Investigating Interaction Between Walleye and Black Bass in Northern Wisconsin Lakes

Walleye and black bass are popular game fish, walleye being the most intensively stocked and harvested fish species in Wisconsin, while black bass are the most popular game fish species in the nation.  Current management practices in Wisconsin often seek to simultaneously enhance populations of these species in lakes where both occur.  Past studies have indicated that this may not be a feasible goal, because the species may interact negatively.  My objective was to determine if available evidence supported the conclusion that walleye and black bass interact in northern Wisconsin lakes.  I used data collected from 1,862 northern Wisconsin lakes over 74 years to create indices of abundance, growth, population size structure, and recruitment.  I used rank correlation and measurement error ratio regression to test for relationships between these population demographics to determine if black bass and walleye populations may interact.  I determined whether a high abundance of one species is significantly related to any population demographic of the others.  I found a significant negative relationship between largemouth bass abundance and walleye abundance, a significant positive relationship between largemouth bass abundance and walleye growth and size structure, and a significant negative relationship between largemouth abundance and walleye recruitment.  These results may be indicative of largemouth bass preying on juvenile walleye.  I found no clear or consistent relationship between walleye and smallmouth bass.  These findings suggest that management practices for all three species may need to be changed to account for the impossibility of enhancing populations of walleye and largemouth bass in one lake simultaneously.  I recommend further study to more precisely determine the extent of the interactions between walleye and largemouth bass.