Consumers sit at the top of the supply chain, driving demand. In our model, consumer demand for fish products is constantly growing, as the world population increases and economic growth allows more consumers worldwide to purchase pricier foods. Growing consumer demand drives prices of wild fish up because, with fish stocks fully to over-exploited, production can not grow to match it.
Consumer demand is price sensitive. Consumers will purchase more if prices are low, and will substitute other protein sources, buying less, when prices are high. This means that scarcity of high quality yellowfin tuna from Mindoro would drive its price up, but not enough to compensate for the income loss for fishers, exporters, and intermediaries.
Over the course of the simulation, the population of consumers grows at a constant rate, essentially the world growth rate for demand of fish products. The consumption of each individual depends on the consumer price of Mindoro tuna: at higher price they will buy less; at a lower price, they will buy more.