Archives of The Cold Blooded News

The Newsletter of the Colorado Herpetological Society

Volume 33, Number 2;   February, 2006

Back from the Brink?

by Tina Butler

Under the bright florescent lights of the reptile house in the Bronx Zoo of New York, a colorful exotic toad makes its final stand. Once gathering by the thousands in the waterfalls of the Kihansi Gorge of Tanzania, the population of the Kihansi Spray Toad (Nectophrynoides asperginis) now stands at less than 200 individuals (at one point they were thought to be extinct in the wild - MSH Ed.). The hasty construction of a desperately needed dam, built with good intentions by the World Bank, has relegated this species to the fringe of existence.

A decade ago the Kihansi Spray Toad thrived in its thoroughly unique habitat, the waterfalls of the Kihansi River, part of an ecosystem that is one of only 25 Global Biodiversity Hotspots on the planet. (Hotspots are regions noted for their extensive range of species in a very small area.) The gorge is located in the Southern Udzungwa Mountains of South Central Tanzania, which possess the greatest biodiversity in all of Tanzania.

Prior to the construction of the dam, the Kihansi River descended 700 meters through the gorge in a spectacular series of cascades. The spray from the falls maintained an almost constant temperature and humidity to the area and its specifically adapted inhabitants including the Kihansi Spray Toad.

The Kihansi Spray Toad is a dwarf toad, with adults reaching no more than three quarters of an inch long. The diminutive, mustard-colored amphibian notably bypasses the tadpole stage of development and gives birth to purple-hued toadlets.

That the Kihansi Spray Toad possesses this particular .developmental feature -- though not exclusive to the species -- may or may not be a function of the ephemeral nature of its environment. Due to the unique conditions of the spray zone habitat, many endemic species have made adaptations to survive. Another local amphibian, the Torrent Frog, has modified suction mouth parts that enable it to cling to the slick rocks at the base of the falls. The Kihansi Gorge environment was so specialized that the toad has not been found in any surrounding wetlands or gorges. The toad had one of the smallest geographic ranges -- approximately two hectares -- of any four-legged vertebrate species in the world.

Trouble for the toad, then unknown to science, began in the mid 1980s when the Tanzanian power authority took notice of the falls and its potential as a significant power source for the energy-strapped region. In July of 1994, the Tanzanian government began preliminary construction of the 180 mega-watt Lower Kihansi Hydropower Project (LKHP) in order to meet growing electricity demands from mining and tourist industries. The $275 million project was jointly funded by the World Bank and several international development agencies. A year into construction, researchers carrying out the first environmental survey discovered the Kihansi spray toad along with two endemic plant species. Despite the findings, construction continued uninterrupted, and late in 1999, dam operators began diverting water to produce the badly needed electricity. Within six months the original flow of the Kihansi River was reduced to 25 percent, having an immediate impact on the Kihansi Spray Toad. In the absence of the spray, the critically endangered amphibian and at least two endangered plant species, including a type of wild coffee that grew only in the waterfall spray zone, suddenly sat on the brink of extinction.

The decreased river flow caused the spray zone wetlands to rapidly dry out, and Kihansi Spray Toads congregated by the tens of thousands on rocks at the base of the falls, where the minimal bypass flow created a negligible amount of mist. Over 90 percent of the gorge's unique spray zone habitat was destroyed, and the toad counts began to plummet.

To address the collapsing toad population, from July 2000 to March 2001, a sprinkler system was installed over a limited section of the original spray zone wetlands to simulate the cascade's former mist, but the system suffered chronic clogging of sprinkler heads from silt. In the fall of 2000, more aggressive efforts to rescue the toads commenced, primarily through an ex situ or captive breeding program, developed and led by the Wildlife Conservation Society (WCS), a consortium of zoos in the United States. After finalizing an agreement with the Tanzanian Ministry of Natural Resources and Tourism in late November 2001, WCS reptile keeper Jason Searle collected 500 toads which were transported to the Bronx Zoo in New York. 238 of the animals were then transferred to the Detroit Zoo's National Amphibian Conservation Center.

This article is edited from one published on June 7, 2005 by Mongabay.com, who "aims to raise interest in and appreciation of wild lands and wildlife."