An assessment of the impacts of sand mining and increased silting levels on the fish species composition and abundance along the river nile, Namasagali catchment area, Kamuli District

Abstract

Sand mining is a widespread practice in Uganda, posing significant environmental challenges to freshwater ecosystems, including habitat destruction, water pollution, and loss of biodiversity. The Namasagali catchment area, a sub-basin of the Victoria Nile River, is one of the affected regions, with sand mining activities threatening the livelihoods of local communities’ dependent on fishing and agriculture. This study aimed to investigate the impacts of sand mining and increased siltation on fish species composition and abundance within the Namasagali catchment area of the Nile Kamuli district. Specific objectives included: (1) to determine the changes in riverbed substrate composition due to sand mining; (2) to assess the impacts of sand mining on fish species composition and abundance; and (3) to evaluate the effects of sand mining on fish catches and catch rates. A retrospective experimental approach with control sites was employed, combining quantitative and qualitative data collection methods. Line transects, grab samples, scoop nets and standard gill nets were used to assess riverbed substrate composition and fish populations The results showed significant differences in sand and cobbles percentages among the four study sites, with Kabeto A having significantly higher sand percentage (53.2%) compared to Nsangabiire (46.1%). Fish catches varied among sites, with Nsangabiire having the highest number of fish caught (19 fish) and Kabeto A having the lowest (8 fish). Local fishers reported significant variations in average number of individuals per species among the sites, with Nile tilapia (Oreochromis niloticus) being the most abundant species (4.2 kg per site). The study found that sand mining has significant impacts on freshwater ecosystems, including alterations to riverbed substrate composition and fish populations. The findings highlight the need for sustainable management strategies. Recommendations include: (1) enforcing environmental regulations to prevent sand mining in sensitive habitats; (2) promoting alternative livelihoods for sand miners, such as agriculture and tourism; and (3) conducting further research on the long-term impacts of sand mining on freshwater ecosystems.