Red List of South African Species

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

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

Clanwilliam Redfin (Pseudobarbus calidus) is a range restricted species, known from 19 threat defined locations in the Olifants-Doorn River System (ODRS), South Africa. Once widespread, this species underwent a severe decline between 1940 and 2005 due to the spread of invasive fish. Its current extent of occurrence (EOO) is 2351 km2 and area of occupancy (AOO) is 204 km2 (calculated using 2x2 km2 grid). There has been an increase in mature individuals due to conservation projects in the Rondegat and Thee Rivers, alien invasive black Bass (Micropterus spp.) were eradicated from a 4 km stretch in each of these rivers since the last assessment in 2007. Four new subpopulations have also been discovered due to monitoring of relatively inaccessible areas. A number of the subpopulations occur within protected areas where they are protected from alien fish invasion by natural barriers. However, there is still ongoing decline occurring within a number of subpopulations. Due to the success of conservation actions as well as the discovery of new subpopulations, this species has been down listed from Vulnerable to Near Threatened B1b(iii)+2b(iii).

Distribution

This small cyprinid is endemic to the Olifants-Doorn River System (ODRS) of South Africa (Skelton 2001). It was historically recorded in the mainstream of the Upper Olifants near Clanwilliam and Keerom in the 1930s, prior to the introduction of Bass species (Micropterus spp.) (Harrison 1939). It is currently found in the Diepkloof, Dwars, Ratels, Oudste, Thee, Noordhoeks, Boontjies, Boskloof, Heks, Rondegat and Jan Dissels tributaries of the Olifants River and the Brandewyn, Biedouw, Tra Tra, Eselbank, Driehoeks, Matjies, and Breekkrans and Leeu tributaries of the Doring River. Each of these 19 subpopulations can be regarded as separate locations. Although the known distribution range has expanded due to the discovery of new subpopulations, in the upper tributaries it is still restricted and fragmented because of Bass predation. Elsewhere its distribution range has substantially shrunken because of Bass invasions since the 1940s and it is now typically only found in the middle and upper reaches of tributary streams above natural Bass barriers such as small waterfalls (van der Walt 2014).

Population trend

Trend

It is relatively abundant in good habitat where alien fishes are absent above natural barriers, however some of these subpopulations are small and isolated. The presence of invasive alien species serves as a barrier between the 19 subpopulations.

Threats

The most important threat to the Clanwilliam Redfin is predation by invasive alien fishes, especially Bass which dominate large areas of the ODRS. The introduction of Smallmouth Bass (Micropterus dolomieu) and Spotted Bass (Micropterus punctulatus) into the system in the 1930s for angling purposes is regarded as the most severe threat, with additional predatory impacts from Bluegill Sunfish (Lepomis macrochirus) and Rainbow Trout (Oncorhynchus mykiss). Banded Tilapia (Tilapia sparrmani) is a competitor for food and resources. The other major threat is habitat degradation and possible agrichemical pollution as a result of intensive farming of deciduous fruit and citrus (Impson and Swartz 2002). Further impacts are over-abstraction of water during the dry summer months and the planting of orchards within the 1:100 year floodline of the river. The absence of a natural riparian zone, and hence buffer area between the river and intensive agriculture, allows fertilizers and pesticides easy access to the aquatic environment.

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. Translocations of indigenous freshwater fish species are controlled by Cape Nature’s Indigenous Fish Utilisation policy (Jordaan et al. 2016). The Clanwilliam Redfin is not targeted by anglers. It has been kept in public aquaria for awareness purposes.

Conservation

Considerable conservation action since the last assessment has improved the conservation of this species. These include the successful eradication of Smallmouth Bass using rotenone from the lower Rondegat River in 2013, followed by significant recovery of the Clanwilliam Redfin and other threatened cyprinids (Weyl et al. 2014). In addition, Spotted Bass was successfully eradicated by CapeNature from 4 km of the Thee River between 2010 and 2014 using mechanical methods, resulting in significant recovery of Clanwilliam Redfins (Van der Walt et al. unpublished data). The distribution range of the species extends both into provincial nature reserves and Mountain Catchment Areas, but many populations also occur on privately owned land. The upper reaches of the Boskloof, Jan Dissels, Noordhoek and Rondegat rivers are within the Cederberg Wilderness Area whereas the middle Matjies River is within the Matjies River Nature Reserve. The upper reaches of the Thee and Ratels Rivers are situated within the Winterhoek Mountain Catchment Area. Although these rivers are within formally protected areas, this does not imply that they are free of invasive alien fishes or from future invasion. Recently, the local conservation authority CapeNature has published a management-focused report on priority rivers for fish conservation in the ODRS (Impson et al. 2016), which includes almost all rivers where Clanwilliam Redfin occur.

References 

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,]
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