F isheries operate under f luctuating environmental conditions, targeting f ish stocks that appear in varying densities in different areas, often with abrupt and unexpected local changes. Physical conditions, markets and management regulations constrain vessels in different and varying ways. These factors all contribute to forming the f leet diversity we f ind in most f isheries. Here, a simulation model of the Northeast Arctic cod f ishery is used in order to investigate how this diversity is formed and maintained, assuming rational economic behaviour under varying combined constraints. The study also focuses on how the ability of vessels to f ind f ish inf luences f leet diversity, prof itability, stock development and seasonal prof iles of the f ishery. Results indicate that an increased ability to target the most prof itable f ishing grounds may inf luence f leet diversity positively or negatively, depending on overall exploitation level. High exploitation rates also increase the temporal f luctuations in f leet diversity and prof its, which are amplif ied as the f ish-f inding ability increases.