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Listed as Critically Endangered in view of the very restricted area of occupancy (AOO) of 1.5 km2, its small extent of occurrence (EOO) of 25 km2, with all individuals known from only two threat-defined locations that are considered severely fragmented, and a continuing decline in the extent and quality of its habitat.
The distribution of this species was previously thought to extend from the Cape Peninsula to the mountains west of the Breede River Valley in southwestern South Africa. It is now limited to the Cape Peninsula, currently known only from both the Silvermine (known by different names: Kalk Bay Mountain, Muizenberg Mountain, Steenberg Plateau, and Silver Mine Nature Reserve) and Cape of Good Hope sections of the Table Mountain National Park between 60 to 1,000 m asl (Channing et al. 2017). Historically, it was recorded from five breeding sites (as well as a number of single individuals elsewhere) on the Cape Peninsula, with a sixth site discovered in 2010; however, a reduction in the number of sites has been recorded over the last 20 years and recent dedicated surveys have only recovered animals from two breeding sites which are 22 km apart (Cressey et al. 2014). No specimens have been found on Table Mountain itself since 1983 (Cressey et al. 2014).
Its EOO is 25 km2. The furthest record of a toad from either of the two known sites is 600 m (J. Measey and K. Tolley pers. comm. December 2013), suggesting that adults can move at least this distance from the breeding site. Therefore, the AOO was estimated using a buffer of 600 m around each of the sites as 1.5 km2. Naturally-occurring fires in fynbos habitat clears the vegetation and allows breeding sites to expand (K. Tolley and F. Becker, unpub. data 2015). Bush encroachment from lack of fire (in the naturally fire-prone fynbos habitat) and exclusion of grazers as part of the natural ecosystem, apparently caused the contraction of the Silvermine breeding site into a few pools formed in areas disturbed by human foot-traffic. The occurrence of a large bush fire in late February 2015, allowed an opening of the site, and 2015 monitoring indicates that the breeding site size has expanded considerably (from 3 to 17 pools). This cycle is likely to continue and is estimated to represent an extreme fluctuation in the AOO. At the Cape of Good Hope, grazing antelope disturb the vegetation at the breeding site, keeping it free from bush encroachment.
Within the Cape Peninsula only two breeding subpopulations are known, with several other breeding subpopulations having disappeared since the 1980s (Cressey et al. 2014). The declines are enigmatic, as several subpopulations occurred within protected areas and there is no direct link to disease or anthropogenic causes such as habitat loss or fragmentation (Cressey et al. 2014). Tarrant et al. (2013) found no chytrid fungus in the Silvermine subpopulation. The species' population is considered to be severely fragmented as the only two breeding sites are separated by 22 km and a genetic study showed that no mitochondrial haplotypes were shared between them (Cressey et al. 2015).
The species occurs in reasonable numbers at the two currently occupied breeding sites where several hundred males are seen each year (Becker 2014). However, it remains absent from sites with apparently suitable habitat, and this has been validated through ground-truthing those absences, directed by fine scale species distribution models using probability of occurrence at potential sites (Becker 2017). The Silvermine subpopulation has not registered any obvious declines in numbers, but there was previously an inferred decline in the number of mature individuals and low recruitment at the Cape of Good Hope site. This subpopulation appears to have recovered, potentially due to mitigation measures (see threat section) and is likely stable at present (F. Becker and K. Tolley unpub. data 2015). Regardless, an overall 80% population reduction is inferred to have occurred between the 1980s and the 2004 assessment, based on the absence of four breeding subpopulations which can still no longer be found despite searches over the last 10 years.
The main threat identified to this species is the loss, fragmentation and disturbance of its fynbos habitat, due to human disruption of natural processes and direct habitat transformation (Cressey et al. 2014). Direct transformation is no longer a threat, and the remaining populations are within a protected area. However, these toadlets tend to breed in small open patches, and the exclusion of fire for management purposes at some localities in this naturally fire-prone habitat (fynbos) has allowed vegetation to become dense, possibly contributing to local extinctions of formerly known breeding subpopulations. In addition, where present (i.e. Cape of Good Hope) the large mammal fauna cause vegetation disturbance which allow small open patches to persist, and toads tend to breed in these disturbed areas. For these reasons, the loss of the large mammal fauna over the remainder of the Cape Peninsula may be detrimental to the breeding success of this toad. Despite these potential causes, no concrete explanation or threat has been deduced for historical subpopulations now presumed extinct (no individuals recorded from these populations in recent surveys), and so part of this decline still appears enigmatic (Cressey et al. 2014). As all the known individuals are in two subpopulations (corresponding to two locations) with no dispersal between them, they are particularly vulnerable to any stochastic population fluctuation (which is common in toads). For example, the subpopulation at Cape of Good Hope was thought to have low or no recruitment in 2011 due to presumed predation of eggs (Cressey et al. 2014), although that subpopulation has since recovered (Becker 2014), possibly as a result of mitigation measures (see Conservation section). One subpopulation occurs in a public access area and may be negatively impacted by walkers who ignore signs not to enter the area during breeding. It should also be noted that the breeding sites occasionally experience a low rainfall year, and this could impact recruitment, if tadpoles are unable to metamorphose in time to disperse. While such fluctuations are likely natural for this species, the perturbation of the entire system, and the loss of entire breeding sites, make this a potential threat, as there is little to no redundancy in the system.
There are no records of this species being utilized.
Conservation Actions
This species is systematically monitored by South African National Biodiversity Institute and South African National Parks, and it is included in the Table Mountain National Park management plan. The breeding sites are not managed to promote fire and only one breeding site retains grazers in the system. Maintenance of genetic viability over time is essential to mitigate genetic erosion, promote adaptive potential and therefore reduce risk. When inactive, these small toads go largely unnoticed in the environment and assessing presence or absence is expected to be a major impediment to conservation of the species in this genus (Channing et al. 2017).
The Cape of Good Hope population, when originally discovered in 2010, was extremely small with low recruitment. In 2012, predator exclosures were used to mitigate any opportunity for consumption of eggs by small/medium mammals (e.g. mongoose, which were caught on camera trap frequenting the site) and possibly large wading birds. The population began to increase after the introduction of these predator exclosures, and is currently considered large and healthy.
Conservation Needed
Continued and improved management of suitable habitat, especially at the known sites, is required.
Research Needed
Long-term monitoring for population size, distribution and trends, survival rates, life history and ecology, threats and reasons for enigmatic declines is needed.