The captain is perfectly free to do what he wants how he wants with his property, the boat. His boat is useless without crew. The fishermen crew are not his owned slaves (although there are people working to fix that in the USA in all but name) and if he insists on sailing into hurricanes and killing half the crew, or not providing food/water/fair pay, they're perfectly free to raise hell and refuse to work and encourage everyone else not to work until the captain agrees to reasonable demands. He owns the ship, not the crew. If the captain says "I'm going to be a bit reckless and kill half the crew and pay the other half so low their family starves, but I will make an extra 10%, so you'll like it"... well, no, they won't.

The fisherman can't build their own boat because the captains have added enough rules and regs and .gov payoffs and what boil down to bribes in an effort to reduce competition. Its not a free market and the captains like it that way. No surprise there's a wee bit of backlash. If the captains don't like backlash, try not being a crook, then start complaining.

BTW its OK if the captain is pissed off about people "stealing" his capital even if they aren't. To a first approximation a fair and reasonable deal doesn't require everyone to be perfectly happy, just more or less equally unhappy. I'm sure the union fishermen are about equally pissed off at the captain, seeing as he kills about 2% of them annually by being cheap/risky and half of all captains are of course below the median thus they're jerks to work for.