That is not true at all. Mariners are “exempt employees.” Most state and federal labor laws simply don’t apply. No minimum wage required. No overtime required. No holiday pay required. No sick leave required. No parental leave required. No worker’s comp required. Etc etc.
Yes, some of those things might be required by a union contract, or a publicly funded project contract. Fore example, the Army Corp of Engineers, or a State, or port authority might require some of those things in a dredging contract.
It’s not just mariners that are “exempt employees,” some truck drivers, some managers, some bank employees, and certain types of state and federal employees are also “exempt” from certain labor laws.