In the early 1990s, a dramatic decline in freshwater fish species was recorded in the Ok Tedi and upper and mid Fly rivers, PNG. The otoliths, or earbones, of barramundi were examined to see if the Ok Tedi mine was having an effect on barramundi behaviour. When a fish moves through contaminated water, trace metals such as copper and zinc, can replace the calcium in the otolith, providing a record of the fishes' movement or behaviour. The results were inconclusive, but subsequent studies suggest that much of the copper at the confluence of the Ok Tedi and Fly rivers is not bio-available and probably not toxic to aquatic life. Otolith and generic analysis has also been used to study migration of barramundi between the Fly River and coastal fisheries.