The invasibility of small headwater streams by an emerging invader, Clarias gariepinus

Abstract

African sharptooth catfish Clarias gariepinus has been spread globally and is proven to be invasive with demonstrable impacts on a variety of biota in recipient ecosystems. There are concerns that this species will invade headwater stream communities that are already considered fragile and heavily impacted by non-native invasive fishes. There is however no information on the ability of C. gariepinus to penetrate or establish in these environments. This paper uses data collected over a seven year period from three episodic headwater streams in the Cape Floristic Region of South Africa to assess the ability of C. gariepinus to invade headwater habitats from downstream source populations. Data demonstrate that C. gariepinus invaded all three headwater tributaries and was able to penetrate previously non-invaded threatened fish refugia. Clarias gariepinus however failed to establish in headwaters and their presence was casual with individuals migrating from mainstem sources. Headwater incursions were dynamic and C. gariepinus reinvaded streams following their extirpation through drought. These results indicate headwater streams to be invasible by C. gariepinus and an assessment of potential impact on headwater communities requires urgent attention.