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Rapid Colonization of the Potomac River Drainage by the Rainbow Darter (Etheostoma caeruleum) Following Introduction
Jason F. Cessna, Richard L. Raesly, Jay V. Kilian, Daniel A. Cincotta, and Robert H. Hilderbrand

Northeastern Naturalist, Volume 21, Issue 1 (2014): 1–11

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Northeastern Naturalist Vol. 21, No. 1 J.F. Cessna, R.L. Raesly, J.V. Kilian, D.A. Cincotta, and R.H. Hilderbrand 2014 1 2014 NORTHEASTERN NATURALIST 21(1):1–11 Rapid Colonization of the Potomac River Drainage by the Rainbow Darter (Etheostoma caeruleum) Following Introduction Jason F. Cessna1,*, Richard L. Raesly2, Jay V. Kilian3, Daniel A. Cincotta4, and Robert H. Hilderbrand1 Abstract - Etheostoma caeruleum (Rainbow Darter) was first collected from the Potomac River drainage in 1977 and has subsequently expanded its range to include nearly all major tributaries in the system. Analysis of the chronology of Rainbow Darter collection data demonstrates the explosive nature of this range expansion. Using this chronology, we assert that Rainbow Darter is not native to the drainage and likely occurs as a result of human- induced interbasin transfer. Although the ecological impact of non-native Rainbow Darters in the Potomac is unknown, the potential exists for competition with native species. The presence of numerous instream blockages prohibiting colonization of portions of the drainage make this system well suited to study the impacts of introduced darters on native ichthyofauna. Introduction Etheostoma caeruleum Storer (Rainbow Darter) (Teleostei: Percidae) is a small benthic fish, widely distributed in streams and small rivers in central North America and generally known from the Mississippi River and Great Lakes drainages. The species was not known historically from Atlantic Slope drainages, but now occurs in the Hudson and Potomac rivers (Fuller and Neilson 2013, Stauffer et al. 1978). The recent appearance of Rainbow Darters in these systems presents an opportunity to observe factors influencing the dispersal and range expansion of small benthic fishes. Introduced darters have demonstrated rapid range expansion in several North American river drainages, including the Genesee, Susquehanna, Potomac, New, and Colorado rivers (Jenkins and Burkhead 1994, Neely and George 2006, Raesly et al. 1990, Smith 1985, Walford and Bestgen 2008). In these systems, darters have colonized the majority of the drainage within a few decades of introduction. For example, Etheostoma blennioides Rafinesque (Greenside Darter) was first collected from the Susquehanna River drainage in 1962 and had colonized most of the drainage by 2005 (Neely and George 2006). Similarly, the Rainbow Darter was first collected from the Genesee River drainage in 1953 (Carlson and Daniels 2004), where a basin-wide 1University of Maryland Center for Environmental Sciences, Appalachian Laboratory, 301 Braddock Road, Frostburg, MD 21532. 2Frostburg State University, Department of Biology, 101 Braddock Road, Frostburg, MD 21532. 3Maryland Department of Natural Resources, 580 Taylor Avenue C-2, Annapolis, MD 21401. 4West Virginia Division of Natural Resources, Wildlife Resources Section, PO Box 67, Elkins, WV 26241. *Corresponding author - Jcessna@umces.edu. Manuscript Editor: Jay Stauffer Northeastern Naturalist 2 J.F. Cessna, R.L. Raesly, J.V. Kilian, D.A. Cincotta, and R.H. Hilderbrand 2014 Vol. 21, No. 1 survey in 1926 had not revealed its presence (Moore 1927). By the early 1980s, the Rainbow Darter was considered to be in a stage of explosive range expansion in the Genesee and was commonly captured in parts of the drainage (Smith 1985). Stauffer et al. (1978) first collected Rainbow Darters in the upper South Branch Potomac River in 1977. These authors suggested this species was native and had apparently been overlooked by previous collectors due to its isolated location. Esmond and Stauffer (1983) presented morphological and meristic data in support of this indigenous notion. Since this time, this darter has greatly expanded in abundance and distribution. The extent to which the Potomac system had previously been sampled without collecting this species (Davis 1974, Jenkins and Burkhead 1994, Lee et al. 1976, Manseuti 1957, Schwartz 1965, Truitt et al. 1929) raises uncertainty as to whether Rainbow Darter is native to the drainage or occurs as a result of interbasin transfer. Due to its rapid spread, regional investigators have doubted the indigenous status of Rainbow Darters in the basin, but few have addressed this speculation in the literature (Christmas et al. 1998). Herein we review the current status and distribution of Rainbow Darter in the Potomac drainage. Prior to this study, the distribution and range expansion of the species within this river system have not been well documented. We use the dispersal behavior of the species and historical sampling data to suggest that Rainbow Darter should not be considered part of the native ichthyofauna of the Potomac River. Methods We sampled 54 localities in Pennsylvania, Maryland, and Virginia between 2010 and 2012 for the presence of Rainbow Darters. We sampled using a backpack electrofisher for a minimum of 600 seconds beyond the final new species detection at each site, to ensure a representative sampling of all fishes. We queried numerous sources for Rainbow Darter records, including regional ichthyologists, unpublished survey reports, and the scientific literature, as well as the following state and federal agencies: The West Virginia Department of Natural Resources (WVDNR), the Maryland Department of Natural Resources Maryland Biological Stream Survey (MDNR MBSS), the Virginia Department of Game and Inland Fisheries (VDGIF), the Pennsylvania Department of Environmental Protection (PADEP), the Pennsylvania Fish and Boat Commission (PFBC), the US Environmental Protection Agency Mid-Atlantic Integrated Assessment Program (EPA MAIA), the US Geological Survey National Water Quality Assessment Program (USGS NAWQA), and the National Park Service Inventory and Monitoring Program (NPS IMP). Records were considered valid if corroborated by additional nearby collections or the presence of preserved specimens. We used Arc GIS to spatially and temporally analyze the point-locality data. To generate a temporal chronology of Rainbow Darter range expansion, we divided observations into four time intervals from the date of initial discovery: 0–10 years, 11–20 years, 21–30 years, and 31–36 years. We also analyzed the full extent of colonization across temporal intervals in Sideling Hill Creek, a fourth-order tributary to the upper Potomac. Northeastern Naturalist Vol. 21, No. 1 J.F. Cessna, R.L. Raesly, J.V. Kilian, D.A. Cincotta, and R.H. Hilderbrand 2014 3 Results and Discussion We obtained 202 accounts of Rainbow Darter in the Potomac River drainage (Table 1). Three records have been previously noted in the scientific literature (Esmond and Stauffer 1983; Stauffer et al. 1978, 1995), 174 existed in unpublished sources, and 25 are new records arising from our electrofishing efforts. One record obtained from VDGIF was discounted (Quantico Creek) because we could not collect specimens from there or nearby streams. Stauffer et al. (1978) collected the first Rainbow Darters from the Potomac River drainage in 1977, from the North Fork and upper South Branch of the Potomac River, during a state-wide survey of West Virginia. Once established, Rainbow Darters expanded rapidly. Within 25 years of initial detection, this darter’s range expanded over 400 river kilometers (rkm) downstream and had been collected from the lower reaches of every major unimpounded tributary in the system. The WVDNR documented expansion into the South Fork of the South Branch by 1982, some 40 rkm from the initial detection. The following year, this agency collected the species 110 rkm downstream of the initial detection, only 25 rkm from the South Branch’s confluence with the North Branch (Fig. 1). Several more collections of the species were made in the upper South Branch in the subsequent few years. In 1994, Bennett (1997) collected Rainbow Darter in Sideling Hill Creek, a tributary to the middle Potomac, 212 rkm from the point of initial discovery. In 1997, Raesly (1998) documented it much further downstream, near the mouths of Israel Creek, Catoctin Creek, Little Monocacy River, and Broad Run in Maryland (Fig. 2). That same year, MDNR MBSS quantitatively sampled 3 of these 4 tributaries less than 3 rkm upstream of Raesly’s sites without collecting Rainbow Darter, suggesting that the establishment of the species in these tributaries was quite recent. Additionally, VDGIF documented a 1998 record from Goose Creek in northern Virginia. The Goose Creek and Broad Run records are approximately 400 rkm from the initial Stauffer et al. (1978) collection and represented the furthest downstream collections of the species until 2012. Table 1. Sources of unpublished Rainbow Darter records. Source Records MDNR MBSS 75 WVDNR 46 Raesly et al. (2004) 31 MDNR collection permit database 7 EPA MAIA 6 Raesly (1998) 4 VDGIF 2 USGS NAWQA 2 NPS IMP 1 PADEP 1 Bennett (1997) 1 Jennings (1998) 1 Northeastern Naturalist 4 J.F. Cessna, R.L. Raesly, J.V. Kilian, D.A. Cincotta, and R.H. Hilderbrand 2014 Vol. 21, No. 1 By the mid-2000s, Rainbow Darter had expanded into many lower North Branch and upper Potomac tributaries, including Evitts, Town, Licking, Conococheague, and Antietam creeks in Maryland and Sleepy, Back, and Opequon creeks in the Eastern Panhandle of West Virginia. Rainbow Darter also expanded into Mill and Lunice creeks, tributaries to the upper South Branch (Fig. 2). The mid-2000s through early 2010s has seen Rainbow Darter populations continuing to colonize portions of the drainage where it is not blocked by dams (Fig. 3); expanding into south-central Pennsylvania in Sideling Hill, Tonoloway, and Licking creeks and into northern Virginia in Back, Opequon, and Catoctin creeks. In 2012, we documented Rainbow Darter in Cabin John Creek, a tributary just west of the District of Columbia, a few kilometers upstream of the tidal interface. This site represents the known extent of downstream range expansion and was quantitatively sampled in 1995 by Starnes (2002), in 1997 by MDNR MBSS, and in 2004 by Raesly et al. (2004), all efforts that revealed no Rainbow Darters. At present, the Rainbow Darter does not appear to have successfully colonized tributaries downstream of the tidal interface. All major Maryland tributaries to the tidal-fresh Potomac have been sampled by MDNR MBSS within the last 10 years, and we surveyed many Virginia tidal-fresh tributaries in 2012. It is unknown if the Rainbow Darter will be capable of colonizing habitats downstream of the tidal interface. Figure 1. Records of Rainbow Darter in the Potomac River drainage from 1977 to 1986 and from 1987 to 1996. Northeastern Naturalist Vol. 21, No. 1 J.F. Cessna, R.L. Raesly, J.V. Kilian, D.A. Cincotta, and R.H. Hilderbrand 2014 5 However, introduced populations of the Greenside Darter have apparently been unable to do so (Starnes et al. 2011). Analysis of collection points in Sideling Hill Creek (PA and MD), a fourthorder tributary to the upper Potomac, presents an interesting case study of Rainbow Darter colonization of a watershed (Fig. 4). This watershed experienced sufficient sampling intensity to document the extent of colonization at several temporal junctures. Rainbow Darters were not collected in the system during basin-wide sampling conducted by Lebo (1983). By 1994, Bennett (1997) documented the presence of Rainbow Darters extending to 13.5 rkm upstream of the mouth of Sideling Hill Creek. Jennings (1998) documented the extent of colonization an additional 8 rkm upstream in 1996. In 2002, PADEP collected this darter an additional 6 rkm upstream, very near localities that were sampled in 1985 by the Pennsylvania Fish and Boat Commission and in 1994 by PADEP (Pennsylvania Department of Environmental Resources 1994). In 2010, we documented this species in all major tributaries to Sideling Hill Creek and found the extent of colonization to be an additional 22.5 rkm upstream—some 50 rkm upstream of the mouth. These values correspond with a mean upstream colonization rate of 2.6 ± 1.5 rkm per year. The Potomac drainage was extensively surveyed prior to 1977 with no mention of Rainbow Darter (Lee et al. 1976, Schwartz 1965, Truitt et al. 1929, and references therein). As populations continue to grow and spread, it is unlikely that a native Figure 2. Records of Rainbow Darter in the Potomac River drainage from 1997 to 2006. Northeastern Naturalist 6 J.F. Cessna, R.L. Raesly, J.V. Kilian, D.A. Cincotta, and R.H. Hilderbrand 2014 Vol. 21, No. 1 species could have remained undetected until 1977 and then become abundant and widespread within a few decades. Stauffer et al. (1978) suggested that Rainbow Darter was likely overlooked by previous collectors, and Esmond and Stauffer (1983) suggested that this population was geographically isolated and taxonomically distinct from populations in adjacent drainages, asserting that the Potomac population was therefore native. However, by 1983, the year of the Esmond and Stauffer (1983) publication, Rainbow Darter had already significantly extended its range 110 rkm downstream in the South Branch. Additionally, Schwartz (1965) shows a collection point within a few hundred meters of the 1977 collection, which apparently yielded no Rainbow Darters. We believe Rainbow Darter is not native to the Potomac and occurs as a result of human-induced interbasin transfer; most likely a bait-bucket introduction. Many studies have demonstrated the probablilty of introduction events occurring via this vehicle (DiStefano et al. 2009, Kilian et al. 2012, LoVullo and Stauffer 1993, Ludwig and Leitch 1996). Additionally, the first several collections of this darter were made within a stocked trout fishery, where the use of live bait is permitted. The rapid spread of the Rainbow Darter in the Potomac drainage is characteristic of darter invasions in other North American river systems, including the Susquehanna, Genessee, New, and upper Colorado rivers (Jenkins and Burkhead 1994, Figure 3. Records of Rainbow Darter in the Potomac River drainage from 2007 to 2012. Northeastern Naturalist Vol. 21, No. 1 J.F. Cessna, R.L. Raesly, J.V. Kilian, D.A. Cincotta, and R.H. Hilderbrand 2014 7 Neely and George 2006, Raesly et al. 1990, Smith 1985, Walford and Bestgen 2008). The spread of the species throughout the drainage over the last 35 years and the speed with which populations have grown makes it exceedingly unlikely that isolated populations went undetected for decades. It is equally unlikely that such growth is a result of pervasive changes in the ecology of the drainage. The morphological and meristic distinctness of the Potomac River Rainbow Darter populations found by Esmond and Stauffer (1983) may be a founder effect, similar to that reported by Raelsy (1991). Raesly (1991) noted significant morphological distinctness from nearby populations in a recently introduced population of Etheostoma zonale (Cope) (Banded Darter) in the Susquehanna drainage, and genetic analysis revealed a bottleneck consistent with a founder event. Recent range-wide genetic analyses have been conducted for Rainbow Darter (Haponski et al. 2009, Ray et al. 2006), but no studies have evaluated genetic material from Potomac populations. Figure 4. Rainbow Darter colonization of Sideling Hill Creek, a fourth-order tributary to the upper Potomac River. Points represent the known extent of colonization in 1994, 1996, 2002, and 2010. Northeastern Naturalist 8 J.F. Cessna, R.L. Raesly, J.V. Kilian, D.A. Cincotta, and R.H. Hilderbrand 2014 Vol. 21, No. 1 Multiple factors may have influenced the rapid dispersal of Rainbow Darter in the Potomac drainage. In addition to introducing this species to the drainage, humans may have relocated it within the drainage, particluarly as it became more abundant. Basin-wide flooding likely also contributed to rapid downstream range expansion. The flood of 1996 was the Potomac’s largest since 1972, and record flood stages were exceeded in several localities. In the ensuing two years, Rainbow Darter was documented in low abundances over 100 rkm further downstream than previously known. Comparable range expansion after massive flooding has been observed for introduced populations of both Banded Darter and Greenside Darter in the adjacent Susquehanna River drainage (Denoncourt and Stauffer 1976, Neely and George 2006, Raesly et al. 1990). Basin-wide flooding in 1985 may have also contributed to downstream range expansion; however, only one collection of Rainbow Darter was made between 1985 and 1992, which is insufficient sampling intensity to document such expansion. The Rainbow Darter is probably not the only darter recently introduced to the drainage. The Greenside Darter was not collected in the Potomac until 1957 and was also thought to be native (Lee et al. 1976, Miller 1968, Schwartz 1965, Stauffer et al. 1978). However, its recent appearance and rapid range expansion are often cited as evidence of introduction (Christmas et al. 1998, Jenkins and Burkhead 1994, Starnes 2002, Starnes et al. 2011). Greenside Darter is now widespread throughout the drainage, except the North Branch upstream of Cumberland, MD, where dams have been maintained since the mid-1800s Dams have also prevented Rainbow Darter colonization in several major portions of the drainage (Fig. 3). Most notably, almost the entire 7600-km2 Shenandoah River basin has been blocked by Millville Dam. Cacapon River has also apparently been blocked by an old power-plant dam. Additionally, large portions of North Branch, Evitts Creek, Town Creek, Conococheague Creek, Antietam Creek, and Goose Creek have been blocked. Darter species richness has been used in recent years as a favorable metric in stream bioassessments. Since the presence of introduced darters may result in the artificial inflation of indices of biological integrity (IBIs) when compared to localities upstream of watershed impediments (e.g., waterfalls, dams), caution should be used in aquatic community assessments. To avoid erroneous conclusions in darter species richness metrics, we recommend that introduced darters be eliminated from IBI calculations, and/or an inventory of stream blockages or connectivity be incorporated into biological monitoring protocols. A complete inventory of stream blockages in watersheds under evaluation would probably prevent an incorrect assessment of darter and other species richness metrics. In Sideling Hill Creek, for example, undocumented stream blockages have prevented Rainbow Darter colonization in two of the four major tributaries (Fig. 4). The ecological impact of non-native darters in the Potomac River drainage is unknown. There exists potential for overlap in diet and habitat use between introduced darters and other benthic fishes. Of particular concern are the remaining populations of Percina notogramma (Raney and Hubbs) (Stripeback Darter), endangered Northeastern Naturalist Vol. 21, No. 1 J.F. Cessna, R.L. Raesly, J.V. Kilian, D.A. Cincotta, and R.H. Hilderbrand 2014 9 in Maryland and known from only a handful of remaining localities in the Potomac drainage. Given the limited data available on the diet of Stripeback Darter (Flemer and Woolcott 1966) and the breadth of diet overlap of Rainbow Darter with other sympatric species (Adamson and Wissing 1977, Hlohowskyj and White 1983, Paine et al. 1982, van Snik Gray et al. 1997, Welsh and Perry 1998), there exists potential for resource overlap. Competition with other benthic fishes is also possible. The numerous locations where colonization by Rainbow Darter has been prevented by dams reveals a convenient paired study design for observing changes in habitat utilization among native assemblages of benthic fishes when a non-native is introduced. Acknowledgments We would like to thank the Pennsylvania Fish and Boat Commission, the Virginia Department of Game and Inland Fisheries, and the Maryland Department of Natural Resources for scientific collecting permits. Data were provided by many regional biologists: M. Pinder provided VDGIF data; T. Shaw and B. Chalfant provided PA DEP data; M. Kashiwagi and R. Bourquin provided MDNR data; D. Thorne provided WV DNR data; L. Reynolds provided EPA MAIA data; and G. Sanders provided NPS IMP data. Additionally, G.K. Mack provided a lead to the occurrence of Rainbow Darter in Cabin John Creek. J. Epstein, T. Miller, and R. Rambo assisted with field collections. Literature Cited Adamson, S., and T.E. Wissing. 1977. Food habitats and feeding periodicity of the Rainbow, Fantail, and Banded Darters in Four Mile Creek. Ohio Journal of Science 77:164–169. Bennett, A.E. 1997. The relationship between habitat and fish distributions at Sideling Hill Creek, Maryland. M.Sc. Thesis. Frostburg State University, Frostburg, MD. 103 pp. Carlson, D.M., and R.A. Daniels. 2004. Status of fishes in New York: Increases, declines, and homogenization of watersheds. American Midland Naturalist 152:104–139. Christmas, J., R. 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