Frequency, Growth, Return Timing, and Life History Diversity of Steelhead Repeat Spawners in the East Fork (EF) Trask River, Oregon

Unlike most Pacific salmonids (Oncorhynchus spp.) which exhibit life histories with a primary goal of directing all energy into a single spawning event, steelhead (Oncorhynchus mykiss) may spawn more than once in their lifetime.  Steelhead repeat spawning (iteroparity) is thought to be a life history strategy that provides genetic and demographic benefits and a buffer against reproductive failure by spreading genetic contribution over multiple generations.  In this study, we used both scale reading and Floy tags to evaluate steelhead repeat spawning from fish captured at an adult fish trap located at a complete barrier to upstream migration in a coastal Oregon river.  Examining previously tagged repeat spawners allowed us to accurately determine growth and timing between spawning events and to validate results determined from scale reading, overcoming a major limitation of many previous studies which were limited to evaluating steelhead repeat spawning from one-time scale collections.  Preliminary results from this study show the majority of repeat spawners to be female (~80%) and on their second spawning run (~90%), significantly larger growth for repeat spawners that were jacks in their first spawning year (~140mm) than adults (~65mm), and high variability in growth and frequency of repeat spawners between run years.