Environmental niche patterns of native and non-native fishes within an invaded African river system
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2019
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124407 , vital:35605 , https://doi.10.1111/jfb.13988
- Description: To test ecological niche theory, this study investigated the spatial patterns and the environmental niches of native and non-native fishes within the invaded Great Fish River system, South Africa. For the native fishes, there were contrasting environmental niche breadths that varied from being small to being large and overlapped for most species, except minnows that were restricted to headwater tributaries. In addition, there was high niche overlap in habitat association among fishes with similar distribution. It was therefore inferred that habitat filtering-driven spatial organization was important in explaining native species distribution patterns. In comparison, most non-native fishes were found to have broad environmental niches and these fishes showed high tolerance to environmental conditions, which generally supported the niche opportunity hypothesis. The proliferation of multiple non-native fishes in the mainstem section suggest that they form a functional assemblage that is probably facilitated by the anthropogenic modification of flow regimes through inter-basin water transfer. Based on the distribution patterns observed in the study, it was inferred that there was a likelihood of negative interactions between native and nonnative fishes. Such effects are likely to be exacerbated by altered flow regime that was likely to have negative implications for native ichthyofauna.
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An invader within an altered landscape: one catfish, two rivers and an inter-basin water transfer scheme
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2013
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123776 , vital:35494 , https://doi.10.1002/rra.2599
- Description: African sharptooth catfish Clarias gariepinus has become established as a non-native invasive species in Eastern Cape, South Africa, where it was translocated primarily through an inter-basin water transfer scheme into the Great Fish and Sundays rivers. This study examined the patterns in catfish distribution and abundance, and compared trophic niches in relation to the ichthyofauna of the two rivers. Correspondence analysis revealed upstream to downstream gradients associated with the spatial distribution in species richness for most species within the mainstream and mainstream to tributary gradients that were associated mostly with the spatial distribution of native minnows in both rivers. Catfish was predicted to occur widely within the mainstream habitats and to decrease progressively from mainstreams to tributaries. Based on classification and regression trees, the physico-chemical environment was found to be a good proxy for predicting the occurrence and abundance of catfish. Although non-significant relationships were observed between catfish and other native fish species abundances, the study suggests potential impact due to predation and interference in habitats where the invader co-occurs with other fishes. Comparisons of trophic niches indicated higher trophic diversity for the mainstream ichthyofauna than the tributary communities in both rivers, suggesting an upstream to downstream continuum in community structure and resource availability. Catfish within the invaded mainstream had comparable trophic niches and similar dispersion patterns among individuals for both rivers, but indicated differences in shapes of scatter. This suggests that the catfish exhibited a differential response, probably in relation to resource availability, that may be indicative of its dietary plasticity. The study suggests the proliferation of catfish and its probable impact within the mainstream flow-altered habitats where invasion resistance was possibly reduced. Comparisons of trophic niches provided information on its probable impact at different scales and the potential risk of invasion of tributaries inhabited by native minnow species.
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Movement patterns and habitat selection of invasive African sharptooth catfish
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2013
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125276 , vital:35767 , http://dx.doi.10.1111/j.1469-7998.2012.00960.x
- Description: Information on the movement behaviour and habitat use by non-native invasive African catfish Clarias gariepinus is crucial in understanding and possibly mitigating its potential impacts. The aim of this study was to examine catfish movement and habitat selection within an invaded impoundment in the Eastern Cape, South Africa. Acoustic telemetry data for 10 tagged catfish were analyzed to identify spatial patterns in home ranges and seasonal changes in habitat associations. Long-distance movements were observed for most catfish from common central release point, whereas short-distance movements defined their home ranges and utilization distributions that were categorized as localized within single or multiple habitats. Habitat selection was non-random with most catfish utilizing the shallow river mouth and upper section of the reservoir that were dominated by a rocky substratum interspersed with submerged trees. These localities were likely to be preferred for spawning and/or feeding. Utilization of these habitats by catfish is likely to be associated with probable impact due to predation and interference competition for feeding and breeding grounds with other species. Although most catfish maintained their home ranges throughout the study, seasonal shifts in habitat use, which was reflected by the utilization of deep and silt-dominated habitats, were also observed for some catfish. Non-random habitat use and homing behaviour within single and multiple habitats by non-native sharptooth catfish suggests that its impact within the invaded habitats may be associated with particular habitats both at broad spatial and temporal scales. Protection of habitats from catfish invasion should be considered as a management option to conserve native biota.
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Detecting impacts of invasive non-native sharptooth catfish, Clarias gariepinus, within invaded and non-invaded rivers.
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124100 , vital:35539 , https://doi.10.1007/s10531-012-0291-5
- Description: In aquatic ecosystems, impacts by invasive introduced fish can be likened to press disturbances that persistently influence communities. This study examined invasion disturbances by determining the relationship between non-native sharptooth catfish Clarias gariepinus and aquatic macroinvertebrates in the Eastern Cape, South Africa. A Multiple Before–After Control–Impact (MBACI) experimental design was used to examine macroinvertebrate communities within two rivers: one with catfish and another one without catfish. Within the invaded river, macroinvertebrates showed little response to catfish presence, whereas predator exclusion appeared to benefit community structure. This suggests that the macroinvertebrate community within the invaded river was adapted to predation impact because of the dominance of resilient taxa, such as Hirudinea, Oligochaeta and Chironomidae that were abundant in the Impact treatment relative to the Control treatment. High macroinvertebrate diversity and richness that was observed in the Control treatment, which excluded the predator, relative to the Impact treatment suggests predator avoidance behaviour within the invaded river. By comparison, within the uninvaded river, catfish introduction into the Impact treatment plots indicated negative effects on macroinvertebrate community that was reflected by decrease in diversity, richness and biomass. A community level impact was also reflected in the multivariate analysis that indicated more variation in macroinvertebrate composition within the Impact treatment relative to the Control in the uninvaded river. Catfish impact within the uninvaded river suggests the dominance of vulnerable taxa, such as odonates that were less abundant in the Impact treatment plots after catfish introduction. From a disturbance perspective, this study revealed different macroinvertebrate responses to catfish impact, and suggests that within invaded habitats, macroinvertebrates were less responsive to catfish presence, whereas catfish introduction within uninvaded habitats demonstrated invasion impact that was shown by a decrease in the abundance of vulnerable taxa. The occurrence of non-native sharptooth catfish within many Eastern Cape rivers is a concern because of its predation impact and potential to influence trophic interrelationships, and efforts should be taken to protect uninvaded rivers, and, where possible, eradicate the invader.
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Integrating stomach content and stable isotope analyses to elucidate the feeding habits of non-native sharptooth catfish Clarias gariepinus
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124843 , vital:35703 , https://doi.10.1007/s10530-011-0116-6
- Description: Sharptooth catfish Clarias gariepinus was introduced into the Eastern Cape Province, South Africa, in 1976 and there are concerns about its possible negative impacts on native biota. This study investigated its trophic impact by examining its feeding habits. Stomach content and stable isotope analyses were compared from three localities—the Great Fish River, Sundays River and Glen Melville Dam. Stomach content analysis indicated a catholic diet dominated by fish particularly in all localities.Spatially, however, the diets revealed differences based on the dominance of macrophytes that were only present in the rivers, and aquatic invertebrates that appeared more diverse within the Great Fish River compared to other localities. By contrast, stable isotopes revealed a more generalised feeding pattern with no clear dominance of particular prey. Stable isotopes further showed that the catfish was a complex predator, with large catfish being top predators whereas smaller size groups appeared to feed lower in the food chain. An ontogenetic shift in diet was evident, with small fish predominantly consuming aquatic invertebrates and shifting towards fish with increasing size. High dietary overlap suggests the potential risk associated catfish feeding, especially the potential of piscivory by small catfish that are more likely to persist in shallow and marginal where endangered indigenous minnows occur. The alteration of environmental conditions, especially flow by inter basin water transfer (IBWT) schemes, was inferred to have had a probable influence its invasion success. Occurrence of other invaders, which was facilitated by the IBWT together with the catfish, posits the risk of invasion meltdown within the study systems.
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Inter-seasonal persistence and size-structuring of two minnow species within headwater streams in the Eastern Cape, South Africa
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124866 , vital:35705 , https://doi.10.1111/j.1439-0426.2012.02027.x
- Description: This study examined temporal variation in population dynamics and size structuring of two cyprinid minnows, Pseudobarbus afer and Barbus anoplus, in relation to their proximate physical habitats. Population estimates were determined using three-pass depletion sampling during both summer and winter. The habitats were characterised by seasonal variation in all physico-chemical conditions and spatial variation in substrata compositions. Whereas significant differences in population size were noted between seasons for B. anoplus, no differences were found between seasons for density and capture probability for either species. An increase in boulders was associated with increase in population size and density for P. afer; for B. anoplus, increased percentages of bedrock and bank vegetation were associated with an increase in population size and probability of capture, respectively. According to Canonical Correspondence Analysis, size structuring in P. afer was explained predominantly by seasonality, with smaller length classes associated with the seasonal variable of summer, while larger length classes were associated with pH that was higher in winter. By comparison, for B. anoplus, the habitat variables – bank vegetation and bedrock – accounted for much of the explained variance for size structuring. Recruitment appeared to be the major driver of size structuring for the two species; refugia, especially boulders and bank vegetation, also appeared to be important. Overall, the two species were adapted to the headwater streams that were generally variable in environmental conditions. Potential invasions by non-native invasive fishes that occur within the mainstream habitats threaten these two species. Efforts should continue to protect these minnows from such invasions by constructing barriers to upstream migration of non-native fishes into these headwater habitats.
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