Forecasting Pink Salmon Harvest in Southeast Alaska from Juvenile Salmon Abundance and Associated Biophysical Parameters : 2011 Returns and 2012

The Southeast Alaska Coastal Monitoring (SECM) project has been sampling juvenile salmon (Oncorhynchus spp.) and associated biophysical parameters in northern Southeast Alaska (SEAK) annually since 1997 to better understand effects of environmental change on salmon production. A pragmatic application of the annual sampling effort is to forecast the abundance of adult salmon returns in subsequent years. Since 2004, juvenile peak salmon catch per unit effort (CPUE) from SECM, adjusted for highly-correlated biophysical parameters, has been used to forecast harvest of adult pink salmon (O. gorbuscha) in SEAK. The 2011 forecast of 56.2 M fish was 5% lower than the actual harvest of 59.0 M fish. Seven of eight forecasts produced over the period 2004-2011 have been within 0-17% of the actual harvest, with an average forecast deviation of 7%. The forecast for 2006 was the exception; while the simple CPUE model indicated a downturn in harvest, the prediction still overestimated the harvest by 209%. These results show that the CPUE information has great utility for forecasting year class strength of SEAK pink salmon, but additional information may be needed to avoid “misses” such as the forecast for the 2006 return. For the 2012 forecast, model selection included a review of ecosystem indicator variables and considered additional biophysical parameters to improve the simple single-parameter CPUE forecast model. A two-parameter model, including May temperature data as well as juvenile CPUE, was selected as the “best” forecast model for 2012. The 2012 forecast from this model, using juvenile salmon data collected in 2011, was for 18.8 M fish, with an 80% bootstrap confidence interval of 1325 M fish.