This presentation is done by Export Agriculture students of Uva Wellassa University of Sri Lanka as a requirement for the subject which is “Agricultura Resource Management”.
2. Fishery economics
Definition:
The production, distribution, and
consumption of fish and seafood and all
financial aspects of the fishing and seafood
industry (including aquatic life in fresh
water)
2
3. Introduction
• Fishery can be thought as a stock or stocks of
fish and the enterprises that have the
potential to exploit them
• The fish stock measured in terms of biomass,
is the natural capital of the system
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4. • Factors which determine fish biomass;
– Ability to reproduce and provide new recruits
– Growth rate of individuals
– Natural mortality rate
– Rate of fishing mortality
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5. • Fish stock can be increased with time if;
>
Recruitment of
new individuals
&
growth of existing
individual
Natural
mortality
&
fishing
mortality
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6. Special Characteristics of Fisheries Resources
• Mobility
• Renewable
• Highly varied and poorly understood biology
• Dependence on ecosystem
• Tradition of open access
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7. Renewable resource?
• A renewable resource is a natural resource
which can replenish with the passage of time,
either through biological reproduction or
other naturally recurring processes
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8. Reasons to depletion of fish stock
• Overfishing due to;
Technology development
Boats with deep freezer facility
• Satellite technology
• By-catch
• water pollution
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9. Relationship between fish stock & growth rate
when there is no harvesting
Growth Rate
Stock Size(kg)
XMSY
G*(x)
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10. • When there is a small fish stock, the growth of
population is low
• As there are more fish in the water,
reproduction rates go up, causing the
population to grow
• Eventually however, due to crowding effects
and competition for food, the growth rates
decline
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11. • At the far right point, the carrying capacity of
the fishery is reached and the stock is in
equilibrium
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12. • Starting at a low level (the green dot) fish
reproduce in the first period
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Growth Rate
Stock Size(kg)
13. • This leads to growth so that in the second
period the stock has increased
13
Growth Rate
Stock Size(kg)
15. • This process continues until the carrying
capacity of the fishery is reached
Natural equilibrium
for the fishery
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Growth Rate
16. Sustainable yield
• Production of a biological resource (fish)
under management procedures which ensure
replacement of the part harvested by re-
growth or reproduction before another
harvest occurs
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17. What is MSY?
• The highest possible annual catch for a given
fish stock that can be sustained over time, by
keeping the stock at the level producing
maximum growth
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18. Population dynamics
• A fishery population is affected by three
dynamic rate functions:
– Birth rate
– Growth rate
– Mortality
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19. Schaefer logistic Growth model
• x(t) = Size of fish stock at time t
• Growth of fish stock with time
)(
)(
td
tdx
)(
)(
xG
dt
tdx
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20. r= Intrinsic rate of growth
(Rate at which the stock would typically grow
with no external effect)
K= Carrying capacity
(Largest stock size that can be achieved given
food supplies, habitat, etc.)
)1()(
K
xrxxG ttt
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21. • shows that growth is proportional to
stock size
• Adds the complexity that growth
decreases with stock density,
• when stock size= carrying capacity, growth will
fall zero
rx
)1(
k
x
k
x
21
22. • Maximum growth rate can be found by 1st
derivative
• Set it equals to zero & solving for X,
02
K
rxr
2
KxMSY
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23. • A critical issue in fisheries management is
what will happen to stock size over time
• Most purposes, size of an unexploited fish
stock will change through time according to
following relationship;
)()1( ttt xGxx
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24. • With no harvest, stock size next year is the
sum of stock size this year & growth generated
by stock during the period of observation
• In terms of Schaefer model,
stock reach equilibrium when Xt = K
Because, G(Xt)=G(K)=0
So, X(t+1)=Xt
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25. Fish stock & growth rate when there is a
harvesting
• When fishers begin to harvest, part or all of
the growth that occurs in any period is taken
out (harvested)
• so that growth in the stock doesn’t take place
or is reduced
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26. Effect of harvesting to fish stock
Size of
stock
H1
H2
H3
Rate of growth
X’ X”XMSY
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27. Schaefer logistic growth with harvest
• Periodic change in stock size with harvest can
be represented as,
• In this case,
Stock will reach an equilibrium where,
G(Xt) = Harvest
)()1( )( tttt HarvestxGxx
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28. A more formal analysis of commercial
harvest
• Annual yield can be viewed as a function of
stock & amount of fishing effort applied to it
(think effort as a today’s standard boat)
Let Yt represent short run yield,
ttt EqxY
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29. • E- Fishing effort
• q- catchability coefficient
(embodiment of technology that is used to
harvest fish)
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30. • Fisheries production does not obey in
economic law of diminishing marginal
productivity
• Each additional unit of effort or stock size adds
the same amount to catch
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32. • The same amount of effort will produce more
harvest when the stock size is higher & vice
versa
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33. • For long run analysis- can use concept of
sustainable yield
• Sustainable yield curve shows the relationship
between level of fishing effort & level of
sustainable yield
• A sustainable yield is one that can be
maintained indefinitely because,
catch=growth
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34. • To achieve sustainable harvest,
growth must equals to short run yield
qEx
K
xrx )1(
Growth Short run
yield
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41. Sustainable yield function
• Substituting population equilibrium
equation(PEC) into Short run yield equation,
produces an equation for sustainable yield
function as a function of E(effort)
E
r
qKKx )( PEC
ttt EqxY
Short run yield
equation
41
43. • Stock size is obviously an important element
in determining sustainable harvest
• But it is subsumed in equation, because
equilibrium stock size is a function of effort
43
44. Sustainable Yield Curve
Catch/Harvest
Effort
Low level of effort
When E
Sustainable yield
B’coz growth increases with
decreases in stock size
Further increase of E
Decrease yield
B’coz further decrease of stock size
cause growth to fall
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50. • To show the relationship between Effort &
Stock size, it is also useful to look at
sustainable revenue & cost in terms of stock
size
• TSR as a function of stock size;
)1(.
K
xrxPTSRX
Price Growth of fish
stock
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51. • Now, we have identified the basic theories
needed to study the bio-economic equilibrium
• Bio economic equilibrium can be studied as 2
types;
1. Open access equilibrium
2. Private property equilibrium
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55. open access equilibrium
• When all of the excess profits or economic
rent that attracts new entrants to a
developing fishery have been dissipated in the
costs associated with the additional fishing
effort
• The fishery is no longer attractive to new
entrants
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56. • Usually occurs when fishing effort is higher
than that which will obtain the greatest yield
from a fishery
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62. Maximum economic yield
• The value of the largest positive difference
between total revenues and total costs of
fishing (including the cost of labor and capital)
with all inputs valued at their opportunity
costs
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64. Management of fishery resources
• Most important fisheries in the world at the
state of open access
• So, fisheries have to be manage carefully
• Have to change the equilibrium from open
access to private property equilibrium
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65. • This can be done by 2 ways;
– Control the harvest of fish at optimum effort
– Reduce the fishing effort
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66. • Above 2 status can be achieved by;
– Tax
– Quota
Tax
Tax on harvest of
fish
Tax on fishing
effort
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67. Tax on harvest of fish
Effort
TR & TC
Tax
Y*
Y’
E* E
TR
TC
TR’
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68. Tax on fishing effort
TR & TC
Effort
TR
TC’
TC”
TC
E* E
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69. Theories of Agricultural Resource Management
(Past papers)
2009 :-
01.
a). Define the following terms;
1. Renewable resources
2. Non - renewable resources
3. Open access resources
4. Common pool resources
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70. b). 1. Briefly explain the variable in fishery
2. "Increase in fishing effort always increase the
profit in fishery" Comment on this.
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71. 2010 :-
01. a). With the use of suitable illustrations
describe the following in relation to
fishery.
1. Sustainable yield.
2. Maximum sustainable yield.
3. Maximum economic yield.
4. Open access equilibrium level.
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72. b). The effort catch relationship (production function) of a
fishery is given by,
Y = 90E - 2E2
Where Y is the sustainable yield measured in
kilograms of fish and E is fishing effort measured in
number of fishing trips. Each fishing trip costs Rs.
900.00. Fish sell at Rs. 40.00 per kilogram.
Determine the following
1. Maximum sustainable yield, corresponding level
of fishing effort and private profit.
2. Maximum Economic Yield, corresponding level of
fishing effort.
3. Find the open access equilibrium level of effort.
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73. 2013 :-
04.
a). Define the term "Fishery"
b). Briefly explain the variables in fishery.
c). "Increase in fishing effort always increase the
profit in fishery" Comment on this
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74. d). The effort catch relationship ( production function ) of a
fishery is given by,
Y = 1200E - 2E2
Where Y is the sustainable yield measured in kilogram of
fish and E is fishing effort measured in number of fishing
trips. Each fishing trip cost Rs. 900.00. Fish sell at Rs. 40.00.
per kilogram.
Derive the following
1. Maximum effort which yields no yield
2. Maximum sustainable Yield, corresponding level of fishing
effort and private profit.
3. Maximum Economic Yield, corresponding level of fishing
effort.
4. Find the open access equilibrium level of effort.
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