Leif K. Sandal

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Estimation of parameters in the drift and diffusion terms of stochastic differential equations involves simulation and generally requires substantial data sets. We examine a method that can be applied when available time series are limited to less than 20 observations per replication. We compare and contrast parameter estimation for linear and nonlinear(More)
In this paper we study how a stochastic model can be used to determine optimal levels of exploitation of the North-East Arctic Cod (NEAC , Gadus morhua). A noncritical depensation growth model is developed for this species in order to examine both deterministic and stochastic cases. Estimation of the biological and the noise term parameters in the(More)
The Lotka-Volterra predator-prey model exemplifies the implicit and explicit assumptions managers often have regarding species interaction—populations are stable or fluctuate periodically. The reality is often much more complicated and there is overwhelming evidence that many populations fluctuate in a nonperiodic way. Using a discrete predator-prey model(More)
This paper has two main objectives. The first is to develop a dynamic model of commercial fisheries different from most existing models that assume optimizing behavior. The industry is assumed to have a well-defined index of performance based upon which the decision to invest or not is made. We do not, however, assume that the industry or firm is efficient(More)
This paper focus aspects connected to the optimal control of a renewable resource modelled by a stochastic differential equation. The main point is to show how small changes of the problem may cause severe changes in the properties of the control. In particular we show how the introduction of uncertainty may lead to a less conservative policy. In this(More)
The thesis explores how the introduction of a marine protected area influences the optimal management of a marine resource, i.e. a fish stock. Logistic growth functions are applied to a deterministic model with a migration term which is proportional to the difference in density in the two areas. A nonlinear profit function is adopted. The possibility and(More)