The interaction of low flow conditions and spawning brown trout (Salmo trutta) habitat availability

Over-abstraction from surface waters is having a detrimental impact on freshwater dependant ecosystems. Spawning fish are impacted during low flow periods which can be exacerbated by over-abstraction. In this study habitat models were used to assess the impact of low flows on the habitat availability of spawning brown trout. The approach used assesses the habitat availability of spawning brown trout (Salmo trutta) as well as that of their biotic dependants: refugia (Ranunculus fluitans) and food source (Ephemeroptera beraeidae). The analysis uses fuzzy logic to show how habitat availability changes for the three species over a 32 year period with detailed investigation of the role of hydrological extremes. Critical flows were determined below which habitat availability suffers. Results indicated that wet years provide increased habitat availability for spawning brown trout as an individual species, but when the results are combined with their biotic dependants it becomes clear that more habitat for these is available during drier years. The study highlights the importance of the natural flow regime to the dependent freshwater ecosystem components and understanding different species requirements.