Diel variation in habitat use by subyearling Atlantic salmon in two tributaries of Lake Ontario

Although extensive information exists on the habitat use of fish during the day considerably less information is available on habitat use at night.  The few studies that have examined both day and night habitat use of stream salmonids have found important differences.  The habitat use of subyearling Atlantic salmon (Salmo salar) (n=1,067) was examined during both day and night periods during summer in two tributaries of Lake Ontario.  The amount of cover used was the major habitat variable that differed between day and night periods in both streams.  At night subyearling Atlantic salmon were associated with significantly less cover than during the day.  Principal Component Analysis showed that habitat selection of Atlantic salmon fry was more pronounced during the day in both streams and that fry in Orwell Brook exhibited more diel variability in habitat use than fry in Trout Brook.  These results provide important insights into the habitat requirements of subyearling Atlantic salmon for habitat enhancement and habitat protection.