The impact of alien invasive smallmouth bass (Micropterus dolomieu) on the indigenous fish of the Rondegat River : a quantitative assessment with implications for rehabilitation

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dc.contributor.advisorDay, Jennyen_ZA
dc.contributor.advisorImpson, Deanen_ZA
dc.contributor.advisorBills, Rogeren_ZA
dc.contributor.authorWoodford, Darragh Jen_ZA
dc.date.accessioned2014-08-28T14:26:15Z
dc.date.available2014-08-28T14:26:15Z
dc.date.issued2005en_ZA
dc.description.abstractAlien invasive fishes are a growing concern in inland water ecosystems around the world, as they are capable of causing serious damage, especially to indigenous fish populations. Mechanisms include direct predation on indigenous fish by alien predatory species, competition for food and space between native and introduced species, the introduction of alien parasites and pathogens, and general environmental degradation. The Cape Floristic Region (CFR) of South Africa, which is defined by a unique and highly diverse floral kingdom, is also home to a unique and highly threatened ichthyofauna. This ichthyofauna consists of relatively few species, but exhibits the highest proportion of endemicity in the country. Threats to fishes include habitat destruction through bulldozing and water extraction, water quality degradation, restriction of migration by dams and weirs, and alien invasive fishes. The North American smallmouth bass (Micropterus dolomieu Lacepede) has long been regarded by nature conservators as the most threatening invasive species, and much anecdotal and survey data suggests that this species has had a major role in the depletion and extirpation of indigenous fish populations throughout the CFR. However, no study has ever properly quantified this impact relative to other potential threats that could have precipitated the perceived indigenous fish losses. This is a problem, as it makes the implementation of active control measures difficult to justify to a sceptical public and potential sponsors. The Rondegat River is a tributary of the Olifants River, which rises in the Cedarberg Mountains and flows into the Clanwilliam Dam reservoir. It is partially invaded by M dolomieu, which have penetrated the lower quarter of the river up to a waterfall barrier. This river is home to five species of indigenous fish, including the Clanwilliam yellowfish (Labeobarbus capensis Smith), Clanwilliam redfin (Barbus calidus Barnard), fiery redfin (Pseudobarbus phlegethon Barnard), Clanwilliam rock catfish (Austroglanis gilli Barnard) and the Cape galaxiid (Galaxias zebratus Castelnau). This project was designed to quantify the impact of M dolomieu on these species relative to the alternate potential impacts of physical habitat degradation from agriculture and alien invasive riparian trees, and of food availability. Seasonal surveys were conducted at eight sites on the river in September, October and November 2003, and in April 2004. Four sets of riffles and pools were selected upstream of the waterfall barrier, and four below. Quantitative electrofishing was used to survey fish in riffles, while snorkelling surveys were conducted in pools. All fish species were also caught with seine and tyke nets for dietary analyses. Physical habitat variables were measured at each site, and used to assess changing habitat quality between the sites. Invertebrate samples were also taken along with visual abundance estimations of other food types, to gauge food availability. Fish surveys revealed the loss of B. calidus, P. phlegethon, A. gilli and G. zebratus at bass-invaded sites. Galaxias zebratus was only found in the upper reaches of the river, and so was possibly never common in the lower river. Labeobarbus capensis, while still below the waterfall, appeared to be suffering from near-total loss of post spawning recruits. Discriminant function analyses revealed sedimentation to be a key factor of habitat degradation that characterized invaded sites. However, linear regressions between habitat variables and indigenous fish densities indicated sedimentation to not be a significant negative influence on indigenous fish distributions. Although sedimentation did not appear to influence A. gilli densities at non-invaded sites, it is highly likely that it increased the vulnerability of this species to M dolomieu in the lower river, by removing benthic cover used to avoid predation. In the case of all species, food availability did not seem an important factor in dictating fish distributions. Consequently, predation by M dolomieu was confirmed as the critical mechanism behind the loss of B. calidus, P. phlegethon, A.gilli and juvenile L. capensis in the lower river. A rehabilitation plan is proposed for the Rondegat River. Central to this plan is the formation of a conservancy between the land-owners of the catchment and the custodians of the Cedarberg Wilderness Area. The most effective strategy will be to eradicate M dolomieu from the lower river with piscicides, while at the same time taking steps to rehabilitate the riparian zone throughout the river. A holistic rehabilitation programme such as this would provide an excellent model for future rehabilitation efforts within the CFR.en_ZA
dc.identifier.apacitationWoodford, D. J. (2005). <i>The impact of alien invasive smallmouth bass (Micropterus dolomieu) on the indigenous fish of the Rondegat River : a quantitative assessment with implications for rehabilitation</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Biological Sciences. Retrieved from http://hdl.handle.net/11427/6739en_ZA
dc.identifier.chicagocitationWoodford, Darragh J. <i>"The impact of alien invasive smallmouth bass (Micropterus dolomieu) on the indigenous fish of the Rondegat River : a quantitative assessment with implications for rehabilitation."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Biological Sciences, 2005. http://hdl.handle.net/11427/6739en_ZA
dc.identifier.citationWoodford, D. 2005. The impact of alien invasive smallmouth bass (Micropterus dolomieu) on the indigenous fish of the Rondegat River : a quantitative assessment with implications for rehabilitation. University of Cape Town.en_ZA
dc.identifier.risTY - Thesis / Dissertation AU - Woodford, Darragh J AB - Alien invasive fishes are a growing concern in inland water ecosystems around the world, as they are capable of causing serious damage, especially to indigenous fish populations. Mechanisms include direct predation on indigenous fish by alien predatory species, competition for food and space between native and introduced species, the introduction of alien parasites and pathogens, and general environmental degradation. The Cape Floristic Region (CFR) of South Africa, which is defined by a unique and highly diverse floral kingdom, is also home to a unique and highly threatened ichthyofauna. This ichthyofauna consists of relatively few species, but exhibits the highest proportion of endemicity in the country. Threats to fishes include habitat destruction through bulldozing and water extraction, water quality degradation, restriction of migration by dams and weirs, and alien invasive fishes. The North American smallmouth bass (Micropterus dolomieu Lacepede) has long been regarded by nature conservators as the most threatening invasive species, and much anecdotal and survey data suggests that this species has had a major role in the depletion and extirpation of indigenous fish populations throughout the CFR. However, no study has ever properly quantified this impact relative to other potential threats that could have precipitated the perceived indigenous fish losses. This is a problem, as it makes the implementation of active control measures difficult to justify to a sceptical public and potential sponsors. The Rondegat River is a tributary of the Olifants River, which rises in the Cedarberg Mountains and flows into the Clanwilliam Dam reservoir. It is partially invaded by M dolomieu, which have penetrated the lower quarter of the river up to a waterfall barrier. This river is home to five species of indigenous fish, including the Clanwilliam yellowfish (Labeobarbus capensis Smith), Clanwilliam redfin (Barbus calidus Barnard), fiery redfin (Pseudobarbus phlegethon Barnard), Clanwilliam rock catfish (Austroglanis gilli Barnard) and the Cape galaxiid (Galaxias zebratus Castelnau). This project was designed to quantify the impact of M dolomieu on these species relative to the alternate potential impacts of physical habitat degradation from agriculture and alien invasive riparian trees, and of food availability. Seasonal surveys were conducted at eight sites on the river in September, October and November 2003, and in April 2004. Four sets of riffles and pools were selected upstream of the waterfall barrier, and four below. Quantitative electrofishing was used to survey fish in riffles, while snorkelling surveys were conducted in pools. All fish species were also caught with seine and tyke nets for dietary analyses. Physical habitat variables were measured at each site, and used to assess changing habitat quality between the sites. Invertebrate samples were also taken along with visual abundance estimations of other food types, to gauge food availability. Fish surveys revealed the loss of B. calidus, P. phlegethon, A. gilli and G. zebratus at bass-invaded sites. Galaxias zebratus was only found in the upper reaches of the river, and so was possibly never common in the lower river. Labeobarbus capensis, while still below the waterfall, appeared to be suffering from near-total loss of post spawning recruits. Discriminant function analyses revealed sedimentation to be a key factor of habitat degradation that characterized invaded sites. However, linear regressions between habitat variables and indigenous fish densities indicated sedimentation to not be a significant negative influence on indigenous fish distributions. Although sedimentation did not appear to influence A. gilli densities at non-invaded sites, it is highly likely that it increased the vulnerability of this species to M dolomieu in the lower river, by removing benthic cover used to avoid predation. In the case of all species, food availability did not seem an important factor in dictating fish distributions. Consequently, predation by M dolomieu was confirmed as the critical mechanism behind the loss of B. calidus, P. phlegethon, A.gilli and juvenile L. capensis in the lower river. A rehabilitation plan is proposed for the Rondegat River. Central to this plan is the formation of a conservancy between the land-owners of the catchment and the custodians of the Cedarberg Wilderness Area. The most effective strategy will be to eradicate M dolomieu from the lower river with piscicides, while at the same time taking steps to rehabilitate the riparian zone throughout the river. A holistic rehabilitation programme such as this would provide an excellent model for future rehabilitation efforts within the CFR. DA - 2005 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2005 T1 - The impact of alien invasive smallmouth bass (Micropterus dolomieu) on the indigenous fish of the Rondegat River : a quantitative assessment with implications for rehabilitation TI - The impact of alien invasive smallmouth bass (Micropterus dolomieu) on the indigenous fish of the Rondegat River : a quantitative assessment with implications for rehabilitation UR - http://hdl.handle.net/11427/6739 ER -en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/6739
dc.identifier.vancouvercitationWoodford DJ. The impact of alien invasive smallmouth bass (Micropterus dolomieu) on the indigenous fish of the Rondegat River : a quantitative assessment with implications for rehabilitation. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Biological Sciences, 2005 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/6739en_ZA
dc.language.isoeng
dc.publisher.departmentDepartment of Biological Sciencesen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherZoologyen_ZA
dc.titleThe impact of alien invasive smallmouth bass (Micropterus dolomieu) on the indigenous fish of the Rondegat River : a quantitative assessment with implications for rehabilitationen_ZA
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationnameMSc
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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