Individual variability in activity patterns of juvenile Atlantic salmon (Salmo salar) in Catamaran Brook, New Brunswick

Abstract

The activity of juvenile salmonids in streams varies between seasons, age classes, and times of day, but few studies have quantified the magnitude of individual variation in the behaviour of wild individuals. We monitored the activity patterns of 35 young-of-the-year (YOY) (fork length: 25.6–34.6 mm) and eight 1+ (fork length: 68.2–78.7 mm) Atlantic salmon (Salmo salar) over an 8-week summer field season. Age 1+ salmon were more active at night than during the day, whereas YOY fish were almost exclusively active during the day. However, daytime activity did not peak at 16–20 °C, the optimal water temperature range for growth determined in laboratory studies. Rather, the activity of 1+ fish peaked at 21 °C, whereas the activity of YOY fish continued to increase until 23 °C and then leveled off between 23 and 27 °C. There was also considerable individual variability within an age class in how fish responded to environmental variables that was often obscured by the average patterns. In a multiple logistic regression analysis for the activity of the 35 YOY, 18 responded significantly to time of day, 17 to water temperature, and 16 to day of the year. The causes of this individual variability and the consequences for growth and mortality deserve further study.