Influence of waterfalls on patterns of association between trout and Natal cascade frog Hadromophryne natalensis tadpoles in two headwater streams in the uKhahlamba Drakensberg Park World Heritage Site, South Africa

Abstract

Current literature suggests that little, if any, research has been conducted in South Africa to determine the impact of alien trout on indigenous amphibian biodiversity. The aim of this study was to establish whether waterfalls in the uKhahlamba Drakensberg Park, South Africa, are seasonally important in conserving indigenous Natal cascade frog Hadromophryne natalensis tadpole populations from the threat of predation by alien rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta at Injesuthi and Monk's Cowl Nature Reserves, respectively. Relative abundances of trout and tadpoles of Natal cascade frogs were assessed after sampling using electrofishing. Habitat templates were compared for above- versus below-waterfall sites. Trout predation is the most likely causative agent for an observed abrupt decline in H. natalensis tadpole abundance occurring below waterfalls. Tadpole abundance in the study was reduced by a factor of 4.69 and 15.71 below the selected waterfalls at Injesuthi and Monk's Cowl in association with O. mykiss and S. trutta populations, respectively.