Analysis of Trophic Levels and Ecosystem Structure of the Kainji Reservoir Using Ecopath Modelling

Ecosystem-level analysis of energy flows and trophic structure provides critical insights for adaptive fisheries management in large reservoir systems that support extensive artisanal fisheries. This study constructs an Ecopath with Ecosim mass-balance model of the Kainji Reservoir ecosystem, Niger State, North Central Nigeria, to characterise trophic structure, energy flow patterns, and the response of fish communities to fishing pressure over historical and projected time periods. Input parameters for the Ecopath model (production to biomass ratios, consumption to biomass ratios, diet composition matrices, and ecotrophic efficiency) are derived from original field sampling, literature values, and unpublished data from the Kainji Lake Research Institute. Functional groups include phytoplankton, periphyton, zooplankton, macroinvertebrates, omnivorous fish (Tilapia species), piscivorous fish (Lates niloticus, Clarias species), and fishing fleets. Field data collection for biomass estimation uses hydroacoustic surveys and gill net sampling at ten stations during the dry and rainy seasons of 2023 to 2024. The calibrated Ecosim time-dynamic model is driven by a fishing effort time series from 1980 to 2024 to reproduce observed historical trends in fish community composition. Scenario analysis evaluates the ecosystem response to 30 percent and 50 percent reductions in fishing effort on Nile perch. Network analysis metrics including Finn cycling index, system omnivory index, and mean trophic level of the catch are computed. Keywords: Ecopath with Ecosim, Kainji Reservoir, trophic structure, ecosystem modelling, fisheries management