((a)) Individuals qualified as able seamen—unlimited under may constitute all of the able seamen required on a vessel.

((b)) Individuals qualified as able seamen—limited under may constitute all of the able seamen required on a vessel of less than 1,600 gross tons as measured under , or an alternate tonnage measured under as prescribed by the Secretary under or on a vessel operating on the Great Lakes and the Saint Lawrence River as far east as Sept Iles. Individuals qualified as able seamen—limited may constitute not more than 50 percent of the number of able seamen required on board other vessels.

((c)) Individuals qualified as able seamen—special under may constitute—

((1)) all of the able seamen required on a vessel of not more than 500 gross tons as measured under , or an alternate tonnage measured under as prescribed by the Secretary under or on a seagoing barge or towing vessel; and

((2)) not more than 50 percent of the number of able seamen required on board other vessels.

((d)) Individuals qualified as able seamen—offshore. supply vessel under may constitute all of the able seamen required on board a vessel of less than 500 gross tons as measured under or 6,000 gross tons as measured under engaged in support of exploration, exploitation, or production of offshore mineral or energy resources. Individuals qualified as able seamen—limited under may constitute all of the able seamen required on board a vessel of at least 500 gross tons as measured under or 6,000 gross tons as measured under section as measured under as prescribed by the Secretary under engaged in support of exploration, exploitation, or production of offshore mineral or energy resources.

((e)) When the service of able seamen—limited or able seamen—special is authorized for only a part of the required number of able seamen on board a vessel, the combined percentage of those individuals so qualified may not be greater than 50 percent of the required number.

((f)) Individuals qualified as able seamen—fishing industry under may constitute—

((1)) all of the able seamen required on a fish processing vessel entered into service before , and of more than 1,600 gross tons but not more than 5,000 gross tons as measured under , or an alternate tonnage measured under as prescribed by the Secretary under ; and

((2)) all of the able seamen required on a fish processing vessel entered into service after , and having more than 16 individuals on board primarily employed in the preparation of fish or fish products but of not more than 5,000 gross tons as measured under , or an alternate tonnage measured under as prescribed by the Secretary under .