Don’t silence the Large Mouth!
The endangered Orange-fringed River Bream (Chetia brevis) is endemic to the Lomati tributary of the Incomati River in South Africa and some coastal lagoons in the lower Incomati system in Mozambique. According to the IUCN, the population trend of this species is currently declining. To assess the current status of the species in South Africa, we undertook a dedicated survey during August 2021 to obtain data on distribution and abundance, critical habitat condition and an assessment of threats. Alarmingly, out of 45 sites sampled where they were known to occur before, only two small juveniles were collected in the Driekoppies Dam, on the south side of the dam near to the Eswatini border.
The entire Lomati sub-system is in a poor ecological state, as it is impacted by a host of problematic activities, including water abstraction, numerous weirs, alien plants (e.g. water hyacinth), alien fishes (notably the piscivorous Micropterus species and several others), pollution from extensive refuse dumping, agricultural run-off, and pesticides, and sand mining. Consequently, at least in South Africa, the possibility of extinction in the near future is assessed as high and concurs with the 2017 IUCN Red Data assessment. If the current trend continues without mitigation, then the chances are that this species will go extinct.
Conservation action: Restocking dams and re-introductions
Initial translocations of C. brevis from the Lomati and Komati rivers to three impoundments in the Kruger National Park (KNP) were reported as successful in 1975. However, two of these dams, Mpondo and Newu, subsequently dried up and were not restocked. Thus, there is currently a single dam in KNP, Stolznek, where a population of C. brevis may occur. In October 2021, local fishermen reported that C. brevis were present.
It is recommended that the viability of the population in the Stolznek dam be assessed, and should this population be viable, that all the dams in the Crocodile catchment within KNP be stocked with C. brevis with the initial stock for these coming from this dam. The rationale for this recommendation is that the species has not shown itself to be invasive, the species is already present in this subsystem and these dams are off-stream dams that are safe from other introductions of alien species and from pollution. Further, stocking of dams in the Mashushe Shongwe Game Reserve (Mzinti catchment adjacent to the Lomati) are also recommended given that they are also protected off-stream dams. These could then eventually be re-stocked into the Lomati River after current threats there have been mitigated. If successful and managed well, this could be the answer to saving the species from extinction.
This article was originally published in the 2021/2022 Research Report.
