This paper shows how intra-stock relations, such as cannibalism and growth enhancement, define the optimal sharing of a fish resource between heterogeneous harvesting agents. The sharing of resources between different vessel groups is often left for political decision making. Nonetheless, such decisions may have both biological and economic consequences. This becomes quite clear when different harvesting groups exploit different sections (age groups) of a stock that has intra-stock interactions in the form of cannibalism. A two-agent bioeconomic model with cannibalism is developed and used to determine (i) optimal annual harvest sizes (TACS) for cod, and (ii) the optimal proportion of the TAC that should be harvested by the trawler and coastal fleets. Applying biological and economic data in a numerical procedure, and comparing the results obtained to previous studies, it is shown that the presence of cannibalism has a significant impact on who should take what proportion of the TAC, and hence, the standing stock size and discounted economic rent achievable. In sharp contrast to other studies, we find that the optimal harvest requires that both trawlers and coastal vessels should harvest the fish resource. In addition, the results indicate that from a bioeconomic perspective, the existing trawler fleet's harvest share in the cod fishery is too high.