Slide 1Fishery Economics, Part 1Apply what you already know:Interactive (feedbacks)Basic interactive modelInteractive modelSimplified Growth ModelInterpretation of Growth FunctionCritical depensation (Kahn, Figure 10.3)AGEC/FNR 406 LECTURE 29AGEC/FNR 406 LECTURE 26Catch of the day, PalawanFishery Economics, Part 1Characteristics of Fisheries1. Renewable natural resource2. Interactive(stock effects and feedbacks are important)3. Usually open-access property (more on this later)Apply what you already know:1. Goal: maximize net benefitsmarginal condition for static efficiencyMC = MBcomplication is defining cost and benefit functions2. Property rights structureOpen-access or common property in most casesrent is dissipated (know what this means)intervention necessary for efficiencyInteractive (feedbacks)Size of population depends on:1. Biological factorsHabitatSizeQuality - amount of pollutionFood supply2. Actions of societyHarvest levelsBasic interactive modelDefine variables:Xt stock (population) at time tX0 initial stocking levelGt growth during tth time period (function of Xt)Ct catch level during tth time periodInteractive modelStocking level at end of 1st time period is,X1 = Xo + G1 (Xo) - C1And, in general,Xt = Xt-1 + Gt (Xt-1) - CtSimplified Growth ModelGrowth is a function of stock: Gt (Xt-1)Stock is measured as a level (e.g. principal)Growth is a flow (e.g. interest)But growth is complicated: Q: With more stock is growth slower or faster? A: It depends on the level of stockKX2G2Fish population (X)Growth of population (G)G1X1Logistic Growth Function(see Kahn, figure 10.1)Interpretation of Growth FunctionMinimum viable population: X0Population less than X0 will become extinctNatural equilibrium (carrying capacity): KLargest population habitat can supportGrowth equal to mortalityMaximum sustainable yield: MSYMSY stock: XMSYHarvest level equal to growth levelMSY harvest (yield): CMSYCritical depensation(Kahn, Figure 10.3)Growth (G)Population
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