Project Title: Impact of low flows on salmonid river ecosystems.
Summary: Over the past 30 years there has been a marked decline in the abundance of adult Atlantic salmon despite significant reductions in exploitation. Small streams make up approximately 68% of the total river length in England and Wales, and these small upper reaches can produce a higher proportion of salmon smolts than the middle or lower reaches. However, these ecosystems are particularly vulnerability to extreme flow events. Climate change predictions for the UK (UKCP09) suggest significant reductions in summer rainfall in the Southern England by 2050, spreading further north and west with increased emissions. In the relatively stable chalk streams of southern England, summer drought and the accompanying low river discharges is thought to be the biggest threat.
The knowledge of how different salmonid (trout and salmon) life-history stages respond to changes in temporal and spatial availability of suitable habitat, and how the species’ dynamics within our river systems may shift under extreme flow conditions, remains unclear. Using a set of instrumented streams where we have complete control of flows and long-term monitoring using passive integrated transponder (PIT) tag detector systems, there will be investigations into fish prey availability, the diet of trout and salmon, stream food webs and ecosystem dynamics under differing, experimentally manipulated flow conditions. The aim of the project is to determine if poor access to prey (invertebrates) or increased predation (from larger fish) is responsible for any detected changes in habitat use, displacement or mortality in the fish populations under low flow.