CONTRASTING MOVEMENT AND ACTIVITY OF LARGE BROWN TROUT AND RAINBOW TROUT IN SILVER CREEK, IDAHO

Recent radiotelemetry studies demonstrated that stream-dwelling trout are mobile, but few have compared sympatric species. We used radiotelemetry to simultaneously monitor positions of 20 brown trout and 21 rainbow trout from May or June 1994 to February 1995 in Silver Creek, a small spring-fed stream in south central Idaho. Our biweekly observations from May to September indicated that rainbow trout had larger home ranges (medians, 606 m v. 131 m) and moved greater distances (medians, 1109 m v. 208 m) than brown trout. Furthermore, rainbow trout used more positions than brown trout (means, 7 v. 3) over this interval. Hourly diel monitoring revealed no significant difference in 24-h home ranges of rainbow trout and brown trout (means, 77 m v. 105 m). However, activity patterns of the 2 species differed; rainbow trout activity was usually highest during the day, whereas brown trout activity tended to peak at night. Differences in foraging strategies and response to disturbance may be responsible for differences in mobility.