Move or stay: habitat use and movements by Atlantic salmon parr (Salmo salar) during induced rapid flow variations

An experimental factorial approach, in terms of habitat use and movements by Atlantic salmon parr (Salmo salar), was studied in response to induced peaking flow in a bypass river section in southern Norway. Sixteen radio-tagged salmon parr (mean TL 12.9 +/- 0.8 cm) were tracked during a 7-day spring period with manipulations of flow. Total habitat availability was modeled and integrated with fish locations. Parr movements exhibited a wide individual variation in movement behavior with a subsequent large home range which indicated nonrandom patterns involving three types of behavioral response groups: I parr that did not move during experiments; II parr that used a defined area in the stream moving in all directions; and III parr that moved, i.e., traveled longer distances. Movement distances were strongly skewed towards many short (i.e., I and II) and few but long movements mainly on downstream direction (i.e., III). However, flow alterations clearly affected salmon parr movements, which were also significantly related with alterations of discharge and diel variations. As may be expected, parr movements were also positively related to habitat shifts. In conclusion, flow alterations and reduced light may increase Atlantic salmon parr movements.