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The ‘natural flow paradigm’ and Atlantic salmon—moving from concept to practice

The ‘natural flow paradigm’ is becoming an important first principle in the setting of managed flow regimes throughout the world, including Canada. The principle states that managed flow regimes should consider the natural hydrological variability of a river system, both seasonally and interannually, to maintain its ecological integrity. While laudable, this principle is in direct conflict with hydropower development and irrigation interests. Therefore, both regulatory agencies and developers are struggling to identify the elements of hydrological variability that are critical to maintain the ecological health of rivers. In this paper, we identify flow requirements for different life stages of anadromous Atlantic salmon (Salmo salar L.). We then explore the potential effects of different flow regime scenarios on a wild Atlantic salmon population, using Harry's River in Western Newfoundland as an example. First, we link the life history patterns of Atlantic salmon to the scenario of the natural hydrological variability, incorporating the flow requirements for migration, spawning and rearing. In a second scenario, we present a flow regime managed for optimal hydropower production. Finally, we propose a conceptual model for a hypothetical managed flow regime that provides the necessary hydrological flow variations to support the life history requirements of Atlantic salmon, while permitting flow regulation and modification. This exercise identified data gaps and further research needs. Particularly, more information is needed on the amplitude of spring flooding necessary to initiate downstream migration while minimizing spill, which could potential be used for hydropower production. Copyright © 2008 John Wiley & Sons, Ltd.