Research Document 1998/44

Run size forecasts for Fraser River sockeye salmon in 1998

By Al Cass

Abstract

Forecasts are made for 19 individual sockeye stocks and four migratory timing/management groups. Forecasts of adult returns are made using a variety of explanatory variables. For most stocks, forecasts are based on regression models that use spawning escapement to predict adult abundance. Additional explanatory variables are available for some stocks and include fry, smolt, sibling adults and an index of ocean survival. For all models the uncertainty associated with stock-specific forecasts are large and reliable only within an order of magnitude. The major impediment to improvements in accuracy of pre-season run size forecasts are related to our inability to model variations in survival. The total 1998 Fraser sockeye run size forecast is 11.2 million sockeye at the 50% probability level and 6.8 million at the 75% probability level. Forecasts by management group are 175,000 (50%) and 97,000 (75%) for Early Stuart, 640,000 (50%) and 300,000 (75%) for Early summer stocks, 6.6 million (50%) and 3.9 million (75%) for summer run stocks and 3.8 million (50%) and 2.6 million (75%) for late run stocks.

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