MAXIMUM SUSTAINABLE-YIELD WITH CONTINUOUS AGE STRUCTURE AND DENSITY-DEPENDENT RECRUITMENT

The problem addressed is that of finding the harvesting policy that wi ll maximize the yield and maintain a given population in a steady stat e. It is assumed that the equations describing the evolution of the po pulation and the yield are linear but that the equation describing rep roduction is nonlinear (density dependence). The optimal strategy cons ists in harvesting two age classes only: a younger age class is partia lly harvested, and an older age class is completely harvested as in th e linear case. This problem is a particular case of a general abstract maximization problem in which, for example, nonlinear mortality or no nlinear value of the individuals can also be introduced. The appropria te compactness for this problem is obtained from the fact that maximiz ing sequences are decreasing.