Fish health and community assemblage during drought in lower Zambezi tributaries

Background/Question/Methods   Multi-year droughts in Southern Africa occur on decadal time scales, dramatically altering the hydrology and biology of terrestrial and aquatic ecosystems. The frequency of these droughts is expected to increase given current climatic scenarios. During such droughts, reduced river flows may result in a series of ephemeral pools and little is known about the ecology of fishes in these conditions. Aquatic and riparian habitats are under threat from humans who extract ecosystem services from these environments. In order to understand how changing climate and human development will affect these ecosystems, we need to monitor their current conditions. We investigated riparian and aquatic habitat characteristics in four rivers during a severe drought in Northwest Zimbabwe and examined possible differences in fish health and community assemblage. Results/Conclusions Among the four rivers, riparian vegetation species and structural diversity varied little. However, there were significant differences in water quality, likely due to differing demands for water resources by wildlife, livestock and human populations. More interestingly, differences in fish health between rivers varied significantly by family. Fish of the Cyprinidae family were much healthier in rivers with poor water quality based on two measures of health: body condition score and a health assessment index. Conversely, for Cichlidae, the health indices conflicted. These results provide evidence that habitat quality during severe droughts may affect fish health for certain species. Future development and management of water resources during drought should consider the impact on water quality and fish populations, especially in regions vulnerable to changes in precipitation due to global climate change.