Abstract
Headwater stream fish communities are increasingly becoming isolated in headwater refugia that are often cut off from other metapopulations within a river network as a result of nonnative 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-flow survey, a high-magnitude flood (peak flow 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 flood event indicated that there were no longitudinal trends in P. afer abundance before or after the flood, but overall abundance post-flooding in the Fernkloof stream was higher. There were no noticeable changes in P. afer size structure pre- and post-flood. Pseudobarbus afer showed resilience to a major flooding event most likely related to evolution in river systems characterised 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.
Highlights
Headwater stream fishes in South Africa are increasingly being isolated in small fragmented headwater refuges as a result of competition with and predation by non-native fishes, downstream water abstraction, pollution and habitat degradation (Marr et al 2010; Tweddle et al 2009; Weyl et al 2014)
Protected areas play an important role in conserving headwater fishes by preserving habitats and preventing non-native fish introductions (Russell 2011)
Headwater streams are considered susceptible to floods because they have small catchments and are influenced by relatively minor changes in local conditions (Meyer et al 2007)
Summary
Headwater stream fishes in South Africa are increasingly being isolated in small fragmented headwater refuges as a result of competition with and predation by non-native fishes, downstream water abstraction, pollution and habitat degradation (Marr et al 2010; Tweddle et al 2009; Weyl et al 2014). The study was undertaken within the Groendal Wilderness Area on two second-order, episodic headwater tributaries (Fernkloof stream, Waterkloof stream) of the Kwa-Zunga River, a major tributary of the Swartkops River system, Eastern Cape, South Africa (Figure 1).
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