BIOLOGICAL CONSERVATION
Biological Conservation 124 (2005) 451–461 www.elsevier.com/locate/biocon
Distribution, status, and conservation of radiated tortoises (Geochelone radiata) in Madagascar
Thomas E.J. Leuteritz a,*, Trip Lamb b, Jean Claude Limberaza c
a Department of Biology, George Mason University, Fairfax, VA 22030, USA b Department of Biology, East Carolina University, Greenville, NC 27858, USA c ANGAP, Cap Sainte Marie Special Reserve, BP 28 Taolagnaro (Fort Dauphin) 614, Madagascar
Received 19 April 2004
Abstract
The radiated tortoise, Geochelone radiata, one of MadagascarÕs four endemic tortoises, occupies a narrow band of xeric spiny forest along the islandÕs southwest coast. Traditionally avoided by indigenous tribes, these tortoises are now routinely harvested for food. An accurate assessment of human exploitation remains problematic, however, hindered by limited, dated statistics avail- able on tortoise populations. To update the radiated tortoiseÕs status and distribution, we established a series of line transects at seven localities across its range and implemented a mark-recapture study at one of these localities (Cap Sainte Marie). Tortoises currently range from south of Tulear to east of Cap Sainte Marie, at density estimates spanning 27–5744 tortoises/km2. The mark-recapture estimate for Cap Sainte Marie (1905–2105 tortoises/km2) was substantially higher than its transect estimate (654 tortoises/km2) though comparable to actual tortoise captures (1438) there. Thus, our transect density values probably err as under- estimates, and from these data, we calculate a conservative total population size of 12 million radiated tortoises. We also examined mitochondrial DNA sequences (ND4 gene) for two individuals/locality in a preliminary assessment of genetic variation across the speciesÕ range. Only two ND4 haplotypes were recovered, the more common haplotype representing 13 of the 14 individuals. We offer several conservation recommendations in light of our survey results. Ó 2005 Elsevier Ltd. All rights reserved.
Keywords: Radiated tortoises; Geochelone radiata; Distribution; Density; mtDNA variation; Madagascar
1. Introduction 1996; Nussbaum and Raxworthy, 2000). The tortoiseÕs geographic range is roughly coincident with regions The radiated tortoise or sokatra (Geochelone radiata) occupied by the Mahafaly and Antandroy, local peoples is one of four tortoise species endemic to Madagascar who have a taboo (fady) against touching or eating tor- (Ernst and Barbour, 1989; Juvik, 1975). The tortoiseÕs toises (Brown and Mbola Versene, 1997; Lewis, 1995; natural distribution is limited to xeric spiny forests on Nussbaum and Raxworthy, 2000). However, recent the Mahafaly and Karimbola plateaus of southwestern immigrants from other regions do exploit radiated Madagascar (Iverson, 1992). G. radiata is classified as tortoises, often in large quantities. For example, the ‘‘Vulnerable’’ on the IUCN Red List (Hilton-Taylor, Madagascar big-headed turtle (Erymnochelys madaga- 2000), due to threats posed by overcollecting and habitat scariensis) a freshwater turtle of lowland Western Mad- loss (Durrell et al., 1989b; Baillie and Groombridge, agascar is commonly used as a food source by the Sakalava peoples (Kuchling, 1988). Cart and truckloads * Corresponding author. Tel.: +1 909 335 5383; fax: +1 909 307 6952. of tortoises have been observed in the larger cities, where E-mail address: [email protected] (T.E.J. Leuteritz). tortoise meat is especially popular around Christmas
0006-3207/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.biocon.2005.02.003 452 T.E.J. Leuteritz et al. / Biological Conservation 124 (2005) 451–461
(Lewis, 1995; Nussbaum and Raxworthy, 2000). Many the Manombo River (60 km north of Tulear) and found Malagasy also keep tortoises penned with their chickens populations in the southeast to be highly fragmented and ducks as a means to ward off poultry diseases (Dur- east of Cap Sainte Marie. OÕBrien (2002) corroborated rell et al., 1989b; personal observation). Moreover, radi- these patterns of local extirpation in both northern ated tortoises face standard but significant sources of and eastern termini of the speciesÕ historic range. habitat degradation through deforestation, overgrazing, Prior to 1995, efforts to estimate tortoise populations and charcoal production (Nussbaum and Raxworthy, were limited to incidental counts taken by car, i.e., the 2000). number of tortoises seen along a stretch of road. Lewis Historically, the range of G. radiata encompassed a (1995) conducted a two-month field survey to determine 50 km band along the countryÕs southwestern coast the status of radiated tortoise populations throughout (Decary, 1950), from southeast of Morombe to the their range. His density estimates, derived by transect Bay of Ranofatsy (40 km east of Ambovombe). Offering sampling across five sites, varied from 262.2 to 1076.7 minor revision, Juvik (1975) extended the range north to tortoises/km2, from which he extrapolated a conserva- Morombe but observed that populations were ‘‘severely tive total population size of 1.6–4 million. However, Le- depleted’’ north of the Onilahy River (south of Tulear), wisÕ transects were established along existing trails or and further noted that animals were ‘‘rarely encoun- paths, which can result in nonrandom sampling of hab- tered’’ east of Ambondro or Antaritarika along the itat and thereby generate biased counts. southeastern range terminus (Fig. 1). In a subsequent The purpose of this study was to (1) delimit the cur- survey, Lewis (1995) did not observe tortoises north of rent range of G. radiata; (2) establish a series of transects
Fig. 1. Map of southwestern Madagascar depicting the core range (shaded) of Geochelone radiata. Transect sites, indicated by [], are as follows: 1 – Cap Sainte Marie, 2 – Lavanono, 3 – Ankirikirika, 4 – Nisoa-Ambony, 5 – Lavavolo, 6 – Vohombe, and 7 – Lake Tsimanampetsotsa. T.E.J. Leuteritz et al. / Biological Conservation 124 (2005) 451–461 453 across different sites to assess tortoise densities; and (3) At each chosen site, two transects, at least 1 km use these data to estimate population size, both region- apart, were cut through dry spiny forest habitat at a ally and range-wide. Our survey provides a much- bearing of 45° NW. Transects were 1 m wide and 809– needed update and detailed account on the distribution 2244 m in length, depending on accessibility. General and status of G. radiata, complementing OÕBrien et al.Õs qualitative assessments of floristic composition and hab- (2003) recent view on overexploitation of this species. In itat condition were noted for each site. To insure sight- addition, we conducted a preliminary survey of genetic ing consistency, a local guide, an Association Nationale variation to determine whether G. radiata exhibits any Pour La Gestation Des Aires Protegees (ANGAP) ran- degree of phylogeographic structure. Although the radi- ger, and the primary author walked each transect to- ated tortoise has a restricted distribution, its range is gether twice daily on sunny days during peak tortoise roughly contiguous with another endemic tortoise, activity times, 06:30–10:00 h and 15:30–18:00 h. Surveys Pyxis arachnoides (spider tortoise), for which four sub- were conducted in January and February, during the re- species are recognized. Radiated tortoises do not exhibit gionÕs rainy season and period of greatest tortoise move- distinct morphological variation geographically (Love- ment (Durrell et al., 1989b; Lewis, 1995). ridge and Williams, 1957; Bour, 1978). Nonetheless, Perpendicular distances (from transect line to the ani- their congruent distribution with the polytypic P. arach- mal), sighting distances (from observer to animal at mo- noides suggests some potential for historical population ment of detection), and sighting angles (between transect isolation. This possibility, coupled with the tortoiseÕs line and line of sight of the animal) were recorded using ‘‘Vulnerable’’ IUCN status, underscores the prudence a 100 m tape measure (±0.01 m) and an azimuth com- of a range-wide genetic survey. pass for each animal detected along a transect. Time of capture, size, weight, age, sex, behaviour, and habitat were also recorded. Given the time constraints of com- 2. Methods pleting transect runs, tortoises were simply marked with paint to avoid multiple captures. Data were pooled per 2.1. Line transect surveys activity period per site. Transect data were analyzed using DISTANCE 3.5 Ten potential localities, spanning the speciesÕ range software (Buckland et al., 1993; Thomas et al., 1998) (from Tule´ar to Andohahela National Park), were se- to determine tortoise density and population structure. lected and searched for tortoise sign as well as suitabil- The statistical methodology used for line transect ity for transect sampling (Lewis, 1995; WWF, 1998, analysis is based on Fourier analysis, the accuracy of 1999). These localities were chosen for their accessibil- which depends on four assumptions: (1) objects directly ity, minimally disturbed habitat, and, in certain cases, on the line will not be missed; (2) objects are fixed at the their use in previous transect surveys. Three sites – initial sighting position (i.e., they do not move and are Beheloka and Mahaleotse (SE of Tule´ar), and Ando- not counted more than once); (3) distances and angles hahela National Park (20 km NW of Ft Dauphin, are measured exactly; and (4) all sightings are indepen- 100 km NE of Ambovombe) – were determined to dent (Burnham et al., 1980; Buckland et al., 1993). Tor- have too few (or no) tortoises for survey. Six sites toises lend themselves well to this method of estimation; deemed appropriate were sampled during the1999 field unlike mammals and birds, they do not flush upon season and seventh was surveyed in 2000 (Table 1; detection and therefore do not violate key assumptions Fig. 1). of the model (Akin, 1998; Burnham et al., 1980).
Table 1 Density estimates for Geochelone radiata at seven locations throughout southwest Madagascar in 1999–2000 Location Transect length (m) Estimate (tortoises/km2) % CV df 95% Confidence limits This study Lewis (1995) Cap Ste. Marie 1662 653.7 [563.0] 11.83 16 509.2–839.2 Lavanono 7330 953.1 [713.8] 22.24 9 579.7–1566.8 Ankirikirika 4084 1884.6 [1076.7] 47.46 5 591.6–6003.3 Nisoa-Ambony 4014 3484.5 [N/A] 22.65 7 2053.4–5913.2 Lavavolo 4026 4908.3 [602.0] 21.11 4 2748.8–8764.4 Vohombe 3346 5744.0 [N/A] 45.57 14 2262.4–14,583.0 Lac Tsiman 3035 27.45 [262.2] 99.83 2 0.764–98.276 % CV = percent coefficient of variation; df = degrees of freedom. Respective Transect Locality Universal. Transverse Mercator Coordinates: [38J 0516234m E, 7168436m N]; [38J 0484834m E, 7185622m N]; [38J 0461500m E, 7224967m N]; [38J 0405927m E, 7261719m N]; [38J 0394485m E, 7275308m N]; [38J 0382822m E, 7302362m N]; [38J 0373359m E, 7341547m N]. 454 T.E.J. Leuteritz et al. / Biological Conservation 124 (2005) 451–461
2.2. Mark-recapture survey Shell size measurements (carapace length, weight, third vertebral width, anal notch length, and anal fork In addition to transect analysis, the Cap Sainte Marie width) and observations on color or shell patterns were Reserve (CSM) was also selected for a mark-recapture also noted for each individual tortoise to determine if study. A 1.09 km2 area of the reserve was surveyed daily, any pattern of morphological variation occurred across involving random searches during peak activity times, the geographic range. Because of the time constraint in from December 1998 to May 1999 and again from Jan- running transects (our prime goal), we recorded only a uary to June 2000. Tortoises were hand captured when limited number of morphological measurements. located. Data on date and time of capture, temperature, weather, size, weight, age, sex, behaviour, location, and habitat were recorded for each capture. Using a saw 3. Results blade, we notched the marginal scutes of each tortoise (Cagle, 1939), providing a unique identification code 3.1. Status of geographic range with which to recognize recaptured individuals. The Lincoln–Petersen method (Greenwood, 1996) was We did not observe tortoises north of the Onilahy used to estimate population size at CSM based on all River in the area between the river and National Route original captures in 1999 (n = 1030) and recaptures in 7. However, the carapaces of four harvested tortoises 2000 (n = 434). We chose the Lincoln–Petersen method were found on the south side of the river near Mahale- because it requires only two captures/recaptures, whereas otse. Although we did not survey north of Tule´ar, it is other methods (i.e., Schnabel, Burnham & Overton, possible that some remnant populations might occur Removal, and Jolly-Seber) require multiple captures/ there still. OÕBrien et al. (2003) reported a 20.9% decline recaptures (Greenwood, 1996). in the general range size from JuvikÕs (1975) estimate. Taking this reduction into consideration, radiated tor- 2.3. Genetic analysis toises therefore realistically occur from the Onilahy Riv- er southeast to Ambondro and Antaritarika (25 km east Blood samples were collected from P12 adult tor- of CSM, Fig. 1). toises at six of the transect sites (two tortoises at Lac Tsimanampetsotsa) as well as Andohahela National 3.2. Qualitative habitat assessment of transect sites Park, representing the extreme western end of the range. Blood (0.5 ml) was drawn from the dorsal coccygeal vein Floristic composition of the Ankirikirika, Nisoa- using a 1.0 ml syringe (Haskell and Pokras, 1994) and Ambony, Lavavolo, Vohombe, and Lake Tsimanampet- stored in 0.5 ml of buffer (100 mM Tris, pH 8.0, 100 sotsa sites was typical of healthy spiny forests in mM EDTA, 10 mM NaCl, and 1% SDS). Budgetary southern Madagascar. However, transects running constraints posed limits on the scope of our genetic anal- through rocky outcroppings on these sites often had ysis. Nonetheless, we implemented a sampling design of shorter, more dense vegetation. Habitat profiles at Cap two tortoises per site across all sites to provide range- Sainte Marie and Lavanono were notably different. wide coverage and assess, in a preliminary manner, ge- Cap Sainte Marie is characterized by distinctly dwarfed netic variation and possible phylogeographic structuring vegetation, reflecting its proximity to the ocean. The (Fig. 1). habitat at Lavanono, severely degraded from overgraz- Genomic DNA was extracted from 200 ll of blood ing, consisted largely of Opuntia spp. Visual vegetation using the Qiagen QIAamp DNA Mini kit. Variation in profiles for each site are summarized in Table 2. the mitochondrial ND4 gene was examined using the primers ND4 #2and Leu tRNA of Arevalo et al. 3.3. Estimates of tortoise population size (1994) to amplify 600 base pair segment for DNA se- quence analysis. ND4 segments were amplified under a Density estimates across the seven transect sites ran- thermal cycling regime of 34 cycles at 92 °C for 45 s, ged from 27 to 5744 tortoises/km2, with an overall mean 55 °C for 35 s, and 72 °C for 1 min. Amplification of 2522.2 tortoises/km2 (Table 1). The exact number of products, purified over Centri-sep columns, served as tortoises observed at each location, mean Straight Car- templates in cycle-sequencing reactions employing apace Length (SCL), and proportion of males to females dye-labeled terminators (Big Dye Terminator Cycle to juveniles are listed in Table 3. The smallest morpho- Sequencing Ready Reaction Kit, Applied Biosystems logically distinguishable male was 23.8 cm SCL; all Inc.), followed by electrophoresis in an ABI 377 auto- smaller individuals were classified as juveniles. mated DNA sequencer. Forward and reverse se- The core-area of the tortoiseÕs current range – the quences were generated for each sample and aligned Mahafaly and Karimbola plateaus, from Lake Tsima- using the CLUSTAL X program (Thompson et al., nampetsotsa to Cap Sainte Marie – spans approximately 1997). 10,000–16,000 km2. Based on a vegetation map T.E.J. Leuteritz et al. / Biological Conservation 124 (2005) 451–461 455
Table 2 Predominant vegetation found at the seven transect locations throughout southwest Madagascar Predominant type of vegetation Cap Sainte Marie Lavanono Ankirikirika Nisoa-Ambony Lavavolo Vohombe Lac Tsimanampetsotsa Adansonia spp. Alluaudia ascendens Alluaudia comosa Comiphora spp. Didierea spp. Didierea trollii Erythrophysa aesculina Euphorbia spp. Euphorbia stenoclada Fernando madagascariensis Jatropha mahafaliensis Kalanchoe beharensis Obetia spp. Opuntia spp. Physenna sessiflora Salvadora angustifolia
Table 3 Mean straight carapace length (SCL, cm) and the percent of males/females/juveniles for Geochelone radiata at seven transect locations throughout southwest Madagascar Location Date(s) surveyed N Mean SCL (range) cm % M/F/J Cap Ste. Marie* 8 February 2000 23 24.6 (9.6–36.3) 39.1/8.7/52.2 Lavanono* 19–20 January 1999 28 18.5 (6.4–33.5) 14.3/17.9/67.9 Ankirikirika* 23–25 January 1999 15 30.9 (4.6–36.3) 20/66.7/13.3 Nisoa-Ambony 29–31 January 1999 28 25.0 (5.3–36.7) 35.7/28.6/35.7 Lavavolo 2–4 February 1999 38 19.2 (4.8–34.9) 26.3/18.4/55.3 Vohombe 6–8 February 1999 21 28.5 (5.9–34.8) 38.1/42.9/19.0 Lac Tsiman 11–13 February 1999 1 21.7 0/0/100 Note: *indicate transect not on plateau.
(Faramalala, 1992), much of this area is still probably high juvenile recruitment was observed for CSM covered in typical spiny forest. Applying our transect (Fig. 2). density estimates to an area of 10,000 km2 (as did Lewis, 1995), we calculate an overall population mean of 25 3.4. Incidents of tortoise mortality (95% CI: 12–54) million radiated tortoises. The Lincoln–Petersen population estimate calcu- The remains of 68 tortoises were recovered during lated for CSM (area = 1.09 km2) was 1997 tortoises this project (1998–2000), 36 of which were from CSM re- (95% confidence limits, 1905–2105 tortoises). This is serve. Identifiable causes of mortality at CSM involved equivalent to 1832 tortoises/km2. We captured and non-human (likely canine) predation (19%), disease marked 1438 radiated tortoises (13.3% male, 13.1% fe- (8%), trampling by cattle/goats (8%), vehicular fatality male, 4.2% unknown, and 69.4% juvenile – based on (6%), embryo deaths (6%), and human predation (3%). secondary sexual characteristics) over the two-year Cause of death for the remaining 18 animals (50%) at study (Table 4). A bimodal size class distribution with CSM could not be reliably ascertained though drought
Table 4 Summary statistics of straight carapace length (cm) for radiated tortoises Geochelone radiata at Cap Sainte Marie Reserve, Madagascar Statistics All Males Females Unknown Juveniles N 1438 191 188 60 998 Mean 17.8 31.7 29.4 26.9 12.5 SD 9.4 3.2 2.9 1.5 5.4 Median 15.7 32.2 29.5 25.6 11.5 Min 4.1 23.8 24.0 24.2 4.1 Max 39.5 39.5 36 30.6 24.0 456 T.E.J. Leuteritz et al. / Biological Conservation 124 (2005) 451–461
(1995) assessment. In the northern portion of their range, radiated tortoises have been severely impacted by harvesting for food (Lewis, 1995; Nussbaum and Raxworthy, 2000; personal observation) and the pet trade (Behler, personal communication), especially within a 50 km radius of Tulear. The absence of tortoises in otherwise prime habitat at Mahaleotse on both sides of the Onilahy River, along with significant tortoise de- clines in only four years at Lac Tsimanampetsotsa, underscores the current severity of harvesting near Tulear. As suitable habitat becomes severely fragmented southeast of Ambondro and Antaritarika, so do tortoise populations. Xeric forests end at Ranofatsy Bay where Fig. 2. Size class distribution of Geochelone radiata at Cap Sainte Marie Reserve, Madagascar (n = 1438). Unknown = adultÕs sex not the habitat transitions to rainforest (personal observa- known. tion). In early 1999 the Malagasy National Park Service (ANGAP) conducted a two-month survey at Andohah- ela Parcel II and found only 12 animals, several of which stress was a strong possibly, at least for the large juvenile had tether-holes in their marginal scutes, indicating they contingent. Specifically, 28 of the 36 CSM fatalities in- had been previously released by the Park Service. volved juvenile animals (8.3 cm mean SCL), a third of which were marked. Remains of the 32 tortoises ob- 4.2. Estimates of population density served at other transect sites were all adults, presumably killed by Malagasy harvesters (each shell bore the dis- With the exception of Lac Tsimanampetsotsa, density tinctive carapacial hole from which meat is excised). estimates throughout the tortoiseÕs core range were con- sistently higher in 1999 than those reported by Lewis 3.5. Variation in ND4 gene sequences (1995, Table 1). Mean density for the seven 1999/2000 transects was 2522 tortoises/km2 (1249–5,395 tortoises/ DNA amplification products of the ND4 gene con- km2, 95% confidence interval), whereas that of Lewis sisted of 550 base pairs, from which we resolved a (1995) was 643 tortoises/km2 (366–1233 tortoises/km2, 491 base pair fragment for all samples. Only two haplo- 95% confidence interval). However, the upper limit of types were recovered: one characterized 13 of the 14 spec- the 1995 data and the lower limit of the 1999/2000 data imens surveyed whereas the second, differing by a single are comparable. transition, represented a single animal from Lavavolo Despite recent declines near urban areas and along (GenBank Accession Nos. AY792998–AY792999). Haplo- the range termini, radiated tortoise densities are among types were aligned with ND4 sequence for Geochelone the higher estimates observed among tortoises. For denticulata (AF351693) and subsequently translated into example, its sister species, Geochelone yniphora, from amino acids using MACCLADEv. 4.00 (Maddison and northwest Madagascar (Caccone et al., 1999), exhibits Maddison, 2000). The translated reading frames did density levels of only 66 tortoises/km2 (Smith et al., not exhibit any premature stop codons and showed high 1999). Desert tortoises (Gopherus agassizii) in Nevada amino acid homology (97%) with the ND4 sequence for and California have reported density estimates of 1– G. denticulata. These observations, together with base 184 tortoises/km2 (Luckenbach, 1982; Turner and Berry, usage demonstrating an excess of AÕs (0.3711), support 1984; Haley, 1990; and Woodman et al., 1990). Con- the haplotypesÕ authenticity as mtDNA, as opposed to versely, the chaco tortoise (Geochelone chilensis), a des- nuclear-integrated copies (Zhang and Hewitt, 1996). ert scrubland/ semi-xerophitic forest dweller from With respect to mitochondrial ND4, tortoise samples Argentina, also occurs at relatively high densities (300– demonstrate little population variation and no phylogeo- 400 tortoises/km2, Waller and Micucci, 1997). Aldabran graphic structure. giant tortoises (Geochelone gigantea) have reported den- sities upwards of 16,000 tortoises/km2, with a mean of 3850 (Grubb, 1971; Bourn and Coe, 1978;andSwin- 4. Discussion gland and Lessells, 1979). In addition to the comparable estimates of Lewis (1995), our values are also consistent 4.1. Status of geographic range with a recent report by OÕBrien et al. (2003), who esti- mated densities of 1584 and 2439 tortoises/ km2 from The tortoiseÕs current geographic range appears lar- two line transects (also using DISTANCE sampling) in gely congruent with the region delimited in LewisÕs the far southwest sector of the range. T.E.J. Leuteritz et al. / Biological Conservation 124 (2005) 451–461 457
4.3. Line transect vs. mark-capture estimates at Cap from underestimation. A conservative population esti- Sainte Marie mate of radiated tortoises range-wide would approach the lower end of the confidence interval (i.e., 12 million). Why is there such a difference in density estimates be- As mentioned previously, Lewis (1995) established line tween transect and mark-recapture approaches at CSM, transects along existing trails or paths, a design that and which dataset provides the more accurate assess- can sample habitat non-randomly and bias tortoise ment? Of the four assumptions previously mentioned counts. For example, if tortoises prefer thick spiny forest, for DISTANCE sampling, two are particularly critical where trails are seldom blazed, then their numbers would for tortoise surveys: (1) objects directly on or near the be underestimated. Thus, LewisÕs transect placements centerline will not be missed and (2) distances measured may account in part for his lower density estimates. from centerline to object are accurate (Anderson et al., It should be noted that the accuracy and robustness 2001). Visual obstruction in general difficulties in spot- of the density estimates could be greatly improved by ting small tortoises in particular can lead to underesti- increasing the number of transects across the range. Gi- mation. Using models of juvenile tortoises (65 mm ven both logistical and monetary constraints, our survey SCL), Anderson et al. (2001) tested line transect sam- nonetheless provides the ‘‘best available data’’ for this pling as applied to the estimation of desert tortoise species and may for some time. We acknowledge these (Gopherus agassizii) abundance using artificial tortoise limitations of the study and call for further large scale models. They found that only 46% of juvenile models transect sampling to better estimate population size. were detected on or near the centerline regardless of the surveyorÕs experience. A similar underestimation of 4.4. Mitochondrial ND4 variation among tortoise juveniles and, in turn, overall densities is reflected in populations the 1999–2000 data at CSM. The line transect estimate was 654 tortoises/km2 (509–839 tortoises/km2, 95% conf. Mitochondrial ND4 sequences for the seven popula- interval) with 52.2% juveniles. However, the Lincoln– tions we examined revealed little genetic variation with Petersen estimate was 1997 tortoises/km2 (1905–2105 no phylogeographic structure across the tortoiseÕs range. tortoises/km2, 95% conf. interval) with 69.4% juveniles, Although sequencing additional individuals might well which more accurately reflects the actual number of recover a few additional haplotypes, it seems doubtful CSM captures (1438). Therefore, line transects at CSM that substantial increases in sample size would signifi- appear to be biased toward underestimation. cantly alter the population genetic profile for ND4. We believe that the actual number of tortoises at CSM The absence of deep phylogeographic structure among lies between the transect and Lincoln–Petersen estimates. ND4 sequences is not altogether unexpected, given the The transect method may underestimate numbers but the tortoiseÕs small range, with little in the way of current Lincoln–Petersen, depending on adherence to the meth- or historical physiographic barriers to gene flow. Radi- odÕs assumptions, can bias toward overestimation. Of ated tortoises are capable climbers and can readily tra- the five mark-recapture methods (Schnabel, Burnham verse the regionÕs steep cliffs. Movement between the & Overton, Removal, and Jolly-Seber) we considered, Mahafaly or Karimbola plateaus and the coast occurs only the Jolly-Seber method allows for an open popula- routinely, as does inter-population movement along tion in which gains and losses (i.e., birth, immigration, the coast (personal observation). Furthermore, tortoises death, or emigration) are considered (Seber, 1982). exhibit little morphological variation across the range However, we were unable to use this method because it (Loveridge and Williams, 1957; Bour, 1978), though ani- requires multiple captures/recaptures. If closed mark-re- mals from Ankirikirika are larger (SCL) on average capture methods are applied to open populations (ones than tortoises elsewhere (Table 3; Lewis, 1995). with gains and losses), then their sizes tend to be overes- One could argue that the resolution of ND4 as a genetic timated (Greenwood, 1996). To minimize this bias, we marker might be insufficient for recovering the popula- excluded neonate sightings from the second year tion history of radiated tortoises. Although mitochon- (SCL 6 5.5 cm, n = 30) and recalculated the Lincoln– drial protein genes (cytb, ND5, and ND6), evolving at Petersen estimate. Although the estimate remained the comparable evolutionary rates, proved informative with same (1997), the 95% confidence limits shifted down- regard to the giant Gala´pagos tortoises, Geochelone nigra wards from 1905 to 2105 to 1839–2028. This analytical (Caccone et al., 2002), much of the variation ascribed to adjustments is consistent with our assertion that the ac- these genes occurred between islands. Higher levels of se- tual population size at CSM falls between these two val- quence variation with complementary spatial structuring ues and is closer to the actual count (1438). in G. nigra were resolved from the more rapidly evolving If line transect data at CSM are biased toward under- mitochondrial control region (Caccone et al., 2002; Behe- estimation, then our remaining six transect estimates regaray et al., 2003). We are currently collaborating with likely reflect similar bias. Therefore, the overall popula- M.F. Osentoski (Florida International University) to tion estimate derived from these transects may also suffer generate control region sequences for all our radiated 458 T.E.J. Leuteritz et al. / Biological Conservation 124 (2005) 451–461 tortoise blood samples, as well as pursuing analysis of nu- especially around Christmas and Easter. These men eat clear microsatellite loci, both of which may prove useful in tortoises while collecting and carry back 6–8 tortoises detecting additional genetic variation across the range of each, in sacks attached to sticks (local villagers, personal G. radiata. Given our total population estimate (mini- communication). With demand for tortoise meat on the mally,12 million), it would seem that fine-scale genetic rise, otherwise stable populations can dwindle over a structuring may well be disclosed, unless the current num- short period. Lewis (1995) estimated a density of 262.2 bers of radiated tortoises reflect a marked rebound from tortoises/km2 at the Lac Tsimanampetsotsa Nature Re- some drastic population decline. For example, a genetic serve some 75 km south of Tulear. Just four years later survey of the giant tortoises (Dipsochelys, also known as (1999), we observed more emptied carapaces there than G. gigantea) inhabiting islands in the western Indian living tortoises, and estimated a lower density of 27.5 Ocean revealed extremely low variability for cytb (Austin tortoises/km2. In their recent study on radiated tortoise et al., 2003). Efforts to enhance genetic resolution through harvests, OÕBrien et al. (2003) somberly concluded that control region sequencing and microsatellite assay did not if the current rate of exploitation is not stopped or re- recover additional variation (Palkovacs et al., 2003). Con- duced, tortoises will go extinct in the wild. OÕBrien trol region sequences of the 55 Dipsochelys surveyed were (2002) noted, ‘‘implementing conservation measures invariant, and no genetic structuring was detected among prior to massive reductions in population size is essen- eight microsatellite loci. Based on these genetic findings, tial.’’ Our study supports her assertions. Palkovacs et al. (2003) suggested that extant populations Tortoise habitat destruction is occurring through of Dipsochelys are likely descendants of a very recent bot- over grazing of livestock, clearing of agricultural land, tleneck that followed an earlier but recent founder event. and charcoal production (WWF, 1999; Nussbaum and Control region and microsatellite data should enhance Raxworthy, 2000). Most significant habitat loss comes the population genetic profile of G. radiata, providing from overgrazing by long-horned cattle/zebu (Bos indi- both historical perspective and future management cus), goats (Capra sp.) and sheep (Ovis sp.). Livestock strategy. are an integral part of the semi-sedentary pastoral life- style of the Mahafaly and Antandroy. The Food and Agricultural Organization (FAO) estimates 11 5. Conservation overview million cattle inhabit Madagascar. The ratio of cattle to goats to sheep is believed to be 10:2:1 in the south Worldwide, many tortoise species face similar threats (Kaufmann, 1998). of exploitation for food, medicine, and the pet trade, as Cattle and goats appear to impact tortoises in two well as from habitat destruction and disease. Solutions ways. First, they appear to compete for the same resources to these problems are generally complex because conser- (as is the case with other tortoise species such as Gopherus vation must balance tortoise protection and recovery agassizii and Geochelone chilensis; Coombs, 1979; Medica initiatives with human needs (Swingland and Klemens, et al., 1985; Avery and Neibergs, 1997; Waller and Mic- 1989; McDougal, 2000). If conservation programs are ucci, 1997), although no competition studies have been to succeed, local people must be involved for it is they done on G. radiata. Not only does vegetation serve as a who will remain long after research is completed and food source, it also provides tortoises protective cover conservation actions are implemented (Lusigi, 1980; for thermal regulation. The second effect comes from Harmon, 1987; Swingland and Klemens, 1989; Klemens, trampling; cattle trample down vegetation, compact soil, 1997). Local people should not only be included in the and step on juvenile tortoises. Arid ecosystems recover decision-making process, they must also realize some slowly from such destruction (Avery and Neibergs, gains or benefits (Falloux and Talbot, 1993; Kaufmann, 1997); thus trampling can dramatically affect local tor- 1998). A ‘‘bottom-up’’ approach to conservation should toise populations. Clearly, a major challenge for conser- be implemented, in which support comes from within vation will be striking a balance between and the needs the community (Klemens, 1997). of the Malagasy pastoralists and those of endemic fauna For centuries radiated tortoises experienced little hu- and flora, especially within the parks and reserves. man exploitation, largely because the indigenous Mahafaly and Antandroy held strong taboos (fady) 5.1. Conservation recommendations against eating them. Unfortunately, this taboo does not extend to other Malagasy tribes and immigration 1. Captive propagation and reproductive constraints is slowly desensitizing Mahafaly and Antandroy tradi- Captive breeding for reintroduction is not needed tions. Tortoise meat is cheap (3500FMg $0.70/ani- because reproduction is occurring naturally (Leute- mal), and moreover, large females are preferred ritz and Ravolanaivo, 2005) and tortoise densities because they often contain eggs. are high. Instead, the conservation effort should Pirogues from Tule´ar, Ankilibe, and Andovokampy focus on habitat protection and reduction in tor- move some distance down the coast to harvest tortoises, toise exploitation. T.E.J. Leuteritz et al. / Biological Conservation 124 (2005) 451–461 459
Theoretically, tortoise farming/ranching could meet 1999) into the pet trade because of its similarity to food and pet trade demands, relieving undue pres- radiated tortoises. In addition, a new (November sure on natural populations. Confiscated tortoises 2001) market in the turtle liver trade from South- could serve as breeding stock (e.g., Berenty Private east Asia has spread to Madagascar, placing, for Reserve, Ivoloina Zoo) and sale proceeds could go the first time, harvest pressure on spider tortoises back to law enforcement, local peoples, conserva- and even juvenile radiated tortoises (Behler, 2002). tion, and habitat preservation. Verification of 3. Habitat protection farm-raised animals is a key problem because com- Dogs should be prohibited in reserves and pro- mercial operations can serve as a means to ‘‘laun- tected areas because they kill juvenile and subadult der’’ wild caught animals, as has been the case in tortoises as well as other animals (personal the crocodilian trade (Brazaitis et al., 1998). Pro- observation). ceeds marked for conservation are often diverted The impact of cattle/goat grazing on radiated tor- to farming technology, operating budgets, invest- toises should be determined, including an assessment ment profits, or general governmental funds of possible resource. The first step is to examine the (Brazaitis et al., 1998). In addition, replacement plants eaten by both tortoises and cattle/goats, and (i.e., growth to market size) for such long-lived spe- assess their importance to tortoise survival. cies as tortoises is extremely slow, requiring long Opuntia cactus introduced from South America term investment prior to any generation of income. plays an important role in both tortoise nesting and Large female radiated tortoises are prized across diet. Thirty-two percent of nests (n = 22) located at Madagascar because they offer not only meat but CSM were adjacent to Opuntia (Leuteritz and Ravol- eggs. This preference is unfortunate because larger anaivo, 2005). Opuntia was recorded in 7.6% of feed- females allocate more resources to reproduction, ing observations (n = 172) second only to grasses in mainly in larger eggs (Leuteritz and Ravolanaivo, diet throughout the range (Leuteritz, 2003). 2005). Larger eggs produce larger hatchlings, which 4. Education and awareness demonstrate higher survivorship on average (Jan- Pictorial-based posters, which can be distributed to zen, 1993). Larger hatchlings are probably of restaurants, small stores, schools, police, and local particular importance to species that live in unpre- government offices should be created to stop the dictable environments. In 2000, when rainfall was clubbing of tortoises that enter cultivation sites, to lower than in 1999, female tortoises reduced clutch reinforce taboos (fady), and to stress that it is illegal size but not egg size relative to 1999 (Leuteritz and to eat, sell, or take tortoises. Ravolanaivo, 2005). It thus appears that large eggs are important in the life history strategy of G. rad- iata. These findings emphasize why protection of 5.2. Future direction large females should figure prominently in conser- vation efforts. Further research on reproduction, and population 2. Enforcement of law/regulation of trade dynamics should be undertaken at other localities across Although laws currently exist, enforcement is often the range of G. radiata for comparison purposes. This lax. Establishing road check points at Tulear study, together with OÕBrien (2002), is a start, but basic (which should also include boats), Beloha, and life history data are still lacking and should be addressed Ambondro to intercept tortoise shipments would as an integral part of future conservation efforts. One be an important first step. Radiated tortoises are of the more encouraging aspects of radiated tortoise more often plied as a cheap meat in cities than eaten conservation is that their numbers are still quite high; for subsistence in the wild. Abating tortoise trans- there is time to act before populations experience critical port through checkpoint control may cause prices declines. to rise, discouraging some potential buyers. Despite the fact that population estimates are gen- erally high, the radiated tortoise should not be Acknowledgments delisted from CITES Appendix I. Although delist- ing would facilitate captive breeding, it might open We thank R.A. Mittermeier (CI), G. Arnhold the ‘‘flood-gates’’ to other tortoise trade in Mada- (FOCAL), C. Hamblin-Katnick and the Department gascar. Juvenile tortoises are difficult to identify of Biology (GMU), J.L. Behler (WCS) and A.G.J. Rho- to species and small radiated tortoises are often din (CRF) for their financial support of this project. confused with spider tortoises, P. arachnoids,by Thanks to S. Rajaobelina (FANAMBY) for providing local peoples (personal observation). A further dan- a research vehicle and a driver. ger involves moving the rare ploughshare tortoise, Many thanks to R. Ravolanaivo, my research assis- G. yniphora,(Durrell et al., 1989a; Smith et al., tant, for her countless hours of walking when the Range 460 T.E.J. 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