The diagram on this page is referred to as the Gordon-Schaefer Fishery Production Function. The biological yield curve is based on the "Schaefer Curve," developed by fishery scientist M.B. Schaeffer in the 1950s. The economics was added by H. Scott Gordon, also in the 1950s. What the diagram says is that the yield from a fishery will be low when fishing effort is low, yield will increase as fishing effort increases, but will reach a maximum known as the maximum sustainable yield. If fishing effort continues to increase, the yield from the fishery will decline.

The economics combine with the biology in the following way. The yield from the fishery can be expressed in dollars rather than pounds. As fishing effort increases, so does the cost of that effort, as shown by the line labeled "Cost of Effort." When fishing effort is relatively low and biomass is high, the catch per unit effort (CPUE) is high and profits are high. As fishing effort increases and biomass and yield decline, the profit margin between the cost line and the yield in dollars line gets smaller. Eventually, cost increases and yield declines to a point of zero profit. This point is called the "Open Access Equilibrium" and demonstrates the "self-regulating" nature of fisheries. This equilibrium is based on constant conditions such as price, technology, and environment. If these conditions stay the same, entry into the fishery will be balanced by exit from the fishery and the fishery will remain in equilibrium. Changes such as an increase in price (raises the revenue curve and creates more profit) or better technology (lowers the cost curve creating more profit) will create additional profit that will attract new fishing effort.

Open access to fisheries has been criticized for a number of reasons that are illustrated by the yield curve, also called a production function:

1. Under open access, biological yield (pounds) from the resource will be less than the maximum potential.
2. The resource is vulnerable to changes in price and technology which tend to increase fishing effort over time, reducing yield and biomass and threatening the stock with collapse.
3. A great deal of fishing effort, and therefore cost, is wasted. A larger catch could be obtained with less effort and less cost. The standard of living of society could be higher if the excess inputs used to catch fish were used to produce other valuable goods and services.
4. Because average profit levels are low, proposals to reduce catches for the purpose of stock conservation are resisted by fishing firms.

In contrast to the zero rent or excess profit level at the point of open access equilibrium, the point of maximum profit occurs to the left of maximum sustainable yield, the point labeled "MEY" for maximum economic yield. The maximum profit from a fishery is actually obtained when the fishery is kept at relatively low levels of effort compared to the open access equilibrium. Biomass is kept relatively high, catch per unit of effort is high, and profits are high. A fishery that is managed to obtain the maximum economic yield is therefore also managed in a very conservative biological way.