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2006 SOUTHEASTERN NATURALIST 5(1):27–30
Comparison of Two Burrowing Crayfish Trapping Methods
SHANE M. WELCH1 AND ARNOLD G. EVERSOLE1,*
Abstract - A new non-destructive method of sampling burrowing crayfish, the
burrowing crayfish net, was compared to the Norrocky burrowing crayfish trap. The
new sampling method captured significantly more crayfish than did the trap. Captured
crayfish sizes were similar and sex ratios were not biased in the two methods.
Sixteen species of crayfish have been captured with the burrowing crayfish net.
Hobbs (1942, 1981) identified three categories of burrowing crayfish:
primary, secondary, and tertiary. Primary burrowing species spend the
majority of their life in and around burrows and are rarely found in open
water. Secondary burrowing species frequent surface water during wet
periods of the year, but spend much of their life in burrows. Tertiary
burrowers generally live in surface water, but may retreat into simple
burrows for reproduction and to avoid desiccation or freezing.
While some burrowing crayfish may be collected in surface water,
many are collected by the arduous task of excavating the burrow. In
addition to being physically demanding and time consuming, burrow excavation
inevitably destroys the burrow complex, making mark-recapture
studies or release of the specimens impractical. Other methods of collecting
burrowing crayfish include visual night searches (Hobbs 1981),
vernal pools traps (Taylor and Anton 1998), or traps such as the Norrocky
burrowing crayfish trap (NBCT; Norrocky 1984) and variations of it
(e.g., Buchanan 1992) that capture the crayfish at the entrance of the
burrow. Of these methods, trapping at the entrance of the burrow is the
most attractive because it requires minimal effort, many burrows over a
large area can be sampled simultaneously, and sampling does not destroy
the burrows. Success rates of the NBCT vary. Norrocky (1984) reported
13% success trapping Fallicambarus fodiens (Cottle), whereas Johnston
and Figiel (1995) and McGrath (1994) reported no success with the
NBCT. Our interest in improving trapping success led to the design of an
alternative method for capture of burrowing crayfish at the entrance of
the burrow, which we hereafter refer to as the burrowing crayfish net
(BCN). The objective of this study was to compare capture success of the
NBCT to that of the BCN.
1Department of Forestry and Natural Resources, Clemson University, Clemson, SC
29634-0317. *Corresponding author - firstname.lastname@example.org.
28 Southeastern Naturalist Vol. 5, No. 1
The NBCTs were constructed and deployed as outlined by Norrocky
(1984). Briefly, the NBCT was made from a 30-cm length of 4-cm diameter
PVC pipe with a small aluminum sheet metal flap hinged near one end of the
tube. The hinged flap opens one-way, acting as a trap-door. The trap was
inserted into the entrance of a burrow (Fig. 1 a). A crayfish is captured when
its climbs up the pipe and pushes past the metal flap, which falls back into
place behind the crayfish trapping it in the tube.
The BCNs were constructed from rectangular pieces of discarded avian
mist net measuring approximately 20 x 150 cm. Because the BCN was
constructed from discarded net material, net manufactures and mesh sizes
varied. The netting was folded over itself cross-wise several times until the
folded net measured 20 x 20 cm. The middle of the last fold was pinched and
tied with a suitable-length anchor string. The BCNs were deployed by
inserting the net into the entrance of a crayfish burrow and securing the
string to a wire survey flag (Fig. 1b). The crayfish becomes entangled in the
net as it attempts to exit or enter the burrow.
Populations of Distocambarus crockeri (Hobbs and Carlson), a primary
burrowing crayfish endemic to the South Carolina piedmont, were sampled to
compare the two methods. Four trapping sessions were conducted from
February to June, 2001, to compare capture success between the two methods.
Each trapping session involved randomly setting 25 NBCTs and 25 BCNs in
the entrances of burrows of a D. crockeri colony located in the Long Cane
Ranger District of the Sumter National Forest (McCormick County, SC).
Traps were checked approximately every 48 h over the four trapping
sessions. Captured crayfish were sexed, carapace length (CL) measured, and
Figure 1. Schematic of the two methods used to capture burrowing crayfish, a) the
Norrocky burrowing crayfish trap (NBCT), and b) the burrowing crayfish net (BCN).
2006 S.M. Welch and A.G. Eversole 29
the crayfish returned to their respective burrows. A paired T-test was used to
compare capture success between the two methods after assessing the normality
of the data using a Shapiro-Wilks test. A Wilcoxon test was used to
compare the size of captured crayfish, because CL was not normally distributed.
A Fisher's exact test was used to assess the distribution of males and
females because of the low expected capture values. All statistical tests were
preformed with SAS (2002) software, α = 0.05.
Thirty crayfish were caught during the study (Table 1). Significantly more
crayfish were captured using the BCN than the NBCT (t = 3.40, df = 3, P <
0.05). The Wilcoxon test indicated no difference in CL of captured crayfish
between the two methods (z = -1.56, df = 1, P > 0.05). The mean (± SD) CL for
crayfish caught with the BCN was 29.9 ± 4.72 mm and with the NBCT was
27.1 ± 4.43 mm. Sex ratios were random according to the Fisher's exact test.
Table 1. Comparison of crayfish captures (Distocambarus crockeri) using the Norrocky burrowing
crayfish trap (NBCT) and the burrowing crayfish net (BCN).
Trapping Males Females Total Males Females Total
dates (2001) captured captured captures captured captured captures
2/10–2/18 0 1 1 1 5 6
3/19–3/31 1 1 2 2 8 10
5/04–5/11 0 0 0 1 0 1
6/12–6/19 2 0 2 5 3 8
Total 3 2 5 9 16 25
Table 2. Crayfish species and burrowing category of the species caught using the BCN.
Species Burrowing category1
Cambarus diogenes Girard Primary
C. latimanus (Le Conte) Secondary
C. reflexus Hobbs Primary
C. reduncus Hobbs Primary
C. striatus Hay Primary
Distocambarus carlsoni Hobbs Primary
D. crockeri Hobbs and Carlson Primary
D. devexus (Hobbs) Primary
Fallicambarus fodiens (Cottle) Secondary
F. gordoni Fitzpatrick Primary
Procambarus acutus acutus (Girard) Tertiary
P. barbatus (Faxon) Secondary
P. clarkii (Girard) Tertiary
P. lunzi (Hobbs) Tertiary
P. planirostris Penn Secondary
P. troglodytes (LeConte) Tertiary
1Burrowing categories based on Hobbs (1981).
30 Southeastern Naturalist Vol. 5, No. 1
In addition to capturing more crayfish than the NBCT, the BCN has
several other advantages. It is lightweight and compact; 50 BCNs weigh
approximately 100 g and fit into a small back-pack, while the same number
of NBCTs weigh 7.5 kg and require considerably more space. The BCN is
easy to construct compared to the NBCT, and the construction costs of the
BCN are minimal if discarded avian mist net is used. Although the BCN
caught 5 times more crayfish than the NBCT, our overall capture success in
this study was well below that reported by Norrocky (1984). However our
experiences indicate BCN capture success varies over time and may be
considerably higher than that reported in the present study. For example,
capture success among colonies of D. crockeri in one of our studies over 20
months ranged 0–45%, while in another study the capture success among
colonies of Cambarus diogenes (Girard) ranged 0–50% (S.M. Welch and
A.G. Eversole, unpubl. data).
The capture success of the BCN is largely determined by the surface
activity of the target species and thus may be expected to vary over time,
between sites, and among species. We have used the BCN for both aquatic and
terrestrial sampling and captured a range of burrowing crayfish (Table 2). We
anticipate that use of the BCN will aid researchers studying burrowing
crayfish and thus increase our knowledge of these understudied animals.
This research was funded in part by the US Forest Service. Technical Contribution
No. 5122 of the South Carolina Agriculture Station, Clemson University, SC.
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