Pesticides in the Great Barrier Reef catchment area: Plausible risks to fish populations

Abstract

Waterways that drain the Great Barrier Reef Catchment Area (GBRCA) transport pollutants to marine habitats, provide a critical corridor between freshwater and marine habitats for migratory fish species, and are of high socioecological value. Some of these waterways contain concentrations of pesticide active ingredients (PAIs) that exceed Australian ecotoxicity threshold values for ecosystem protection. In this paper, we use a “pathway to harm” model with five key criteria to assess whether the available information supports the hypothesis that PAIs are or could cause harmful effects to fish and arthropod populations. Strong evidence for the first three criteria and circumstantial weaker evidence for the fourth and fifth criteria are presented. Specifically, we demonstrate that exceedances of Australian and New Zealand ecotoxicity threshold values (ETVs) for ecosystem protection are widespread in the GBRCA, that the PAI contaminated water occurs (spatially and temporally) at important habitat for fisheries and that there are clear direct and indirect mechanisms by which PAIs could cause harmful effects. The evidence for individuals and populations of fish and arthropods being adversely affected species is more circumstantial but consistent with PAIs causing harmful effects in the freshwater ecosystems of GBR waterways. We advocate strengthening the links between PAI concentrations and fish health because of the cultural values placed on the freshwater ecosystems by relevant stakeholders and Traditional Owners, with the aim that stronger links between elevated PAI concentrations and changes in recreationally and culturally important fish species will inspire improvements in water quality.