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Natural History of Resident and Translocated Alligator Snapping Turtles (Macrochelys temminckii) in Louisiana
Victor Bogosian III

Southeastern Naturalist, Volume 9, Issue 4 (2010): 711–720

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2010 SOUTHEASTERN NATURALIST 9(4):711–720 Natural History of Resident and Translocated Alligator Snapping Turtles (Macrochelys temminckii) in Louisiana Victor Bogosian III* Abstract - Translocation is often considered a viable conservation strategy, despite the absence of species-specific post-translocation data. Macrochelys temminckii (Alligator Snapping Turtle) populations have declined across their range and they may be considered candidates for translocation, but few studies have examined the response of individuals to movement events. I monitored M. temminckii with radiotelemetry in northwest Louisiana to provide baseline data regarding the species’ response to translocation. I calculated average distances moved per day, measured water depths, and recorded growth of translocated and resident turtles. There was no observed mortality during the study, and translocated turtles gained mass and increased shell dimensions, indicating they effectively located resources after translocation. Resident individual shell dimensions increased, but some residents lost mass, possibly due to early recapture and reweighing dates. Movement distances were within the ranges reported by previous researchers. These data contribute baseline information concerning M. temminckii conservation biology. Introduction Many species of freshwater turtles are critically endangered due to anthropogenic factors (Browne and Hecnar 2007, Garber and Burger 1995), some to the extent that their continued existence may be restricted to captive populations (Gibbons et al. 2000). Recolonization rates may be low due to life-history strategies in some species (Congdon et al. 1993, 1994). In these cases, reintroduction (the movement of individuals within their native range to localities where the species has been extirpated) or translocation (the movement of individuals to localities where the species has not been extirpated) may increase overall population recovery (Gibbons et al. 2000, Tuberville et al. 2005), although these attempts carry with them a great deal of uncertainty. In many published translocation attempts, further investigations of natural history and refinement of translocation techniques are suggested by the authors (Berry 1986, Tuberville et al. 2005). Macrochelys temminckii Harlan (Alligator Snapping Turtle) is a largebodied (>100 kg), long-lived species found in the southeastern United States (Pritchard 1989). Large-scale commercial exploitation of M. temminckii during 1960–1980 (Roman et al. 1999) resulted in the collapse of commercially viable populations and enaction of protective laws (Pritchard 1989, *Museum of Life Sciences, Louisiana State University in Shreveport, One University Place, Shreveport, LA 71115-2399. Current address - Cooperative Wildlife Research Laboratory, Southern Illinois University, Carbondale, IL; vicbogos@siu.edu. 712 Southeastern Naturalist Vol. 9, No. 4 Reed et al. 2002). Commercially preferred minimum body size for profitable butchering coincided with the onset of sexual maturation in M. temminckii (Sloan and Lovich 1995, Tucker and Sloan 1997), and the number of turtles processed annually during this time was very high (Sloan and Lovich 1995). Macrochelys temminckii populations are now protected from commercial harvest across their range (Boundy and Kennedy 2006), suggesting that populations may eventually recover if commercial overharvesting was the primary factor in their decline. Encouraging evidence exists regarding turtle population recovery following removal of factors associated with declines (Gibbs et al. 2008), but demographic models predict that natural recovery of M. temminckii populations may be a lengthy process (Reed et al. 2002). An additional concern for any translocation attempt is the definition and estimation of success. Griffith et al. (1989) defined a successful translocation event as one that presents evidence of a stable, self-sustaining population. These criteria are difficult to confirm for M. temminckii given their long lifespans and delayed sexual maturity (Dobie 1971), as well as the cryptic nature of younger age classes (Boundy and Kennedy 2006); indeed, these criteria are difficult to confirm in unharvested, stable populations. Therefore, acceptance of other metrics of determinants for success of reintroductions of M. temminckii is required, at least in the preliminary stages of conservation actions. I collected movement and location depths following release of resident and translocated turtles at two sites. Small sample size prevented statistical interpretation, but these data may serve as baseline metrics of acclimation to unfamiliar locations. Movement by turtles occurs to satisfy physiological requirements, avoid predators, capture prey, locate suitable habitats, and fulfill reproductive requirements (Gibbons et al. 1990). Movement behavior is commonly used in turtle research as an estimate of an individual’s acceptance or rejection of its surroundings following translocation (Cook 2004, Field et al. 2007, Rittenhouse et al. 2007). Movements of translocated turtles are often longer and more frequent than that of resident turtles (Hester et al. 2008, Rittenhouse et al. 2007), and individuals may disperse from the release site before establishing home ranges (Berry 1986). I also report data on overwintering duration and the growth of individuals during the monitoring period. This information is intended to build upon a body of literature that may be used by future conservation biologists whose efforts are intended to establish stable, self-sustaining populations (Griffith et al. 1989) of M. temminckii. Study Sites My study sites were near Shreveport, LA, and included Cross Lake (approximately bounded geographically by 32.50° and 32.54°N, and 2010 V. Bogosian 713 93.78° and 93.97°W; 3400 ha) and an unnamed lake in the Red River National Wildlife Refuge (RRNWR hereafter, approximately bounded geographically by 32.44° and 32.45°N, and 93.66° and 93.68°W; 80 ha). The RRNWR (translocation site) was a natural oxbow of the Red River. It contained dead flooded Salix spp. (willows) in the lake, was vegetated by a mixture of willows and Quercus spp. (oaks) along the shoreline, and had water depths of 0.5–6.0 m. Shallower portions of the RRNWR were vegetated heavily by Nelumbo lutea Willd (American Lotus) and Ceratophyllum demersum L. (Coontail), and experienced sporadic drying during years with low rainfall. To facilitate recapturing translocated turtles at the end of the study, I selected the translocation site due to its isolation from dispersal routes and its lack of resident M. temminckii populations. Cross Lake (resident site) is a similarly shallow (0.5–3.0 m range) impoundment dammed on the eastern edge. The western half was dominated by Taxodium distichum (L.) Rich. (Baldcypress)-Cephalanthus occidentalis L. (Buttonbush) swamps, and both submergent (C. demersum) and floating (Eichornia crassipes Mart. [Water Hyacinth]) vegetation were common understory components. Although Cross Lake is much larger and thus experiences less periodic drying than the RRNWR, it serves as a municipal water source for Shreveport and typically experiences reduced water levels in late summer and early autumn. Methods I trapped turtles during March–October 2005 using single-throated hoop nets (0.9 m diameter, 2 m length, 2.5 cm mesh size; Memphis Net and Twine, Memphis, TN). Traps were baited with frozen tilapia, Lepisosteus spp. (gar), or canned Thunnus spp. (tuna), and checked daily. Macrochelys temminckii were brought to the laboratory for transmitter attachment and measurement, and all other captured turtles were released immediately. Two M. temminckii (1 male, 1 female) were acquired from commercial trappers in August 2004, and one was captured by hand at Cross Lake in October 2005. The trappers were reluctant to divulge their trap sites, so I could not determine the exact location of capture for acquired turtles, and considered them to be translocated. Radiotransmitters (Holohil Inc., ON, Canada) were attached to the middle of the carapace using quick-drying marine epoxy. I measured straight-line carapace length (CL) using forestry calipers (± 1 mm, Forestry Supply Company, Jackson, MS) and mass using a Pesola scale (± 0.1 kg) for each individual, and classified turtles as adults or subadults based on measurement partitions provided by Dobie (1971). I did not attempt to determine the gender of subadult turtles, and determined the gender of adult turtles via preanal tail length (Dobie 1971). To permanently identify individuals, PIT tags (Biomark, Inc., Boise, ID) were injected into the tail musculature. 714 Southeastern Naturalist Vol. 9, No. 4 Some turtles were held in captivity for extended periods of time before their release (Table 1). Long-term captive individuals were housed at the Natchitoches National Fish Hatchery and were offered dead fish on a weekly to bi-weekly basis. Shorter-term captive individuals were housed in metal or plastic containers at the Louisiana State University in Shreveport Museum of Life Science and were also offered fish weekly to bi-weekly. Remaining individuals were housed similarly as shorter-term captives and released within 1–2 days of capture. I released resident turtles at their capture locations, and released translocated turtles at a single location at the edge of the shoreline at the RRNWR. Turtles were tracked 1–4 times per week during May–October (2005) and March–April (2006), and 1–2 times every 2 weeks during November–February (2005–2006), all time and weather permitting. Turtles were relocated from a 4.3-m boat using an R-1000 receiver (Communications Specialists, Inc., Orange, CA) and folding 3-element Yagi antenna (Wildlife Materials, Inc., Murphysboro, IL). The location of each telemetry check was recorded with a handheld GPS unit (Trimble GeoXT, ArcPad 6.1, ± 1 m accuracy) and water depth was measured using a lead line (± 0.1 m). I recaptured telemetered turtles using nets, poles, and by hand during March–April 2006. Recaptured turtles were re-weighed and measured, and their transmitters and all epoxy residue removed. Resident turtles were released at their last point of telemetry relocation, and translocated turtles that were recovered were released at their last known location of native capture. I determined distance moved between relocations using ArcView 3.3 (ESRI, Redlands, CA). Because of the highly aquatic nature of M. temminckii (Reed et al. 2002), movement paths were restricted to aquatic routes (i.e., paths between two locations were not allowed to cross land). I divided the distance between relocation points by the number of days between each relocation event (corrected movement distance). Individual M. temminckii become sedentary during the colder winter months and may exhibit long periods of inactivity or little movement (Harrel et al. 1996, Riedle et al. 2006). I did not include inactive season movements/ non-movements or depths when calculating summary statistics. A turtle was defined as inactive if it did not move for >1 week during the months of October–February. Results and Discussion I captured 8 M. temminckii (7 in hoop nets, 1 by hand at Cross Lake). In addition, 2 acquired individuals provided a telemetry sample size of 10 (7 resident and 3 translocated turtles). One subadult animal was lost from telemetric monitoring for 19 days before being located 7 km away. To account for this unusually large movement, I report data for resident individuals both 2010 V. Bogosian 715 Table 1. Residency status and morphology of telemetered turtles near Shreveport, LA, 2005–2006. † indicates individuals acquired from commercial trappers (8/15/04). Turtle Capture Days in Residency Initial Initial Recapture Final Final CL growth Mass change ID Sex date captivity status CL (cm) mass (kg) date CL (cm) mass (kg) (cm/wk) (kg/wk) 170 Male 10/25/2005 2 Resident 46.6 25.8 3/25/2006 46.6 25.5 0.000 -0.014 206 Male 5/2/2005 1 Resident 40.0 17.8 Radio detachment - - - - 231 Subadult 8/8/2005 1 Translocated 25.6 4.1 4/1/2006 26.6 4.2 0.021 0.003 253 Female 8/13/2005 2 Resident 39.8 15.4 4/11/2006 39.8 15.2 0.000 -0.006 271 Female 8/14/2005 2 Resident 35.0 10.4 3/21/2006 35.0 9.2 0.000 -0.039 311 Subadult 3/26/2005 36 Resident 25.8 4.5 4/21/2006 26.3 4.8 0.010 0.006 331 Male † ≥259 Translocated 43.0 22.1 Radio detachment - - - - 353 Female † ≥259 Translocated 36.9 13.0 3/28/2006 37.4 13.2 0.011 0.004 371 Male 3/23/2005 39 Resident 44.3 21.3 3/25/2006 45.0 22.2 0.015 0.019 396 Subadult 3/26/2005 36 Resident 32.7 9.1 3/31/2006 33.3 9.2 0.013 0.002 716 Southeastern Naturalist Vol. 9, No. 4 with and without this individual (where applicable, bracketed data values are means and standard errors that do not include this individual). I obtained 458 telemetry observations, but censored the dataset to include only 288 (248 without the wide-ranging individual) active-season relocations. Observed corrected movement distances (Table 2) were within ranges published in other studies of M. temminckii in Louisiana (resident: 59.4 ± 7.2 m [56.7 ± 7.7 m]; translocated: 60.3 ± 11.9 m), but movement frequency rates were higher than those reported in the literature (84.8 [80.0] and 79.6%, resident and translocated turtles, respectively, compared to a range of values of 26.8 – 65.0% for subadult male and female turtles [Harrel et al. 1996]). The daily movement distances I observed were much lower than those reported by Riedle et al. (2006), potentially due to their study being conducted in a series of small creeks versus the impounded lake my study was conducted in. I could not compare my movement frequency data with Riedle et al. (2006) due to data reporting discrepancies. Turtles in my study may have moved more due to variation in study sites (i.e., Harrel et al. [1996] studied turtles in a flowing water system, and I studied turtles in impoundments). Turtles may have moved more often than telemetry checks detected due to observation rates of less than 1 check per day. Depths selected by resident (0.81 ± 0.03 m [0.80 ± 0.03]) and translocated (1.1 ± 0.2 m) turtles were shallower than values reported by Harrel et al. (1996). I was unable to recapture 2 individuals (both adult males, one per treatment group) due to transmitter detachment. Both recaptured translocated individuals (n = 2) increased in CL (0.016 ± 0.008 cm/week) and mass (0.004 ± 0.001 kg/week), whereas 3 of 6 resident individuals exhibited no growth in CL and lost mass (Table 1). Some turtles (n = 4; 1 translocated, 3 residents) made short (less than 19 m daily corrected distance) and infrequent (< 2 observed movements per individual of both treatment classes) movements during the inactive period. Residency status did not appear to affect the time spent inactive (resident: 100.6 ± 7.1 days, translocated: 107.7 ± 6.2 days). Previous research on the movement of M. temminckii has indicated a tendency to return to the same area and microsites (Harrel et al. 1996, Riedle Table 2. Movement of telemetered turtles near Shreveport, LA, 2005–2006. Turtle ID Sex n movements Mean ± SE m/day 170 Male 11 32.1 ± 8.3 206 Male 43 28.2 ± 4.6 231 Subadult 24 18.4 ± 1.7 253 Female 27 44.0 ± 13.1 271 Female 19 38.1 ± 10.9 311 Subadult 39 71.7 ± 19.6 331 Male 38 77.7 ± 26.4 353 Female 41 84.7 ± 14.6 371 Male 39 143.3 ± 29.9 396 Subadult 46 31.0 ± 7.4 2010 V. Bogosian 717 et al. 2006, Sloan and Taylor 1987). Overall, my observations did not detect many instances of movement away from and returning to a specific site, but the low frequency of telemetry observations may have missed short forays away from a preferred location. Individuals occasionally returned to the same approximate areas, but I did not find them at the same structure more than once. Homing is often exhibited by terrestrial chelonians (Berry 1986) and occasionally by aquatic chelonians (DeRosa and Taylor 1980) after translocation. The origin of some translocated turtles in this study was unknown, and intentionally attempting to prevent homing response by translocationsite selection prevents interpretation of movement in terms of homing. Large movement distances were noted for one turtle (individual 331) following release at the RRNWR, but these were not consistently in any one direction. The other translocated individuals did not move as far in the first 24 hours following release. Additionally, long-distance movement of resident M. temminckii have been observed by researchers (Boundy and Kennedy 2006, Riedle et al. 2006), suggesting that occasional long movements may be typical behavior for some individuals. Translocated turtles did not select the deepest habitat available. The translocation site did not have high availability of cypress-buttonbush habitat (or equivalent overhanging canopy), which M. temminckii prefer (Harrel et al. 1996, Howey and Dinkelacker 2009, Sloan and Taylor 1987, Riedle et al. 2006), whereas the resident site did. Use of areas with overhanging vegetation by M. temminckii is probably related to physiological requirements (i.e., thermoregulation; Riedle et al. 2006), but the lack of such habitat at the translocation site did not appear to cause turtles to occupy deeper portions of the lake. The influence of a high drought period most likely influenced depth use by all turtles in this study. In the late summer of 2005, both study sites experienced considerable water depth reduction due to drought. Summer 2005 was one of the lowest periods of rainfall on record for the Shreveport area (National Climatic Data Center, www.ncdc.noaa.gov), and all study sites experienced mild to moderate desiccation, but experienced high rainfall events during hurricanes in the fall. These unusual hydrologic events may have influenced movements and depth occupancy. The rates of growth and mass change were probably influenced by several factors, including age class, period of observation, and date of recapture. The fact that relocated individuals gained mass and length indicates that they can effectively forage in novel environments. The growth rates were lower than reported mean growth values (0.03 cm/week CL, n = 3; Harrel et al. 1997) for M. temminckii for either treatment group, potentially due to shorter monitoring periods and time in captivity. Overwinter survival of translocated individuals taken together with increased mass and shell dimensions the following spring suggests translocated individuals were able to locate suitable overwinter sites. 718 Southeastern Naturalist Vol. 9, No. 4 My results suggest that translocated M. temminckii can find suitable habitat to experience growth despite abundant non-preferred habitat types at release sites. However, these results can only be interpreted in shortterm temporal settings. Premature claims of success have been noted in literature involving herpetofauna translocation (Dodd and Seigel 1991), and interpretation of these results as support for translocation of M. temminckii without further research or longer post-release monitoring is discouraged. Additional data (i.e., population structure, rates of dispersal, nesting and recruitment rates) must be collected and analyzed from both resident and translocated populations before managers and scientists can determine if conservation resources are best used in attempting to re-establish M. temminckii populations by headstarting programs, translocations, or repatriations. Acknowledgments All research activities were funded by a Louisiana Department of Wildlife and Fisheries grant (state wildlife grant T24, M. McCallum, initial principal investigator [2004], L.M. Hardy, principal investigator [2005–2006]) and were conducted according to guidelines provided by the Society for the Study of Amphibians and Reptiles. Assistance in the field and laboratory was rendered by A. Crnkovic, M. Hamilton, J. Lewis, M. Lewis, A. Menasco, R. Menasco, H. Neve, N. Neve, C. Spaulding, H. Spaulding, C. Sumner, J. Waguespack, and E. Walsh. Assistance with boat motors was provided by J. Bertrand and A. 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