Between a bass and a hard place: the fragmented distribution of an endangered redfin in the Heuningnes River System of the Cape Fold Ecoregion

Morch, Casper

Between a bass and a hard place: the fragmented distribution of an endangered redfin in the Heuningnes River System of the Cape Fold Ecoregion

Thesis / Dissertation

2024

Publisher

University of Cape Town

Department

Department of Biological Sciences

Faculty

Faculty of Science

Abstract

Native freshwater fish are globally in decline due to anthropogenic impacts, including changes to water quality, over-abstraction, climate change, and introduction of nonnative species. The Cape Fold Ecoregion (CFE) of South Africa is recognised as a hotspot for freshwater fish endemism. It is also recognised as one of six hotspots for freshwater fish invasions. Hence, 36% of native and 66% of endemic freshwater fish are considered threatened (vulnerable, endangered, or critically endangered). The Heuningnes redfin (Pseudobarbus sp Burchelli Heuningnes) is one such fish. It is considered endangered (SANBI Red List of Threatened Species) and currently occupies a small number of tributaries within the Heuningnes River System (HRS). The Heuningnes redfin co-occurs with Cape kurpers and Cape galaxias, some of which are currently being described as new and unique lineages. As such, the HRS is of critical conservation significance. This study analysed a data set collected by Keir Lynch in March of 2018, that consists of 22 water quality, geographic, and habitat-related environmental variables. The goal was to determine whether the distribution of native fish is independent of the distribution of non-native fish, as well as what environmental variables best predict the presence and abundance of Heuningnes redfin in the HRS. The data suggest non-native species appear to be excluding native species from invaded reaches. Moreover, redfins prefer warmer, more acidic water with complex habitats in the form of woody debris and gravel substrate, allowing them to hide from predators. Their abundance is negatively correlated with phosphorous, which may indicate that they are affected by pollution from agricultural runoff. Moving forward, conservation practitioners should consider non-native eradication projects, through either chemical or mechanical removal. Additionally, they should also consider creating a buffer of indigenous vegetation, which could mitigate the impacts of agricultural effluents and provide benefits for the currently endangered renosterveld. Additional surveys are necessary to determine the exact extent bass have invaded the system, as well as to obtain an accurate measure of how different land uses are affecting the distribution of native fishes.

Keywords

Biological Sciences

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