Lower Duncan River Kokanee Spawning Monitoring. Implementation Year 10. Data Reports and Conclusions 2008-2017

Author: E. Plate, J. Thorley, M. Zimmer

This report summarizes ten years of kokanee monitoring in the lower Duncan River (LDR). It describes several aspects of kokanee spawning in the LDR (relative distribution, relative intensity, spawn mapping, potential egg deposition, and egg losses) and estimates spawning abundance through Area Under the Curve (AUC) modeling.

1. LDR discharge (m3/s) and water temperature (°C):
Water temperatures followed a similar trend to previous years showing a correlated decrease following the decrease in discharge. Lower Duncan River discharge was regulated through DDM in consideration of Lardeau River flows in September and October 2017 to manage for protection of Kokanee spawning in the LDR.
2. Area Under the Curve (AUC) estimates:
The 2017 Kokanee spawning population in the Lower Duncan River was estimated to be 1,349 fish, with a lower 95% Confidence Interval (CI) of 244 fish and an upper 95% CI of 3,764 fish. In comparison to previous years, the 2017 estimate is the lowest on record, about 66% of the previous lowest estimate of 2,104 Kokanee in 2015 (Lower CI = 725; Upper CI = 4,488) and about 4% of the highest estimate of 32,182 in 2011 (Lower CI = 16,057; Upper CI = 65,504). Similar to the results of previous years, both Meadow Creek (4,346 fish) and the Lardeau (6,281 fish) system had a higher estimated number of spawners than the LDR in 2017, but both systems also experienced by far the lowest Kokanee escapement over the last ten years.
3. Relative distribution of Kokanee spawners in the LDR:
In 2017, Kokanee were observed to spawn between Rkm 9.5 at the downstream end of the LDR, close to Kootenay Lake and Rkm 1.4 at the upstream end of the LDR close to Duncan Dam. Most notable concentrations of spawning Kokanee in 2017 were found between Rkm 1.5-3.1 where 70% of the spawning Kokanee within the study reach were observed. These main concentrations of redds were observed in areas where substrate composition (gravel) and flow (estimated between 0.3-0.8 m/s) appeared ideal for Kokanee spawning. Many areas that also provided spawning habitat characteristics were not used in 2017 due to the low overall number of fish. The general spawning utilization of sidechannels, even those that have only a slightly lower flow than the main channel, just like the overall number fish observed, was reduced when compared with previous years and limited to small sections of SCs 1.1R, 4.1R and 4.4R pre- and post-flow reduction
4. Kokanee spawn mapping, PED, and egg losses:
The total area used by spawning Kokanee pre-flow reduction in the LDR mainstem in 2017 was approximately 4,412 m2 or the smallest area recorded as part of DDMMON-4. In 2017, this spawning area was estimated to contain 26,852 eggs (AMEC fecundity estimate) or 87,480 eggs MFLNRO fecundity estimate) that were deposited before the flow reduction. There was no loss in spawning area in 2017 in the side channels as a consequence of the flow reduction. Therefore, egg loss due to flow reduction did not appear to have occurred in 2017. However, the low use of side channels may be a result of a continued drastic decrease in spawner escapement.

1. LDR discharge (m3/s) and water temperature (°C):
Water temperatures followed a similar trend to previous years showing a correlated decrease following the decrease in discharge. Lower Duncan River discharge was regulated through DDM in consideration of Lardeau River flows in September and October 2017 to manage for protection of Kokanee spawning in the LDR.
2. Area Under the Curve (AUC) estimates:
The 2017 Kokanee spawning population in the Lower Duncan River was estimated to be 1,349 fish, with a lower 95% Confidence Interval (CI) of 244 fish and an upper 95% CI of 3,764 fish. In comparison to previous years, the 2017 estimate is the lowest on record, about 66% of the previous lowest estimate of 2,104 Kokanee in 2015 (Lower CI = 725; Upper CI = 4,488) and about 4% of the highest estimate of 32,182 in 2011 (Lower CI = 16,057; Upper CI = 65,504). Similar to the results of previous years, both Meadow Creek (4,346 fish) and the Lardeau (6,281 fish) system had a higher estimated number of spawners than the LDR in 2017, but both systems also experienced by far the lowest Kokanee escapement over the last ten years.
3. Relative distribution of Kokanee spawners in the LDR:
In 2017, Kokanee were observed to spawn between Rkm 9.5 at the downstream end of the LDR, close to Kootenay Lake and Rkm 1.4 at the upstream end of the LDR close to Duncan Dam. Most notable concentrations of spawning Kokanee in 2017 were found between Rkm 1.5-3.1 where 70% of the spawning Kokanee within the study reach were observed. These main concentrations of redds were observed in areas where substrate composition (gravel) and flow (estimated between 0.3-0.8 m/s) appeared ideal for Kokanee spawning. Many areas that also provided spawning habitat characteristics were not used in 2017 due to the low overall number of fish. The general spawning utilization of sidechannels, even those that have only a slightly lower flow than the main channel, just like the overall number fish observed, was reduced when compared with previous years and limited to small sections of SCs 1.1R, 4.1R and 4.4R pre- and post-flow reduction
4. Kokanee spawn mapping, PED, and egg losses:
The total area used by spawning Kokanee pre-flow reduction in the LDR mainstem in 2017 was approximately 4,412 m2 or the smallest area recorded as part of DDMMON-4. In 2017, this spawning area was estimated to contain 26,852 eggs (AMEC fecundity estimate) or 87,480 eggs MFLNRO fecundity estimate) that were deposited before the flow reduction. There was no loss in spawning area in 2017 in the side channels as a consequence of the flow reduction. Therefore, egg loss due to flow reduction did not appear to have occurred in 2017. However, the low use of side channels may be a result of a continued drastic decrease in spawner escapement.