Red List of South African Species

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Vulnerable (VU)
B1ab(iii,iv)+2ab(iii,iv)
Assessors: Martine Jordaan Albert Chakona
Facilitators: Dewidine Van Der Colff
Reviewers: Olaf Weyl

Rationale (Changed due to New Information)

The Breede lineage of Pseudobarbus burchelli (hereafter Pseudobarbus sp. nov. 'breede') is distributed in three isolated river systems, the Breede, Duiwenhoks and Goukou, in the Cape Fold Ecoregion (CFE). Comprehensive surveys conducted between 2008 and 2015 indicated that redfins have been extirpated from the mainstem sections of the Breede, Duiwenhoks and Goukou rivers where this species does not co-occur with non-native Black Bass (Micropterus spp.) and African Sharptooth Catfish (Clarias gariepinus). Remnant populations now persist in headwater tributaries that have not been invaded by non-native species, particularly Rainbow Trout (Oncorhynchus mykiss) and Smallmouth Bass (Micropterus dolomieu) (Chakona & Swartz 2012). Major population declines for the redfin likely occurred shortly after the introduction and subsequent establishment of these species during the mid 20th century. There are no data on the timing and magnitude of these declines, therefore Criterion A does not apply. Most of these 20 subpopulations are relatively large and are likely to persist into the future and are unlikely to be affected by the lack of connectivity due to presence of instream physical barriers (weirs) and non-native fishes in the mainstem. At least seven locations exist and these were evaluated based on the threat of non-native fish. Its current extent of occurrence (EOO) ranges from 12,777 km2 and area of occupancy (AOO) ranges from 348 km2 (calculated using 2x2 km2 grid) based on known extant localities. Habitat loss is likely ongoing and expected to worsen given the predictions of climate change for the Cape Fold Ecoregion (CFE). Predictions for the region include increases in temperature and decreases in surface runoff, both of which will result in a deterioration of habitat quantity and quality for stream fishes in the region. This is likely to be exacerbated by an increase in the demand for water for agriculture which may result in excessive and unsustainable water abstraction. While this taxon has a number of viable subpopulations within nature reserves, the majority of populations occur outside formally protected areas. The lineage qualifies as Vulnerable under criterion B1ab(iii, iv)+B2b(iii,iv).

Distribution

Pseudobarbus sp. nov. 'Breede' is distributed across three isolated river systems, the Breede, Duiwenhoks and Goukou, in the Western Cape Province, South Africa (Chakona et al. 2013, Swartz et al. 2014). The historical range of this lineage would have included the mainstem sections of these rivers, but invasion by non-native piscivores, initially Black bass and subsequently African Sharptooth Catfish, caused severe population fragmentation. Remnant populations persist in headwater tributaries that have not been invaded by Rainbow Trout and Smallmouth Bass (Chakona and Swartz 2012, Shelton et al. 2015). At least 19 viable populations exist in a number of tributaries of the Breede, including the Witte (Bainskloof area), Jan du Toits (Worcester area), Sanddrif, Amandel, Hex (De Doorns area), Willem Nels (Robertson area), Hoeks (McGregor), upper Riviersonderend and Du Toits (upstream of Theewaterskloof Dam), Meul, Gobos, Baviaans, Soetmelksvlei, Slang (Greyton area), Mardouw, Leeu, Keurbooms, Koornlands (Swellendam area) and the Melkhout (Witsand area). In addition, populations exist in the Titus, Tierhokskloof and Dwars Rivers (Ceres area), upper Nuy River and upper Keisie River (Montagu area) but the viability of these populations are uncertain. Viable populations also exist in the Duiwenhoks and Goukou River systems. A large and viable extralimital population exists in the Eerste River (Stellenbosch area) but this population is excluded from the assessment until further investigation of its origins.

Population trend

Trend

There is limited information about overall number of mature individuals, but in localities where this lineage occurs, it is usually abundant. There are at least 18 subpopulations of this taxon in the Breede River System while the Duiwenhoks and Goukou constitute two additional subpopulations. Several of the populations are likely declining, but no specific information is available on population trends.

Threats

As with the majority of indigenous fish species of the CFE, non-native fishes and excessive water abstraction are considered the primary threats to Pseudobarbus sp. nov. 'breede' (Chakona & Swartz 2012, Darwall et al. 2009, Shelton et al. 2014a). The major impact on this taxon is likely to have occurred following the introduction of Smallmouth Bass which was introduced into South Africa in the 1930s for recreational angling purposes (Ellender and Weyl 2014). Cambray and Stuart (1985) reported that during their surveys, Redfins were collected only once in the main channel of the Breede River and all the other collections were from the tributaries of this river system, and that redfins did not co-occur in these habitats with either Black Bass or Rainbow Trout. The African Sharptooth Catfish has recently invaded and has become established in the Breede River System where it poses a new threat particularly to the remnant tributary populations of native fishes as it could be capable of moving across some of the instream physical barriers that have for years protected native fishes from potential invasion by bass. African Sharptooth Catfish has been found to be able to invade tributaries and headwater streams elsewhere in the CFE (Ellender et al. 2015).
Monitoring the spread of this species in the headwaters of the Breede should thus be made a priority. Recent research on the impacts of Rainbow Trout in headwater streams of the Breede River system by Shelton et al. (2014a) has indicated that native fish density for three native species, including Pseudobarbus sp. nov. 'breede', was significantly reduced in the presence of trout and that trout completely displaced native fish at more than 50% of the study sites. Furthermore, juvenile native fish were largely absent from invaded streams but abundant in non-invaded areas, suggesting that trout impacts endemic fishes through size-selective predation. Shelton et al. (2014b) also highlighted the important role of instream barriers for preventing Smallmouth Bass invasion to the upper Witte River, a tributary of the Breede River System. The upper Witte remains highly vulnerable to invasion by African Sharptooth Catfish which has now penetrated up to the small waterfall which is an effective barrier to Smallmouth Bass (Shelton et al. 2014b). 
Additional threats to Pseudobarbus sp. nov. 'breede' and its habitat is agricultural development which results in agrichemical pollution, disturbance of instream and riparian habitat and excessive water abstraction. Cambray and Stuart (1985) noted that the times of spawning and hatching of Redfin fry (spring and summer) coincide with the periods of high water demand and increased abstraction, as well as increased levels of agrichemical use. This likely results in mortality of larval and juvenile life stages and can thus impact on recruitment.
Pseudobarbus sp. nov. 'breede' is also likely to be extremely sensitive to impacts associated with predicted climate change, such as increased temperatures and decreased surface flows. Dallas et al. (2017) investigated environmental variables associated with the presence and absence of redfins in their native range and reported that this taxon was sensitive to water quality parameters including increased conductivity and reduced oxygen levels. Their results suggest that redfin populations are reliant on flowing water and are unlikely to persist in habitats where flow stops in summer as these conditions are associated with water quality variables which are outside their tolerance ranges.
At least seven locations exist, identified based on the major threat of alien invasive fish. Known locations are the Witte and upper Riviersonderend River locations, situated upstream of invasive fish barriers in formally protected areas. There are also the Hoeks and Baviaans River locations where this taxon persists upstream of gauging weirs which serve as invasion barriers. As limited information exist about instream barriers to invasive fish in the rest of the Breede River System, the rest of the populations in this system are viewed as one location due to potential future invasion by non-native piscivores from the mainstem. Other locations are the Duiwenhoks and Goukou River systems.

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 Breede River Redfin is not targeted by anglers.

Conservation

No specific conservation plans are in place for this taxon despite the fact that the majority of populations exist outside of formally protected areas. Populations that do occur in protected areas upstream of invasive fish barriers are those in the Witte River in Limietberg Nature Reserve, the upper Riviersonderend and Du Toits Rivers in the Hottentots Holland Nature Reserve and the Baviaans River in the Riviersonderend Nature Reserve. Other smaller subpopulations are also present in reserves such as the Meul, Gobos and Jan du Toits populations, but these lack instream barriers and are open to invasion by non-native fishes. African Sharptooth Catfish have already invaded the Gobos River from the mainstream Riviersonderend where they are established (Jordaan et al. unpublished data). While monitoring has been initiated in the Gobos River in 2014, the impacts of this invader in tributary habitat is not clearly understood. Many off-reserve populations, such as those in the Hex, Amandels and Sanddrif Rivers are threatened by the presence of Rainbow Trout.

References 

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,]
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