Life-History and Growth Characteristics of Lake Superior Steelhead Trout

The non-native salmonids of Lake Superior are little studied and it is currently unclear how their distinctive life-history characteristics may be impacting local fish communities.  This study characterizes populations of steelhead trout (Oncorhynchus mykiss) in three streams in the South-Central Lake Superior watershed; Sevenmile Cr., Mosquito R., Hurricane R.. We examined steelhead trout life-history parameters including length at age, condition at age, cohort and individual growth rates, habitat use, and distribution patterns using data collected from 2004-2011.  Scale analysis was used to determine age of individuals and circuli measurements were performed to determine growth rates and growth patterns. There were three age classes (YoY, Age 1, and Age 2) present in the streams at times other than spring; during spring, adults of multiple ages join the community.  Adults present in the streams in later months were determined to be stream residents.  Juvenile steelhead in our study streams typically smolt at age 2, outmigrating in late May/early July.  Migrating adults return back to the streams to spawn in late March/early April, first returning at an age of 4-5 and many repeat spawn in subsequent years.  Lake Superior steelhead exhibit life-history characteristics similar to those seen in ocean run populations; both are composed of a combination of resident and migratory individuals. Early life growth patterns may provide a key to understanding what differentiates between these eco-types.