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Forecasting Pink Salmon Harvest in Southeast Alaska from Juvenile Salmon Abundance and Associated Environmental Parameters: 2009 Harvest and 2010 Forecast
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2010
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[PDF-447.57 KB]
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Description: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 this 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, modified by other environmental parameters as appropriate, has been used to forecast harvest of adult pink salmon (O. gorbuscha) in SEAK. The 2009 return of 38.0 million fish was 17% below the forecast of 44.4 million. This represents the fifth forecast over the period 2004-2009 which was within 0-17% of the actual harvest. Conversely, the forecast for 2006 did not follow this pattern and was 200% higher than the actual harvest; however, the simple CPUE forecast model did indicate a downturn in harvest that year. These results show that the CPUE information has great utility for forecasting year class strength of SEAK pink salmon, but additional environmental data are needed to avoid "misses" such as the forecast of the 2006 return. Beginning with the forecast for the 2007 return, the simple CPUE forecast model was enhanced to include stepwise multiple regression, jackknife hindcast analysis, and bootstrap confidence intervals. For 2010, a three-parameter model was selected as the "best" forecast model. Juvenile pink salmon CPUE in northern SEAK accounted for 82% of the variability in annual harvest of SEAK pink salmon over the period 1997-2009. The amount of variability explained was improved to 94% when the May 20-m integrated sea water temperatures and an index of the El Niño Southern Oscillation (ENSO) were included in the model. The forecast for the 2010 harvest was 26.8 million fish, with an 80% bootstrap confidence interval of 18-35 million fish. Preliminary end of the season pink salmon harvests for 2010 are currently 23.4 million (17 Sept 2010, Alaska Department of Fish and Game) and are within 15% of the SECM 2010 harvest forecast.
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