Biological monitoring of the impacts of the Ok Tedi copper mine on fish populations in the Fly River system, Papua New Guinea.

Monitoring of the impacts of the Ok Tedi copper mine on fish populations in the Fly River system in Papua New Guinea has recorded approx. 100 species of fish representing 32 families. Fish catches have shown considerable temporal and spatial variability but, since the commencement of mine operations and the input of mine-derived waste material into the headwaters of the system, long-term monitoring has revealed significant reductions in fish catches at most riverine sites in the Ok Tedi, upper and middle Fly River. However, no significant declines in fish catches have been recorded in the lower Fly or delta areas. Possible mechanisms accounting for the declines in fish catches in the river are discussed. Although catches in some floodplain habitats have also declined, these changes are thought to be associated with the effects of natural climatic phenomena, particularly El Nino droughts. Introduced species and increased commercial and artisanal fishing may also have had an effect. Levels of copper, zinc, lead and cadmium were found to be elevated in tissues from a range of fish species taken from riverine and floodplain sites sampled in the Ok Tedi and Fly Rivers. Metal levels were generally much higher in liver and kidney than from flesh. There was a general trend for metal concentrations to decrease with distance downstream from the mine, suggesting a mine-related effect. Significantly higher metal concentrations were recorded at 'impact' compared to 'control' sites. The intake of dietary copper by humans consuming fish taken from the river is well within guidelines set by the World Health Organisation and does not constitute a health risk. Ok Tedi Mining Limited has recently initiated a programme of mitigation works aimed at reducing the adverse effects of mine wastes on the river environment.