Poaching and the Success of Marine Reserves

Suresh A. SethiSchool of Aquatic and Fisheries Sciences

7/06

BackgroundMarine reserves are proposed as tools to augment fisheries:-habitat protection-spillover-age structure protection

These are best case scenarios…poaching within reserves may significantly affect the biological and economic outcomes of reserves.

Photo from NMFS

Questions1. What are the biological effects of poaching inside and out of reserves?

-Abundances, age structure, yield

2. What are the economic effects? -Closely linked to the biological effects

through CPUE.

3. What are the drivers of poaching?-Wealth status, expected profits,

opportunity cost of time

4. What are effective enforcement measures?

-Monitoring, fines, rewards, education

Biological Effects: Age structure analysis with maternal effects on larval survival

Some Assumptions:-B-H recruitment relationship-Sedentary adults, common pool larvae mixture (abalone, scallop, rockfish)-Lingcod life history characteristics-Asymptotic knifedge selectivity, maturity-Maternal effects on larval survival:Relative Larval Survival with Age

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15 20 25 30 35

Age

RL

S

RLS = -1.58 + 2.58(1-e^(-.247*age))

Age Structure

Effort Readjusts Outside30% Closure: ELO and Yield Relative to B40% Reserve Base Case when Effort

Outside Readjusts to Maintain B40%

0.8

1

1.2

1.4

1.6

1.8

0 0.1 0.2 0.3 0.4 0.5u of poach

Re

lati

ve

Ind

ex (

to n

o p

oa

ch b

as

e

case

)

0

0.05

0.1

0.15

0.2

0.25

F O

uts

ide

ELO

Yield (legal)

ELO B40% No Reserve

Yield B40% No Reserve

F Outside

Effort Constant Outside

30% Closure: ELO and Yield Relative to B40% Reserve Base Case when Yield Outside Remains Constant (F out of .2328)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 0.1 0.2 0.3 0.4 0.5

u of poach

Rela

tive I

nd

ex (

to n

o p

oach

base c

ase) SSB

ELO

Yield (legal)

ELO B40% No Reserve

Yield B40% No Reserve

B40% Rule for Outside Only

30% Closure: ELO, SSB when population in the reserve is excluded from B40% rule (f=.095)

0.3

0.5

0.7

0.9

1.1

1.3

1.5

0 0.1 0.2 0.3 0.4 0.5

u of poach

Rel

ativ

e In

dex

(to

no

po

ach

bas

e ca

se)

SSB w/ Poach

ELO w/ Poach

Yield (legal) w/ Poach

Yield B40% no reserve

ELO B40% no reserve

Conclusions:-Yield is lower with a reserve in place

-Poaching can quickly reduce the age structure benefits from marine reserves by reducing SSB in reserves and resulting ELO.

-If age structure protection is a primary goal of reserves, enforcement of reserve will be a key determinant in the success of the reserve.

-Raises question about whether or not populations inside the reserve should be considered in the B40% rule.

Age Structure

Photo from Fisheries and Oceans Canada

Biological Effects: 2Box model with logistic growth, adult movement, and poaching as a function of profit

2Box Model

(1) intNRouttRR

tRtRtR mNmN

K

NrNN ,,

,,1, ]

)(1(1[

(1’) tRintNRouttRR

tRtRtR CmNmN

K

NrNN ,,,

,,1, ]

)(1(1[

(2) tNR

outtRintNRR

tNRtNRtNR CmNmN

K

NrNN

,,,

,,1, ]

)1((1(1[

(3) 1,)/( tRE

Participation distribution

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.5 1 1.5 2 2.5

Potential Profits/Effort

0

0.10.2

0.30.4

0.5

0.60.7

0.80.9

1

effortpoachmaxionparticipatE tR ,

Total Numbers

350

400

450

500

550

600

650

700

750

800

0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6

Reserve Proportion

Nu

mb

ers

0

10

20

30

40

50

60

Po

ac

hin

g E

ffo

rt

With Poaching

No Poaching

No Reserve MSY

Poaching Effort

Catch and Profit/Effort Outside

0

10

20

30

40

50

60

70

80

0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6

Reserve Proportion

Nu

mb

ers

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Pro

fit/

Eff

ort

Catch Out w/ PoachingCatch Out No PoachingNo Reserve MSY CatchProfit/Effort Out w/ PoachingProfit/Effort out No PoachingNo Reserve MSY Profit/Effort

Future WorkAge Structure Model:-incorporate movement and space

2Box Logistic Model:-expand into spatial model-alternative ways of modelling poaching behavior-poaching in open areas-heterogeneous costs based on location (space)

Thank You!

Funding:

SAFS

ARCS

Thanks to R. Hilborn and his lab, and A. Haynie.

Age Structure

Biological Effects: Age structure analysis with maternal effects on larval survival

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Age Structure

Biological Effects: Age structure analysis with maternal effects on larval survival

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Previous

Work

Majority of prior modeling work considers reserves to be 100% effective, i.e. no poaching.

Of 800+ papers on marine reserves, only 3 consider noncompliance within reserve boundaries. 

Previous

Work

Little et al. (2005), Kritzer (2004):-2D spatial models to examine the effects of poaching on different shaped reserves. -Found if poaching is a function of distance from an edge, single large reserves are more robust than several small reserves. -Poaching negated benefits of reserves even at high F.

Hallwood (2005):-Analytical model of sustainable rents in a reserve-fishery complex when there is costly enforcement of reserve areas. -Optimization finds that m. benefit of policing = m. cost of policing, optimal stock size may be smaller than size without poaching

No S-R Relationship

30% Closure: ELO and Yield Relative to B40% Reserve Base Case when Effort Outside Readjusts to Maintain B40%

0.7

0.8

0.9

1

1.1

1.2

1.3

0 0.1 0.2 0.3 0.4 0.5 0.6

u of poach

Re

lati

ve

In

de

x (

to n

o p

oa

ch

b

as

e c

as

e)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

F O

uts

ide

ELO

Yield (legal)

ELO B40% No Reserve

Yield B40% No Reserve

F Outside

No S-R Relationship

30% Closure: ELO and Yield Relative to B40% Reserve Base Case when Yield Outside Remains Constant (F out of .474)

0

0.2

0.4

0.6

0.8

1

1.2

0 0.1 0.2 0.3 0.4 0.5 0.6

u of poach

Rela

tive I

nd

ex (

to n

o p

oach

base c

ase)

SSB

ELO

Yield (legal)

ELO B40% No Reserve