In this paper, a numerical model is developed where the role of species life history and age structure for the optimal management of a harvested resident species which is exposed to an invasive species. It is shown that reproduction and mortality characteristics of both species as well as age structure of the invader at the time of invasion are important for the costs of invasions when the invader and resident species compete for scarce resources. Species with low juvenile survival and high reproduction is found to be most robust against invasions and more damaging as an invader. Properties of the harvesting cost function as well as the discount rate are shown to be of importance for the development of the invader population. Hence, it is possible to identify specific combinations of biological and economic conditions under which invasions cause particularly large economic and ecologic damage.