The aim of this paper is to analyze the optimal management of two ecologically interdependent, competing species, roe deer (Capreolus capreolus) and fallow deer (Dama dama). To this end, we develop a numerical stage-structured model, accounting for species-specific life history characteristics, gender, and stage-specific hunting values. Two contrasting management regimes are considered: optimal joint management of the two species and management where the decision maker is ignorant about interspecific competition. Results from our case study show that the presence of interspecific competition reduces roe deer population size and harvest by 30% and 47%, respectively, and reduces the net present value by 9%. High interspecific competition could lead to the exclusion of the roe deer from the area. In contrast, ignorance about the level and consequences of interspecific competition has no impact on harvest decisions and revenues. The explanation is the higher hunting benefits for fallow deer. Summary for Managers Wildlife managers need bioeconomic models for decisions on ecologically interdependent species. This study investigates optimal joint management of roe and fallow deer when the fallow deer exerts a negative impact on roe deer due to interspecific competition. Results show that interspecific competition reduces the net present value of hunting at the study site by 9%. Regulations will not increase the net present value of hunting in a situation where the manager is ignorant of interspecific competition.