Whaling Convention Amendments Act of 2018 This bill amends the Whaling Convention Act of 1949 to require the Department of Commerce to authorize aboriginal subsistence whaling if the whaling: (1) is for subsistence purposes, including the sale of authentic native articles of handicrafts and clothing; (2) does not include the striking, taking, or killing of calves or a whale accompanied by a calf; and (3) is not accomplished in a wasteful manner. Commerce must establish catch limits for subsistence whaling by Alaska Natives if: (1) the International Whaling Commission (IWC) fails to establish the limits, and (2) Commerce determines that subsistence whaling is sustainable based on IWC's most recent review of the status of the affected whale. The bill exempts actions taken under the Act with respect to a stock of a whale species from environmental review requirements under the National Environmental Policy Act of 1969 if Commerce determines that the action is sustainable based on the most recent review of the status of the stock by the IWC's Scientific Committee.