Nocturnal habitat use of Atlantic salmon parr in winter

Abstract

We completed 22 night snorkeling surveys between November and March 1995-1997 to quantify Atlantic salmon (Salmo salar) parr habitat use relative to habitat availability in the Rock River, Vermont, U.S.A. On average, post-young-of-the-year (PYOY) parr selected greater water depths in winter than young-of-the-year (YOY) parr, whereas YOY and PYOY parr both selected water velocities (19 cm/s) that were significantly lower than random measurements (46 cm/s). Maturity of PYOY parr had no significant influence on habitat selection. The majority of YOY and PYOY parr at night were found in contact with the stream bottom resting on silt-sand or gravel substrates in velocity dead-zone habitats created by the stream edge or depositional habitats created by midstream rocks and boulders. The strong selection that nocturnal Atlantic salmon parr exhibit for low water velocity areas in winter indicates the importance of maintaining large instream cover that provides refuges from high flows. The similarity that YOY and PYOY parr exhibited in many elements of habitat selection suggests that both stages may be similarly susceptible to habitat limitations in winter.