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Spray toad reintroduced to Tanzanian gorge

01/11/2012 08:52:45

A diminutive Kihansi spray toad newborn rests on the back of an adult female. Credit: Julie Larsen Maher/Wildlife Conservation Society

Man-made mist recreates toads natural habitat
October 2012. 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 coloured 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.

University of Dar es Salaam professors, Dr. Charles Msuya and Dr. Kim Howell, one of the scientists to discover the toad in 1996, jointly wrote, "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. Very few species of amphibians can survive in this habitat.

Gives birth to live young
The KST is also unusual because its life cycle does not have a free swimming tadpole stage, but rather, females give birth to tiny froglets."

Dam and chytrid fungus probably extirpated wild population
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.

Preliminary ‘soft’ release studies involving toads within mesh cages situated in the native habitat have shown success. Photo credit Global Wildlife Conservation.

Preliminary ‘soft’ release studies involving toads within mesh cages situated in the native habitat have shown success. Photo credit Global Wildlife Conservation.

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.

Misting system replicates spray zone
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.

The missing amphibian that has been the focus of much attention in Tanzania and around the world was returned to its niche within this unique ecosystem on October 30th 2012. The initial release represents a total of 2,500 animals flown to Tanzania from the Toledo and Bronx Zoos in June and earlier this month. The animals made their international journey safely and were acclimatized before their release. Future releases are expected as researchers work towards re-establishing a viable population in the wild.

"Most reintroductions for amphibians and reptiles have been designed to establish or augment a population of a rare species, but it is extremely exciting to be involved in actually returning a species that was extinct in the wild back to its native habitat." said Dr. Kurt Buhlmann and Dr. Tracey Tuberville, research scientists with the University of Georgia's Savannah River Ecology Laboratory.

The reintroduction of the Kihansi Spray Toad is being led by researchers from the University of Dar es Salaam, the National Environment Management Council of Tanzania, and Tanzania Wildlife Research Institute, in international collaboration with scientists from the University of Georgia's Savannah River Ecology Laboratory, Toledo Zoo, Wildlife Conservation Society, IUCN SSC Amphibian Specialist Group, and Global Wildlife Conservation.

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