The Eco² Model – a Basic Bio-Economic Module for the Description of the Dynamics of Cohort Biomass in Response to Exploitation

The presented approach is based on two growth equations which are commonly used to describe individual growth in mass: The von Bertalanffy-growth function for wild fish stocks and a simple exponential growth model primarily used in aquaculture. Here both models are merged into a single model. The resulting equation in conjunction with the traditional abundance equations offers crucial advantages for modeling the changes in biomass of a single cohort of a fish stock as a function of assimilation rate, maintenance rate, natural mortality, fishing mortality and time. This approach provides also the development of a simple link between ecology and economy. The result of the derivations is a set of equations which can be used as a basic bio-economic module for the composition of large ecosystems and the description of the dynamics of dependent species regarding ecology and economy in response to exploitation. The use of the model is explained by a simple example in which the use of an ecosystem is controlled solely by changing the mesh size. Two management strategies are compared based on their net present values.