Middle Columbia River juvenile fish stranding assessment (Year 2013

Author: R. Tomlinson, G. Sykes

The objective of this four year study was to assess the risk of fish stranding in a discrete portion of the Columbia River potentially influenced by the operation of five units at Revelstoke Dam. Specifically, the goals of the study were to characterize the level of stranding that currently occurs at the Greenslide Creek Side channel and other side channel sites downstream of the Trans-Canada Highway Bridge and to determine if stranding risk is likely to increase in extent, magnitude, duration, or frequency with the addition of a fifth generator (Rev 5) at the dam. The study involves two years of pre-Rev 5 data collection as well as two years of post-Rev 5 data collection, with this report representing the second year of post-Rev 5 data collection.

1. Are fish strandings occurring in side channels near Greenslide Creek under the current four units operations in the area of influence of Rev 5?

Daily fish strandings resulting from fluctuating water levels due to Revelstoke Dam releases are not occurring at the Greenslide Creek Side Channel. However, seasonal isolation of habitat in the Greenslide Creek Side Channel does occur as the reservoir elevation drops in the fall, which potentially results in fish mortalities. Based on 2009, 2010, and 2013 sampling results, juvenile carp, Prickly Sculpin, tench, chub, and suckers are the most susceptible species. The absence of important habitat features including but not limited to: gravel substrates, cover and flow limit the potential to encounter sport fish within the Greenslide Creek Side Channel (sport fish captures were limited to one juvenile Rainbow Trout).

2. If fish strandings are found to occur in these side channels under the present regime, are they likely to increase in extent, magnitude, duration, or frequency under the five-unit operations?

Fish strandings will increase if additional high-risk areas (e.g., low-gradient sites where shallow channels and depressions form) not currently wetted during daily flow fluctuations become wetted as a result of the expected 20 per cent increase in daily peak flow magnitude. However, this was not observed in 2011 or 2013 (first- and third-year following installation of Rev 5) because discharge during the sample period did not approach the maximum forecasted levels.

3. What is the relationship between abundance of stranded fishes (stranding risk) and time of day, wetted history, substrate, and cover type in the area of influence of Rev 5?

Fish strandings time of day
– Fish strandings typically occur in the early morning (3:00 a.m. to 5:00 a.m.) on nights when the discharge from the dam is ramped down (Rates ranging from 7.9 – 132.5 cm/hr.). There is a delay of approximately 20 minutes before the drop in flows is noticeable at the Highway Bridge site and 3 hours before they are noticeable at the Begbie site.

Fish strandings time of year
– Stranding potential is highest from fall to spring when the reservoir elevation is lower and a greater proportion of the river is influenced by flow regulations from the dam.

Fish strandings wetted history

– Fish strandings occur over a wide range of discharge on the falling limb of the hydrograph. Site conditions (e.g., channel morphology and bank slope) and rates of change will affect overall stranding risk. Sites frequently wetted and dewatered may be avoided by fish due to unpredictable conditions, thereby reducing stranding in those areas.

Fish strandings substrate type
– Fish strandings resulting from dam operations occur primarily at low-gradient sites where multiple narrow and shallow channels, depressions, and pools form as water levels drop. These narrow and shallow channels and depressions typically have gravel and cobble substrates.

Fish strandings cover type
– Fish strandings resulting from dam operations occur primarily at low-gradient sites where multiple narrow and shallow channels, depressions, and pools form as water levels drop. These narrow and shallow channels and depressions typically lack cover such as large woody debris.

4. What species and life stages are most likely to be stranded?
Species Sampling results from CLBMON-17 in the vicinity of the Highway Bridge site from 2009 to 2011 and 2013 suggested that based on abundance, sculpin and Mountain Whitefish were most likely to be stranded. 2010 stranding sampling results identified three Mountain Whitefish mortalities at the site, which supports the CLBMON 17 data. 2009 stranding results showed coarse fishes such as Peamouth Chub, Largescale Sucker, Redside Shiner, and sculpin were most likely to be stranded in the area downstream of the Illecillewaet River. In general, sport fishes at the study sites were associated primarily with deeper pools that would not be expected to dewater, or were associated with areas that remain connected to the main channel. These fishes also have a high velocity preference, which would enable them to detect reduction in velocities associated with decreasing flows; therefore they would move out of potential stranding areas.

Life stages Captured fishes and observed mortalities were typically juveniles, with the exception of the occasional adult Redside Shiner and sculpin. In 2010, several adult Kokanee were observed building redds in areas that became dewatered as flows ramped down.

1. Are fish strandings occurring in side channels near Greenslide Creek under the current four units operations in the area of influence of Rev 5?

Daily fish strandings resulting from fluctuating water levels due to Revelstoke Dam releases are not occurring at the Greenslide Creek Side Channel. However, seasonal isolation of habitat in the Greenslide Creek Side Channel does occur as the reservoir elevation drops in the fall, which potentially results in fish mortalities. Based on 2009, 2010, and 2013 sampling results, juvenile carp, Prickly Sculpin, tench, chub, and suckers are the most susceptible species. The absence of important habitat features including but not limited to: gravel substrates, cover and flow limit the potential to encounter sport fish within the Greenslide Creek Side Channel (sport fish captures were limited to one juvenile Rainbow Trout).

2. If fish strandings are found to occur in these side channels under the present regime, are they likely to increase in extent, magnitude, duration, or frequency under the five-unit operations?

Fish strandings will increase if additional high-risk areas (e.g., low-gradient sites where shallow channels and depressions form) not currently wetted during daily flow fluctuations become wetted as a result of the expected 20 per cent increase in daily peak flow magnitude. However, this was not observed in 2011 or 2013 (first- and third-year following installation of Rev 5) because discharge during the sample period did not approach the maximum forecasted levels.

3. What is the relationship between abundance of stranded fishes (stranding risk) and time of day, wetted history, substrate, and cover type in the area of influence of Rev 5?

Fish strandings time of day
– Fish strandings typically occur in the early morning (3:00 a.m. to 5:00 a.m.) on nights when the discharge from the dam is ramped down (Rates ranging from 7.9 – 132.5 cm/hr.). There is a delay of approximately 20 minutes before the drop in flows is noticeable at the Highway Bridge site and 3 hours before they are noticeable at the Begbie site.

Fish strandings time of year
– Stranding potential is highest from fall to spring when the reservoir elevation is lower and a greater proportion of the river is influenced by flow regulations from the dam.

Fish strandings wetted history

– Fish strandings occur over a wide range of discharge on the falling limb of the hydrograph. Site conditions (e.g., channel morphology and bank slope) and rates of change will affect overall stranding risk. Sites frequently wetted and dewatered may be avoided by fish due to unpredictable conditions, thereby reducing stranding in those areas.

Fish strandings substrate type
– Fish strandings resulting from dam operations occur primarily at low-gradient sites where multiple narrow and shallow channels, depressions, and pools form as water levels drop. These narrow and shallow channels and depressions typically have gravel and cobble substrates.

Fish strandings cover type
– Fish strandings resulting from dam operations occur primarily at low-gradient sites where multiple narrow and shallow channels, depressions, and pools form as water levels drop. These narrow and shallow channels and depressions typically lack cover such as large woody debris.

4. What species and life stages are most likely to be stranded?
Species Sampling results from CLBMON-17 in the vicinity of the Highway Bridge site from 2009 to 2011 and 2013 suggested that based on abundance, sculpin and Mountain Whitefish were most likely to be stranded. 2010 stranding sampling results identified three Mountain Whitefish mortalities at the site, which supports the CLBMON 17 data. 2009 stranding results showed coarse fishes such as Peamouth Chub, Largescale Sucker, Redside Shiner, and sculpin were most likely to be stranded in the area downstream of the Illecillewaet River. In general, sport fishes at the study sites were associated primarily with deeper pools that would not be expected to dewater, or were associated with areas that remain connected to the main channel. These fishes also have a high velocity preference, which would enable them to detect reduction in velocities associated with decreasing flows; therefore they would move out of potential stranding areas.

Life stages Captured fishes and observed mortalities were typically juveniles, with the exception of the occasional adult Redside Shiner and sculpin. In 2010, several adult Kokanee were observed building redds in areas that became dewatered as flows ramped down.