They might last for decades - but I tend to think that would be quite a stretch.
And remember. Lobster’s gotta have a good reason to go in there. And seeing his dead mother in law might not cut it!
(trap has no bait...)
Those rubber-dipped galvy cages would certainly last for decades underwater. The entire cage is dipped and the metal is sealed. The doors use rubber hinges. The entire point is to make them last forever. The solution is to make them with doors that will fall open after a few months.
And yes, the lobsters to “bait themselves.” I saw it myself in 80% of the dozens of lost traps I checked out. You would see shell parts, full carapaces, dead rotten bugs, new dead bugs, and live new bugs. It was a continuous chain of death-—for nothing. I love to eat em, but wiping them out stupidly for NOTHING is beyond stupid.