3.5 Lesson Name: Environmental Effects -- Deterministic 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 deterministic mode using different values for the future EV Scalars for each run of the model. In this case we will choose the Snake River Fall Chinook stock because it is listed under the Endangered Species Act.

How To Do It:

1. Launch and run the model.
2. Set the Default Stock to Lyons Ferry.
3. Click the Stock Menu.
4. Click Stock Graphs.
5. Click Escapements.
6. Record the trend and value in year 2017.
7. Close the Escapement Graph.
8. Click the Stock/EV Scalars button.
9. Click the tab with year 2000.
10. Record the EV Scalar value used during the simulation period.
11. Click the "Y Box" at the top of the EV Scalar window.
12. Set the EV Scalar for year 2000 to 3.0 (note that this changes all the simulation years to 3.0, also).
13. Click apply and OK.
14. Close the EV Scalar window.
15. Click the run button on the tool bar.
16. Repeat steps 3 through 16 using EV Scalar values of 1.0 through 6.0.

1. What EV Scalar value for the Lyons Ferry stock gives a stable escapement trend?
2. What do you think would happen if the EV Scalar value changed every year instead of remaining constant?