Research Document - 2001/147

Pre-season run size forecast for Fraser River Sockeye in 2002

By Cass, A.

Abstract

The 2002 cycle line is noted for the historically dominant Lower Adams River (Shuswap Lake) sockeye returns. This cycle line was once the highest of the four cycle lines averaging 15.5 million/year since 1980 compared to 8.9 million/year for the other three cycles. Together, Adams River sockeye and other late run Shuswap Lake stocks accounted for about 50% of the total returns on the 2002 cycle. The sub-dominant Quesnel run has rebuilt within the last two decades and escapements in the 1998 brood year were equal to the dominant Late Shuswap escapement at 1.2 million sockeye.

Forecasts for 2002 are provided at various probability levels of achieving specified run sizes by stock and run-timing group. The forecast of sockeye at the 50% level for all stocks combined is 12.9 million fish (105,000 Early Stuart, 493,000 Early Summer, 9.0 million Summer and 3.3 million Late run). This forecast compares to an average return on the 2002 cycle of 15.5 million sockeye/year (1980-2000). The reason for the disparity between the forecast and mean return since 1980 is due primarily to a decline in returns of Late run stocks. The Summer Run forecast in 2002 accounts for 70% of the total forecast. Quesnel (6.5 million) and Late Shuswap (2.3 million) sockeye together account for 70% of the total forecast.

Migratory conditions in the Fraser River in 1998 were poor for many stocks as a result of high water temperatures. The effect of stress on survival of the progeny from those fish that spawned in 1998 is not known. Indicators of freshwater survival throughout the watershed for the brood were variable. Low freshwater survival was evident for Early Stuart sockeye at two of three site as well as for Chilko and Shuswap lakes. Channel fry survival rates, however, showed no indication of poor egg-to-fry conditions.

Oceanographic and meteorological conditions in the northeast Pacific returned to near normal values in 1999 (2002 age-5 ocean entry year) (Anon. 2000b). Moderate La Nina conditions occurred in 2000 and ocean temperatures were normal to slightly below normal and salinity was near normal in the north Pacific region in 2000 (2002 age-4 ocean entry year).

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