Sustainable harvest of Finnish moose population

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Sustainable harvest ofFinnish moose population?

• Esa Ranta, Anne Luoma, Veijo Kaitala
• FGFRI

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Contents

• Basic information on Finnish moose population and
  harvest

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Contents

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

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Contents

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

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Contents

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

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Moose (Alces alces)
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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)

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100 000
Winter population
80 000
Harvest
60 000
Number of moose
40 000
20 000
0
2000
1930
1950
1970
1990
The moose population and the annual harvest in
Finland 1930 - 2000.
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Killed animals (ind/100km2)
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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
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Question 1

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

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Probability of population decline
Hunting rate of females
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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)

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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)

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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?
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• Real Estimated
• Population size in winter
• 10 000 8 000 - 12 000
• Targeted population size 5 000
• Population size in autumn
• According to model 1.5 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

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Different types of estimation errors
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Realistic population structure
Population sizes after hunting
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Realistic population structure
Cumulative sum
Population size after hunting
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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)

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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
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Question 3

• How does landscape structure influence risk of
  moose population decline due to harvesting?

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Moose populatin in landscape
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Moose population in landscape
Dispersal success
Risk of population decline
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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

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Question 4

• What is the hunting strategy yielding the highest
  harvest with a given targeted population size?

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Moose harvest in Finland
Harvest, ind. 10 km-2
Winter herd, ind. 10 km-2
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Harvest scenarios
Harvest
Winter herd size
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Maximum harvest, target 4 ind. km-2
Intercept
Slope
Total harvest, ind. km-2
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Answer 4
Harvest
Winter herd size
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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

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Conclusions

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

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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