Population trend
Trend
This mainstem species is naturally found at relatively low population densities and based on comprehensive population studies by Kleynhans (1984) its historic relative abundance in relation to other fish species sampled from appropriate habitat was 2.8% and catch per unit effort (CPUE) was 0.18 fish/minute electrofishing. O’Brien et al. (2014) assessed the different CPUE trends dating back to 1989 (Kleynhans 1992, James 1992) and also conducted seven fish surveys from March 2002 to August 2006. The CPUE rates during these surveys the for Incomati Suckermouth ranged between 0.04 and 1.73 fish/minute electrofishing, In 2013 the Mpumalanga Tourism and Parks Authority (MTPA) conducted a comprehensive study on the Ecostatus of the Crocodile River Catchment during which 56 biomonitoring sites were sampled (Roux and Selepe 2013). Chiloglanis bifurcus were only sampled from three of the 56 sampling sites, two in the Elands River and one in the Crocodile River, close to its confluence with the Elands River. In conjunction with a small number of sites from which this fish was sampled, the CPUE 0.06 fish/minute electrofishing was indicative of a drastic decline in the population. Particularly relevant was that no Incomati Suckermouth were recorded at the type locality in the Crocodile River downstream of the 50 m high Kwena Dam (formerly Braam Raubenheimer Dam). It would appear that stream regulation from the dam has had a detrimental effect on the downstream population of this species. During this study the species was also not recorded in the Houtbosloop tributary as intensive forest fires in 2010 resulted in excessive siltation and sedimentation altering and reducing its available habitat.In September 2013 and April 2014 high flow and low flow surveys were conducted to determine stream flow conditions in the Elands River relating to the impact of the Sappi Paper Mill at Ngodwana (Diedericks and Roux 2014). During the low flow period survey no Incomati Suckermouth were sampled despite the collection of 477 individuals of other fish species during an electrofishing sampling effort of 97 minutes. During the high flow period surveys only four adults were recorded, resulting in a CPUE of 0.04 fish/minute electrofishing and a relative contribution to the fish community of 1.23%. Thus for both the high and low flow surveys the average combined CPUE value was 0.02 and a population density of 0.49%. In comparison to the historical CPUE of 0.18 fish/minute electrofishing the 2013/14 survey indicated a decline in the population density of Incomati Suckermouth (Kleynhans 1986). In 2016 an intensive study was conducted to determine the overall status of the Incomati Suckermouth population across its extent of occurrence. In the Ngodwana River, described as a sanctuary area (James 1992), three adult individuals were collected from two sites that were surveyed with a combined sampling effort of 138 minutes resulting in a CPUE value of 0.02 individuals/minute electrofishing (relative abundance= 0.24%). This observed reduction can possibly be related to the presence of the invasive alien species such as Rainbow Trout (Oncorhynchus mykiss). For the other seven biomonitoring sites on the Elands River and tributaries only ten adults were sampled with a CPUE value of 0.03 (relative abundance = 0.36%). These recent surveys indicate that the population in the Elands River catchment and tributaries has suffered a >90% reduction in distribution and a decline in AOO as well as a loss of habitat quality. Further, the subpopulation in the Crocodile River reach below the Kwena Dam is likely to be extinct and the population recorded in the Ngodwana River is now fragmented and threatened by alien fishes. For the subpopulation recorded in the Upper Mlumati River, Swaziland, very little information is available. However, due to unregulated forestry activities, most of these streams in Swaziland are severely sedimented and it is suspected that this subpopulation is also at risk.
