Dynamic patterns of overexploitation in fisheries

- For the first time, the “predator-prey” model is used for the quantitative description of an economic predatory dynamic in real-world fisheries.
- A simple “mind-sized” model highlights the driving forces that lead to the resources' overexploitation and the collapse of a production system.
- A renewable fish stock can behave as a non-renewable resource when exploited at a speed much higher than its carrying capacity.
- Coupled feedback effects are the origin of overexploitation and collapse in real-world fisheries.

Understanding overfishing 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 specifically designed to isolate and to study the role of depletion on production. The model is based on the well-known Lotka-Volterra model, or Prey-Predator mechanism, assuming that the fish stock and the fishing industry are coupled variables that dynamically affect each other. In the model, the fishing industry acts as the “predator” and the fish stock as the “prey”. If the model can fit historical data, in particular relative to the productive decline of specific fisheries, then we have a strong indication that the decline of the fish stock is driving the decline of the fishery production. The model doesn't 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 describe several historical cases of fisheries whose production decreased and collapsed, indicating that the overexploitation of the fish stocks is an important factor in the decline of fisheries.

The “mind-sized” model of overexploitation in fisheries 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.98