Conservation introduction of the Cape platanna within the Western Cape, South Africa

Summary

The Cape platanna (Xenopus gilli), an Endangered frog confined to a narrow, disjunct strip of South Africa's southwestern coast, had disappeared from 60% of known localities by the late 1980s, leaving the western population effectively restricted to Cape of Good Hope Nature Reserve. To establish a backup population safe from the invasive common platanna and reduce disease risk, 154 newly metamorphosed frogs from the genetically pure Gilli Dam population were translocated about 25 km to four acid blackwater sites within Silvermine Nature Reserve on 23 April 1988, with most (69) released into Nellie's Pool, judged the most suitable habitat. Monitoring through 1990 confirmed several frogs persisted at Nellie's Pool, but formal records then lapsed for nearly two decades; when researchers returned in 1998, six females were captured and three freeze-branded for future identification, and a subsequent 2008 survey of all four original release sites found frogs present only at Nellie's Pool, including two individuals still bearing 1998 freeze brands. A single female recaptured in August 2011, matched by belly pattern to the same 1998-branded individual, demonstrated the species can survive over 13 years in the wild, suggesting some frogs may be the very animals released in 1988. Major difficulties included finding enough suitable acid blackwater habitat, no lowland habitat restoration, and insufficient funding for systematic monitoring of dispersal or recruitment across the more than 20-year study period. The project rates itself Partially Successful, noting that only one of four release sites sustained a persisting population while the others lacked suitable habitat or held predatory fish.