Rationale
Extensive surveys by Greig and Burdett (1976) extended the distribution range of Chersobius boulengeri substantially, which led the authors to propose that the species is not rare, as was previously believed, but that individuals were seldom encountered because they were so well camouflaged. The conservation status of C. boulengeri was considered to be Least Concern on the 1996 IUCN Red List (TTWG 2014, 2017), but as possibly Vulnerable at a Tortoise and Freshwater Turtle Specialist Group Red Listing workshop in late 2013. It was subsequently listed as Near Threatened on the IUCN Red List in 2017 based on an earlier 2013 assessment (Hofmeyr and Baard 2014, Bates et al. 2014). Surveys conducted between 2005 and 2017 indicated that most localities (30 of 35) where populations previously occurred no longer harbor viable populations and that the species is no longer being found by farmers. Habitat destruction and degradation maps of South Africa (Hoffman et al. 1999) show that nearly 50% of the range of C. boulengeri is either moderately or severely degraded, which may explain the species’ decline. Chersobius boulengeri is associated with rocky outcrops in specific vegetation types, qualifying it as a habitat specialist, which increases its risk of extinction. The documented population declines will be exacerbated by the effects of climate change and associated vegetation change. Monitoring over recent decades showed that grasses are invading the Karoo, replacing the dwarf shrubs, with an increasing fire-hazard in the habitat (Stevens et al. 2015). The Nama-Karoo is considered the second most threatened biome in South Africa under all climate scenarios. Predictions are that savanna and desert vegetation will expand into large portions of the current biome (Driver et al. 2012; DEA 2013). Such changes would intensify grazing pressure by livestock and reduce food and cover for tortoises. Predation by baboons was high at one site visited during surveys (M. Hofmeyr pers. obs.) and crow predation may be on the increase (Juvik and Hofmeyr 2015). A serious new emerging threat involves shale gas exploration and development, which would require substantial large-scale infrastructure to support the drilling and operation of wells and extraction sites. Based on these factors, C. boulengeri is assessed as Endangered under criterion A4ace, based on an estimate of a reduction in population size of approximately 30% over the past 25 years (one generation), and a projected reduction of at least another 30% over the next 50 years (two generations), for a total reduction over three generations of approximately 60%.