Assessing fish community response to water quality and habitat stressors in KwaZulu-Natal, South Africa

The degradation of freshwater ecosystems can be attributed to stressors associated with the increased demand for water and other aquatic resources. Freshwater ecosystems face such challenges in supporting agriculture, industry, and high-density urban areas in KwaZulu-Natal (KZN) province, South Africa. In this study, the presence of fish species and their abundance was quantified at 40 sites in KZN on 16 major rivers systems. Surveys were done during a drought period between February 2015 and April 2016, as part of the River Health Programme, a national river monitoring assessment. The Fish Response Assessment Index (FRAI) was used to evaluate the condition of the sites, and redundancy analysis was used to evaluate the habitat, water quality and fish community relationships. The FRAI scores showed four sites to be in a 'Seriously Modified' condition. These areas were associated with intensive agricultural activities and urban environments. The presence of invasive fish species, abstraction and industrial use all had negative impacts on the ecological state of the rivers. When compounded by excessive water use, the drought resulted in poor fish community integrity, highlighting the vulnerability of fish communities in this region. The absence or low abundances of some indigenous fish alongside the high presence of invasive fish requires additional investigation. Results highlight the importance of mitigation measures against anthropogenic impacts should be enforced to ensure sustainable use of KZN water resources.