Research Document - 1999/186
Forecast for northern British Columbia coho salmon in 1999
By B. Holtby, B. Finnegan, and B. Spilsted
Abstract
This paper documents forecasts of marine survival and abundance for the coho of northern British Columbia including the upper Skeena conservation area.
Marine survival:
Marine survival at the three northern indicators is expected to be above average for 1999.
| Indicator | Model | Ŝ1999 | (50% CI) |
|---|---|---|---|
| Lachmach | sibling regression | 0.175 | (0.143-0.215) |
| Toboggan Creek hatchery | from Lachmach | 0.046 | (0.028-0.075) |
| Fort Babine hatchery | from Lachmach | 0.033 | (0.014-0.076) |
The forecast for Fort Babine is poorly defined. Based on three years observations the survival rate of wild Toboggan Creek coho should be 0.176, which is the same as the forecast for the Lachmach. We note though that survival rate forecasts for the Skeena were optimistic in 1998.
Abundance forecast:
After the application of stock-recruitment and time-series models to reconstructions of abundance in eight aggregates in northern B.C. we conclude the following about abundance in 1999:
| Aggregate | 1999 Abundance Forecast | Confidence in Forecast |
|---|---|---|
| Babine Lake Upper Skeena | Well below average | High |
| Lower and Middle Skeena | Below average | Moderate |
| Area 3 | Below average | High |
| Area 5 | Below average | Low |
| Area 6 | Well below average | Low |
| Area 7 & 8 | Below average | Low |
Average abundance was calculated over the period 1950 to 1998 for the Statistical Area aggregates and over the period 1946 to 1998 for Babine Lake. Abundance forecasts relative to this period are not necessarily indicative of aggregate status.
Abundance was not forecast for Area 9 (Rivers Inlet) and Area 10 (Smith Inlet). The escapement data for those areas in the 1990's is insufficient to make a forecast. Escapement data in 1998 suggest that both areas are similar to Area 8. Abundance was not forecast for the Queen Charlotte Islands because of a lack of an exploitation rate time series.
We note that these forecasts were derived from the more conservative of the two approaches considered. Given that survival is forecast to be above average at least in the northern area, it is possible that our forecasts are in fact very conservative. It is probable however, that even with above average survival, that total abundance of the Babine Lake and upper Skeena aggregates will remain sufficiently low to warrant considerable caution in managing fisheries in 1999. It would be prudent to extend that caution to Areas 5 and 6.
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