Impacts of trout on aquatic macroinvertebrates in three Drakensberg rivers in KwaZulu-Natal, South Africa

Global literature suggests that trout, when introduced as alien species into local streams, have had deleterious impacts on aquatic community structure and function. Prior to defining management actions regarding trout in the rivers of the Ukhahlamba-Drakensberg Park (UDP), data are required on their impacts on local aquatic communities. In February 2007, aquatic macroinvertebrate communities were sampled at three locations in streams in the UDP. Paired sites were separated by waterfalls, with no trout occurring upstream but occurring at low densities downstream. Differences in aquatic macroinvertebrate communities between upstream and downstream sites were apparent but, within the constraints of this study, such differences could not be directly attributed to trout predation. Further studies are recommended in order to provide additional information on seasonal variation in these patterns, as well as on density-dependent effects of trout on aquatic macroinvertebrate communities.