Survival and Traits of Reconditioned Kelt Steelhead Oncorhynchus Mykiss in the Yakima River, Washington

We evaluated the traits and survival to release of reconditioned kelt steelhead Oncorhynchus mykiss in the Yakima River (Washington State, USA).  From 2001-2011 we captured a total of 9,738 downstream migrating kelts at an irrigation diversion facility, on average about 27% of each annual wild steelhead return.  Captured kelts were reared for 4.5-10 months in an artificial environment, treated for diseases and parasites, and fed both krill and pellets.  Surviving reconditioned fish were released into the Yakima River coincident with the peak of upstream pre-spawn steelhead migration.  Reconditioned steelhead kelts were predominantly (>92%) female.  Annual survival to release ranged from 20-62% and averaged 38% over the course of the study with surviving reconditioned kelts showing increases in fork length, weight, and Fulton’s K condition factor.  Kelts in good condition and those with bright coloration at the time of collection were more likely to survive.  Post-release upstream migration timing of reconditioned kelts was spread out over several months and correlated well with run timing of upstream pre-spawn migrants.  The empirical results we observed demonstrate the potential of kelt reconditioning to provide recovery benefits for imperiled wild repeat spawning populations in highly developed river systems.