Lower selectivity as a consequence of higher
fuel costs? A simple bio-economic model and an
application to the french Nephrops fishery in the bay of
Biscay
Claire Macher and Jean Boncoeur
UMR AMURE, Université de Brest, France
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008
Introduction
« Technical measures » aimed at increasing selectivity = an important
component of the standard fisheries management toolbox
Social benefits expected due to positive consequences on noncommercial and commercial species (biomass and age
structure)
However, selectivity also generates costs because it decreases CPUE
of marketable individuals
Balance between social benefits and costs depends on the level
of effort
Plan of the presentation
1.
Simplified bioeconomic model
2.
Numerical application to the Nephrops fishery in the bay of
Biscay
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008
1. Simple bio-economic model and optimal equilibrium analysis:
Bio-economic model specifications
Only one stock exploited by an homogenous fleet
2 age groups 1 and 2
Constant Fishing mortality per age group
CPUE proportional to biomass: Fi = q i E
Catchability for age 2=1
Catchability for age 1: q1 = 1 − s
With s a technical parameter for selectivity:
s=1: selective technique no joint production, catches of age 2 only
s=0 : non selective technique joint production
Catchability for age 1 and 2 equal to 1
0<s<1 : imperfect selectivity
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008
Exogenous Recruitment (1)
a>0: a parameter catching individual weight growth and natural mortality
assumed to occur once at the beginning of the fishing season
ap 2 > p1 if it is not fished, biomass value is higher at age 2 than at
age 1 (otherwise non selective technique is optimal in any case)
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008
Impact of selectivity on catches
Age group 1
Age group 2
Y1
Y2
s=0
a
4
E
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008
s=0
E
Impact of selectivity on catches
Age group 1
Age group 2
∆s > 0
∆s > 0
Y2
Y1
s=0
0 < s <1
a
4
E
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008
0 < s <1
s=0
E
Impact of selectivity on catches
Age group 1
Age group 2
∆s > 0
∆s > 0
Y2
Y1
a
s=0
0 < s <1
s =1
a
4
s =1
E
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008
0 < s <1
s=0
E
Impact of selectivity on landed value
V = p1Y1 + p2Y2
V
ap 2
V max, s = 0
s=0
p1
~
E
Eˆ s = 0
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008
E
Impact of selectivity on landed value
V = p1Y1 + p2Y2
V
ap 2
V max, 0 < s <1
V max, s = 0
0 < s <1
s=0
p1
~
E
Eˆ s = 0 Eˆ 0< s <1
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008
E
Impact of selectivity on landed value
V = p1Y1 + p2Y2
V
ap 2
s =1
V max, 0 < s <1
V max, s = 0
0 < s <1
s=0
p1
~
E
Eˆ s = 0 Eˆ 0< s <1
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008
E
Envelope : landed value as a function of the effort, assuming optimal technique
V
s
~
E
E
Selective
technique
Non
selective
technique
~
E
E
Switch point
undetermined technique
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008
Optimal equilibrium of the fishery: optimum effort and selectivity
Effort and selectivity maximizing the rent: Π = V − CE
Assuming breakeven point C > p 2 a + p1
~
E* is given by ∂Π = 0 ⇒ ∂V = C
∂E
∂E
According to cost level:
~
∂V
∂E
1 global optimum
(non selective) C
s=0
2 local optima
C
(non selective / selective)
1 global optimum C
(selective)
s =1
~
E
EI *
E II *
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008
E
Difference of rent between non selective technique and selective
technique Π I * −Π II *: increasing function of fishing cost C
Π I * −Π II * is negative and then positive when C rises
There is a value of fishing cost C~ such that:
Π I * −Π II * = 0
and
~
C > C ⇒ Π I * −Π II * > 0
Global optimum is obtained with non
selective technique
~
C < C ⇒ Π I * −Π II * < 0
Global optimum is obtained with the
selective technique
Conclusion: High fishing costs are a challenge to selectivity
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008
2. Application to the Nephrops fishery in the bay of Biscay
250 trawlers operating in the bay of biscay and targeting Nephrops
most of the year
Nephrops gross return: 30 millions euros
Total gross return: 80 millions euros
High levels of by-catches and discards
60% of the Nephrops in number are discarded
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008
BIOLOGICAL MODEL
R constant
Fishing mortality by age group
Selectivity factor by age group
% and discards mortality by age group
Nephrops
Stock Biomass
by age group
Catches
by age group
Discards
by age group
Fishing
effort:
number of
days at sea
Landings
by age group
10 sub-fleets
Criteria:
- 2 Geographic segments
- 5 crew categories
Costs structure
(variable and fixed costs)
Price per grade
Total gross
return
Nephrops
Total gross
return other
species
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008
wages
Profits
Producer surplus
ECONOMIC MODEL
Selectivity measures tested
statu quo
Sel 1
Sel 2
Sel 3
Age 3
8.8 cm
MLS
Age 4
10.4 cm
Sel 4
Sel 5
(alternative
gear)
Age 2
6.3 cm
Age 5
11.8 cm
Age 6
13.1 cm
Analysis of the potential impacts of these scenarios on the
producer surplus at equilibrium for several levels of effort modeled
as a variation of a mF
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008
According to the current fishing effort level :
At equilibrium scenario 4 is the most profitable to the fishery
80
statu quo
sel 1
sel2
sel3
sel4
sel5
70
60
millions euros
50
40
30
20
10
0
-10
0.2
0.4
0.6
0.8
1
1.2
-20
mF
Producer surplus at equilibrium
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008
1.4
1.6
1.8
Optimal selectivity and effort
mF=0.4
mF=1
80
70
millions euros
60
50
40
30
20
10
0
statu quo
sel 1
sel2
sel3
sel4
Scenarios statu quo and sel 1 are technically inefficient (discards)
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008
sel5
By simulating an important increase in fuel costs (*5) we show that
optimal effort decreases from 1.2 to 0.8, scenario 4 remains optimal,
very high costs of effort are required to reach the switch point
statu quo
sel 1
sel2
sel3
sel4
sel5
40
20
millions euros
0
0.2
0.4
0.6
0.8
1
1.2
-20
-40
-60
-80
-100
Producer surplus at equilibrium
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008
1.4
1.6
1.8
Concluding Remarks
• Increasing costs of the fishing effort would conduce fishermen to
reduce their effort and to adopt a non selective technique
• Application to the Nephrops fishery shows however that very high
costs of effort are required to reach the switch point, selective
scenario still generates the highest social benefits when fuel costs*5
• It was however not implemented by the Nephrops trawlers
• Due to mutual negative externalities, individual and social benefit of
selectivity are not the same
free riders temptations raise from non observable selectivity
• A gear change like pot adoption instead of trawling could enable
- to increase selectivity and to make it observable
- to reduce fishing costs
Macher and Boncoeur, IIFET 2008, Nha Trang, Vietnam, 22-25 July 2008