Footprint Impacts of BC Hydro Dams on Kokanee Populations in the Columbia River Basin

Author: S. Arndt

Prior to dam construction, kokanee in the Columbia Basin were indigenous to lentic habitats in Kootenay, Duncan, Trout, Upper and Lower Arrow, and Slocan lakes. Introduced populations were found in several smaller lakes. In Kootenay Lake, kokanee from the north, west, and south arms were considered to be distinct stocks based on differences in life history and morphometrics. Footprint dam impacts affecting kokanee include habitat loss (spawning) and gain (lentic), habitat fragmentation, nutrient and turbidity changes, entrainment, and changes in aquatic-terrestrial interactions. Construction of dams expanded lentic habitat in the basin by approximately 700 km2 , including new reservoirs and increased surface area in previously-existing lakes. Introduced kokanee populations now occupy the new lentic habitat in Kinbasket, Revelstoke, and Kookanusa (Bonneville Power Administration) reservoirs, and utilize suitable spawning habitat in the upper Columbia and Kootenay drainages that previously was inaccessible.

In contrast to lentic area, the quantity and quality of spawning habitat was reduced by inundation for key indigenous populations. More than 100 km (4.4 km 2 area) of low gradient river and stream habitat that was previously accessible to fish from Kootenay Lake was blocked by Duncan Dam. This included significant areas in the Duncan River that were used by large numbers of kokanee for spawning. Riverine parts of the west arm with spawning potential were also inundated. In addition to the reduction in spawning habitat, historical spawning tributaries to the south arm of Kootenay Lake are not currently utilized. For Arrow Lakes kokanee, 132 km (3.2 km2 ) of low and moderate gradient streams (orders 1-7) were blocked or inundated by Revelstoke and Keenleyside dams. It is likely that the inundated spawning areas included much of the better quality habitat since alluvial fans and low gradient reaches ideal for kokanee spawning were typically in the lower reaches that were lost.

Assessment of changes in population status in relation to footprint impacts was hampered by substantial uncertainty in regards to pre-dam kokanee abundance, and potential causes of declines (BC Hydro versus non-BC Hydro dams,footprint versus operational impacts, and important non-dam impacts such as mysid introductions and nutrient enrichment from fertilizer manufacturing). Key limiting factors for the populations are also as yet not well understood. In general, kokanee habitats in the FWCP area can be grouped into three categories: non-impacted lakes, new reservoirs or greatly enlarged lakes, and impacted historical lakes. Non-impacted, or minimally impacted areas, include Slocan, Trout and Whatshan lakes. New reservoirs, Kinbasket, Revelstoke, and Koocanusa, support robust populations. Duncan Reservoir has an expanded lentic area that may support more kokanee than the historical lake if the remaining spawning habitat or reservoir volume during drawdown is not limiting.

Impacted lakes are Arrow and Kootenay, which supported the largest and most regionally significant kokanee populations prior to dams. Population changes due to dams in these lakes are uncertain because of scarce data and the influence of other factors that affected kokanee abundance before and shortly after dam construction. Available pre-dam kokanee counts for Kootenay Lake were made during a period of phosphorus enrichment from a fertilizer plant so the un-impacted pre-dam abundance could not be determined. However, in these two lakes, stock diversity has decreased and abundance has decreased or could have decreased without intervention. Studies over the last 40 years provide good support for the hypothesis that Kootenay and Arrow populations were primarily regulated by lake productivity prior to dam construction; however the loss of major portions of spawning habitat may have caused reductions without intervention.

Prior to dam construction, kokanee in the Columbia Basin were indigenous to lentic habitats in Kootenay, Duncan, Trout, Upper and Lower Arrow, and Slocan lakes. Introduced populations were found in several smaller lakes. In Kootenay Lake, kokanee from the north, west, and south arms were considered to be distinct stocks based on differences in life history and morphometrics. Footprint dam impacts affecting kokanee include habitat loss (spawning) and gain (lentic), habitat fragmentation, nutrient and turbidity changes, entrainment, and changes in aquatic-terrestrial interactions. Construction of dams expanded lentic habitat in the basin by approximately 700 km2 , including new reservoirs and increased surface area in previously-existing lakes. Introduced kokanee populations now occupy the new lentic habitat in Kinbasket, Revelstoke, and Kookanusa (Bonneville Power Administration) reservoirs, and utilize suitable spawning habitat in the upper Columbia and Kootenay drainages that previously was inaccessible.

In contrast to lentic area, the quantity and quality of spawning habitat was reduced by inundation for key indigenous populations. More than 100 km (4.4 km 2 area) of low gradient river and stream habitat that was previously accessible to fish from Kootenay Lake was blocked by Duncan Dam. This included significant areas in the Duncan River that were used by large numbers of kokanee for spawning. Riverine parts of the west arm with spawning potential were also inundated. In addition to the reduction in spawning habitat, historical spawning tributaries to the south arm of Kootenay Lake are not currently utilized. For Arrow Lakes kokanee, 132 km (3.2 km2 ) of low and moderate gradient streams (orders 1-7) were blocked or inundated by Revelstoke and Keenleyside dams. It is likely that the inundated spawning areas included much of the better quality habitat since alluvial fans and low gradient reaches ideal for kokanee spawning were typically in the lower reaches that were lost.

Assessment of changes in population status in relation to footprint impacts was hampered by substantial uncertainty in regards to pre-dam kokanee abundance, and potential causes of declines (BC Hydro versus non-BC Hydro dams,footprint versus operational impacts, and important non-dam impacts such as mysid introductions and nutrient enrichment from fertilizer manufacturing). Key limiting factors for the populations are also as yet not well understood. In general, kokanee habitats in the FWCP area can be grouped into three categories: non-impacted lakes, new reservoirs or greatly enlarged lakes, and impacted historical lakes. Non-impacted, or minimally impacted areas, include Slocan, Trout and Whatshan lakes. New reservoirs, Kinbasket, Revelstoke, and Koocanusa, support robust populations. Duncan Reservoir has an expanded lentic area that may support more kokanee than the historical lake if the remaining spawning habitat or reservoir volume during drawdown is not limiting.

Impacted lakes are Arrow and Kootenay, which supported the largest and most regionally significant kokanee populations prior to dams. Population changes due to dams in these lakes are uncertain because of scarce data and the influence of other factors that affected kokanee abundance before and shortly after dam construction. Available pre-dam kokanee counts for Kootenay Lake were made during a period of phosphorus enrichment from a fertilizer plant so the un-impacted pre-dam abundance could not be determined. However, in these two lakes, stock diversity has decreased and abundance has decreased or could have decreased without intervention. Studies over the last 40 years provide good support for the hypothesis that Kootenay and Arrow populations were primarily regulated by lake productivity prior to dam construction; however the loss of major portions of spawning habitat may have caused reductions without intervention.