Comprehensive surveys of the Breede and associated river systems were conducted from 2008 to 2010 to identify unique lineages and map their distributions. These surveys demonstrated that the lineage of Galaxias which was referred to as Galaxias sp. nov.‘Riviersonderend’ in Chakona et al. (2013) is widely distributed in the Riviersonderend sub-catchment of the Breede River System. All known subpopulations of this lineage are suspected to be small and isolated, but more surveys are required to comprehensively map its distribution. Particularly assessing whether there are remnant subpopulations in the mainstem sections of the Riviersonderend and its extent of occurrence along the vegetated margins of the Theewaterskloof Dam. The lineage has an extent of occurrence (EOO) of 1318 km2 and an area of occupancy (AOO) of 64 km2 and the subpopulations are suspected to be severely fragmented, however more surveys are required to confirm this. There are currently eight known locations and the lineage is likely to be experiencing continuous decline due to the impacts of invasive alien fish and excessive water abstraction. Some of the localities where this lineage have been recorded are moderately protected as they fall within the Hottentots Holland Nature Reserve and the Greyton Nature Reserve in the Riviersonderend complex, however, there are no instream physical barriers to prevent invasion of these tributaries by invasive alien species such as Bass (Micropterus spp) and the African Sharptooth Catfish (Clarias gariepinus) from the mainstem Riviersonderend and Breede rivers. This lineage meets the qualifying thresholds of Vulnerable under criterion B1ab(ii,iii,v)+2ab(ii,iii,v).
Distribution
This lineage occurs in the Upper Riviersonderend and six of its tributaries (Du Toits, Amandel, Meul, Gobos Soetmelksvlei and an unnamed tributary in Happy Valley) as well as in the Keurbooms River just below the confluence of the Breede and the Riviersonderend (see Chakona et al. 2013), in the Western Cape Province of South Africa. This lineage also occurs in the Palmiet River, a separate river system that drains the Hottentots Holland Mountain Range (Chakona et al. 2013) which flows through the town of Grabouw. This lineage was also recorded along the vegetated margins of the Theewaterskloof Dam during snorkel surveys in 2009.
All known subpopulations of this lineage are highly fragmented and connectivity is likely to be limited by the presence of alien predators in the mainstems as well as habitat degradation mainly due to bulldozing and complete abstraction of water which leaves downstream sections of the tributaries completely dry. Further surveys are required to determine the population sizes and long-term viability of the remnant subpopulations of this lineage. However it is suspected that most of the subpopulations have small population sizes due to predation by invasive alien fish species.
Threats
Invasive alien species and excessive water abstraction are the key threats to this lineage. There is complete water abstraction from weirs located in the upper reaches of some of the tributaries and excessive bulldozing in the lower sections of many of the tributaries where the lineage occurs. Galaxias sp. nov. 'Riviersonderend' prefers pool habitats (it was never recorded in the riffles and fast flowing sections of the rivers), which makes it highly susceptible to predation from invasive alien species such as Bass species (Micropterus spp) and African Sharptooth Catfish (Clarias gariepinus) which prefer such habitats.
Conservation
There are currently no conservation plans in place to protect this lineage.
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