AUTHORS: Kristen Bouska, U.S. Geological Survey, Upper Midwest Environmental Sciences Center; Levi Solomon, Illinois Natural History Survey, Illinois River Biological Station; Andy Bartels, Wisconsin Department of Natural Resources; Jim Lamer, Illinois Natural History Survey, Illinois River Biological Station; Hae Kim, Missouri State University; Quinton Phelps, Missouri State University
ABSTRACT: Vital rates (i.e., recruitment, growth, and mortality) are the processes responsible for changes in abundance and biomass of a population through time. Knowledge of vital rates and the factors that contribute to interannual variability in vital rates can provide critical information in determining why fish population abundances increase or decrease across time and space. Between 2018 and 2020, over 2,500 individual Bluegill were collected from five study reaches on the Upper Mississippi River and one study reach on the Illinois River. Together these study reaches span nearly 1500 river kilometers and 7 degrees of latitude and represent gradients such as temperature, discharge, and clarity. From the collected individuals, otoliths were extracted, and ages were estimated. Hierarchical growth models were used to estimate growth model parameters and mean-length-at-age for each species and study reach. Logistic regression was used to estimate average age and length at maturity. Study reach-specific age-length keys were created to assign ages to unaged fish collected during standardized sampling and used to estimate indices of recruitment, stock and annual mortality. We first investigated patterns in growth, maturity, recruitment, and mortality across study reaches. Next, we sought to understand the relative contribution of stock density, habitat availability, temperature gradients, and disturbance dynamics on population dynamics. With this presentation, we aim to improve our understanding of how and why bluegill populations vary across these two large rivers and plan to extend our analyses to several other species of interest.
