Oregon Sea Grant

Movement of redband trout (Oncorhynchus mykiss gairdneri) was tracked between March 2007 and June 2009 in the Donner und Blitzen River (Blitzen River). We had three primary study objectives: 1) examine redband trout spawning locations and spawning migration timing, 2) evaluate redband trout passage at diversion dams, and 3) investigate seasonal migration patterns of redband trout as they relate to stream temperature dynamics. We tagged 96 redband trout with radio transmitters and 706 with PIT tags. Radio tracking included both mobile and fixed station detections. We established PIT tag readers at Cato Bridge (Rkm 1), Busse Dam (Rkm 35), Grain Camp Dam (Rkm 48), and Page Dam (Rkm 76) for additional data on large-scale movement patterns. With the PIT antennas at the three diversion dams, we placed one antenna below the dam and one at the upstream exit of the fish ladders to evaluate the passage delays at each dam. Stream temperature was recorded at 10 locations in the Blitzen River throughout the study. Scales of 257 migratory trout were interpreted for age and spawning history. Our results indicated that the majority of Blitzen redband trout migrated upstream of Page Dam to spawn and that most trout spawned in the mainstem and not the tributaries. Upstream trout migration occurred from March to July, but the peak migration occurred during late April and early May. Passage problems were recorded at two of the three dams evaluated. Trout were delayed longest at Busse Dam and 44% of radio-tagged trout that approached the dam were never able to pass. Trout experienced less delay at Grain Camp Dam and only 8% of radio-tagged trout failed to pass the dam. At Page Dam, which has a recently upgraded fish ladder, trout delays were short and only 5% of trout that approached the dam were unable to pass. Potentially stressful or lethal temperatures (>24.3°C) were recorded at all monitoring locations downstream of Fish Creek, except at the site just below Page Springs. The migratory population ranged in age from 1+ to 5+, but only age 3+ and older trout were reproductively mature. This suggests that the spring upstream migration includes both adult trout seeking suitable spawning habitats and immature trout making a seasonal habitat shift for thermal refuge. A fraction of the PIT-tagged fish were observed to make two or three migrations from below Busse Dam to above Page Dam in the spring and returning back to the lower river in the fall. We recommend prioritizing fish passage at the Busse Dam and Grain Camp Dam for conservation and enhancement efforts.