The Kihansi Spray Toad (Nectophrynoides asperginis) was restricted to the smallest known range for any vertebrate species, with an estimated historic wild population of 17,000 toads found within 2 hectares of waterfall spray zone in the Kihansi Gorge of the Udzungwa Mountains in south-central Tanzania. Only discovered by scientists in 1996, the thumbnail-sized golden colored toad was believed to be extirpated from its small patch of habitat in 2004, and was officially declared Extinct in the Wild by the International Union for Conservation of Nature (IUCN) in October 2009.
The Kihansi Spray Toad is unique because of its specialized habitat. It was endemic to Tanzania, in the ‘spray meadows’ at the base of the Kihansi Falls that received more than 70 mm of ‘rain’ per day in the form of spray from the falls prior to the construction of the Lower Kihansi Hydropower Project dam. The species is also rare in the amphibians in that it is oviviparous, which means its life cycle does not include a free swimming tadpole stage, but rather, females give birth to tiny froglets.
The species’ rapid decline followed hydroelectric dam construction upstream from its habitat that resulted in a nearly complete loss of the “spray meadow” habitat that the species depended on, and coincided with the emergence of the amphibian chytrid fungus, a disease that has been implicated in amphibian extinctions in several parts of the world. In November 2000, at the invitation of the Tanzanian Government, 499 toads were collected and transferred to the Wildlife Conservation Society’s Bronx Zoo, and later the Toledo Zoo, to initiate a captive breeding program which is now represented by over 6,000 toads. In 2010, a captive colony was established in Tanzania by University of Dar Salaam and National Environmental Management Council researchers who had facilities constructed specifically for the conservation of the small toad in Dar es Salaam and at the base of the Kihansi Gorge.
In 2010, the Lower Kihansi Environmental Management Project (LKEMP) within Tanzania’s National Environmental Management Council (NEMC) and the University of Dar Salaam organized Tanzanian researchers and an international team of conservation biologists and pathologists from the Toledo Zoo, the Wildlife Conservation Society, the IUCN SSC Amphibian Specialist Group, the IUCN SSC Re-introduction Specialist Group, Global Wildlife Conservation, and other partners to develop a plan for reintroducing the Kihansi Spray Toad to its native habitat. The reintroduction plan set a timeframe to address causes of the KST decline as well as carry out a series of experiments to ensure the species’ survival in the wild. At this stage, preliminary ‘soft’ release studies involving toads within mesh cages situated in the native habitat have shown success.
Prior to its reintroduction, several initiatives were made to restore the Kihansi Gorge ecosystem. These included the installation of an expansive misting system designed to replicate the spray zone habitat that was lost after dam construction, and building of bridges and walkways to facilitate monitoring of the gorge. Funded by the World Bank and the Government of Norway, the misting system has been running since late 2000 in order to restore and maintain the native vegetation that the toads once lived amongst, and the invertebrates upon which they fed.
A third of the world’s approximately 7,000 amphibian species are threatened with extinction. Hundreds of species are thought to have gone extinct within the past few decades due to habitat loss, disease, and other factors. The reintroduction of the Kihansi Spray Toad represents a tremendous success story in amphibian conservation thanks to swift action by the Tanzanian government and an international effort by collaborating organizations. It is one of only a handful of amphibian species, globally, to have been saved from extinction through an intensive captive breeding program. Now that it has returned to its restored habitat, the Kihansi Spray Toad represents the world’s first reintroduction of an ‘Extinct in the Wild’ amphibian.