Shifts in composition of fish species of fishery in Lake Naivasha, Kenya: Trend implications for fishing effort, yields and revenue

Abstract

Assessing fisheries resource composition and exploitation trends is vital for the sustainable management of fish stocks. Accordingly, the present study analysed datasets of fish catches and market values from 1991 to 2019, and from 2004 to 2019, respectively, to determine shifts and trends in fish species composition, fishing effort, fish yield and revenue. The annual percentage weight composition and relative biomass of different fish species in the lake were calculated over the study period. Fishery time series data comprised fishing effort, fish yield, catch per unit effort (CPUE), revenue and revenue per unit effort (RPUE). Moving average (MA) trends at 5-year intervals were plotted and the Mann–Kendall (MK) method applied to detect trends at the 95% confidence limit. The results identified shifts in fish species composition during various periods, with Nile tilapia Oreochromis niloticus comprising 94% of the total weight of fish landed in 2019, with an overall mean relative biomass of 4221.4 ± 2229.7 kg/km². The mean total fish catch (1683.5 ± 420 ton/year), CPUE (10.6 ± 2.0 ton/boat/year) and modal effort (176 boats) were highest from 2014 to 2019 period. The fishery revenue increased in 2019 (US$ 4,096,490) with a RPUE of US$ 22,263.5/boat/year. The fishing effort, fish yields, CPUE, revenue and RPUE trends increased significantly (p < .01), likely being related to the shifts in species composition. Lake Naivasha is a learning model for improving fisheries management and yields through stock enhancement interventions. Nevertheless, the increasing level of fishing effort warrants a precautionary approach to ensure sustainability of the fishery resource.