Playing devil's advocate, this "captain" may have one defense, which is that he was captain in name only. For example, if he was simply the primary boat-driver, but he was not a financial benefactor (other than paid hourly/salary), nor a boss, nor responsible for hiring and firing, nor the owner of the boat. If there is another owner or boss, perhaps this captain has a defense?
Or perhaps he wouldn't have a defense if there is some kind of legal definition and responsibilities around boat captains.
IMO, the biggest culprit in this incident is whoever ran this boat on the cheap, hired low-skill unmotivated labor, didn't pay for adequate safety measures, and didn't ensure there were safety protocols in place. In other words, whose choice would it be, to pay for additional safety equipment, hire workers, or fire workers? That person may indeed be this "captain" or may be someone else. I'm curious if anyone can dig up or knows that info.
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And to devil's advocate the devil's advocate, I think there's a good argument that practically every crew member has some liability in this. And when asking "which crew member is most responsible" the most obvious answer would be "the captain."
The person with the title captain of a vessel holds the responsibility for ensuring the safety of the crew and passengers of the vessel
if someone isn't up to the task of this responsibility they have no business being a vessel captain, and if a company won't give the captain the tools necessary to keep their ship safe the prudent captain makes the company find a new one
This counts for 6 pack fishing charters up to a cruise ship with 6,000 people on it