COS 240-1 - Patchy habitats create patchy responses of native fish communities to the removal of an invasive predator.

Abstract: As invasive species continue to spread into new ecosystems, it is important to understand the potential benefits of suppressing their populations after establishment. A modest number of long-term studies suggest that responses of native fish to the suppression of an invader can be variable, counterintuitive, or slow to materialize. We report the responses of eight native fish species across a 23-year smallmouth bass removal experiment in a mid-sized lake in upstate New York. The entire shoreline of the lake is sampled through boat electrofishing surveys. Sites are categorized as being either sedimented or rocky and by the presence or absence of large woody debris. Early reports from the first 7 years of this experiment document rapid increases in the abundance of both native fishes and juvenile smallmouth bass. Using the long-term records, we assessed species responses across size cohorts and across habitats, asking whether ontogenetic shifts in habitat preferences create a spatial mosaic of responses to the invasive predator suppression. Specifically, we assess how habitat influences the timing and direction of species’ response to removal across their ontogeny and if the relative abundance of smallmouth bass influences the magnitude of a species’ habitat-specific response. We found that the timing and direction of a species’ response varies across space and life stage. Positive responses are most frequent among < 100-mm fish, with the highest number of positive responses being observed in sedimented, wooded sites. Sites that are sedimented, without large quantities of woody debris, show the second highest frequency of positive responses, followed by rocky and wooded rocky sites. For several species, that show responses at both the woody and non-woody sites within a substrate-defined habitat type, we find that responses occur earlier when woody debris is present. The relative abundances of two native minnows were found to be lower at sites with higher densities of juvenile smallmouth bass, however all other species showed habitat- and size-based responses that were independent of smallmouth bass. Overall, our results show that habitat mediates community responses to invasive species suppression. In the future, targeted invasive species removal in habitats of highest importance for early life stages of native species may enhance the speed and magnitude of their responses.