Water Level Fluctuations and Fish Yield Variations in Lake Naivasha, Kenya: The Trends and Relationship

Abstract

Water level fluctuations (WLF) influence the distribution and abundance of aquatic species. This study analyzed Lake Naivasha's WLF and fish yield datasets from 1980 to 2019 to determine their trends and interrelationships for sustainable fishery management. Trends detection applied the Mann-Kendall formula, while the effect of WLF on fish yield was tested using simple linear regression. Results show an average annual water level elevation of 1887.4 m above sea level and average annual fish yield of 446.1 tonnes·year-1. Both WLF and fish yield depicted significant monotonic increasing trends (p<0.0001 and p<0.0001, respectively). Fish yield and WLF showed a positive relationship. Simple linear regression confirmed that fish yield could be predicted by trends in WLF. Significant regression equations were found in both direct (p = 0.0227; r2 = 0.1396) and indirect (p = 0.005; r2 = 0.2096) datasets. Periodic WLF affect available fish habitat area and stock abundance, with consequent implications for total annual fish yield. Given the fluctuating water level conditions, effective control of fishing effort in Lake Naivasha is likely to have positive influence on its annual fish yield. Sustainable management of the lake’s fishery resource should include measures aimed at mitigating both human and climate-induced impacts on the lake level.