Spatial and temporal variability in Atlantic salmon spawning habitat in braided river channels: a preliminary assessment

The distribution of Atlantic salmon redds was recorded during two spawning seasons (2005 and 2006) along a 4 km braided reach of the river Feshie in the Cairngorm mountains, Scotland. Within this complex reach, four main channels types were differentiated on the basis of geographical water sources, channel morphology and hydrochemistry: (1) the main braided channels of the river Feshie; (2) groundwater channels fed by seepage at the edge of the floodplain; (3) hillslope tributary channels and (4) mixed channels downstream of confluences of two or more of types 1–3. The 2005 season was characterised by high and variable flows. In total, 223 redds were observed which were mainly (64%) located in groundwater channels, with relatively few (9%) in the more extensive sections of main channel. The second year had much lower and more stable flows. Here, a total of 337 redds were observed. The largest number were again located in the groundwater channels (44%), though spawning was more evenly distributed in the other channel types, including the main river (19%). It is hypothesised that the apparently more suitable characteristics of groundwater-fed channels relate to a more stable, richer environment for embryo development and juvenile growth, whilst hydraulic conditions and sediment stability in the main channel may create more adverse conditions for successful recruitment.