CLBMON-45 Lower Columbia River Fish Population Indexing Survey 2016 Report

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

This monitoring program was initiated in September 2007 and will be carried out over 13 years. CLBMON-45 gathers baseline information on fish distribution, life history characteristics, and population abundance data for three index species (i.e., Mountain Whitefish, Rainbow Trout, and Walleye), and also monitors the effect of Mountain Whitefish and Rainbow Trout flows on these three species. The objectives of CLBMON-45 (BC Hydro 2007) are: - to extend time series data on the abundance, distribution, and biological characteristics of nearshore and shallow water fish populations in the LCR; - to examine long-term trends in key index fish populations (i.e., Mountain Whitefish, Walleye, and Rainbow Trout) during the continued implementation of Mountain Whitefish and Rainbow Trout flows in the LCR; - to build upon previous investigations for the further refinement of sampling strategy, sampling program, and analytical procedures to establish a long-term monitoring program for fish populations in the LCR; - to update the existing electronic storage and retrieval system for fish population and habitat monitoring data for the Columbia River; - to establish linkages between other biological monitoring programs being undertaken in the LCR, in particular, the Physical Habitat and Ecological Productivity Monitoring Program (CLBMON-44); and - to identify gaps in data and understanding of current knowledge about fish populations and procedures for sampling them, and to provide recommendations for future monitoring and fisheries investigations.

The sampling program conducted since 2001 provides a high-quality, long-term dataset to address the first management question, which regards changes in fish population metrics over time in the LCR. Hierarchical Bayesian models suggested that the abundance of adult Rainbow Trout increased substantially between 2001 and 2016, and high abundances in recent years coincided with a decline in body condition and survival, suggesting density dependence. Data for Walleye also suggested density-dependence with a decrease in abundance and increase in body condition in recent years (2012 to 2016). The estimated abundance of Mountain Whitefish abundance declined since 2001 but was relatively stable during the most recent five years (2011-2016). The data suggested larger length-at-age of age-0 Mountain Whitefish and greater body condition in 2016 than previous years, suggesting good conditions for growth.
The second management question for this monitoring program pertains to the effects of inter-annual flow variability on fish population metrics of the index species. One of the ways that flow variability can affect fish populations is through egg dewatering during discharge reductions. The effect of egg dewatering on fish abundance was assessed through the analysis of age ratios as a recruitment index and through stock-recruitment models that included egg loss as a covariate. There was no significant relationship between the age-1:2 recruitment index and estimated egg losses. Egg loss was not a significant covariate in the stock-recruitment model for Mountain Whitefish.
The stock-recruitment analysis had large variability in Mountain Whitefish recruitment for a particular level of egg loss or spawner abundance, which resulted in weak predictive ability and suggested that other unknown factors likely have a large influence on recruitment in the LCR. For Rainbow Trout, there was no evidence of negative effects of egg losses on recruitment at the observed levels of egg loss, which were less than 3% in all years. These conclusions for both Mountain Whitefish and Rainbow Trout should be considered tentative because of the poor fit in modelled relationships, and the possibility that sampling biases or environmental variability masked real effects of egg dewatering.
Flow variability in the LCR is expected to have less of an effect on Walleye than Rainbow Trout and Mountain Whitefish because the abundance of Walleye is thought to depend on spawning and early life history survival outside of the study area. In addition, effects of flow variability on invertebrate productivity, if they occur, would not have direct effects on food availability that could impact the condition or growth of a piscivorous species like Walleye.

The sampling program conducted since 2001 provides a high-quality, long-term dataset to address the first management question, which regards changes in fish population metrics over time in the LCR. Hierarchical Bayesian models suggested that the abundance of adult Rainbow Trout increased substantially between 2001 and 2016, and high abundances in recent years coincided with a decline in body condition and survival, suggesting density dependence. Data for Walleye also suggested density-dependence with a decrease in abundance and increase in body condition in recent years (2012 to 2016). The estimated abundance of Mountain Whitefish abundance declined since 2001 but was relatively stable during the most recent five years (2011-2016). The data suggested larger length-at-age of age-0 Mountain Whitefish and greater body condition in 2016 than previous years, suggesting good conditions for growth.
The second management question for this monitoring program pertains to the effects of inter-annual flow variability on fish population metrics of the index species. One of the ways that flow variability can affect fish populations is through egg dewatering during discharge reductions. The effect of egg dewatering on fish abundance was assessed through the analysis of age ratios as a recruitment index and through stock-recruitment models that included egg loss as a covariate. There was no significant relationship between the age-1:2 recruitment index and estimated egg losses. Egg loss was not a significant covariate in the stock-recruitment model for Mountain Whitefish.
The stock-recruitment analysis had large variability in Mountain Whitefish recruitment for a particular level of egg loss or spawner abundance, which resulted in weak predictive ability and suggested that other unknown factors likely have a large influence on recruitment in the LCR. For Rainbow Trout, there was no evidence of negative effects of egg losses on recruitment at the observed levels of egg loss, which were less than 3% in all years. These conclusions for both Mountain Whitefish and Rainbow Trout should be considered tentative because of the poor fit in modelled relationships, and the possibility that sampling biases or environmental variability masked real effects of egg dewatering.
Flow variability in the LCR is expected to have less of an effect on Walleye than Rainbow Trout and Mountain Whitefish because the abundance of Walleye is thought to depend on spawning and early life history survival outside of the study area. In addition, effects of flow variability on invertebrate productivity, if they occur, would not have direct effects on food availability that could impact the condition or growth of a piscivorous species like Walleye.