Understanding how changing river temperatures and flow regimes associated with climate change will influence the UK's freshwater fish populations, and how negative impacts may be mitigated, represents a major challenge for fisheries managers.
Under current climate change projections, southern England may experience higher mean temperatures and lower summer precipitation. For cold-adapted fish species, at the southern limit of their UK distribution, extended periods of high temperatures (close to their upper thermal tolerance) may result in increased stress, and reduced foraging and growth. In warming rivers with reduced flows, thermal and flow refugia may provide increasingly important habitat for cold-adapted salmonids (such as brown trout, Salmo trutta). Appreciation of how salmonids use such refugia and how to preserve, or restore these areas of potentially critical habitat, will form an important part of fisheries management strategies. However, the benefits of refugia use may be outweighed by greater risk of predation, disease transmission and reduced fitness.
Research funded by the Game and Wildlife Conservation Trust, Environment Agency, and Centre for Ecology and Hydrology aims to identify salmonid use of thermal and flow refugia in a southern English chalk rivers, the impact of such behaviour on survival, and ways to adapt river habitats to mitigate the negative impacts of climate change. Objectives include describing thermal heterogeneity in streams, determining salmonid use of cold water and flow refugia, documenting salmonid behavioural thermo-regulation as part of wider resource allocation and predicting behavioural responses to future climate change projections.
