The Pacific red snapper (Lutjanus peru) fishery in the southwestern Gulf of California was analyzed with an age-structured simulation model. In addition to natural mortality (M) and fishing mortality (F), the model incorporates juvenile by-catch mortality (f) caused by the shrimp fishery in the zone. Four simulated scenarios were tested in which different levels of mortality were combined. Contrary to what is established in the National Fishing Charter, simulation outputs showed that the Pacific red snapper fishery cannot be developed if both F and f are kept unregulated as presently occurs. According to the model, the fishery could only be developed with an effective regulation of these mortality sources, which implies control measures for both the artisanal fleet and the shrimp fleet.