Economic impacts of changes in fish population dynamics:

the role of the fishermen’s behavior

Dipl.-Geogr. Peter Michael Link, BAResearch Unit Sustainability & Global Change

Center for Marine and Climate ResearchUniversity of Hamburg, Germany

Outline of the presentation

• Context of the study

• Characteristics of the bioeconomic model

• Simulations with adaptive harvesting strategies:What are the impacts of changes in reproductiverates or carrying capacities?

• Simulations with rational behavior:To what extent are stocks and harvest amountsaffected by changes in population dynamics?

Economic impacts of changes in fish population dynamics:the role of the fishermen’s behavior

How does the economic impact change depending

on the harvesting strategies of the fishermen?

The research project INTEGRATION

INTEGRATION looks at the impacts on ecosystems and society caused by a regional or global breakdown of the thermohaline circulation. This is done along two paths:

1. ocean circulation climate change in Europe agriculture and forestry economy and society

2. ocean circulation plankton fish fisheries (economy and society)

Economic impacts of changes in fish population dynamics:the role of the fishermen’s behavior

Structure of the model covering two fish species and three fleet types

environmentalchange

cod: age 0

recruitment

cod: age 1

cod: age 2

cod: age N

capelin: age 0

recruitment

capelin: age 1

capelin: age 2

capelin: age N

fishing effort

fixed costs,variable costs

profits

revenue

total catch

fishing effort

fixed costs,variable costs

profits

revenue

total catch

fishing effort

fixed costs,variable costs

profits

revenue

total catch

cod stock capelin stock

coastalfisheries

trawlers purse seinefisheries

Economic impacts of changes in fish population dynamics:the role of the fishermen’s behavior

Adaptive strategies: development of the cod stockfor different reductions of the rate of reproduction

500

750

1000

1250

1500

1750

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2250

2500

20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

year

tota

l sto

ck b

iom

ass

in 1

000

tons

R unchanged R -10%

R -20% R -30%

R -40% R -50%

Economic impacts of changes in fish population dynamics:the role of the fishermen’s behavior

Adaptive strategies: development of the capelin stockfor different reductions of the rate of reproduction

1500

1750

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2250

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2750

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3250

3500

20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

year

tota

l sto

ck b

iom

ass

in 1

000

tons

R unchanged R -10%

R -20% R -30%

R -40% R -50%

Economic impacts of changes in fish population dynamics:the role of the fishermen’s behavior

Adaptive strategies: development of total cod catchesfor different reductions of the rate of reproduction

0

50

100

150

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250

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400

20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

year

tota

l ann

ual c

atch

es in

100

0 to

ns

R unchanged R -10%

R -20% R -30%

R -40% R -50%

Economic impacts of changes in fish population dynamics:the role of the fishermen’s behavior

Adaptive strategies: development of total capelin catchesfor different reductions of the rate of reproduction

300

400

500

600

700

800

900

1000

1100

20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

year

tota

l ann

ual c

atch

es in

100

0 to

ns

R unchanged R -10%

R -20% R -30%

R -40% R -50%

Economic impacts of changes in fish population dynamics:the role of the fishermen’s behavior

Adaptive strategies: net present value of profits for different levels of reduction of reproductive rates

600,00

605,00

610,00

615,00

620,00

625,00

unch

ange

d-5

%-1

0%-1

5%-2

0%-2

5%-3

0%-3

5%-4

0%-4

5%-5

0%

change in R

mill

ion

NO

K

735,00

740,00

745,00

750,00

755,00

760,00

NPV trawlers NPV coastal vessels NPV purse seiners

Economic impacts of changes in fish population dynamics:the role of the fishermen’s behavior

Impacts of changes in fish population dynamicswhen fishermen follow adaptive strategies

• The stock sizes of cod and capelin decrease over time if the population dynamics of the species are negativelyaffected. This in turn leads to smaller total annual catches.

• Therefore, there is a negative long-term development of the fisheries. This trend is in some cases masked by theshort-term increase of the the returns from fishing whichoccurs despite a continued decrease of the stock sizes.

• The net present value of profits in years 50-65 changes only marginally since the significant effect on catches occurs mainly in the second half of this period of interest.

Economic impacts of changes in fish population dynamics:the role of the fishermen’s behavior

Rational behavior: development of the cod stockfor different reductions of the rate of reproduction

500

750

1000

1250

1500

1750

2000

2250

2500

20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

year

tota

l sto

ck b

iom

ass

in 1

000

tons

R unchanged R -10%

R -20% R -30%

R -40% R -50%

Economic impacts of changes in fish population dynamics:the role of the fishermen’s behavior

Rational behavior: development of total cod catchesfor different reductions of the rate of reproduction

0

100

200

300

400

500

600

700

800

20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

year

tota

l ann

ual c

atc

hes

in 1

00

0 to

ns

R unchanged R -10%

R -20% R -30%

R -40% R -50%

Economic impacts of changes in fish population dynamics:the role of the fishermen’s behavior

Rational behavior: development of the capelin stockfor different reductions of the rate of reproduction

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

year

tota

l sto

ck b

iom

ass

in 1

000

tons

R unchanged R -10%

R -20% R -30%

R -40% R -50%

Economic impacts of changes in fish population dynamics:the role of the fishermen’s behavior

Rational behavior: development of total capelin catchesfor different reductions of the rate of reproduction

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

year

tota

l ann

ual c

atch

es in

100

0 to

ns

R unchanged R -10%

R -20% R -30%

R -40% R -50%

Economic impacts of changes in fish population dynamics:the role of the fishermen’s behavior

Impacts of changes in fish population dynamicswhen fishermen seek profit maximization

• The stock sizes of cod and capelin show no clear trend withdecreasing rate of reproduction. A smaller reproductive ratein the capelin stock can be offset by a reduced predationpressure. The extent of the impact on the cod stock depends on how heavily exploited the fish stock is.

• Catches of cod can fluctuate drastically, indicating that fishing operations take place on the edge of profitability.Capelin catches generally follow the development of thestock, taking advantage of less predation by cod.

Economic impacts of changes in fish population dynamics:the role of the fishermen’s behavior

Comparison of the observed effectswith regard to the harvesting strategy emloyed (1)

• Fishing with the goal of profit maximization removes all oldage classes. With adaptive strategies all age classes remainpresent in the stock throughout the simulation period.

• Adaptive strategies: trawlers and coastal vessels share codfishery with coastal vessel share increasing over time

• Profit maximization: change of age structure practically forces coastal vessels out of the market. Almost the entireshare of cod catches come from trawlers.

Economic impacts of changes in fish population dynamics:the role of the fishermen’s behavior

Comparison of the observed effectswith regard to the harvesting strategy emloyed (2)

• The overall profits of trawlers are similar when populationdynamics are affected only marginally. For large reductionsof the reproductive rate the cod fishery becomes

unprofitable under profit maximization.

• Changes in the rate of reproduction have a slightly higher impact on the capelin fishery under profit maximization except for the cases in which larger and less predated stockleads to a increased landings and therefore higher returnsfrom fishing.

Economic impacts of changes in fish population dynamics:the role of the fishermen’s behavior

Comparison of the observed effectswith regard to the harvesting strategy emloyed (3)

• Changes in population dynamics would only affect stocksmarginally without the presence of fisheries. The absenceof harvesting activities can lead to a stable stock size despite a significantly lower rate of reproduction.

• Complete stock failures only occur in simulations with adrastically reduced carrying capacity and significant fishing activity.

Economic impacts of changes in fish population dynamics:the role of the fishermen’s behavior

Thank you very much for your attention.

Economic impacts of changes in fish population dynamics:the role of the fishermen’s behavior