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Rationale (Changed due to New Information|Incorrect data used previously|Knowledge of criteria)

The Smallscale Redfin (Pseudobarbus asper) is restricted to the Gouritz and Gamtoos river systems within the Cape Fold Ecoregion (CFE) of South Africa (Skelton 2001). This species was reported to have experienced a major reduction in population size and distribution range in the Groot River, a tributary of the Gamtoos River System, due to the presence of the African Sharptooth Catfish (Clarias gariepinus) (E. Swartz, pers. comm.). Within the Gouritz System, this species historically had a wide distribution range, favouring larger tributaries and mainstream type habitats (Skelton 2001). However, recent survey data indicate that this species’ historical range has declined and it currently persists as fragmented subpopulations largely due to multiple impacts including habitat degradation and invasion of the mainstem sections of the rivers by non-native predatory piscivores, mainly Black Bass species (Micropterus spp.), Bluegill Sunfish (Lepomis macrochirus) and African Sharptooth Catfish. Almost all of the Gouritz subpopulations constitute a single location based on the threat of alien invasive fishes, which are both widespread and established in the mainstem sections of the Gouritz River and some of its major tributaries such as the Olifants and the Groot. The only known exceptions the Wynands and Aaps Rivers, which have barriers that would prevent upstream movement of non-native fishes. Smallscale Redfin was recorded both above and below these barriers. The size of the subpopulations above the barriers are not known but these populations are likely to be large enough to be viable in the long term. Hence, there are four known locations, namely the Gouritz, Aaps and Wynands, with the Gamtoos as a fourth location. The species’ current area of occupancy (AOO) ranges from 444 km² to 556 km² (calculated using 2x2 km² grid), including uncertain records, that need to be confirmed. Habitat loss is ongoing and expected to worsen given the predictions of climate change for the CFE (Shelton et al. 2017). At least two localised extirpations have occurred in tributary streams as a result of loss of habitat from upstream water abstraction sources coupled with invasive alien fish impacts from the mainstream. As this species is not a headwater specialist like the Slender Redfin (Pseudobarbus tenuis), it cannot seek refuge in headwater streams and is not well protected by the existing protected area network of the region. The species qualifies as Vulnerable under criterion B2ab(ii,iii,v) and localities currently listed as uncertain need urgent monitoring as species might be extirpated at these localities, which will result in the uplisting of the specie to Endangered.

Distribution

This species prefers mainstream areas of the Gamtoos and Gouritz River systems but also occurs in lower reaches of tributary streams in the latter system (Skelton 2001, Swartz 2005). In a 2016 survey of the central Gouritz River System, viable Smallscale Redfin subpopulations were detected in a number of tributary rivers, namely the Touws, Buffels, Nels (upstream of Calitzdorp Dam), Kruis, Moeras, Wynands, Groot (Meiringspoort), Aaps and Grobbelaars Rivers (Jordaan et al. unpublished data). Although not detected during the survey, subpopulations are also likely present in the Seweweekspoort, Nels, Meul, Oshoekshang and Swartbergs tributaries as historical records exist for Smallscale Redfins in these rivers downstream of the sampling sites. Additional subpopulations were reported by Swartz (2005) in the Weyers, Langtou and Kamma tributaries and their viability and persistence were confirmed in a recent survey that was conducted in early 2018 (Jordaan et al. unpublished data 2018).
There are historical records of the Smallscale Redfin subpopulations from the mainstem sections of major tributaries of the Gouritz, namely the Groot, Olifants, Kammanassie and Gamka Rivers. However, the status of these subpopulations are unknown, but it is possible that some of them have been locally extirpated or have experienced considerable decline in population sizes. Comprehensive surveys of these areas are a priority to determine the status of these populations.

Habitat View more ecological information

Population trend

Trend

There is no information about overall number of mature individuals, but in river sections where the species still persists, it is usually quite abundant. The species has however experienced a major reduction in population size in the Groot River, a major tributary of the Gamtoos River System due to invasion by African Sharptooth Catfish, as well as other anthropogenic impacts. The entire population within the Gamtoos River System represents a single location based on the threat from invasive alien species. Within the Gouritz River System, the Smallscale Redfin was historically widely distributed in the mainstem sections of the river, but currently the species persists as highly fragmented subpopulations within the system. Ten subpopulations of this species in the Gouritz River System were defined as Touws, Groot-Buffels-Swartbergs, Nels (upstream of Calitzdorp Dam), Aaps-Groot (Meiringspoort), Kobus-Seweweekspoort, Moeras, Kruis-Wynands, Oshoekshang, Nels-Meul-Grobbelaars and Langtou-Weyers-Kamma. All of these can be considered viable and recruiting. Historical records exist for Smallscale Redfin subpopulations in the main tributaries of the Gouritz, namely the Groot, Olifants, Kammanassie and Gamka Rivers. The status of these subpopulations are unknown but it is highly unlikely that they are viable, given the known impacts of several invasive fish species that are established in these rivers and the non-detection of the species during recent surveys.

Threats

The Smallscale Redfin prefers mainstream and large tributary habitat, making it very vulnerable to a number of anthropogenic threats such as loss of habitat, pollution and over-abstraction of water. These threats are likely to be exacerbated in the future due to the predicted increase in extreme weather conditions in the CFE as a result of climate change (Dallas & Rivers-Moore 2014). Current water abstraction practices often involves the use of diversion weirs located high up in tributary streams which often result in the lower sections of tributaries running dry for extended periods of time as no provision is made for environmental flow allocations (Jordaan et al. unpublished data).

Alien fish invasions are also a major threat to the Smallscale Redfin as a number of non-native fishes are established in the Gouritz and Gamtoos systems. The main threat to this species in the Gamtoos System appears to be the African Sharptooth Catfish but this require further investigation. During a survey in 2000 (E. R. Swartz unpublished), the African Sharptooth Catfish were recorded far upstream in the Gamtoos River System and only a single specimen of the Smallscale Redfin was recorded from three localities during the survey. The continued persistence of this species in this system is therefore highly uncertain. The Gouritz River and its main tributaries have been poorly sampled to date. Recent ad hoc surveys of the mainstream Gouritz River at Vaalhoek Nature Reserve as well as the Olifants and Gamka River tributaries revealed that several alien invasive fish species have become established and are now abundant in these river sections (Black bass species (Micropterus dolomieu and Micropterus salmoides), African Sharptooth Catfish, Common Carp (Cyprinus carpio), Banded Tilapia (Tilapia sparrmanii), Bluegill Sunfish and Smallmouth Yellowfish (Labeobarbus aeneus)). Ongoing decline in the numbers and distribution ranges of native species in the Gouritz and Gamtoos systems is therefore likely due to these multiple impacts.

The mainstem and lowland habitat requirement of this species also means that it is not well represented by the formal protected area network of the CFE. Within the Western Cape, the Touws and Buffels rivers are associated with the Anysberg Nature Reserve, but the protection value of this is low as both rivers have their upstream reaches located outside the formally protected area. This is also the case for the Groot Swartberg Nature Reserve where the upper reaches of the Groot River, which represents one of the most important remaining stronghold population of the Smallscale Redfin are located outside the protected area. A specimen of the highly invasive African Sharptooth Catfish was recently (2017) recorded in the lower Groot River near De Rust (van der Walt, unpublished data) which is a significant cause for concern given the conservation value of this river to the Smallscale Redfin and its sister species the Slender Redfin (Pseudobarbus tenuis). The African Sharptooth Catfish has been illegally introduced into the Floriskraal Dam located on the upper reaches of the Buffels River, thereby posing a significant invasion risk to downstream Smallscale Redfin habitat. The only rivers where both the headwater reaches of the river as well as the preferred habitat for the Smallscale redfin are located inside a protected area, are the Kamma River originating in the Ruitersbos Nature Reserve and the Oshoekshang River in the Gamkaskloof Nature Reserve.

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 Smallscale Redfin is not targeted by anglers.

Conservation

No conservation actions are in place for this species, mainly because it has not been perceived as threatened in the past. However, the rapid loss of range due to invasion of the Gamtoos by the African Sharptooth Catfish represents a serious conservation concern. The illegal introduction of African Sharptooth Catfish into Floriskraal Dam, and potentially other large storage dams in the Gouritz System (Kamanassie Dam and Stompdrift Dam in the Oustshoorn area) has resulted in a significant invasion risk to the Gouritz system as a whole. Long term monitoring should be initiated in areas where there is significant invasion risk into Smallscale Redfin habitats (especially the Groot River in the Groot Swartberg Nature Reserve) to provide scientifically defensible data on the impacts of African Sharptooth Catfish to be able to inform future conservation action.

References

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 author = {Shelton JM, Weyl OLF, Chakona A, Ellender BR, Esler KJ, Impson ND, Jordaan MS, Marr SM, Ngobela T, Paxton BR, Van Dee Walt JA & Dallas HF},
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,]

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