I'm not sure training will be a sustainable solution here. Back when they were free-diving, there were fewer risks (shallow water blackout being one of them). As the lobsters ran low, they hit the physical barrier from free diving, and slowed down to what the fisheries can provide.
Once they moved to open circuit, they can now access a much greater depth range. In the beginning, it was great - until they cleaned up the newly accessible depth range too - requiring deeper dives, longer divers, and more repetitive dives.
Option 1:
It's not hard to tell someone "Hey, no more than 3 dives to 130 feet per day." In fact, an education campaign can be easily spread top-down through the lobster supply chain if the establishment really wanted that - but they're not going to listen because they're trying harder to find that last bug. For an individual fisherman, following these strict guidelines won't work unless everyone does (and drives the prices of labor up to be competitive at 3 dives) because if you're only willing to make 3 dives when everyone else makes 15, you're either not going to be paid as well, or you won't be hired.
Option 2:
Solving the problem from a technological stand point, assuming they move to close circuit trimix - the problem gets solved for just a few years as they quickly clean out the lobster stock in the safe operating ranges that have just been opened to them. Then we'll just hear about these people dying because they spent too long, too deep once the stocks are depleted at the newly accessible ranges.
I feel the only sustainable option are regulations on the fishery itself to be sustainable. Set rules like "Only take males of certain length" so each year, divers can get a full quota simply by diving to 20-30 feet. In a properly managed fishery, the divers can probably obtain more lobster, with less risk, than what they have right now: cleaning the remnants of a rapidly collapsing fishery [within the operating depths]
