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