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Distribution and Abundance of the Alligator Snapping Turtle (Macrochelys temminckii) in Southwestern Louisiana
Cybil C. Huntzinger, Irvin Louque Jr., Will Selman, Peter V. Lindeman, and Eddie K. Lyons

Southeastern Naturalist, Volume 18, Issue 1 (2019): 65–75

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Southeastern Naturalist 65 C.C. Huntzinger, I. Louque Jr., W. Selman, P.V. Lindeman, and E.K. Lyons 22001199 SOUTHEASTERN NATURALIST Vo1l8.( 118):,6 N5–o7. 51 Distribution and Abundance of the Alligator Snapping Turtle (Macrochelys temminckii) in Southwestern Louisiana Cybil C. Huntzinger1, Irvin Louque Jr.1, Will Selman2,4,*, Peter V. Lindeman3, and Eddie K. Lyons1 Abstract - High harvest rates during the 1900s led to declines of Macrochelys temminckii (Alligator Snapping Turtle) throughout much of its range. Recent research to determine the status of Alligator Snapping Turtles has been completed in some regions of Louisiana, but information is lacking for the southwestern region of the state. To determine the distribution and abundance of Alligator Snapping Turtles in southwestern Louisiana, we conducted trapping efforts in the lower Calcasieu, Mermentau, and lower Sabine river systems from March 2012 through October 2013 using baited hoop nets. In 731 trap nights, we captured 14 individuals (2 M, 4 F, 8 Juv) in the Mermentau and Calcasieu river systems. Our trapping efforts did not detect Alligator Snapping Turtles at Sabine River sites, although one individual was found dead on a fishing hook of a hanging limb line. Our catch per unit effort (CPUE) was 0.021 across the 3 river drainages. Population levels appear to be smaller than observed elsewhere in Louisiana and in neighboring southern states. We recommend that future surveys be conducted to determine population trajectories and that a system be implemented for monitoring commercial fishing bycatch and recrea tional harvest. Introduction Habitat loss, unsustainable harvest rates, environmental pollution, and numerous other threats have led to global declines of many amphibian and reptile species (Gibbons et al. 2000). Overharvesting likely has been one of the leading causes for Macrochelys temminckii (Troost) (Alligator Snapping Turtle) declines throughout the species’ range in the southeastern United States (Pritchard 1989). Following recent taxonomic revision, the range of Alligator Snapping Turtle includes the lower Mississippi River watershed and other major Gulf of Mexico river drainages from the western Florida panhandle to the San Antonio River of Texas (Turtle Taxonomy Working Group 2017). It inhabits major river channels, streams, bayous, oxbows, sloughs, and canals (Pritchard 1989). Because of its large body size and wide geographic distribution, the Alligator Snapping Turtle was heavily harvested for its meat and parts from the 1960s through the 1980s (Pritchard 1989, Sloan and Lovich 1995). Rapid population declines raised concerns among state agencies (Boundy and Kennedy 2006) and led 1Harold and Pearl Dripps School of Agricultural Sciences, McNeese State University, Lake Charles, LA 70605. 2Rockefeller Wildlife Refuge, Louisiana Department of Wildlife and Fisheries, Grand Chenier, LA 70643. 3Department of Biology and Health Sciences, Edinboro University of Pennsylvania, Edinboro, PA 16444. 4Current address - Biology Department, Millsaps College, Jackson, MS 39210. *Corresponding author - will.selman@millsaps.edu. Manuscript Editor: Brad Glorioso Southeastern Naturalist C.C. Huntzinger, I. Louque Jr., W. Selman, P.V. Lindeman, and E.K. Lyons 2019 Vol. 18, No. 1 66 to a ban on commercial harvest and sale of Alligator Snapping Turtle meat in the mid-1990s in most range states (Ernst and Lovich 2009). Among all range states, commercial harvest of Alligator Snapping Turtles was most recently banned in Louisiana in December 2004 (Boundy and Kennedy 2006). Recreational harvest is still permitted in Louisiana with a basic or non-resident fishing license, but take is limited to 1 individual of any size class per day (LDWF 2018). Distribution and abundance surveys for Alligator Snapping Turtles have been conducted in many states throughout its historic range. Studies conducted at the northern periphery of the range suggest declines in Alligator Snapping Turtle populations and a decrease in overall distribution (e.g., Oklahoma [Riedle et al. 2005] and Missouri [Lescher et al. 2013]), including possible extirpation from Kansas (Shipman 1993), Illinois (Bluett et al. 2011), and Kentucky (Baxley et al. 2014). Surveys in the southern portion of the range suggest Alligator Snapping Turtles are still relatively widespread, and higher catch-per-unit-effort (CPUE) results indicate more robust populations than observed in northern portions of the range (Folt and Godwin 2013, Howey and Dinkelacker 2013, Jensen and Birkhead 2003, Moler 1996, Wagner et al. 1996). However, despite this relatively widespread distribution and higher CPUE, population demographics of Alligator Snapping Turtle in portions of Arkansas (Howey and Dinkelacker 2013, Wagner et al. 1996), Florida (Moler 1996), and Georgia (Jensen and Birkhead 2003) are indicative of overharvesting, with a higher relative abundance of juveniles and subadults to adults. Prior field surveys in Louisiana by Boundy (2003, 2008) were completed in southeastern, south-central, and central Louisiana, and these studies found that Alligator Snapping Turtles were in “relatively low abundance” in comparison to other states and had a higher proportion of juvenile turtle captures. There are limited data on the distribution and abundance of Alligator Snapping Turtles in southwestern Louisiana, where only 7 records exist (Battaglia et al. 2015, Boundy 1994, Dundee and Rossman 1989, Ecrement 2011, Williams 2002) from 7 parishes (Acadia, Allen, Beauregard, Calcasieu, Jefferson Davis, Vermilion, and Vernon parishes). Thus, the objective of our study was to determine the distribution and abundance of the Alligator Snapping Turtle in southwestern Louisiana and document morphometrics of captured individuals. Methods We trapped for Alligator Snapping Turtle at 15 sites in southwestern Louisiana in the Calcasieu (n = 6 sites), Mermentau (n = 6 sites), and Sabine (n = 3 sites) river drainages (Fig. 1). We selected sites based on apparently suitable habitat for Alligator Snapping Turtles (Ernst and Lovich 2009, Pritchard 1989) and proximity of available public boat launches. Individual trap locations were chosen near side channels, downed trees, log jams, and mammal lodges. All sites were dominated by Taxodium distichum L. (Baldcypress), Nyssa aquatica L. (Swamp Tupelo), and Acer rubrum L. (Red Maple). Exotic aquatic vegetation was present at our sites in all 3 rivers including Salvinia minima (Baker) (Water Spangles) and S. molesta (Aubl.) (Giant Salvinia), Eichhornia crassipes (Mart. Solms) (Water Hyacinth), Southeastern Naturalist 67 C.C. Huntzinger, I. Louque Jr., W. Selman, P.V. Lindeman, and E.K. Lyons 2019 Vol. 18, No. 1 and Alternanthera philoxerides (Mart. Griseb.) (Alligator Weed). Most sites had silty/muddy bottoms, but 4 upstream sites had more sandy bottoms (sites 1, 2, 14, and 15; Table 1, Fig. 1). We trapped turtles from March to October in 2012 and 2013 using singlethroated hoop nets consisting of four 0.91-m diameter hoops with 2.54–cm mesh Figure 1. Map of southwestern Louisiana showing trapping sites for Alligator Snapping Turtles in the Calcasieu, Mermentau, and Sabine watersheds. Numbers correspond to sites listed in Table 1. Southeastern Naturalist C.C. Huntzinger, I. Louque Jr., W. Selman, P.V. Lindeman, and E.K. Lyons 2019 Vol. 18, No. 1 68 Table 1. Trapping results for turtle species captured from March 2012 through October 2013 in southwestern Louisiana. Abbreviations used: TN = trap nights, CPUE = catch per unit effort, Mt = Macrochelys temminckii (Alligator Snapping Turtle, M = male, F = female, J = juvenile), As = Apalone spinfera LeSueur (Spiny Softshell), Cs = Chelydra serpentina L. (Snapping Turtle), Gs = Graptemys sabinensis Cagle (Sabine Map Turtle), Gp = Graptemys pseudogeographica Gray (False Map Turtle), Ks = Kinosternon subrubrum Lacepède (Eastern Mud Turtle), Ts = Trachemys scripta Thunberg in Schoepff (Pond Slider), Pc = Pseudemys concinna LeConte (River Cooter), Sc = Sternotherus carinatus Gray (Razor-backed Musk Turtle), So = Sternotherus odoratus Latrielle (Eastern Musk Turtle). Site River TN Mt (M,F,J) Mt CPUE As Cs Gs Gp Ks Ts Pc Sc So Total 1. Birds Creek Calcasieu 34 1 (0,1,0) 0.029 0 0 0 0 0 0 0 2 1 4 2. HWY 190 Calcasieu 20 3 (0,0,3) 0.150 1 0 0 1 0 3 0 8 0 16 3. Holbrook Park Calcasieu 12 1 (0,0,1) 0.067 0 0 0 0 0 1 0 0 0 2 4. Houston River Calcasieu 16 2 (0,1,1) 0.077 0 0 0 0 0 2 0 0 0 4 5. Sam Houston Jones S. P. Calcasieu 116 7 (3A,0,4A) 0.056 0 0 2 1 0 2 0 2 0 14 6. White Oak Park Calcasieu 96 0 0.000 0 0 0 0 0 32 0 11 0 43 7. Bayou Nezpique Mermentau 53 0 0.000 0 0 0 0 0 45 0 6 1 52 8. Bayou Plaquemine Brule Mermentau 68 0 0.000 4 0 1 0 1 44 0 4 4 58 9. Lake Arthur Mermentau 34 2 (0,2,0) 0.059 0 0 0 0 1 14 0 4 0 21 10. HWY 14 Mermentau 18 0 0.000 0 0 0 0 0 3 0 1 0 4 11. HWY 90 Mermentau 67 0 0.000 0 0 0 0 0 8 1 5 0 14 12. Meyers Landing Mermentau 8 0 0.000 0 0 0 0 0 0 0 2 0 2 13. Alligator Park Sabine 28 0 0.000 0 0 0 0 0 0 0 1 0 1 14. Nibletts Bluff Park Sabine 109 0 0.000 0 0 0 0 0 28 0 0 0 28 15. HWY 12 Sabine 52 0 0.000 0 1 0 0 0 5 0 1 0 7 TotalA 731 16 0.021 5 1 3 2 2 187 1 47 6 270 ARecaptured M. temminckii individuals (1 male and 1 juvenile) are included. Southeastern Naturalist 69 C.C. Huntzinger, I. Louque Jr., W. Selman, P.V. Lindeman, and E.K. Lyons 2019 Vol. 18, No. 1 netting. At each site, we set 6 to 10 nets and checked them the following 3 mornings. We reset nets on a few occasions due to water-level fluctuations and net theft. We recorded the locations of nets using a handheld GPS unit (Garmin Ltd, Olathe, KS) and generated location maps using ArcMap 9.3 (ESRI, Redlands, CA). Sites on the Sabine River were heavily influenced by the Toledo Bend Dam due to periodic releases of reservoir water. Thus, we relocated traps in this drainage frequently due to rapid changes in water levels. We set nets so that the throats were completely submerged (Bluett et al. 2011, Boundy and Kennedy 2006) and, when possible, to within ~7–15 cm of their tops. To prevent possible drowning of captured turtles, we inserted floats into each net. From March to July 2012, we used canned sardines, canned tuna fish, cat food, and Ictiobus bubalus (Rafinesque) (Smallmouth Buffalo) as bait, but we did not catch any Alligator Snapping Turtles; however, we captured many other local turtle species during this time. The bait type was switched in August 2012 to frozen Brevoortia patronus (Goode) (Gulf Menhaden), and all captures were made with this bait. We changed bait daily. For each individual captured, we measured straight midline carapace length (CL) to the nearest mm using 40- or 60-cm tree calipers (Haglöf; Långsele, Sweden), depending on the CL of the individual. We weighed turtles to the nearest 0.1 kg using a 20-kg spring scale (Pesola; Schindellegi, Switzerland), but a Pesola 100-kg digital hanging scale was used for larger individuals. All individuals were uniquely marked on their posterior marginal scutes with a power drill, photographed, and released. Along with Alligator Snapping Turtles, we also collected similar morphologic data on other turtle species we captured for related studies. We separated Alligator Snapping Turtles into 2 age classes (juvenile and adult) based on CL. All turtles less than 300 mm were considered juveniles (Dobie 1971), and we made no attempt to sex juveniles. Alligator Snapping Turtles are considered sexually mature at ~300 mm CL (Howey and Dinkelacker 2013), and they were sexed by measuring the distance between the base of the plastron and the cloacal aperture (Dobie 1971, Harrel et al. 1996). Results In total, we captured 270 turtles of 10 species in 731 trap nights (Table 1) including 14 individual Alligator Snapping Turtles (an average of 0.018 turtles per trap night [TTN] for new captures); 2 of these individuals were later recaptured (0.021 TTN for all captures). The Calcasieu River had the highest CPUE (12 in 294 TN; 0.041 TTN; 0.048 including recaptures), and we captured Alligator Snapping Turtles at 5 of 6 sites. The Mermentau River had the second highest CPUE (2 in 248 TN; 0.008 TTN), and we captured Alligator Snapping Turtles at only 1 of 6 sites. We did not capture any Alligator Snapping Turtles at Sabine River sites (189 TN), but 1 individual was found dead on the hook of a hanging limb line (aka, bush hook). Alligator Snapping Turtles were confirmed in 6 parishes where records already existed (Allen, Beauregard, Calcasieu, Jefferson Davis, Vermilion, and Vernon). The record for Vermilion Parish is the first with specific locality information Southeastern Naturalist C.C. Huntzinger, I. Louque Jr., W. Selman, P.V. Lindeman, and E.K. Lyons 2019 Vol. 18, No. 1 70 (Boundy 1994). Despite having no captures during the first 5 months of 2012 when we were trying different bait types, we saw no dramatic impacts in the overall trap success across years; catch per unit effort was similar for 2012 (0.018 TTN) and 2013 (0.024 TTN). Of the 14 individuals we captured, 8 were juveniles and 6 were adults (2 males, 4 females), with turtles varying in size from 160 mm to 467 mm CL and from 0.8 kg to 22.9 kg (Table 2). The low number of captures precluded morphological comparisons among drainages or sites. Discussion We confirmed the presence of Alligator Snapping Turtles in all 3 river systems sampled, indicating that they remain relatively widespread in the southwestern portion of the state. However, low overall CPUE suggests low abundance of Alligator Snapping Turtles, and the limited number of captures suggests a population structure skewed towards smaller adults and juveniles in this region. This pattern is similar to what has been found in other areas previously subjected to high harvest pressure (Jensen and Birkhead 2003, Wagner et al. 1996). Though we did not capture Alligator Snapping Turtles at our lower Sabine sites, we were able to confirm the presence of Alligator Snapping Turtles at 1 site where a juvenile was opportunistically found dead on a fishing hook of a hanging limb line (aka, bush hook). Our field efforts on the Sabine River were limited to 3 locations with reliable water levels and boat launches. However, during June 2013 in a related trapping effort, we captured another juvenile (197 mm CL) in the Sabine Table 2. Individual carapace length (CL) and mass across drainages for Macrochelys temminckii (Alligator Snapping Turtle) captured in southwestern Louisiana. Sex ID Drainage CL (cm) Mass (kg) Male 0–12 Calcasieu 46.4 n/a 10–10 Calcasieu 38.7 15.9 Female 11,12–0 Calcasieu 35.0 9.7 400A Calcasieu 39.9 12.6 n/aB Mermentau 41.0 15.6 11–11 Mermentau 40.7 16.8 Juvenile 11–0 Calcasieu 31.6 6.4 12–0 Calcasieu 29.5 5.9 9–0 Calcasieu 25.1 3.7 9,12–0 Calcasieu 23.2 2.9 0–2 Calcasieu 26.6 4.5 11–10 Calcasieu 19.3 1.6 3–0 Calcasieu 26.7 4.1 8–8 Calcasieu 16.9 1.1 AThe ID of this individual was from a different numbering system and was included as part of a related study on Fort Polk. BThis individual drowned in the trap due to a trap float malfunction precluding the need for identification. Southeastern Naturalist 71 C.C. Huntzinger, I. Louque Jr., W. Selman, P.V. Lindeman, and E.K. Lyons 2019 Vol. 18, No. 1 River ~2 river km south of the mouth of Bayou Anacoco (Beauregard Parish; P.V. Lindeman, unpubl. data). We suspect that Alligator Snapping Turtles may occur in lower abundance at our Sabine River sites because of altered river hydrology, including pulsed hydroelectric water releases made from the Toledo Bend Reservoir upstream of our Sabine River sites (e.g., 1.8–2.4 m added depth following releases; LDWF 2017). Additionally, water quality issues in the Sabine River may also impact Alligator Snapping Turtle abundance. For example, a fish consumption advisory due to elevated mercury levels is in effect near our site at Niblett’s Bluff (LDWF 2017). Collectively, these factors may lead to changes in turtle population structure and population fragmentation (Bodie 2001), and may ultimately lead to declines or extirpation. Future surveys should investigate Alligator Snapping Turtle populations above and below reservoirs to document presence or abundance shifts relative to dam operations. In the Mermentau watershed, we captured Alligator Snapping Turtles at only 1 of 6 sites sampled. The Mermentau River has poor water quality, mainly because of urban and suburban runoff, agricultural and silvicultural runoff, and dredging (Holcomb et al. 2015). Since its settlement in the late 1800s, the Mermentau River basin has been transformed from the historic “Cajun Prairie”, where ranching was the most common land use, to an intensively managed agricultural landscape used for rice, sugar cane, and crawfish farming (US Department of Agriculture [2017] as visualized in Cropscape). Declines of aquatic fauna from the Mermentau River system have been described, including the near extirpation of Graptemys pseudogeographica (False Map Turtle; Ilgen et al. 2014) and declines of freshwater mussel species (Vidrine 2010). Our finding of more Alligator Snapping Turtles in the Calcasieu River system is not surprising given that land uses in the basin are less intense than observed in the Mermentau basin. The Calcasieu basin is primarily forested, has less agriculture than the Mermentau watershed, and has no reservoirs on major river tributaries. Thus, riverine processes are intact relative to the other 2 river systems we surveyed. Within the Calcasieu watershed, we captured Alligator Snapping Turtles at 5 of 6 sites, with both sexes and most size classes represented (Table 2). The only site in the drainage where we failed to detect the species was White Oak Park, located on the main channel of the East Fork of the Calcasieu River. Even though the habitat appeared suitable, we did not capture any Alligator Snapping Turtles in 96 trap nights. However, 3 individuals were captured upstream at the Highway 190 site, confirming their presence in the East Fork of the Calcasieu River. Sam Houston Jones State Park, on the West Fork of the Calcasieu River, was our most productive site for Alligator Snapping Turtles (n = 7) in southwestern Louisiana. At both successful and unsuccessful sites, Alligator Snapping Turtles were conspicuously absent from main river channels. We caught all individuals in smaller side channels off the main river channel. Main river channels have multiple boat ramps to provide easy boating access, whereas smaller side channels are more difficult to access by boat. Thus, we suspect that the absence of Alligator Snapping Turtles from main river channels may be due to continued recreational harvest Southeastern Naturalist C.C. Huntzinger, I. Louque Jr., W. Selman, P.V. Lindeman, and E.K. Lyons 2019 Vol. 18, No. 1 72 pressure or incidental take via commercial (e.g., hoop nets submerged below the water surface) or recreational (e.g., trot lines) fishing gear. The presence of recreational fishing activity was evident by the numerous fishing lines (both limb and trot lines) observed on the main river channels. Given the history of overharvesting of Alligator Snapping Turtles, individuals on the main rivers may have been “fished out” during the mid-1900s to early 2000s with only remnant source populations left in backwater areas. Alternatively, big river habitat may be suboptimal for Alligator Snapping Turtles and may lack certain microhabitat features that were not quantified in this study (e.g., submerged deadwood). Indeed, much of the lower Mermentau River system has been extensively modified by channelization (Ilgen et al. 2014). Regardless of the exact scenario, the absence of the species from the main river channels is a concern because the species has been caught in high abundance in other large southeastern US river channels (e.g., Folt and Godwin 2013). In comparison to other regions in Louisiana, southwestern Louisiana has the lowest CPUE (0.021 TTN), two- to fourfold lower than other regions surveyed in the state (southeastern: 0.057 TTN, south-central: 0.046 TTN, northern: 0.088 [Ouachita River] and 0.069 [Red River] TTN; Boundy 2003, 2008; Boundy and Kennedy 2006). In these studies, 541 Alligator Snapping Turtles were trapped in 8421 trap nights at 123 sites (0.064 TTN; Boundy 2003, 2008). However, comparing prior Louisiana data proves difficult due to the use of a professional turtle trapper in other regions of Louisiana (Boundy 2003, 2008; Boundy and Kennedy 2006), whereas a similarly trained individual was not used in this study or prior studies across the rest of the range of the Alligator Snapping Turtle. Presumably, CPUE is likely greater when a more experienced individual is trapping. Low CPUE values and smaller size classes suggest that populations of Alligator Snapping Turtles in southwestern Louisiana (0.021 TTN) and throughout the state of Louisiana (0.046–0.088 TTN) are more similar to other populations studied near the periphery of the species’ geographic range or from historically harvested areas. For example, in the peripheral range state of Oklahoma, Riedle et al. (2005) captured 63 individuals in 1085 TN (0.058 TTN). In Missouri, another peripheral range state, Lescher et al. (2013) documented significantly lower CPUE at 6 sites sampled in 2009 (0.116 TTN) compared to data collected from the same sites in 1993 and 1994 (0.195 TTN, 2 recaptures; Shipman and Riedle 2008). Lescher et al. (2013) also found more juveniles than adults in 2009 and a lower adult CPUE, and this result is similar to that from Louisiana in our study and the study by Boundy and Kennedy (2006). In areas with reported historic commercial harvesting in southern Alabama (e.g., Tensaw River), Folt and Godwin (2013) also reported low CPUE data (0.067 TTN total). For comparison, Folt and Godwin (2013) suggested that one of their sites in Alabama, the Fowl River, may be more representative of historical Alligator Snapping Turtle abundance (0.478 TTN). This CPUE is ~23x greater abundance than what we observed in southwestern Louisiana.. Even though legal commercial harvesting of Alligator Snapping Turtles was eliminated in Louisiana in 2004, anecdotal reports from fishermen in southwestern Louisiana indicate that adult Alligator Snapping Turtles are still legally harvested Southeastern Naturalist 73 C.C. Huntzinger, I. Louque Jr., W. Selman, P.V. Lindeman, and E.K. Lyons 2019 Vol. 18, No. 1 recreationally. It also seems possible that Alligator Snapping Turtles are captured as bycatch or drown in submerged commercial fishing hoop nets (Larocque et al. 2012, Midwood et al. 2015). Consequently, their recovery may be prolonged or compromised in areas still subjected to recreational or incidental harvest. Indeed, Folt et al. (2016) found annual adult survivorship values for males (0.98) and females (0.95) in a stable Georgia population, and they found that the population growth rate of Alligator Snapping Turtle populations is most sensitive to adult survival (i.e., population growth rate decreases with decreased adult survival). Thus, populations of Alligator Snapping Turtles in Louisiana may benefit from additional recreational regulations (e.g., an annual bag limit or seasons or regions closed to harvest) to limit the additional take of individuals from regions that exhibit depressed populations and/or a juvenile-skewed population. In addition, reporting of incidental bycatch by commercial and legal take by recreational fishermen would provide valuable information to help determine the rate, location, and number of individuals that are taken intentionally or incidentally from state waters. If implemented, these collective efforts have the potential to positively impact the conservation and management of Alligator Snapping Turtle populations in Louisiana. Acknowledgments Funding for this project was provided by the Louisiana Department of Wildlife and Fisheries, US Fish and Wildlife Service Division of Scientific Authority, and US Fish and Wildlife Service State Wildlife Grant Program (Grant T–094). This study was conducted under the Louisiana Department of Wildlife and Fisheries Scientific Collecting Permit (LNHP-12-026; LNHP-13-056) and McNeese State University IACUC 14022012. We thank K. Cantrelle, J. Eaker, J. Dupre, and M. Guidry for assisting with field research. We also thank M. Guidry for his added knowledge of the area. A. Bass, S. Holcomb, B. Folt, and 2 anonymous reviewers provided valuable feedback to improve the manuscript. Literature Cited Battaglia, C.D., C.R. Faidley, A.N. Hudson, M.D. Brown, T.M. Pardue, M.L. Reid, A.A. Bass, C.L. Townsend, and J.L. 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