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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
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
Adaptive strategies: development of the capelin stockfor different reductions of the rate of reproduction
1500
1750
2000
2250
2500
2750
3000
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
200
250
300
350
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