3.6 Lesson Name: Environmental Effects -- Stochastic Mode

Fishery biologists know that salmon survival during the first year of life is highly variable from year to year. This is called the "brood year survival rate" and is represented in model by the EV (Environmental Variability) Scalars. What happens to the model predictions if future survival rates don't match what the scientists predict?

Analysis Approach:

Select a stock of interest and run the model in stochastic mode, allowing the EV Scalars to vary randomly from year to year during a given run of the model.

How To Do It:

1. Launch and run the model.
2. Click the Run Menu.
3. Click Monte Carlo.
4. Set the number of games to 1.
5. Click Run Monte. When the run is completed, an escapement graph for the selected default fishery appears.
6. Click the Stock Menu.
7. Click Stock Graphs.
8. Click Escapements and notice that the escapement for the selected stock varies considerably from year to year.
9. Resize and move the Escapement Graph so the map icons are visible.
10. Click the Stock/EV Scalars button.
11. Click the tabs for years beyond 1995 to examine the EV Scalar values that were used during this Monte Carlo run.
12. Pick out the year with the highest EV Scalar value and notice that the resulting high escapement occurs several years later when the fish are mature.
13. Close the EV Scalar window.
14. Click the Wand button at the upper left of the Escapement Graph window.
15. Move the mouse pointer over other stock icons to produce Escapement Graphs for other stocks and observe their variable escapement.
16. Examine EV Scalars for other stocks also.

1. What fresh water environmental factors affect brood year survival rates?
2. What marine environmental factors affect brood year survival rates?
3. What types of human activities affect brood year survival rates?