Fisheries - Renewable Resources and Fisheries Contents...

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Renewable Resources and Fisheries Contents: General Overview A Biomedical Model of a Fishery Optimal Fish Harvest in Steady-State with Interest Rate of Zero Open Access and Competitive Behavior Renewable Resources Management in Steady –State Open Access Market Failures Shifting the Growth Function: Fish Feeding General Overview Renewable resources are resources that replenish themselves. Unlike nonrenewable resources in which a fixed stock is depleted over time, renewable resources can reproduce, grow, and die. Economically important renewable resources include: Forests Fisheries Grasslands (used for grazing) Issues for Analysis Growth functions and equations of motion for renewable resources systems. Steady-state behavior of renewable resources systems. Open access, inefficient market outcomes, and policy corrections. Dynamic behavior of renewable resource systems. A steady-state is a permanent level of stock that is maintained throughout time. An Equation of Motion is a formula that defines what happens to the stock over time. For example, when S t denotes the resource inventory at period t: If S t + 1 -S t > 0, then the resource stock is growing over time If S t + 1 -S t < 0, then the resource stock is shrinking over time If S t + 1 -S t = 0, then the resource stock is in steady state (S t = S t+1 =S t+2 …) For clarity, we will consider only one stock variable (for example, only one species of fish) in each of our renewable resource models. More complex models consider multiple stock variables. Models with multiple stock variables may be required if, for example, two species interact in a predator-prey relationship. We will also use a single indicator variable for the resource, which is Stock. Many times having only one indicator variable of a species is not effective. For example, when the renewable resource is trout in a lake:
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Need to know the number of fish (Stock) Also need to know the number of juvenile fish (Cohorts) Yet, the use of a single indicator variable allows us to formulate tractable models that give us information about how we should manage the resource. These models can get quite complicated with multiple stock variables and more than one indicator variable. For now, let us focus our analysis on biological renewable resources. We will consider non-biological renewable resources (i.e. groundwater) later on in the course. Economic models of biological resources combine biological models and economic models. For this reason, such combined models are called bioeconomic models. Shaefer’s (1954) biomass model is a classic example of a biological model used in bioeconomic models. The following discussion of growth functions, steady-state, carrying capacity and equations of motion is based on Shaefer’s model.
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