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Sustainable harvest of Finnish moose population?. Esa Ranta, Anne Luoma, Veijo Kaitala & FGFRI. Contents. Basic information on Finnish moose population and harvest. Contents. Basic information on Finnish moose population and harvest Stochastic IBM model. Contents.

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Sustainable harvest ofFinnish moose population?

Esa Ranta, Anne Luoma, Veijo Kaitala

&

FGFRI


Contents

  • Basic information on Finnish moose population and harvest


Contents

  • Basic information on Finnish moose population and harvest

  • Stochastic IBM model


Contents

  • Basic information on Finnish moose population and harvest

  • Stochastic IBM model

  • Four questions


Contents

  • Basic information on Finnish moose population and harvest

  • Stochastic IBM model

  • Four questions

  • Four answers


Moose (Alces alces)


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)


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)


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.


Killed animals (ind/100km2)


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


Populationrenewal

Maturation

Calves

(Male)

Bulls

2-Years

-old

Bulls

Calves

(Female)

Cows

2-Years

-old

Maturation

Cows

Mortality

Mortality

Hunting mortality


Question #1

  • Given the current population status

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


Probability of population decline

Hunting rate of females


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)


Populationrenewal

Maturation

Calves

(Male)

Bulls

2-Years

-old

Bulls

Calves

(Female)

Cows

2-Years

-old

Maturation

Cows

Mortality

Mortality

Hunting mortality


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)


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?


  • RealEstimated

  • 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


Peak:

No peak

10000

11500

8500

800012000

800012000

Real population

size = 10 000

Real

Real

Real

Different types of estimation errors:


200

100

0

200

100

0

8000

8000

0

2000

4000

6000

0

2000

4000

6000

”Realistic” population structure

Population sizesafter hunting


1000

500

0

9000

0

1000

3000

5000

7000

”Realistic” population structure

Cumulative sum

Population size after hunting


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)


Populationrenewal

Maturation

Calves

(Male)

Bulls

2-Years

-old

Bulls

Calves

(Female)

Cows

2-Years

-old

Maturation

Cows

Mortality

Mortality

Hunting mortality


”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


Question #3

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


Moose populatin in landscape


Moose population in landscape

Dispersal success

Risk of population decline


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


Populationrenewal

Maturation

Calves

(Male)

Bulls

2-Years

-old

Bulls

Calves

(Female)

Cows

2-Years

-old

Maturation

Cows

Mortality

Mortality

Hunting mortality


Question #4

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


Moose harvest in Finland

Harvest, ind. 10 km-2

Winter herd, ind. 10 km-2


Harvest scenarios

Harvest

Winter herd size


Maximum harvest, target = 4 ind. km-2

Intercept

Slope

Total harvest, ind. km-2


Answer #4

Harvest

Winter herd size


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


Conclusions

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


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


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