The US has around 10,000 Jones Act vessels, mostly smaller vessels, in domestic trade with well over 50,000 jobs for US mariners. Without the Jones Act, it would be damn few US vessels and only a few hundred US jobs.
The US privately owned foreign going merchant fleet is only about 60 vessels and maybe 5,000 jobs. It’s still shrinking.
Most countries have cabotage laws similar to the Jones Act. Those that don’t, like Australia, have damn few jobs for mariners.