Red List of South African Species

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Near Threatened (NT)
Assessors: Riaan Van der Walt Martine Jordaan Roger Bills Dean Impson
Facilitators: Dewidine Van Der Colff
Reviewers: Domitilla Raimondo Rajeev Raghavan Jörg Freyhof

Rationale (Changed due to Knowledge of criteria|New Information)

Clanwilliam Rock Catfish (Austroglanis gilli) is endemic to the Olifants-Doring River System (ODRS), South Africa, where it has been recorded from 16 tributaries (16 locations). Its extent of occurrence (EOO) is 2080 km2 (calculated using minimum convex polygon) and area of occupancy (AOO) is 196 km2 (calculated using a 2 km2 grid). Recent conservation efforts have increased the viability of two locations (Rondegat and Thee River). Five locations are located in formal conservation areas. In the previous assessment (2007) the number of locations was regarded as five now there are 16 locations identified, based on a better understanding of the criteria. However, these locations are currently still experiencing continuous decline in habitat quality and the extent of occurrence due to unsustainable water abstraction and other threats. The species was previously listed as Vulnerable but has been reclassified as Near Threatened B1b(i,iii)+2b(i,iii) due to conservation efforts and more information available on the number of locations.

Distribution

Clanwilliam Rock Catfish (Austroglanis gilli) is endemic to the Olifants-Doring River System (ODRS) in the Western Cape, South Africa. It occurs in tributaries of the Olifants (Ratel, Oudste, Thee, Noordhoeks, Boontjies, Boskloof, Heks, Rondegat, Jan Dissels, Dwars) and Doring (Biedouw, Tra Tra, Eselbank, Matjies, Krom and Breekkrans) basins of the ODRS and also occurs in the mainstream Olifants River near the Heks tributary (Bills 1999, Van der Walt 2016).

Population trend

Trend

There are large subpopulations (possibly more than 1,000 mature individuals) in the Oudste, Thee, Noordhoeks, Boskloof, Heks (including the mainstream Olifants nearby), Rondegat, Jan Dissels, Dwars, Breekkrans and Krom tributaries and smaller populations (possibly less than 1,000 mature individuals) in the Ratel, Boontjies, Biedouw, Tra Tra, Eselbank and Matjies tributaries (Bills 1999).

Threats

The introduction of alien fishes, particularly Smallmouth Bass (Micropterus dolomieu) into the Olifants-Doring River System (ODRS) in the 1940s, probably caused a major reduction in their range and numbers in mainstem habitats. Since then, the decline due to alien fish predation and competition has reduced due to the inability of Smallmouth Bass and Spotted Bass (Micropterus punctulatus) to move above some barriers in tributary streams. Currently, the cobble habitat found in the tributaries are their preferred habitat, where in some streams they co-exist with alien invasive Bass species. There appears to be an interaction between the amount of sand cover over cobbles (exacerbated in rivers in heavily farmed areas) and vulnerability to impacts from Micropterus spp. (Woodford et al. 2005). Further research is required to assess the specific impacts of invasive alien fish, currently there is evidence that it has negative impacts on the abundance of Austroglanis gilli. Large parts of the ODRS, especially the fertile river valleys are heavily farmed for citrus. Unsustainable water abstraction for irrigation purposes during the hot dry season (November to March) is a major threat that affects the middle to lower reaches of almost all the tributary streams as well as most mainstream areas. Rates of abstraction are usually so severe it stops river flow, resulting in habitats being reduced to warm shallow pools that are not the preferred habitat of this species. The effect of insecticides has not been quantified, but could have an increasing impact in the future as more orchards are being established (Bills 1999).

Uses and trade

This small species is not a target of subsistence or recreational anglers, and is not kept in aquaria, except for public awareness purposes under permit.

Conservation

In 2012 and 2013, about 4 km of the Rondegat River in the ODRS was successfully treated with rotenone to remove invasive Smallmouth Bass (M. dolomieu) which has led to substantial recoveries of several threatened fish species (Weyl et al. 2014) and this should also lead to increases in the population size in that section of the river. Further rotenone treatments are planned for the Biedouw and Breekkrans Rivers to remove Bass species (Micropterus spp.) and this is expected to increase population sizes of Austroglanis gilli and several threatened cyprinid species. In the Thee River of the ODRS, invasive Spotted Bass (Micropterus punctulatus) were successfully removed using mechanical methods between 2010 and 2014 from a 5 km stretch of the lower river which should benefit A. gilli. Five of the 16 locations for the species are partly in formal conservation areas (for example Cederberg Wilderness Area). In addition, Impson and Bills (2013) have prepared a conservation plan for the Catfishes (Austroglanis spp.) of the ODRS. This details actions needed to more effectively conserve these species. Recently, a report has been written by the conservation authority CapeNature on the priority rivers for fish conservation in the ODRS, which includes management actions required for effective protection of its habitat (Impson et al. 2016)

References 

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 author = {Mthombeni, V. },
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,@article{2427,
 author = {Woodford, A.J., Impson, N.D.,Day, J.A. & Bills, I.R.},
 journal = {African Journal of Aquatic Science},
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 title = {The predatory impact of invasive alien smallmouth bass, Miicropterus dolomieu (Teleostei: Centrarchidae), on indigenous fishes in a Cape Floristic Regions mountain stream.},
 volume = {30},
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}
,]
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