Genetic differences between hatchery and wild steelhead for survival, growth, dispersal, and male maturation in a natural stream (Study site: Twenty-Mile Creek; Stocks: Dworshak hatchery and Selway River wild; Year classes: 1994 and 1995)

This study was initiated in the early 1990s to provide managers with data comparing genetic fitness for natural rearing, as measured by survival of juveniles in freshwater, between steelhead Oncorhynchus mykiss from Dworshak National Fish Hatchery and wild steelhead from the Clearwater River, Idaho. We artificially spawned hatchery steelhead and wild steelhead from the Selway River, a Clearwater River tributary, released the resulting genetically marked (at the PEPA allozyme locus) progeny (HxH, HxW from hatchery females and wild males, and WxW) as unfed fry in a second order tributary of the South Fork Clearwater River, and monitored fish residing in the stream or emigrating from it for five years. Barrier falls prevented access to the stream by naturally produced steelhead. Over 90% of the emigrants were one or two years of age and too small to be smolts (mean fork length at age-2 = 103 mm). Per fry released, the HxH cross produced 0.64-0.83 times as many emigrants as the WxW cross (P