Middle Columbia River White Sturgeon Spawning Monitoring (CLBMON-23A

Author: Wood

The primary objectives of the CLBMON-23A monitoring program are to: 1. Assess sturgeon incubation sites and conditions downstream of Revelstoke Dam; 2. Relate egg stranding risk to discharge from the dam and water elevation of Arrow Reservoir; 3. Assess the feasibility of underwater videography or other remote sensing techniques for monitoring presence of White Sturgeon spawners (already covered under CLBMON-23B); 4. Select and implement the most effective method (egg mats or videography or other remote sensing) for ongoing monitoring of spawning of White Sturgeon (already covered during previous studies conducted under CLBMON-23A and 23B); 5. Provide input to recommendations for the water allocation schedule for White Sturgeon spawning and incubation.

Where are the primary White Sturgeon incubation sites below Revelstoke Dam?

Based on White Sturgeon spawning studies conducted below Revelstoke Dam since 1999, the primary White Sturgeon incubation area is located within a 2.2 km river section between Km 227.9 and 230.1, which encompasses the area adjacent to the Revelstoke golf course. All 393 eggs and 56 free embryos collected since 1999 have been captured in this area. White Sturgeon eggs have consistently been documented in this relatively small area despite past sampling at other potentially suitable areas between 1 km downstream of Revelstoke Dam (Km 234) and the Illecillewaet River (Km 223.5). Revelstoke Dam is located at Km 235. The boundaries of this small spawning/ incubation area may shift slightly depending on flows and ALR elevation, but remains relatively similar between years.

How do dam and reservoir operations affect egg and free embryos survival in this area? Specifically, do significant numbers of eggs become dewatered as a result of operations?

Estimates of egg or larval survival are difficult to calculate for sturgeon species, even in systems where more data are available. In this program, the ability to estimate survival of early life stages was not possible due to the low number of eggs/larvae that were collected. The effect of reservoir operations on physical parameters within the REV egg incubation area has been investigated further under CLBMON-20 and 54.

Minimum flows implemented following the addition of a 5th turbine at REV in 2011 have increased the permanently wetted river bed area in the middle Columbia River and reduced the exposure of shallow gravel bars within the egg incubation area to the extent that egg and larval stranding is likely minimal. Stranding surveys were conducted in 2009, 2011 and 2014, with stranded eggs located on an exposed gravel bar only observed in 2009 before minimum flows were implemented. A desktop assessment of stranding risk over the duration of this monitoring program found the proportion of time that flows were below a threshold where incubating eggs or larvae would be at risk (between 0 and 142 m3/s) was 0% since the implementation of the minimum flow. The evaluation also indicated that since 2016, minimum flows have not been below 250 m3/s when early life stages were in the study area. Results demonstrate low stranding risk under current operations that include the minimum flow with less of the spawning grounds exposed when eggs are incubating and recently hatched embryos are hiding in the substrate. Additional field verification may be warranted for operations during the spawning period (July-September) where flows are less than 142 cms.

What is the most effective method for monitoring spawning of White Sturgeon?

Based on the broadcast spawning of the species, the most effective method for monitoring White Sturgeon spawning in the mid-Columbia River is a combination of egg mats and drift nets. Egg mats sample continuously and can identify the duration of spawning with less intensive effort compared to drift nets. Drift nets are more efficient in collecting eggs and larvae and they can be placed downstream of the known spawning site. In addition they identify the downstream dispersal of larvae, especially once spawning has been identified and time of hatch has been estimated. During the past 12 years of this program, an average of 126 egg mats have been deployed per spawning season for approximately 21,223 hours which resulted in an average catch-rate of 0.01 eggs/free embryos per hour. In contrast, an average of 40 drift nets have been deployed per spawning season for approximately 213 hours which resulted in an average catch-rate of 0.14 eggs/free embryos per hour. Although drift nets seem to have higher catch-rates, they do not fish continuously like egg mats.

Can modifications be made to operation of Revelstoke Dam and Arrow Lakes Reservoir to protect or enhance White Sturgeon incubation habitat?

It is unknown at this time whether additional modifications to REV/ALR operations can be made to protect or enhance White Sturgeon incubation habitat. Flow modifications have already occurred with the addition of REV5. For example, a 142 m3/s minimum flow requirement was initiated concurrent with REV5 coming online (December 2010). Preliminary information collected during this monitoring program before and after REV5 suggests that operational modifications have reduced White Sturgeon egg and larval stranding due to an increase in minimum flow. In addition, spawning has been recorded 7 of the 8 years following the addition of REV5.

The influence of REV operations and ALR elevation on physical conditions observed at the spawning area was also assessed during concurrent BC Hydro water use plan programs including: CLBMON-15a (Middle Columbia River Physical Habitat Monitoring), CLBMON-20 (Middle Columbia River White Sturgeon Spawning Habitat Assessment), CLBMON27 (Middle Columbia River Sturgeon Incubation and Rearing Study) and CLBMON-54 (Middle Columbia River Effects of Flow Changes on Incubation and Early Rearing Sturgeon). Results of these studies related to White Sturgeon incubation habitats are briefly discussed.

Where are the primary White Sturgeon incubation sites below Revelstoke Dam?

Based on White Sturgeon spawning studies conducted below Revelstoke Dam since 1999, the primary White Sturgeon incubation area is located within a 2.2 km river section between Km 227.9 and 230.1, which encompasses the area adjacent to the Revelstoke golf course. All 393 eggs and 56 free embryos collected since 1999 have been captured in this area. White Sturgeon eggs have consistently been documented in this relatively small area despite past sampling at other potentially suitable areas between 1 km downstream of Revelstoke Dam (Km 234) and the Illecillewaet River (Km 223.5). Revelstoke Dam is located at Km 235. The boundaries of this small spawning/ incubation area may shift slightly depending on flows and ALR elevation, but remains relatively similar between years.

How do dam and reservoir operations affect egg and free embryos survival in this area? Specifically, do significant numbers of eggs become dewatered as a result of operations?

Estimates of egg or larval survival are difficult to calculate for sturgeon species, even in systems where more data are available. In this program, the ability to estimate survival of early life stages was not possible due to the low number of eggs/larvae that were collected. The effect of reservoir operations on physical parameters within the REV egg incubation area has been investigated further under CLBMON-20 and 54.

Minimum flows implemented following the addition of a 5th turbine at REV in 2011 have increased the permanently wetted river bed area in the middle Columbia River and reduced the exposure of shallow gravel bars within the egg incubation area to the extent that egg and larval stranding is likely minimal. Stranding surveys were conducted in 2009, 2011 and 2014, with stranded eggs located on an exposed gravel bar only observed in 2009 before minimum flows were implemented. A desktop assessment of stranding risk over the duration of this monitoring program found the proportion of time that flows were below a threshold where incubating eggs or larvae would be at risk (between 0 and 142 m3/s) was 0% since the implementation of the minimum flow. The evaluation also indicated that since 2016, minimum flows have not been below 250 m3/s when early life stages were in the study area. Results demonstrate low stranding risk under current operations that include the minimum flow with less of the spawning grounds exposed when eggs are incubating and recently hatched embryos are hiding in the substrate. Additional field verification may be warranted for operations during the spawning period (July-September) where flows are less than 142 cms.

What is the most effective method for monitoring spawning of White Sturgeon?

Based on the broadcast spawning of the species, the most effective method for monitoring White Sturgeon spawning in the mid-Columbia River is a combination of egg mats and drift nets. Egg mats sample continuously and can identify the duration of spawning with less intensive effort compared to drift nets. Drift nets are more efficient in collecting eggs and larvae and they can be placed downstream of the known spawning site. In addition they identify the downstream dispersal of larvae, especially once spawning has been identified and time of hatch has been estimated. During the past 12 years of this program, an average of 126 egg mats have been deployed per spawning season for approximately 21,223 hours which resulted in an average catch-rate of 0.01 eggs/free embryos per hour. In contrast, an average of 40 drift nets have been deployed per spawning season for approximately 213 hours which resulted in an average catch-rate of 0.14 eggs/free embryos per hour. Although drift nets seem to have higher catch-rates, they do not fish continuously like egg mats.

Can modifications be made to operation of Revelstoke Dam and Arrow Lakes Reservoir to protect or enhance White Sturgeon incubation habitat?

It is unknown at this time whether additional modifications to REV/ALR operations can be made to protect or enhance White Sturgeon incubation habitat. Flow modifications have already occurred with the addition of REV5. For example, a 142 m3/s minimum flow requirement was initiated concurrent with REV5 coming online (December 2010). Preliminary information collected during this monitoring program before and after REV5 suggests that operational modifications have reduced White Sturgeon egg and larval stranding due to an increase in minimum flow. In addition, spawning has been recorded 7 of the 8 years following the addition of REV5.

The influence of REV operations and ALR elevation on physical conditions observed at the spawning area was also assessed during concurrent BC Hydro water use plan programs including: CLBMON-15a (Middle Columbia River Physical Habitat Monitoring), CLBMON-20 (Middle Columbia River White Sturgeon Spawning Habitat Assessment), CLBMON27 (Middle Columbia River Sturgeon Incubation and Rearing Study) and CLBMON-54 (Middle Columbia River Effects of Flow Changes on Incubation and Early Rearing Sturgeon). Results of these studies related to White Sturgeon incubation habitats are briefly discussed.