4.3 - Production Processes

For each stock, the relationship between Spawners in year y and progeny (termed AgeOneFish) in year y + 1 is perhaps the most critical component of the model. It is through this relationship that time dynamics are incorporated into the analysis of alternative stock rebuilding strategies.

Stocks in the PSC Chinook Model are divided into two categories based on their production type: hatchery or natural. In general, hatchery production is modeled as a simple linear relationship between Spawners and AgeOneFish while natural production is modeled by a truncated Ricker curve relating spawners to adult recruitment, which is then corrected to AgeOneFish through a procedure outlined in detail later.

For both types of stocks, AgeOneFish are adjusted to make allowances for recruitment variability by incorporating "Environmental Variability" (EV) scalars. EV scalars can be thought of as pre-recruitment (i.e., prior to age one) survival scalars that compensate for both environmental variation and any bias in the original production parameter estimates. EV scalars for the calibration period are determined during calibration, while EV scalars for the simulation period are specified by the user. Model results are known to be very sensitive to the choice of EV scalars during the simulation period.