Data from: Can interbreeding of wild and artificially propagated animals be prevented by using broodstock selected for a divergent life history?

Two strategies have been proposed to avoid negative genetic effects of artificially propagated individuals on wild populations: (i) integration of wild and captive populations to minimize domestication selection, and (ii) segregation of released individuals from the wild population to minimize interbreeding. We tested the efficacy of the strategy of segregation by divergent life history in a steelhead trout, Oncorhynchus mykiss system, where hatchery fish were selected to spawn months earlier than the indigenous wild population. Up to 80% of the naturally produced steelhead in any given year were hatchery-wild hybrids. The proportion of wild ancestry smolts and adults declined by 10 to 20% over the three generations since the beginning of the program, due to an increase in hybrids. Regression model selection analysis suggested that proportions of hybrid smolts and adults were positively correlated with the number of naturally spawning hatchery-produced adults. Furthermore, the proportion of smolt hybrids was higher in years with high stream discharge allowing hatchery fish to bypass the weir protecting wild spawning habitat. Divergent life history failed to prevent interbreeding when physical isolation was compromised following changes in environmental conditions, an inadequacy of the segregation strategy that is likely to prevail in many other situations.