King, I am not fully informed about the situation or problem.
Are you suggesting that at a distance ( whatever that is 1/2 mile or more? ) there is significant differential in the noise to the ears of the residents between a 12 gauge 2 3/4" 1 1/8 oz load and a 3 1/2" 1 1/2 oz load? What is the comparative decibel reading? Is it the cummulative effect of numerous guns which disturbs the populace or the perception that the big noises must be more dangerous to persons?
Years ago ducking clubs established non hunting times - hours , days etc. and this went a long way towards better decoying of local birds. Likewise club memberships and guests were controled as to numbers in the marsh and where they hunted to make it a better experience for all. Granted these were mostly inland marshes not open coast. Restrictions that are self imposed by the sporting community will be better thought through and more responsive to the needs of the waterfowland quality hunting experience than those imposed by local governments. Personally I am opposed to setting limits on gauge or shot weights etc. In fact I believe that 10 gauge guns with well balanced loads of the obligatory non toxic shot in the hands of a good shot would be more effective in cleanly killing waterfowl than 12 gauge 3 1/2" loads. Fewer shots taken by hunters on decoying birds would mean less noise wouldn't it? We sacrificed the 8 gauge guns for waterfowl without much respect to logic. Should we sacrifice 10 gauges as well? Perhaps we would be better served by educating members of the hunting fraternity as to self imposed disciplines on decoying, range of shot etc. I have friends who take only 20 rounds with them to the marsh. They figure if they can't get a reasonable number of birds with 20 shots they require more practice and skill not more ammunition. As I said I am not familiar with your situation but what happens in one locality seems to find fertile minds for instituting similar restrictions in others.