Forecasting Pink Salmon Harvest in Southeast Alaska from Juvenile Salmon Abundance and Associated Biophysical Parameters : 2013 Returns and 2014 Forecast

The Southeast Alaska Coastal Monitoring (SECM) project has been sampling juvenile salmon (Oncorhynchus spp.) and associated biophysical parameters in the northern region of 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 (CPUEcal), adjusted for highly-correlated biophysical parameters, has been used to forecast adult pink salmon harvest (O. gorbuscha) in SEAK. The 2013 SEAK pink salmon harvest was an all-time record 94.7 million fish, the largest harvest since catch records were recorded dating back to 1900. The SECM forecast was for a strong harvest of 53.8 M fish, but the forecast was 43% lower than the actual record harvest. Eight of ten forecasts over the 2004-2013 period have been within 17% of the actual harvest, with an average forecast deviation of 7%. The forecast for 2013 joins the forecast of 2006 as exceptions to this degree of accuracy. In both of these years, the CPUEcal model did correctly indicate the direction of the harvest trends (lower in 2006, higher in 2013), but underestimated the degree of these trends. These results show that the CPUEcal 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 2014 forecast, model selection included a review of ecosystem indicator variables and considered additional biophysical parameters to improve the simple single-parameter juvenile CPUEcal forecast model. We also examined the use of a different CPUE parameter using catch per distance trawled, CPUEttd. The “best” forecast model for 2014 included two parameters, the Icy Strait Temperature Index (ISTI) and juvenile CPUEcal. The 2014 forecast of 29.9 M fish from this model, using juvenile salmon data collected in 2013, had an 80% bootstrap confidence interval of 2638 M fish.