Seasonal Effects of Suspended Sediment on the Behavior of Juvenile Atlantic Salmon

Short‐term increases in suspended sediment levels significantly influenced the behavior of juvenile Atlantic salmon in both fall and winter trials. The initial introduction of sediment (20 mg/L, or ≈15 nephelometric turbidity units [NTU]) increased foraging activity, which subsequently declined at sediment levels greater than 180 mg/L (≈35 NTU). Cover use also declined as fish emerged to forage. No fish returned to cover at sediment levels greater than 60 mg/L (≈22 NTU) in the fall trials, whereas some fish in the winter trials never emerged from cover. A rapid decline in territorial behavior and an avoidance response (i.e., alarm reaction) at sediment levels ranging from 60 to 180 mg/L (≈22‐42 NTU) were also noted in fall trials but not winter trials. Seasonal differences in the response of juvenile Atlantic salmon to suspended sediments may be explained by temperature‐related changes in diel activity patterns.