LATE SUMMER AND FALL USE OF STREAM MARGINS BY YOUNG-OF-YEAR BROWN TROUT IN A HIGH-ELEVATION STREAM

We determined the relative abundance of young-of-year (YOY) brown trou t (Salmo trutta) from late summer to fall during day and night in stre am margin habitats of Douglas Creek, Wyoming. No significant differenc es in relative abundance were observed from August 14 through October 26. Few YOY brown trout were observed during the day over the entire s ampling period, but significantly greater numbers were seen at night. Within stream margins, YOY brown trout of 36-75 mm total length primar ily resided in concealment cover among interstices of cobble during th e day and emerged at night. Because no significant change in relative abundance was observed throughout the study period, we conclude that a shift to winter habitat did not occur up until three days prior to ic e formation when the diurnal range in water temperature was 2.5-7.5 de grees C.