|Red List Category & Criteria:
||Jordaan, M., Lubbe, A., Bragg, C., Paxton, B.R., Schumann, M., Van der Walt, R. & Ngobela, T.
||Raimondo, D., Weyl, O. & Freyhof, J.
||Impson, D. & Swartz, E.R.
||Van Der Colff, D.
Historically, Clanwilliam Sandfish (Labeo seeberi) were widespread throughout the Olifants-Doring River System (ODRS) (Van Rensburg 1966) but significant declines occurred in main stream populations as a result of the introduction of predatory black Bass (Micropterus spp.) in the 1930s (de Moor and Bruton 1988) and the construction of large instream dams which probably disrupted spawning migrations. This species is believed to be extinct from the Olifants River System, and the Doring River subpopulations are severely fragmented (small, non-viable isolated subpopulations) (Paxton et al. 2002). Quantitative surveys have been conducted post 2000 but population size reductions could not be determined given the lack of comparable historical data. The current extent of occurrence (EOO) is 3357 km2 (based on the total area within a minimum convex polygon around all known occurrences) and the area of occupancy (AOO) is about 48 km2 (based on a 2x2 km2 grid overlay on all occurrences). The number of remaining remnant subpopulations is seven, consisting of six locations in the Doring catchment area and one in the Doring River mainstem. Despite there being more than five locations, Clanwilliam Sandfish qualifies as Endangered B1ab(iii,v)+2ab(iii,v) based on the severely fragmented nature of the remaining subpopulations, the low population numbers in the Doring River (and absence of juvenile and sub-adult individuals) and continuous threat of high numbers of predatory invasive fish species in all tributaries where the species is known to occur. This species also experiences population fluctuations as a result of summer drought and water abstraction. While these fluctuations are not extreme, they should be monitored. It must be noted that the current method of determining AOO (2x2 km2 grid overlay) significantly overestimates the AOO for this species and that the actual occupied habitat, when considering mean river width and river length (AOO = 3.11 km2, see Table 1 in supplementary material), is only a small fraction of the reported AOO value of 48 km2.
|Previously published Red List assessments:|
- 2015 – Critically Endangered (CR)
- 2007 – Endangered (EN)
- 1996 – Critically Endangered (CR)
- 1994 – Endangered (E)
- 1990 – Rare (R)
- 1988 – Rare (R)
|Range Description:||Clanwilliam Sandfish is endemic to the Olifants-Doring River System (ODRS) in the Western and Northern Cape provinces of South Africa (Skelton 2001). There is evidence that the species has been extirpated from the Olifants River as, despite sampling efforts, no Clanwilliam Sandfish have been collected from the Olifants River since the mid-1980s (CapeNature research observation). The remaining population is therefore confined to remnant subpopulations in the Doring River main stream and isolated tributaries of the Doring River namely the Oorlogskloof-Koebee, Gif, Kransgat, Biedouw, Tra-Tra, and Matjies rivers where they have been recorded in the last five years (Van der Walt 2014), see Figure 1 in the Supplementary Material. The Oorlogskloof-Koebee River in the Oorlogskloof Nature Reserve is home to the only remaining viable and recruiting subpopulation of this species as it provides suitable spawning habitat in the absence of predatory alien fish species. Due to very low numbers of adult fish and predation by alien invasive fish species, recruitment contributions from the remainder of the remnant subpopulations in the catchment are not expected to be significant.
South Africa (Northern Cape Province, Western Cape)
|♦ Estimated area of occupancy (AOO) - km2:||48|
|♦ Number of Locations:||7|
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Historically, the main stream Doring River has been poorly sampled with very limited quantitative data collected prior to 2000. Extensive surveys were conducted in 2003 and again in 2011 and 2013 (Paxton et al. unpublished). Clanwilliam Sandfish (Labeo seeberi) catch data between main stream sites was variable for all surveys and the species was generally absent or present in low numbers and only adult fish were detected. The Clanwilliam Sandfish subpopulation of the Doring River main stream as a whole can be characterized as relatively rare and heterogeneously distributed, with little to no recruitment taking place. This is supported by quantitative data from 2003, 2011 and 2013 Doring River main stream surveys. Figure 2 (see Supplementary Material) indicates that the Doring main stream system is dominated by predatory alien invasive fish species, predominantly Smallmouth Bass (Micropterus dolomieu), Spotted Bass (Micropterus punctulatus) and Bluegill Sunfish (Lepomis macrochirus). The relative abundance of Clanwilliam Sandfish sampled decreased from 5.8% of all fish sampled in 2003 to 0.9% and 5.1% of the total catch in 2011 and 2013 respectively. In both 2011 and 2013, the number of sites at which the species were caught decreased by more than 50% compared to the 2003 survey. Similarly, the catch per unit effort (CPUE) values decreased from 4.3 in 2003 to 0.6 and 2.3 fish per netting effort in 2011 and 2013 respectively. This illustrates the heterogeneous distribution of this subpopulation, which is likely to be influenced by their migratory and schooling habits, and environmental conditions such as flow and food availability, which would influence their habitat selection and distribution. The ca 50% decrease in presence/absence and CPUE over the last decade in the Doring section of the system suggests that the population is likely to be decreasing and becoming more fragmented in the Doring River main stream. |
The available data suggest that the persistence of the current Clanwilliam Sandfish population in the Doring River may be due to the population now being predominantly comprised of old, large fish which are beyond the prey size class of the predatory alien invasive species. This is evident from the size class distribution of the different species sampled during the 2013 Doring River main stream survey (Figure 3; see Supplementary Material). No indigenous fish species smaller than 400 mm (for example no juveniles or sub-adults) were recorded, indicating that there is no or minimal recruitment taking place. In addition to the Doring River main stream, Clanwilliam Sandfish presence has been reported in a number of Doring River tributaries, namely the Biedouw, Tra-Tra, Matjies, Kransgat, Oorlogskloof-Koebee and Gif Rivers (Figure 1; see Supplementary Material). These tributaries were surveyed in 2012, 2013 and 2014. All tributary subpopulations are confined to very limited stretches of river where they are protected from alien invasive fish species by natural barriers such as small waterfalls (Van der Walt 2014). With the exception of the Oorlogskloof, all tributary subpopulations consist of very low numbers of adult individuals and are not considered viable. The Oorlogskloof Nature Reserve is the last remaining viable and recruiting subpopulation, and it is likely that this is the primary source of adult Clanwilliam Sandfish for the Doring River main stream, with only a minimal contribution to subpopulation growth from spawning in other tributaries. The Oorlogskloof Nature Reserve subpopulation is therefore critical in terms of the survival of this highly threatened species.
|Current Population Trend:||Decreasing|
|♦ Continuing decline of mature individuals:||Yes|
|♦ Extreme fluctuations:||Unknown||♦ Population severely fragmented:||Yes|
|♦ No. of subpopulations:||7|
The primary threat to the persistence of Labeo seeberi is predation and competition from alien invasive fish species, notably the centrarchids Bass (Microptera spp.) and Bluegill Sunfish (Lepomis macrochirus) which were introduced in the 1930s as sport fish (de Moor and Bruton 1988, Paxton et al. 2002). These alien species have resulted in the extirpation of Clanwilliam Sandfish from approximately 80% of its historical distribution, and in most instances these invasions are near impossible or prohibitively expensive to reverse. Additionally, an early phase invasion of African Sharptooth Catfish (Clarias gariepinus) has been confirmed in the Olifants-Doring system (ODS). This species has been introduced, illegally in most cases, into all four primary river systems of the Western Cape (Jordaan et al. 2012). The impact of African Sharptooth Catfish has not yet been quantified in the rivers of the Cape Fold Ecoregion, but there is evidence to suggest that their impact will be severe (Cambray 2003, Clark et al. 2009, Breede River unpublished River Health Programme Survey 2009). Their invasive success and associated impacts on indigenous fish fauna can be attributed to a range of factors, including their ability to survive in and adapt to a range of environmental conditions, their ability to survive desiccation, their omnivorous feeding habits, high fecundity and fast growth rate (Weyl et al. 2016). Banded Tilapia (Tilapia sparrmanii) have also invaded the Oorlogskloof River which is the only stable and recruiting subpopulation. Tilapia are less predatory than the centrarchids but is still expected to impact on the native fish population through predation on juvenile fish and competition for resources.
Despite the limited understanding of the biological requirements of Clanwilliam Sandfish, impacts on the natural flow regimes of the Doring River are expected to adversely affect this species. There is substantive evidence, both anecdotal and from the known biology and ecology of closely related species, to support the contention that the species is a synchronous rheophilic spawner requiring optimal flow and temperature conditions for successful reproduction. Natural hydrological variability, together with water regulation and abstraction, is therefore likely to play a major role in recruitment success. Water resources in the Doring River catchment are heavily exploited for agricultural irrigation, particularly during the dry summer months. It is considered highly probable that further water resources development on the Doring River will negatively impact on Clanwilliam Sandfish subpopulations persisting in the main stream. In addition to major water resource developments and utilization, localized impacts are evident from farming activities (livestock and agricultural return flows) and invasion of riparian zones by invasive alien tree species which alters riparian habitats and reduces run off. Reduced water quality due to livestock grazing; particularly goats in the Biedou Valley area within the riparian zone may contribute to mortality of tributary populations over the summer when fish are concentrated in isolated pools.