Acoustic Monitoring of Fish Biodiversity in the Deep Channels of River Niger, Kogi State

Passive acoustic monitoring using underwater hydrophones offers a powerful non-invasive tool for assessing fish biodiversity and habitat use in turbid freshwater environments where visual survey methods are ineffective. This study applies passive acoustic monitoring to characterise fish biodiversity and diel sound production patterns in the deep channels of River Niger within Kogi State, North Central Nigeria, a geographically central section of the river system lying near the Lokoja confluence with the Benue River. Four calibrated omnidirectional hydrophones are deployed at channel depths of six to fifteen metres at three river stations for continuous recording over six weeks during both the dry season (December to January) and wet season (June to July) of 2023 to 2024. Recorded soundscapes are analysed using automated spectrogram analysis in MATLAB and manual call identification to detect and classify fish sound-producing species, including weakfish (Sciaenidae), which produce characteristic spawning calls, and catfish species known to produce agonistic sounds. Acoustic indices including the acoustic complexity index, bioacoustic index, and spectral entropy are computed to quantify biodiversity and habitat quality. Concurrent gill netting and electrofishing surveys provide conventional species inventory data for comparison with acoustic detections. Environmental co-variates (water temperature, conductivity, turbidity, flow velocity) are related to acoustic metrics using mixed-effects models. Findings are expected to validate passive acoustic monitoring as a complementary river biodiversity assessment tool with particular value in deep, turbid channels inaccessible to visual methods. Keywords: passive acoustic monitoring, fish biodiversity, River Niger, bioacoustics, freshwater sound