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Forecasting Pink Salmon Harvest in Southeast Alaska from Juvenile Salmon Abundance and Associated Biophysical Parameters : 2015 Returns and 2016 Forecast
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2016
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[PDF-460.25 KB]
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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 SECM forecast was for an excellent odd-year harvest of 54.5 M fish. However, the actual 2015 SEAK harvest was 35.1 million fish, the lowest odd-year harvest since 1997. Thus the 2015 SECM forecast was 56% over the actual harvest. Nine of 12 forecasts over 2004-2015 have been within 20% of the actual harvest, with an average forecast deviation of 9%. Most (66%) of the harvest was in northern SEAK, consistent with strong returns in more northerly regions of the Gulf of Alaska, e.g., Prince William Sound and Kodiak. For the 2016 forecast, model selection included a review of ecosystem indicator variables and consideration of additional biophysical parameters to improve the simple single-parameter 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 2016 included two parameters, the ecosystem rank index and a measure of May water temperatures in Icy Strait. The 2016 forecast from this model, using juvenile salmon data collected in 2015, was 30.4 M with an 80% regression model prediction interval of 16-45 M fish.
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