Bioeconomic Modelling of the Kainji Lake Fishery: Optimal Harvest Policies Under Uncertainty

This research developed a bioeconomic model of the Kainji Lake fishery in Niger and Kebbi states, Nigeria, to identify optimal harvest policies under multiple sources of ecological and economic uncertainty. Kainji Lake is Nigeria's largest man-made lake and supports one of the country's most significant inland fisheries, yet its management has proceeded without a quantitative bioeconomic foundation. A Gordon-Schaefer surplus production model was parameterised using 20 years of catch and effort data from state fisheries agencies, supplemented by original stock assessment surveys. Economic parameters including input costs, market prices, and discount rates were derived from primary data collection among 200 artisanal fishing households. Model uncertainty was addressed through a Bayesian estimation framework and stochastic scenario analysis incorporating ecological uncertainty from stock-recruitment variability and economic uncertainty from market price volatility. Optimal control analysis identified harvest paths maximising net present value of the fishery over a 30-year horizon under constraints reflecting community food security minimum yield requirements. Results demonstrated that current fishing effort exceeds the bioeconomically optimal level by approximately 45 percent, and that the fishery is currently operating in a region of economic overfishing. Stochastic simulations confirmed that a precautionary effort reduction of 30 percent, combined with adaptive management responses to annual stock assessment updates, yielded the highest expected present value with acceptable variance. The study delivers the first published bioeconomic model for Kainji Lake and recommends its institutionalisation as a decision-support tool within the Federal Department of Fisheries management planning cycle. Keywords: bioeconomic modelling, Kainji Lake, optimal harvest policy, bioeconomic optimisation, fisheries management