Postrelease Performance of a New Steelhead Line Derived from Hatchery Parents Collected by Angling in Northeast Oregon

Adult summer steelhead Oncorhynchus mykiss from a hatchery program in the Grande Ronde River basin in northeast Oregon stray at high rates into the Deschutes River, a tributary to the Columbia River.  Migrating adult steelhead use cool Deschutes River flows as thermal refuge from warm summer flows in the Columbia River, a behavior that may encourage straying.  We hypothesized that adults returning to the Grande Ronde River in autumn encounter cooler Columbia River water temperatures and stray less than individuals returning later in the migration season.  To test this hypothesis we created four brood years (2004-2007) of a new line of F1 offspring from hatchery steelhead collected by angling in the Grande Ronde River in autumn (hereafter, the Autumn Line) and we compared their postrelease performance to standard hatchery progeny released at the same location.  We estimated survival and migration timing using passive integrated transponder tags.  Over four release years, average juvenile outmigration travel time to Lower Granite Dam on the Snake River differed by about 1 d between the two broodstock lines.  Outmigration survival ranged between 72% and 84%, but the average survival difference was less than 1%.  Upstream migrating adults from the Autumn Line arrived at Bonneville Dam on the lower Columbia River about one week earlier than standard hatchery adults, and the difference in arrival date to upstream dams grew progressively larger.  Average smolt-to-adult survival to Bonneville Dam was 29% higher for the Autumn Line than for standard hatchery groups, a difference that was statistically significant.  Coded-wire-tagging was used to estimate straying.  Preliminary straying results, based on incomplete tag recoveries, indicate higher straying of the Autumn Line into the Deschutes River compared to the standard hatchery progeny.  This study has been extended through four brood years of the F2 generation, with future evaluations to also include fisheries contributions from the two broodstock lines.