Summer Steelhead Kelts

     A multi-agency project by UI FERL, the US Army Corps of Engineers, and the Columbia River Inter-Tribal Fish Commission examined post-spawn steelhead (known as “kelts”) outmigration survival and return rates over four years.  Kelts represent an important life history component for summer steelhead, as they can spawn multiple times and contributed disproportionately to population productivity.  Kelts were collected at dam bypass facilities after spawning, and ultrasound imaging was used to assess maturation status.  Several thousand kelts were radio- and/or PIT-tagged to evaluate postspawn migration behaviors, and iteroparity (repeat spawning) patterns.  A portion of the fish was also used to test the potential benefits of downstream transport in barges.

     In the study, more than 13,000 adult steelhead were examined in fish bypass systems at Columbia and Snake River dams and 89% were kelts.  Kelts were disproportionately female (> 80%) and majorities were of wild origin, unlike prespawn steelhead at these sites.  For kelts that outmigrated in-river, annual iteroparity estimates varied from 3-9% for fish PIT-tagged at lower Columbia River dams were generally < 1.5% for those tagged in the Snake River. 

     Across kelt samples, there was strong evidence for condition-dependent mortality, with iteroparity rates an order of magnitude higher for good- versus poor-condition kelts.  Proportionately more females than males and more wild than hatchery fish also returned, providing potentially valuable genetic and demographic benefits for the Columbia’s threatened steelhead populations.  Iteroparity rates for Snake River kelts transported downstream in barges were ~2.3 times higher than those for in-river migrants, with the largest transport benefits for good condition wild females.  Results provide important baseline data for evaluating Columbia River kelt mortality mitigation efforts and basic life history information for steelhead conservation planning.