Research Document - 2001/063

Pre-season run size forecasts for Fraser River sockeye and pink salmon in 2001

By Cass, A.

Abstract

Forecasts are made for each of 18 individual sockeye stocks and four timing groups and for Fraser River pink salmon, all spawning populations combined. Adult returns of sockeye to the Fraser River on the 2001 cycle line are the highest of the four cycle lines averaging 15.9 million/ year (1980-97) compared to 9.3 million/year for the same period on the other three cycle lines combined. Forecasts 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 (420,000 Early Stuart, 202,000 Early Summer, 11.7 million Summer and 528,000 Late run). The total forecast at the 50% probability level is nearly two times the forecast at the 75% level (6.8 million). Quesnel, Late Stuart and Chilko sockeye are the three largest stocks anticipated in 2001. The 2001 pink forecast at the 50% probability level is 5.5 million fish or about half of the long-term odd-year return mean of 10.5 million/yr. Migratory conditions in the Fraser River for the early-timed sockeye runs (i.e. Early Stuart and Early Summer sockeye) in brood-year 1997 were poor as a result of high river discharge rates. The effect of stress on survival of the progeny from those fish that spawned in 1997 is not known. Except for low egg-to-fry survival of Early Stuart sockeye at one of two sites sampled, there is no evidence of anomalous freshwater conditions that signal low freshwater survival in the egg-to-fry stages where data exist (Early Stuart and Quesnel). There is, however, inadequate sampling throughout the watershed to reliably predict freshwater survival. The recent intense El Ninos were associated with poor marine survival of Fraser sockeye in ocean entry years 1993 and 1997 and over-forecasts in return years 1995 and 1997. Oceanographic and meteorological conditions in the northeast Pacific returned to near normal values in 1999 (2001 age-4 ocean entry year) and there is little evidence based on oceanographic conditions that adverse marine sockeye survival conditions prevailed in ocean-entry-year 1999 of age-4 sockeye returning in 2001. Fraser River pinks returning to spawn in 2001 entered the ocean as fry in 2000. Based on preliminary information on oceanographic condition that prevailed in 2000, there is no evidence to indicate adverse survival conditions.

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