A Novel Tool for Steelhead Restoration: Enhancing Iteroparity

Iteroparity, the ability to repeat spawn, is a natural life history strategy expressed by some species from the family Salmonidae.  Observed iteroparity rates for steelhead Oncorhynchus mykiss in the Columbia River Basin are currently depressed due to anthropogenic development including operation of the hydropower system and other habitat degradations.  To test the efficacy of utilizing steelhead kelt as a management and recovery tool, different scenarios were investigated ranging from little intervention (collect and return fish to river) to high intensity (collect and feed fish in captivity until rematuration).  Kelts collected and transported and released below Bonneville Dam include groups from John Day Dam, Prosser Dam (both fed and unfed groups), and Lower Granite Dam.  Return rates to Bonneville Dam for these treatments were 12.55%, 5.81%, 2.96%, and 2.10% for Lower Granite, Prosser Fed, Prosser Unfed, and Lower Granite Dam groups respectively, based on weighted means over all years.  Kelts transported from Lower Granite Dam showed the highest transport benefit (2.11) relative to in-river control groups, followed by Prosser Fed groups (1.54), and the John Day group (1.29).  All groups showed transportation benefits relative to the repeat spawners in the run at large at Bonneville Dam ranging from 18.22 at John Day Dam to 2.57 at Lower Granite Dam.  Survival from release through migration to the ocean was estimated for several of the Prosser transport groups using sequential detections of acoustic tags.  Release to ocean survival estimates were 46.89% for unfed groups and 48.68% for fed groups.  The highest survival was 70.37% for the fed group released in 2007 and the lowest survival was 10.71% for the 2005 fed group.  Based on these data significant mortality occurs on transported kelts between Bonneville Dam and the Pacific Ocean reach.  Survival through long-term reconditioning was highest for fish reconditioned at Prosser Hatchery.  The weighted mean survival estimate of 37.90% as calculated over 10 years indicates that steelhead kelts can be successfully reconditioned.  Fish reconditioned at Prosser Hatchery had a 10.04 times increase in survival over fish left untreated in the river.  Compared to the proportion of repeat spawners in the run at large at Bonneville Dam, long-term reconditioned kelts at Prosser Hatchery had an increased survival 70.78 times greater than untreated fish. In Omak Creek, reconditioning led to a 32.95 times increase in survival.  Long-term reconditioning shows great promise as a tool for restoration based on these data.