Chapter 14. How Should We Measure Habitat Productivity?
My Results for Exercises 3 and 5:

2. How Will the Smolt-to Spawner Ratio Respond to a Degradation in Habitat?
3. My Results:

My results are shown here in case you want to see an illustrative answer to check against your own simulation. (The font is difficult to read, so the scales are explained below the time graph.) The smolt migration loss fraction is shown in red; the Tucannon carrying capacity in black; the smolts per spawner in blue. The variations in the smolts per spawner in the first few years are caused by the initial conditions and the S-shaped growth of the population. After around ten years, however, the smolts per spawner settles down to a fluctuating pattern -- it varies from a low of 25 to a high of around 50. Then , in the 240th month, the carrying capacity is reduced, reaching 200 thousand by the 480th month. But the smolts per spawner seems to follow almost the same pattern as before. The simulation suggests that the smolts per spawner would not alert us to a decline in habitat productivity under these test conditions.

Smolts per spawner (in blue) scaled from 0 to 200 Tucannon Carrying Capacity (in black): scaled from 0 to 400 thousand smolts smolt migration loss fraction (in red): scaled from 0.80 to 1.00 Time runs from 0 to 960 months.

4. How Will the Smolt-to-Spawner Ratio Respond when both the Habitat and the River Corridor are Degraded Over Time?
5. My Results:

My results are shown here in case you want to see an illustrative answer to check against your own simulation. The smolts per spawner ratio is shown in blue as before. (The font is difficult to read, so the scales are explained below the time graph.) The test shows a decline in carrying capacity AND an increase in the smolt migration loss fraction between the 240th and 480th month. The model shows an increase in the smols per spawner during the 2nd half of the simulation. This test alerts us to the possibility of an erroneous conclusion on habitat productivity. If we focus on the smolts per spawner, we would conclude that the habitat has improved during this simulation.

Smolts per spawner (in blue) scaled from 0 to 200 Tucannon Carrying Capacity (in black): scaled from 0 to 400 thousand smolts smolt migration loss fraction (in red): scaled from 0.80 to 1.00 Time runs from 0 to 960 months.

Discussion Questions

These tests reveal serious problems using the smolt to spawner ratio as a measure of habitat productivity.
What other "measure" could we use to show changes in habitat productivity?
Do you think it would be difficult to obtain data on how your "measure " has changed over the past 3-4 decades?