Middle Columbia River Juvenile Fish Habitat Use (Year 6) CLBMON-17. Report prepared for B.C

Author: Triton Environmental Consultants Ltd

CLBMON-17 was a 6-year study (2008-2013) that aimed to 1) provide information on Juvenile fishes use of the Middle Columbia River and on the suitability of these habitats to meet critical life history requirements and 2) assess the effects of the implementation of the 142 m3/s minimum flow and REV 5 on the recruitment of juvenile life stages of fishes of the Middle Columbia.

1. What are the seasonal abundances and distribution of juvenile life stages of fishes in the Middle Columbia River (MCR)?
– Seasonal abundances and distribution of juvenile species are variable in the MCR. Generally, abundance was higher in the fall than in the spring and summer from Year 1 to 6. Several of the Reaches experience significantly greater numbers of fish in the fall than in the spring or summer. However, variable ALR and discharge conditions during the summer and fall trips likely influenced distribution and catchability. Fish usage both before and after minimum flow/REV5 tended to be higher and more consistent in the lower reaches (Reaches 1 and 2) than the higher reaches (Reaches 3 and 4).
2. How do juvenile fishes use the mainstem habitats in the Middle Columbia River?
– Juvenile habitat use in the Middle Columbia River is primarily associated with rearing (April to September). In addition it is reasonable to assume that overwintering likely occurs within the study area since depths and habitat conditions would be suitable. However, sampling did not occur in the winter and therefore this assumption cannot be validated.
3. What factors affect recruitment of juvenile life stages in the Middle Columbia River?
a. Do operational strategies for Revelstoke Dam and Arrow Lake Reservoir influence the availability of juvenile fishes preferred habitats?
– All habitats sampled in Years 1-6 of the study were accessible and no changes in habitat quality, quantity or accessibility were noted post-minimum flow. The minimum base flow and influence of the ALR do not limit habitat access.
– Habitat characteristics of sites with high abundance of the most common species were similar throughout Years 1 to 6 suggesting that operational strategies have not influenced the availability of preferred habitats. Although overall catch-per-unit-effort of juvenile fish decreased post-minimum flow, the difference was not statistically significant. In the spring when conditions were most consistent across the 6 years of study, there were no differences in CPUE at any reach pre- vs. post-minimum flow. In the summer, CPUE pre-minimum flow was higher at all reaches but in the fall was only higher in Reach 4.
b. Do current operational strategies affect availability of the food base for juvenile fish life stages?
– Length, weight and condition factor data of the most abundant species in the system were stable in Years 1 6 with no apparent trend with respect to the change in flow associated with minimum flow and Rev 5.
– Data from CLBMON-15b (Ecological Productivity) was reviewed and preliminary analysis shows that increasing the amount of time the food base (periphyton and invertebrates) is submerged, increases overall biomass of these organisms. Further conclusions are expected as CLBMON-15b progresses in coming years.
c. Do predators influence fish recruitment and habitat use in the Middle Columbia River?
– Adult piscivorous fish such as large Rainbow Trout, Bull Trout, Sculpins and Redside Shiners are present in the system and are known to prey on other species. Review of the results of CLBMON 16 (Fish Population Indexing) show that the adult population of potential predators has been relatively constant throughout 2008 to 2013 suggesting that the implementation of minimum flows has not effected predator populations. As the results of CLBMON-17 also show a relatively stable juvenile fish community it is likely that predation pressure has also remained relatively constant. Consequently, whatever effect predation had on juvenile recruitment pre-Rev 5, the same pressure exits post Rev 5.

1. What are the seasonal abundances and distribution of juvenile life stages of fishes in the Middle Columbia River (MCR)?
– Seasonal abundances and distribution of juvenile species are variable in the MCR. Generally, abundance was higher in the fall than in the spring and summer from Year 1 to 6. Several of the Reaches experience significantly greater numbers of fish in the fall than in the spring or summer. However, variable ALR and discharge conditions during the summer and fall trips likely influenced distribution and catchability. Fish usage both before and after minimum flow/REV5 tended to be higher and more consistent in the lower reaches (Reaches 1 and 2) than the higher reaches (Reaches 3 and 4).
2. How do juvenile fishes use the mainstem habitats in the Middle Columbia River?
– Juvenile habitat use in the Middle Columbia River is primarily associated with rearing (April to September). In addition it is reasonable to assume that overwintering likely occurs within the study area since depths and habitat conditions would be suitable. However, sampling did not occur in the winter and therefore this assumption cannot be validated.
3. What factors affect recruitment of juvenile life stages in the Middle Columbia River?
a. Do operational strategies for Revelstoke Dam and Arrow Lake Reservoir influence the availability of juvenile fishes preferred habitats?
– All habitats sampled in Years 1-6 of the study were accessible and no changes in habitat quality, quantity or accessibility were noted post-minimum flow. The minimum base flow and influence of the ALR do not limit habitat access.
– Habitat characteristics of sites with high abundance of the most common species were similar throughout Years 1 to 6 suggesting that operational strategies have not influenced the availability of preferred habitats. Although overall catch-per-unit-effort of juvenile fish decreased post-minimum flow, the difference was not statistically significant. In the spring when conditions were most consistent across the 6 years of study, there were no differences in CPUE at any reach pre- vs. post-minimum flow. In the summer, CPUE pre-minimum flow was higher at all reaches but in the fall was only higher in Reach 4.
b. Do current operational strategies affect availability of the food base for juvenile fish life stages?
– Length, weight and condition factor data of the most abundant species in the system were stable in Years 1 6 with no apparent trend with respect to the change in flow associated with minimum flow and Rev 5.
– Data from CLBMON-15b (Ecological Productivity) was reviewed and preliminary analysis shows that increasing the amount of time the food base (periphyton and invertebrates) is submerged, increases overall biomass of these organisms. Further conclusions are expected as CLBMON-15b progresses in coming years.
c. Do predators influence fish recruitment and habitat use in the Middle Columbia River?
– Adult piscivorous fish such as large Rainbow Trout, Bull Trout, Sculpins and Redside Shiners are present in the system and are known to prey on other species. Review of the results of CLBMON 16 (Fish Population Indexing) show that the adult population of potential predators has been relatively constant throughout 2008 to 2013 suggesting that the implementation of minimum flows has not effected predator populations. As the results of CLBMON-17 also show a relatively stable juvenile fish community it is likely that predation pressure has also remained relatively constant. Consequently, whatever effect predation had on juvenile recruitment pre-Rev 5, the same pressure exits post Rev 5.