Population trend
Trend
Cape Grysbok are normally solitary and cryptic in their behaviour and therefore seldom seen. They are particularly difficult to see in dense vegetation, which is exacerbated in fire-prone areas such as the fynbos of the Western Cape (Castley and Lloyd 2013). Estimates of population sizes are scarce and it is therefore difficult to extrapolate data from individual studies or locations to discern the status of the population nationally. Some studies are also relatively dated and more recent data are needed. For example, Scott (1991) studied the distribution of small antelopes in De Hoop Nature Reserve between 1985 and 1987 and recorded densities of 0.21 animals / 100 km travelled for Cape Grysbok compared with 2.64 for Steenbok (Raphicerus campestris). Castley and Lloyd (2013) suggest that comparisons such as this may not be accurately accurate estimates of Cape Grysbok populations given their relative lack visibility and dense habitat preferences. Once again this highlights the need for more robust estimates of Cape Grysbok subpopulations from sites throughout their distribution. All indications are however that Cape Grysbok occur “freely” in the landscape—on and off protected areas, on agricultural land, on game farms, and in vineyards.
Based on available habitat, and a requirement of between 6 and 456 ha per animal depending on the vegetation type, Cape Grysbok numbers could be up to 231,448 in the Cape Floristic Region, down from an estimated population of 322,977 in the pre-habitat transformation model (Kerley et al. 2003). This modelled estimate is almost an order of magnitude higher than earlier estimates (East 1999). Current data from CapeNature indicate that Cape Grysbok occur on 58 provincial protected areas, with a total estimated abundance of 1,196 individuals. Using the number of land parcels (2,438) on which Cape Grysbok are either present (720 land parcels) or persist (indicating that the subpopulation is persistent and breeding; 1,718 land parcels) in the Western Cape Province, at the calculated densities of 6 to 456 hectares per animal it is estimated that the 77,269 ha of protected area could sustain between 1,704 to 129,544 animals. In the City of Cape Town area, Cape Grysbok occur in high densities on some relatively small (less than 100 ha) isolated properties, such as False Bay Nature Reserve, Zandvlei, University of the Western Cape and Millerton Race Course. The reduced predation from dogs and natural predators and the lack of competition from Common Duiker (Sylvicapra grimmia) are possible reasons for these elevated densities (C. Dorse pers. comm. 2015). Cape Grysbok are present in Table Mountain National Park (D. Winterton pers. comm. 2015), West Coast National Park (Avery 1990), Bontebok National Park (Novellie et al. 1994), Agulhas National Park (M. Raselabe pers. comm. 2016), Garden Route National Park (L. Moolman-van der Vyver pers. comm. 2016), Baviaanskloof and Groendal Nature Reserve (D. Peinke unpubl. data), and Addo Elephant National Park (AENP) but are absent from Namaqua and Tankwa Karoo National Parks. This is according to the Mammals Tool that the Cape Research Centre produced in 2011, based on putative distribution maps (Skinner and Chimimba 2005), as well as the references mentioned above.
No comprehensive subpopulation trend data are available but the population is suspected to be stable (for example, aerial counts suggest a stable subpopulation on Baviaanskloof Nature Reserve between 2008 and 2014; D. Peinke unpubl. data), although there are indications of localised declines. Anecdotal evidence suggest that numbers of Cape Grysbok and Bushpig (Potamochoerus larvatus) both declined in the Main Camp section of AENP as mega-herbivore numbers increased (Tambling et al. 2013, G. Castley unpubl. data) and no evidence could be found of their presence there in 2014/2015 (G. Kerley unpubl. data).