Exploring the main threats to the threatened African spurred tortoise Centrochelys sulcata in the West African Sahel F ABIO P ETROZZI,EDEM A. ENIANG,GODFREY C. AKANI,NIOKING A MADI E MMANUEL M. HEMA,TOMAS D IAGNE,GABRIEL H OINSOUDÉ S EGNIAGBETO L AURENT C HIRIO,GIOVANNI A MORI and L UCA L UISELLI Abstract The African spurred tortoise Centrochelys sulcata Keywords CITES, conservation, pet trade, Sahel, spurred is the second largest terrestrial turtle, with a scattered distri- tortoise, tortoise–livestock competition, transhumant graz- bution across the West African Sahel. This species is threa- ing system, wildfires tened and declining consistently throughout its range, but The supplementary material for this article can be found on- little is known about the causes of its decline. It has been hy- line at https://doi.org/./S pothesized that the decline is attributable to () competition with domestic cattle, () wildfire, and () the international pet trade. We conducted a series of analyses to investigate these three causes. Hypotheses and were analysed Introduction using a spatially explicit approach, using a database of the Food and Agriculture Organization of the United Nations he African spurred tortoise Centrochelys sulcata and logistic regression modelling; hypothesis was tested T(Plate ) is a native species of the Sahara Desert and by analysing the CITES trade database for –.We the Sahel, where its distribution is fragmented (Trape found a significant negative correlation between intensity et al., ; Petrozzi et al., , ). All populations of − of grazing (expressed as density of cattle, km ) and the this large tortoise (up to kg weight) are reported to be de- presence of spurred tortoises, and this negative effect in- clining, mainly as a result of two independent threats: com- creased when coupled with high fire intensity, whereas wild- petition with domestic livestock for food and space (Branch, fires alone did not have a significant influence on the ), and collection for the pet trade (CITES, ) and for species’ distribution at the global scale. There was a decrease subsistence (Branch, ). The species is categorized as in the annual export of wild individuals for the pet trade Vulnerable on the IUCN Red List (Tortoise & Freshwater after the introduction of export quotas by country and by Turtle Specialist Group, ). year, but trade data must be considered with caution. The hypothesis that cattle are negatively affecting the tortoise’s status and distribution had not been tested previ- ously but is theoretically valid because of the characteristics of the Sahel ecosystem where the species occurs. The Sahel is a transitional ecoregion of semi-arid grasslands, savannahs FABIO PETROZZI*, GODFREY C. AKANI,NIOKING AMADI and LUCA LUISELLI† and thorn shrublands across Burkina Faso, the Central (Corresponding author) Department of Applied and Environmental Biology, African Republic, Chad, Eritrea, Ethiopia, Mali, Rivers State University of Science and Technology, Port Harcourt, Nigeria E-mail [email protected] Mauritania, Niger, Nigeria, Senegal and Sudan (Trape et al., ; Mallon et al., ). In the Sahel, which includes EDEM A. ENIANG Department of Forestry and Natural Environmental Management, Faculty of Agriculture, University of Uyo, Akwa Ibom State, several of the world’s economically poorest regions, most Nigeria people rely on cattle grazing and derivate activities to sur- EMMANUEL M. HEMA Université Ouaga 1 Professeur Joseph Ki ZERBO/CUP-D, vive (Touré et al., ; Barry et al., ; Kagoné, ). laboratoire de Biologie et Ecologie Animales, Ouagadougou, Burkina Faso Two main types of grazing systems tend to coexist in coun- TOMAS DIAGNE African Chelonian Institute, Ngaparou-Mbour, Senegal tries of Sahelian Africa: traditional extensive systems and GABRIEL HOINSOUDÉ SEGNIAGBETO Department of Zoology, Faculty of Sciences, modern, semi-intensive to intensive ones (Kagoné, ). University of Lomé, Togo Traditional systems are low-input systems, with no supple- LAURENT CHIRIO Grasse, France mented food or chemicals being used except during emer- GIOVANNI AMORI National Research Council (CNR) Institute of Ecosystem gency periods when forage availability is scarce. They Studies, Rome, Italy include the transhumant Fulani system (c. % of total cattle *Also at: Ecologia Applicata Italia srl, Rome, Italy stock), sedentary village stock-raising, and stock rearing in †Also at: IDECC–Institute for Development, Ecology, Conservation and Cooperation, via G. Tomasi di Lampedusa 33, I-00144 Rome, Italy developed pastoral areas. In the Fulani system, herds may be Received June . Revision requested July . single-species (Sudanian Fulani zebu) or mixed, with small Accepted September . First published online January . ruminants and cattle, and cattle are fed by opportunistic Oryx, 2018, 52(3), 544–551 © 2017 Fauna & Flora International doi:10.1017/S0030605316001125 Downloaded from https://www.cambridge.org/core. IP address: 170.106.35.93, on 30 Sep 2021 at 14:53:16, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0030605316001125 Threats to the Sahel tortoise 545 were poor and were not considered in the analysis, although spurred tortoises do occur in these countries (Largen & Spawls, ). From these data we deleted records of specimens that were not observed directly in the wild, as indicated in Petrozzi et al. (, ), or from areas where the species is now extinct (e.g. Cameroon; Chirio & LeBreton, ). For each presence point we used the longitude and latitude graticule used by Trape et al. (), in which each grid cell was , km ( × km), in QGIS .. (QGIS Development Team, ). We deleted grid cells with . % of the area covered by sea, leaving cells (n = ). Using QGIS we drew a minimum convex polygon inclu- ‘ ’ PLATE 1 An adult Centrochelys sulcata in the W National Park, sive of all presence points (n = ). Within this we created Niger, West Africa. Photograph by B. Cornelis. random absence points, using QGIS functions (Fig. b). When randomly selected absence grid cells coincided with exploitation of forage resources according to a yearly se- presence cells the cells were replaced with new, random ab- quence of grazing involving five seasons and the various sence cells. Square grid cells (Trape et al., ) were used for types of pasture available (Barry et al., ; Kagoné, both the presence and absence points. ). Both this system and modern intensive grazing are Livestock density distribution data were extrapolated invasive for the natural vegetation of the Sahel and, as a con- from Robinson et al. (). We clipped a raster of cattle sequence, large areas have been altered (Kagoné, ) and density (Robinson et al., ) with a shape file covering many species are threatened (Mallon et al., ). the whole of the species’ range, in which both presence Sahelian pastoralists burn wide areas to facilitate cattle and absence grid cells were included (Fig. c). We then re- grazing, and fires also spread naturally throughout the classified the resulting raster file using the FAO format, with Sahelian region (Behnke, ; Smet & Ward, ; eight classes of density for livestock, yielding eight raster Solomon et al., ). It is predicted that the spread of files. These were transformed into shape files, which were fires may have a negative effect on the distribution of then merged into a single shape file. This was clipped for spurred tortoises throughout the region. each presence and absence grid cell. The hypothesis that the international pet trade may be a All the shape files (classified shape files, merged shape factor in the depletion of spurred tortoise populations had file, and presence and absence grid cells with cattle density) not previously been analysed in depth, as it is difficult to were processed using SpatiaLite v. .. (Furieri, )to test with field data. Nonetheless, CITES data are available correct potential invalid geometries, thus obtaining an out- and may provide some insight into potential conservation put file (.sql) for each grid cell. The .sql files were imported issues. into QGIS and saved as a new shape file to obtain the surface Our aims were () to explore the tortoise–livestock com- of all the classes, both for each grid cell and in total. From petition hypothesis by evaluating whether the distribution the surface of each livestock class in each grid cell we calcu- of spurred tortoises is negatively correlated with the density lated the percentage of cell territory covered by the various of domestic livestock, () to analyse whether there is an ap- classes of livestock density. Eight classes of livestock density parent effect of the spatial distribution of fires on the distri- were used, as also used by FAO. Classes of predicted live- bution of tortoises, and () to analyse the CITES database to stock density (expressed as number of animals per km ), identify general patterns in the international trade of as obtained from the FAO dataset (FAO, ) and used Centrochelys sulcata. in our analyses, were: –; –; –; –; –; –; –; . Methods Fire analysis Data sources and geographical information system (GIS) The distribution of fire across the Sahelian region was calcu- procedures lated using historical MODIS (Moderate-resolution Imaging Spectroradiometer) data (NASA, )for–;fires We extracted distribution data for spurred tortoises in West detected covered at least , m . A point shape file was Africa from the literature (Trape et al., ; Petrozzi et al., clipped, as for cattle distribution,