Three of the case studies (studies 1, 2, and 3) examined the RRS of hatchery fish with different degrees of hatchery ancestry.
The Wenatchee Chinook and Umpqua coho studies (Thériault et al. 2011; Ford et al. 2012) followed a similar design to the Hood River steelhead study and compared hatchery fish with different degrees of hatchery ancestry.
Of the 30 studies comparing hatchery and wild fish in Table 5, only five compared hatchery fish derived from the same local population as the wild fish, and without confounding environmental and genetic differences or some degree of intentional artificial selection in the hatchery, which is not a typical element of captive breeding programs (see Table 5 footnotes).
The degree of crystallization itself was a good determinant of which adults were of hatchery origin, and has been observed in other populations of coho in the Strait of Georgia [23].
There was, however, no evidence that the degree of spatial genetic structuring among populations had changed significantly with the onset of hatchery operations that use native broodstock; the hierarchical analysis of allele frequency variation highlights the congruence in θ (P = 0.61) between the oldest (θ = 0.022) and most recent (θ = 0.029) samples within hatchery supplemented rivers.
Cross, T. F. & King, J. Genetic effects of hatchery rearing in Atlantic salmon.
By any measure, the life of hatchery trout tends to be brief.
However, by 2006 and despite higher releases of hatchery fish from rivers in the area, the percentage of hatchery fish caught in the Strait of Georgia had dropped significantly [4].
The degree of threat posed by artificially propagated fish on natural patterns of genetic and potentially adaptive variation (Utter et al. 1993) depends on several factors, including the source of the hatchery fish, the proportion of hatchery fish in a population, and the duration of the hatchery program.
Hatchery populations can be perpetuated solely by spawning hatchery-origin fish (segregated broodstock), or by spawning a combination of hatchery and wild fish (integrated broodstock).
