Strategic Modelling and Business Dynamics: A Feedback Systems Approach

1.5. Operating a Simple Harvested Fishery

Imagine you are living in a small fishing community where everyone's livelihood depends on the local fishery. It could be a town like Bonavista in Newfoundland, remote and self-sufficient, located on a windswept cape 200 miles from the tiny provincial capital of St Johns, along deserted roads where moose are as common as cars. 'In the early 1990s there were 705 jobs in Bonavista directly provided by the fishery, in catching and processing' (Clover, 2004). Let's suppose there is a committee of the town council responsible for growth and development that regulates the purchase of new ships by local fishermen. This committee may not exist in the real Bonavista but for now it's a convenient assumption. You are a member of the committee and proud of your thriving community. The town is growing, the fishing fleet is expanding and the fishery is teeming with cod.

Figure 1.8 shows the situation. The fish stock in the top left of the diagram regenerates just the same as before, but now there is an outflow, the harvest rate, that represents fishermen casting their nets and removing fish from the sea. The harvest rate is equal to the catch, which itself depends on the number of ships at sea and the catch per ship. Typically the more ships at sea the bigger the catch, unless the fish density falls very low, thereby reducing the catch per ship because it is difficult for the crew to reliably locate fish. Ships at sea are increased by the purchase of ...