Summary

Impacts on aquatic ecosystems resulting from exposure to acid sulphate soil discharge are well documented. Less is known about the long-term impacts of chronic acid sulphate run-off. Such run-off may create barriers to movement, potentially affecting the migration of fish and invertebrate species, including commercially and recreationally important species. Avoidance of such discharges by adults may affect spawning migrations, while similar behaviour by juveniles may affect migration to nursery habitats. As a result, the capacity of fish to access important habitats beyond the discharge point may be reduced with potential consequences for stock size.

This study examined the possible existence of acid sulphate avoidance behaviour in juveniles of three commercial fish species and one commercial prawn species. Schools of ten individuals were given a simultaneous choice between two different water qualities in paired channels of a laboratory stream, i.e., a preference-avoidance simulation. All species avoided acidified water, indicating that the acidic component of acid sulphate run-off alone has the potential to affect migration of these species in the field. The pH levels avoided in these experiments were well within the magnitude in natural systems. Thus, chronic acid sulphate run-off in the field could impact detrimentally on commercial and recreational fisheries.