Population Dynamics of Largescale Suckers in the Kootenai River, Idaho: Effects of Nutrient Enhancement and Discharge on Growth and Recruitment

The largescale sucker Catostomus macrocheilusis a widespread species in Idaho and an ecologically-important species throughout the Pacific Northwest.  Largescale suckers are ubiquitous in the Kootenai River and make up the majority of the vertebrate biomass in the Idaho portion of the river.  Largescale suckers have been thought to positively respond to an ongoing nutrient addition project in the river.  There is little information on the population dynamics of largescale suckers and the factors potentially influencing growth and recruitment, particularly in the Kootenai River.  As such, we evaluated the population characteristics (i.e., age structure, growth, recruitment, mortality) and described the influence of nutrient addition, discharge, and temperature on growth rates and recruitment of largescale suckers of the Kootenai River, Idaho.  We used a repeated-measures mixed-effects model to evaluate the influence of the factors effecting growth rates and recruitment variability where we treated age as a fixed effect and year as a random effect.  We used an information theoretic approach to select the best multiple-regression model that explained the most variation in growth and recruitment.  This research will help to inform management by evaluating the influence of a nutrient addition project and seasonal discharge on an important species in the Kootenai River.