This species is restricted to southeastern South Africa, where it ranges from Manubi State Forest Reserve (Venter and Conradie 2015) in the Eastern Cape Province, to southern and central KwaZulu-Natal Province. It is restricted to lowland riparian forest patches within this range. Its elevational range is between 50 and 900 m asl. Its extent of occurrence (EOO) is 11,631 km2 and its area of occupancy (AOO) is 188 km2.
Habitat and Ecology
It is a habitat specialist, inhabiting rocky streams in dense scarp and gallery forests, where it is usually found close to water, and does not occur in open areas. The species is a semi-arboreal specialist, requiring clear shallow streams with overhanging vegetation and large rocks for egg clump attachment. They are also good swimmers and are well camouflaged in their environment of leaf-litter and rocks. They have extended breeding season from August to June, peaking between December and April (J. Tarrant unpublished data). Males have a very quiet call which they issue from the river bank or elevated positions on rocks or vegetation above the water. Gelatinous masses consisting of 75–95 eggs are deposited on rock surfaces or vegetation overhanging pools. Females have been observed keeping the egg clutches moist with liquid from their cloacas. Tadpoles hatch after about six days and drop into the water to complete development, which takes approximately two months (Kok and Seaman 1989, du Preez 2004).
Little population information is available for this species. It is considered to be severely fragmented as 50% of individuals are in isolated patches and the distances between subpopulations are considered to be too great for dispersal within one generation. A population genetic study has commenced to address these questions, and a monitoring protocol has been developed and tested to help provide information on local abundance and breeding success. Where habitat and conditions are suitable, the species is locally abundant, but does appear sensitive to stressors such as drought and siltation, which affect breeding output (J. Tarrant pers. comm. August 2016). The species is considered to be extinct at sites around Pietermaritzburg, including Chase Valley and Oribi, as searches at the sites have been unable to detect it. Its presence at Kranskop was first and last recorded in 1958 by Poynton; however, there has been little search effort at this site and its presence there remains uncertain.
Much of the forest habitat of this species has been historically lost to sugarcane cultivation and other agriculture, woodcutting, afforestation and urbanization, all of which are ongoing threats to the subpopulations of KwaZulu-Natal Province. Mining of the Marble Delta in in the Oribi/Port Shepstone area is also likely to have caused, and continues to cause, direct habitat loss. It is also threatened by pollution and siltation of streams. An emerging threat includes alien invasive vegetation.
It occurs in several protected areas, including Vernon Crookes, Oribi Gorge, Krantzloof, Umtamvuna, and Umbumbazi Nature Reserves in KwaZulu-Natal and Dwesa-Cwebe Nature Reserve in the Eastern Cape (du Preez 2004). It has more recently been confirmed at Silaka Nature Reserve, Hluleka Nature Reserve and Manubi State Forest in the Eastern Cape (Venter and Conradie 2015), and at Crowned Eagle Conservancy, Springside Nature Reserve and Tanglewood Nature Reserve in KwaZulu-Natal (J. Tarrant pers. comm. August 2016). A monitoring protocol has been developed and implemented at several sites through volunteers, pupils and reserve rangers (Vernon Crookes, Crowned Eagle Conservancy, Silaka, Hluleka, and Dwessa-Cwebe Nature Reserves).
Improvement of the management in place in the protected areas where the species occurs would be important, together with additional habitat and headwater protection.
A priority for conservation research is to estimate the population size of adults in subpopulations, as well as determining the cause of direct threats. Further studies on its population size, distribution and trends, as well as on it's life history and ecology are needed. Additional surveys are need at sites where the species presence is uncertain. A genetic study is currently underway to examine the subpopulation structure and connectivity between the populations (J. Tarrant pers. comm. August 2016). This study also aims to provide information on effective population size, through the analysis of long-term monitoring data, and genetic diversity present within populations.
Red List Status
Listed as Endangered because its area of occupancy (AOO) is 188 km2, its distribution is considered severely fragmented, and there is a continuing decline in both extent and quality of its habitat and area of occupancy.
IUCN SSC Amphibian Specialist Group & South African Frog Re-assessment Group (SA-FRoG) 2016. Natalobatrachus bonebergi. The IUCN Red List of Threatened Species 2016: e.T58076A77159820. http://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T58076A77159820.en .Downloaded on 17 January 2019