2007 NORTHEASTERN NATURALIST 14(4):507–518
Invasion of the Upper Susquehanna River Watershed by
Rusty Crayfi sh (Orconectes rusticus)
Mark L. Kuhlmann1,* and Peter D. Hazelton1,2
Abstract - Orconectes rusticus (rusty crayfish) has spread from its original
range throughout much of northeastern North America. Invading rusty crayfish
can completely replace native crayfish and impact other parts of the community
through changes in consumption, disturbance, and other effects. Our main
objectives were to document rusty crayfish distribution in streams of the upper
Susquehanna River watershed, NY, and to determine the extent of changes in
crayfish community composition since the last major survey. We sampled streams
during 1999–2005 to describe the current distribution of crayfish species and to
document short-term temporal changes. To determine long-term changes in species
composition and distribution, we compared our data to museum specimen
collection records. We found significant changes in the crayfish community; our
surveys found 2 species not previously reported from the upper Susquehanna River
watershed and failed to find 2 species previously reported. We also found that
rusty crayfish are widespread in the watershed and continues to expand, while the
ranges of native congeners are retracting.
Introduction
Invasions by nonindigenous species are a significant threat to the diversity
and function of communities (Lodge et al. 2000, Mack et al. 2000,
Richter et al. 1997). Freshwater communities are especially threatened by
invasions because high rates of endemism in certain taxa (e.g., mussels,
crayfish) make species with small ranges more vulnerable to extinction
(Lodge et al. 1998, Mack et al. 2000). Furthermore, although natural
overland dispersal by aquatic species over even short distances is rare,
human-assisted dispersal across these barriers can be common, making
short-range introductions of species among regional watersheds relatively
frequent (Lodge et al. 2000, MacIsaac et al. 2001).
Crayfish in particular represent a significant invasion threat to aquatic
ecosystems. Often the largest invertebrates in freshwater communities,
crayfish play significant roles through the food web, as both consumers
and prey, and as agents of disturbance (e.g., bioturbation, macrophyte
destruction; reviewed by Momot 1995). Thus, changes in the crayfish community
could have large effects on biodiversity, community structure, and
ecosystem function (but see Helms and Creed 2005, Nyström and Strand
1996, Nyström et al. 1999).
1Biology Department, Hartwick College, Oneonta, NY 13820. 2Current address -
Warnell School of Forest Resources, University of Georgia, Athens, GA 30602.
*Corresponding author - kuhlmannm@hartwick.edu.
508 Northeastern Naturalist Vol. 14, No. 4
Orconectes rusticus (Girard) (rusty crayfi sh) is native to the Ohio River
drainage, but since at least the 1960s has spread from its original range
throughout much of northeastern North America, probably by bait-bucket
introductions (Berrill 1978, Butler and Stein 1985, Capelli and Magnuson
1983, Crocker 1979, Gunderson 2002). In some areas (e.g., Wisconsin
lakes), O. rusticus often completely replaces native or previously established
congeners (Butler and Stein 1985, Lodge et al. 1986, Perry et al. 2001). Invading
O. rusticus often attains a higher population density than the species
it replaces, and thus can impact the rest of the community through changes
in consumption, disturbance, and other effects (Lodge et al. 1985, Olsen et
al. 1991, Wilson et al. 2004).
Orconectes rusticus was not reported from the upper Susquehanna
River watershed in New York at the time of the last description of the
region’s crayfish community (Crocker 1957). There are no published
accounts of O. rusticus in the region since then, although it has been
reported in other New York drainages, including the adjacent Mohawk
watershed (Crocker 1979, Daniels 1998). Unpublished reports suggest
that O. rusticus became common in Otsego Lake, headwaters of the
Susquehanna River, in the early 1970s (Harman 1976, Phillips 1977), but
no information is available for the streams.
Given O. rusticus’ known ability to invade and displace other crayfish
species, our objectives in this study were to document O. rusticus’ distribution
in streams of the upper Susquehanna River watershed and to determine
the extent of changes in crayfish community composition since the last
major survey. We used geographical information from the New York State
Museum’s specimen collection database to map the historical distribution
of crayfish species in the region, and we conducted semi-quantitative annual
sampling of streams to describe the current distribution of crayfish
species and to document short-term temporal changes.
Methods
To determine the historical species composition and distribution of the
crayfi sh community, we examined records from the New York State Museum
(NYSM) specimen collection. The earliest collections in the NYSM database
correspond to those reported by Crocker (1957): specimens from a 1935
stream survey by the New York State Conservation Department and collections
made by D.W. Crocker in 1952. The NYSM database includes specifi c
locality information for each specimen, not reported in Crocker (1957), so
we were able to map the location of earlier collections and compare the
historical distribution with the fi ndings of our recent surveys. The NYSM
database also includes a small number of collections made after Crocker’s
(1957) report.
To measure the current distribution of crayfi sh, we conducted rapid, semiquantitative
sampling of the upper Susquehanna River watershed annually
2007 M.L. Kuhlmann and P.D. Hazelton 509
during the summers (June–August) of 1999–2005. Our sampling region, centered
around Oneonta, NY (42.45°N, 75.08°W), included the Susquehanna
River mainstem upstream of Bainbridge, NY, to its headwaters at Otsego Lake
and most of the 2nd–3rd order tributaries in the region (Fig. 1).
To reduce sampling effort per site to maximize the geographical extent of
our study, we focused on a limited range of habitats that were common in all
streams in our region, could be sampled rapidly with a standardized protocol,
and were most likely to contain crayfi sh: shallow (<0.8 m depth) stream
reaches with rocky substrate. These habitat criteria include riffl es and shallow
runs but exclude pools, stream reaches with unconsolidated sediments,
and deeper portions of the larger rivers. Thus, although our sampling did not
include all potential crayfi sh habitats, it allowed us to make within-habitat
comparisons among streams within our sampling region.
On each stream, 2–7 sites were selected for sampling, largely on the
basis of habitat type (see above) and access. Most sampling locations
were at bridges or public access points (e.g., parks, fishing access easements),
except for a few sites on the Susquehanna River reached by canoe
in 2000. Using mostly publicly accessible sites could bias our results
(e.g., if nonindigenous species are more likely at sites with easy access).
However, data from sites bordered by private property (n = 8, mostly on
the Susquehanna River and Charlotte Creek) and from additional intermediate
points on Charlotte Creek accessed by canoe in 2006, fit the overall
pattern from the other sites, suggesting that the sampled sites were representative
of the overall pattern of crayfish distribution. All sites were not
sampled every year because of limited time and adverse conditions (e.g.,
flooding), but at least some sites on 5 of the 8 streams were sampled during
at least 4 years (Fig. 1).
At each site, we established 3–4 cross-stream transects at 10-m intervals
upstream of a starting point selected by blindly tossing a weighted marker.
We sampled at 3 points (occasionally fewer if the stream was very narrow)
along each transect, haphazardly placed by blindly tossing a weighted
marker, but stratifi ed to include both the edge and center of the stream. The
maximum water depth we could effectively sample in was about 0.8 m, but
summer water levels were typically much shallower. At sites with greater
depth (the 2 lower sites on the Unadilla River and the 5–6 lower sites on
the Susquehanna River, depending on stream levels), we sampled along
transects from one bank out to ≈0.8 m depth.
We used 2 main methods to sample crayfi sh: semi-quantitative kicknetting
(when current was suffi cient) and quadrat sampling (in slow-moving,
shallow water). The modifi ed kicknet (Hauer and Resh 1996), 1 m wide
x 1 m tall with a ≈0.5-m bag made of 3-mm mesh, was positioned across
the current and held against the substrate with two poles by one person. A
second person turned over all rocks and stirred up the substrate in a 0.6-m2
trapezoidal sampling area upstream of the net, allowing the current to carry
disturbed crayfi sh into the net. During quadrat sampling, a 1-m2 area was
510 Northeastern Naturalist Vol. 14, No. 4
2007 M.L. Kuhlmann and P.D. Hazelton 511
searched carefully by hand, capturing the crayfi sh in small aquarium nets.
During 1999–2004, the number of crayfi sh captured by semi-quantitative
methods from 6 sites was low, so we supplemented these samples with collections
by hand nets. During June–September 2005, we sampled 11 sites in
conjunction with other studies, mostly using non-quantitative methods. All
captured crayfi sh were identifi ed in the fi eld to species based on external
morphological features (R.A. Daniels, New York State Museum,Albany, NY
unpubl. data; Peckarsky et al. 1990).
Results
Historical distribution
Historical records of crayfi sh distribution in the upper Susquehanna watershed
are few. Extant records from the 1935 stream survey provide crayfi sh
species identifi cation at only six locations: Orconectes immunis (Hagen)
(calico crayfi sh) and Orconectes limosus (Rafi nesque) (spinycheek crayfi sh),
each at one site (Fig. 1), and Cambarus bartonii (Fabricius) (Appalachian
brook crayfi sh) at four sites (all headwater streams not shown on Fig. 1).
Crocker (1957) collected crayfi sh at seven locations in 1952: Orconectes
propinquus (Girard) (northern clearwater crayfi sh) at three locations, O.
limosus at three, O. immunis at one, and C. bartonii at three sites. The next
records in the NYSM collection are from 1982: O. propinquus was collected
at one and C. bartonii at two sites. A collection from one location on the
Susquehanna River in 1991 contained O. rusticus, O. obscurus (Hagen) (Allegheny
crayfi sh), and C. bartonii (Fig. 1).
Recent distribution
During 1999–2005, at a total of 38 locations on the upper Susquehanna
River and its tributaries, we captured n >4000 crayfish of four species:
O. rusticus, O. propinquus, O. obscurus, and C. bartonii. Cambarus
bartonii was primarily found in the upper reaches of the tributaries we
sampled (Fig. 1, Table 1), but was also common in small headwater streams
(M.L. Kuhlmann, pers. observ.). Orconectes rusticus was by far the most
abundant and widely-distributed species, occurring throughout most of
the upper Susquehanna River, the upper Unadilla River, and the lower
reaches of most other tributaries (Fig. 1, Table 1). The other Orconectes
species, O. propinquus and O. obscurus, were most common in the upper
reaches of tributaries and were also initially found in a few other locations
Figure 1 (opposite page). Map of the upper Susquehanna River watershed study
area. North is towards the top in all maps. (A) Locations of specimens in the New
York State Museum (NYSM) database (1935–1991). Species and collection date are
indicated adjacent to the collection location. Inset (lower right) shows the location
of the study area in New York State. (B) Sites sampled (x) during the present study
(1999–2005). Numbers in parentheses next to the site symbols indicate the number
of sample years. Stream map modifi ed from 3-D Topo Quads, © DeLorme, Yarmouth
ME. State map modifi ed from www.netstate.com.
512 Northeastern Naturalist Vol. 14, No. 4
without O. rusticus. Orconectes obscurus was only found in two areas:
the upper reaches of Schenevus Creek plus Ouleout Creek and (initially)
the Susquehanna River adjacent to the mouth of Ouleout Creek. Orconectes
propinquus was found in all other tributaries and at one site on the Susquehanna
River (Fig. 1, Table 1).
Table 1. Crayfi sh species distribution in streams of the upper Susquehanna River watershed
during 1999–2005. Distance upstream measures the stream km from the mouth, except for the
Susquehanna River, where distance is measured from Bainbridge, NY, the sampling point farthest
downstream. For site locations, see Figure 1-B. • = species present in at least one year.
Distance Orconectes O. O. Cambarus Years
River upstream (km) rusticus propinquus obscurus bartonii sampled
Susquehanna River 0 • • 2
14 • • 6
19 • • 1
24 • 1
32 • 1
46 • 4
48 • 3
85 • 1
Unadilla River Mouth* • • 2
21 • 1
29 • • 2
48 • 1
70 • 1
Butternut Creek 5 • 4
28 • • 4
46 • • 1
Ouleout Creek Mouth* • • 6
1 • • • 6
5 • • • 4
6 • • 1
Otego Creek 1 • 1
12 • • • 1
18 • • • 1
28 • • 1
Charlotte Creek 0 • 5
6 • • • 2
8 • • 6
10 • • 3
15 • • • 1
19 • • • 7
23 • • • 2
25 • • • 6
Schenevus Creek Mouth* • 5
11 • • • 7
14 • • • 4
18 • • • 4
22 • • • • 7
30 • • • 3
Cherry Valley Creek 10 • 1
21 • 1
*Mouth = nearest sampling point on the Susquehanna River.
2007 M.L. Kuhlmann and P.D. Hazelton 513
During our study, we collected O. rusticus at an increasing number of
sites. In three of the four tributaries sampled repeatedly, O. rusticus was
found at more sites and further upstream after 1999 (Figs. 2A, 2B, and 2C).
Butternut Creek, a tributary of the Unadilla River, was the only exception to
this pattern; it remained without O. rusticus throughout the sample period
(Table 1). In the Susquehanna River, O. rusticus was initially not found at
our lower 2 sampling sites, but was collected there by 2005. Simultaneously,
we collected O. propinquus at fewer sites in Charlotte Creek and O. obscurus
at fewer sites in Schenevus Creek and the Susquehanna River as the study
progressed (Figs. 2A, 2B, and 2C).
Discussion
The crayfi sh community of the upper Susquehanna River watershed has
changed considerably over the last 70 years. Our extensive recent sampling,
including sites where O. limosus and O.immunis were previously collected,
failed to produce those species (Fig. 1). Thus, it is likely that O. limosus and
O.immunis are now absent from streams in the region. Because our sampling
did not cover deep habitats with slow current, such as pools, it is possible
that either of these species persists in those habitats. Additional sampling in
these other habitats is necessary to conclusively determine the status of these
species in the watershed.
Figure 2A. Temporal patterns
(1999–2005) of crayfi
sh species distribution along
Ouleout Creek in the upper
Susquehanna River watershed.
Distance upstream measures
the stream km from the mouth.
Symbols indicate sites where
a given species was present.
When a species was present at
more than one site, adjacent
points are connected for clarity.
If a site was not sampled
in a given year, no species
has a symbol at that distance.
Data for the mouth (plotted at
distance = 0 km) are from the
nearest sampling point on the
Susquehanna River.
514 Northeastern Naturalist Vol. 14, No. 4
We found two crayfi sh species not reported in the upper Susquehanna
River watershed prior to 1991: O. obscurus and O. rusticus. The current
disjunct distribution of O. obscurus is suggestive of multiple recent introductions,
perhaps from adjacent watersheds where it occurs (Crocker
1979, Daniels 1998). However, O. obscurus occurs in lower parts of the
Susquehanna River watershed (Crocker 1957), so its presence in the upper
watershed did not necessarily result from human introduction. Since none
of the streams where O. obscurus occurs were sampled before 1991, it is
possible that it was simply missed in earlier surveys. Given its presence in
other parts of the Susquehanna River watershed and the paucity of historical
samples in our study area, we tentatively classify O. obscurus as native.
Orconectes rusticus is clearly a recent introduction. Its distribution and
pattern of expansion (Table 1; Figs. 2A, 2B, and 2C) suggest at least two
separate points of introduction: the headwaters of the Susquehanna River,
possibly one of the lakes, and the upper Unadilla River. As its population
Figure 2B. Temporal patterns
(1999–2005) of crayfi sh species
distribution along Schenevus
Creek in the upper
Susquehanna River watershed.
Distance upstream measures
the stream km from the
mouth. Symbols indicate sites
where a given species was
present. When a species was
present at more than one site,
adjacent points are connected
for clarity. If a site was not
sampled in a given year, no
species has a symbol at that
distance. Data for the mouth
(plotted at distance = 0 km)
are from the nearest sampling
point on the Susquehanna
River.
2007 M.L. Kuhlmann and P.D. Hazelton 515
appears to expand, O. rusticus may be replacing the native (or previously
established) congeners O. propinquus and O. obscurus in some locations.
Cambarus bartonii is typically associated with headwater streams
(Crocker 1957), although it was collected at numerous locations in the larger
streams of the upper Susquehanna River watershed in the past (Fig. 1), implying
that it was fairly common there. In contrast, we found C. bartonii at
relatively few sites, all in the upper reaches of the streams we sampled. We
cannot determine a cause for this apparent change in distribution. It seems
unlikely that the invasion of O. rusticus was the direct cause, since C. bartonii
and O. rusticus overlap little now. Cambarus bartonii is most common
in small headwater streams, which in this area typically lack other crayfi sh
(M.L. Kuhlmann, pers. observ.), so it will likely persist in those habitats.
Comparisons between our recent sampling and earlier surveys indicate
that the crayfi sh community in the upper Susquehanna River watershed has
changed greatly over the past 70 years, with the apparent loss of 2 species,
the addition of 1 or possibly 2 species, and apparent changes in the distribution
of others. The apparent contractions of the ranges of O. propinquus
and O. obscurus might be related to the expansion of the introduced species
Figure 2C. Temporal patterns
(1999–2005) of crayfi
sh species distribution along
Charlotte Creek in the upper
Susquehanna River watershed.
Distance upstream measures
the stream km from the mouth.
Symbols indicate sites where
a given species was present.
When a species was present
at more than one site, adjacent
points are connected for clarity.
If a site was not sampled in
a given year, no species has a
symbol at that distance.
516 Northeastern Naturalist Vol. 14, No. 4
O. rusticus. Unfortunately, the lack of data between 1952 and 1999 make it
impossible to determine the cause of the apparent loss of O. limosus and O.
immunis and the decline of C. bartonii in larger streams.
During our sampling, we noted that O. rusticus seems to achieve a much
higher population density than the other crayfi sh species in the watershed.
For example, at sites with only O. rusticus, median estimated density was 7.6
individuals/m2 with a maximum of >19 individuals/m2. In comparison, O.
propinquus had a median estimated density of only 1.8 individuals/m2 when
by itself, with a density of >5 individuals/m2 in only two samples. Since O.
rusticus occurs primarily in the Susquehanna River and the lower reaches
of tributary creeks (Table 1; Figs. 2A, 2B, and 2C), it is possible that this
is a result of differences between the habitats where each species is found
rather than differences between the species. Unfortunately, we do not have a
suffi cient number of observations at sites where the transition from native to
introduced species occurred to completely rule out this possibility. However,
this apparent pattern of higher O. rusticus density is consistent with what has
been reported from other areas O. rusticus has invaded (Lodge et al. 1985,
Wilson et al. 2004).
Because crayfish have significant roles in stream communities as consumers
and agents of disturbance, an increase in crayfish density as a result
of the invasion by O. rusticus should have important direct and indirect effects
on many parts of the stream community (Momot 1995, Statzner et al.
2000, Usio and Townsend 2004, Zhang et al. 2004). O. rusticus has higher
per-gram consumption rates of invertebrates and plants than O. propinquus
(Olsen et al. 1991), making the impact of the invasion even greater. As generalist
omnivores, crayfish can have direct consumptive effects on a wide
range of species, including snails, aquatic insects, macroalgae, and diatoms,
which may cascade through the food web to indirectly affect many
more species. Through disturbance (e.g., bioturbation), they act as ecosystem
engineers and have additional indirect effects (Creed and Reed 2004,
Crooks 2002, Jones et al. 1994, Statzner et al. 2000, Usio and Townsend
2004, Zhang et al. 2004). Thus, if low densities of O. propinquus and O.
obscurus are replaced by higher densities of invading O. rusticus, we
would expect widespread effects on many parts of the upper Susquehanna
River watershed community.
Acknowledgments
We thank J. Sullivan, A. Prisciondaro, M. Irland, G. Hamilton, and S. Caldwell
for help in the fi eld and R. Daniels for providing the NYSM specimen data, confi rming
species identifi cations, and helpful suggestions. The staff of Hartwick College’s
Pine Lake Environmental Center provided logistical support. This manuscript was
greatly improved by comments from R. Daniels, P. Fauth, members of the Grossman
Lab at the University of Georgia, R. DiStefano, and 3 anonymous reviewers. Partial
support for this research came from the Faculty Research Grants Program and a
Wandersee Scholar-in-Residence award, both from Hartwick College.
2007 M.L. Kuhlmann and P.D. Hazelton 517
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