Invasive species represent a threat to aquatic ecosystems globally; however, impacts can be heterogenous across systems. Documented impacts of invasive zebra mussels (Dreissena polymorpha) and spiny water fleas (Bythotrephes cedarstroemi; hereafter Bythotrephes) on native fishes are variable and context dependent across locations and time periods. Here, we use a hierarchical Bayesian analysis of a 35-year dataset on two fish species from 9 lakes to demonstrate that early life growth of ecologically important fishes are influenced by these aquatic invasive species. Walleye (Sander vitreus) grew more slowly throughout their first year of life, and were on average 12 or 14% smaller at the end of their first summer following invasion by Bythotrephes or zebra mussels, respectively. Yellow perch (Perca flavescens) growth was less affected by invasion. Yellow perch on average grew more slowly in their first year of life following invasion by zebra mussels, although this effect was not statistically distinguishable from zero. Early life growth of both walleye and yellow perch was less tightly coupled to degree days in invaded systems, as demonstrated by increased variance surrounding the degree day-length relationship. Smaller first-year size is related to walleye survival and recruitment to later life stages and has important implications for lake food webs and fisheries management. Future research quantifying effects of zebra mussels and Bythotrephes on other population-level processes and across a wider gradient of lake types is needed to understand the mechanisms driving observed changes in walleye growth.
Data files contain code for fitting Bayesian Hierarchical model of age-0 walleye and yellow perch growth, which generates output of predicted lengths and parameter estimates for generating figures. Model output is also included as .rds files. Also included is code for predicting age-0 walleye and yellow perch length as a function of zebra mussel and Bythotrephes invasion status across a range of degree day values based on model estimated parameters, which generates figures 3-6 from Hansen et al. manuscript. Length data for both species were collected simultaneously, we have separated walleye and yellow perch data into two files for analysis. Code for model fitting (WalleyeModel.R and PerchModel.R) are identical except for they call and analyze species-specific datasets. Code for generating figures (Predicted_lengths_figures_WAE.R and Predicted_lengths_figures_YEP.R) can call model fitting code (WalleyeModel.R and PerchModel.R) and fit models to generate outputs required for figures or call .rds files to avoid model fitting. These files are identical except for they call and use species-specific datasets and model outputs. Lengths of age-0 walleye and yellow perch collected using beach seines in Minnesota's large lakes. Data were collected by the Minnesota Department of Natural Resources as part of the Large Lakes Sampling program.
Sponsorship: Research funding was provided by the Minnesota Environmental and Natural Resources Trust Fund as recommended by the Minnesota Aquatic Invasive Species Research Center (MAISRC) and the Legislative-Citizen Commission on Minnesota Resources (LCCMR).