The Proportionate Natural Influence (PNI) Concept and its Use in Supplementation Monitoring.
Craig Busack and Todd Pearsons
Washington Department of Fish and Wildlife
600 Capitol Way N.
Olympia, WA 98501-1091
Integrated hatchery programs involve gene flow from the natural to the hatchery environment and the hatchery to the natural environment. A simple mathematical model for integrated programs developed by Ford suggests that the degree of domestication, expressed as the change in means at equilibrium at one or more traits, depends in absolute terms on heritability, strength of selection, gene flow rates, and trait optima in the two environments. Examination of this model by the Hatchery Scientific Review Group (HSRG) has shown that if a few simple assumptions are made that the change expressed in relative terms depends almost entirely on the gene flow rates between the two environments. PNI is a simple estimate of the relative trait equilibrium, and is expressed mathematically as
, where 
is the proportion pf
natural-origin fish in the broodstock and 
is the proportion of
hatchery-origin fish on the spawning grounds.
Because it is a unifying concept for the understanding of domestication in all programs, the PNI concept has become a key aspect of hatchery reform planning in western Washington. It is also a useful variable for understanding supplementation projects. Comparison of the PNI values for the YKFP spring Chinook program with those for the Tucannon, Wenatchee, and Methow programs shows that the YKFP program has considerably higher PNI values, so (other things being equal) will incur considerably less domestication than the other programs.