Modeling widespread declines in walleye recruitment following zebra mussel invasion in Minnesota lakes

Invasive zebra mussels (Dreissena polymorpha) alter lake ecosystems and can negatively affect first-year growth of walleye (Sander vitreus), potentially lowering walleye recruitment success. We quantified walleye recruitment responses to zebra mussel invasion in Minnesota lakes using data from 1,438 electrofishing surveys across 348 lakes collected between 1993 and 2019 to measure walleye recruitment, defined as relative abundance of age-0 walleye in their first fall. We fitted Bayesian hierarchical models to data from both invaded and uninvaded lakes to quantify the effects of zebra mussels on walleye recruitment while accounting for the effects of lake temperature, surface area, and water clarity. Age-0 walleye recruitment was ~41% lower (95% CI: 38 - 44%) in lakes containing zebra mussels compared to uninvaded lakes. Recruitment did not decline in lakes that remained uninvaded. Walleye recruitment was higher in larger lakes and lakes with lower water clarity. Water temperature, indexed by degree days (base 5 °C), had little effect on walleye recruitment. Our results demonstrate negative effects of zebra mussels on walleye recruitment at a landscape scale.

The code release contains three files: two .Rmd files and a .stan file. The file EF_WAE_ZM_Model3.rmd contains the R code that imports data and runs stan model code (Pois_model_zip3.stan) and includes calculations of summary statistics found in Table 1 at the bottom of the code. The file Figures.rmd contains R code to create the figures found in the manuscript along with calculated summaries of the data.