Using Scales to Help Understand Life History Strategies of Wild and Hatchery Steelhead in Omak Creek

Life history traits are a crucial component in understanding the basic ecology of anadromous fishes.  Scales are commonly used to estimate life history characteristics such as age at migration, age at maturity, and spawning history for steelhead trout Oncorhynchus mykiss.  We used scales to help understand steelhead life history strategies and population dynamics in Omak Creek, a tributary to the Okanogan River.  Scale samples were collected from juvenile and returning adult steelhead at a juvenile rotary screw trap and adult weir from 2008 through 2015.  The age at migration for most wild steelhead was two years.  The number of ocean years for wild adult steelhead returning to Omak Creek ranged from one to three years compared to one to two years for hatchery reared steelhead.  Our results suggest wild steelhead return from multiple brood years and the majority of hatchery steelhead return in their first ocean year.  Many samples did not show a complete record due to excessive resorption, cracking and regeneration which could lead to an inaccurate life history determination. Ageing adult and juvenile steelhead is and art but can be an effective tool for determining life history patterns of wild and hatchery steelhead in Omak Creek.