Ecosystem-based fisheries management: an introduction Villy Christensen and Daniel Pauly Fisheries...

Ecosystem-based fisheries management: an introduction

Ecosystem-based fisheries management: an introduction

Villy Christensen and Daniel PaulyFisheries Centre

University of British ColumbiaVancouver, Canada

Villy Christensen and Daniel PaulyFisheries Centre

University of British ColumbiaVancouver, Canada

SUMBER: innri.unuftp.is/pauly/Iceland%202%20Dec%2016%2002.ppt

Under the UN Convention on the Law of the Sea, nations have accepted:

Under the UN Convention on the Law of the Sea, nations have accepted:

• A mutual obligation to consider the impact of their policies on marine ecosystems;

• to take all appropriate actions to preserve the marine environment; and

• to manage ecosystem resources based on the interdependence of the system components...

“in accordance with their capabilities.”

• A mutual obligation to consider the impact of their policies on marine ecosystems;

• to take all appropriate actions to preserve the marine environment; and

• to manage ecosystem resources based on the interdependence of the system components...

“in accordance with their capabilities.”


We cannot and should not replace the top predators

We cannot and should not replace the top predators

• Many examples exist of ecosystem disasters due to fishing down of predators;

• To maintain or improve catches we must maintain functioning ecosystems;

• We already assert major influence over the marine environment:

• Many examples exist of ecosystem disasters due to fishing down of predators;

• To maintain or improve catches we must maintain functioning ecosystems;

• We already assert major influence over the marine environment:


Ecosystem effects of fishingEcosystem effects of fishing

• Removal of large sharks in South Africa more small sharks less of their prey fish;

• Removal of grazers (such as these surgeonfishes) led to Jamaican reefs being overgrown by algae and more susceptible to hurricane damage.

• Removal of large sharks in South Africa more small sharks less of their prey fish;

• Removal of grazers (such as these surgeonfishes) led to Jamaican reefs being overgrown by algae and more susceptible to hurricane damage.


Ecosystem effects of fishingEcosystem effects of fishing• Overfishing triggerfish,

pufferfish, hump-head wrasse, and triton (which all feed on juvenile crown-of-thorns) led to crown-of-thorns outbreaks on coral reefs

• Overfishing triggerfish, pufferfish, hump-head wrasse, and triton (which all feed on juvenile crown-of-thorns) led to crown-of-thorns outbreaks on coral reefs



• Overfishing removed pufferfishes, the predators of sea urchins:

• Overfishing removed pufferfishes, the predators of sea urchins:



Overfishing removes the predators of sea

urchins: pufferfishes.

Obviously, the sea urchins of any given reef will have more than one species of predators. However, the one shown here

was dominant.

Overfishing removes the predators of sea

urchins: pufferfishes.

Obviously, the sea urchins of any given reef will have more than one species of predators. However, the one shown here

was dominant.


Trophic level: the concept Trophic level: the concept T

rop

hic

leve

lT

rop

hic

leve

l

PhytoplanktonPhytoplankton

Top predatorsTop predators

Prey fishPrey fish

ZooplanktonZooplankton

. . . . . . .... .. .. .. .. .. .. .. *.*. ..

.. ... .

..*.*.*.*.*.*.

*.*.*.*.*.*.

*.*.

10% 10%

10% 10%

10% 10%

*.*.

44

33

22

11


• Initially fisheries target the upper-trophic level species, the top predators;

• As these decline in abundance focus is gradually shifted toward the prey of the top predators;

• Ultimately only the lower-trophic level species (small fish and invertebrates) are left to be caught.

• Initially fisheries target the upper-trophic level species, the top predators;

• As these decline in abundance focus is gradually shifted toward the prey of the top predators;

• Ultimately only the lower-trophic level species (small fish and invertebrates) are left to be caught.

Processes involved in ‘fishing down’Processes involved in ‘fishing down’


Fishing down the food web:succession of target organisms

TimeTime

Top

pred

ator

s

Top

pred

ator

s

Prey s

peci

es

Prey s

peci

es

Cat

chC

atch


Fishing down the food web:succession of target organisms

TimeTime

Top

pred

ator

s

Top

pred

ator

s

Prey s

peci

es

Prey s

peci

es

Cat

chC

atch

Sustainability?Sustainability?


Artisa

nal

Artisa

nal

Sem

i-ind

ustri

al

Sem

i-ind

ustri

al

Indu

stria

l

Indu

stria

l

TimeTime

Fis

hing

eff

ort

Fis

hing

eff

ort

Fishing down the food web:succession of fleets


Science March 1998, 279

2.7

2.8

2.9

3.0

3.1

3.2

3.3

3.4

1970 1975 1980 1985 1990

TL

of

lan

din

gs

MarineMarine

FreshwaterFreshwater

Global fishing down the food web


Gulf of Thailand fisheries

3.1

3.2

3.3

3.4

66 67 68 68 70 71 72 73 74 75 76 77 78 79 80 81

Year

Tro

ph

ic l

ev

el

of

ca

tch

Science, October 1998

Fishing down the food web


Gulf of Thailand fisheries

3.1

3.2

3.3

3.4

0 200 400 600 800 1000

Catch (thousand tonnes)

TL

of

catc

h

19661966

19811981

19741974

Science, October 1998SUMBER: innri.unuftp.is/pauly/Iceland%202%20Dec%2016%2002.ppt

Feeding triangles: North Sea

Other fish

KrillKrill

Norwaypout

Norwaypout

CopepodsCopepods

4

1

505

17

100

11

2


Other fish

Other fish

KrillKrill

Norwaypout

Norwaypout

CopepodsCopepods

44

11

505

17

100

11

22



Other fish

Other fish

KrillKrill

Norwaypout

Norwaypout

CopepodsCopepods

44

11

505055

1717

100100

1111

22



Requirements for adoption of ecosystem-based approaches:

Requirements for adoption of ecosystem-based approaches:

• A framework for integrating the wealth of information available at the species level;

• Basic understanding of ecosystem structure and function;

• Concepts and software integrating first two items in a transparent, practice-oriented context.

• A framework for integrating the wealth of information available at the species level;

• Basic understanding of ecosystem structure and function;

• Concepts and software integrating first two items in a transparent, practice-oriented context.


Do we have tools for ecosystem-based management?

Do we have tools for ecosystem-based management?

• Yes, using Ecopath with Ecosim we can incorporate ecological, economic and social considerations into a rigorous framework

• Based thereon we can use Ecosim and Ecospace to explore policy options for ecosystem based management

• Yes, using Ecopath with Ecosim we can incorporate ecological, economic and social considerations into a rigorous framework

• Based thereon we can use Ecosim and Ecospace to explore policy options for ecosystem based management


Policy exploration

• Policy may be defined as an approach towards

reaching a broadly defined goal;• In fisheries policies are often implemented via TACs

that are recalculated annually, and through regulation

that affects fleet and deployment;• The task of fisheries scientists is to advise both on

policy formulation and on its implementation;• So far much fisheries research is on implementation

only;• Ecosystem-based policy exploration is in its infancy.

• Policy may be defined as an approach towards

reaching a broadly defined goal;• In fisheries policies are often implemented via TACs

that are recalculated annually, and through regulation

that affects fleet and deployment;• The task of fisheries scientists is to advise both on

policy formulation and on its implementation;• So far much fisheries research is on implementation

only;• Ecosystem-based policy exploration is in its infancy.


Some policy objectives

1 Maximize fisheries rent;2 Maximize social benefits;3 Mandated rebuilding of species;4 Maximize ecosystem ‘health.’

Ecopath with Ecosim offers a method for evaluating the fleet configuration and effort levels that optimizes each of these objectives individually or jointly.


Maximizing profit

1 Profits are calculated as:the value of the landings (landings * price, by species) less the cost of fishing (fixed + variable costs);

2 Often optimization is achieved by: • phasing out most fleets except the most

profitable ones; and • wiping out ecosystems groups competing

with or preying on the more valuable target species.


Maximizing social benefits

1 Social benefits are expressed through the employment supported by each fleet;

2 The benefits are calculated as job / catch value, and is fleet specific;

3 Therefore social benefits are largely proportional to fishing effort;

4 Optimizing efforts often leads to more extreme scenarios than optimizing profit.


Mandated 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 this corresponds to setting a threshold biomass (relative to the biomass in Ecopath) and optimizing towards the fleet effort structure that will ensure this objective;

3 Implications will be case-specific: consider Monk seal/shark interaction in Hawaii, or Steller sea lion/Alaska pollock in the Eastern Bering Sea.


Maximizing ecosystem ‘health’

1 The ecosystem ‘health’ definition is inspired by Odum’s description of ecosystem ‘maturity’, wherein mature ecosystems are dominated by large, long-lived organisms;

• The group-specific biomass/production ratio provides the default weighting factor for the maximization of overall biomass;

• The ‘health’ optimization often implies:phasing out of all fisheries except those targeting species with low weighting factors.


Balancing economic, social and ecological objectives

1 The starting values of the objective functions have each been standardized relative to their base values (from Ecopath), making them roughly comparable;

2 Two of the measures tend to pull towards increasing fishing, and two pull towards reducing fishing. Care should be taken to consider this balance when giving relative weightings to the objectives;

3 Optimizations should be performed with a range of weighting factors for each objective function.


KESIMPULAN

1. A transition to ecosystem-based management of fisheries is unavoidable, if we are not to lose more of our fisheries resources

2. Such transition if actually happening in some countries, if only in the form of ecosystem consideration informing single-species management;

3. In the longer term, detailed simulation of trophic interactions within exploited ecosystems, along with explicit consideration of environmental effects, may allow for forms of fishing that are compatible with the continued existence of the underlying ecosystem, something we presently do not have.


Ecosystem-based fisheries management: an introduction Villy Christensen and Daniel Pauly Fisheries...

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