Reproductive development in captive reconditioned female steelhead kelts: Evidence for consecutive and skip spawning life histories

Abstract

Reconditioning of post-spawned anadromous rainbow trout (steelhead kelts, Oncorhynchus mykiss) is being implemented as a recovery tool on the Yakima River in the mid-Columbia River Basin. We assessed reproductive development in female Yakima River kelts by measuring plasma estradiol-17β (E2) and vitellogenin (VG) levels during reconditioning in 2009-2011. Plasma E2 and VG levels showed that fish separated into rematuring (consecutive spawning) and nonrematuring (presumed skip spawning) cohorts by October. Rematuration rates varied from 25% to 65%. Rematuring fish were consistently detected migrating toward spawning areas after release, whereas nonrematuring fish were occasionally detected on spawning migrations the following year. Rematuring fish grew more rapidly than nonrematuring fish over the reconditioning period and had higher muscle lipid levels and condition factor in October. Plasma E2 was elevated in rematuring fish by June-July, whereas plasma VG was elevated by June-August, suggesting that maturation decisions occur early in reconditioning. Rematuring and nonrematuring females could be separated by plasma E2 and VG levels by August-September, enabling separate management of consecutive and presumed skip spawners.