Cyclic Dominance in Fraser River Sockeye Salmon Is Maintained by Inter-Cohort Suppression of Juvenile Growth Coupled with Depensatory Predation

Sockeye salmon stocks rearing in a number of Fraser River lakes cycle on a four year pattern with a very large spawner abundance in one year (dominant year) followed by a  large but usually smaller subdominant year and then followed by two small nondominant years.  We detected significant negative interactions between sequential cohorts of Fraser River sockeye salmon (Oncorhynchus nerka) that rear in Shuswap and Quesnel Lakes.  Prior year juvenile populations, as indexed by parent effective female spawners, exerted significant negative effects on juvenile growth and resulting adult productivity at lags of one to three years.  Effects of dominant line juvenile sockeye foraging may be responsible for following line early juvenile growth limitations.  We hypothesize that suppression of juvenile growth combined with depensatory mortality plays a vital role in the maintenance of cyclic dominance in Fraser River sockeye populations.  Such intrinsic control of cycles suggests that management policies which seek to even out escapements in attempts to increase yields may be counterproductive as increases to escapements could result in suppressed growth and recruitment rates across all cycle lines.  Thus, we suggest that maintenance of a cyclic pattern of escapement may optimize overall yield.