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Barbus erubescens

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA ACTINOPTERYGII CYPRINIFORMES CYPRINIDAE

Scientific Name: Barbus erubescens
Species Authority: Skelton, 1974
Common Name(s):
English Twee River Redfin

Assessment Information [top]

Red List Category & Criteria: Critically Endangered B2ab(ii,iii,v) ver 3.1
Year Published: 2007
Date Assessed: 2007-03-01
Assessor(s): Impson, D. & Swartz, E.
Reviewer(s): Snoeks, J. (Freshwater Fish red List Authority) & Darwall, W. (Freshwater Biodiversity Assessment Unit)
Justification:
The population has declined since 1987. It is likely that population decline started with the advent of intensive agriculture in the catchment in the 1960s and 1970s. These declines have been accelerated by the introduction of several species of fish, and it is possible that at least a 50% decline has occurred since 1987, but this is speculative. More substantiated records are needed to apply criterion A. Criterion B applies because of the very small size of the species distribution range, increasing levels of threats and the fragmented nature of populations. Adult Barbus erubescens were stocked about 10 months ago into off-stream dams; too soon to benefit the overall population size of the species or to assess whether the introduction was successful. Its current actual area of occupancy (AOO) is 9 km² according to protocol using a 1 km² grid overlay. It therefore qualifies as Critically Endangered under B2ab(iii,v). Although it is known from two locations, defined as the Suurvlei and Heks (little recruitment in Twee), these two subpopulations are probably too small to survive on their own long-term so the population is considered severely fragmented.
History:
1996 Critically Endangered
1994 Endangered (Groombridge 1994)
1990 Vulnerable (IUCN 1990)
1988 Vulnerable (IUCN Conservation Monitoring Centre 1988)
1986 Vulnerable (IUCN Conservation Monitoring Centre 1986)

Geographic Range [top]

Range Description: Endemic to the Twee River and its tributaries, part of the Olifants River System in the Western Cape Province of South Africa (Skelton 1974). It is found in the Heks, Suurvlei and Middeldeur Rivers, and the Twee River to just before its confluence with the Leeu River. Its distribution range has shrunk substantially in the Suurvlei and Twee rivers due to alien fish invasion and habitat degradation (Marriot 1998).
Countries:
Native:
South Africa (Western Cape)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: The species is relatively abundant in good habitat where alien fishes are absent (e.g., upper Suurvlei and Middeldeur rivers). It is absent or uncommon elsewhere in its range because of predation by alien Labeobarbus capensis and competition with alien Sandelia capensis. A recent population estimate is 4,100 adult fish (Marriot 1998).
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: Adults prefer sheltered areas in pools, particularly near overhanging vegetation and caves formed by boulders. Juveniles are usually found in pools, forming schools in the upper water column, near palmiet (Prionium serratum) beds or beneath overhanging vegetation. Adults reach a maximum age of six years, maturing after two at an average size of 45 mm in males and 42 mm in females (Marriot 1998). Spawns in late spring (October) to early summer (December), with an asynchronous, iteroparous pattern of egg development (Marriot 1998). Females contain up to 400 ova at various stages of development (Marriot 1998). The body and fin bases of both sexes develop an overall reddish hue during the breeding season, with males also characterised by having small nuptial tubercles on the head (Skelton 1988). The diet of Barbus erubescens is dominated by benthic invertebrates although adults frequently feed on drift material and terrestrial insects floating on the water surface (Marriot 1998).
Systems: Freshwater

Threats [top]

Major Threat(s): The biggest threat is invasive alien fishes. Several species of fish have been introduced into the Twee River for a variety of purposes. The first introduction was Sandelia capensis, alien to the Olifants River System, but indigenous to most rivers of the Western Cape. A local farmer introduced Sandelia capensis to an off-stream dam in the early 1980’s in a misguided attempt to use an “indigenous” fish for mosquito control (Hamman et al. 1984). Sandelia capensis is now common and widespread in the Suurvlei River where it competes with Barbus erubescens for food; with adult Sandelia capensis also a likely predator on juvenile Barbus erubescens (Marriot 1998). In the late 1970s Labeobarbus capensis was introduced above its natural range above three waterfall barriers into the upper and middle Twee River by the Cape Department of Nature Conservation in another misguided attempt to create a sanctuary for an "indigenous" fish. This species is common and widespread, particularly in the Twee River. Oncorhynchus mykiss and Lepomis macrochirus were illegally stocked into the catchment in the 1990s, and have invaded the Twee river, where they appear to be present in low numbers due to high summer water temperatures (26°C, a deterrent to trout) and strong winter flows (a deterrent to Lepomis macrochirus). The other major threat is habitat degradation caused primarily by intensive farming of deciduous fruit and citrus. There is over-abstraction of water during the dry summer months and orchards are planted within the 1:1 yr floodline of the river. The use of pesticides is not well understood, but the absence of a natural riparian zone, and hence buffer area between the river and intensive agriculture allows fertilisers and copper- based pesticides easy access to the aquatic environment.

Conservation Actions [top]

Conservation Actions: The distribution range of Barbus erubescens is entirely within privately owned land. The species is listed as endangered by the provincial Nature Conservation Ordinance, preventing capture of the species. The Twee River system has been identified as a priority freshwater environment for fish conservation (Impson et al. 1999). Conservation staff and researchers have made riparian land-owners in the Twee catchment aware of the uniqueness of the river. Barbus erubescens from the highly restricted Suurvlei sub-population have been stocked in off-stream dams in the Suurvlei catchment as recommended by Swartz (2000) and have been moved above a small waterfall on the upper Suurvlei River to hopefully substantially increase the size of this currently small population. A conservation plan for the Twee River is being developed by CapeNature and the South African Institute of Aquatic Biodiversity and captive breeding studies at the University of Johannesburg are currently being undertaken.

Citation: Impson, D. & Swartz, E. 2007. Barbus erubescens. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 22 August 2014.
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