that portion of the taxable income of the owner or lessee for the taxable year (computed under chapter 1 of the Internal Revenue Code of 1986 (
26 U.S.C. ch. 1) but without regard to the carryback of net operating loss or net capital loss or this chapter) that is attributable to the operation of agreement vessels in the foreign or domestic trade of the United States or in the fisheries of the United States;