The Invasion of Procambarus clarkii (Decapoda:
Cambaridae) into Maryland Streams Following its
Introduction in Outdoor Aquaculture Ponds
Jay V. Kilian, Jason Frentress, Ronald J. Klauda, Andrew J. Becker,
and Scott A. Stranko
Northeastern Naturalist, Volume 16, Issue 4 (2009): 655–663
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2009 NORTHEASTERN NATURALIST 16(4):655–663
The Invasion of Procambarus clarkii (Decapoda:
Cambaridae) into Maryland Streams Following its
Introduction in Outdoor Aquaculture Ponds
Jay V. Kilian1,*, Jason Frentress2, Ronald J. Klauda1, Andrew J. Becker1,
and Scott A. Stranko1
Abstract - We provide locality data for stream populations of Procambarus clarkii
(Red Swamp Crawfish) in Maryland. This non-native species is now established in
14 watersheds in the Coastal Plain, including all watersheds where it was historically
raised in aquaculture ponds. Our surveys indicate that the introduction of Red
Swamp Crawfish in Maryland has largely resulted from aquaculture, although the
aquarium, biological supply, and live-bait industries are other potential vectors. The
effects of Red Swamp Crawfish on the composition and diversity of stream fauna and
flora in Maryland are unknown. The establishment of this species may have negative
effects on native crayfishes, especially the congeneric P. acutus (White River
Crawfish). These locality records provide baseline information for future monitoring
of this non-native species and assessment of its effects on Maryland’s stream ecosystems
and native crayfishes.
Introduction
Non-native crayfish introductions are considered the largest threat to
North America’s crayfish fauna, the second-most imperiled fauna on the
continent (Lodge et al. 2000a; Stein and Flack 1997; Taylor et al. 1996,
2007). The documentation of non-native crayfish introductions into new areas
is necessary to assess the effects of these species on ecosystem function
and native crayfish diversity (Cooper et al. 1998).
Procambarus clarkii Girard (Red Swamp Crawfish), native to the southcentral
United States and northern Mexico, is the most widely cultured and
distributed crayfish in the world (Huner 2002) and has been introduced on
all continents except Australia and Antarctica, usually with negative consequences
(Hobbs et al. 1989). The first known introduction of Red Swamp
Crawfish in Maryland occurred in 1963 at the Patuxent National Wildlife
Refuge in Laurel in the Patuxent River basin. Several individual crayfish
were introduced to shallow water impoundments as a potential food source
for wading birds (Matthew Perry, USGS-Patuxent Wildlife Research Center,
Laurel, MD, 2006 pers. comm.).
Red Swamp Crawfish have also been introduced into outdoor ponds
for the purposes of commercial aquaculture in Maryland. The Worcester
1Maryland Department of Natural Resources, Monitoring and Non-tidal Assessment,
580 Taylor Avenue, Annapolis, MD 21401. 2Oregon State University, Water
Resources Science, 2075 Cordley Hall, Corvallis, OR 97331. *Corresponding author
- jkilian@dnr.state.md.us.
656 Northeastern Naturalist Vol. 16, No. 4
County Soil Conservation District initiated a crayfish aquaculture trial
in 1981, during which seed-stock purchased from Louisiana was used
to stock impoundments in the Pocomoke River (Pattys Branch) and
Nanticoke River (Rewastico Creek) basins to examine the feasibility of
crayfish culture in Maryland (Bruce Nichols, Hebron, MD, pers. comm.).
The results of this trial indicated that sustained, profitable crayfish production
could occur in Maryland. In 1983, the Mid-Atlantic Crawfish
Association was established. With 250 members at its peak, this group
of farmers and landowners promoted crayfish aquaculture in the Mid-
Atlantic region. The original Louisiana seed-stock was used to stock
Red Swamp Crawfish in outdoor ponds for commercial aquaculture on
the Delmarva Peninsula and in Southern Maryland (Bruce Nichols, pers.
comm.). It was also used to stock culture ponds on the University of
Maryland Eastern Shore campus for research (David O' Neill, Community
College of Baltimore County, Baltimore, MD, pers. comm.). Most of the
stocking of Red Swamp Crawfish promoted by the Mid-Atlantic Crawfish
Association occurred prior to the establishment of aquaculture permit
regulations by the Maryland Department of Natural Resources (MDNR)
in 1990. Many locations where Red Swamp Crawfish were introduced
were not formally documented and are unknown. There are seven known
locations where Red Swamp Crawfish were historically introduced into
outdoor ponds for culture in Maryland; commercial aquaculture is still
conducted at two of these locations.
In 2006, we examined the role of aquaculture as a source of introduction
of Red Swamp Crawfish in Maryland streams. We conducted targeted
surveys in streams adjacent to all seven aquaculture facilities. We also collected
data on stream crayfishes at sites sampled as part of the Maryland
Department of Natural Resources’ Maryland Biological Stream Survey
(MBSS). These surveys documented populations of this non-native species
in streams and rivers on Maryland’s coastal plain. The goals of this report
are to 1) compile all known records of Red Swamp Crawfish to document its
current distribution in Maryland, and 2) to discuss the likely vectors responsible
for the introduction of this species. Documentation of these records
will prove useful for examining changes in the distribution of this species
over time.
Methods
Locations of aquaculture ponds where Red Swamp Crawfish were cultured
were provided by MDNR Fisheries Service personnel, crayfish farmers, and
researchers (Richard Bohn, MDNR Fisheries Service, Annapolis, MD, pers.
comm.; Bruce Nichols, pers. comm.; David O' Neill, pers. comm.; Matthew
Perry, pers. comm.). We sampled 16 sites in non-tidal streams adjacent to
seven aquaculture ponds. Crayfishes were collected using dip-nets. Crayfish
burrows in stream banks were excavated by hand. Dip-netting was supplemented
with backpack electrofishing at sites where dip-netting was not
2009 J.V. Kilian, J. Frentress, R.J. Klauda, A.J. Becker, and S.A. Stranko 657
considered sufficient to provide a representative sample of crayfish species
present. All crayfishes captured were identified to species. One record of
Red Swamp Crawfish from a stream adjacent to an aquaculture pond in the
Nanticoke River was provided by David O' Neill of the Community College
of Baltimore County.
Crayfish sampling was also conducted at 172 sites as part of the annual
Maryland Biological Stream Survey. Backpack electroshockers (Smith-Root
Model 12; Haltech Model HT-2000) were used to sample non-tidal stream
sites. Non-wadeable rivers and freshwater impoundments were sampled
using a jonboat outfitted with a Smith-Root Model KVA electrofisher. Boat
electroshocking was supplemented by seining (1.5 m x 3.0 m, 0.3-cm mesh;
1.8 m x 7.6 m, 0.6-cm mesh) in shallow, heavily vegetated shoreline habitats
at three sites sampled in the tidal Potomac River. All crayfishes collected at
each MBSS site were field-identified to species. All Red Swamp Crawfish
specimens collected in 2006 were preserved in alcohol and are currently
stored at the MDNR in Annapolis, MD.
Results
Non-native Red Swamp Crawfish were collected at 35 sites in 14 watersheds
(Maryland 8-digit HUC) in the coastal plain on the western shore
of Chesapeake Bay and on the Delmarva Peninsula (Fig. 1, Appendix 1).
Populations were documented in streams adjacent to all known ponds where
Figure 1. Stream sites where Red Swamp Crawfish were collected.
658 Northeastern Naturalist Vol. 16, No. 4
Red Swamp Crawfish were once cultured and in portions of the Patuxent,
Potomac, and Chester rivers (Fig. 2).
Discussion
The most important vectors responsible for the introduction of non-native
crayfishes throughout North America are the aquaculture, aquarium, biological
supply, and live-bait industries (Lodge et al. 2000b). The results of this
study indicate that the introduction of Red Swamp Crawfish in Maryland has
largely resulted from aquaculture. This species is now established in streams
adjacent to all aquaculture ponds where it was introduced for commercial
culture or for aquaculture-related research.
The vector or vectors responsible for the introductions of Red Swamp
Crawfish in the Potomac and Chester Rivers are unknown. Although no
aquaculture facilities in the Potomac River or Chester River basins are
or were registered with the MDNR Fisheries Service, these introductions
may have resulted from undocumented aquaculture in these areas. It is also
likely that these populations are the result of the inadvertent introduction of
Red Swamp Crawfish as bait, or intentional release by aquarium hobbyists.
The population documented in the Western Branch watershed of the Patuxent
River was approximately 70 river km from the original introduction
site in the Patuxent National Wildlife Refuge. This population could have
Figure 2. Maryland watersheds (8-digit HUC) with established stream populations
of Procambarus clarkii (Red Swamp Crawfish) and locations of aquaculture ponds
where this species was originally introduced.
2009 J.V. Kilian, J. Frentress, R.J. Klauda, A.J. Becker, and S.A. Stranko 659
originated from the downstream dispersal of Red Swamp Crawfish within
the Patuxent River or from a separate introduction event.
The effects of Red Swamp Crawfish on ecosystem function and the
composition and diversity of aquatic fauna and flora in Maryland are
unknown. Many transplants of this species throughout the world have resulted
in crop damage, damage to levees and dams as a result of burrowing
activity, or changes to regional flora and fauna (Hobbs et al. 1989, Holdich
1988, Lowery and Mendes 1977). The establishment of this species
in Maryland waters may have negative effects on native crayfishes, especially
the congeneric P. acutus Girard (White River Crawfish). Red Swamp
Crawfish, the more aggressive of the two species, may likely out-compete
White River Crawfish for shelter or other limited resources, and ultimately
displace the native species (Gherardi and Daniels 2004) as appears to have
occurred in portions of North Carolina (Cooper and Armstrong 2007). Native
displacement by non-native crayfishes is a phenomenon that has been
documented extensively (Capelli 1982, Capelli and Munjal 1982, Holdich
1988, Lodge et al. 2000a, Schwartz et al. 1963), prompting many states to
establish regulations on the import, culture, and sale of these potentially
damaging species (Lodge et al. 2000b). In Maryland, an aquatic nuisance
species list drafted in 2006 seeks to limit the import and transport of several
problematic invasive species (COMAR 2006). Non-native crayfishes
on this list include Red Swamp Crawfish, Orconectes virilis Hagen (Virile
Crayfish), and O. rusticus Girard (Rusty Crayfish). The establishment of
stream populations of Red Swamp Crawfish as a result of the aquaculture
of this species in outdoor ponds has major management implications and
should be considered in decisions involving the culture of this and other
non-native species in other states.
Efforts to eradicate Red Swamp Crawfish have been extensive and costly
in other areas of the country (Barbaresi et al. 2004, Hobbs et al. 1989), and
future attempts will likely prove futile in Maryland and could harm native
species. Pesticide application is likely to harm non-target species (Bills and
Marking 1988, Olden et al. 2006), and toxicants may be ineffective on Red
Swamp Crawfish individuals in protected burrows. Other approaches such as
trapping would be labor-intensive and may also be ineffective. Red Swamp
Crawfish is likely to spread into new watersheds in Maryland’s coastal plain.
Changes in the physical and chemical characteristics of streams that occur
above the Fall Line may prevent it from invading the piedmont of Maryland.
Its spread on the coastal plain will likely be limited by saltwater.
The new records presented here improve our understanding of the distribution
of this non-native species and establish a baseline for future crayfish
surveys in Maryland. Since the culture of Red Swamp Crawfish generally
results in the establishment of breeding populations in surrounding water
bodies (Hobbs et al. 1989, Lodge et al. 2000a), it is likely that additional
extant populations of Red Swamp Crawfish exist in Maryland watersheds
660 Northeastern Naturalist Vol. 16, No. 4
beyond those that are reported here. Undocumented stocking of Red Swamp
Crawfish mentioned above is likely to have occurred in watersheds not
surveyed during 2006. Additional surveys are necessary to determine the
distributional limits of Red Swamp Crawfish throughout Maryland. Also,
the effects of this species on native crayfishes and other aquatic fauna and
flora are unknown and require further research and additional monitoring.
Acknowledgments
We thank David O’Neill for providing his records and history of Red Swamp
Crawfish culture at UMES and John Cooper for providing information on Maryland
crayfishes and information on Red Swamp Crawfish in North Carolina. We thank
Arnold Norden for sharing his knowledge of Maryland crayfishes. We are also grateful
to Bruce Nichols, Matthew Perry, Ralph Andrews, and Eric May for providing
invaluable information on the history of crayfish aquaculture in Maryland. We also
thank Rebecca Chalmers, Karl Hellman, Richard Raesly, Gerald Mack, Joseph Smith,
Virginia Eaton, Rachel Gauza, Matthew Kline, Matthew Sell, Aaron Gates, Ryan Utz,
Ann Roseberry-Lincoln, Mark Southerland, Chris Millard, and Dan Boward for their
efforts in crayfish data collection. This study was funded in part by State Wildlife
Grant funds provided to the state wildlife agencies by US Congress, and administered
through the Maryland Department of Natural Resources’ Natural Heritage Program.
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Appendix 1. Collection records of Procambarus clarkii (Red Swamp Crawfish) summarized by river basin and watershed (Maryland 8-digit
Hydrologic Unit).
Site River basin Watershed (8-digit) Location Latitude (NAD83) Longitude (NAD83) Collection date
1 Patuxent Patuxent River upper Goose Pond outlet stream 39º01'46" 76º47' 55" 26 July 2006
2 Patuxent Western Branch Tributary to Collington Branch 38º56'09" 76º45'17" 15 July 2006
3 Patuxent Western Branch Tributary to Collington Branch 38º56'10" 76º45'17" 15 July 2006
4 Patuxent Western Branch Tributary to Lottsford Branch 38º58'11" 76º48'29" 15 July 2006
5 Potomac Nanjemoy Creek Mill Run 38º29'01" 77º05'09" 18 July 2006
6 Potomac Potomac Middle Tidal Tributary to Mallows Bay 38º28'15" 77º15'31" 10 May 2006
7 Potomac Potomac Middle Tidal Tributary to Mallows Bay 38º28'30" 77º15'26" 09 June 2006
8 Potomac Potomac Middle Tidal Tributary to Mallows Bay 38º28'14" 77º15'34" 12 June 2006
9 Potomac Potomac Middle Tidal Tributary to Mallows Bay 38º28'27" 77º15'45" 25 June 2006
10 Potomac Potomac Middle Tidal Tributary to Mallows Bay 38º28'29" 77º15'22" 25 June 2006
11 Potomac Potomac Middle Tidal Potomac River 38º28'15" 77º15'57" 25 July 2006
12 Potomac Potomac Middle Tidal Tributary to Wades Bay 38º26'30" 77º15'23" 08 June 2006
13 Potomac Potomac Middle Tidal Tributary to Wades Bay 38º26'11" 77º15'09" 08 June 2006
14 Potomac Potomac Middle Tidal Tributary to Wades Bay 38º25'48" 77º15'03" 07 June 2006
15 Potomac Mattawoman Creek Mattawoman Creek 38º35'47" 77º08'14" 22 Aug 2006
16 Potomac Mattawoman Creek Mattawoman Creek 38º35'26" 77º07'17" 22 Aug 2006
17 Potomac Potomac Upper Tidal Bryan Point 38º41'46" 77º03'59" 21 Aug 2006
18 Chester Corsica River Three Bridges Branch 39º03'34" 76º00'43" 18 July 2006
19 Chester Corsica River Three Bridges Branch 39º03'36" 76º00'39" 18 July 2006
20 Chester Corsica River Three Bridges Branch 39º03'07" 76º02'24" 26 Sept 2006
21 Chester Corsica River Three Bridges Branch 39º03'16" 76º03'02" 31 July 2006
22 Chester Corsica River Alder Branch 39º04'18" 76º04'00" 24 July 2006
23 Chester Corsica River Gravel Run 39º02'56" 76º03'47" 31 July 2006
24 Chester Lower Chester River Swan Creek 39º11'38" 76º13'07" 26 July 2006
25 Nanticoke Manokin Branch Manokin Branch 38º12'57" 75º39'55" 03 Aug 2006
2009 J.V. Kilian, J. Frentress, R.J. Klauda, A.J. Becker, and S.A. Stranko 663
Site River basin Watershed (8-digit) Location Latitude (NAD83) Longitude (NAD83) Collection date
26 Nanticoke Fishing Bay Roadside ditch at Egypt Road 38º28'33" 76º06'04" 21 June 2006
27 Nanticoke Fishing Bay Blackwater National Wildlife Refuge 38º26'51" 76º05'21" 21 June 2006
28 Nanticoke Fishing Bay Blackwater National Wildlife Refuge 38º26'51" 76º05'11" 21 June 2006
29 Nanticoke Fishing Bay Tributary to Little Blackwater River 38º32'34" 76º05'12" 21 June 2006
30 Nanticoke Nanticoke River Rewastico Creek 38º24'39" 75º45'16" 1989*
31 Pocomoke Lower Pocomoke River Pattys Branch 38º10'18" 75º22'19" 29 Aug 2006
32 Pocomoke Lower Pocomoke River Bachelors Branch 38º05'50" 75º29'22" 26 Aug 2006
33 Pocomoke Upper Pocomoke River Old Mill Branch 38º16'32" 75º18'21" 23 Oct 2006
34 Atlantic Chincoteague Bay Tributary to Pawpaw Creek 38º09'44" 75º17'55" 26 June 2006
35 Atlantic Chincoteague Bay Tributary to Scarboro Creek 38º09'32" 75º18'10" 26 June 2006
*Record provided by David O'Neill, Community College of Baltimore County, MD.