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Rationale (Changed due to Same category but change in criteria)

The natural distribution of Orange-fringed River Bream (Chetia brevis) is restricted to the Lomati River (tributary of the Incomati River System). Since the 1980s there has been a continuous decline of the population due to intensive agriculture in the Lowveld region as well as the over-abstraction of water in this river. With the completion of the Driekoppies Dam (KOBWA – Komati Basin Water Authority) in 2005, the population was fragmented into two relatively small subpopulations and isolated from each other. This species is still experiencing continuous decline due to impacts of invasive alien fish, water-abstraction and impacts of dam regulation. It has lost more than 50% of its population over the last 10 years due to these threats, and these threats are expected to continue in the next five years (generation length of <5 years). The species is known from two severely fragmented subpopulations which constitutes two locations and has an extent of occurrence of (EOO) of 780 km² and an area of occupancy of (AOO) of 44 km² and is experiencing continuous decline in its habitat quality as well as the number of mature individuals. It is therefore assessed as Endangered A4ace; B1ab(iii,v)+2ab(iii,v).

Distribution

Orange-fringed River Bream (Chetia brevis) occurs naturally in the Lomati and Komati rivers (Inkomati River System) in Mpumalanga, South Africa and Swaziland (Gaigher 1969; Kleynhans 1982, 1984; Skelton 1987). An unconfirmed record exists of this species in a coastal lake in Mozambique, but this record needs to be verified (Gaigher 1969, Skelton 1987) and hence has been excluded from this assessment. Successful translocations of this species from the Lomati River to impoundments in the Kruger National Park were done in 1975 (Pienaar 1978, Skelton 1987).

Habitat View more ecological information

Population trend

Trend

The species is relatively abundant in good habitat where alien species are absent such as deep pools (> 1 m) with a sandy substrate and dense riparian zone. Surveys by Kleynhans (1982, 1984) in the Lomati and Komati rivers indicate low relative abundance of 4.4% of the total fish community. In favourable habitats such as the Lomati Draai Dam in the Lomati River Catchment the relative abundance increased to 21.7% of the total fish population (Kleynhans 1982). This indicates the adaptability of this species to altered environments. During the surveys Kleynhans (1984) found Orange-fringed River Bream at nine of the eleven monitoring sites in the Komati and Lomati rivers. In recent surveys this species was only found at one of the nine monitoring sites in the Lomati River (Roux and Selepe 2015). This site was situated at a relatively high altitude (333 m.a.s.l.) in the Lomati River in Swaziland just downstream of the Phophonyane River confluence. In total only six adults were found. No individuals were located in the Komati River (Roux and Selepe 2015). Based on these surveys an overall reduction of more than 50% over the past 10 years in the population is estimated based on a reduction of range, as in some surveys few or no individuals have been re-collected. Furthermore, with the completion of the Driekoppies Dam (KOBWA – Komati Basin Water Authority) in 2005, the population was fragmented into two isolated subpopulations.

Threats

Agricultural development, instream habitat alteration, water abstraction, siltation, sedimentation and agricultural pollutants are the major threats in the limited natural range of this species (Skelton 1987). All of these practices resulted in a reduction of available fish habitat to this species. The introduction of the invasive alien species, Largemouth Bass (Micropterus salmoides) in Driekoppies Dam (KOBWA – Komati Basin Water Authority) was most likely responsible for eliminating this species from the dam basin area. Furthermore intense flow regulation downstream of this dam has altered habitat. A population reduction of more than 50% has been observed in the last 10 years (Roux and Selepe 2015) and a further reduction in the next five years is suspected as these threats have not ceased. The numerous impoundments and weirs in this river system were thought to be beneficial to this species, however, the introduction of invasive alien species such as Largemouth Bass have been responsible for its elimination from its former distribution range. The alien fish species Nembwe (Serranochromis robustus) and the Redclaw Crayfish (Cherax quadricarinatus) is also present in the Lomati and Komati rivers and it is unknown what the impact of these alien species will be on Orange-fringed River Bream. River regulation from the Driekoppies Dam have further impacted on this species in changing the river regime to a more lotic habitat which is unsuitable to this species.

Conservation

Successful translocation of Orange-fringed River Beam (Chetia brevis) from the Lomati and Komati rivers to four impoundments in the Kruger National Park were made in 1975 (Skelton 1987). The status of these translocated populations in Kruger National Park is unknown. The status and habitat of this species in the Lomati River requires regular monitoring.

References

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,]

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