Abstract:
The resources derived from lotic ecosystems are threatened due to overexploitation by man. This has led to alteration of its habitat, water quality and aquatic biota creating a constant need to assess its integrity for management and conservation. The current study employed use of River Kuja to assess its ecosystem integrity. This is because the river ecosystem is scantly studied despite numerous activities that might be threatening its integrity. Sampling was done for 10 months from November 2016 to August 2017 at seven stations. The stations were selected based on the accessibility and longitudinal human activities done adjacent to the river. Seven physico-chemical parameters were measured and recorded at every station. Nine habitat characteristics were also assessed and used to develop habitat quality index. The selected metrics were rated, scored and summation computed. Fish samples were collected using an electrofisher and a seine net of mesh size 10 mm. The specimens were identified to species level and categorized as exotic or indigenous, rheophilic, tolerant or intolerant species using the standard laid down procedures and literatures. These characteristics were used to come up with a fish-based index of biotic integrity. The twelve metrics were scored and summed up. Fish diversity was estimated using Shannon-Wiener, Simpson, evenness and species richness indices. Data analysis was carried out using statistical package for the social sciences in comparing means and correlating variables. A total of 3920 fish constituting of 27 species were caught. Labeobarbus altianalis was the most dominant species (66.2%) while Amphilius jacksonii, Gnathonemus longibarbis and Barbus paludinosus were the least with 0.026% each. Shannon-Wiener, Simpson and evenness diversity indices generally had an increasing trend downstream. However, species richness had a general decreasing trend downstream. Means for fish-based and habitat quality indices and fish abundance were highest at Kanga, where farming was done as a major activity, with 44.00 ± 1.660, 23.70 ± 0.213, and 169.90 ± 19.904 and lowest at Wath Ong’er, where settlement, water abstraction and mining were practiced, with 26.00 ± 1.890, 11.25 ± 0.164 and 6.13 ± 1.076, respectively. Fish-based index of biotic integrity strongly correlated positively with Shannon-Wiener, habitat quality, species richness and fish abundance. Habitat quality index strongly correlated positively with species richness and fish abundance but showed a strong negative correlation with temperature and total phosphorous. Fish-based index of biotic integrity showed a strong relationship with habitat quality index, fish population size and species richness. This information can be used to monitor the ecosystem integrity other human-induced rivers in Lake Victoria Basin.
