fisheries
efficient harvests
• biology
• economic
biological dimension
• Schaefer model (1957)
• abstracting from water temp / quality, age
structure, etc.
• relationship btw. growth of popn and size
of popn
growth as a function of stock
carrying capacity vs. minimum viable popn
•
S : carrying capacity / natural equilibrium
•
stable, movements away set forces in motion
back towards it
S : minimum viable popn
below growth is negative
unstable
• to right, growth to natural equilibrium
• to left, decline to extinction
“sustainable yield”
• catch growth rate each period, catch and
population can be maintained forever
• S*: “maximum sustainable yield” (MSY)
– yields maximum growth
– largest catch that can be perpetually
sustained
economics: efficient yield
• is MSY synonymous with efficiency? (no)
• for efficient solution: maximize net
benefits from use of resource
• need to include costs and benefits of
harvest, not just quantity
• examine static efficient sustainable yield
(largest annual net benefit)
3 assumptions
• price of fish constant
• MC fishing effort constant
• fish caught per unit effort is proportional
to size of population (smaller popn, fewer
fish caught per unit effort)
efficient sustainable yield
efficient fishing effort
• TR follows Schaefer model since price constant
• TC linear since MC effort constant
• Em: further effort reduces sustainable catch and
•
•
revenue for all years (MSY)
net benefit: vertical distance btw B & C
Ee: efficient effort, where net benefits
maximized
 MB (slope of TB) = MC (slope of constant TC curve)
efficient fishing effort
• effort > Ee inefficient, since additional cost
exceeds value of fish obtained
• MSY not efficient unless MC effort = 0 (why?)
• efficient level of effort LESS than MSY
• efficiency implies LESS harvesting and LARGER
population
efficient vs. market allocation
• with well-defined property rights, sole
owner of fishery would max profit by
increasing effort until MR=MC
– harvest at Ee (efficient)
• but…fisheries typically OPEN ACCESS
open access solution
• sole owner of fishery chooses to not expend >
Ee because to do so reduces profit of fishery
(personal loss)
• if unrestricted access, decision to expend > Ee
reduces total profit, but not to individual fisher
• in open access, Ec effort (net benefits zero)
fishery prisoner’s dilemma
Fisher B
Fisher A
Fish more!
Fish less
Fish more!
2,2
4,1
Fish less
1,4
3,3
Note: Payoffs in thousands $ (A, B)
too much effort! policy responses
• increase MC– require fishing farther from shore, use
smaller nets, boats, or motors
– but artificially increasing cost inefficient
• total allowable catch – restrictions on effort or size of
catch
– monitoring, enforcement difficult, also creates race to catch
• individual transferable quotas –quotas allocated, then
trade
– no race, allows most efficient fishers to buy rights from
inefficient fishers
Sample problem
• Costs fisher $20 to fish salmon
• Salmon sells for $10
• Harvest rate given X fishers is S = 30X-2X2
• How many people will go fishing, how
many salmon will be caught, and what are
total profits under
– Open access
– Limited entry (how many fishers should be
allowed to maximize profit?)