DDMMON-10: Duncan Reservoir Fish Habitat Use Monitoring Year 9

Author: A. Duncan, I. Zwart, M. Zimmer

This monitoring program was initiated in 2009 and completed in 2016. The objective of the monitoring program was to monitor habitat use of reservoir fish species of interest (Rainbow trout, Kokanee, Bull trout and Burbot), reservoir water quality variables, and spawning timing data on a seasonal basis.

The recommended reservoir operations (Alternative S73) have had little effect on reservoir elevations compared to historical operations and therefore little to no change in productivity is expected. Though limited data from prior to this study to use as a baseline for comparison.

The low productivity associated with reservoirs may have an indirect effect on Kokanee by reducing the availability of food. However, the implementation of Alternative S73 in 2010 is not expected to result in any significant changes in productivity compared to reservoir operations prior to 2010.

Reservoir operations potentially influence Bull Trout in the following three areas:
1. Productivity issues that affect Kokanee abundance may also affect Bull Trout since Kokanee are a key prey species for Bull Trout.
2. Drawdown of the reservoir in the spring results in a reduced reservoir volume, and this may lead to an increased harvest of Bull Trout at this time in a recreational fishery on the reservoir. However, drawdown of the reservoir in the spring is similar between pre and post implementation of- Alternative S73.
3. Reservoir operations may affect Bull Trout passage through the Duncan Dam. Passage requires manipulation of the low level operating gates (LLOG), and under some circumstances, other reservoir operations may take precedence over Bull Trout passage. For example, extreme precipitation events in July 2012 meant that the LLOGs were used to reduce the amount of spill occurring at the dam in an attempt to reduce total gas pressure impacts to fish downstream of the dam. As a result, no Bull Trout transfers were conducted between mid-July and mid-August.

The recommended reservoir operations (Alternative S73) have had little effect on reservoir elevations compared to historical operations and therefore little to no change in productivity is expected. Though limited data from prior to this study to use as a baseline for comparison.

The low productivity associated with reservoirs may have an indirect effect on Kokanee by reducing the availability of food. However, the implementation of Alternative S73 in 2010 is not expected to result in any significant changes in productivity compared to reservoir operations prior to 2010.

Reservoir operations potentially influence Bull Trout in the following three areas:
1. Productivity issues that affect Kokanee abundance may also affect Bull Trout since Kokanee are a key prey species for Bull Trout.
2. Drawdown of the reservoir in the spring results in a reduced reservoir volume, and this may lead to an increased harvest of Bull Trout at this time in a recreational fishery on the reservoir. However, drawdown of the reservoir in the spring is similar between pre and post implementation of- Alternative S73.
3. Reservoir operations may affect Bull Trout passage through the Duncan Dam. Passage requires manipulation of the low level operating gates (LLOG), and under some circumstances, other reservoir operations may take precedence over Bull Trout passage. For example, extreme precipitation events in July 2012 meant that the LLOGs were used to reduce the amount of spill occurring at the dam in an attempt to reduce total gas pressure impacts to fish downstream of the dam. As a result, no Bull Trout transfers were conducted between mid-July and mid-August.