Assessment and Management of Invasive Aquatic Species in the Anambra River Basin, South East Nigeria

This study assesses the distribution, abundance, and ecological impacts of invasive aquatic species in the Anambra River Basin, South East Nigeria, and evaluates management options. Invasive alien species are a global biodiversity threat, and water hyacinth Eichhornia crassipes is progressively expanding in the Anambra basin with significant consequences for fish community structure and artisanal fisheries. A systematic reach-level survey of the main river channel and 12 tributaries was conducted to map water hyacinth coverage using GPS tracking and drone imagery. Biological sampling beneath and outside water hyacinth mats compared macroinvertebrate and fish diversity across coverage levels. Ecological impact scores were calculated using a standardised impact assessment protocol. Interviews with 60 fishing households quantified livelihood impacts. Water hyacinth covered approximately 18 percent of the total surveyed water surface area, concentrated in slow-flowing backwater channels. Macroinvertebrate diversity beneath dense mats was 46 percent lower than in open water. Fish species associated with oxygenated open water were virtually absent beneath dense mats. Fishing household income declined by an estimated 28 percent in the most affected communities. Integrated management options evaluated included mechanical removal, biocontrol using Neochetina weevils, and community-based harvesting for compost production. The study recommends a phased integrated management plan prioritising biocontrol introduction and community harvesting and proposes institutional coordination between Anambra State agencies and the Anambra-Imo River Basin Development Authority. Keywords: invasive species, water hyacinth, Anambra River, aquatic ecology, management.