Response of barramundi, Lates calcarifer, populations in the Fly River, Papua New Guinea to mining, fishing and climate-related perturbation

Migrating barramundi (Perciformes : Centropomidae) spawners support a valuable artisanal fishery on the coast of south-western Papua New Guinea. This fishery declined dramatically during the 1990s shortly after the large Ok Tedi copper mine began in the headwaters of the large Fly River nearby. In order to understand the factors causing the decline, populations were sampled quarterly with gill-nets at over 20 sites throughout the Fly River from 1987 to 2001. Barramundi were most abundant in the middle and upper reaches of the Fly River. No evidence was found that output from the large Ok Tedi mine was negatively impacting on barramundi catch rates. However, the commercial fishery in the middle Fly River was found to have a negative impact on the weight of barramundi in monitoring catches in that region. Additionally, catch rates of juvenile barramundi (1 year olds) in the Fly River were negatively correlated with the amount of rainfall on the breeding grounds during the previous monsoon. This suggests that the reduced catch rates in the coastal commercial fishery in the late 1980s and early 1990s may have been affected by both the riverine commercial fishery and the El Niño (ENSO) that occurred at that time.