DDMMON-11 Duncan Reservoir Burbot Habitat Mapping, Modelling & Optimization. Final Report Prepared for BC Hydro Burnaby

Author: Amec Foster Wheeler

This monitoring program was initiated in 2009 and completed in 2016. In 2013, after three years of attempting to monitor adult Burbot spawning with little success and to capture juvenile Burbot with no success, this program changed its methods from direct biological monitoring to a physical modelling approach. This program mapped potential Burbot habitat and monitored temperature in the upper Duncan Reservoir drawdown zone. The Burbot habitat mapping and modelling occurred in August 2015 and associated temperature monitoring was completed in 2016.

– Current water temperature monitoring suggests the Duncan Reservoir Burbot spawning and incubation period occurs from January to March, which is within the range that radio tagged Burbot were suspected to be spawning in Duncan Reservoir and within the range indicated for the species in nearby watersheds.
– Water depths in the Burbot monitoring target area were optimal for Burbot spawning. Burbot spawning has been observed in depths between >0 and 10 m (AMEC 2014).
– Water velocity (measured as average column velocity) in the Burbot monitoring target area was mostly within the parameters for Burbot spawning. Burbot spawning has been observed in water velocities 0-0.25 m/s (AMEC 2014). The majority of the Burbot monitoring target area was described as pool habitat and there was no or very low flow observed in most areas. The exception to this was within the defined Upper Duncan River channel upstream of Rkm 26.5 where average velocity was nearly 0.5 m/s.
– All substrates that were observable in 2015 were suitable for Burbot spawning and possibly for rearing. Burbot spawning has been observed in areas with silt, sand, gravel, cobble, and possibly boulder and bedrock (references cited in AMEC 2014). Burbot rearing habitats include cobble, boulder and possibly silt substrates (references cited in AMEC 2014). The majority of habitat observed in the Burbot monitoring target area was silt with some small gravel areas, however, water clarity was low and it was difficult to conclusively describe the substrate in some areas.
– In late March 2015, turbidity was notable within the Burbot monitoring target area and ranged from 8 to 32 NTU, whereas conditions in the historic Duncan Lake (Rkm 15) were clear (<1 NTU). - The type of cover observed in the Duncan Burbot monitoring area is likely suitable for Burbot spawning and rearing. According to available literature, ice, braided channels, gravel bars and sidechannels are considered cover for spawning Burbot. For rearing Burbot, cover includes large woody debris, weeds, rocks, cutbanks, interstitial spaces and shoreline littoral areas. For Duncan Reservoir Burbot, estimation of spawning success cannot be based on spawning observations, since Burbot spawning has not been directly observed. Therefore, an alternative method for estimating Burbot spawning success in the Duncan Reservoir included water temperature monitoring, physical habitat mapping in the field, estimating suitable spawning/incubation habitat (ha) based on criteria from the literature (i.e., depth, velocity, substrate, turbidity, cover) and linking physical habitat availability with reservoir operations. Based on best available information, river km 20.6-28.0 represents the most likely spawning/egg incubation area that could be impacted by reservoir operations for a portion of the Burbot spawning population in the Duncan Reservoir. Based on current water temperature monitoring, the estimated Burbot spawning/incubation period for Duncan Reservoir is early January to mid-March. During typical operational years, Duncan Reservoir is around 564 m in early January and declines to approximately 552 m by mid-March when eggs may be incubating in the substrates (Figure 2-1). Modelled habitat area is estimated at 1111 ha and 979 ha for the 564 m and 552 m elevation scenarios, respectively (Table 4-2; Appendix C). Therefore, it is estimated that approximately 130 ha of habitat may be dewatered during the incubation period indicated above. Based on habitat area and the assumption that optimal habitat criteria remained throughout reservoir drawdown, Burbot spawning success may have been estimated at 88% because 12% of the total spawning/incubation area was dewatered for the predicted hatch/swim up period (assuming a higher amount of habitat equates to higher spawning success).

– Current water temperature monitoring suggests the Duncan Reservoir Burbot spawning and incubation period occurs from January to March, which is within the range that radio tagged Burbot were suspected to be spawning in Duncan Reservoir and within the range indicated for the species in nearby watersheds.
– Water depths in the Burbot monitoring target area were optimal for Burbot spawning. Burbot spawning has been observed in depths between >0 and 10 m (AMEC 2014).
– Water velocity (measured as average column velocity) in the Burbot monitoring target area was mostly within the parameters for Burbot spawning. Burbot spawning has been observed in water velocities 0-0.25 m/s (AMEC 2014). The majority of the Burbot monitoring target area was described as pool habitat and there was no or very low flow observed in most areas. The exception to this was within the defined Upper Duncan River channel upstream of Rkm 26.5 where average velocity was nearly 0.5 m/s.
– All substrates that were observable in 2015 were suitable for Burbot spawning and possibly for rearing. Burbot spawning has been observed in areas with silt, sand, gravel, cobble, and possibly boulder and bedrock (references cited in AMEC 2014). Burbot rearing habitats include cobble, boulder and possibly silt substrates (references cited in AMEC 2014). The majority of habitat observed in the Burbot monitoring target area was silt with some small gravel areas, however, water clarity was low and it was difficult to conclusively describe the substrate in some areas.
– In late March 2015, turbidity was notable within the Burbot monitoring target area and ranged from 8 to 32 NTU, whereas conditions in the historic Duncan Lake (Rkm 15) were clear (<1 NTU). - The type of cover observed in the Duncan Burbot monitoring area is likely suitable for Burbot spawning and rearing. According to available literature, ice, braided channels, gravel bars and sidechannels are considered cover for spawning Burbot. For rearing Burbot, cover includes large woody debris, weeds, rocks, cutbanks, interstitial spaces and shoreline littoral areas. For Duncan Reservoir Burbot, estimation of spawning success cannot be based on spawning observations, since Burbot spawning has not been directly observed. Therefore, an alternative method for estimating Burbot spawning success in the Duncan Reservoir included water temperature monitoring, physical habitat mapping in the field, estimating suitable spawning/incubation habitat (ha) based on criteria from the literature (i.e., depth, velocity, substrate, turbidity, cover) and linking physical habitat availability with reservoir operations. Based on best available information, river km 20.6-28.0 represents the most likely spawning/egg incubation area that could be impacted by reservoir operations for a portion of the Burbot spawning population in the Duncan Reservoir. Based on current water temperature monitoring, the estimated Burbot spawning/incubation period for Duncan Reservoir is early January to mid-March. During typical operational years, Duncan Reservoir is around 564 m in early January and declines to approximately 552 m by mid-March when eggs may be incubating in the substrates (Figure 2-1). Modelled habitat area is estimated at 1111 ha and 979 ha for the 564 m and 552 m elevation scenarios, respectively (Table 4-2; Appendix C). Therefore, it is estimated that approximately 130 ha of habitat may be dewatered during the incubation period indicated above. Based on habitat area and the assumption that optimal habitat criteria remained throughout reservoir drawdown, Burbot spawning success may have been estimated at 88% because 12% of the total spawning/incubation area was dewatered for the predicted hatch/swim up period (assuming a higher amount of habitat equates to higher spawning success).