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. Introduction 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 - aevrsl@clemson.edu. 28 Southeastern Naturalist Vol. 5, No. 1 Methods 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. Results 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). Method NBCT 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 Discussion 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. Acknowledgments This research was funded in part by the US Forest Service. Technical Contribution No. 5122 of the South Carolina Agriculture Station, Clemson University, SC. Literature Cited Buchanan, J.B. 1992. The burrowing crayfishes (Decapoda: Cambaridae) of the Cahaba River-system. M.Sc. Thesis. University of South Alabama. Mobile, AL. Hobbs, Jr., H.H. 1942. The crayfishes of Florida. University of Florida Publications, Biological Science Series 3:1–179. Hobbs, Jr., H.H. 1981. The crayfishes of Georgia. Smithsonian Contributions to Zoology 318:1–549. Johnston, C., and C. Figiel. 1995. Population estimates, microhabitat parameters, and life history characteristics of Fallicambarus burrisi and Fallicambarus gordoni, two crayfishes associated with pitcher plant bogs in southern Mississippi. Final report to the Mississippi Natural Heritage Program, Jackson, MS. McGrath, C. 1994. Status of the Greensboro burrowing crayfish (Cambarus (Depressicambarus) catagius Hobbs and Perkins, 1967). Nongame Project Report for the US Fish and Wildlife Service. Nongame and Endangered Wildlife Program, North Carolina Wildlife Resource Commission, Raleigh, NC. Norrocky, M.J. 1984. Burrowing crayfish trap. Ohio Journal of Science 84:65–66. SAS Institute, Inc. 2002. SAS OnlineDoc®, Version 9. Cary, NC. Taylor, C.A., and T.G. Anton. 1998. Distribution and ecological notes on some of Illinois’ burrowing crayfish. Transactions of the Illinois State Academy of Science 92:137–145.