Determination of Invasive Round Goby Populations Within the Main Stem of French Creek and Their Potential Impact on Benthic Fishes
The introduction of Round Gobies (Neogobius melanostomus) in the French Creek Watershed (Lake LeBoeuf) was probably via bait bucket and were first discovered in 2014. This was the first documented invasion outside of the Lake Erie Basin in Pennsylvania. This was alarming in large part because the Round Goby has become the most abundant benthic (bottom dwelling) fish in the Laurentian Great Lakes after only being discovered in 1989.
Round Gobies throughout the Laurentian Great Lakes are known to eat dressenid mussels (Dreissenidae), but consumption of either dressenids or native mussels (Unionidae) in tributaries to Lake Erie is minimal based on low populations of any bivalves. The French Creek watershed, however, harbors 29 species of native freshwater mussel as well as introduced Fingernail Clams (Sphaeriidae; Corbicula fluminea). In addition, Round Gobies have never been introduced to a lotic system with such high biodiversity of fishes, and the implications of this introduction were unknown.
For this project, we 1) determined whether Round Gobies had moved into the main channel of French Creek from its initial introduction location at Lake LeBoeuf, 2) documented the diet of Round Gobies in the French Creek watershed to determine whether consumption of native, freshwater mussels was taking place and 3) investigated the effects of the presence of Round Gobies on the habitat choices of native benthic fishes of French Creek.
Round Gobies were collected in the summer months (May -September) via kick seine in 4 locations, dissected, and stomach contents identified to lowest possible taxa from 2016 – 2018. Round Gobies were collected in the main stem of French Creek and downstream movement was documented throughout this study. Since the 2014 discovery in Lake LeBoeuf, the Round Goby has been able to expand its range every year. When collected, Round Gobies were separated into categories based on size classes so that we could determine if diet changed with increased size and age. Unionid mussels were consumed by all size classes, particularly in the size class 1 (30-44mm), but diet shifted to a dominance of sphaeriids in size class 4 (>75mm). Round Gobies also consumed benthic aquatic macroinvertebrates, a large percentage of which were chironomids (greater than 24% in all size classes). This is the first documentation of unionid consumption by Round Gobies in Pennsylvania and poses uncertain threats to native mussels both directly through consumption of glochidia as well as indirectly through outcompeting host fishes.
To measure the effects of the invasion on native fishes, we followed the methods established by Stauffer et al. (1996) and van Snik Gray and Stauffer (1999) to snorkel and observe the microhabitat of benthic fishes at sites that are known to contain Round Gobies as well as sites that have yet to be invaded. We compared the microhabitat preferences of species across sites to see if the Round Goby caused a shift in these preferences. We were able to show that the presence of the Round Goby did in fact cause shifts in microhabitat choices, especially with choices regarding water velocity. In summary, the Round Goby consumed native unionid mussels and shifted the habitat occupied by native darters.
Bradshaw-Wilson, C., Stauffer Jr., J. Wisor, J., Clark, K., and S. Mueller. 2018. Documentation of Freshwater Mussels (Unionidae) in the Diet of Round Gobies (Neogobius melanostomus) within the French Creek Watershed. Pennsylvania. American Midland Naturalist. In press.
Mueller, S., Stauffer Jr., J., Wisor, J., and C. Bradshaw-Wilson. 2017. Expansion of the invasive Round Goby (Neogobius melanostomus) into Allegheny River tributaries: LeBoeuf and French creeks in Pennsylvania. J Pa Acad Sci., 91(2): 105-111.
Wisor, J. 2018. The invasion of the Round Goby (Neogobius melanostomus) and its effect on the habitat partitioning of benthic fishes in French Creek. A Thesis in Wildlife and Fisheries Science (master’s thesis). The Pennsylvania State University.