Importance of Temperature and Streamflow Variables for Explaining Variation in Relative Abundance of Age-0 Smallmouth Bass in Southwestern Wisconsin Streams
Justin M. Haglund, John Lyons, and Paul Kanehl
Abstract.—Identifying abiotic variables that influence fish recruitment patterns is crucial to understanding, assessing, and managing populations. Smallmouth Bass Micropterus dolomieu have been sampled from five streams in southwestern Wisconsin since 1989 with the goals of explaining variation and describing patterns of annual age-0 relative abundance. Summer water temperature and stream stage data have been collected annually since 2010 and United States Geological Survey modeled stream temperature and stage data were acquired from 1990–2009. Catch-per-unit-effort (CPUE) of age-0 fish was highly variable within and among streams and ranged from 0 to 48.54 fish/100 m across all streams. Random forest models with stepwise variable selection processes were used to determine the relative importance of stream temperature and stream stage variables in describing variation in CPUE from 2010–2016. July mean water temperature and maximum summer temperature explained 69.7% of the variation in CPUE of age-0 Smallmouth Bass. July mean temperature and maximum summer temperature were positively related with CPUE of age-0 fish from 2010–2016; however, modeled July mean water temperatures and modeled maximum summer temperatures were not significantly correlated with CPUE from 1990–2008. We conclude that caution must be taken when using models to predict CPUE of age-0 Smallmouth Bass from temperature or flow variables, as variability in both recruitment patterns and climatic conditions may reduce model application over longer time frames.