The properties are explored of the response to exploitation of the predator–prey system defined by the equations:[Formula: see text]This type of equation is perhaps a suitable representation of the type of natural situation in which a predator (N2) is not wholly dependent on one species of prey (N1) for food, and in which factors other than predators may regulate prey abundance. Yield- and value-isopleths are presented for sample values of the above parameters and for various rates of fishing.