Conservation, Biology, and Natural History of Crayfishes from the Southern US 2010 Southeastern Naturalist 9(Special Issue 3):11–32 The Status and Distribution of Maryland Crayfishes Jay V. Kilian1,*, Andrew J. Becker1, Scott A. Stranko1, Matthew Ashton1, Ronald J. Klauda1, Jay Gerber2, and Martin Hurd3 Abstract - Over 45 years have passed since the last examination of Maryland’s crayfish fauna. We compiled crayfish records from over 1400 sites sampled since 1989 and present an update on the current status and distribution of Maryland’s 9 native species. Five non-native species have become established in Maryland waters and represent the greatest threat to Maryland’s native species. Orconectes virilis (Virile Crayfish), the most widespread invasive species in the state, has been primarily introduced by anglers as bait and has rapidly expanded its distribution in central Maryland. The spread of this species has been followed by concurrent declines in native species including O. limosus (Spinycheek Crayfish) and O. obscurus (Allegheny Crayfish). Non-native Cambarus thomai (Little Brown Mudbug), O. rusticus (Rusty Crayfish), Procambarus clarkii (Red Swamp Crawfish), and P. zonangulus (Southern White River Crawfish) are now established in Maryland as a result of aquaculture and bait introductions. Recent taxonomic revisions have also added C. carinirostris (Rock Crawfish) to the list of species present in the state. Introduction Maryland’s crayfish fauna has received sporadic attention from astacologists since the late 19th century. In 1885, Walter Faxon, in his “Revision of the Astacidae,” published the first account of the crayfishes of Maryland. In his work, he attributed 6 native species to the state, including Procambarus acutus (Girard) (White River Crawfish) (as Cambarus blandingii), Orconectes limosus (Rafinesque) (Spinycheek Crayfish) (as C. affinis), C. bartonii (Fabricius) (Common Crayfish), C. acuminatus Faxon (Acuminate Crayfish) (as C. bartonii, var. robusta), C. diogenes Girard (Devil Crawfish), and Fallicambarus fodiens (Cottle) (Digger Crayfish) (as C. uhleri). At the time of his publication, he considered Maryland to be “one of the best explored states in the Union.” In the early 20th century, Arnold Ortmann published 2 landmark assessments of Pennsylvania’s crayfish fauna, in which he commented on the distributions of species in Maryland, specifically C. diogenes, C. dubius Faxon (Upland Burrowing Crayfish) (as C. carolinus), O. limosus (as C. limosus), and O. obscurus (Hagen) (Allegheny Crayfish) (as C. obscurus) (Ortmann 1905, 1906; see also Bouchard et al. 2007). In 1959, following a 50-year lull in astacological study in Maryland, William Meredith and Frank Schwartz published the first focused account of the state’s fauna. These authors expanded this work the following year, publishing “Maryland Crayfishes” in 1960. Meredith and Schwartz 1Maryland Department of Natural Resources, 580 Taylor Avenue C-2, Annapolis, Maryland 21401. 2 Pennsylvania Department of Environmental Protection, 909 Elmerton Avenue, Harrisburg, PA 17110. 3 Tetra Tech, Inc., 10306 Eaton Place, Fairfax, VA 22030. *Corresponding author - Jkilian@dnr.state.md.us. 12 Southeastern Naturalist Vol. 9, Special Issue 3 (1960) mapped the distribution of 242 museum collections. They presented the first description of the statewide distributions of 8 native species, including P. acutus (as P. blandingii), O. limosus, O. obscurus, C. acuminatus, C. bartonii, C. diogenes, C. dubius (as C. carolinus), and F. fodiens (as C. uhleri). Meredith and Schwartz (1960) were also the first to mention the presence of the non-native O. virilis Hagen (Virile Crayfish) in Maryland. This work remains the most comprehensive treatment of the fauna to date. Schwartz et al. (1963) conducted a survey of the Patapsco River and documented the spread of O. virilis and subsequent decline of native O. limosus throughout the basin. This study was one of the first published accounts of native crayfish displacement following the introduction of a non-native crayfish. The contributions by Faxon (1885), Ortmann (1905, 1906), Meredith and Schwartz (1959, 1960), and Schwartz et al. (1963) provide the historical context for our evaluation of the current status of Maryland’s crayfishes presented herein. Maryland’s crayfish fauna has changed considerably since the publication of Meredith and Schwartz (1960). Taxonomic revision of the subspecies of C. bartonii (Thoma and Jezerinac 1999) has added C. carinirostris to Maryland’s native crayfish fauna, bringing the state total to 9. Introductions of non-native crayfish species have been widespread. Orconectes virilis has expanded its range throughout central Maryland at the expense of several native crayfishes. Four additional non-native crayfishes including C. thomai Jezerinac (Little Brown Mudbug), O. rusticus (Girard) (Rusty Crayfish), P. clarkii (Girard) (Red Swamp Crawfish), and P. zonangulus Hobbs and Hobbs (Southern White River Crawfish) are established in many Maryland watersheds. Non-native, invasive crayfishes now represent the greatest threat to Maryland’s native species. As a result of increased attention to crayfish imperilment brought forth by Taylor et al. (1996), and in recognition of immediate threats to Maryland crayfishes posed by invasive species and projected human population growth, astacological surveys in Maryland have increased considerably since 1996. These efforts have generated over 1400 records, providing much needed information on the distribution of native and non-native species. With this study, we intend to 1) provide an update on the distributions of 14 species now established in Maryland, 2) describe the current status of Maryland’s 9 native species, and 3) discuss the threat of non-native, invasive species on native crayfishes in the state. Data Acquisition and Field Methods We compiled crayfish records from 1469 sites (Fig. 1). The majority of these records were generated during 2 collection efforts by the Maryland Department of Natural Resources (MDNR) as part of the Maryland Biological Stream Survey (MBSS). During the first sampling period (1996 and 1997), crayfishes were collected using a backpack electroshocker (Smith- Root Model 12) from 858 wadeable stream sites. A representative sample of crayfishes from each site was preserved in 70% alcohol, and later identified to species in the laboratory (see Kazyak et al. 2005). 2010 J.V. Kilian et al. 13 From 2006 to 2007, crayfish data were collected from 446 sites. Sites were located in wadeable streams, non-wadeable rivers, seepage wetlands, and floodplains. MBSS field crews collected stream-dwelling crayfishes using backpack electroshockers (Smith-Root Model 12; Haltech Model HT-2000), dip nets, and kick seines following protocols described in Stranko et al. (2007) and Ashton and Kilian (2007). Crayfishes from large, non-wadeable rivers and impoundments were collected concomitantly with fishes using a boat-mounted electrofisher and seines. Primary burrowing crayfishes were collected from stream banks, floodplains, and seepage wetlands via handdigging. Crayfishes collected by MBSS (2006–2007) were field identified to species, if possible. Specimens that could not be identified in the field were preserved in 70% alcohol and later identified in the laboratory. Additional crayfish records were provided by Matthew Sell and Michael Lutmerding (University of Maryland Appalachian Laboratory, MD), Thomas Jones and Casey Swecker (Marshall University, WV), Zachary Loughman (West Liberty University, WV), and David O’Neill (Community College of Baltimore County, MD). Results and Discussion Regional context The distributions of Maryland’s 9 native species have been largely influenced by the historical events that have shaped the 4 major river drainages: the Monongahela, Potomac, Susquehanna, and Delaware (Fig. 2). The Figure 1. Locations of 1469 sites (circles) sampled for crayfishes from 1989 to 2007. Light gray lines demarcate physiographic provinces and darker lines demarcate major river drainages. 14 Southeastern Naturalist Vol. 9, Special Issue 3 drainage patterns of these ancient rivers have changed over time (Lee 1976). Historical shifts in drainage patterns and species dispersal across breached drainage divides have profoundly influenced the freshwater fish fauna of the Mid-Atlantic region (Hocutt et al. 1986). These historical events have also significantly influenced the distribution of Maryland crayfishes. The majority of Maryland is located on the Atlantic Slope and is dominated by the Potomac and Susquehanna River drainages. A small portion of the upper Delmarva Peninsula falls within the Delaware River drainage, and the southeastern portion of the peninsula is drained by small tributaries to the coastal bays of the Atlantic Ocean. Many species are shared among these Atlantic Slope drainages (Table 1). The western portion of the state lies within the Monongahela River drainage, the only Maryland tributary to the Mississippi River basin. The eastern continental divide, separating the Mississippi and Atlantic drainages, creates 2 distinct regions of aquatic fauna in Maryland. Although these regions have many aquatic species in common, several species of freshwater fishes (Hocutt et al. 1986, Lee 1976), amphibians, and reptiles (Harris 1975) are unique to each. In crayfishes, this regional pattern is most apparent in the allopatric distribution of C. carinirostris and C. bartonii (Table 1). In Maryland, C. carinirostris is confined to the Monongahela River drainage, while the related species, C. bartonii, is found only in drainages of the Atlantic slope. The landscape of Maryland is diverse and changes dramatically from the Appalachian Mountains to the Atlantic Coast. Maryland encompasses 5 physiographic provinces including (from west to east) the Appalachian Plateau, Ridge and Valley, Blue Ridge, Piedmont, and Coastal Plain (Fig. 3). These 5 physiographic provinces differ in underlying geology, soil types, elevation, and climate and support a diversity of aquatic habitats. The distribution of Figures 2. The major river drainages of Maryland. 2010 J.V. Kilian et al. 15 Table 1. Conservation status and distribution of native crayfishes by major river drainages and physiographic provinces in Maryland. River drainages are Monongahela (M), Potomac (P), Susquehanna (S), Delaware (D), and Atlantic Coastal (AC). Physiographic provinces are Appalachian Plateau (AP), Ridge and Valley (RV), Blue Ridge (BR), Piedmont (P), and Coastal Plain (CP). Status ranks are as follows: apparently secure (G4), demonstrably secure (G5, S5), and watch list (S3). River drainage Physiographic province Status Species M P S D AC AP RV BR P CP Global State Cambarus acuminatus Faxon x x x x G4 S3 (Acuminate Crayfish) C. bartonii bartonii (Fabricius) x x x x x x x G5 S5 (Common Crayfish) C. carinirostris Hay x x G5 S5 (Rock Crawfish) C. diogenes Girard x x x x G5 S5 (Devil Crawfish) C. dubius Faxon x x x xH xH G5 S5 (Upland Burrowing Crayfish) Fallicambarus fodiens (Cottle) xH xH xH xH G5 S5 (Digger Crayfish) Orconectes limosus (Rafinesque) x x x x xH x x x G5 S5 (Spinycheek Crayfish) Orconectes obscurus (Hagen) x xU xI x xU xU x* xH G5 S3 (Allegheny Crayfish) Procambarus acutus (Girard) xI x x x xI xI x G5 S5 (White River Crawfish) IIntroduced population. HHistorical record where recent surveys have not detected this species in this physiographic province. UNative status uncertain. *Native status uncertain in Potomac River and introduced in Susquehanna River. Figures 3. The major physiographic provinces of Maryland. 16 Southeastern Naturalist Vol. 9, Special Issue 3 Maryland’s native crayfishes across this diverse landscape has been largely governed by each species’ environmental tolerances and habitat preferences (Table 1). Aquatic habitats important to crayfishes in the western Maryland highlands (i.e., Appalachian Plateau, Ridge and Valley, and Blue Ridge) include bogs, forested seepage wetlands, high-gradient coldwater streams, highland rivers, and reservoirs. Important crayfish habitats in the Piedmont include vernal pools, forested seepage wetlands, coldwater streams, warmwater streams and rivers, and reservoirs. Coastal Plain habitats include warmwater and blackwater streams and rivers, non-tidal wetlands, beaver and man-made impoundments, vernal pools, and depressional wetlands known as Carolina bays (MDNR 2005). More recently, the distributions of Maryland’s native crayfishes have been altered by human actions, including the introduction of native species outside of their native ranges. Procambarus acutus, a species previously distributed exclusively in the Coastal Plain, has been introduced into several impoundments in western Maryland. Orconectes obscurus, a species primarily found in western Maryland, has been introduced (likely as bait) into tributaries to the Susquehanna River (Bouchard et al. 2007). The introduction of non-native crayfishes has also had profound effects on the distributions of native species. Their effects are discussed in more detail below. Status and distribution of native Maryland crayfishes Descriptions of the status and distribution of Maryland’s 9 native species are arranged herein by genera and species in alphabetical order. Maps of species distributions depict historical records from Meredith and Schwartz (1960) and recent records (1989–2007) provided by the collectors referenced above. Historical records from Meredith and Schwartz (1960) of C. bartonii in the Monongahela River drainage are treated as C. carinirostris. Maps also depict Maryland’s major river drainages and physiographic provinces. Latin and common names are provided for each species following Taylor et al. (2007). The global and state conservation status of each native species is provided following Taylor et al. (2007) and MDNR (2007). Genus Cambarus Cambarus acuminatus belongs to a species complex that is distributed from southeastern Pennsylvania (Lieb et al. 2007) to South Carolina (Hobbs 1969). New species from this complex have recently been described in North Carolina (Cooper 2001, 2006a, 2006b), but the taxonomic status of northern members of the complex remains poorly understood and awaits further examination (Lieb et al. 2007). In Maryland, C. acuminatus is distributed in tributaries to the Potomac and Patuxent rivers near Washington, DC, in the Piedmont and Coastal Plain (Fig. 4). There is one historical record from the Patapsco River (Meredith and Schwartz 1960); however, this species has not been collected in the Patapsco River recently. In watersheds without large numbers of non-native crayfishes, C. acuminatus can be found from small headwater streams to large (3rd-order) streams. Given its restricted distribution in Maryland, it is currently on Maryland’s watch list (Table 1). 2010 J.V. Kilian et al. 17 Cambarus bartonii is distributed from the eastern continental divide to the Coastal Plain (Fig. 5). It is most abundant in small, high-gradient streams and is present in low abundance in larger streams (3rd-order and higher) in the absence of non-native crayfishes. Cambarus bartonii is also found in the Coastal Plain in tributaries to the Potomac River in southern Maryland. It is currently stable in Maryland (Table 1). Cambarus carinirostris is distributed primarily in small, headwater streams in the Monongahela River drainage (Youghiogheny and Casselman rivers) in the Appalachian Plateau (Fig. 6). It is currently considered stable in Maryland (Table 1). Figures 4. The distributions of Cambarus acuminatus (upper) in Maryland. Figures 5. The distributions of Cambarus bartonii in Maryland. 18 Southeastern Naturalist Vol. 9, Special Issue 3 Cambarus diogenes is the most common burrowing species in the Coastal Plain and Piedmont of Maryland (Fig. 7). It is most often found in floodplain habitats along streams and rivers. This species is considered stable in Maryland (Table 1). Cambarus dubius is the most widespread, burrowing species in the Appalachian Plateau (Fig. 8). It is common in seepage wetlands and roadside ditches in this region (Loughman 2009). This species was also historically reported from Prince Georges County along the Fall Line between the Piedmont and the Coastal Plain (Meredith and Schwartz 1960). The continued presence of this species in the Piedmont appears unlikely given the lack Figures 6. The distributions of Cambarus carinirostris in Maryland. Historical records from Meredith and Schwartz (1960) of C. bartonii in the Monongahela River drainage are presented here as records of C. carinirostris. Figures 7. The distributions of Cambarus diogenes in Maryland. 2010 J.V. Kilian et al. 19 of recent records from this region. Cambarus dubius has not been recently collected outside of the Appalachian Plateau. This species is currently considered to be stable in Maryland (Table 1). Genus Fallicambarus Fallicambarus fodiens is a burrowing species distributed in Maryland’s Coastal Plain in the lower Potomac River and in the southern portion of Delmarva Peninsula (Fig. 9). This species is considered stable in Maryland (Table 1). It has not been collected during recent surveys, but the lack of recent records is likely an artifact of sampling effort focused in streams and floodplain habitats. Targeted surveys in the vernal pool, roadside ditch, Figure 8. The distributions of Cambarus dubius in Maryland. Figure 9. The distributions of Fallicambarus fodiens in Maryland. 20 Southeastern Naturalist Vol. 9, Special Issue 3 and Carolina bay habitats preferred by this species are needed to assess its current status in Maryland. Genus Orconectes Historically, O. limosus was considered to be the most abundant crayfish in Maryland (Meredith and Schwartz 1960). It is present, but uncommon, in the Appalachian Plateau in tributaries to the North Branch Potomac River. Its occurrence in tributaries to the Potomac River in the Appalachian Plateau and Ridge and Valley provinces may be the result of dispersal through the low-gradient Chesapeake and Ohio Canal (Bouchard et al. 2007). Today, it is uncommon west of the Piedmont (Fig. 10). Its range in the Piedmont province has also significantly declined. This decline has been coincidental with the expansion of the non-native O. virilis in the region. Orconectes limosus remains common in watersheds in the Piedmont where non-native species are absent. It is also common in streams and rivers in Maryland’s Coastal Plain. Although some populations are threatened by non-native species, O. limosus is considered stable statewide (Table 1). Orconectes obscurus is primarily a stream-dwelling species distributed from the Piedmont to the Appalachian Plateau (Fig. 11). It can also be found in impoundments in the Appalachian Plateau and Ridge and Valley provinces. Jezerinac et al. (1995) considered O. obscurus native to the Potomac River drainage. However, Ortmann (1906) suggested that O. obscurus was introduced (likely by anglers) east of the continental divide in Wills Creek, a tributary to the Potomac River near Cumberland, MD. At the time of his survey, O. obscurus was restricted to “eight to nine miles” of Wills Creek, and not present within the Potomac River and tributaries upstream and downstream of Cumberland. Ortmann (1906) also ruled out stream capture as a potential source of this species to Wills Creek given its restricted distribution and absence from headwater portions of both Wills Creek and the closest tributaries to the Casselman River (e.g., Flaugherty Creek) across the continental divide. Figure 10. The distributions of Orconectes limosus in Maryland. 2010 J.V. Kilian et al. 21 Although the origin and native status of this species in the Potomac River is uncertain, its presence in Octoraro Creek, a tributary to the Susquehanna River in the Piedmont, is most certainly the result of its use as bait by anglers (Bouchard et al. 2007). This species was collected historically from the Coastal Plain (Meredith and Schwartz 1960); however, recent collection efforts have not detected this species east of the Fall Line. Orconectes obscurus is currently a watch-list species in Maryland (Table 1). Genus Procambarus Procambarus acutus, Maryland’s only native Procambarus species, is distributed throughout Maryland’s Coastal Plain in lentic and lotic habitats (Fig. 12). It is found in most tributaries on the Delmarva Peninsula and be- Figure 11. The distributions of Orconectes obscurus in Maryland. Figure 12. The distributions of Procambarus acutus in Maryland. 22 Southeastern Naturalist Vol. 9, Special Issue 3 low the Fall Line in western tributaries to Chesapeake Bay and the lower Potomac River. Two recent records of this species in the Piedmont of Maryland are likely introductions. This species has been introduced in Deep Creek Lake and Youghiogheny Lake in the Appalachian Plateau (Loughman 2009, Norden and Norden 1985). Procambarus acutus is currently considered stable in Maryland (Table 1). Non-native crayfishes in Maryland Although none of Maryland’s 9 native crayfishes are currently under threat of extirpation, individual populations of several species are threatened by non-native crayfishes. The introduction of non-indigenous crayfishes has been identified as the single greatest threat to global crayfish biodiversity (Lodge et al. 2000a, Taylor et al. 2007). In Maryland, introductions of nonnative, invasive crayfishes have occurred in many watersheds. These species now threaten populations of several native species through direct predation, competition, and hybridization. The aquarium and pond trade, biological supply trade, live-bait trade, and aquaculture have been identified as important vectors in the introduction of non-native crayfishes worldwide (Lodge et al. 2000b). All of these are potential vectors of introduction in Maryland. We have observed several nonnative crayfish species, including O. virilis, P. clarkii, and P. alleni (Faxon) (Everglades Crayfish), for sale in pet stores throughout Maryland. Orconectes virilis and P. clarkii have been observed for sale in Maryland bait shops. We have also received reports of school teachers releasing non-native crayfishes, purchased for educational purposes through biological supply companies, into Maryland waters. Introduction of non-native crayfishes resulting from the intentional release of animals purchased in pet stores or from biological supply companies has not been confirmed in Maryland. Based on data collected from recent astacological surveys, it appears that aquaculture and live bait are the most important vectors responsible for introductions of 5 non-native species now established in Maryland waters. These species include C. thomai, O. rusticus, O. virilis, P. clarkii, and P. zonangulus. Aquaculture has been an important vector responsible for the introduction of P. clarkii and P. zonangulus. Procambarus clarkii was first introduced to Maryland in impoundments on the Patuxent National Wildlife Refuge in 1963 as forage for wading birds and migrating waterfowl (Kilian et al., in press). Through the 1980s, it was introduced for the purposes of aquaculture into farm ponds and impoundments located primarily in the Coastal Plain in southern Maryland and the Delmarva Peninsula. Procambarus clarkii has since invaded streams and rivers adjacent to every known facility where it was introduced for culture in outdoor ponds (Kilian et al., in press). It is now common in several river basins in the Coastal Plain in southern Maryland and on the Delmarva Peninsula (Fig. 13). Procambarus clarkii is abundant in the tidal, freshwater Potomac River below Washington, DC. These populations may have resulted from introductions by anglers. The effects of P. clarkii on native species in Maryland are currently unknown, but it will 2010 J.V. Kilian et al. 23 likely negatively affect the congeneric P. acutus (Cooper and Armstrong 2007, Gherardi and Daniels 2004). Procambarus zonangulus is commonly cultured with P. clarkii in many areas of the country (Huner 2002). It was part of the original seed stock used in the aquaculture of P. clarkii in farm ponds and impoundments in the Coastal Plain in the 1980s. Procambarus zonangulus is currently only known from 3 aquaculture ponds on the Delmarva Peninsula (Fig. 14). Identification of these specimens was confirmed by H. Hobbs III (Wittenberg University, Springfield, OH) in the fall of 2006. Procambarus zonangulus was also reported from an impoundment on the University of Maryland Eastern Shore campus in Princess Anne, Maryland in 1989 (D. O’Neill, Community College of Figure 13. The distributions of Procambarus clarkii in Maryland. Figure 14. The distributions of Procambarus zonangulus in Maryland. 24 Southeastern Naturalist Vol. 9, Special Issue 3 Baltimore County, Dundalk, MD, pers. comm.). Surveys of this pond in 2006 by the MDNR did not detect this species. Procambarus zonangulus may be widespread in Maryland’s Coastal Plain, especially if it has been as successful as P. clarkii at invading streams and rivers. The presence of P. zonangulus in Maryland brings into question all records of native P. acutus collected since 1996, many of which involved field identifications, because differentiating P. zonangulus from P. acutus is difficult. Species-level identification requires a form I reproductive male and the use of magnification. It is unclear at this time if records of P. acutus from streams and rivers throughout Maryland’s Coastal Plain (Fig. 12) include misidentified specimens of P. zonangulus. The transfer and inadvertent introduction of live, non-native crayfishes by anglers has been widespread in Maryland. This vector is primarily responsible for introductions of O. virilis and O. rusticus in the state, and is likely responsible for the introduction of C. thomai, a burrowing species found in western Maryland (Loughman 2007). Cambarus thomai is currently only known from four localities around Deep Creek Lake, a man-made impoundment in the Youghiogheny River basin (Fig. 15). It has not invaded habitats outside of Deep Creek Lake. Its effects on native species have likely been minimal since its introduction. Orconectes virilis was first introduced into the Patapsco River and was initially reported from five locations near Woodstock, MD (Meredith and Schwartz 1960). Following an intensive survey of the Patapsco River basin in 1961, Schwartz et al. (1963) reported the apparent expansion of this species throughout the entire basin. This expansion resulted in the replacement of the once common O. limosus and displacement of C. bartonii from the Patapsco River mainstem (Schwartz et al. 1963). As of 1961, O. virilis was only known to occur in the Patapsco River (Schwartz et al. 1963). Figure 15. The distributions of Cambarus thomai in Maryland. 2010 J.V. Kilian et al. 25 Since 1961, the distribution of O. virilis has expanded extensively throughout the Piedmont of Maryland (Fig. 16), where it has become the most common crayfish species in larger tributaries to the Potomac River and Chesapeake Bay. Natural dispersal of O. virilis cannot explain its rapid expansion in the region. Natural movement of this species from the Patapsco River to adjacent river basins is hindered by ridge tops forming drainage divides, and by the saltwater barrier formed by Chesapeake Bay. Its widespread expansion is more likely the result of introductions by anglers. We have observed its sale as bait in several bait shops in central Maryland. Orconectes virilis has also been introduced into man-made impoundments in western Maryland. It can be found in small numbers in tributaries entering and leaving these impoundments, but has not yet become widespread in lotic systems in this portion of Maryland (Loughman 2009). As first observed by Schwartz et al. (1963) in the Patapsco River, the spread of O. virilis in the Piedmont of Maryland was followed by a concurrent decline in the distribution of the congeneric O. limosus (Table 2). Once considered a common species in the Piedmont (Meredith and Schwartz 1960, Schwartz et al. 1963), O. limosus is now relatively uncommon in the region and is only found in tributaries in which O. virilis is absent or not abundant. Co-occurrence of these two species is very rare (Table 2). Observed shifts in Figure 16. The distributions of Orconectes virilis in Maryland. Table 2. Changes in the percent occurrence of the native Orconectes limosus and non-native O. virilis in the Piedmont physiographic province since 1960. Percent occurrence is based on collections presented by Meredith and Schwartz (1960) and recent collections (1989–2007). Meredith and Schwartz Recent records Species (1960, n = 61) (1989–2007, n = 553) O. limosus 62% 11% O. virilis 8% 46% Co-occurrence Not reported 1% 26 Southeastern Naturalist Vol. 9, Special Issue 3 the distributions of O. limosus and O. virilis over the past 40 years suggest that O. limosus is actively displaced by O. virilis in Maryland. Displacement can occur rapidly. Complete displacement of O. limosus by O. virilis occurred within three years in a portion of Red Run in the Patapsco River (A. Norden, MDNR, Annapolis, MD, pers. comm.). Orconectes virilis has also played a significant role in the decline of O. limosus in southeastern Pennsylvania (Bouchard et al. 2007) and in West Virginia (Jezerinac et al. 1995), where O. limosus is now believed to be extirpated (Swecker et al. 2010). Although complete extirpation of O. limosus from Maryland may be unlikely, populations in the Piedmont are threatened. Continued spread of O. virilis may lead to the eventual extirpation of O. limosus from the Piedmont. Orconectes obscurus is also threatened by the spread of O. virilis. Orconectes virilis has displaced O. obscurus from a large portion of the Monocacy River, a tributary to the Potomac River. Orconectes virilis will become a larger threat to O. obscurus if it successfully invades lotic systems of western Maryland. Since the publication of Schwartz et al. (1963), displacement of native species by non-native congeners has been widely documented (Capelli 1982; Capelli and Munjal 1982; Holdich 1988; Lodge et al. 2000a; Taylor et al. 1996, 2007). Mechanisms implicated in the displacement of native crayfishes by non-native species include disease introduction, differential risk of predation, competition for limited resources, differential growth rates between species, reproductive interference, and hybridization (Capelli and Munjal 1982, DiDonato and Lodge 1993, Evans and Edgerton 2002, Hill et al. 1993, Klocker and Strayer 2004, Perry et al. 2001). The exact mechanisms responsible for the apparent displacement of congeneric species by O. virilis in Maryland are unclear, but O. virilis attains a larger size than native congeners. Growth rate and body size may give O. virilis competitive advantage over native species (Hill et al. 1993). Hybridization and genetic introgression have been documented between native and non-native crayfishes and have the potential to reduce reproductive success of native species (Perry et al. 2001, 2002). In 2007, a suspected hybrid of O. obscurus and O. virilis was collected from the Monocacy River in Maryland (T. Jones and C. Swecker, Marshall University, Huntington, WV, pers. comm.) and hybridization may be much more widespread than is currently known. Data on the genetic composition of Maryland crayfishes are needed to determine if hybridization and introgression are important mechanisms of displacement among Orconectes species in the state. The effect of O. virilis may not be limited to congeneric species. Schwartz et al. (1963) reported the displacement of C. bartonii from the Patapsco River mainstem following the invasion of O. virilis. As a result, the distribution of C. bartonii was restricted to headwater tributaries of the system (Schwartz et al. 1963). Stream-dwelling Cambarus species, including C. acuminatus, may also be affected by O. virilis. The restricted distribution of C. acuminatus in Maryland and Washington, DC includes streams infested 2010 J.V. Kilian et al. 27 with O. virilis. In watersheds with low abundance of O. virilis, C. acuminatus are abundant from small, headwater streams to 3rd-order tributaries. Conversely, C. acuminatus appeared to be absent in portions of Little Paint Branch, a tributary to the Anacostia River, where O. virilis was abundant. Orconectes rusticus has been introduced throughout southeastern Pennsylvania, including streams and rivers that ultimately enter Maryland (Bouchard et al. 2007). Introductions by anglers have occurred in Pennsylvania tributaries to the Monocacy and Susquehanna rivers. Orconectes rusticus has since dispersed downstream into Maryland. It was first discovered in the Monocacy and Susquehanna rivers in 2007 and is currently only known from these two rivers (Fig.17). Orconectes rusticus is likely to continue spreading throughout these watersheds, and may invade other Maryland river basins. If O. rusticus becomes as widespread as it has in southeastern Pennsylvania (Bouchard et al. 2007), it will have profound affects on Maryland crayfishes. The further spread of this species into other Maryland watersheds will likely cause dramatic changes in the distributions of congeneric native and non-native species over time. Preliminary results of a survey in the Monocacy River watershed suggest that O. rusticus has displaced the nonnative O. virilis from the upper Monocacy River mainstem. The native O. obscurus and O. limosus, historically found in the watershed, were also not collected in areas where O. rusticus was abundant. Efforts to control the introduction and spread of invasive crayfishes in Maryland Although aquaculture has played a significant role in the introduction of non-native crayfishes (specifically P. clarkii and P. zonangulus) in Maryland, future introductions as a result of this vector are unlikely. Crayfish aquaculture in Maryland has declined considerably since it peaked in the 1980s (Kilian et al., in press). There are currently only two facilities on Figure 17. The distributions of Orconectes rusticus in Maryland. 28 Southeastern Naturalist Vol. 9, Special Issue 3 the Delmarva Peninsula that are actively culturing crayfishes. Given that P. clarkii has become established in streams adjacent to every known facility where it was previously cultured, it is unlikely that new permits will be issued for the outdoor culture of any non-native crayfish in Maryland. The release of live crayfishes purchased as bait, from pet stores, or from biological supply companies remains an important potential vector of introduction in Maryland. In 2006, MDNR drafted the first Maryland regulation specifically aimed to prevent importation and the transport of aquatic invasive species, including several crayfish species (COMAR 2006). This Aquatic Nuisance Species Regulation prohibited the sale and possession of O. rusticus, and sought to limit the further transfer of species already established in Maryland waters, specifically prohibiting the movement of O. virilis, P. clarkii, and P. zonangulus between watersheds. Although this “black list” approach is a positive step to reduce the threat of new introductions, enforcement of this regulation is limited. The bait and pet industries in Maryland operate with little oversight by state agencies, and monitoring of species imported into the state and distributed to local bait and pet stores is virtually non-existent. With the exception of O. rusticus, the sale of all crayfish species as pets or for use as bait remains legal. Lodge et al. (2000b) recommended that states ban the use of crayfishes as bait. We agree that this would be the most effective control of non-native crayfishes and would significantly reduce the further movement of species into and within Maryland. The discovery of O. rusticus in the Monocacy and Susquehanna rivers in 2007 prompted an emergency regulation, passed in June 2008, prohibiting the capture, use as bait, or possession of crayfishes in the Monocacy and Susquehanna rivers. This regulation is intended to contain O. rusticus and prevent its spread by anglers into other Maryland watersheds. MDNR is currently pursuing a statewide ban of the sale and use of live crayfishes as bait and has also undertaken efforts to increase awareness among anglers and the general public regarding the threat of non-native crayfishes. MDNR has also contacted school districts throughout the state to halt the release of live crayfishes used in classrooms. Future efforts Since the publication of Meredith and Schwartz (1960), 5 species, including C. carinirostris, C. thomai, O. rusticus, P. clarkii, and P. zonangulus have been added to the list of crayfishes known to occur in Maryland. Maryland’s 9 native crayfishes are not currently at risk of extirpation; however, significant threats to this fauna exist and will likely become more important in the near future. Without stricter regulations on the sale and use of live crayfishes as bait, non-native, invasive crayfishes already in Maryland will continue to spread into new watersheds. If O. virilis is able to spread throughout streams and rivers of western Maryland, it will become a significant threat to O. obscurus. Orconectes virilis continues to be a significant threat to O. limosus populations in the Piedmont, and O. rusticus is poised to spread throughout central 2010 J.V. Kilian et al. 29 Maryland. Recent regulations should reduce the movement of the latter species by anglers, but natural dispersal of O. rusticus is eminent. If this species reaches the Potomac River through natural dispersal, it will likely invade other Maryland tributaries, and congeneric species will likely decline as a result. Other non-native crayfishes not yet in Maryland may be introduced without increased enforcement and oversight of the bait and pet industries. The sale of non-native crayfishes over the internet is another avenue through which problematic species may enter Maryland (Taylor et al. 2007). This is not easily regulated and may play a role in future introductions. In addition to the threat of non-native, invasive crayfishes, habitat loss and degradation will become increasingly important as Maryland’s human population continues to increase. Landscape alterations associated with these changes will undoubtedly cause the loss or degradation of habitats important to Maryland crayfishes. Surveys focused on Maryland’s crayfish fauna in recent years have provided invaluable information on the current distributions of native and non-native crayfishes in Maryland. Spatial data presented in this study provide a baseline to track changes in distributions of native species in response to increasing threats from invasive species and landscape alteration. Continued, regular monitoring will be important in the conservation of Maryland’s native crayfishes (Souty-Grosset et al. 2004, Taylor 2002). Research examining the effects of abiotic stressors (e.g., urban development, eutrophication, physical habitat degradation) on Maryland crayfishes is needed to provide information on the environmental tolerances and habitat requirements of these species. Despite recent survey efforts, many habitats in the state occupied by crayfishes have yet to be thoroughly surveyed, and the current distributions of some species (e.g., F. fodiens, C. acuminatus) are not completely understood. The crayfish communities of large rivers, tidal fresh rivers, reservoirs, depressional wetlands, vernal pools, and small impoundments are not wellunderstood at this time. The streams and rivers of the Ridge and Valley physiographic province have also not been sufficiently surveyed. Surveys focused in these areas are needed to better define the distributions of native and non-native crayfishes in Maryland. Despite a dearth of information for over 45 years following Meredith and Schwartz (1960), our current knowledge of the status and distribution of Maryland crayfishes is more complete than ever. Dramatic effects from non-native species on native species have become boldly apparent. The Maryland Department of Natural Resources is working to control the spread of non-native species in order to conserve native crayfish species diversity. Effective conservation will be a substantial challenge given that five non-native species are now established and that habitats important to native crayfishes are likely to degrade as the human population grows. 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