Red List of South African Species

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Critically Endangered (CR)
B1ab(iii)
Assessors: Francios Roux Andre Hoffman
Contributors: Johan Engelbrecht Roger Bills
Facilitators: Dewidine Van Der Colff
Reviewers: Domitilla Raimondo Edward Harrison

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

The geographic range of Treur River Barb (Enteromius treurensis) is restricted to a 4.5 km stretch of the upper reaches of the Blyde River, Limpopo River system (Kleynhans 1982, 1984). Previously this species was reported from the Treur River (a tributary of the Blyde River) where the type locality for this species was recorded. However, the introduction of alien and invasive species such as Rainbow Trout (Oncorhynchus mykiss), Brown Trout (Salmo trutta) and Smallmouth Bass (Micropterus dolomieu) in the late 1960s led to the disappearance of this species in the Treur River. The remaining population in the Blyde River is protected by a downstream waterfall (Christmas pools) (Kleynhans 1982, 1984; Skelton 1987). In 1995 a re-introduction of this species from the Blyde River into the Treur River was conducted when 504 individuals collected in the Christmas pools below the waterfall barrier was translocated (Engelbrecht and Roux 1999). Since this introduction, surveys revealed that the population established itself and downstream re-colonization has taken place. There are thus at present two known viable subpopulations in the upper catchments of the Blyde River that are severely fragmented as the subpopulations are small and isolated. These small subpopulations are relatively low in abundance and the geomorphology of these rivers consists mainly of mountain headwater streams and mountain streams with large waterfalls restricting migration between the two subpopulations. Furthermore, the presence of trout (Oncorhynchus mykiss and Salmo trutta) in the lower Blyde River before the confluence of the Treur River further restricts movement of overspill from both subpopulations. This species is currently experiencing a continuous decline in habitat quality as it is distributed within commercial forestry areas and is potentially threatened by invasive alien species. Enteromius treurensis has a very restricted range with an area of occupancy (AOO) of 16 km2 and an extent of occurrence (EOO) of 46 km2 and is experiencing continuous decline in quality of habitat. It is thus assessed as Critically Endangered B1ab(iii).

Distribution

The only remaining natural subpopulations are in the upper Blyde River (tributary of the Limpopo River system). This population is restricted to a 4.5 km stretch of river above a waterfall (Kleynhans 1982, 1984, 1996). A re-introduction of this species was done into the Treur River (part of its natural distribution) in 1995 and has established in a stretch of river of approximately 7 km long (Engelbrecht and Roux 1999).

Population trend

Trend

The Treur River Barb (Enteromius treurensis) subpopulation in the upper reaches of the Blyde River has been estimated by Kleynhans (1982, 1984) to vary between 7,245 (2.3 fish per meter available habitat) and 25,000 (8 fish per meter available habitat) individuals during the period January–July 1979. Monitoring during 1985, 1994 and 2005 indicate a similar order of abundance (Kleynhans pers. comm. 1999, Engelbrecht pers. comm. 1999, Roux 2005). The re-introduced subpopulation established in a section of approximately 7 km in the Treur River, represents a small population with a relative low abundance of 5 fish per meter available habitat as determined by population estimate studies (Engelbrecht and Roux 1999). The subpopulation in the Blyde River has remained stable overtime; however the condition of the subpopulation in the Treur River has not been assessed since 1999. There are thus two relatively small subpopulations present which are severely fragmented as a result of the geomorphology of these mountain headwater streams with numerous waterfalls which further isolate these subpopulations from each other. The presence of trout (Oncorhynchus mykiss and Salmo trutta) in the lower reaches further impact on the overspill, making it impossible to connect the two subpopulations.

Threats

Alien fish species, in particular Smallmouth Bass (Micropterus dolomieu), are responsible for eliminating Treur River Barb (Enteromius treurensis) from all but the single portion of its former range. The introduction of Brown Trout (Salmo trutta) and Rainbow Trout (Oncorhynchus mykiss) in the Blyde/Treur River catchment have further contributed to the extirpation of this species. Any introduction of these alien and invasive species into the localities of the two subpopulations would have a detrimental effect on this species. The upper Blyde River and Treur River where the two remaining subpopulations are found, falls within a commercial forestry area where the catchment hill slopes are planted with Pinus species. Stream flow has probably been affected and other forestry operations such as logging and pesticide spraying constitute a continuous threat to this species. Another forestry related impact, siltation and sedimentation, has been recorded due to high road density networks and river crossings. These forestry activities are causing habitat degradation.

Conservation

Both subpopulations in the upper Blyde River and Treur River (past conservation intervention resulted in successful reintroduction) fall outside formally protected areas. The previous land owners, Mondi Timbers, were sympathetic to the conservation of the Treur River Barb (Enteromius treurensis) and declared both areas of occupancy National Heritage sites to protect the species. National Heritage sites are not classified as formal conservation areas, leaving the species unprotected and has not prevented all threats to the species. No formal agreement regarding the conservation of this species has been reached with the new landowners, York Timbers.

References 

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