Geometric tortoise (Psammobates geometricus)

Mohamed bin Zayed Species project number 12253776

Psammobates geometricus is endemic to southwestern South Africa, where it is associated with specific vegetation units in the West Coast Renosterveld and Southwest Fynbos Bioregions (Rutherford et al., 2006). Due to urban and agricultural developments, the species is now restricted to small pockets of natural vegetation west of the Elandsberg Mountains (near Hermon), in the Upper Breede River Valley (near Worcester) and in the Ceres Valley (Baard & Hofmeyr, in press). The geometric tortoise is listed as one of the world’s 25 most endangered tortoises and freshwater turtles (Turtle Conservation Coalition, 2011) and is considered among the 100 most threatened animal, plant and fungi species in the world (Baillie & Butcher 2012).

 

Most habitat fragments are too small to support viable populations and the largest remaining habitat, and geometric tortoise population, occurs west of the Elandsberg Mountains. Population size of this species decreased from several thousand to several hundred over the past 25 years, mainly due to the increasing frequency of wild fires and predation, concurrent with episodes of drought. The situation was compromised further by a wild fire in January 2012 that killed more than 50% of the western population and destroyed most of their habitat. Forty-six tortoises, rescued after the fire, are now held in predator-resistant enclosures of natural vegetation until the habitat has recovered.

 

Although we aim to support the species in all habitat fragments by developing a Biodiversity Management Plan for geometric tortoises, our initial efforts will be focussed on mitigating the effects of the wildfire on the western population.

 

Our objectives for the project supported by the Mohamed bin Zayed Species Conservation Fund included:

• Surveys of the burnt areas to rescue geometric tortoise hatchlings that hatched after the fire during the first autumn rains. These hatchlings will have no or little chance to survive once the first flush of new annual plants dies down in early summer.

• An assessment of geometric tortoise diet to support rescued hatchlings and adults over the next years. We propose to use histological evaluation of plant epidermi in faecal samples to assess diet and food selection.

• To monitor the health of rescued adults and hatchlings, and assess the reproductive status of females. The latter will be done by ultrasound scanning and will commence soon after the first winter rains when geometric tortoise females are known to ovulate (Hofmeyr et al., 2006). Normal follicle development, followed by ovulation and oviposition, would show that the females have adapted to semi-captive conditions and would indicate if a head-start program for geometric tortoises is feasible.

Baard EHW, Hofmeyr MD (in press) Psammobates geometricus (Linnaeus, 1758). In: Bates MF, Branch WR, Bauer AM, Burger M, Marais J, Alexander GJ, de Villiers MS (eds), Atlas and Red List of the Reptiles of South Africa, Lesotho and Swaziland, SANBI, Pretoria.

 

Baillie JEM, Butcher ER (2012) Priceless or worthless? The world’s most threatened species. Zoological Society of London, London.

 

Hofmeyr MD, Henen BT, Baard EHW (2006) Conservation action plan for the Endangered geometric tortoise. Chelonii 4: 101-105.

 

Rutherford MC, Mucina L, Powrie LW (2006) Biomes and bioregions of Southern Africa. In: Mucina L and Rutherford MC (eds), The Vegetation of South Africa, Lesotho and Swaziland. Strelitzia 19, South African National Biodiversity Institute, Pretoria.

 

Turtle Conservation Coalition (2011) Turtles in Trouble: The World’s 25+ Most Endangered Tortoises and Freshwater Turtles—2011. Lunenburg, MA: IUCN/SSC Tortoise and Freshwater Turtle Specialist Group, Turtle Conservation Fund, Turtle Survival Alliance, Turtle Conservancy, Chelonian Research Foundation, Conservation International, Wildlife Conservation Society, and San Diego Zoo Global, 54 pp.