How large-capacity hatcheries can alter interannual variability of Salmon production

A theoretical model of salmon hatchery production dynamics exhibits dramatic year-to-year variation in salmon abundance. The model is a two-parameter Ricker curve with a fixed upper boundary on stock size imposed by hatchery capacity. In this model returns to large-capacity hatcheries, including yields to the fishery, fluctuate in response to enhanced productivity of returns per parent at low parental densities. The mechanism responsible for the model's dynamic behavior is the nonlinear Ricker curve. Qualitatively similar results hold for any dome-shaped, spawner-return relationship provided it is sufficiently steep-sided. These results suggest theoretical limits on hatchery capacity and caveats for the effectiveness of salmon enhancement or ocean ranching programs.