Forecast of Adult Returns for coho and Chinook Salmon

2011 was characterized by the continuation of La Niña conditions that were initiated in July of 2010. Combined with persistently negative PDO values throughout the year and a high biomass of lipid-rich northern copepods supporting the base of the food-chain, 2011 had the potential to be a good year for supporting juvenile salmon entering the ocean. However, this positive bio-physical outlook is tempered by observations of low winter-time ichthyoplankton (larval stages of fish-prey for salmon) abundance and poor upwelling (both in terms of the total amount and duration) throughout the year. Considering the previous two years (2009 and 2010) were characterized by below-average ocean conditions, we suggest that 2011 was an intermediate year with the foundation to support a rich biological community if the ocean conditions remain positive in 2012.

As 2012 begins to unfold, all signs are that ocean conditions will be among the best observed in recent years. Our annual update of ecosystem indicators during 2011 is here, and our “stoplight” rankings and predictions are shown below in Table 1, Table 2, and Figure A.

Figure A shows correlations between adult Chinook and coho salmon counts at the Bonneville Dam and coho salmon smolt to adult survival versus a simple composite integrative indicator — the mean rank of all indicators (the second line from the bottom) in Table 2. This index explains about 50% of the variance in adult returns. A weakness of this simple non-parametric approach is that each indicator is given equal weight, an assumption that may not be true, thus Brian Burke (NWFSC/FE) has begun to explore a more quantitative analysis of the ocean indicators shown in Table 3, using principal component analysis (PCA). PCA was run on the indicator data, a procedure which reduces the number of variables in a dataset as much as possible, while retaining the bulk of information contained in the data (a sort of weighted averaging of the indicators). Another important feature of PCA is that the principal components (PCs), which are the new, rotated data, are uncorrelated. This eliminates one of the original problems with the indicator data set (i.e., multi co-linearity). We used the PCs obtained from the PCA as new predictor variables in a linear regression analysis of adult salmon returns (this process is termed principal component regression, or PCR) and results are shown below in Figure B.

Figure A.	Salmon returns versus the mean rank of ecosystem indicators. Arrows show the forecasted returns of Chinook salmon in 2012 and 2013 (upper four panels) and Coho salmon in 2012 (lower left two panels). With a mean rank of the ecosystem indicators of 8.1 in 2010, the spring and fall Chinook salmon forecast for 2012 (top left two panels) is 160,000 and 325,000 adults returning to the Bonneville dam respectively. With a more favorable mean rank (6.5) of the ecosystems indicators in 2011, the forecasted adult returns of spring and fall Chinook are expected to be slightly higher at 177,000 and 400,000 adult fish returning to the Bonneville dam in 2013 (upper right two panels). Coho adult returns to the Bonneville Dam in 2012 are expected to be approximately 119,000 fish and the smolt to adult survival of coho to Oregon coastal streams is expected to be approximately 2.9% in 2012 (lower left two panels).

Figure B.	Comparison between adult salmon returns to Bonneville Dam and the smolt to adult survival rate (OPIH, blue circles) of coho and the predicted returns calculated from a principal components regression analysis (yellow diamonds). The x-axis indicates the out-migration year that corresponds to the year we characterize with ecosystem indicators (e.g. mean rank of ecosystem indicators). Predicted returns (purple diamonds) for spring Chinook in 2012 and 2013 are 150,000 and 233,000 (top panel) and the predicted returns for fall Chinook in 2012 and 2013 are 364,000 and 302,000. The predicted smolt to adult survival rate (OPIH) of coho salmon to Oregon coastal streams in 2011 is 2.58%, and for 2012 it is 3.31%. Results are from work done by Brian Burke (NWFSC/FE).

In summary, we have received mixed signals from ocean ecosystem indicators over the past three years and the variable ocean conditions in 2011 made our forecasts less certain for returns of coho salmon in 2012 and Chinook salmon in 2013. Our best guess is to expect average to above-average returns of coho in 2012 and Chinook in 2013. Based on a simple comparison to adult counts at Bonneville (Figure A), this translates to 177,000 spring Chinook, 400,000 fall Chinook, and 119,000 coho. Perhaps the most positive sign is that the ocean became very cold (and the PDO signal strongly negative) in summer 2010 and has remained so to date. If the cold conditions continue to persist into 2012, we may be seeing some of the better ocean conditions among the past 15 years.