Ecosystem Integrity And Fish Population Dynamics Of River Awach Kibuon: Towards Management Of Lake Victoria Basin

Abstract

Healthy rivers provide important ecosystem services and goods to the society. However, most medium-sized rivers worldwide are degraded by anthropogenic activities thereby reducing their usefulness. One such river is the 52-km long Awach Kibuon that drains the southern part of Lake Victoria Basin, Kenya. It provides water and fish to the riparian Gusii and Luo communities. However, its ecological health is threatened by poor anthropogenic practices in the basin. This study sought to determine its spatio-temporal ecosystem integrity and fish population dynamics based on water quality assessment, habitat characterization and fish community assessment. Eight monthly sampling surveys were carried out at 9 strategically picked sites along its channel. Purposive and random sampling designs were used to study river ecosystem integrity and fish population dynamics, respectively. Selected physico-chemical parameters were measured in situ using YSI Professional Plus multi-parameter water quality meter. Habitat quality assessment was conducted quantitatively using various tools. Fish samples for ecosystem integrity assessment were obtained by electro-fishing and from commercial catches for population dynamics studies. Fish population parameters (asymptotic length L∞, growth curvature K, growth performance index θ′, exploitation rate E and mortality rates Z, M and F) were estimated by ELEFAN I routines in FISAT II Software Version 1.2.2. The study hypothesized that there are no significant spatio-temporal ecosystem integrity variations and no overexploitation of fish species in River Awach Kibuon. Spatio-temporal variations of physico-chemical parameters were tested using one-way ANOVA and two-sample t-test. Correlations between physico-chemical parameters and fish species abundance were determined by Canonical Correpondence Analysis (CCA). All physico-chemical parameters except pH varied significantly spatially (α ˂ 0.05) but not temporally (α ˃ 0.05). Most parameters conformed to natural longitudinal trends except turbidity, total dissolved solids (TDS) and nutrients whose levels indicated a river undergoing degradation. Habitat quality was poor upstream, moderate midstream and good at the river mouth. Four out of nine stations studied lacked ecosystem integrity characterized by poor habitat quality and low fish species diversity. All the four studied fish populations (Oreochromis nioticus, Synodontis victoriae, Clarias gariepinus and Protopterus aethiopicus) in River Awach Kibuon are overexploited with exploitation rates that are greater than optimum sustainable exploitation rate (E0.5) and maximum sustainable exploitation rate (Emax). There was a strong significant positive association between river Habitat Quality Index (HQI) and Fish Index of Biotic integrity (FIBI) of fish communities in River Awach Kibuon (rs (39) = 0.97, p = .005). Canonical Correspondence Analysis (CCA) indicated that electrical conductivity, total dissolved solids (TDS) and surface water velocity significantly influenced the abundance of fish in River Awach Kibuon (p ˂ .05).The study recommends restoration of natural riparian buffer vegetation, reduction of fishing pressure on all the four overexploited species and close monitoring of fishing activities in riverine fisheries by the State Department of Fisheries and Kenya Fisheries Service to ensure sustainable utilization.