YELLOWFISH WORKING GROUP - YWG Newsletter: August 2017

Dear All,
For August we present an abstract from Wesley Evans' M.Sc thesis titled:

Evans, W.D., Downs, C.T. and O'Brien, G.C.
School of Life Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville
3209, Pietermaritzburg, South Africa .

Labeobarbus natalensis, colloquially known as the KwaZulu-Natal (KZN) yellowfish or Scaly, is ubiquitous in KZN, South Africa. Populations that have historically been found in almost all rivers within the province have declined in response to increased use of water resources. Major determinants of the decline include habitat loss, altered water quality and quantity, and the establishment of barriers such as dams and weirs that hinders migrations. In this study we evaluated the wellbeing of the KwaZulu-Natal (KZN) yellowfish populations at 42 sites sampled quarterly between February 2015 and March 2016 within 16 major rivers in KZN as a part of the regional 2015/6 River Health Programme study. In this study fish were collected using a range of sampling techniques appropriate to the habitats observed in the rivers sampled and included the use of electrofishing and passive and active netting techniques. Fish collected were identified, standard length (SL) measured and then released. The occurrence of yellowfish and the population structures were evaluated and compared with known historical distributions of yellowfish. This allowed for an update of the 2008 state of KZN yellowfish wellbeing assessment. Considering that genetic diversities of KZN yellowfish are known the ecological importance of each population is considered to be high. The study was undertaken during a severe drought in the region which was partially attributed to the general reduction in the wellbeing of yellowfish throughout KZN. Additional stressors identified include the increase in range of alien precious and competing fishes and a range of land use activities. The yellowfish populations in the Mkuze and Mlazi Rivers in particular were observed to be in a poor state with low abundances and poor population structures of the species in the Mkuze River and no yellowfish observed in Mlazi system. Thereafter populations in reaches of rivers associated with urban and industrial use were poor and populations in northern KwaZulu-Natal in particular seemed to have been negatively affected by the recent drought. Populations in southern KZN rivers of the Mkomazi, Mzimkhulu and Mtamvuna Rivers appear to be intact. High frequencies of occurrence, healthy population structures and good recruitment of yellowfish were observed in these rivers. Populations in the uMngeni, and upper and middle Thukela Rivers were observed to occur in a suitable condition although high abundances were not consistently observed. In the last ten years the overall wellbeing of yellowfish populations in KZN has declined in response to consistent increases in stressors observed in the province due to increasing use of water resources and expansion of alien fish distributions. River rehabilitation and conservation measures proposed in 2008 have not been implemented. We recommend that the genetic diversity of yellowfish in KZN should urgently be addressed to identify unique populations. And that if any unique populations include those identified here to be in a poor condition, urgently conservation action should be undertaken. The yellowfish of KZN represent an important socio-ecological resource of the province that is generally out of sight and out of mind, we need to do more to promote this species and their contributions to regional ecosystem services that we depend on.

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