A more recently developed index of our forecasting suite is based on the presence/absence of two alternate copepod community types. Data sets upon which this index is based are from our zooplankton samples off Newport, OR, taken biweekly since 1996, and from zooplankton samples taken since 1998 during June and September surveys of juvenile salmonid.
As an ocean ecosystem indicator, copepod community structure is based on multidimensional scaling (MDS), an ordination technique that helps visually represent non-numerical data (Figure CCI-01). The full ordination is not shown, but rather the averaged X- and Y-axis scores: these two alone accounted for about 85% of the variability between copepod communities, with the X-axis accounting for 73% and the Y-axis for 11%. CCI-01 compares these summer-average scores.
The different community types are clearly a function of the state and phase of the Pacific Decadal Oscillation (Figure CCI-02). Negative X–axis scores are associated with negative PDO and vice versa. This relationship seems to be related to advection. That is, a negative–phase PDO results in more boreal water coming into the northern California Current from the north; whereas a positive–phase PDO results in more subtropical water coming in either from the south (as during the large El Niño events of 1983 and 1998) or from offshore (as during the El Niño–like event of 2005).
Coho survival is related to the copepod community structure in that when a cold–water community dominates, coho survival is often high, and vice versa (Figure CCI-03). The link between copepods and salmon is almost certainly through the food web, since when a cold–water copepod community prevails, a cold–water fish community probably prevails. Since juvenile coho and Chinook salmon feed primarily on fishes, we hypothesize that copepods index the abundance of cold–water coastal fishes such as herring, smelt, and sand lance.