Effects of trout farms on stream macroinvertebrates: Linking farm-scale disturbance to ecological impact

Abstract

Trout farms are a significant component of the Australian aquaculture industry, but there have been no studies on the ecological impacts of Australian trout farms. I analysed biological monitoring data from 5 trout farms in the Goulburn Valley, Victoria, Australia. Using multivariate ordination and a Bayesian hierarchical model, I compared macroinvertebrate assemblages from upstream of the farms to those downstream, and related upstream-downstream differences in invertebrate assemblage condition to 5 farm-scale indices of disturbance. I found clear, but small, ecological impacts of individual farms (i.e. upstream to downstream differences in invertebrates), with between-farm variation in impacts largely explained by the indices of disturbance. The greatest impacts were seen for farms with high production intensity that utilise a high proportion of stream discharge, export a high relative load of nitrogen to the stream and are in areas of good biological condition. Recent research has explored operational and engineering solutions that reduce the downstream ecological impacts of trout farms. Adoption of such practices may help such farms to minimise impacts on streams.