Sustainable harvest of Finnish moose population?

1. Sustainable harvest ofFinnish moose population? Esa Ranta, Anne Luoma, Veijo Kaitala & FGFRI

2. Contents • Basic information on Finnish moose population and harvest

3. Contents • Basic information on Finnish moose population and harvest • Stochastic IBM model

4. Contents • Basic information on Finnish moose population and harvest • Stochastic IBM model • Four questions

5. Contents • Basic information on Finnish moose population and harvest • Stochastic IBM model • Four questions • Four answers

6. Moose (Alces alces)

7. Economically important game animal -> pressure to keep the size of the harvestable population high Economical damages(forest damages, traffic accidents) -> pressure to decrease the population size (expecially the winter population size)

8. Moose population in Finland • Population size estimates: • Hunter observations (during the hunting season) • +their estimate of post-harvest pop.size • Wildlife triangle (snow track census) • Aerial surveys • 20-50% of population is killed annually. • Age structure of population is controlled. • Reproduction rate is high(mostly due to high harvest rate of young animals)

9. 100 000 Winter population 80 000 Harvest 60 000 Number of moose 40 000 20 000 0 2000 1930 1950 1970 1990 Themoose population and the annual harvest in Finland 1930 - 2000.

10. Killed animals (ind/100km2)

11. Modelling moose population dynamics • with individual based, • stochastic model Annual reproduction rate = 0.9 calves/ a female Non-hunting mortality = 5% of winter population Hunting mortality (hunting rate) 15 - 25% of the harvestable population

12. Populationrenewal Maturation Calves (Male) Bulls 2-Years -old Bulls Calves (Female) Cows 2-Years -old Maturation Cows Mortality Mortality Hunting mortality

13. Question #1 • Given the current population status • What is the risk of moose population decline?(10 year time-window)

14. Probability of population decline Hunting rate of females

15. Answer #1 • The risk of moose population decline increases substantially when annual harvest fraction inceseses from 15% of the harvestable population size(10 year time-window)

16. Populationrenewal Maturation Calves (Male) Bulls 2-Years -old Bulls Calves (Female) Cows 2-Years -old Maturation Cows Mortality Mortality Hunting mortality

17. Question #2 • Given the current population status, with errors in population estimates • The wish is to reduce current population to a much lower lewel • What will happen?(10 year time-window)

18. There are reasons to limit the population size. But if we want to get the pop. size really low, It is important to know: What if.. - the population size is overestimated or underestimated? - estimations tend to be biased? How crucial effects do inaccurate estimates have on moose population?

19. Real Estimated • Population size in winter: • 10 0008 000 - 12 000 • Targeted population size 5 000 • Population size in autumn: • According to model1.5 * winter pop. • (realistic and productive populations); • 10 000 - winter= 12 000 - 18 000 • mortality + birth • Hunting (h): h = Estimated pop. size - 5 000 animals • Left: • pop. in autumn - h = ? estim.pop. - h = 5 000

20. Peak: No peak 10000 11500 8500 8000 12000 8000 12000 Real population size = 10 000 Real Real Real Different types of estimation errors:

21. 200 100 0 200 100 0 8000 8000 0 2000 4000 6000 0 2000 4000 6000 ”Realistic” population structure Population sizesafter hunting

22. 1000 500 0 9000 0 1000 3000 5000 7000 ”Realistic” population structure Cumulative sum Population size after hunting

23. Answer #2 • With uncertain population estimates reduction of curent population size to a lower targeted size will yield to population sizes that are much lower than the target (10 year time-window)

24. Populationrenewal Maturation Calves (Male) Bulls 2-Years -old Bulls Calves (Female) Cows 2-Years -old Maturation Cows Mortality Mortality Hunting mortality

25. ”Mooses come walking over the hillMooses come walking, they rarely stand stillWhen mooses come walking they go where they willWhen mooses come walking over the hill”- Arlo Guthrie

26. Question #3 • How does landscape structure influence risk of moose population decline due to harvesting?

27. Moose populatin in landscape

28. Moose population in landscape Dispersal success Risk of population decline

29. Answer #3 • Under many different dispersal scenarios risk of population decline is the highest in the corner units, then come the border units • The risk is the lowest in the central units

30. Populationrenewal Maturation Calves (Male) Bulls 2-Years -old Bulls Calves (Female) Cows 2-Years -old Maturation Cows Mortality Mortality Hunting mortality

31. Question #4 • What is the hunting strategy yielding the highest harvest with a given targeted population size?

32. Moose harvest in Finland Harvest, ind. 10 km-2 Winter herd, ind. 10 km-2

33. Harvest scenarios Harvest Winter herd size

34. Maximum harvest, target = 4 ind. km-2 Intercept Slope Total harvest, ind. km-2

35. Answer #4 Harvest Winter herd size

36. Conclusions • The simple IBM model on moose population renewal has served us well in answering a few basic questions on the future of moose and moose harvesting in Finland

37. Conclusions • The model does not rely upon very complex assumptions (births, deaths, sex, harvesting), yet we believe it captures the essence of moose life

38. Conclusions • The model prompts where more information is needed • dispersal, population estimates, harvest management • Some of the answers would not necessarily have called for an IBM model