The management measures that you describe other than MPAs can be things such as seasons or quotas, that type of thing. With MPAs, the conservation objective can be about a specific species. That does happen. However, MPAs can be very broad as well and take in biodiversity, multispecies, that type of thing. Depending on what your objective is at the time, that would determine your best tool to use.
For fisheries management, it might simply be something under the Fisheries Act that doesn't require an MPA. However, if science dictates it, maybe the best tool is an MPA.