Does Inadvertent Selection on Juvenile Growth Rate Explain Low Fitness of Hatchery Steelhead in the Wild?

To increase the size of declining salmonid populations, supplementation programs release fish raised in hatcheries into the wild.  Recently, individuals of hatchery origin have been found to have substantially lower fitness than their wild counterparts.  A plausible hypothesis for the reduced fitness is that hatcheries select for an accelerated growth rate that is maladaptive in the wild.  Steelhead (Oncorhynchus mykiss) in the Columbia River basin take 1-3 years before smoltification in the wild, hatchery steelhead are raised to smolt after a single year.  To determine whether hatcheries select for an accelerated growth rate, we performed a common garden experiment using Hood River steelhead.  Wild and 1st generation hatchery fish were reared in a hatchery to investigate whether hatchery ancestry increases growth rate to age 1.  In independent tests from two different run-years, we found no additive effect of parental origin (hatchery or wild) on growth rate of offspring.  A maternal effect was found during the 1^st year while an effect of cross date was found in the 2^nd year.  After two years of study, we see no evidence that selection on growth rate in the hatchery explains the difference in fitness between hatchery and wild steelhead from the Hood River.