Differential habitat use by the round goby (Neogobius melanostomus) and Dreissena spp. in coastal habitats of eastern Lake Michigan

Shoreline modifications in Lake Michigan drowned river mouth (DRM) lakes can indirectly create habitats for the invasive round goby (Neogobius melanostomus) and dreissenid mussels (Dreissena spp.), possibly resulting in their proliferation. To test this hypothesis, we sampled round gobies and dreissenids in Lake Michigan nearshore waters at pierheads and at adjacent DRM lake habitats containing natural and hardened shoreline features. Dreissenids were sampled by SCUBA diving and collecting specimens by hand, while round gobies were sampled using overnight replicate baited minnow traps. Round goby overall catch per unit effort (CPUE, number/trap night) was significantly higher at pierheads compared to the two DRM lake habitats; however, there was no significant difference in CPUE between the natural and the hardened DRM lake habitats. Similarly, dreissenid density was significantly higher at pierheads compared to natural DRM habitats; however, there was no significant difference between the hardened and the natural DRM lake habitats. We did not find any differences in the mean size or age of round goby among habitats. Stomach content analysis showed that soft-bodied prey comprised a larger portion of the round goby diet at pierheads, suggesting that round goby show preference for soft-bodied prey. Our results suggest that the current level of shoreline modification at DRM lake habitats may not be sufficient to evoke a biological response akin to what we found at pierheads; however, given continued shoreline hardening, DRM lake habitats will likely facilitate the proliferation of these invasive species.