Effect of Size at Release on Tendency of Trinity River Hatchery Steelhead (Oncorhynchus mykiss) to Return as Half-Pounders

I used scale analysis to estimate the half-pounder frequency among wild and hatchery steelhead from the Trinity River 2011 and 2012 smolt years and compare those estimates to the half-pounder frequency from 1993 until 2008. Hatchery steelhead from 2011 and 2012 had higher half-pounder tendencies than those from 1993 until 2008. Wild steelhead from 2011 and 2012 also showed increased half-pounder tendencies. This supports the hypothesis that increased size at release of hatchery steelhead is related to decline in the half-pounder life history, but also suggests that another factor influences the half-pounder tendency of these steelhead.