I hear this general thought repeated by numerous professionals on this forum, and I have often thought that I should comment, so now I will. I believe that statements like this are gross generalizations and very mis-leading. The fact is, we will never really know the exact effect on natural populations of many of our hatchery programs particularly some of the programs that have been in operation for over 100 years. For some populations (Puget Sound Chinook for instance) these long-standing programs have produced natural spawners that have had little influence from the natural environment for nearly thirty generations, and while we will never know the exact impact this has had (since we didn't start monitoring this stuff 100 years ago) some genetic models developed by very reasonable scientists suggest that the impact can be quite significant. To cite one example - In a risk assessment modeling project for the Bonneville Power Administration, some very good fisheries scientists including Drs. Busack, Currens, Mobrand, and Pearsons, relying on a comprehensive survey of 44 scientists with expertise in genetics and practical knowledge and experience with salmon culture, developed a fitness model (FITFISH) to look at the potential effect of different types of hatchery programs. In the case that I described above, where hatchery programs have operated for a long time with most of the spawners being made up of hatchery fish and no natural influence in the hatchery broodstock, the opinion of this group was that the loss of productivity to the natural population could be as high as 70% compared to a fully fit natural population. I don't know about you, but it seems to me that a potential loss of 70% in productivity puts the risk of some hatchery programs right up there with the risk from habitat loss. It certainly is within the same order of magnitude, and in my opinion should not be dismissed by anyone interested in recoverying/conserving (or any other term you want to use) salmon populations.

Reference: ftp://ftp.bpa.gov/pub/efw-RAMP/RAMP%20Report%20Final.pdf