Trends in Abundance and Pre-season 2000 Stock Size Forecasts for Major Sockeye, Pink, and Chum Salmon Stocks in the Central Coast and Selected Salmon Stocks in Northern British Columbia

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Abstract

This document includes pre-season 2000 stock size forecasts for nine sockeye, five pink, and five chum salmon stocks or stock groupings in central and northern British Columbia, statistical areas 1-10. The recommended forecasts are based on simple models that have been evaluated in a previous working paper (S95-12).

The recent 5-yr mean model is a simple time-series approach that effectively accommodates gradual changes (autocorrelated anomalies) in productivity. For northern populations of sockeye salmon this model has performed as well, or better than other models because variations in the independent variables used by other models have been small, and their effects have been obscured by other factors. However, for Skeena River sockeye, the 5-yr mean model should again be rejected in favour of the “sibling age-class” model that includes the effect of measured record low smolt production from the 1995 brood year. For Rivers and Smith Inlet sockeye the 5-yr mean model should also be rejected because it performed very poorly in 1999. Alternative models were evaluated that incorporate the measured effects of the extremely poor 1994 and 1995 brood year (1996 and 1997 sea-entry years) marine survival, and the possibility of continued poor survival in 1998 sea-entry year. Although the average sibling/smolt forecast is statistically the best model, we recommend the “like sea-entry 1996” sibling/smolt forecast be used to guide management decisions in 2000 following the precautionary approach.