DDMMON-15 Lower Duncan River Stranding Protocol Development and Finalization

Author: Golder Associates Ltd., Poisson Consulting Ltd

This annual summary document tracks information related to management questions associated with the ASPD up to December 2013 and provides recommendations consistent with both the approach of the ASPD and the results of the studies. It has been developed as a framework to track ASPD objectives, hypotheses and management questions, and document progress toward meeting those objectives on an annual basis. Annual revisions or amendments will be made to this document as required to ensure it is consistent with the best available information. This report also addresses requirements for 2013 and the long-term approach to Protocol finalization in 2018. Protocol recommendations are vetted through BC Hydro to ensure the operating recommendations are appropriate and consistent with the Duncan Dam Water Use Plan before discussing with regulatory agencies. Interagency discussions also take place at the Columbia Operations Fisheries Advisory Committee (COFAC) annual meetings. Final changes to the Protocol and updated references to the Protocol integrated with its operating orders for the DDM are managed by BC Hydro. The Year 10 report is in progress and will be submitted in the 2020 annual report. The project schedule is extended to the end of 2019 in order to integrate findings from DDMMON-1, DDMMON-3, DDMMON-4 and DDMMON-16 into the report.

MQ: How effective are the operating measures implemented as part of the ASPD program?
Based on the current state of knowledge, the flow reduction measures implemented under the water use plan are effective at reducing fish stranding. The current water use plan protocol reduces stranding rates by requiring daytime reductions at rates that result in slow stage changes rates (< 10 cm/hr) at the majority of identified stranding sites. MQ: What are the levels of impact to resident fish populations associated with fish stranding events on the lower Duncan River? Index sites were not originally selected to be representative of the entire LDR, but to focus on sites believed to have the highest amounts of stranding based on amount dewatered area and suitable habitat. Index sites tend to be of lower gradient and wider than the non-index sites, therefore more area dewaters at these sites. In the Year 4 analysis, the number of pools per unit area of exposed habitat did not vary between index and non-index sites nor did the number of fish per pools. Stranding rates per lineal distance do not differ between index and non-index sites, but differ due to greater dewatered area within index sites. Therefore, the greater area dewatered in index sites strands higher numbers of fish in comparison to non-index sites. Index sites appear to provide an estimate that is biased high. Therefore, hypothesis Ho1 is rejected. This will be re-examined in the Year 7 in-depth interpretive report with all available project data to determine if complete dataset supports the rejection of hypothesis Ho1. Estimates for the number of Rainbow Trout juveniles stranded in pools were relatively low and precise. While interstitial stranding is likely to be biologically important, the current estimates were upwardly biased and are uncertain. There was a seasonal component to pool stranding, with higher stranding in fall, but at this point it cannot be determined whether this was due to less fish in the system in the spring vs. the fall or to a decreased risk of stranding. Mountain Whitefish encounters have been minimal in all study years. This consistently low level of stranding was not considered significant and will likely not result in a population level effect. Similar to previous study years, with the most recent abundance and stranding estimates for Rainbow Trout, hypothesis Ho2 was rejected. Therefore, based on the current project dataset Rainbow Trout fry populations are significantly impacted by fish stranding events. Several factors affect fish populations including: predation, out migration, food availability, availability of suitable rearing habitats, winter mortality, as well as inter- and intra-species competition. Whether stranding events kill the fish that would succumb to these factors, or kill fish which would survive these factors is unknown.

MQ: How effective are the operating measures implemented as part of the ASPD program?
Based on the current state of knowledge, the flow reduction measures implemented under the water use plan are effective at reducing fish stranding. The current water use plan protocol reduces stranding rates by requiring daytime reductions at rates that result in slow stage changes rates (< 10 cm/hr) at the majority of identified stranding sites. MQ: What are the levels of impact to resident fish populations associated with fish stranding events on the lower Duncan River? Index sites were not originally selected to be representative of the entire LDR, but to focus on sites believed to have the highest amounts of stranding based on amount dewatered area and suitable habitat. Index sites tend to be of lower gradient and wider than the non-index sites, therefore more area dewaters at these sites. In the Year 4 analysis, the number of pools per unit area of exposed habitat did not vary between index and non-index sites nor did the number of fish per pools. Stranding rates per lineal distance do not differ between index and non-index sites, but differ due to greater dewatered area within index sites. Therefore, the greater area dewatered in index sites strands higher numbers of fish in comparison to non-index sites. Index sites appear to provide an estimate that is biased high. Therefore, hypothesis Ho1 is rejected. This will be re-examined in the Year 7 in-depth interpretive report with all available project data to determine if complete dataset supports the rejection of hypothesis Ho1. Estimates for the number of Rainbow Trout juveniles stranded in pools were relatively low and precise. While interstitial stranding is likely to be biologically important, the current estimates were upwardly biased and are uncertain. There was a seasonal component to pool stranding, with higher stranding in fall, but at this point it cannot be determined whether this was due to less fish in the system in the spring vs. the fall or to a decreased risk of stranding. Mountain Whitefish encounters have been minimal in all study years. This consistently low level of stranding was not considered significant and will likely not result in a population level effect. Similar to previous study years, with the most recent abundance and stranding estimates for Rainbow Trout, hypothesis Ho2 was rejected. Therefore, based on the current project dataset Rainbow Trout fry populations are significantly impacted by fish stranding events. Several factors affect fish populations including: predation, out migration, food availability, availability of suitable rearing habitats, winter mortality, as well as inter- and intra-species competition. Whether stranding events kill the fish that would succumb to these factors, or kill fish which would survive these factors is unknown.