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Forecasting Pink Salmon Harvest in Southeast Alaska from Juvenile Salmon Abundance and Associated Biophysical Parameters : 2014 Returns and 2015 Forecast
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2015
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Description: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 2014 SEAK harvest was 37.2 million fish, the largest even-year harvest since 2004. The SECM forecast was for a relatively strong even-year return of 29.9 M fish, which turned out to be 20% lower than actual. Nine of 11 forecasts over 2004-2014 have been within 20% of the actual harvest, with an average forecast deviation of 9%. The 2014 harvest is indicative of continued recovery of the even-year run since the very poor return in 2006. However, most (89%) of the harvest was in southern SEAK, and some areas in northern SEAK had very poor escapements. For the 2015 forecast, model selection included a review of ecosystem indicator variables and consideration of additional biophysical parameters to improve the simple singleparameter juvenile CPUE forecast model. Two measures of CPUE were examined for forecast efficacy: CPUEcal, the time series of CPUE calibrated for changes in sampling vessels; and CPUEttd, catch per distance trawled. An alternative model using the regression of harvest and the average ranks of select ecosystem indicators, was also considered. The “best” forecast model for 2015 included two parameters, the Icy Strait Temperature Index (ISTI) and juvenile CPUEcal. The 2015 forecast of 54.5 M fish from this model, using juvenile salmon data collected in 2014, had an 80% bootstrap confidence interval of 48-58 M fish.
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