Once widely distributed throughout the Krom River System, Pseudobarbus senticeps has suffered severe decline in its historical distribution range. Comprehensive surveys of the Krom River system in 2011 suggest that mainstem populations of this species may have been extirpated due to invasion by alien predators mainly Largemouth Bass (Micropterus salmoides), deterioration in habitat and water quality as well as excessive water abstraction. Remnant populations of this species are now confined to a few relatively undisturbed and uninvaded tributaries of the Krom River system, but they remain under increasing threat from water abstraction for agriculture, invasion by alien invasive predatory fish from the mainstem and pollution. The once continuous population is now fragmented and there are little or no opportunities for genetic exchange between the isolated subpopulations due to the presence of aliens between the tributary subpopulations, as they can move through the entire system. The species has a extant of occurrence (EOO) of 22 km2 and is known from one location as defined by the impacts of alien invasive species and it is experiencing continuous decline in the number of mature individuals as well as in the quality of its habitat due to invasive alien fish, water abstraction and pollution. Pseudobarbus senticeps qualifies as Critically Endangered B1ab(iii,v). Further this species has an area of occupancy (AOO) of 20 km2 (based on the IUCN approach of a 2x2 km2 grid over known localities), while the actual AOO is less than 1 km2 based on available habitat.
Distribution
Pseudobarbus senticeps is endemic to the Krom River System in the eastern Cape Fold Ecoregion of South Africa (Chakona and Skelton submitted; Swartz et al. 2007, 2009). The species has a restricted known distribution range, within a single sub-quaternary catchment with a few extant subpopulations in the Assegaaibosch River and a few tributaries of the upper Krom (Chakona and Skelton submitted). Recent surveys suggest that mainstem populations of this species may have been extirpated by the impacts of threats.
Remnant subpopulations of this species are now confined to a few relatively undisturbed and uninvaded tributaries of the Krom River system.
Threats
Ongoing decline of remnant subpopulations of this species is likely due to the presence of alien invasive fish species, ongoing habitat degradation, water abstraction and pollution. The remaining populations are heavily fragmented and have small known population sizes. The Assegaaibosch River population in particular is impacted by excessive pollution from settlements in the sub-catchment. It is likely that the presence of alien invasive species in the mainstem sections may limit or prevent genetic exchange between isolated subpopulations, leading to increased risk of inbreeding. This can reduce the reproductive fitness and long-term evolutionary flexibility and adaptive response of Pseudobarbus senticeps to the projected environmental changes in the region (Dallas and Rivers-Moore 2014).
Conservation
Pseudobarbus senticeps needs to be prioritized as it is represented by very few remaining subpopulations which are isolated and have very small known population sizes. Eradication of non-native fishes and control of effluent discharge are the immediate conservation actions required to secure remaining populations of P. senticeps. The small isolated populations of P. senticeps and the absence of migration among them increases the risk of inbreeding and loss of heterozygosity (Keller and Waller 2002). This can have both immediate and long-term consequences on the persistence of these populations due to loss of reproductive fitness and genetic variability (Keller and Waller 2002). Studies are needed to identify measures that need to be implemented to effectively manage the small isolated subpopulations of P. senticeps so as to prevent loss of genetic variability and maintain the species’ long-term adaptability to environmental changes.
[@electronic{2426,
address = {www.iucnredlist.org},
author = {IUCN},
title = {The IUCN Red List of Threatened Species. Version 2017-3},
year = {2017}
}
,@article{2573,
author = {Cambray JA },
journal = {Environmental Biology of Fishes},
pages = {247--268},
title = {The comparative reproductive styles of two closely related African minnows (Pseudobarbus afer and P. asper) inhabiting two different sections of the Gamtoos River system},
volume = {41},
year = {1994}
}
,@article{18477,
author = {Dallas H and Rivers-Moore N },
journal = {South African Journal of Science },
pages = {1--11},
title = {Ecological consequences of global climate change for freshwater ecosystems in South Africa},
volume = {110},
year = {2014}
}
,@article{57498415,
author = {Swartz ER, Skelton PH and Bloomer P },
journal = {Molecular Phylogenetics and Evolution },
pages = {75--84},
title = {Phylogeny and biogeography of the genus Pseudobarbus (Cyprinidae): Shedding light on the drainage history of rivers associated with the Cape Floristic Region},
volume = {51},
year = {2009}
}
,@article{57498415,
author = {Swartz ER, Skelton PH, Bloomer P },
journal = {Journal of Biogeography },
number = {12},
pages = {2086--2099},
title = {Sea-level changes, river capture and the evolution of populations of the Eastern Cape and fiery redfins (Pseudobarbus afer and Pseudobarbus phlegethon , Cyprinidae) across multiple river systems in South Africa},
volume = {34},
year = {2007}
}
,@article{107654052,
author = {Chakona A and Skelton PH },
journal = {ZooKeys},
pages = {109--140},
title = {A review of the Pseudobarbus afer (Peters, 1864) species complex (Teleostei, Cyprinidae) in the eastern Cape Fold Ecoregion of South Africa},
volume = {657},
year = {2017}
}
,@article{107662143,
author = {Keller LF and Waller DM },
journal = {Trends in Ecology and Evolution},
number = {230-241},
title = {Inbreeding effects in wild populations},
volume = {17},
year = {2002}
}
,]
