Northeastern Naturalist Vol. 23, No. 3 J.R. Stauffer Jr., J. Schnars, C. Wilson, R. Taylor, and C.K. Murray 2016 395 2016 NORTHEASTERN NATURALIST 23(3):395–407 Status of Exotic Round Goby and Tubenose Goby in Pennsylvania Jay R. Stauffer Jr.1,*, Jeanette Schnars2, Casey Wilson1, Richard Taylor1, and Charles K. Murray3 Abstract - The relative abundance of Neogobius melanostomus (Round Goby) in the Pennsylvanian waters of Lake Erie, has increased dramatically since 1996. Associated with this increase, all benthic species in the main portion of the lake, except Percopsis omiscomaycus (Trout-perch), decreased in occurrence or were extirpated. Proterorhinus semilunaris (Tubenose Goby), which has established a reproducing population in Presque Isle Bay, Lake Erie, coexists with the Round Goby and Etheostoma exile (Iowa Darter), a candidate species for rarity listing by the Pennsylvania Fish and Boat Commission. Conversely, the decline in potadromous populations of Percina caprodes (Logperch) may be exacerbated by direct competition in the lake, and the presence of Round Gobies in the breeding grounds of tributaries (e.g., Twentymile Creek). In Elk Creek, the presence of Round Goby is associated with dietary shifts of Etheostoma caeruleum (Rainbow Darter), although Rainbow Darters co-exist with the Round Goby. The Round Goby has established a reproducing population in LeBoef Creek, a tributary of French Creek (Allegheny River), and we documented its presence in the main channel of French Creek. We suggest that natural barriers (e.g., waterfalls) may prevent the upstream migration of gobies. Furthermore, providing substrate to facilitate spawning and recruitment of native benthic species may impede the spread of invasive species throughout the tributaries of Lake Erie. Introduction The homogenization of the Earth’s biota by the introduction and spread of non-native species is one the most damaging anthropogenic impacts on biodiversity today (Kolar and Lodge 2002, Mills et al. 1994). Degradation of aquatic ecosystems by the introduction of non-native fish species is exemplified in the Laurentian Great Lakes. Native fish communities in this region have been irreparably harmed by introductions, both accidental and intentional, of exotic species (Jude et al. 1995). Infamous piscine invaders such as Petromyzon marinus L. (Sea Lamprey), Alosa pseudoharengus (Wilson) (Alewife), and Osmerus mordax (Mitchill) (Rainbow Smelt) have had cascading detrimental effects on the native biota of the Great Lakes (Fuller et al. 1999, Jude et al. 1995). The most recent round of aquatic invaders that have impacted the integrity of the Great Lakes are mainly Ponto- Caspian natives including 2 bivalve species (Dreissena polymorpha Pallas [Zebra Mussel] and Dreissena bugenis Andrusov [Quagga Mussel]) and 3 fish species 1Ecosystem Science and Management, Penn State University, University Park, PA 16802- 4302. 2Tom Ridge Environmental Center, 301 Peninsula Drive, Suite 9, Erie, PA 16505. 3Pennsylvania Fish and Boat Commission, 2000 Lohrer Road, Fairview, PA 16415. *Corresponding author - vc5@psu.edu. Manuscript Editor: David B. Halliwell Northeastern Naturalist 396 J.R. Stauffer Jr., J. Schnars, C. Wilson, R. Taylor, and C.K. Murray 2016 Vol. 23, No. 3 (Gymnocephalus cernuus L. [Ruffe], Neogobius melanostomus [Round Goby], and Proterorhinus semilunaris [Heckel] [Western Tubenose Goby]). Of the 3 most recent fish introductions, Round Gobies are the most prolific and widespread, and currently occur throughout the Laurentian Great Lakes and their tributaries, many Eurasian rivers, and the Baltic Sea (Charlebois et al. 1997). Introduced Round Goby have also established numerous populations in Eurasia (Kornis et al. 2012). The Round Goby is a small, benthic, nocturnally feeding fish that is native to the Sea of Azov, the Caspian Sea, the Black Sea, and the Sea of Marmara (Charlebois et al. 1997, Hayden and Miner 2009, Hensler and Jude 2007). Brown and Stepien (2009) and Kornis et al. (2012) listed the likely source of Round Goby in the Great Lakes as the Dnieper River, Kerson, Ukraine. Round Goby were first discovered by anglers in the Laurentian Great Lakes in 1990 in the St. Clair River at Sarnia, ON, Canada, where they were assumed to have been introduced from ballast waters of freighters (Charlebois et al. 1997, Hayden and Miner 2009, Hensler and Jude 2007, Jude et al. 1992, Mills et al. 1993). The Round Goby was thought to be confined to the St. Clair River; however, in 1993 new populations were documented in the Calumet River near Lake Michigan and in Grand River Harbor, OH (Charlebois et al. 1997), and they were found in western Lake Michigan and eastern Lake Erie in 1995 (Charlebois et al. 1997). Since that time, Round Goby have spread rapidly to all of the Great Lakes, presumably by inter-basin ballast transfer (Clapp et. al 2001, Kornis et al. 2012). However, based on our observations in Pennsylvania, natural dispersal and release/escape from bait buckets could have also aided their dispersal. The first Round Goby found in the Pennsylvania waters of Lake Erie was by the Pennsylvania Fish and Boat Commission (PFBC) in 1996. Harka and Bíró (2007) indicated that in its native range, Round Goby are found in lakes and large, slow-flowing rivers. In Eurasia, they are rare in faster-flowing waters; however, they have invaded several tributaries 10–40 stream km above the stream mouths, including those to Lake Michigan (Kornis et al. 2013) and the Ontario side of Lake Erie (Poos et al. 2010). Based on our collections from 2006–2016, Round Goby are abundant in the mouths and below the first riffle above the mouth in small tributaries (e.g., Elk Creek, Sixteen Mile Creek, Twentymile Creek) of Lake Erie. The presence of Round Goby has been associated with the extirpation of Cottus bairdi (Mottled Sculpin) in Calumet Harbor in southern Lake Michigan (Jansen and Jude 2001) and the decline of Etheostoma nigrum Rafinesque (Johnny Darter; Lauer et al. 2004). Round Goby have been found to prey on eggs of Percina caprodes (Logperch) and those of several other native species (Chotkowski and Marsden 1999). Under experimental conditions, Round Goby prey on Etheostoma caeruleum (Rainbow Darter) and Etheostoma blenniodes Rafinesque (Greenside Darter) (Jude et al. 1995). Studies have demonstrated competition between Round Goby and native species for food and habitat (French and Jude 2001, Jansen and Jude 2001). Conversely, the spread of the Tubenose Goby has been slow compared to that of the Round Goby (Grant et al. 2012) and has been partially restricted to the Northeastern Naturalist Vol. 23, No. 3 J.R. Stauffer Jr., J. Schnars, C. Wilson, R. Taylor, and C.K. Murray 2016 397 connections between Lake Huron and Lake Erie, and the western portions of Lake Erie and Lake Superior (Grant et al. 2012, Kocovsky et al. 2011). The potential for the Tubenose Goby to displace native species is not well understood, but the species may have the potential to compete for habitat and food (French and Jude 2001, Grant et al. 2012, Kocovsky et al. 2011). The objectives of this study are to report on the status of the Round Goby in the Lake Erie watershed of Pennsylvania, to determine if there was a shift in diet of the native fishes when Round Goby were present in selected Pennsylvanian tributaries (i.e., Elk Creek, Twentymile Creek) of Lake Erie, and to compare the diet of the Tubenose Goby in Lake Erie with the syntopic native Iowa Darter. Materials and Methods We anesthetized in MS222, fixed in a 10% formalin solution for 2 weeks, and transferred to 70% ethanol for later identification all fishes kept for further analyses. Voucher specimens of the sampled fish were catalogued into the Penn State University Fish Museum. We followed all protocols required by the Animal Use and Care Committee at Penn State (IACUC# 35338). Presence/absence of benthic fishes in Lake Erie We employed trawls (trawl aperture = 5.88 m2, wingspread = 5.44 m, gape height = 1.08 m, mesh size in the cod-end liner = 0.64 cm) to sample Round Goby in off-shore habitats in Pennsylvania’s portion of Lake Erie. Pennsylvania’s portion of Lake Erie totals 1193 km2, or 7.8% of the total area of the lake, and includes the southeastern portion of the central basin and southwestern portion of the eastern basin. We conducted most of the trawls near long-term monitoring stations off Walnut Creek (42°4'37.28''N, 80°14'22.95''W), Trout Run (42°3'32.49''N, 80°16'22.02''W), Presque Isle Peninsula (42°10'14.97''N, 80°5'59.82''W), Eightmile Creek (42°10'49.60''N, 79°59'6.38''W), and Sixteenmile Creek (42°14'33.92''N, 79°49'55.41''W) (Fig. 1). We conducted an average of 14 trawls annually from 1985 through 2012, ranging from as few as 2 trawls in 1997 to as many as 28 in 1987. Due to logistical constraints, no trawling was conducted in 2006, 2010, and 2011. Annual assessment by the PFBC Lake Erie Research Unit (LERU) included offshore (>12 m) bottom-trawling during the summer and fall. The program was not specifically designed to determine the density of benthic fishes; thus, we used the percentage of the trawl samples in which benthic fishes were present as an indicator of relative abundance. Impact of Round Goby on fishes in Twentymile Creek We collected fishes in Twentymile Creek on 17 July 2003 from the mouth of the stream to the waterfall (site 1: 42º15'38.71''N, W9º46'49.33''W) and above the waterfall just below an old railroad bridge (site 2: 42º15'29.48''N, 79º46'39.68''W) with a battery-powered backpack electro-fishing unit (Aquashock Solutions; 300 volts DC). We chose the 2 sites based on physical similarities and our previous investigations, which indicated a similar species composition and the absence of Northeastern Naturalist 398 J.R. Stauffer Jr., J. Schnars, C. Wilson, R. Taylor, and C.K. Murray 2016 Vol. 23, No. 3 Round Goby at the upstream site. At each site, we shocked from shore to shore while moving upstream. We did not use block nets to segregate the area shocked. We continued to collect at both sites, until we were convinced that further sampling would not yield additional species (Barila et al. 1981, Hocutt 1978). We identified to species fishes collected, then counted and released all except for the voucher specimens we retained for each species. For each site, we calculated percent community composition, population estimates, and Brillouin’s diversity indices (H = Nln [N!N!N2!...Ns!]), where H = diversity index, N = the total number of individuals in the sample; N1, N2…, is the number of individuals in species 1, 2, …, and s is the total number of species in the collection; Pielou 1977). Based on the work of Pielou (1975, 1977), Kaesler et al. (1978) concluded that Brillouin’s index is the preferred metric for the type of data we obtained because it actually measures the diversity of the sample rather than just statistically estimating it. Diet selectivity We used non-treated plywood to construct 9 boxes with 2 m x 4 m x 10 cm inside dimensions and an open top. We filled them with 3 different types of substrate: 2b gravel (small substrate), #1 gravel (medium substrate), and rip-rap (rocks 4–10 cm diameter). In May 2012, we submerged the boxes in a 3 x 3 design in Elk Creek at the first riffle above the mouth (42°1'10.65"N, 80°22'17.09"W). Sampling began 30 d after we placed the plots in the stream; we conducted a 24-h sample once per month from June until September 2012. On sampling days, we electrofished 3 of the 9 plots every 8 h, 1 from each substrate type (small, medium, and rip-rap). We positioned a seine downstream to collect the fishes. At the end of the 24-h hour sampling period, we used D-frame kick-nets to collect macroinvertebrates residing in the substrate of each plot. We preserved samples from the kick-nets in 70% ethanol, and examined them under dissecting microscopes in the laboratory to Figure 1. Trawl sites sampled by the Pennsylvania Fish and Boat Commission in Lake Erie. Northeastern Naturalist Vol. 23, No. 3 J.R. Stauffer Jr., J. Schnars, C. Wilson, R. Taylor, and C.K. Murray 2016 399 search for macroinvertebrates. Although we placed no substrate boxes upstream of the waterfalls in Elk Creek (42°0'24.90"N, 80°21'13.89"W), we collected macroinvertebrates and fishes there in June 2012 with a D-frame kick-net and backpack electro-fishing unit, respectively, and preserved samples as described above. In the laboratory, we dissected and removed the stomachs of all benthic fishes. We examined macroinvertebrates from the gut contents and the D-frame kick-net collections, and enumerated and identified them to the lowest possible taxon (family or genus) using Merritt et al. (2008). We compared the relative abundance of selected organisms in the stomachs to the relative abundance in the environment by calculating electivity indices (Ilev 1961) using the formula (ri – pi ) / (ri + pi ), where ri is the percent composition of a macroinvertebrate taxon in the gut and pi is the percent composition of the taxon in the D-frame kick-net sample. Thus, we were able to determine if macroinvertebrate taxa were being selected, avoided, or eaten in the same ratio of abundance that they were found in the environment. If taxa were absent from either the D-frame kick net samples or the stomachs, an electivity index could not be calculated. Tubenose Gobies were not present in any lotic systems; thus, we sampled fishes in Presque Isle Bay during the periods 9–10 September and 7–8 October 2011 to search for Tubenose Gobies. We employed a benthic electric trawl that generated an electrical field to stun fishes and increase capture efficiency as described by Freedman et al. (2009). We conducted the trawls just west of Perry Monument on the north side of the bay in Presque Isle State Park (42°9'13.96"N, 80°5'24.80"W). We preserved fishes as described above. Results Presence/absence of benthic fishes in Lake Erie Round Gobies were first found in the Pennsylvanian portion of Lake Erie 1996, when they were present in less than 20% of the trawls taken by the PFBC (Fig. 2). Of the native benthic fishes, Percopsis omiscomaycus (Wahlbaum) (Trout-perch) was present in the highest proportion of the trawls prior to the occurrence of the Round Goby in 1996. Its presence in the trawl samples was comparable before and after 1996. The Mottled Sculpin was routinely collected with the trawls, but disappeared entirely after 1999. The Logperch was erratically present, but was last captured in 2003 (Fig. 2). The Johnny Darter disappeared in all trawl samples after 1999 and Ammocrypta pellucida (Putnam) (Eastern Sand Darter) was last collected in 2005 (Fig. 2). Impact of Round Goby on fishes in Twentymile Creek We found Round Goby only downstream of the first waterfalls in Twentymile Creek. We collected 17 species below and 18 species above the waterfall (Table 1). In addition to the Round Goby, we documented Lepisosteus osseus (Longnose Gar), Cyprinella spiloptera (Spotfin Shiner), Luxilus cornutus (Common Shiner), Notropis atherinoides (Emerald Shiner), Hypentelium nigricans (Northern Hog Sucker), Noturus flavus (Stonecat), and Micropterus dolomieu (Smallmouth Bass) at the Northeastern Naturalist 400 J.R. Stauffer Jr., J. Schnars, C. Wilson, R. Taylor, and C.K. Murray 2016 Vol. 23, No. 3 Figure 2. Proportion of trawls where Round Goby and native benthic fishes (Trout Perch, Mottled Sculpin, Logperch, Johnny Darter, and Eastern Sand Darter) were captured. Northeastern Naturalist Vol. 23, No. 3 J.R. Stauffer Jr., J. Schnars, C. Wilson, R. Taylor, and C.K. Murray 2016 401 downstream site but not above the waterfalls. We collected Salmo trutta (Brown Trout), Luxilus chrysocephalus (Striped Shiner), Pimephales notatus (Bluntnose Minnow), Rhinichthys cararactae (Longnose Dace), Semotilus atromaculatus Mitchill, Catostomus commersoni (White Sucker), Ameiurus nebulosus (Brown Bullhead), Logperch, and Mottled Sculpin above the falls, but not below the falls. Round Goby comprised 45% of the total fishes at the lower site, while Rainbow Darters comprised 35%. In total, Rainbow Darters constituted the greatest percentage of the benthic-species composition at both sites, when Round Goby were excluded from the downstream site data. Brillouin’s diversity index values below the falls and above the falls were 1.39 and 2.11, respectively. Diet selectivity The July kick-net samples downstream in Elk Creek yielded primarily dipterans (Chironomidae) and ephemeropterans (Baetidae, Caenidae) (Table 2). The only taxon that had a positive electivity index for the Round Goby was Chironomidae. The Rainbow Darter selectively fed on Tricoptera and Ephemeroptera. The kick-net Table 1. Fishes collected downstream and upstream of the waterfall on Twentymile Creek, 22 June 2003. Species Downstream Upstream Ambloplites rupestris (Rafinesque) (Rock Bass) 1 1 Ameiurus nebulosus (Lesuer) (Brown Bullhead) 0 2 Campostoma anomalum (Rafinesque) (Stoneroller) 17 53 Catostomus commersoni (Lacepède) (White Sucker) 0 1 Cottus bairdi Girard (Mottled Sculpin) 0 11 Cyprinella spiloptera (Cope) (Spotfin Shiner) 1 0 Etheostoma caeruleum Storer (Rainbow Darter) 88 48 Etheostoma flabellare Rafinesque (Fantail Darter) 2 6 Hypentelium nigricans (Lesuer) (Northern Hog Sucker) 1 0 Lepisosteus osseus (L.) (Longnose Gar) 1 0 Lepomis gibosus (L.) (Pumpkinseed Sunfish) 2 2 Lepomis macrochirus Rafinesque (Bluegill) 2 1 Luxilus chrysocephalus Rafinesque (Striped Shiner) 0 22 Luxilus cornutus (Mitchill) (Common Shiner) 1 0 Micropterus dolomieu Lacepède (Smallmouth Bass) 7 0 Neogobius melanostomus (Pallas) (Round Goby) 113 0 Nocomis micropogon (Cope) (River Chub) 4 124 Notropis atherinoides Rafinesque (Emerald Shiner) 1 0 Noturus flavus Rafinesque (Stonecat) 3 0 Oncorhyncus mykiss (Walbaum) (Rainbow Trout) 4 15 Percina caprodes (Rafinesque) (Log Perch) 0 4 Pimephales notatus (Rafinesque) (Bluntnose Minnow) 0 1 Rhinichthys atratulus (Hermann) (Blacknose Dace) 2 59 Rhinichthys cataractae (Valenciennes) (Longnose Dace) 0 26 Salmo trutta L. (Brown Trout) 0 1 Semotilus atromaculatus (Mitchill) (Creek Chub) 0 4 Total number of species 17 18 Total number of individuals 250 388 Brillouin’s diversity index 1.39 2.11 Northeastern Naturalist 402 J.R. Stauffer Jr., J. Schnars, C. Wilson, R. Taylor, and C.K. Murray 2016 Vol. 23, No. 3 samples taken in September at the downstream site in Elk Creek yielded primarily Ephemeroptera and Diptera (Table 3). The only taxon that had a positive electivity index for the Round Goby was Chironomidae. The Rainbow Darter selectively fed on Diptera. The June kick-net samples upstream in Elk Creek (Table 4) yielded primarily Diptera, Trichoptera, and Coleoptera. The Rainbow Darters in this reach consumed primarily Ephemeroptera and Plecoptera. Table 2. Comparison between percentages of macroinvertebrates from kick-net samples in July 2012 and stomach contents of Rainbow Darter and Round Goby with calculated electivity-index. % in stomach Macroinvertebrates % in Rainbow Electivity Round Electivity Order/Family environment Darter (n =32) index Goby (n = 24) index Amphipoda Gammaridae 0.52 Coleoptera Elmidae 0.78 Diptera Chironomidae 82.72 67.12 0.09 87.40 0.03 Nymphomyudae 0.04 Tipulidae 0.04 Simulidae - 0.58 TOTAL Diptera 82.80 Ephemeroptera 1.78 Baetidae 2.08 Heptageniidae 1.08 Leptohyphidae 4.94 17.58 0.27 9.00 -0.06 Siphlonuridae 0.22 TOTAL Ephemeroptera 10.10 Hirudinea 0.04 Isopoda Asellidae 0.04 Megaloptera Corydalidae 0.74 Sialidae 0.87 TOTAL Megaloptera 1.61 Bivalva 0.04 Odonata Coenagrionidae 0.04 Aeshnidae - TOTAL Odonata 0.04 Plecoptera 0.13 Perlidae 0.13 Pternoarcyidae 0.09 TOTAL Plecoptera 0.35 Trichoptera 0.09 Hydopsychidae 0.26 Hydophilidae - Polycentropodidae 0.13 3.48 0.74 0.40 -0.13 Hydroptilidae 0.04 TOTAL Trichoptera 0.52 Unidentified macroinvertebrate 9.55 3.20 Northeastern Naturalist Vol. 23, No. 3 J.R. Stauffer Jr., J. Schnars, C. Wilson, R. Taylor, and C.K. Murray 2016 403 Grant et al. (2012) reported Tubenose Goby in the Pennsylvanian portion of Lake Erie on 28 June 2012. As of this writing, Tubenose Goby had not been collected outside of Presque Isle Bay in Pennsylvania. Our collections with the electric trawl in Presque Isle Bay on 9–10 September 2011 and 7–8 October 2011, resulted in the capture of Tubenose Goby. The Round Goby, Tubenose Goby, and the native Iowa Darter all consumed Zebra Mussels, but these mussels comprised almost the entire diet of the 2 goby species (Table 5). Iowa Darter fed primarily on freshwater shrimp species. Discussion Within Lake Erie in Pennsylvania, Round Goby have occurred in the vast majority of the trawls since 1998. Although Trout-perch are still routinely collected in off-shore trawls, the occurrence of Logperch, Mottled Sculpin, Johnny Darter, and Table 3. Comparison between percentages of macroinvertebrates from kick-net samples for data collected in Elk Creek in September 2012 and stomach contents of Rainbow Darter and Round Goby with calculated electivity-index. % in stomach Macroinvertebrates % in Rainbow Electivity Round Electivity Order/Family environment Darter (n = 7) index Goby (n = 17) index Amphipoda Gammaridae 0.26 Coleoptera Elmidae 0.68 Hydrophilidae 0.83 Psephenidae 0.15 TOTAL Coleoptera 1.66 Diptera Chironomidae 5.69 69.29 0.85 43.82 0.77 Ephemeroptera Baetidae 0.12 Caenidae 60.61 Heptigeniidae 0.79 Leptohyphidae 27.37 TOTAL Ephemeroptera 88.89 17.14 -0.68 50.29 -0.28 Gastropoda Physidae 0.87 Planorbidae 0.08 TOTAL Gastropoda 0.95 Hirudinea 0.04 Isopoda Asellidae 0.15 Odonata Coenagrionidae 2.34 Gomphidae 0.04 Libellulidae 0.04 TOTAL Odonata 2.42 Trichoptera Hydroptilidae - 13.57 - 5.88 - Northeastern Naturalist 404 J.R. Stauffer Jr., J. Schnars, C. Wilson, R. Taylor, and C.K. Murray 2016 Vol. 23, No. 3 Eastern Sand Darter have decreased since the establishment of the Round Goby and these 4 native species have not been found at all in the trawl samples since 2007. In Twentymile Creek, the Mottled Sculpin is found upstream of the falls but is absent downstream of the falls, where Round Goby is established. We also collected Logperch above the falls, but not below the falls. Over the past 15 years, we have observed a population of Logperch that are resident in the tributaries year-round, and a lake population, which migrates into tributaries to spawn. Perhaps the decreased occurrence of the Logperch in Lake Erie is attributable both to direct competition with the Round Goby in the lake and the invasion of Round Goby into the spawning grounds in the tributaries. As stated previously, Table 5. Average percentages of items found in stomach contents of Iowa Darters, Round Goby, and Tubenose Goby collected 11 September 2011 from Presque Isle Bay, Lake Erie. Prey taxon Iowa Darter (n = 13) Round Goby (n = 26) Tubenose Goby (n = 5) Zebra Mussel 3.8 67.0 27.0 Mussel species 0.0 2.9 0.0 Freshwater shrimp 30.4 0.0 0.0 Insect species 0.4 0.8 0.0 Fish eggs 0.0 0.0 1.0 Table 4. Percentages of macroinvertebrates from kick-net samples and stomachs from Rainbow Darters (n = 17) in Elk Creek above first waterfall. Macroinvertebrates Order/Family % in environment % in stomach Electivity index Tricladida 11.72 0.00 -1.00 Trichoptera Hydopsychidae 8.45 Polycentropodidae 15.80 14.00 -0.27 TOTAL 24.25 Coleoptera Psepehenidae 7.08 0.00 -1.00 Elmidae larvae 1.63 Elmidae adult 0.27 TOTAL 8.98 Ephemeroptera Baetidae 15.53 58.50 0.60 Plecoptera Perlidae 0.54 1.10 0.30 Diptera Chironomidae 37.60 17.60 -0.37 Simulidae 0.27 TOTAL 37.87 Amphipoda Gammaridae 0.27 0.00 -1.00 Oligochaeta 0.82 0.00 -1.00 Megaloptera 0.00 3.10 - Odonata Coenagrionidae 0.00 6.20 - Northeastern Naturalist Vol. 23, No. 3 J.R. Stauffer Jr., J. Schnars, C. Wilson, R. Taylor, and C.K. Murray 2016 405 Chotkowski and Marsden (1999) documented the predation of Logperch eggs by Round Goby. In Elk Creek, the Round Goby selected chironomids during July and September. Our data indicate that the Round Goby was a selective feeder; Rosca et al. (2010) reached the same conclusion for populations on the Black Sea Coast. In the same reach, Rainbow Darters chose Trichoptera and Ephemeroptera. Above the waterfalls in Elk Creek, where Round Goby were absent, Rainbow Darters avoided Trichoptera and fed primarily on Ephemeroptera and Plecoptera. Nevertheless, the Rainbow Darter has been successful in co-habiting with the Round Goby. In the Lake Erie basin, Rainbow Darters in lotic environments and Iowa Darters in lentic habitats apparently continue to maintain viable populations. Unlike many other benthic species (e.g., Mottled Sculpin, Logperch, and Eastern Sand Darter), we consistently collect Rainbow Darters in areas invaded by Round Goby. To date, the Round Goby has not been successful in colonizing upstream of the first natural barrier (e.g., waterfalls) in Pennsylvania’s tributaries of Lake Erie. In 2014, we documented Round Goby in LeBoef Creek, a tributary of French Creek (Allegheny River), and by July 2015 we found them in the main channel French Creek below LeBoef Creek. Round Gobies were first found in the lake drained by LeBoef Creek, and we hypothesize that their presence was a result of bait-bucket introductions. The invasion of the Round Goby into the Allegheny River drainage suggests that the upstream areas of the tributaries of Lake Erie are vulnerable to colonization via bait-bucket transfer. Irrespective of the means of transfer (e.g., bait bucket, ballast water) the success of an introduced population of Round Goby depends to some extent on the biological components that presently inhabit the area in question. Certain environments are saturated with species, while other areas are considered to be depauperate. At one time, it was assumed that the predominant factor that controlled the organization of natural communities was interspecific competition (Dunham et al. 1979). This assumption was inferred from niche shifts and morphological changes in the form of character displacement, which were correlated with geographic variation (Dunham et al. 1979). Simberloff and Wilson (1969), however, suggested that competition might not be as important as previously thought, at least for insular areas. Based on work by several authors, Pianka (1981) stated that the outcome of interspecific competition depends upon (1) initial population densities (Neyman et al. 1956), (2) environmental conditions (Park et al. 1964), and (3) the genetic constitution of competing populations (Park et al. 1964). Thus, one management strategy that may impede the establishment of viable populations of invasive species may be to artificially raise and stock native fishes to increase their density. A diverse and abundant native benthic fish fauna may in fact slow the spread of species such as the Round Goby. Acknowledgments Funding was provided by the Pennsylvania Water Resources Research Center, Coastal Zone Management, and The Pennsylvania State University Sea Grant Program. We extend special thanks to Elizabeth Boyer and Robert Light. Northeastern Naturalist 406 J.R. Stauffer Jr., J. Schnars, C. Wilson, R. Taylor, and C.K. Murray 2016 Vol. 23, No. 3 Literature Cited Barila, T.Y., R.D. Williams, and J.R. Stauffer Jr. 1981. The influence of stream order and selected stream-bed parameters on fish diversity in Raystown Branch, Susquehanna River Drainage, Pennsylvania. Journal of Applied Ecology 18:125–131. Brown, J.E., and C.A. Stepien. 2009. 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