CLBMON-16 Middle Columbia River Fish Population Indexing Survey 2017 Report

Author: Golder Associates Ltd., Poisson Consulting Ltd., Okanagan Nation Alliance

The objective of this study is to systematically collect fish population data prior to and following the implementation of the 142 m3/s minimum flows and REV5 to quantitatively assess the changes in abundance, growth, diversity and distribution of fishes in the middle Columbia River.

Is there a change in the abundance of adult life stages of fish using the MCR that corresponds with the implementation of a year-round minimum flow?

Density estimates of sucker species initially increased after the flow regime change (2011 to 2014) but decreased in 2016 and 2017. Bull Trout and Mountain Whitefish abundance estimates did not change substantially after the flow regime change. Rates of population growth of Burbot, Northern Pikeminnow, and Rainbow Trout were significantly lower after the flow regime change than before. There were also decreases in the probability of occupancy of Burbot, Northern Pikeminnow, Rainbow Trout, and sculpin species that coincided with the timing of the new flow regime. It is unknown whether the flow regime change caused these changes.

Is there a change in growth rates of adult life stages of the most common fish species using the MCR that corresponds with the implementation of a year-round minimum flow?

Estimates of the von Bertalanffy growth coefficient for Bull Trout initially declined after the flow regime change but were within the range of values recorded before the flow regime change. The decrease was likely related to concurrent decreases in Kokanee abundance. Mountain Whitefish growth coefficients did not indicate any change coincident with the flow regime. Growth of all other species could not be estimated because of small numbers of recaptured fish

Is there a change in body condition (measured as a function of relative length to weight) of adult life stages of fish using the MCR that corresponds with the implementation of a year-round minimum flow?

Estimates of body condition of Bull Trout and adult Largescale Sucker decreased after the flow regime change. The decrease in Bull Trout body condition coincided with a decrease in the abundance of Kokanee, which are an important prey item. The decrease in Largescale Sucker body condition coincided with an increase in the density of sucker species and abundance estimates of Largescale Sucker, suggesting competition for resources. It is not possible to conclude whether the flow regime change contributed to the changes in body condition.

Is there a change in spatial distribution of adult life stages of fish using the MCR that corresponds with the implementation of a year-round minimum flow?

There was an upstream shift in the distribution of some species in years following the flow regime change. The difference was statistically significant for Bull Trout and Rainbow Trout but not significant for sucker species. These results provide support for rejection of this hypothesis.

Is there a change in the abundance of adult life stages of fish using the MCR that corresponds with the implementation of a year-round minimum flow?

Density estimates of sucker species initially increased after the flow regime change (2011 to 2014) but decreased in 2016 and 2017. Bull Trout and Mountain Whitefish abundance estimates did not change substantially after the flow regime change. Rates of population growth of Burbot, Northern Pikeminnow, and Rainbow Trout were significantly lower after the flow regime change than before. There were also decreases in the probability of occupancy of Burbot, Northern Pikeminnow, Rainbow Trout, and sculpin species that coincided with the timing of the new flow regime. It is unknown whether the flow regime change caused these changes.

Is there a change in growth rates of adult life stages of the most common fish species using the MCR that corresponds with the implementation of a year-round minimum flow?

Estimates of the von Bertalanffy growth coefficient for Bull Trout initially declined after the flow regime change but were within the range of values recorded before the flow regime change. The decrease was likely related to concurrent decreases in Kokanee abundance. Mountain Whitefish growth coefficients did not indicate any change coincident with the flow regime. Growth of all other species could not be estimated because of small numbers of recaptured fish

Is there a change in body condition (measured as a function of relative length to weight) of adult life stages of fish using the MCR that corresponds with the implementation of a year-round minimum flow?

Estimates of body condition of Bull Trout and adult Largescale Sucker decreased after the flow regime change. The decrease in Bull Trout body condition coincided with a decrease in the abundance of Kokanee, which are an important prey item. The decrease in Largescale Sucker body condition coincided with an increase in the density of sucker species and abundance estimates of Largescale Sucker, suggesting competition for resources. It is not possible to conclude whether the flow regime change contributed to the changes in body condition.

Is there a change in spatial distribution of adult life stages of fish using the MCR that corresponds with the implementation of a year-round minimum flow?

There was an upstream shift in the distribution of some species in years following the flow regime change. The difference was statistically significant for Bull Trout and Rainbow Trout but not significant for sucker species. These results provide support for rejection of this hypothesis.