Altering natural streams and rivers rarely happens without impact on surrounding environments and connecting waterways. Minor dams are often mitigated by the installment of fish ladders and simple operational regulations for the dam, but in remote areas it can be challenging to evaluate the functionality of a fish ladder. In 2008 and 2009 Kintama participated in a study involving a fish ladder at the BC Hydro diversion site on the Salmon River, Vancouver Island. This dam was built in 1958, approximately 58 km from the Salmon River mouth to divert and increase water flow available to the BC Hydro power stations located in the Campbell River system. At the time of construction no additional fish passage was required as the main river was naturally obstructed down-river. Following removal of the obstruction and stocking of the upper watershed, the Canadian Department of Fisheries and Oceans installed a seven-step fish ladder in 1992 to facilitate upstream fish migration. Since then the functionality of the fish ladder has been questioned and our aim was to investigate the migratory behavior of adult coho upon reaching the BC Hydro diversion dam, preferably under various flow conditions. The velocity of water falling over the steps has to be sufficient to attract fish to the ladder, yet not so great that fish gets pushed back downstream or exhausted. At the Salmon River dam fish appear to be attracted to the sluice gate, rather than the fish ladder, but the flow through the sluice gate is often too great for the fish to navigate.
Kintama installed multiple acoustic receivers up- and down-river from the dam and in addition to these, a receiver was installed inside the fish ladder. Both in 2008 and 2009 wild, adult coho were caught below the diversion dam and implanted with V9 tags. The movement pattern of each individual fish was investigated and mapped. Although several fish were detected inside of the fish ladder at some point, none of the tagged coho were detected above the dam, suggesting that only a small proportion of the adult coho are able to cross the diversion dam.
A solution that would allow continual successful passage of the Salmon River dam would open ~40 km of additional river to coho, steelhead and other fish. The Campbell River Salmon Foundation is currently looking at two different fish ladder locations as well as modifications to the sluice gate.
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