Red List of South African Species

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Endangered (EN)
B1ab(ii,iii,v)+2ab(ii,iii,v)
Assessors: Riaan Van der Walt Ernst Swartz Roger Bills Dean Impson Martine Jordaan
Facilitators: Dewidine Van Der Colff
Reviewers: Domitilla Raimondo Rajeev Raghavan Jörg Freyhof

Rationale (Changed due to Same category and criteria)

A range restricted species, known from three locations (Heks, Thee and Noordhoeks tributaries) in the Olifants-Doring River System (ODRS), South Africa. Its extent of occurrence (EOO) is 164 km2 and area of occupancy (AOO) is 36 km2. There is continuous decline in the number of mature individuals, AOO and quality of habitat due to predation from alien invasive fish and water abstraction. The species' habitat may also be threatened by pesticide runoff from the agricultural activities located next to the rivers. While it does not occur in any provincial nature reserves, all three tributaries are located within the Cederberg Mountain Catchment Area and the upper section of the Heks River is located within the Cederberg Wilderness Area. This species is listed as Endangered under criteria B1ab(ii,iii,v)+2ab(ii,iii,v).

Distribution

This species is endemic to three tributary streams of the Olifants branch of the Olifants-Doring River System (ODRS), Western Cape Province, South Africa. The ODRS drains the Cederberg and Koue Bokkeveld Mountains (Bills 1999). It has previously been recorded from the mainstream of the Olifants River at the Heks River confluence, but unsustainable water extraction has caused these areas to dry up several times in the last few years, suggesting that this area is recolonized from the Heks subpopulation.

Population trend

Trend

Although the range of this species is reasonably well known, information about population trends is lacking. There has most likely been a loss of mainstream habitats in the last ten years, and the distribution range in the Noordhoeks tributary has fluctuated depending on where water extraction occurs. However, more accurate information is needed to study long-term trends. The last population estimate was done by Bills in 1999 and he estimated a total of 5020 individuals (Bills and Impson 2013).

Threats

Alien invasive species have severely fragmented subpopulations of this species in the past. Smallmouth Bass (Micropterus dolomieu) and Spotted Bass (M. punctulatus) probably caused a major reduction in population size just after their introduction into the ODRS in the 1940s. The Noordhoeks and Thee Rivers are currently free of Micropterus spp. but are invaded by Banded Tilapia (Tilapia sparrmanii) (Mhombeni 2009, van der Walt et al. 2016). The third subpopulation is in the Hex River which is invaded by Smallmouth Bass and Bluegill Sunfish (Lepomis macrochirus). Here this species co-exists with these aforementioned alien fish species, but probably in reduced numbers because of predation. Unsustainable water extraction in summer is a major threat, especially the low gradient sections of tributary streams that this species seems to prefer. There is almost 100% abstraction from the lower reaches of the three tributary streams during the dry season (November to March), with the result that this species only survives above extraction points. The effect of agrichemicals, mainly insecticides, has not been quantified, but all the tributary streams have orchards planted alongside them and it is likely that insecticide runoff effects all three subpopulations (Bills 1999).

Uses and trade

All indigenous fish species of the Western Cape Province are listed as Endangered Wild Animals under Schedule 1 of the Provincial Nature Conservation Ordinance for the Western Cape, thereby preventing the collection and trade of the species without a permit. Translocation of indigenous freshwater fish species are controlled by CapeNature’s Indigenous Fish Utilisation policy (Jordaan et al. 2016).

Conservation

Impson and Bills (2013) have developed a conservation plan for both Austroglanis species that occur in the ODRS. Impson et al. (2016) have produced a report on priority rivers in the ODRS for fish conservation, awareness and management purposes. Plans are underway to do river rehabilitation for other species in the Cederberg Mountains, and if successful it can be attempted for tributary streams where this species occurs. In 2013, an alien fish barrier was constructed above the Keerom road bridge that crosses the Noordhoeks River. This should prevent Micropterus spp. from invading the river above this point. An invasive population of Spotted Bass was successfully removed using mechanical methods from the Thee River between 2010 and 2014. Despite the headwaters of all three tributaries being within the Cederberg Mountain Catchment Area, the current distribution of A. barnardi is not within any provincial nature reserves.

References 

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,@article{2426,
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 title = {Biology and conservation status of the Clanwilliam rock catfish and spotted rock catfish},
 year = {1999}
}
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}
,@techreport{2426,
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}
,@techreport{2426,
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 author = {Bills, R. & Impson, D},
 institution = {South African Institute of Aquatic Biodiversity},
 title = {Conservation biology of endangered freshwater fishes – Linking conservation of endangered freshwater fishes with river conservation, focusing on the Cederberg},
 year = {2013}
}
,@article{2426,
 author = {Van der Walt, J.A., Weyl, O.L.F., Woodford, D.J. & Radloff, F.G.T. },
 journal = {Aquatic Conservation: Marine and Freshwater Ecosystems},
 pages = {736--748},
 title = {Spatial extent and consequences of black bass (Micropterus spp.) invasion in a Cape Floristic Region river basin.},
 volume = {26},
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}
,@electronic{2426,
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,@phdthesis{2426,
 author = {Mhombeni, V},
 school = {Rhodes University},
 title = {The biology of Austroglanis gilli and Austroglanis barnardi (Siluriformes: Austroglanididae) in the Olifants River system , South Africa. MSc dissertation},
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}
,@techreport{2426,
 address = {Pretoria},
 author = {Impson, D. & Bills, R},
 institution = {Water Research Commission},
 title = {Developing a conservation action plan for rock catfishes and the Twee River redfin in the Olifants-Doring River System},
 year = {2013}
}
,]
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