishways are effective for salmonids in the Columbia-Snake River system, other co-migrating species have lower passage rates, highlighting the need for species-specific design and evaluation wherever passage facilities impact fish management and conservation goals.

High egg retention in Chinook Salmon Oncorhynchus tshawytscha carcasses sampled downstream of a migratory barrier

“…Dams and other barriers restrict the movement of species through rivers (Silva et al ., 2018) and this is often only partially overcome with fishways (Noonan et al ., 2012). In the Yukon River, O. tshawytscha passage failure is considerable at the WHP relative to passage rates at other hydro plants in this species' range (Keefer et al, 2021; Twardek et al . , 2021).…”

“…Dams and other barriers restrict the movement of species through rivers (Silva et al, 2018) and this is often only partially overcome with fishways (Noonan et al, 2012). In the Yukon River, O. tshawytscha passage failure is considerable at the WHP relative to passage rates at other hydro plants in this species' range (Keefer et al, 2021;Twardek et al, 2021). Though numerous telemetry studies have documented failed salmon passage at dams and other barriers, very few studies have directly measured the reproductive consequences of a fishway, particularly after failed passage (Roscoe & Hinch, 2010).…”

Attraction, Entrance, and Passage Efficiency of Arctic Grayling, Trout, and Suckers at Denil Fishways in the Big Hole River Basin, Montana

“…2018; Keefer et al. 2021); our results could be extrapolated to barriers throughout the basin based on their hydraulic characteristics to estimate these effects. Designation of critical habitats and determination of specific Arctic Grayling movement patterns would help prioritize where fishway modifications would be most useful.…”

“…Our results could be applied to a basinwide connectivity assessment for Arctic Grayling in the Big Hole River. Access to critical habitats could be essentially precluded considering the potential compounding effects of passing multiple sequential barriers with limited overall efficiencies (Cutting et al 2018;Keefer et al 2021); our results could be extrapolated to barriers throughout the basin based on their hydraulic characteristics to estimate these effects. Designation of critical habitats and determination of specific Arctic Grayling movement patterns would help prioritize where fishway modifications would be most useful.…”

Evaluating the Consequences of Physical Barriers on Fish During Long-distance Upstream Migrations Through Rivers

“…Current research considers three primary components of fishway performance that comprise overall efficiency of a fishway; attraction, entrance, and passage efficiency. Attraction efficiency describes the proportion of all potential fish that come within close proximity to the entrance of a passage structure, entrance efficiency describes the proportion of fish attracted to the structure that enter, while passage efficiency describes the proportion of fish entering the structure that actually pass (as per Keefer et al 2021). Even when passage is successful, sublethal consequences can exist that impact the fitness of an individual fish.…”