Forecasting Pink Salmon Harvest in Southeast Alaska from Juvenile Salmon Abundance and Associated Biophysical Parameters : 2012 Returns and 2013 Forecast

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, peak juvenile pink salmon catch-per-unit-effort (CPUE), adjusted for highly-correlated biophysical parameters, has been used to forecast adult pink salmon harvest (O. gorbuscha) in SEAK. The 2012 forecast of 18.8 M fish was 12% lower than the actual harvest of 21.3 M fish. Eight of nine forecasts produced over the period 2004-2012 have been within 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 substantially overestimated the harvest. 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 forecast “misses.” For the 2013 forecast, model selection included a review of ecosystem indicator variables and considered additional biophysical parameters to improve the simple single-parameter juvenile CPUE forecast model. The “best” forecast model for 2013 included two parameters, the Icy Strait Temperature Index (ISTI) and juvenile CPUE. The 2013 forecast of 53.8 M fish from this model, using juvenile salmon data collected in 2012, had an 80% bootstrap confidence interval of 48-60 M fish.