Partial dam removal restores passage for a threatened salmonid

Abstract

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, accommodatingyear-round stream flows and providing hydraulic conditions suitable for fish passage without costly engineering or construction.

Brook trout (Salvelinus fontinalis) movement and survival after removal of two dams on the West Branch of the Wolf River, Wisconsin

“…These relatively mobile fish may serve as the conduit by which newly accessible habitats are utilised following dam removals, but extensive utilisation of these habitats may take years if few fish move through areas where dams previously existed. Similarly, these relatively mobile fish may be important to re‐establishing gene flow and increasing genetic diversity among populations that were previously isolated by dams (Allendorf, Luikart, & Aitken, ; Méndez, Tella, & Godoy, ; Sullivan et al, ).…”

“…Although we removed the antennas in mid‐November (2016) and early December (2017), we believe that if we missed any movement to overwintering habitat, movement back into the WBWR during early spring would have been detected, it is possible, however, that these fish may not have moved back into the WBWR. Similarly, Sullivan et al, () assessed bull trout Salvelinus confluentus movements after a dam removal that restored passage within Forty Mile Creek, Alberta. During this study, transmitter life was maximised by turning off the transmitters during the winter, but manual tracking in the spring suggested minimal winter movement likely occurred (Sullivan et al, ).…”

“…Similarly, Sullivan et al, () assessed bull trout Salvelinus confluentus movements after a dam removal that restored passage within Forty Mile Creek, Alberta. During this study, transmitter life was maximised by turning off the transmitters during the winter, but manual tracking in the spring suggested minimal winter movement likely occurred (Sullivan et al, ).…”

“…Top panel (a) is the upstream temperature located by Upper Bass Lake and the lower panel (b) is the downstream temperature located by the culvert approximately 13 km downstream from Upper Bass Lake. The dotted line defines the observed maximum temperature for brook trout reported by Wehrly et al, (2007) isolated by dams (Allendorf, Luikart, & Aitken, 2013;Méndez, Tella, & Godoy, 2011;Sullivan et al, 2019).…”

“…Although we removed the antennas in mid-November (2016) and early December (2017), we believe that if we missed any movement to overwintering habitat, movement back into the WBWR during early spring would have been detected, it is possible, however, that these fish may not have moved back into the WBWR. Similarly, Sullivan et al, (2019) assessed bull trout Salvelinus confluentus movements after a dam removal that restored passage within Forty Mile…”