Factors Affecting Recruitment of Smallmouth Bass in Southwestern Wisconsin Streams

Recruitment plays a fundamental role in structuring fish populations and is influenced by many abiotic and biotic variables. Identifying the variables that influence recruitment patterns in fish populations is crucial to understanding, assessing, and managing those populations.  Populations of Smallmouth Bass from seven streams in Southwest Wisconsin have been sampled intensively since 1989.  Scale samples were collected and catch per effort (CPE) data was calculated during each year of the study.  Beginning in 2010, crews collected water temperature and streamflow data annually.  Stream temperatures and flow characteristics were assessed to determine how changes in these variables influence Smallmouth Bass populations. Regression tree analyses, using the randomForest package in the R statistical program, were used to determine the importance of stream temperature and flow variables on recruitment of age-0 Smallmouth Bass from 2010-2015. July mean temperatures explain the majority of variation in CPE of Smallmouth Bass populations from 2010-2015.  Temperature may be more influential than previously thought; however, six years of data may not be sufficient to fully explain what and how environmental variables affect riverine Smallmouth Bass populations in Southwestern Wisconsin.