ecosystem-scale optimization policies incofish ewe workshop, cape town, september 2006 incofish ewe...
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Ecosystem-scale optimization policiesEcosystem-scale optimization policies
IncoFish EwE Workshop,
Cape Town, September 2006
IncoFish EwE Workshop,
Cape Town, September 2006
Villy Christensen
Optimum fishing policyOptimum fishing policy
Ecosim (www.ecopath.org) provides formal optimization methods to search for fishing policies that would maximize a particular policy goal or ‘objective function’ for management.
Ecosim (www.ecopath.org) provides formal optimization methods to search for fishing policies that would maximize a particular policy goal or ‘objective function’ for management.
• Maximize fisheries rent• Maximize social benefits• Maximize mandated rebuilding• Maximize ecosystem structure
We evaluate the fleet configurations that optimize each of these conflictive objectives (individually or jointly)
• Maximize fisheries rent• Maximize social benefits• Maximize mandated rebuilding• Maximize ecosystem structure
We evaluate the fleet configurations that optimize each of these conflictive objectives (individually or jointly)
Policy objectivesPolicy objectives
Optimizing profits
• Profits are calculated as landed value of the catch less the cost of fishing;
• Often optimization is achieved by • reducing effort;• phasing out most fleets except the most
profitable ones; and • hitting ecosystems groups competing with or
preying on the more valuable target species.
• Profits are calculated as landed value of the catch less the cost of fishing;
• Often optimization is achieved by • reducing effort;• phasing out most fleets except the most
profitable ones; and • hitting ecosystems groups competing with or
preying on the more valuable target species.
Optimizing social benefits
1 Social benefits are expressed through the
employment supported by each fleet;
2 The benefits are calculated as
fleet specific jobs/value of catch;
1 Social benefits are expressed through the
employment supported by each fleet;
2 The benefits are calculated as
fleet specific jobs/value of catch;
Mandated rebuildingMandated rebuilding1 External pressure (or legal decisions) may force
policy makers to concentrate on preserving or rebuilding the population of a given species in a given area;
2 In Ecosim: set a threshold biomass, and optimize towards the fleet effort structure that will ensure this objective;
1 External pressure (or legal decisions) may force policy makers to concentrate on preserving or rebuilding the population of a given species in a given area;
2 In Ecosim: set a threshold biomass, and optimize towards the fleet effort structure that will ensure this objective;
Maximizing ecosystem structure Maximizing ecosystem structure
1 The ‘ecosystem structure’ definition is inspired
by Odum’s description of ecosystem ‘maturity’
wherein mature ecosystems are dominated by
large, long-lived organisms;
2 The group-specific biomass/production ratio
provides the default weighting factor for the
maximization of overall biomass;
1 The ‘ecosystem structure’ definition is inspired
by Odum’s description of ecosystem ‘maturity’
wherein mature ecosystems are dominated by
large, long-lived organisms;
2 The group-specific biomass/production ratio
provides the default weighting factor for the
maximization of overall biomass;
Balancing objectives: Pauly’s favorite Balancing objectives: Pauly’s favorite
1 lost leg
1 war
2 wives
+1 ulcer
=5
1 lost leg
1 war
2 wives
+1 ulcer
=5
Balancing objectivesBalancing objectives
• The starting values of the objective functions have each been standardized relative to their base values (from Ecopath);
• Equal weighting, in essence, means that an increase in profit of, e.g., 10% is considered to have the same value to society as a 10% increase in jobs or ecosystem structure.
• Society as sole agent
• The starting values of the objective functions have each been standardized relative to their base values (from Ecopath);
• Equal weighting, in essence, means that an increase in profit of, e.g., 10% is considered to have the same value to society as a 10% increase in jobs or ecosystem structure.
• Society as sole agent
Single- & Multi-agentsSingle- & Multi-agents
• Up to now we have assumed that society serves as sole-owner of the resources;
• More often there are multiple stakeholders whose privileges have to be considered;
• Such multi-agent considerations are incorporated by optimizing for each fleet individually
• Up to now we have assumed that society serves as sole-owner of the resources;
• More often there are multiple stakeholders whose privileges have to be considered;
• Such multi-agent considerations are incorporated by optimizing for each fleet individually
Optimizing for profit
Optimizing jobs
Biomass diversity
0.0 0.2 0.4 0.6 0.8 1.0
Weight placed on profit, jobs or ecology
0.6
0.8
1.0
1.2
1.4
1.6
Div
ers
ity in
de
x
Ecology
Profit
Jobs
Optimizing profits & jobsProfits Jobs (value) Ecology
Diversity TL of catch Catch weight
Wei
ght o
n jo
bs
Weight on profits
Optimizing profits & ecologyProfits Jobs (value) Ecology
Diversity TL of catch Catch weight
Wei
ght o
n ec
olog
y
Weight on profits
Optimizing ecology and jobsProfits Jobs (value) Ecology
Diversity TL of catch Catch weight
Weight on ecology
Wei
ght o
n jo
bs
Guidelines
• Fit the model to time series data first – Without it we have no way of knowing if the
model is realistic
• Consider what time period to search over– Historic?– Forward, leaving fishing as in time series?
• Repeat the simulations using random start values
Conclusions
• Unrealistic model unrealistic run• There can be weightings that improve the
situation for all objectives• There may be fleets loosing out
• Unrealistic model unrealistic run• There can be weightings that improve the
situation for all objectives• There may be fleets loosing out
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