SAK Does Not Work in Earn-A-Buck Units

1. SAK Does Not Work in Earn-A-Buck Units • Key Assumption of SAK: • Buck Harvest can Index Population Trends • Buck Harvest Rates are Relatively Stable • Buck Harvest Rates Affected by: • Earn-a-buck Permit Structure

2. 1996 Earn-A-Buck Units • 16 farmland management units • Developed a accounting-style model • Patterned after POP-II • commercially available big game population model • Similar to bear and furbearer population model we have used for many years

3. Accounting Population Models • Deterministic: checkbook accounting style models • Simulates changes over time in number of deer in each sex- and age-class. • Model does not directly estimate population size: • Requires input of population size in initial year • Simulate seasonal changes in population size over several years • Simulated trends sensitive to initial population size • Can estimate likely population size if independent population trend data exists • Assess effects of future harvest strategies

4. Population Model Inputs • Initial population size, sex & age composition • Harvest mortality by sex and age • Age- & year-specific pregnancy rates, litter size • Age-specific rates of summer and winter non-harvest mortality • Registration compliance

5. Population Model Logic 1. Create pre-birth population for initial year A. Initial number of deer B. Sex ratio of adults in initial year C. Age composition in initial year 2. Determine fawn production A. Age-specific pregnancy rates B. Mean litter size C. Age composition of females in pre-birth population D. Sex ratio of fawns 3. Add fawn production to pre-birth population for post-birth population and increase ages by 1 (eg. fawns become yearlings, etc.)

6. Population Model Logic 2 4. Subtract summer non-harvest mortality from post-birth population to determine pre-hunt population 5. Determine harvest by age and sex using: A. Total registered harvest by antlered/antlerless (mandatory registration) B. Age structure of harvest (aging data) C. Estimate of registration compliance 6. Subtract harvest from pre-hunt population to determine post-hunt population 7. Subtract overwinter non-harvest mortality from post-hunt population to determine pre-birth population in year 2 8. Repeat steps 2-7 for year 2, year 3, etc.

7. Example of calculations used to create pre-birth population in year 1

8. Example of calculations used to determine kit production

9. Kit production is added to pre-birth population for post-birth population

10. Summer losses =post-birth population * summer non-harvest mortality rates

11. Subtract summer losses from post-birth population to determine pre-hunt population

12. Harvest by sex and age

13. Subtract harvest related mortality from pre-hunt population to determine post-hunt population

14. Winter Losses =Post-Hunt Population * Winter Non-Harvest Mortality Rates

15. Subtract Winter Losses From Post-Hunt Population to Determine Pre-Birth Population in Year 2

17. Simulated Population Trend for Wisconsin Fishers

18. Simulated trend sensitive to initial population size

19. Fisher Tracks/Transect, Statewide, 1980-2003

20. Calibrate simulated population to independent information on population trend

21. Population Model Assumptions • Does Not Assume: • Harvest age structure reflect population age structure • Buck harvest rates are stable • Does Assume: • Initial population size and composition can be accurately estimated • Nonharvest mortality rates and reproduction can be accurately estimated

22. Accounting Models Most Useful • When long histories (10+ years) of independent estimates of population size or trend are available