Research Document - 2003/102
Forecast for southern and central British Columbia coho salmon in 2003
By Simpson, K., Chamberlain, M., Fagan, J., Holtby, B.,
Sweeting, R. and Tanasichuk, R.W.
Abstract
This Working Paper presents 2003 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 southern BC. Forecasts of survival for these stocks are:
| Management Unit |
Indicator | Recommended Model |
Predicted Survival in 2003 (50% CI) | Change (2003 forecast minus 2002 observed S) |
|
|---|---|---|---|---|---|
| GB West | Big Qualicum | LLY | 0.016 | (0.010 - 0.027) | 0% |
| GB West | Quinsam | 3YRA | 0.014 | (0.011 - 0.018) | 8% |
| GB West | Black (wild) | 3YRA | 0.043 | (0.030 - 0.061) | −12% |
| Lower Fraser | Chilliwack | RAT3 | 0.040 | (0.029 - 0.055) | 21% |
| Lower Fraser | Inch | LLY | 0.021 | (0.009 - 0.047) | 0% |
| Lower Fraser | Salmon (wild) | LLY | 0.036 | (0.048 - 0.083) | 0% |
| GBW, Lower Fraser | All hatcheries | CPUE | 0.014 | (0.011 - 0.017) | −33% |
| SWVI, NWVI | Robertson | Sibling | 0.047 | (0.029 - 0.017) | 0% |
| SWVI, NWVI | Carnation (wild) | Euphausiid | 0.055 | (0.053 - 0.058) | 8% |
Survivals on the west side of the Str. of Georgia (GBW) are expected to range from 1.5% for hatcheries to 4.3% for higher productivity wild stocks. This represents little change from 2002. Survivals are also forecast to remain about the same in the lower Fraser (LowFr) area but at higher levels than on the Vancouver Island shore (6.3% for wild coho). Overall for the Georgia Basin, we characterise survivals as poor (GBW) to below average (LowFr), basing this qualitative assessment on previously higher survivals and on calculations of the survivals needed to sustain stocks of low to average productivity. CPUE data also indicate low survivals, less than last year. There is little data for the east side of the strait but other information suggests survivals are no better than in GBW.
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 a strong ‘inside’ year, the proportion is expected to be more ‘inside’ than in 2002 and the mean of the last 10 years.
On the west coast of Vancouver Island (wVI), survival of wild coho is forecast to be 5.5%, which is similar to the Georgia Basin survivals. Survival of Robertson Hatchery coho is forecast to be more than Georgia Basin hatcheries, as it has been for many years. These forecasts are similar to survivals in 2002. Both indicators are in SW Vancouver Island but results are also applied to NW Vancouver Island, which lacks indicators.
The abundance of Thompson River coho is expected to be 35,700. This is significantly less than the 51,000 in 2002 but more than the brood year abundance of 15,800. Returns in 2001 and 2002 also exceeded their brood year returns. This stock aggregate is slowly recovering.
The abundance forecasts for central 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:
| Aggregate | Model | Forecast P1 | Characterization |
|---|---|---|---|
| Area 7 | 3YRA | 28% | Below Average |
| Area 8 | 3YRA | 15% | Below Average |
| Area 9-11 | 3YRA | 38% | Average |
| Area 12 | 3YRA | 13% | Well Below Average |
| Area 13 | 3YRA | 2% | Well Below Average |
| Aggregate | Model | Forecast P1 | Charecterization | % of Smax 2 |
|---|---|---|---|---|
| Area 7 | 3YRA | 58% | Average | 38% |
| Area 8 | 3YRA | 40% | Average | 43% |
| Area -11 | 3YRA | 91% | Well Above Average | 129% |
| Area 12 | 3YRA | 48% | Average | 27% |
| Area 13 | 3YRA | 19% | Below Average | 6% |
1 Proportions of observed abundances from 1950 to 2002 that are less than the 2003 forecast.
2 The escapement that on average produces the maximum recruitment, as determined from the S-R analysis.
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