Empirical assessment of potential interactions between walleye and smallmouth bass

The expansion of smallmouth bass Micropterus dolomieu throughout North America has created substantial changes in some food webs and created novel interactions with native predators in many systems through competition and predation, causing declines in native predator populations. In this study, we examined potential interactions between smallmouth bass (introduced) and walleye Sander vitreus (a native predator) in two Missouri River reservoirs and four natural lakes in South Dakota, USA, using historical standardized sampling data, which indexed four fitness-related factors (relative abundance, size structure, condition, and growth) of both species. Of the 24 total relationships tested among all water bodies, three (13%) were determined to be significant (size structure in Pickerel Lake: P=0.06; condition in Lake Kampeska: P=0.06, and growth at Brant Lake: P=0.02). Of these three, two relationships were negative as would be expected if negative interactions exist between these two species (size structure in Pickerel Lake: r=-0.61; condition in Lake Kampeska: r=-0.61); the remaining relationship was positive (growth at Brant Lake: r=0.75). Further, no water body consistently demonstrated significant negative interactions in all relationships tested. The results of our study did not support the concept that introduced smallmouth bass interfere with walleye populations in South Dakota waters. Rather, it is more likely that other environmental factors influence the observed variability in walleye demographics and dynamics observed in this study. At this time, we believe that both fisheries will continue to co-exist. However, continuous monitoring of both species is warranted as changing environmental conditions in the future could allow these interspecific relationships to shift toward the dominance of smallmouth bass over walleye.