in practice the national marine fisheries service and regional fishery management councils typically set an overfished threshold as part of designating what are called status determination criteria for the stock when stock abundance falls below the threshold the agency designates the stock as overfished and requires the relevant regional council to develop and implement a rebuilding plan as part of a fishery management plan or plan amendment the plan must also include management measures to constrain the fishing mortality level to rebuild the stock within this time period when a population increases to above the overfished threshold but remains below the rebuilding target it is considered not overfished but still rebuilding