Agricultural intensification, declining stream health and angler use: a case example from a brown trout stream in Southland, New Zealand [article]

Cohen Stewart, Rasmus Gabrielsson, Karen Shearer, Robin Holmes, University Of Canterbury
2020
The Otapiri Stream brown trout (Salmo trutta) fishery (Southland, New Zealand) has undergone a dramatic decline over the past five decades. Over the same period, agriculture has intensified in the catchment, switching from low intensity sheep and beef grazing to dairy support and forage crop. We compared historic (1960's) and recent (2016) benthic invertebrate and electric fishing data and demonstrate substantial deterioration of the invertebrate community and reduced trout abundance. Compared
more » ... ith the baseline data, Ephemeroptera, Plecoptera and Trichoptera (EPT) abundance declined by 84% in riffles. The greatest decline (98%) occurred in pool habitat. Disproportionately high decline of EPT abundance in pool habitat highlights a potential issue with standard invertebrate sampling methodologies used to collect data to inform national-scale stream health assessments. By sampling only faster water habitat types (i.e., riffle and runs), the impacts of land use intensification (e.g., sedimentation) could be being underestimated. In line with the observed decline in %EPT abundance, brown trout density has declined by approximately 71% and angler use of the fishery declined by 76% between 1994 and 2016. We contend that the decline in angler use of the Otapiri Stream is a result of land use intensification within the catchment, driving changes in the trout invertebrate foodbase (EPT abundance) leading to reductions in adult trout density.
doi:10.26021/444 fatcat:c3qvonii65axnovd4ahp4siyoy