Comparison of Reproductive Hormone Levels and Energy Reserves Between Reconditioned Female Yakima River Steelhead Kelts and Migrating Natural Spawners

Repeat spawning rates in Columbia River Basin steelhead are low.  Projects to capture and recondition downstream migrating kelts are underway, with the goal of releasing rematuring fish into rivers to spawn.  Some reconditioned Yakima River female steelhead remature after one summer (consecutive spawners), whereas others require two years (skip spawners). To meet project goals, reproductive development and body energy reserves in released reconditioned kelts must be sufficient for successful spawning.  However, how reconditioned kelts compare with maiden spawners in terms of these parameters is not known. Blood levels of reproductive hormones and indicators of energy reserves were compared between consecutive spawning reconditioned kelts and maiden females sampled during spawning migration at Prosser dam near the mouth of the Yakima River during 2012 and 2013. Condition factor was higher in reconditioned kelts in both years.  Plasma estradiol and muscle lipid levels were elevated in kelts versus maidens in 2012 but not 2013.  Plasma vitellogenin levels were higher in 2012 than 2013, but did not differ between kelts and maidens.  These results suggest that ovarian development in kelts is at least as advanced as in maiden spawners, and that kelts have greater energy reserves at the same point in the spawning migration.