Research Document - 2004/135

Forecast for southern and central British Columbia coho salmon in 2004

By Simpson, K., M. Chamberlain, J. Fagan, R. Tanasichuk, D. Dobson

Abstract

This Working Paper presents 2004 forecasts of marine survival, abundance and distribution of coho in southern and central British Columbia (Areas 7 to 29: the Fraser River system and coastal waters south of approximately 53° N).

There are five hatchery and three wild coho indicator stocks in the Georgia Basin and west coast of Vancouver Island (wVI). Forecasts of survival for these stocks are:

Survival of coho on the east coast of Vancouver Island is expected to be poor, ranging from approximately 1% for hatcheries to 4.7% for higher productivity wild stocks. Although the wild forecast and the Quinsam hatchery forecast are larger than the survivals in 2003, there is an increased risk this year, based on sibling forecasts of hatchery survival, that survivals may be lower than last year. Survivals are forecast to remain about the same in the lower Fraser (LowFr) area. Although there is not a time series of survivals for the mainland shore of the Strait (the Georgia Basin East Management Unit), measured survivals suggest that coho survivals have been poorer in this Unit than elsewhere in the Georgia Basin. Overall for the Georgia Basin, we characterise survivals as poor, basing this qualitative assessment on previously higher survivals and on calculations of the survivals needed to sustain stocks of low to average productivity.

We forecast that an average proportion of coho that originated in the Georgia Basin will rear in the Strait of Georgia in the spring and summer before spawning. Although not a prediction of either an’ inside’ year or an ‘outside’ year, the proportion is expected to be more ‘inside’ than several of the last 10 years.

Survival of coho is forecast to be approximately 3% on wVI (SWVI and NWVI). This is about one third of the very good survival in 2003. Survival of Robertson Hatchery coho is forecast to be more than Georgia Basin hatcheries, as it has been for many years. The return of coho to the wild indicator, Carnation Creek, is forecast to decline from above average in 2003 to well below average. In summary the forecast is for a sharp reduction in survival and for returns to be below average or well below average.

The abundance of Thompson River coho in 2004 is expected to be ~34,271 animals. This is significantly more than the ~14,610 coho observed in 2003, but less then the brood year (2001) abundance of ~53,000. Returns in 2003 did not exceed their brood year return as well. While some individual Interior Fraser River populations are remaining stable or have increased slightly over the brood abundance, as a whole the abundance of this stock aggregate continues to remain low and is not recovering rapidly.

The abundance forecasts for central coastal British Columbia remain the only method of forecasting for this area. Forecasting methods conform to those of past forecasts in this area. The forecasts of total abundance and escapement for the five Central Coast aggregates are given in the following table. Note that the abundance of coho in Area 13 (Johnstone Strait) is expected to be very poor:

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