Evaluation of Fish Passage Facilities and Their Effectiveness at Kainji Dam, Niger State

This study evaluates existing fish passage infrastructure and its effectiveness at Kainji Dam on the Niger River in Niger State, located in Nigeria's North Central geopolitical zone. Kainji Dam has been a significant physical barrier to migratory fish for over five decades, and the status and functionality of fish passage facilities installed during dam construction have never been formally evaluated against modern fish passage engineering standards. An engineering and biological assessment was conducted combining physical inspection and hydraulic measurements of the existing bypass channels with upstream and downstream gill net sampling to compare fish community composition and migration indices. Acoustic fish telemetry was deployed for six months using 15 tagged Labeo coubie and Citharinus citharus, species known to perform lateral migrations in the Niger system. Hydraulic assessment revealed that bypass channel water velocities exceeded the maximum sustained swimming speeds of all target migratory species at current discharge levels, rendering the existing structures ineffective. Telemetry data confirmed complete blockage of all tagged individuals attempting to pass the dam. Fish diversity and abundance below the dam were significantly higher than above for migratory species. The study proposes a dam modification feasibility assessment framework and recommends retrofitting with pool-and-weir style fish passes designed to the passage requirements of the dominant migratory species, accompanied by translocation programmes for species with critical upstream spawning habitat requirements. Keywords: fish passage, Kainji Dam, migratory fish, fish barrier, Niger River.