Research Document - 1999/129

Run Size Forecasts for Fraser River Sockeye and Pink Salmon in 1999.

By A. Cass

Abstract

Run size forecasts for 1999 Fraser River sockeye and pink returns presented here are based on methods previously approved by PSARC. Forecasts are made for 18 individual sockeye stocks and four migratory timing / management groups. Forecasts of pink salmon are made for all Fraser pink populations combined. Forecasts are based on 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 and smolt abundance estimates. Environmental indices are also used to help explain variation in ocean survival of Chilko sockeye and pink salmon. Methods that incorporate attributes of escapement-based and juvenile-based models are explored that pool results from individual sockeye forecast models (i.e. Baysian approach) where time series of different life stages are available. Sibling models were not considered suitable candidate models for forecasting 1999 returns because estimates of age-3 jack returns in 1998 are considered to be particularly unreliable and because of the poor performance of sibling models in recent years compared to other forecast models.

The total 1998 Fraser sockeye run size forecast is 8.2 million sockeye at the 50% probability level (the chance the run will exceed the forecast) and 4.8 million at the 75% probability level. Forecasts by management group are 318,000 (50%) and 197,000 (75%) for Early Stuart, 477,000 (50%) and 244,000 (75%) for Early summer stocks, 5.3 million (50%) and 3.3 million (75%) for summer run stocks and 2.1 million (50%) and 1.1 million (75%) for late run stocks. The 1999 forecast of Fraser pink is 8.1 million at the 50% probability level and 6.4 million at the 75% level (Table 1). A particular cautious note is warranted for 1999 sockeye returns. Sockeye smolts that return as adults in 1999 entered the ocean during the intense 1997 El Nino. Sockeye returns in 1995 that went to sea during the less intense 1993 El had very low survival rates for all major stocks. If the intense El Nino in 1997 resulted in low sockeye survival then forecasts presented here significantly over-estimate returns of Fraser sockeye in 1999.

Complete document (PDF, 215 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.