I wrote an explanation of the model which you can find here: https://docs.google.com/document/d/1yRTtZvOOrFiBlK6pkvbpSUv_ajvGMKSAbfthRTBPU-8/edit?usp=sharing 

Fishing is a classic example for use of a renewable resource. Unless overfished, fish populations If is hardly by fishing, then the fish population will persist at a constant size corresponding to its specific ecological envi­ ronment If the stock is overfished, the juvenile generation becomes too small to fully replace the adult generation. If overfishing continues. the population cannot recover and will collapse in short time. Even if fish catch stops now/, it could take decades until the fish population recovers to its original size if it hasn't become extinct meanwhile. In many of the world overtlshing has led, and still leads, to the complete collapse of formerly huge tlsh populations: herring in the North Sea, codtlsh in the Northern Atlantic. tuna, whales to name only a few. With the collapse of fish stocks came the collapse of the t1shing industry in many regions. Employment and

incomes disappeared: whole regions (like Newfoundland) lost their economic base.​

System Zoo Z404 Prey and two Predator Populations from Hartmut Bossel (2007) System Zoo 2 Simulation Models. Climate, Ecosystems, Resources