This final rule implements the measures of Framework Adjustment 13 to the Atlantic Mackerel, Squid, and Butterfish Fishery Management Plan. This action establishes a 5-year rebuilding program for Atlantic mackerel, sets 2019-2021 Atlantic mackerel specifications and a river herring and shad cap for the Atlantic mackerel fishery, modifies the Mid-Atlantic Fishery Management Council's risk policy, and modifies in-season closure measures. This action is necessary to prevent overfishing and rebuild the Atlantic mackerel stock based on a recent stock assessment that found the Atlantic mackerel stock to be overfished and subject to overfishing. The intended effect of this final rule is to sustainably manage the Atlantic mackerel fishery and achieve optimum yield on a continuing basis.