Observations and Analysis of Shore Spawning Kokanee (Oncorhynchus nerka) in the West Arm of Kootenay Lake. Report prepared for the Department of Fisheries & Oceans

Author: Redfish Consulting Ltd

Project Objectives: 1) Determine temporal and spatial distribution of shore spawning kokanee at 3 index sites (Harrop, Duhamel and Sitkum Creeks) 2) Determine spawner abundance using area under the curve (AUC) methods (Hill and Irvine 2001) 3) Determine redd spatial and temporal distribution 4) Determine/estimate redd numbers 5) Assess cumulative impacts of drawdown on kokanee shore spawning sites from spawning through to emergence

In general, the 2009 kokanee shore spawning within the West Arm of Kootenay Lake occurred in shallow water (< 2.0 m) during late September and extended into early October. Compared to West Arm kokanee stream spawners the number of shore spawners appeared to be very small as suggested by Andrusak et al. (2007). In 2009, virtually no spawning occurred or redds observed in water depths < 0.5 m when the surveys commenced. The majority of spawning, based on observed redd distributions, occurred at depths 0.5-2.0 m. While standardized daytime surveys were conducted to estimate spawner numbers similar to previous years, very few fish were observed at any of the index sites during the daytime. While these counts were feasible the observed number of redds were always higher than numbers of fish counted. The nighttime snorkel surveys provided invaluable information on the diurnal behaviour patterns and confirmed that far more spawners could be observed at night compared to the day. The marking of redds in the fall and springtime excavations demonstrated that redd identification during spawning was quite accurate.

The four shore spawning sites had a number of physical characteristics in common that appear to reflect habitat preference. Spawning kokanee are known to select groundwater upwelling sites which can enhance incubation success, even though these areas may have lower water velocities and a higher proportion of fine sediments than redds without groundwater influence (Garrett et al. 1998). All four sites displayed varying degrees of hyporheic groundwater which is likely associated with the alluvial fans that these sites are located on (Douglas 2006). One characteristic of hyporheic groundwater is that it is often lower in dissolved oxygen than surface water, and more variable in oxygen concentration (Peterson and Quinn 1996, in Quinn 2005). This may be a limiting factor for West Arm shore spawning success. Moreover, Garette et al. (1998) noted enhanced success of shore spawning was attributed to higher temperatures (+2.5°C) that accelerate rates of development and protect embryos from freezing and may increase survival of fry recruiting the lake. Not surprisingly, temperatures profiles at most West Arm sites displayed similar patterns of declining surface water from fall to spring and groundwater that remained constant throughout the winter at approximately 7 °C. The groundwater most likely buffered developing eggs from freezing temperatures. However, the groundwater at the Sitkum site appeared to be influenced by some surface water as there was more variation during the winter months. Since most of the redds were associated with upwelling’s or seepages it is logical to suggest that the eggs were most likely developed based on groundwater temperatures. The ATUs projected from groundwater suggests full development to free swimming fry would occur within 1-2 weeks of surface water ATUs. i.e. mid February to early March. These projections were confirmed during spring time redd excavations when fully developed fry were found.

Analysis of the redd distribution data vs. lake levels suggests the possibility of some of redds being were dewatered during the 2009-2010 incubation and development period. However, the spring time redd excavations also demonstrated that live and dead eggs, alevins and fry were present, even though the redds were dewatered due to receding lake level. Many of the spring observations suggest that groundwater upwelling’s permitted alevins/fry to remain alive within the redds but the fry were nonetheless stranded as a result of the receding lake levels. Furthermore, it is questionable whether these fry could survive until the lake elevation is raised nearly two months later. i.e. lack of food and predation would most likely be very severe constraints to their survival. A more intensive investigation is required to improve upon the estimated losses of the redds.

The scope of this project was limited such that an estimate of egg-to-fry fry survival could not be made. It is speculated that some shore produced fry do survive since a few shore spawners are present each year. Until DNA analysis is completed there is an equal possibility that these shore spawners are displaced stream spawners (Andrusak et al. 2007). There is doubt about actual numbers of shore spawners since nighttime counts made in 2009 suggest that previous year’s daytime counts are unreliable as an index of abundance and certainly can’t be used for AUC methodology to estimate total numbers. Future counts should be conducted at night.

In summary, the 2009-2010 study investigating the spawning success of shore spawning kokanee in the West Arm of Kootenay Lake indicates severe constraints and high mortality are imposed on these fish due to receding lake levels. Regardless, of the factors related to spawn and emergence timing or ecotypic divergence, evidence from field observations indicate that the majority of redds were distributed within the zone of impact adversely affected by drawdown. While it is acknowledged that lake levels fluctuation are implicated as problematic on fish populations (Hirst et al. 1991), further data is required if a more accurate estimate of drawdown impact is required. Meanwhile it is believed that some mitigative measures can be considered either by changing the drawdown pattern and or experimenting with some modified incubation boxes that utilize existing groundwater.

In general, the 2009 kokanee shore spawning within the West Arm of Kootenay Lake occurred in shallow water (< 2.0 m) during late September and extended into early October. Compared to West Arm kokanee stream spawners the number of shore spawners appeared to be very small as suggested by Andrusak et al. (2007). In 2009, virtually no spawning occurred or redds observed in water depths < 0.5 m when the surveys commenced. The majority of spawning, based on observed redd distributions, occurred at depths 0.5-2.0 m. While standardized daytime surveys were conducted to estimate spawner numbers similar to previous years, very few fish were observed at any of the index sites during the daytime. While these counts were feasible the observed number of redds were always higher than numbers of fish counted. The nighttime snorkel surveys provided invaluable information on the diurnal behaviour patterns and confirmed that far more spawners could be observed at night compared to the day. The marking of redds in the fall and springtime excavations demonstrated that redd identification during spawning was quite accurate.

The four shore spawning sites had a number of physical characteristics in common that appear to reflect habitat preference. Spawning kokanee are known to select groundwater upwelling sites which can enhance incubation success, even though these areas may have lower water velocities and a higher proportion of fine sediments than redds without groundwater influence (Garrett et al. 1998). All four sites displayed varying degrees of hyporheic groundwater which is likely associated with the alluvial fans that these sites are located on (Douglas 2006). One characteristic of hyporheic groundwater is that it is often lower in dissolved oxygen than surface water, and more variable in oxygen concentration (Peterson and Quinn 1996, in Quinn 2005). This may be a limiting factor for West Arm shore spawning success. Moreover, Garette et al. (1998) noted enhanced success of shore spawning was attributed to higher temperatures (+2.5°C) that accelerate rates of development and protect embryos from freezing and may increase survival of fry recruiting the lake. Not surprisingly, temperatures profiles at most West Arm sites displayed similar patterns of declining surface water from fall to spring and groundwater that remained constant throughout the winter at approximately 7 °C. The groundwater most likely buffered developing eggs from freezing temperatures. However, the groundwater at the Sitkum site appeared to be influenced by some surface water as there was more variation during the winter months. Since most of the redds were associated with upwelling’s or seepages it is logical to suggest that the eggs were most likely developed based on groundwater temperatures. The ATUs projected from groundwater suggests full development to free swimming fry would occur within 1-2 weeks of surface water ATUs. i.e. mid February to early March. These projections were confirmed during spring time redd excavations when fully developed fry were found.

Analysis of the redd distribution data vs. lake levels suggests the possibility of some of redds being were dewatered during the 2009-2010 incubation and development period. However, the spring time redd excavations also demonstrated that live and dead eggs, alevins and fry were present, even though the redds were dewatered due to receding lake level. Many of the spring observations suggest that groundwater upwelling’s permitted alevins/fry to remain alive within the redds but the fry were nonetheless stranded as a result of the receding lake levels. Furthermore, it is questionable whether these fry could survive until the lake elevation is raised nearly two months later. i.e. lack of food and predation would most likely be very severe constraints to their survival. A more intensive investigation is required to improve upon the estimated losses of the redds.

The scope of this project was limited such that an estimate of egg-to-fry fry survival could not be made. It is speculated that some shore produced fry do survive since a few shore spawners are present each year. Until DNA analysis is completed there is an equal possibility that these shore spawners are displaced stream spawners (Andrusak et al. 2007). There is doubt about actual numbers of shore spawners since nighttime counts made in 2009 suggest that previous year’s daytime counts are unreliable as an index of abundance and certainly can’t be used for AUC methodology to estimate total numbers. Future counts should be conducted at night.

In summary, the 2009-2010 study investigating the spawning success of shore spawning kokanee in the West Arm of Kootenay Lake indicates severe constraints and high mortality are imposed on these fish due to receding lake levels. Regardless, of the factors related to spawn and emergence timing or ecotypic divergence, evidence from field observations indicate that the majority of redds were distributed within the zone of impact adversely affected by drawdown. While it is acknowledged that lake levels fluctuation are implicated as problematic on fish populations (Hirst et al. 1991), further data is required if a more accurate estimate of drawdown impact is required. Meanwhile it is believed that some mitigative measures can be considered either by changing the drawdown pattern and or experimenting with some modified incubation boxes that utilize existing groundwater.