Monday, March 6, 2006
In two American zoos, 300 Kihansi spray toads, mustard-colored, fingernail-size amphibians from Tanzania, are the last remnants of a species a dam destroyed.
Link: CONSERVATION BIOLOGY: The Lost World of the Kihansi Toad
An excerpt of the Science report:
The Kihansi spray toad is 12,800 kilometers from home: Kihansi Gorge, in Tanzania's remote Udzungwa Mountains. For millions of years a great waterfall filled this gorge with perpetual spray and wind, creating a singular environment where the toad and other endemic creatures lived. In 2000, a hydropower dam cut off 90% of the water, and the ecosystem withered. Since then, scores of scientists in many disciplines have performed elaborate, unprecedented deeds to salvage the toad and its lost world. They have managed to raise the toads in captivity, documented the ecosystem's myriad responses to the dam, and engineered in the gorge what may be the world's largest sprinkler system. Their story shows that although human technology can easily upset nature, even the best science may not suffice to restore it.
The cool, high peaks of the Udzungwas jut from a sea of dry savanna, forming part of the Eastern Arc Biodiversity Hotspot, a crescent-shaped archipelago of nine mountain ranges. Here are some of the world's oldest rainforests, where long isolation and stable climate have given biota tens of millions of years to evolve. Thousands of plants and animals are endemic to the nine ranges, to one range, or, as in Kihansi, one locale. The spray toad has what may be the smallest range of any vertebrate--2 hectares. Some biologists think it has lived in the gorge or nearby for at least 10 million years.
The gorge begins where the Kihansi River plunges 100 meters off an escarpment, then rushes another vertical 750 meters through 4 kilometers of violent twists and cascades. The river flows year-round, whereas the region's other streams disappear in dry season. The slippery cliffs and the water's ferocity long excluded people, allowing the mist-world creatures to live undisturbed and undiscovered.
Steep drop and dependable flow also are ideal for hydropower. In 1983, engineers envisioned diverting water via a dam above the gorge to a turbine-filled tunnel; flow would bypass the gorge and return to the riverbed at the bottom. A survey of the modest 20-hectare proposed reservoir suggested an environmentally benign project, and in 1994, construction began on the $270 million effort, initially funded by World Bank loans. Development banks in Norway, Sweden, and Germany later joined but insisted that downstream biota be surveyed too.
Thus in 1996, with the dam infrastructure already partly built, biologists including herpetologist Kim Howell of the University of Dar es Salaam managed to climb down into several steep, mist-engulfed meadows. Here they found an estimated 50,000 of the skinny, endearing toads, hiding in deep moss mats. Although they have relatives in the region, several unusual features set the toads apart, including flaps over nostrils (possibly to keep out excess spray) and live births (eggs might wash away). Their chit-chit-chit-chit call can ramp up to high frequencies inaudible to humans, possibly to overcome constant low-end waterfall roar, says evolutionary biologist Corinne Richards of the University of Michigan, Ann Arbor. The toads ate hundreds of wetland insect species, most still unidentified. Biologists also found at least four new endemic plants in the gorge, including a new coffee species, plus rare trees and threatened primates and birds.
But even as they explored the gorge world, biologists had scant hope for preserving it. "As soon as we found this place, we knew it would be going extinct," says one foreign consultant--who, like several others, feared being quoted by name because of the fierce politics surrounding the dam. To compensate, biologists sought possible toad transplant sites but turned up nothing. They recommended letting half the river's flow continue to the gorge, but that recommendation was not followed. In 1999, European newspapers got wind of unpublished studies, along with the published description of the toad, Nectophrynoides asperginis. Groups such as Friends of the Earth accused the banks and Tanzania of violating the International Convention on Biological Diversity, which forbids projects that would wipe out species.
The government and lenders compromised. With an added $6 million loan to cover conservation studies and mitigation, the gorge would get 10% of its previous flow. Part was to be channeled into a several-kilometer-long, gravity-fed pipe system snaking down rock walls to the toad meadows, where hundreds of spray nozzles would spurt mist--a setup meant to mimic natural spray with a fraction of the water. Covering a quarter of the toads' original habitat, the sprinklers are "probably the most highly engineered recovery system for any species ever," says William Newmark, a conservation biologist at the Utah Museum of Natural History advising the World Bank.
But the sprinklers were not ready when the water was to be choked off in early 2000. The shutoff proceeded anyway, and by the time the sprinklers came on 9 months later, the ecosystem had dried up catastrophically. Common plants from adjacent dry areas had invaded former spray meadows; mosses had declined almost 95%; insect diversity had dropped; and only 2000 toads were left alive.
Doing the downstream conservation work only after the dam was well under way was a "huge mistake: Planning was not preceded by a thorough and complete environmental impact assessment," admits conservation biologist Wilfred Sarunday, coordinator of Tanzania's Lower Kihansi Environmental Management Project, which oversees studies and mitigation at the gorge....