Red List of South African Species

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Endangered (EN)
B1ab(ii,iii,v)+2ab(ii,iii,v)

Rationale

A recent comprehensive survey of the Verlorenvlei River System in 2015 showed that the distribution of Pseudobarbus verloreni is fragmented. Remnant subpopulations of this species occur in the Krom Antonies and Kruismans Rivers, and a series of pools in the lower Verlorenvlei River (Chakona et al. 2014, Chakona et al. in prep). The Krom Antonies River population appears to be the only one that is viable as the riparian zone and water quality in the Krom Antonies River sub-catchment is relatively undisturbed. The other remnant subpopulations are unlikely to be viable in the long term. The upper Kruismans River remnant subpopulation occurs in a very short stretch of river, and is represented by a small known population size. This species was found in two remnant pools in the mainstem section of the Kruismans River in January 2015, but it is unlikely that these pools would have persisted throughout the dry season. There was also a high abundance of non-native Banded Tilapia (Tilapia sparrmanii) in these small isolated pools which could potentially have negative effects on the native species through increased competition and predation on juvenile redfins. The lower Verlorenvlei River population, near the town of Redelinghuys, was only represented by juveniles and sub-adult, suggesting that these pools could potentially be acting as sinks, whereas the Krom Antonies River and upper Kruismans River subpopulations may potentially act as the sources. This, however, needs to be further investigated in future surveys. The lower Verlorenvlei is heavily polluted and heavily invaded by Banded Tilapia. There are no instream physical barriers to protect the remnant subpopulations of P. verloreni from invasion by non-native species, thus the three remnant subpopulations constitute one location. Water abstraction is also a significant threat that affects long term persistence of isolated pools which provide refugia for the species in the intermittent Verlorenvlei River System during the dry season. There are further threats from proposed tungsten mining in the Krom Antonies River subcatchment, which will affect the remaining stronghold subpopulation of this species. While there is potentially more available habitat for this species in the lower Verlorenvlei (there are a series of large pools in the lower section of the river), the current known available habitat is less than 1 km2 (based on 2015 surveys by Chakona et al, in prep). With an area of occurrence (AOO) of 40 km2 and an extent of occurrence (EOO) of 329.7 km2, there is one location defined by the distribution of invasive alien fish, which is present throughout the system, and causing continuous decline in the AOO, habitat quality and a reduction in the number of mature individuals. P. verloreni qualifies for Endangered B1ab(ii,iii,v)+2ab(ii,iii,v).

Distribution

Pseudobarbus verloreni is endemic to the Verlorenvlei River System on the west coast of South Africa (Chakona et al. 2014). The species’ historical distribution range possibly extended into the neighbouring Langvlei River System, but recent surveys suggest that the Langvlei population may have been extirpated due to complete water abstraction (Chakona et al. in prep).

Population trend

Trend

A recent survey in 2015 (Chakona et al. in prep) identified three remnant subpopulations of this species (the Krom Antonies, the upper Kruismans and the lower Verlorenvlei Rivers). While this species was found in three small isolated pools in the mainstem Kruismans River during this survey, these pools are unlikely to have persisted throughout the dry season. Historically, the Verlorenvlei River System would have receded into a series of isolated pools sustained by ground flow, but excessive water abstraction in this extremely dry catchment is affecting long term persistence of these refugial pools. Much of the river was found to be completely dry during the 2015 survey (Chakona et al. in prep). Given that the upper Kruismans River remnant subpopulation occurs in a very short stretch of river (possibly less than 500 m long), and that the riparian zone is heavily infested by the non-native Populus tree vegetation, while the lower Verlorenvlei River has both been heavily invaded by non-native fishes and impacted by pollution from the adjacent town of Redelinghuys, these remnant subpopulations are considered to be at high risk and may not be viable in the long-term. The Krom Antonies River subpopulation is the only remaining stronghold for this species.

Threats

The species was possibly widespread throughout the Verlorenvlei and Langvlei River systems in the past, but numbers are likely to have declined during the last century due to predation and competition from introduced fish species, pollution and habitat degradation. The presence of non-native piscivorous Black Bass species (Micropterus spp.) and potential competitors, such as Banded Tilapia (Tilapia sparrmanii), Mozambique Tilapia (Oreochromis mossambicus) and Common Carp (Cyprinus carpio), habitat degradation and excessive water withdrawal for agricultural purposes pose the greatest threat to the survival of this species.

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 (Ordinance 19 of 1974) for the Western Cape, thereby preventing the collection and trade of the species without a permit. It is envisaged that the listing will be amended to include P. verloreni and other newly described species of the region. Translocation of indigenous freshwater fish species are controlled by CapeNature’s Indigenous Fish Utilisation policy (Jordaan et al. 2016).

Conservation

Protection of critical habitats and establishment of sanctuaries are some of the most immediate conservation measures required to prevent further decline. The effectiveness of current protected areas in the conserving of Pseudobarbus verloreni is limited because they largely encompass upland areas where this species does not occur. The recent establishment of the Krom Antonies Protected Environment (PE) under the National Environmental Management: Protected Areas Act will contribute to the long term conservation of P. verloreni as the entire catchment area of the Krom Antonies River is included within the area that is now formally protected. Prevention of alien fish introductions and maintaining ecological functioning of the river through sustainable water allocations would however need to form part of the management objectives of the PE in order to afford protection to P. verloreni. Long term measures to protect and prevent extinction of this species may have to include eradication of alien fishes and the construction of barriers to prevent re-invasion where feasible, and restoration of existing habitats to facilitate recovery. An alien fish barrier is planned in the Krom Antonies River, 2 km below the upper limit of P. verloreni. This section of the Krom Antonies River was recently invaded by Largemouth Bass (Micropterus salmoides) and the plan is to eradicate the Bass species with mechanical methods after the construction of the alien fish barrier.

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