The influence of canalisation on juvenile salmonid habitat

There have been few mechanistic studies linking local ecological characteristics of streams to morphological pressures. This paper reports the findings of an investigation of the impacts of canalisation on salmonid habitat. Habitat use by Atlantic salmon and brown trout, fry and parr was assessed using Generalised Additive Models (GAMs) based on seasonal electrofishing survey data and output from 2-dimensional hydraulic models. By overlaying the habitat models onto the physical characteristics of the canalised reach, it was possible to determine where and when environmental bottlenecks occurred, and for which species and life stages. The canalised reach was characterised by relatively uniform sedimentary and hydraulic characteristics compared to other reaches. Although it was generally well suited to fry, the lack of coarser substrate and low velocity areas during winter made the canalised reach unfavourable for salmon and trout parr respectively. Given the insights provided by this study, we suggest the approach of combining physical channel characterisation with locally derived seasonal habitat models is well suited to future research focussed on assessing the ecological impact of morphological pressures.