The point of departure for this paper is the familiar prototype fisheriesmodel where a fictitious sole owner harvests a fish population to maximizepresent discounted profits. The paper answers analytically the followingquestion. ``What happens to a policy when the sole owner also valuesbiodiversity, as well as profits?'' It turns out that the size of the steady-state stock and the number of species preserved are both higher, whenspecies diversity is positively valued. This paper provides a sharpcharacterization of the optimal policy in terms of the usual economicparameters and an exogenously introduced willingness-to-pay function forspecies preservation.