THE IMPACTS OF CHANGING GEOCHEMISTRY ON THE FISH ASSEMBLAGES OF THE LOWER OK TEDI AND MIDDLE FLY RIVER, PAPUA-NEW-GUINEA

The Ok Tedi mine commenced gold production in May 1984 and copper production in March 1987. The gold circuit was shut down in August 1988, and the mine now operates purely as a copper mine. Mine wastes have been discharged into the Ok Tedi, producing geochemical changes in the river system. The period of operations has been characterised by increasing suspended solids levels with concomitant increases in dissolved and particulate copper. During gold production some residual cyanides were released into the river system, which were predominantly associated with copper complexes of low toxicity. The fish assemblages at two sites in the Ok Tedi and one in the Fly River were examined. At the most upstream site, catches were reduced to low levels shortly after mine operations commenced. In the lower Ok Tedi, there were distinct changes in the fish assemblage during the different mine phases. The fish responded to high dissolved copper levels in a different way from that to high cyanide, suspended solids and particulate copper. In the Fly River the changes in the fish assemblage were more gradual, with no separation of the responses to the different chemical parameters.