Dams represent one of the major forms of river alteration. As these structures reach the end of their lifespan, they often require extensive refurbishments or removal. A small-scale water supply dam in Banff National Park (Alberta, Canada) was partially removed, creating a breach that allowed water to scour a new passage resembling a nature-like fishway. We investigated the permeability of the partially removed dam as a means of validating the conservation benefits of the partial dam removal. We quantified the proportion of bull trout (Salvelinus confluentus), a threatened species in Canada, that approached and passed the fishway using radio telemetry receiver stations. The proportion of bull trout that approached the fishway was low (37.0%; N = 27 of 73), but was consistent with upstream reference sites (33%; N = 20 of 60). For those that did approach, the proportion of bull trout that passed yielded a high passage efficiency (77.8%; N = 21 of 27 that approached). The probability that a fish passed the fishway was related to water depth and time of day. Bull trout were more likely to pass when water depths were high (>0.40 m), and at night. Passage duration ranged from 5-mins to 13-days, suggesting that this resident species used the fishway for a variety of purposes (e.g., station holding and foraging) and not just transiting. Some individuals underwent large-scale movements 2-km upstream (15.1%; N = 11 of 73), or 2-km downstream (2.7%; N = 2 of 73) following a successful passage event. This study provides new insight on how, in some instances, a breach in a dam can function as a nature-like fishway, accommodating year-round stream flows and providing hydraulic conditions suitable for fish passage without costly engineering or construction.

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River Research and Applications
Department of Biology

Sullivan, B.G. (Brittany G.), Taylor, M.K. (Mark K.), Carli, C. (Chris), Ward, T.D. (Taylor D.), Lennox, R.J. (Robert J.), & Cooke, S.J. (2019). Partial dam removal restores passage for a threatened salmonid. River Research and Applications. doi:10.1002/rra.3426