Temporal and spatial ecology of an iconic Labeobarbus spp. in a socio-economically important river

Understanding the biological response to increasing anthropogenic stressors is an important consideration to make when evaluating ecosystem well-being. Among aquatic ecological indicators, fish are effective as they are mobile and can be monitored relatively easily. The socio-economically important uMngeni River in South Africa is a highly regulated 'working river' and has seen a reduction in the numbers of its iconic Labeobarbus spp. as a result, primarily the KwaZulu-Natal yellowfish Labeobarbus natalensis. To understand how this species has adapted to these anthropogenic changes, we evaluated the reach-scale movements and habitat use of L. natalensis (n = 43) from August 2018 to August 2019 between Midmar and Albert Falls Dams. We included monitoring environmental parameters using radio telemetry methods. We found that L. natalensis showed facultative movements and typically exhibited diurnal activities. Habitat availability was important and appeared to depend on refugia during the austral winter (May to July) and spawning or body condition during austral summer (December to February). Upstream reach-scale movements were cued primarily by water temperature where flow provided access and maintained available habitats for breeding. Maintaining adequate flows during critical periods of movement and spawning is important and will assist in maintaining the population of L. natalensis. Furthermore, removing redundant instream barriers or fitting these with adequate fish passages will improve the fragmented population resilience of L. natalensis. These mitigation measures will improve ecosystem resilience and reduce the impacts of increasing anthropogenic stressors associated with socio-economically important rivers.

Automated summary

This study evaluated how the yellowfish population in the uMngeni River in South Africa has adapted to anthropogenic stressors, finding that water temperature, seasonal activities, and habitat availability play important roles. Recommendations were made to maintain adequate flows, improve fish passage, and reduce the impacts of anthropogenic stressors on important river ecosystems.