Status and Distribution of the Angonoka Tortoise (Geochelone Yniphora) of Western Madagascar

Biological Conservation 91 (1999) 23±33 www.elsevier.com/locate/biocon Status and distribution of the angonoka tortoise (Geochelone yniphora) of western Madagascar Lora L. Smith a,b,*, Don Reid b, Bourou Robert c, Mahatoly Joby c, Sibo CleÂ ment c aDepartment of Wildlife Ecology and Conservation, University of Florida, Gainesville, FL 32611, USA bJersey Wildlife Preservation Trust, Les AugreÂs Manor, Trinity, Jersey JE3 5BP Channel Islands, UK cJersey Wildlife Preservation Trust, B.P. 8511, Antananarivo 101, Madagascar Received 26 October 1998; received in revised form 27 February 1999; accepted 2 March 1999 Abstract From 1993 to 1995, ®eld surveys were conducted in western Madagascar to assess the current status of the angonoka tortoise (Geochelone yniphora) in the wild. Tortoise presence was documented at 10 of 11 localities surveyed. These localities represent at least ®ve populations, all within a 30-km radius of Baly Bay, near the town of Soalala. The populations occur on fragments of habitat ranging from <50 to 4±6000 ha in size. One hundred and forty-®ve tortoises were marked in the ®ve populations. Hatchling or juvenile tortoises were observed in all populations, indicating that reproduction was occurring. Most of the 145 tortoises (68%) were marked on Cape Sada, where monthly surveys were conducted. The tortoise density on the c. 150 ha peninsula was 0.66 tortoises/ha. The remains of 22 dead juveniles were found on Cape Sada over the 2-year period. This evidence, combined with the low number of juveniles in intermediate size classes in the Cape Sada population suggests that juvenile mortality may be high. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Testudines; Testudinidae; Geochelone yniphora; Angonoka; Ploughshare tortoise; Madagascar 1. Introduction southwest Madagascar (Vaillant, 1889). The natural distribution of the species was not discovered until the The angonoka or ploughshare tortoise (Geochelone early 20th Century when Voeltzkow (Siebenrock, 1903) yniphora) is considered one of the rarest tortoises in the collected a wild specimen at Cape Sada in northwestern world (Angel, 1931; Juvik et al., 1981; Groombridge, Madagascar. 1982; Curl, 1986a; Durrell et al., 1989). This species has Although the natural range of the angonoka was dis- a distinctly domed carapace (Fig. 1) and received its covered in the early 20th Century, little was known of English common name from its single elongate gular the status of wild populations until the 1970s when a projection. The angonoka is endemic to Madagascar series of ®eld surveys in the Baly Bay region were con- and occurs only in bamboo-scrub habitat in the Baly ducted (Juvik and Blanc, 1974; Juvik et al., 1981). They Bay region in the western part of the island (Blanc, estimated that the population density of G. yniphora 1974; Juvik, et al., 1981; Curl et al., 1985). All known was unlikely to exceed ®ve tortoises per km2. They fur- localities of G. yniphora occur within a 30-km radius of ther estimated that with <100-km2 of habitat remaining, Baly Bay. Geochelone yniphora was ®rst described from the total population size was likely to be no more than a specimens obtained from Arab sailors in the Comoro few hundred tortoises. In 1983, Curl et al (1985) con- Islands in 1884 (Vaillant, 1889). The specimens were ducted ®eld surveys and verbal interviews in the region thought to have originated from an island north-north- and estimated that as few as 100±400 angonoka existed east of Comoro, in the vicinity of Aldabra. A later spe- in the wild and that only 40±80-km2 of bamboo-scrub cimen was thought to have come from Tulear in habitat remained. Later surveys primarily were focused at Cape Sada, the most accessible tortoise population (Reid, 1991; Reid, 1993; Juvik et al., 1997). Results of * Corresponding author. these surveys suggested that the Cape Sada population E-mail address: angonoka@u¯.edu (L.L. Smith) was very small (<30 individuals) and vulnerable. 0006-3207/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0006-3207(99)00044-0 24 L.L. Smith et al. / Biological Conservation 91 (1999) 23±33 the program was to establish a secure breeding population of tortoises, with the intent of augmenting wild populations if necessary. In 1993, a 2-year ecological study of the Cape Sada angonoka population was initi- ated. In 1994 and 1995 JWPT ®eld teams conducted regional surveys to assess the status of all wild populations of angonoka. This paper summarizes the results of these surveys. 2. Methods 2.1. Description of study area The study area, hereafter referred to as the Baly Bay region, is located on the west coast of Madagascar c. 90- km south of the city of Mahajanga (lat. 16 2' S, long. 45 20' E). The climate in the Baly Bay region is tropical with a distinctly seasonal rainfall pattern. Nearly all rainfall occurs in the 6-month period from November to April (Donque, 1972). The mean annual temperature at the town of Soalala on Baly Bay is 26.5C, with monthly means ranging from 26CinJulyto28Cin April. Dry deciduous forest, savanna, and mangrove swamps are three distinct vegetation types in the Baly Bay region. The bamboo-scrub habitat of the angonoka Fig. 1. Bourou Robert with an adult angonoka (Geochelone yniphora) may be a secondary stage of the dry deciduous forest from Cape Sada. (Curl et al., 1985). Bamboo-scrub habitat consists of a mosaic of shrubs, bamboo, savanna grasses, and open, The reasons for the rarity of the angonoka are not unvegetated areas. The shrubs are generally <2-m in fully understood. However, past commercial exploita- height, and the most common species are Bauhinia sp. tion may have been a contributing factor. Historic and Terminalia spp. Bamboo (Perrierbambos mada- records indicate that during the 17th Century, large gascariensis) occurs in dense thickets within the habitat. numbers of G. yniphora were exported to the Comoro A few shrubs and satrana palms (Hyphaene shatan) are Islands where they were sold as food (Vaillant and interspersed in the bamboo thickets, but ground cover Grandidier, 1910). Today, local people generally do not vegetation is largely absent. Small savanna-like patches eat angonoka and because the species has become so and unvegetated rocky areas occur within the scrub- rare, commercial trade is minimal. However, tortoises shrub habitat. Grasses in the savanna-like patches are sometimes kept as pets by local people (Durbin et include Aristida sp., Eragrostis sp., and Heteropogon al., 1996). Additional factors that may have contributed contortus. to the endangered status of the angonoka include habitat loss as a result of anthropogenic brush ®res and 2.2. Data collection predation of eggs and young tortoises by the non-native African bush pig (Potamochoerus larvatus) (Juvik et al., In 1993, a ®eld research station was established at 1981; Groombridge, 1982; Curl et al., 1985; Durrell et Cape Sada, on the eastern side of Baly Bay (Fig. 2). al., 1989). Brush ®res are set to promote growth of Detailed ecological data were collected on the Cape grasses for free ranging cattle and to drive cattle from Sada angonoka population from October 1993 to June the forest. Fires also are used to maintain a clearing 1995 (Smith, 1995; Smith et al., in press). The research around vegetable gardens to keep bush pigs away station also was used as a base from which regional (Durbin et al., 1996). The African bush pig is wide- tortoise surveys were conducted. spread in the Baly Bay region (Juvik et al., 1997). Regional ®eld surveys were conducted from October In 1986, Jersey Wildlife Preservation Trust (JWPT), 1994 through April 1995 at 11 localities. Areas surveyed in collaboration with the Malagasy Direction des Eaux were chosen based on both historic records and on et ForeÃts, began a captive breeding program for the interviews with local villagers. Surveys were con- angonoka in Madagascar (Curl, 1986b). The purpose of centrated in the wet season (from December to April), L.L. Smith et al. / Biological Conservation 91 (1999) 23±33 25 Fig. 2. Map of the study area depicting localities of the angonoka tortoise Geochelone yniphora in western Madagascar. All localities occur in a 30 km radius of Baly Bay. when angonoka are most active. The localities surveyed apart, depending upon the density of the vegetation. In and ®eld trip dates are listed in Table 1. Surveys were heavily vegetated areas, where visibility was low, trans- conducted monthly at Cape Sada (from October 1993 to ects were as close as necessary to search each area thor- March 1995), in an attempt to mark all individuals in oughly. The number of survey participants ranged from the population. All surveys generally were conducted three to seven individuals including trained ®eld biolo- between 0600±1100 h and 1500±1800 h. gists and local guides. To minimize observer variation, at The bamboo-scrub habitat contains impenetrable least three highly experienced observers were used for all patches of shrubs and bamboo that precluded the use of surveys. Local guides typically had no formal training formal transect surveys. Rather than clear transects but were familiar with the terrain and habits of ango- through the habitat, surveys in this study consisted of noka. The observation rate for each area was calculated timed searches for tortoises. During these searches, par- as the number of tortoises observed per survey-hour. ticipants walked roughly parallel transects looking for When a tortoise was encountered, the date, time, tortoises,

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