Forecasting Pink Salmon Abundance In Southeast Alaska From Juvenile Salmon Abundance And Associated Environmental Parameters

The Southeast Alaska Coastal Monitoring (SECM) project has been sampling juvenile salmon (Oncorhynchus spp.) and associated environmental 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 environmental parameters, has been used to forecast harvest of adult pink salmon (O. gorbuscha) in SEAK. The 2010 forecast of 26.8 M fish was 15% higher than the actual harvest of 23.4 M fish. Six forecasts produced over the period 2004-2010 have been within 0-17% of the actual harvest, with an average forecast deviation of 7.9%. However, the forecast for 2006 did not follow this pattern. The simple CPUE forecast model indicated a downturn in the harvest, but the prediction was 209% higher than the actual 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 ―misses‖ such as the forecast for the 2006 return. For the 2011 forecast, model selection included a review of ecosystem indicator variables and considered additional environmental parameters to improve the simple single-parameter CPUE forecast model. The single parameter model was selected as the ―best‖ forecast model for 2011. Juvenile pink salmon CPUE in northern SEAK accounted for 82% of the variability in annual harvest of SEAK pink salmon over the period 1997-2010. The 2011 forecast from this model, using juvenile salmon data collected in 2010, was 56.2 M fish, with an 80% bootstrap confidence interval of 47-62 M fish. Over the past seven years, the use of the SECM time series of CPUE data and associated environmental parameters has largely been successful in forecasting year-class strength of pink salmon in SEAK.