Seasonal migrations of adult and sub‐adult redband trout in a high desert basin of Eastern Oregon,USA

Abstract – Redband trout (Oncorhynchus mykiss gairdneri) migrations were tracked between March 2007 and June 2009 in the Donner und Blitzen River, Oregon, USA, using radio telemetry and PIT tags. We investigated the upstream extent and timing of spawning migrations for two groups of trout, considered the factors that influenced the rate of trout migration and explored the seasonal patterns of redband trout migration related to temperature and flow conditions. We found that trout made long‐distance migrations (up to 91 km) to spawn. Spawning trout from the lower river and middle river migrated to the same reaches, but lower river trout reached spawning habitats later than individuals from the middle river. Migration rate had a positive relationship with fork length and mean river discharge. We also found that redband trout made upstream spring migrations as sub‐adults and as adults. Whereas adult trout migrated to spawn, immature individuals migrated to river segments with more favourable thermal conditions. In both cases, migrations occurred where seasonally appropriate or life‐stage‐specific habitat patches for growth, survival, or reproduction were spatially segregated.