Sustainable harvest Sustainable harvest ofof

Finnish moose Finnish moose population?population?

Esa Ranta, Anne Luoma, Veijo KaitalaEsa Ranta, Anne Luoma, Veijo Kaitala

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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)

Economical damages (forest damages,traffic accidents)-> pressure to decrease the population size (expecially the winter population size)

Economically important game animal-> pressure to keep the size of the harvestable population high

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)

Moose population in Finland

The moose population and the annual harvest in Finland 1930 - 2000.

0

20 000

40 000

60 000

80 000

100 000Winter population

Harvest

1930 1950 1970 1990

Nu

mb

er

of

moose

2000

QuickTime™ jaGraphics pakkauksen purkuohjelmatarvitaan elokuvan katselemiseen.

y = 0.45*x - 11.36

Population size before hunt (ind/100 km2)

0

10

20

30

40

50

60

0 20 40 60 80 100 120

Kill

ed a

nim

als

(in

d/1

00km

2 )

• with individual based,• stochastic model

Modelling moose population dynamics

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

Hunting mortalityMortality Mortality

Cows

Bulls Bulls 2-Years -old

Cows 2-Years -old

Calves (Male)

Calves(Female)

Population renewal

Maturation

Maturation

Question #1

• Given the current population status

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

Pro

bab

ilit

y o

f p

op

ula

tio

n d

ecli

ne

Hunting rate of females

QuickTime™ jaGraphics pakkauksen purkuohjelmatarvitaan elokuvan katselemiseen.

0

0.2

0.4

0.6

0.8

1

0

0.2

0.4

0.6

0.8

1

0.1 0.15 0.2 0.25 0.3 0.35 0.1 0.15 0.2 0.25 0.3 0.35

Mortality = 0.01

Mortality = 0.01

Mortality = 0.05

Mortality = 0.05

(A) (B)

(C) (D)

0.7 calves1 calves

Birth rate:

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)

Hunting mortalityMortality Mortality

Cows

Bulls Bulls 2-Years -old

Cows 2-Years -old

Calves (Male)

Calves(Female)

Population renewal

Maturation

Maturation

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 estimateshave on moose population?

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 + birthHunting (h): h = Estimated pop. size - 5 000 animalsLeft:pop. in autumn - h = ? estim.pop. - h = 5 000

Different types of estimation errors:

8500 11500 10000 No peakPeak:

Real population size = 10 000

Real Real Real

8000 12000 8000 12000

”Realistic” population structure

Population sizes after hunting

0 2000 4000 60000

100

200

0 2000 4000 6000

0

100

200

8000 8000

”Realistic” population structure

0

500

1000

0 1000 3000 5000 7000 9000

Population size after hunting

Cu

mu

lati

ve s

um

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)

Hunting mortalityMortality Mortality

Cows

Bulls Bulls 2-Years -old

Cows 2-Years -old

Calves (Male)

Calves(Female)

Population renewal

Maturation

Maturation

”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 landscapeQuickTime™ and aGraphics decompressorare needed to see this picture.

QuickTime™ and aGraphics decompressorare needed to see this picture.

0

0.25

0.5

0.75

1

0.1 0.15 0.2 0.25 0.3

Hunting rate of females

(D) An example

0

0.25

0.5

0.75

1

0 1 2 3 4

c = 0.25

c = 0.75

(A) The landscape (B) Dispersal

Distance

(C) An example of a spatial patternemerging

c = 0.75, m = 0.1, b = 1, harvest = 0.2

H CenterE BorderB Corner

Moose population in landscape

Ris

k o

f p

op

ula

tio

n d

ec

lin

e

Dis

pe

rsa

l s

uc

ce

ss

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

Hunting mortalityMortality Mortality

Cows

Bulls Bulls 2-Years -old

Cows 2-Years -old

Calves (Male)

Calves(Female)

Population renewal

Maturation

Maturation

Question #4• What is the hunting

strategy yielding the highest harvest with a given targeted population size?

Moose harvest in Finland

QuickTime™ and aGraphics decompressorare needed to see this picture.

0

1

2Varsinais-Suomi

Uusimaa

Kymi

Etelä-Häme

Satakunta

Pohjois-Häme

Etelä-Savo

Österbotten

Pohjanmaa

Keski-Suomi

Pohjois-Savo

Pohjois-Karjala

J CowsB BullsE Calves

0

1

2

0

1

2

1 2 3 1 2 3 1 2 3 1 2 3

Winter herd, ind. 10 km-2

Har

vest

, in

d. 1

0 km

-2

Harvest scenariosQuickTime™ and aGraphics decompressorare needed to see this picture.

(A) (B)

COWS

BULLS

CALVES

(C)

COWS

BULLS

CALVES

Har

vest

Winter herd size

Maximum harvest, target = 4 ind. km-2

QuickTime™ and aGraphics decompressorare needed to see this picture.

(A) Cows, aL

(C) Bulls, aS

(E) Calves, aV

(B) Cows, bL

(D) Bulls, bS

(F) Calves, bV

-0.8

-0.6

-0.4

-0.2

0

0.6 0.8 1 1.2

0

0.5

1

1.5

2

0.6 0.8 1 1.2

-0.8

-0.6

-0.4

-0.2

0

0

0.5

1

1.5

2

-0.8

-0.6

-0.4

-0.2

0

0

0.5

1

1.5

2

Total harvest, ind. km-2

Inte

rcep

t

Slo

pe

Answer #4QuickTime™ and aGraphics decompressorare needed to see this picture.

COWS

BULLS

CALVES

Winter herd size

Har

vest

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