Slide 1


IPFC &  ASFB 2009 Conference

Evaluating how food webs and the fisheries they 

support are affected by fishing closures in 

temperate Western Australia

Neil Loneragan

Russ Babcock

Hector Lozano



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Motivation  

Applications:

· Dynamics of target species 

· Commercial vs Recreational fishing

· Climate variability scenarios 

· Provide useful ecosystem indicators  

Goal:

· Evaluate how food webs and the fisheries they support are likely to be 

influenced by fishing closures

· Investigate how changes in abundance of key fished species (e.g. rock 

lobster, snapper, dhufish) are likely to influence other species

Rationale:

· Explore the ecosystem impacts of fishing



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30O

31O

Green Head

Grey

Wedge

Ecopath model : 2006 

• Boundaries of the model: 

Marine Park to 30m depth  

Area = 823 km2

• Period: Average year 2006 (2003-2008).

• 80 groups (> 200 species)

• Fishing gears

Jurien Bay Marine Park

8 commercial ~480 tonnes ·year-1 (70% Lobster)

6 recreational ~ 38 tonnes ·year-1

Scientific 

Reference 

Zone

Sanctuary 

Zone

10 km

Management Zones 

(WA Department of Environment and Conservation)



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Functional groups

• Fish = 24

• Special interest = 10

• Invertebrates = 19

• Primary producers = 11

• Zooplankton = 4

• Non-Fish = 5

• Non-Living = 7

Iconic/special interest

Pink snapper 

Dhufish

Baldchin grouper

Breaksea cod

Foxfish

King wrasse

4 stages of rock lobster



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One column layout

2) Conservation of energy (between groups):

Consumption = Production + Respiration+ Unassimilated food

3) Biomass dynamics: 

D Biomass = Growth + Immigration – Predation - Mortality

Production = Yield + Predation + Biomass Acc. + Migration

GSBQBPTMQGSBPBBQB )/()1()1()/()/(

Ecopath & Ecosim core equations:

1) Mass-balance (within groups):



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• Model captures 

general variability

• Model can 

reproduce known 

history

Model Calibration: Wester Rock Lobster 

(data from Department of Fisheries, WA)

Biomass estimated by depletion analysis

Biomass predicted by the model Panulirus cygnus



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-0.3 -0.2 -0.1 0 0.1 0.2 0.3

Bivalves

Roe abalone

Chaetognaths

Octopus

Detritus

Baldchin grouper

Sea turtles

Small sharks

Lobster - adult

Fox fish

Rays

Lobster - post puerulus

Crabs

Lobster - juvenile

Infauna

Large herb. gastropods

Small mobile herbivores

Epifauna

Gillnetting

longlining

Rock lobster

Re lative  impact

Results: trophic role of Ecklonia (kelp)

Ecklonia sp (kelp)

• Ecklonia, seagrasses and macroalgal 

assemblages are the major sources of 

habitat and food for marine invertebrates 

and fish.

• Ecklonia provided substrata for food 

(epiphytes and epifauna) and shelter from 

predators. 

E
c

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F
is

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Ecosim scenario: Reduction of F by 50% over 20 years 

(2.5% year-1) of dhufish and pink snapper

pink snapper

dhufishrock lobster (adult)

Baldchin grouper



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0.00

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0.25

2007 2013 2019 2025

B
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t 
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pink snapper

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0.2

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2007 2013 2019 2025

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dhufish

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2007 2013 2019 2025

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Baldchin grouper

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rock lobster adolscent

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2007 2013 2019 2025

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rock lobster post-

puerulus

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2007 2013 2019 2025

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mullets

Ecosim scenario: Reduction of F by 50% over 20 years 

(2.5% year-1) of dhufish and pink snapper



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-1.5 -1 -0.5 0 0.5 1 1.5 2

Carnivorous Jellyf ish

NDR reef  ass. zoobenthos f eed.

Chaetognaths

Squid

Inshore pelagic zooplankton f eed

NDR seagrass ass. carnivore

NDR pelagic zooplankton Feed.

Small Zooplankton

Small mobile herbivores

Inshore reef  ass. zoobenthos f eed.

NDR sand ass. zoobenthos f eed.

NDR sand ass. carnivore

Breaksea cod

NDR reef  ass. carnivore

Inf auna

Inshore reef  ass. omnivore

Photo. corals/sponges

Lobster - Adolescent

Large Carn. Gastropods

Perenial seagrasses

Inshore reef  ass. herbivore

Microphytobenthos

NDR benthopelagic carnivore

Ephemeral seagrasses

NDR reef  aa. zooplankton f eed

NDR reef  ass. herbivore

Lobster Adult

Inshore seagrass ass. zoob. f eed.

Dhuf ish

Inshore sand ass. omnivore

Pink snapper

Lobster-post puerulus

Proportion of change after 20 years

Ecosim scenario: Reduction of F by 50% over 20 years 

(2.5% year-1) of dhufish and pink snapper



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Scenario 1: ~10% of the park

Deep zone (>30m)= out of the park. 
No considered in the model

N

Ecospace: Spatial modelling of Jurien Bay

N

Scenario 2: No fishing closures

Scenario 3: Fishing closures up to 30%

Jurien 

Bay

Green Head
30o

31o



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Thank you

CSIRO Marine and Atmospheric Research

HECTOR LOZANO-MONTES

Phone: +61 8 9333 6520

Email: hector.lozano-montes@csiro.au

Web: www.cmar.csiro.au

Picasso, 1913

Ecopath models are like cubism 
art….abstract, ambiguous, with 
random angles, but 
(probably/possibly) realistic. 



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1985 1990 1995 2000 2005 2010 2015 2020 2025

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Scenario: Reduction of F by 50% (2.5% year-1) of dhufish, pink 

snapper & baldchin grouper

Western Rock Lobster

Panulirus cygnus



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Model’s Performance: Mortalities

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Fishing mortality (F) Predator mortality

Mortalities predicted by the model

P/B= Z= F +M2
F = C/B

Production = Fishery yield + Natural Mortality 

Natural Mortality (M)



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0 5 10 15 20 25

Perenial seagrasses

Ecklonia

Large herb. gastropods

Lobster - Adolescent

Lobster - juvenile

Octopus

Squid

Cuttlefish

Large crabs

Large mobile herb. invert

Small mobile herbivores

Small mobile epifauna

N.R. sand ass. omnivore

N.R. reef ass. carnivore

N.R. reef ass. omnivore

Inshore reef ass. zoob. feed.

Inshore reef ass. herbivore

Breaksea cod

Western fox fish

King wrasse

Baldchin grouper

Dhufish

Rays

Large coastal sharks

Sea lions

Index of Sensitivity

Trophic Level

Sensitivity Analysis - (change biomass of each living group)

• Index of Sensitivity = the number 

of groups affected (± 30%) by 

50% of biomass for each group.

• The Ecopath model is relatively 

insensitive to parameter values 

for most living groups (only 34 

groups produced Index sensitivity 

>10).

• Changes in parameters of 

Dead carcasses and sediment 

detritus exert the greatest

influence (living groups) in the 

system. 

+

- 0 10 20 30 40 50 60 70
Detached seagrass

Detached brown algae
Detached algae other

Dead carcasses
Bait

Water column detritus
Sediment detritus

Perenial seagrasses
Ecklonia

Large herb. gastropods
Lobster - Adolescent

Lobster - juvenile
Octopus

Squid
Cuttlefish

Large crabs
Large mobile herb. invert
Small mobile herbivores

Small mobile epifauna
N.R. sand ass. omnivore
N.R. reef ass. carnivore
N.R. reef ass. omnivore

Inshore reef ass. zoob. feed.
Inshore reef ass. herbivore

Breaksea cod
Western fox fish

King wrasse
Baldchin grouper

Dhufish
Rays

Large coastal sharks
Sea lions

Index of Sensitivity

Non-living groups

• The importance/sensitivity of 

the model to sediment detritus

emphasises the ultimate 

desirability of developing Atlantis

type model.
0 50402010 30 7060

Index of Sensitivity

Gropers, blennies, 

skipjack trevally



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Ecosystem attributes of Jurien Bay  

• Jurien Bay is a relatively complex ecosystem. 

• This ecosystem could be considered in an Intermediate-Low development 

stage, dominated by lower trophic levels. (overall network analysis results). 

• Medium/High productive system. More energy produced than respired 

within the system (Primary Production/Respiration = 1.23). 

• Dynamic system. There is a low-medium level of biomass accumulation 

(Primary Production/ Biomass= 1.68).

• Low rates of cycling (proportion of flows originated from detritus ~ 10%)  

• Ecosystem dominated by the benthic community (Ratio of biomass 

benthic/pelagic groups = 1.27). 

• Ecosystem function related to Bottom-up control, but wasp-waist 

predator-prey and top-down interactions were identified.  



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Trophic structure and fisheries

• Mean trophic level of the catch = 2.96

• Total Catch = 0.68 t/km2 (560 tonnes taken within the park in 2005, 

where almost 90% was removed by commercial fishing)

• Gross Efficiency (Catch/Primary Production) = 0.00041

Some of these attributes 

could be used as 

‘indicators’ to identify 

overfishing  in the future.

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Trophic Level

Catch by TL (tonnes/km2/year)

Total Catch  = 0.68 t/km2 (560 tonnes)

Jurien Bay Marine Park



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Outline: Results from Ecosim 

Ecosim

• Scenario evaluation: 

Workshop November, 2007: Participants + Steering group

Scenario Species Fishing effort (%) year
-1

Duration Rationale

Commercial ( C) Recreational ( R) (years)

1 Lobster ↓ 2.5 ↓2.5 20 Ecological role

2 Lobster ↑2.5 ↑2.5 20 Ecological role

3 Pink snapper ↑15 ↑15 20 Ecological role

4 Pink snapper ↓ 2.5 ↓2.5 20 Ecological role

5 All ↓ 2.5 ↓2.5 20 Impact of fisheries and closure areas

6 All Close ↓2.5 20 Impact of fisheries and closure areas



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Role of western rock lobster 

Reduction in fishing 

mortality of the western 

rock lobster is unlikely to 

produce important 

trophic cascade effects 

in the system. 

Fishing mortality in 2006 (F=0.62)

↑ Lobster ~ 30% 

↓ Biomass prey up to 20%

Low impact on other groups

Scenario 1: Reduction of lobster fishing mortality from 0.6 to 0.3 in 20 years

Fishing mortality in 2026 (F=0.3)

Its prey have high 

productivity and short 

life cycles (i.e. 

coralline algae and 

crustaceans)

Lobster adult



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Pink snapper
Total catch

Dhufish

Lobster adult

Large sharks↓ Lobster ~ 20% 

↓ Dhufish, pink snapper, king wrasse, up to ~ 20%

↓ Sharks & Rays ~ 30% 

↓ Ecklonia/seagrass <5%

↓ Total catch ~ 20%

↑ Herring, Mullets, Cardinal-fishes ~20%

↑ Sea urchins ~ 20

King wrasse

Herring
Mullets

Sea urchins

Rays



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Pink snapper

Mullets

Labrids

Lobster

Herring

Dhufish

↓ Pink snapper >90% 

↓ Herring ~ 30%

↓ Fox fish, Breaksea cod, Octopus, Squid ~ 20%

↑ Lobster ~10%

↑ Sea urchins ~ 70%

↑ Dhufish ~ 40%

↑ Sharks ~ 20%

↑ Rays ~ 90%

RaysSea urchins



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Pink snapper

Sharks Dhufish

Herring

Sea urchins

↑ Pink snapper ~ 2.5x

↑ Sea urchins ~ 70%

↑ Dhufish & Sharks ~ 30%

↓ Squid, Octopus ~ 40%

↓ Baldchin grouper, Breaksea cod, Western Foxfish < 20%

Lobster no change

Rays



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Pink snapper

Rays
Dolphins

Herring

Sea urchins

↑ Pink snapper ~ 3x 

↑ Sea urchins ~ 20%

↑ Dolphins

↓ Squid, Octopus ~ 50%

↓ Baldchin grouper, Breaksea cod, Western Foxfish < 10%

Lobster no change



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Large Sharks

Sea lions Small sharks

Dhufish

Lobster

Pink snapper↑ Large sharks ~ 30%

↑ Carangids, Clupeids ~ 25%

↑ Sea urchins, seagrass ~ 20%

↓ Sea lions ~ 40%

↓ Dhufish, pink snapper ~ 30%

↓ Small sharks ~ 40%

Lobster no change

Carangids ClupeidsSea urchins

Seagrass



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Total catch

Lobster 
Large sharks

Dhufish

Pink snapper

Octopus
Breaksea cod

Western foxfish

Sea urchins 

↑ Total catch ~ 40%

↑ Breaksea cod, Foxfish ~ 30%

↑ Octopus, squid ~ 30%

↓ Pink snapper ~ 50%

↓ Dhufish ~ 40%

↓ Lobster adult ~ 30%

↓ Sea urchins ~ 25%

↓ Sharks ~ 20%



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Total catch

Lobster 

Large sharks

Dhufish Pink snapper

Octopus
Blennies

Western Foxfish

Sea urchins 

↑ Foxfish ~ 30%

↑ Blennies ~ 20%

↑ Octopus ~ 10%

↓ Total catch ~ 30%

↓ Sharks ~ 60%

↓ Lobster adult ~ 90%

↓ Pink snapper, Dhufish, >90%

↓ Sea urchins > 90%



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Total catch

Lobster adult

Large sharks

Dhufish
Pink snapper

Western Foxfish

Small sharks

↓ Total catch ~ 90%

↑ Lobsters ~ 80%

↑ Pink snapper ~ 100%

↑ Dhufish & Sharks ~ 50%

↑ Sea urchins ~ 70%

Sea urchins

Breaksea cod



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Large sharks

Lobster adult

Pink snapper

Squid

Sardines

Labrids

Octopus

↓ Total catch ~ 10%

↑ Pink snapper ~ 25%

↑ Sharks ~ 20%

↑ Baldchin grouper, Foxfish,   
Breaksea cod ~ 10%

• Lobsters ~ no change

↓ Octopus ~ 10%

↓ Sardines ~ 60%



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Lobster adult

Pink snapper

Small sharks

Dhufish

Large sharks



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Pink snapper

Total catch

Dhufish

Flatheads



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Pink snapper

Rays

Dhufish

Octopus

Lobster adult

Squid

↑ Lobster ~ 20% 

↑ Dhufish, Pink snapper ~ 80%

↓ Octopus, Western fox fish ~ 30%

↓ Breaksea cod, Squid ~ 10%



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Relative fishing mortality imposed by all gears (2006)

↓ Total catch ~ 30%

↓ Zoop. Feed. (clupeids) ~ 20%

↑ Lobster adults ~ 10%

↑ Sharks ~ 30%

↑ Pink snappers ~ 40%

Large Sharks

Non depth restricted Benthopelagic carnivores 

(Carangids, Urolophids)

Total catch

Lobster

Pink snapper

Inshore pelagic zooplankton feeders (clupeids, atherinids)



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Large Sharks

Sea lions
Dolphins

Small gastropods

Squid
Lobster

mullets

↓ Large sharks reduced by 70% after 20 years.

↑ Sea lions ~ 50%

↓ Lobster ~ 20%

↓ Lower trophic levels up by 30% (Potential cascade of effects).



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Total system flow was 22,067 ton km-2 year-1

Internal 

consumption

56%

Respiration

25%

Detritus

10%

Export

11%

Jurien Bay trophic structure

Energy flow in Jurien Bay



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