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The role of river flow in the migration of adult Atlantic salmon, Salmo salar, through estuaries and rivers


Correspondence: Nigel J. Milner, APEM Ltd, c/o Bangor University, School of Biological Sciences, Brambell Building, Deiniol Rd, Bangor LL57 2UW, UK (e-mail:


An assumption of Atlantic salmon, Salmo salar L., management is that river flow influences their upstream migration; but the quantitative relationships between flow and movements are variable and inconsistent. A consensus has emerged that standard rules on salmon flow needs for water management across all rivers are unattainable. However, this does not preclude an underlying conceptual framework that should guide a consistent scientific basis to flow management for protecting salmon. This article examines the potential for a conceptual framework from a British Isles perspective, assuming that upstream migration is an emergent property from selection to optimise lifetime fitness. The template for this adaptation is the diversity of river types and hydro-morphology in British rivers coupled with life-history and migration adaptations that may be influenced by flow-related factors. Models of adult salmon migration through estuaries and rivers are outlined that may provide a basis for developing generic guidance.