Internal Report 443
B Pidgeon, D Buckle, C Humphrey, J Boyden & R Luxon
Supervising Scientist Division
About the report
Shallow lowland billabongs and channel billabongs downstream of Ranger Uranium Mine (RUM) potentially can receive and accumulate mine related waste substances. The shallow billabongs are technically lagoons formed by levees at the confluence of the main creek channel with side streams. They receive water from the main channel at high (main channel) flows and flow back to the main stream at lower flows and hence are also termed back-flow billabongs. Some of these water bodies are important sources of food for traditional owners of the area as well as acting as dry season refuges for fish. Consequently, there is the potential for either direct toxicity (low risk) or bioaccumulation of wastes, especially metals, in these organisms and subsequent adverse effects on populations of some aquatic species. The risk of transfer of contaminants to human consumers, however, is regarded as small (Humphrey and Dostine 1994). It is likely that bioaccumulation would be a gradual process over many years and adverse effects on animal populations may occur only after harmful levels have been reached. Monitoring for detection of long-term effects on fish communities in these habitats is, therefore, important for the assurance of environmental health and management of the RUM.
Research by eriss on monitoring of fish communities in lowland billabongs began in 1979. Initially gill nets and seine nets were used for sampling. However, following the removal of feral water buffalo from the area during the mid 1980's these techniques were rendered ineffective in the shallow lowland billabongs due to increases in aquatic plant density (Pidgeon & Humphrey 1991). The composition of species in the fish community was also altered by the vegetation change and some larger growing fish species were excluded from the shallow reaches of billabongs where buffalo once wallowed and fed. This situation made it necessary to develop different methods for sampling fish in dense vegetation. After trialling a number of possible techniques, “pop-net” traps were found to be the most effective in shallow water and this technique is now used for monitoring this habitat.
The numbers of fish of different species present are used to determine the differences in fish communities amongst the billabongs and the change in fish communities over time. Natural changes are distinguished from change caused by mining or other human activities by: (1) the comparison of control sites (with no possible contamination from mining) with exposed sites (potentially exposed to mine wastes) and (2) the use of chemical and physical water parameters and a set of habitat structure variables as potential covariates of the fish community structure. Multivariate statistical analysis is used to compare the sites over time and to identify any environmental variables that correlate with the difference between sites and with any temporal changes in community structure.