Resilience of imperilled headwater stream fish to an unpredictable high-magnitude food

Abstract

Headwater stream fish communities are increasingly becoming isolated in headwater refugia that are often cut off from other met populations within a river network as a result of non-native fish invasions, pollution, water abstraction and habitat degradation downstream. This range restriction and isolation therefore makes them vulnerable to extinction. Understanding threats to isolated fish populations is consequently important for their conservation. Following a base-fow survey, a high-magnitude food (peak fow of 1245 m-3s-1) provided an opportunity to investigate the response of endangered Eastern Cape redfin Pseudobarbus afer populations to a natural disturbance in the Waterkloof and Fernkloof streams, two relatively pristine headwater tributaries of the Swartkops River system within the Groendal Wilderness Area, Eastern Cape Province, South Africa. Pseudobarbus afer had limited distributions, occupying 3 km in both the Fernkloof and Waterkloof streams. Fish population assessments before and after the food event indicated that there were no longitudinal trends in P. afer abundance before or after the food, but overall abundance post-fooding in the Fernkloof stream was higher. There were no noticeable changes in P. after size structure pre- and post-food. Pseudobarbus afer showed resilience to a major flooding event most likely related to evolution in river systems characterized by environmental stochasticity. Conservation implications: This research provides insight into the population level responses of native headwater stream fishes to unpredictable natural disturbance. Of particular relevance is information on their ability to withstand natural disturbances, which provides novel information essential for their conservation and management especially as these fishes are already impacted by multiple anthropogenic stressors.