Dynamic patterns of overexploitation in fisheries

Abstract

Understanding overfishing phenomenon and regulating fishing quotas is a major global challenge for the 21st Century both in terms of providing food for humankind and to preserve the oceans ecosystems. However, fishing is a complex economic activity, affected not just by overfishing but also by such factors as pollution, technology, financial factors and more. For this reason, it is often difficult to state with complete certainty that overfishing is the cause of the decline of a fishery. In this study, we developed a simple dynamic model based on the earlier, well-known Lotka-Volterra model or Prey-Predator model. To describe exploitation patterns, we assume that the fish stock and the fishing industry are coupled stock variables in the model and they dynamically affect each other, with the fishing yield proportional to both the fishing capital and the fish stock. The model is based on the concept that the fishing industry acts as the predator of the resource and that its growth and subsequent decline is directly related to the abundance of the fish stock. If the model can be fit historical data relative to specific fisheries, then it is a strong indication that the fishing industry is strongly affected by the magnitude of the fish stock and that, in particular, the decline of the yield and the decline of the stock are linked to each other. The model does not pretend to be a general description of the fishing industry in all its varied forms; however, the data reported here show that the model can indeed qualitatively describe several historical case of the collapse of fisheries. The model can also be used as a qualitative guide to understand the behavior of several other fisheries. These result indicate that one of the main factors causing the present crisis of the world's fisheries is the overexploitation of the fish stocks.