Evaluating Steelhead Management Scenarios to Increase Iteroparous Spawners in the Yakima River Basin

All steelhead Oncorhynchus mykiss populations in the interior Columbia River Basin are listed as threatened or endangered under the Endangered Species Act.  One factor believed to be limiting survival of Columbia River kelt (post-spawned) steelhead is poor migration success to the ocean past a number of dams. We evaluated three management scenarios for wild steelhead captured as downstream migrating kelts in the Yakima River Basin from 2002 to 2011: transport and release below Bonneville dam; short-term artificial reconditioning with transport; and long-term artificial reconditioning. These treatment scenarios were compared to an in-river migration control group to identify differences in the rate at which kelts survived and returned for a potential repeat-spawning event. The long-term reconditioning scenario exhibited the highest rate of repeat spawners (estimated range of 10.6% – 16.2%). The short-term reconditioning effort with transport had a 3.2% rate of return. The transport only scenario exhibited the lowest rate of repeat spawners (0.9%), with 2.7% of the control group returning. Our results indicate that long-term reconditioning can be successfully used to increase the abundance of repeat spawning steelhead on the spawning grounds and that it provides greater recovery benefits for highly altered river systems than transportation or in-river migration alternatives.