You don't find the progeny of wild/ hatchery crosses in many places because they do not live. They just waste the life of the wild involved in the cross.
The Willapa study looked at naturally produced (gravel-borne) smolts and found a significant proportion of H/W hybrids. They also observed some H/W hybrids in the returning adults. I saw no mention of H/H adult recruitment.
OK... I went back to the actual study.
The key data is best encapsulated by a Figure 4 (sorry can't produce it here) discussed on pages 8-9 in the original paper.
Over the study period, the proportion of adult hybrids returning to Willapa increased from roughly 20% to 60% of the return. W X W adults decreased from 70% to 40%. H x H adults were undetectable in half of the 10 returns observed.... typically 10% or less in the years they were observed.
These observations are quite different from the Kalama data which showed very poor survival of hybrids. The extremely poor survival of H x H to adulthood was consistent in both studies.
What the Willapa study shows is that the longer a hatchery program operates, the greater the potential for hybridization over time.... yes, even when it's a "segregated" program. With the continual infusion of hatchery fish, the hybrids can eventually overwhelm the native population.... in direct proportion to the volume of hatchery plants introduced to the population.
If these are the observations for "segregated" hatchery populations, the genetic mixing of integrated populations is certain to be even greater. These findings are sure to have significant genetic implications for integrated programs.
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