Red List of South African Species

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

Rationale (Changed due to Knowledge of criteria)

This once widespread and abundant species suffered major declines in population size and distribution range between 1940 and 1970 following the introduction of Smallmouth Bass (Micropterus dolomieu) into the Olifants-Doring River System (ODRS) in the 1940s. The current population is, however, still likely to be suffering a continued slow decline (reduction in the number of mature individuals, habitat quality and reduction in area of occupancy (AOO)) as a result of range expansions of invasive alien fishes. The extent of occurrence (EOO) is approximately 7872 km2 and the AOO is approximately 120 km2 and it is known from 15 locations, consisting of eight locations in the Olifants catchment area and seven in the Doring catchment area. Because the number of locations exceeds 10, the species cannot be listed as threatened, but qualifies as Near Threatened B1b(ii,iii,v)+2b(ii,iii,v). This species should be monitored to detect deterioration in its status.

Distribution

The Clanwilliam Yellowfish (Labeobarbus seeberi - previously Labeobarbus capensis) is endemic to the large Olifants-Doring River System (ODRS) on the West Coast of South Africa (Skelton 2001). It was once widespread in both the Olifants and Doring rivers and many of their tributaries until the introduction of bass (Micropterus spp.) in the 1940s (Harrison 1938, van Rensburg 1966, de Moor and Bruton 1988). It is now uncommon in the Olifants and Doring rivers, except the upper Olifants in the gorge and several tributaries where alien bass are not present (Impson 2007). They are still widespread but uncommon in the Doring River (Paxton et al. 2002). The number of locations is at least 15, consisting of the Olifants Gorge on the upper Olifants River and the Dwars, Ratels, Thee, Noordhoek, Boskloof, Rondegat, and Jan Dissels tributaries of the Olifants River, and  the Oorlogskloof, Brandewyn, Biedou, Tra Tra, Eselbank, Driehoeks-Matjies and the Groot-Leeu tributaries of the Doring River. The locations include impoundments in or adjacent to the river, for example Beaverlac Dam in the Ratels catchment. There are two extra-limital subpopulations in the ODRS in the Twee River and Boontjies River, where it was stocked by the local conservation agency CapeNature above a waterfall barrier.

Population trend

Trend

Anecdotal reports indicate very large numbers of Clanwilliam Yellowfish were present in suitable habitat before the introduction of Smallmouth Bass into the system in the 1940s (Harrison 1938, Wells 1949). Currently, most healthy recruiting subpopulations of Clanwilliam Yellowfish are found only in areas free of alien fishes. There are at least 15 subpopulations, with limited genetic exchange between them because of impacts of alien fishes dominating the Olifants and Doring rivers. Rivers that have the largest subpopulations are the Driehoeks-Matjies, Olifants (gorge area), Oorlogskloof-Kobee, Ratels and Rondegat. A new subpopulation has recently been found in the Dwars River, a tributary of the upper Olifants. There is also a large subpopulation in the Beaverlac Dam, an off-stream dam on the Ratels River (Impson 2010). The species has two notable extra-limital subpopulations in the Twee River above a waterfall barrier (Impson et al. 2007) and the Boontjies River catchment (Agter Pakhuis), where it occurs above a waterfall barrier in an instream dam at Bushmanskloof Game Reserve and the river itself (Impson and Tharme 1998). These healthy populations are in areas that probably represent less than 10% of its original distribution range. The species is also present in several other rivers, where it is common but not plentiful due to the presence of alien fishes (for example Doring River) or because of limited habitat (for example Thee River, Noordhoeks River). However, as the Olifants-Doring River System is large, the healthy population presenting only 10% of the original distribution, still equates to a large population size.

Threats

The major threat to the species has been the predatory impact of invasive alien fish species, especially Smallmouth Bass (van Rensburg 1966, Gaigher 1973, Bills 1999) and, to a lesser extent, Bluegill Sunfish (Lepomis macrochirus), Largemouth Bass (Micropterus salmoides) and Spotted Bass (Micropterus punctalatus). Juvenile Clanwilliam Yellowfish also compete with Banded Tilapia (Tilapia sparrmanii), and Bluegill Sunfish for food. Habitat degradation is another substantial threat as the Olifants catchment and some tributaries are the focus for intensive citrus, deciduous fruit and vineyard development. Two large instream dams (Clanwilliam and Bulshoek) act as barriers to fish migration, and rivers are over-abstracted to fill hundreds of smaller farm dams. Over-abstraction is a very serious problem in the dry season (summer). The lower reaches of many tributaries have been bulldozed and canalised for flood protection purposes. The excessive use of fertilisers and pesticides (many copper based) also poses a substantial threat to indigenous fishes (Bills 1999). Climate change is a future threat to the region, with rainfall expected to decrease and become more erratic and temperatures to increase.

Uses and trade

This species is esteemed by anglers, especially fly fishermen because of its appearance and power. It was bred in the 1980s and 1990s at the Clanwilliam Yellowfish hatchery then stocked into dams and some rivers. Stockings are now controlled by CapeNature’s Indigenous Fish Utilisation policy (Jordaan et al. 2016). It is kept in public aquaria for awareness and education purposes.

Conservation

Clanwilliam Yellowfish is nationally listed as a Threatened and Protected species under the National Environmental Management: Biodiversity Act of 2004 and listed as ‘endangered’ by the provincial Nature Conservation Ordinance making catch and release compulsory. The upper reaches of several tributaries (e.g., Rondegat, Driehoeks, Matjies Rivers) with good Clanwilliam Yellowfish populations are situated in protected areas such as the Cederberg Wilderness Area. The Greater Cederberg Biodiversity Corridor (GCBC), which encompasses the majority of the Olifants-Doring catchment, was established in 2004 to enable authorities and private land-owners to jointly manage valuable conservation areas. 
The most important tributaries and mainstem areas for indigenous fish conservation in the Olifants River system have been identified as “Fish Sanctuary Areas” in the national Atlas of Freshwater Ecosystem Priority Areas (Nel et al. 2011). The provincial conservation authority, CapeNature, has initiated successful river rehabilitation projects using rotenone to eradicate alien fishes such as bass from “Fish Sanctuaries Areas” in the ODRS. The Rondegat River has been the recent successful focus of this programme, with a combined project to eradicate Smallmouth Bass from 4 km river (Impson et al. 2013, Weyl et al. 2014) as well as invasive vegetation from the riparian zone (Impson et al. 2013). Clanwilliam Yellowfish and several other threatened fish species are successfully re-colonising the area cleared of bass (Weyl et al. 2014). Three more rivers (Krom, Biedouw, Breekkrans) are now the focus of the programme and successful operations will substantially assist the conservation of this species. South Africa’s national yellowfish working group, established in 1997, includes in its aims promoting awareness of threatened yellowfishes and increasing research and monitoring effort on such fishes culminating in a South African status report on the yellowfish group (Impson et al. 2007). The local conservation agency, CapeNature, recently published a report on priority rivers in the ODRS for fish conservation to improve management of these rivers (Impson et al. 2016).

References 

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,]
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