16.2 Analysis goal

Our goal is to look for the underlying level (trends) in the rivers and studying whether there is evidence of synchronicity (correlated trend changes across rivers). In looking at the data, we have a couple problems.

1. There are strong cycles in the annual data due to the life cycle of sockeye which return 4-5 years after their brood year (year they were spawned). But unfortunately the cycles do not occur regularly every 5 years. Sockeye produce cycles that are 5 years apart but the cycle might break down for a year or two and then restart after a year or two. Thus the cycle appears to shift.
2. The amplitude of the cycle changes over time.

Both of these will cause us problems when we try to estimate a stochastic level.

ACF of the spawners showing the 5-year cycle in most of the rivers.