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Archives of The Cold Blooded NewsThe Newsletter of the Colorado Herpetological SocietyVolume 31, Number 10; October, 2004 |
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Snake Charming Introduced Virus Kihansi Spray Toad Relocated Rattlesnakes Pumiliotoxin Alkaloids Courses in Herpetology Snake Evolution PREVIOUS ISSUES September 2004 August 2004 July 2004 June 2004 May 2004 April 2004 March 2004 February 2004 January 2004 2003 Index 2002 Index Earlier Issues About the Cold Blooded News CHS Home Page |
Decline of the Kihansi Spray Toad, Nectophrynoides asperginis, from the Udzungwa Mountains, Tanzaniaby Che Weldon & Louis H. du PreezReprinted from FrogLog, the newsletter of the Declining Amphibian Populations Task Force, No.62, April 2004.The Kihansi spray toad, Nectophrynoides asperginis, is distinctive in Africa in terms of the habitat it occupies. Its entire known habitat is restricted to less than 5km² of a unique vegetation type. Continuous spray generated by the Kihansi River, as it flows over the Udzunqwa scarp, showers patches of herbaceous vegetation to create a series of spray wetlands. N. asperginis is considered to be critically endangered and is listed under Appendix 1 of the Convention on International Trade on Endangered Species. Concurrent with the description of the Kihansi spray toad in 1998, concerns were felt about the chances of survival of this Tanzanian endemic (Poynton et al. 1998). The spray wetlands were in danger of undergoing severe alteration because of a reduction in water flow due to the requirements of a hydro-power plant. The bypass flow released from the newly constructed dam above the main Kihansi falls was not enough to generate the spray. Consequently, the N. asperginis population experienced a decline in spray toad numbers. The Lower Kihansi Environmental Management Program (LKEMP) instigated the construction of an elaborate sprinkler system to simulate the spray zone conditions. Following these mitigation measures the spray toad population rebounded in the affected areas. During July/August 2003, population numbers of N. asperginis unexpectedly plummeted. The estimated population size was the lowest since the construction of the sprinkler system, causing renewed concern for the survival of the critically endangered spray toad of Kihansi. No apparent explanation could be given for the mass disappearance and the only evidence was a few spray toad carcasses. The dead specimens were collected for post mortem examination. Histological sections of skin tissue revealed the presence of the amphibian chytrid fungus, Batrachochytrium dendrobatidis in some of the specimens. Shortly after this discovery was made, LKEMP assigned an amphibian survey of the Kihansi and the adjacent Udagaji Gorge to determine the status of chytridiomycosis in the remaining spray toads and other anurans. The survey was conducted in November by C.W., Jeremy Thompson (Technical Advisor for LKEMP) and James P. Gibbs (Conservation Biologist, State University of the New York College of Environmental Science and Forestry). More that three months had passed since the last sighting of a live N. asperginis had been made. Despite intensive searching during the day and at night, we did not find any spray toads in any of the spray wetlands where the species is known to occur. Five species of anurans were found through simultaneous searches along streams and amongst forest litter in the gorge: Schoutedenella xenoudactyla, Nectophrynoides tornieri, Afrixalus fornasinii, Arthroleptides yakusini, and Ptychadena aequiplicata. Chytridiomycosis was subsequently detected in P. aequiplicata from Kihansi Gorge and in A. yakusini from Udagaji Gorge. It is suspected that the prevalence of chytridiomycosis in N. asperginis played a role in the species' decline. Mass mortality of amphibians associated with the amphibian chytrid fungus is widely documented. The full extent of the Kihansi decline is not completely understood. Multiple stressors that might have acted in combination with chytridiomycosis are being investigated. The current status of the Kihansi spray toad is unresolved as spray wetlands continue to be monitored by LKEMP staff. The failed efforts to detect N. asperginis could predict the extinction of this species in the wild. Part of the mitigation measures for this species was the establishment of a captive population of spray toads in the United States. In recent months, however, the captive animals have suffered from nutritional disorders, among other setbacks; while numbers are continuing to drop (Lee 2004). An imminent danger is the likelihood that the amphibian chytrid fungus could spread to other amphibians in the region, which could lead to similar results in species that are susceptible to disease. The Udzungwas form part of the Eastern Arc Mountains, a biodiversity hotspot well known for its diverse and endemic amphibian species. A document containing amphibian disease management was compiled for Kihansi Gorge following the survey and discussed for implementation at a panel meeting in Washington D.C. in January 2004. Maintenance of the sprinkler system and monitoring of spray wetlands implies that the opportunity for human induced transmission of the amphibian chytrid fungus remains high. Apart from the advantages of staff and researchers practicing sterilization procedures for the well being of amphibians within Kihansi Gorge, it will restrict the spread of diseases to other areas. Acknowledgements References Contact Copyright © 1998 - 2006, Colorado Herpetological Society. All rights reserved. | ||
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