Evaluating a Two-Year Smolt Rearing Program for Steelhead As a Hatchery Reform Tool to Enable Transition to Use of Locally-Derived Natural Broodstock

The combination of natural broodstock spawn timing and cold water temperatures precludes production of yearling smolts for some steelhead supplementation programs.  We compared the performance (survival, migration, maturation, and residualism) of yearling smolts (S1) from non-local broodstock, and two-year smolts (S2) from local broodstock released from the Winthrop National Fish Hatchery over five release years. The majority (75-97%) of S1 and S2 males were immature; however, in two release years there was a significantly higher proportion of S2 males that were either precocious parr, or initiating maturation for the following year.  S2 apparent survival was greater or equal to S1 survival in all 5 years and related to body size.  Outmigration travel times were faster for S2 steelhead in all years.  Residualism was similar in both programs and related to average size at release.   Fifteen years of hatchery records show S1 steelhead are smaller and more variable than S2 at release, suggesting an S1 program produces smaller smolts with lower survival, slower travel time, and higher residualism than an S2 program.  The S2 program minimizes genetic risks of nonlocal broodstock and ecological risks associated with reduced S1 smolt performance characteristics.