Metal concentrations in Hydrocynus vittatus (Castelnau 1861) populations from a premier conservation area: Relationships with environmental concentrations

• This is the first study to ascertain concentrations of metals in aquatic biota from more than a single river from the world renowned Kruger National Park (KNP) and is the first assessment of metal concentrations in aquatic biota from the Luvuvhu and Letaba River sections within the KNP and the first assessment from the Olifants River in nearly two decades.
• Results revealed that the selected bioindicator, namely the Tigerfish (Hydrocynus vittatus) from the Olifants River contained the highest concentrations and is not surprising as the Olifants River is regarded as South Africa's most used and abused systems. The surprising result was that metal concentrations in tigerfish from the Letaba and Luvuvhu Rivers were comparable to those from the Olifants River, even though these systems are regarded as being far less impacted.
• The results further showed temporal differences, with the initial surveys to each of the rivers having higher metal concentrations as opposed to the later surveys, and was attributed to the extreme high flows and floods that occurred in these rivers during the sampling period. These flows may have ‘flushed’ the system of long term metal contamination, thus reflecting within the biota.
• Metal concentrations in tigerfish were below levels found in previous studies and studies from contaminated sites around the world, but levels were however higher than other polluted sites in South Africa, which is of concern to managers of the KNP.
• Tigerfish were found to be successful bioindicators within the studied systems as they reflected the long term exposure of contamination that was seen in sediments from corresponding sampling sites.

Metals are known to have deleterious effects on aquatic ecosystems, so monitoring the bioaccumulation of these pollutants is important for the assessment of potential impacts. The aim of the study was therefore to determine the degree to which aquatic biota in selected rivers of the world renowned Kruger National Park (KNP) are exposed to metals entering from the catchments outside the KNP and to determine how these metal levels reflect what is occurring within the environment. Many of these rivers have never previously been assessed and those which have, have not been assessed within the past two decades. Tigerfish (Hydrocynus vittatus) is an economically important apex predator and was selected as the bioindicator for this study. Fish were sampled from the KNP sections of the Luvuvhu, Letaba and Olifants Rivers during the high and low flow periods from 2009 to 2011. The analysis of various metals from the aforementioned systems revealed spatial and temporal related variation in metal level patterns of the chosen bioindicator, with concentrations in fish from the Olifants River>Letaba River>Luvuvhu River and 2009>2010>2011. Although there were differences between rivers, metal concentrations were comparable and indicate that all of the studied KNP rivers, even those considered to be in a natural state are affected to some degree by anthropogenic activities. However, concentrations found during this study were much lower than previous studies in the area, as well as contaminated sites across the world, but were higher than concentrations in fish from contaminated sites in the Vaal River, South Africa. Bioaccumulated metals showed no correlation to metals in the water column, but some were correlated to sediment metal concentrations and the contamination and bioavailability of these metals within the sediments. This is of concern when managing the water resources of the conservation area since the contaminants enter the park from outside the borders and pose potential risks to the mandated conservation of aquatic biota within the KNP.