Groenvlei in the Western Cape is one of only a handful of natural freshwater lakes in South Africa. The lake is home to two native and five non-native fish species. Introduced over an extended period some of these non-native fish have arguably added value to the water. However local anglers, subsistence fishers, and environmental managers have become increasingly concerned that illegally introduced common carp Cyprinus carpio have altered water quality and led to a decline in target sport and food fish. Carp control measures using both conventional netting as well as bow-fishing have been employed. This study draws together a wealth of data sources to explore the ecology and impact of carp in this environment and examine the efficacy and acceptability of management options tested.
Changes in the lake flora have been recorded in photographic records and satellite imaging. Catch data from angling competitions, population surveys and from removal efforts has been used to monitor population changes in carp and co-occurring species. Socioeconomic data from angling competitions and a large user survey completes the human element of the story.
The results show a highly successful invader thriving in it new environment, whilst changing it dramatically at a variety of levels. The human dimension reveals both conflicts and synergies between different groups of the local community surrounding this species and its management. The lessons from this case study provide a valuable insight into the impacts and control options for this species highlighting the successes and failures in both monitoring and management.