Crewmember means an individual who is:
(1) Onboard a vessel acting under the authority of a credential issued under this subchapter, whether or not the individual is a member of the vessel's crew; or
(2) Engaged or employed onboard a vessel owned in the United States that is required by law or regulation to engage, employ, or be operated by an individual holding a credential issued under this subchapter, except for the following:
(i) Individuals on fish processing vessels who are primarily employed in the preparation of fish or fish products, or in a support position, and who have no duties that directly affect the safe operation of the vessel;
(ii) Scientific personnel on an oceanographic research vessel;
(iii) Individuals on industrial vessels who are industrial personnel, as defined in this chapter; and
(iv) Individuals not required under part 15 of this subchapter who have no duties that directly affect the safe operation of the vessel.