Using constrained optimal control to model a socially sustainable fishery

In the so-called sole-owner-case of a renewable resource harvesting, it is known that the optimal policy includes a period with no harvesting, if the population is insufficiently small. Therefore, the fishermen have no income in this phase. To avoid this problem, the optimal control problem was enhanced in two different ways. First, the capital accumulation rate was bounded from below what generated a global mixed constraint. Second, lower bounds for the capital stock at a finite number of time points were introduced, which at first led to one and afterwards several isolated inequality constraints. For the resulting constrained optimal control problems, the necessary conditions were derived and an iterative algorithm was implemented to calculate the solutions in several numerical examples. Copyright © 2010 John Wiley & Sons, Ltd.