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

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...

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Main Author: Morch, Casper
Other Authors: Griffiths, Charles
Format: Thesis
Language:Eng
Published: Department of Biological Sciences 2025
Subjects:
Biological Sciences
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access_status_str Open Access
author Morch, Casper
author2 Griffiths, Charles
author_browse Griffiths, Charles
Morch, Casper
author_facet Griffiths, Charles
Morch, Casper
author_sort Morch, Casper
collection Thesis
description 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.
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institution University of Cape Town (South Africa)
language Eng
last_indexed 2026-06-10T12:34:39.078Z
license_str Not specified — see source repository
provenance_str_mv Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository
publishDate 2025
publishDateRange 2025
publishDateSort 2025
publisher Department of Biological Sciences
publisherStr Department of Biological Sciences
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source_str UCTD — University of Cape Town Open Access Repository
spelling oai:open.uct.ac.za:11427/41150 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 Griffiths, Charles Cunningham Susan Biological Sciences 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. 2025-03-11T11:53:24Z 2025-03-11T11:53:24Z 2024 2025-03-11T11:50:45Z Thesis / Dissertation Masters MSc http://hdl.handle.net/11427/41150 Eng application/pdf Department of Biological Sciences Faculty of Science University of Cape Town
spellingShingle Biological Sciences
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_degree_str Master's
title Between a bass and a hard place: the fragmented distribution of an endangered redfin in the Heuningnes River System of the Cape Fold Ecoregion
title_full Between a bass and a hard place: the fragmented distribution of an endangered redfin in the Heuningnes River System of the Cape Fold Ecoregion
title_fullStr Between a bass and a hard place: the fragmented distribution of an endangered redfin in the Heuningnes River System of the Cape Fold Ecoregion
title_full_unstemmed Between a bass and a hard place: the fragmented distribution of an endangered redfin in the Heuningnes River System of the Cape Fold Ecoregion
title_short Between a bass and a hard place: the fragmented distribution of an endangered redfin in the Heuningnes River System of the Cape Fold Ecoregion
title_sort between a bass and a hard place the fragmented distribution of an endangered redfin in the heuningnes river system of the cape fold ecoregion
topic Biological Sciences
url http://hdl.handle.net/11427/41150
work_keys_str_mv AT morchcasper betweenabassandahardplacethefragmenteddistributionofanendangeredredfinintheheuningnesriversystemofthecapefoldecoregion

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